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Aromatic amines (AA) are carcinogenic compounds that can enter the human body through many sources, one of the most important being tobacco smoke. They are excreted with the urine, from which they can be extracted and measured. To that end, hollow fiber-liquid-phase microextraction (HF-LPME) and parallel artificial liquid membrane extraction (PALME) were optimized for the analysis of representative aromatic amines, as alternatives to liquid–liquid extraction (LLE). Relevant extraction parameters, namely organic solvent, extraction time, agitation speed, and acceptor solution pH, were studied, and the two optimized techniques—HF-LPME: dihexyl ether, 45 min, 250 rpm, and pH 1; PALME: undecane, 20 min, 250 rpm and pH 1—were compared. Comparison of the optimized methods showed that significantly higher recoveries could be obtained with PALME than with HF-LPME. Therefore, PALME was further validated. The results were successful for nine different AA, with regression coefficients (R2) of at least 0.991, limits of detection (LOD) of 45–75 ng/L, and repeatability and peak area relative standard deviations (RSD) below 20%. Furthermore, two urine samples from smokers were measured as proof of concept, and 2-methylaniline was successfully quantified in one of them. These results show that PALME is a great green alternative to LLE. Not only does it use much smaller volumes of toxic organic solvents, and sample—enabling the study of samples with limited available volumes—but it is also less time consuming and labor intensive, and it can be automated. Graphical Abstract

The analysis of fatty acid methyl esters (FAMEs) is of high relevance for monitoring and control of various industrial processes and biological systems. In this study, a novel, green analytical approach for the determination of 24 FAMEs from aqueous samples is proposed, which is based on a headspace solid-phase microextraction (SPME) arrow followed by gas chromatography coupled to tandem mass spectrometry (GC–MS/MS). The method was substantially accelerated to a run time of 44 min per sample by thorough optimization and automation of the relevant parameters. The limiting parameters, mostly based on expediting equilibrium attainment, were found to be parameters of extraction: material, pH, time, and temperature, which were optimized to divinylbenzene polydimethylsiloxane (DVB-PDMS), pH 2, 20 min, and 70 °C, respectively. The optimization and automation of the method led to low method detection limits (9–437 ng L−1) and high selectivity. Evaluation of the method on real samples was done by analyzing the aqueous phase of a bioreactor, whereby the matrix effect could be greatly reduced due to dilution and headspace sampling. The rapid, sensitive, selective, and matrix-reduced approach is found to be not only a novel method for water analysis but is promising for further applications, e.g., with solid and gaseous samples containing FAMEs. Graphical abstract

Compound-specific stable isotope analysis (CSIA) is a unique analytical technique for determining small variations in isotope ratios of light isotopes in analytes from complex mixtures. A problem of CSIA using gas chromatography (GC) and liquid chromatography-isotope ratio mass spectrometry (LC-IRMS) is that any structural information of the analytes is lost due to the processes involved in determining the isotope ratio. To obtain the isotopic composition of, for example, carbon from organic compounds, all carbon in each analyte is quantitatively converted to CO

Some aromatic amines (AA) have been classified as carcinogens to humans. After entering the body, mainly through tobacco smoke, they can be detected in urine. Thus, their trace analysis as biomarkers in biofluids is of high relevance and can be achieved with gas chromatography (GC–MS), usually after derivatization. This study compares three gas chromatographic methods for the analysis of ten iodinated derivatives of AA: GC–MS in single-ion monitoring (SIM) mode with (1) electron ionization (GC-EI-MS) and (2) negative chemical ionization (GC-NCI-MS), and (3) GC-EI-MS/MS in multiple reaction monitoring (MRM) mode using electron ionization. All methods and most analytes showed good coefficients of determination (R2 > 0.99) for broad linear ranges covering three to five orders of magnitude in the picogram-per-liter to nanogram-per-liter range, with one and two exceptions for (1) and (2) respectively. Excellent limits of detection (LODs) of 9–50, 3.0–7.3, and 0.9–3.9 pg/L were observed for (1), (2), and (3) respectively, and good precision was achieved (intra-day repeatability α = 0.05) higher concentrations among smokers. Graphical Abstract

Effect-directed analysis (EDA) that combines effect-based methods (EBMs) with high-performance thin-layer chromatography (HPTLC) is a useful technique for spatial, temporal, and process-related effect evaluation and may provide a link between effect testing and responsible substance identification. In this study, a yeast multi endocrine-effect screen (YMEES) for the detection of endocrine effects is combined with HPTLC. Simultaneous detection of estrogenic, androgenic, and gestagenic effects on the HPTLC plate is achieved by mixing different genetically modified Arxula adeninivorans yeast strains, which contain either the human estrogen, androgen, or progesterone receptor. Depending on the yeast strain, different fluorescent proteins are formed when an appropriate substance binds to the specific hormone receptor. This allows to measure hormonal effects at different wavelengths. Two yeast cell application approaches, immersion and spraying, are compared. The sensitivity and reproducibility of the method are shown by dose-response investigations for reference compounds. The spraying approach indicated similar sensitivities and higher precisions for the tested hormones compared to immersion. The EC10s for estrone (E1), 17β-estradiol (E2), 17α-ethinylestradiol (EE2), 5α-dihydrotestosterone (DHT), and progesterone (P4) were 95, 1.4, 10, 7.4, and 15 pg/spot, respectively. Recovery rates of E1, E2, EE2, DHT, and P4 between 88 and 120% show the usability of the general method in combination with sample enrichment by solid phase extraction (SPE). The simultaneous detection of estrogenic, androgenic, and gestagenic effects in wastewater and surface water samples demonstrates the successful application of the YMEES in such matrices. This promising method allows us to identify more than one endocrine effect on the same HPTLC plate, which saves time and material. The method could be used for comparison, evaluation, and monitoring of different river sites and wastewater treatment steps and should be tested in further studies.

A GCxGC-MS system was employed with a non-polar × mid-polar column set for the metabolic non-target analysis of Cobetia marina, the model bacteria for marine biofouling. C. marina was treated with ozone to investigate the intracellular metabolic state change under oxidative stress. A minimal inhibitory concentration test was involved to guarantee that the applied ozone dosages were not lethal for the cells. In this study, non-target analyses were performed to identify the metabolites according to the NIST database. As a result, over 170 signals were detected under normal living conditions including 35 potential metabolites. By the comparison of ozone-treated and non-treated samples, five compounds were selected to describe observed trends of signals in the contour plots. Oleic acid exhibited a slight growth by increasing ozone dosage. In contrast, other metabolites such as the amino acid l-proline showed less abundance after ozone treatment, which was more evident once ozone dosage was raised. Thus, this work could provide a hint for searching for up/downregulating factors in such environmental stress conditions for C. marina.

Reversed-phase liquid chromatography (RPLC) used for water analysis is not ideal for the analysis of highly polar and ionic contaminants because of low retention. Capillary electrophoresis (CE), on the other hand, is perfectly suited for the separation of ionic compounds but rarely applied in environmental analysis due to the weak concentration sensitivity when coupled to mass spectrometry (MS). However, novel interface designs and MS technology strongly improve the sensitivity. Here, a method is presented enabling the screening of anionic micropollutants in drinking water without sample pretreatment by coupling of CE to an Orbitrap mass spectrometer by a nanoflow sheath liquid interface. Targeted analysis of halogenated acetic acids, trifluoromethanesulfonic acid, and perfluorooctanoic and perfluorooctanesulfonic acid was conducted in drinking water samples which were chlorinated for disinfection. A bare fused silica capillary with an optimized background electrolyte (BGE) for separation consisting of 10% acetic acid with 10% isopropanol with large volume sample injection and optimized interface parameters offer limits of quantification in the range of 0.993) and repeatability (14% standard deviation in area). Concentrations of the target analytes ranged from 0.1 to 6.2 μg/L in the water samples. Masses corresponding to halogenated methanesulfonic acids have been found as suspects and were subsequently verified by standards. Mono-, dichloro-, and bromochloro methanesulfonic acid were quantified in a range of 0.2 to 3.6 μg/L. Furthermore, five sulfonic acids, four organosulfates, and the artificial sweeteners acesulfame and cyclamate as well as inorganics such as halides, halogenates, phosphate, and sulfate could be determined as suspects among more than 300 features in a non-targeted screening. Overall, this approach demonstrates the great potential of CE-nanoESI-MS for the screening of ionic contaminants in environmental samples, complementary to chromatographic approaches. Electronic supplementary material The online version of this article (10.1007/s00216-020-02525-8) contains supplementary material, which is available to authorized users.

With the increasing demand for ultrapure water in the pharmaceutical and semiconductor industry, the need for precise measuring instruments for those applications is also growing. One critical parameter of water quality is the amount of total organic carbon (TOC). This work presents a system that uses the advantage of the increased oxidation power achieved with UV/O3 advanced oxidation process (AOP) for TOC measurement in combination with a significant miniaturization compared to the state of the art. The miniaturization is achieved by using polymer-electrolyte membrane (PEM) electrolysis cells for ozone generation in combination with UV-LEDs for irradiation of the measuring solution, as both components are significantly smaller than standard equipment. Conductivity measurement after oxidation is the measuring principle and measurements were carried out in the TOC range between 10 and 1000 ppb TOC. The suitability of the system for TOC measurement is demonstrated using the oxidation by ozonation combined with UV irradiation of defined concentrations of isopropyl alcohol (IPA).

N-containing heterocycles (NCHs) are largely used as precursors for pharmaceuticals and can enter the environment. Some NCHs have been shown to be toxic, persistent, and very mobile in the environment. Thus, they have received increasing attention in the past years. However, the analysis of these polar compounds in environmental samples is still a challenge for liquid chromatography. This paper investigates the use of mixed-mode liquid chromatography (MMLC), which has reversed-phase and ion exchange characteristics for measurements of NCHs in water. NCHs with low pKa (i.e., Ka (i.e., > 5) interact by a mixture of reversed-phase/ion exchange/HILIC mechanism. It was also shown that the presented method performs well in the quantification of the majority of the selected NCHs in surface water with MDLs between 3 and 6 μg/L, a low matrix effect and recoveries in the range of 77–96% except for pyridazine exhibiting 32% were achieved. The method was successfully employed to follow the degradation of NCHs in ozonation.

High-resolution mass spectrometry is widely used in many research fields allowing for accurate mass determinations. In this context, it is pretty standard that high-resolution profile mode mass spectra are reduced to centroided data, which many data processing routines rely on for further evaluation. Yet information on the peak profile quality is not conserved in those approaches; i.e., describing results reliability is almost impossible. Therefore, we overcome this limitation by developing a new statistical parameter called data quality score (DQS). For the DQS calculations, we performed a very fast and robust regression analysis of the individual high-resolution peak profiles and considered error propagation to estimate the uncertainties of the regression coefficients. We successfully validated the new algorithm with the vendor-specific algorithm implemented in Proteowizard’s msConvert. Moreover, we show that the DQS is a sum parameter associated with centroid accuracy and precision. We also demonstrate the benefit of the new algorithm in nontarget screenings as the DQS prioritizes signals that are not influenced by non-resolved isobaric ions or isotopic fine structures. The algorithm is implemented in Python, R, and Julia programming languages and supports multi- and cross-platform downstream data handling.

The anthropogenic entry of organic micropollutants into the aquatic environment leads to a potential risk for drinking water resources and the drinking water itself. Therefore, sensitive screening analysis methods are needed to monitor the raw and drinking water quality continuously. Non-target screening analysis has been shown to allow for a more comprehensive investigation of drinking water processes compared to target analysis alone. However, non-target screening is challenging due to the many features that can be detected. Thus, data processing techniques to reduce the high number of features are necessary, and prioritization techniques are important to find the features of interest for identification, as identification of unknown substances is challenging as well. In this study, a drinking water production process, where drinking water is supplied by a water reservoir, was investigated. Since the water reservoir provides surface water, which is anthropogenically influenced by wastewater treatment plant (WWTP) effluents, substances originating from WWTP effluents and reaching the drinking water were investigated, because this indicates that they cannot be removed by the drinking water production process. For this purpose, ultra-performance liquid chromatography coupled with an ion-mobility high-resolution mass spectrometer (UPLC-IM-HRMS) was used in a combined approach including target, suspect and non-target screening analysis to identify known and unknown substances. Additionally, the role of ion-mobility-derived collision cross sections (CCS) in identification is discussed. To that end, six samples (two WWTP effluent samples, a surface water sample that received the effluents, a raw water sample from a downstream water reservoir, a process sample and the drinking water) were analyzed. Positive findings for a total of 60 substances in at least one sample were obtained through quantitative screening. Sixty-five percent (15 out of 23) of the identified substances in the drinking water sample were pharmaceuticals and transformation products of pharmaceuticals. Using suspect screening, further 33 substances were tentatively identified in one or more samples, where for 19 of these substances, CCS values could be compared with CCS values from the literature, which supported the tentative identification. Eight substances were identified by reference standards. In the non-target screening, a total of ten features detected in all six samples were prioritized, whereby metoprolol acid/atenolol acid (a transformation product of the two β-blockers metoprolol and atenolol) and 1,3-benzothiazol-2-sulfonic acid (a transformation product of the vulcanization accelerator 2-mercaptobenzothiazole) were identified with reference standards. Overall, this study demonstrates the added value of a comprehensive water monitoring approach based on UPLC-IM-HRMS analysis. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03263-1.

Honey is the oldest and nowadays widely used natural sweetener for food worldwide. Its composition is associated with its botanical and geographical origin and honey is often mislabeled and has a high potential for food fraud. Thus, quick easy and sensitive analyses are required. For the first time, we developed and applied an automated, fast, sensitive and robust, in-tube extraction dynamic headspace in-tube extraction-dynamic headspace (ITEX-DHS) method for a variety of Honey containing VOCs in connection with GC-MS. Another advantage of ITEX is, that it is a green analytical solventless method. The method provides very low method detection limits (MDL) from 0.8 to 47 ng g

Regarding endocrine disrupting chemicals, an impact on aquatic organisms at already very low concentrations is observed. Consequently, there is a need for sensitive analytical methods. Currently, no instrumental analysis methods exist that fulfil this requirement. To overcome these limitations, effect-based methods (EBMs) are one option for screening and quantification. Determination of agonistic effects caused by estrogens are the focus of current research activities due to environmental impacts and regulatory measures. However, antagonistic effects have to be considered to be able to correlate effects to single compounds, which is still necessary due to regulatory requirements. Since not much is known about relevant antagonists, this review highlights the perspectives and limitations of EBMs. The relevance of antagonistic acting compounds shows the potential of a systematic identification by effect-directed analysis. Collected data of already known antagonists are presented and discussed in a harmonized fashion as basis for future studies.

The analysis of microplastics is mainly performed using Fourier transformation infrared spectroscopy/microscopy (FTIR/ μFTIR). However, in contrast to most aspects of the analysis process, for example, sampling, sample preparation, and measurement, there is less known about data evaluation. This particularly critical step becomes more and more important if a large number of samples has to be handled. In this context, it is concerning that the commonly used library searching is not suitable to identify microplastics from real environmental samples automatically. Therefore, many spectra have to be rechecked by the operator manually, which is very time-consuming. In this study, a new fully automated robust microplastics identification method is presented that assigns over 98% of microplastics correctly. The main concept of this new method is to detect and numerically describe the individual vibrational bands within an FTIR absorbance spectrum by curve fitting, which leads to a very compact and highly characteristic peak list. This list allows very accurate and robust library searching. The developed approach is based on the already published microplastics identification algorithm (μIDENT) and extends and improves the field of application to μFTIR data with a special focus on relevant broad, overlapped, or complex vibrational bands.

One of the most critical steps in nontarget screening of organic micropollutants (OMP) in complex environmental samples is handling of massive data obtained from liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). Multivariate chemometric methods have brought about great progress in processing big data obtained from high-dimensional chromatographic systems. This work aimed at a comprehensive evaluation of two LC-Q-Orbitrap mass spectrometry full-scan data sets for target and nontarget screening of OMPs in drinking and wastewater samples, respectively. For each data set, following segmentation in the chromatographic dimension, at first multivariate curve resolution alternating least-squares (MCR-ALS) was employed for simultaneous resolution of global matrices. The chromatographic peaks and the corresponding mass spectra of OMP were fully resolved in the presence of highly co-eluting irrelevant and interfering peaks. Then partial least-squares-discriminant analysis was conducted to investigate the behavior of MCR-ALS components in different water classes and selection of most relevant components. Further prioritization of features in wastewater before and after ozonation and their reduction to 24 micropollutants were then obtained by univariate statistics. Two-way information retrieved from MCR-ALS of LC-MS

In liquid chromatography coupled to isotope ratio mass spectrometry (LC-IRMS), analytes are separated on an LC system and consecutively oxidized to CO2, which is required for the determination of compound-specific carbon isotope ratios. Oxidation is performed in an online reactor by sulfate radicals. Reaction conditions in the interface depend on the flow conditions determined by the LC method and the flow rates and concentrations of oxidation agent and phosphoric acid added in the interface. To determine accurate isotope ratios, a quantitative conversion of the carbon contained in the analyte to the CO2 measurement gas is a prerequisite. Oxidation efficiencies are not commonly evaluated during method development, although certain analytes are known to be difficult to be oxidized by sulfate radicals. For the assessment of the oxidation efficiency of the LC-IRMS system, three different approaches were evaluated. (1) Residual organic carbon in the eluent stream of the interface was determined to calculate oxidation yields depending on the initial analyte concentration. (2) The IRMS response was calibrated to an inorganic carbon reference material to determine oxidation efficiencies with the help of the IRMS as a detector. (3) The oxidation temperature was deliberately reduced while monitoring the δ13C and signal intensity. The common assumption that a linear relation of IRMS signal to analyte concentration is an indicator for complete oxidation in LC-IRMS could be disproved. All three approaches can be applied for future method development in LC-IRMS, monitoring of existing flow injection applications, as well as for verification of complete oxidation in established LC-IRMS methods.

Taste and odor compounds are organic chemicals produced via biochemical processes, and their presence, even at low nanogram-per-liter concentrations, can make water useless for drinking purposes. In this work, a very sensitive and completely automated analytical procedure, based on solid-phase microextraction, has been developed and optimized for determination of seven taste and odor compounds in water media, well below their odor threshold. The selected analytes were isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, geosmin, 2-methylisoborneol, 2,4,6-trichloroanisole, 2,4,6-bromoanisole, and beta-ionone. Compared with a conventional approach, the recently introduced PAL SPME Arrow showed a significant enhancement in sensitivity and also outstanding robustness and stability. Three commercially available fiber coatings, as well as experimental parameters of the headspace extraction procedure, such as extraction temperature, time, and ionic strength of the aqueous sample, were investigated to optimize the method. The linearity of the response was assessed over a three-orders-of-magnitude range, with R2 values higher than 0.9914. The method was satisfactorily precise, with RSDs less than 11% at the second lowest calibration point (10–26 ng L−1). The calculated LODs (S/N = 3) were below odor thresholds of the target analytes and varied between 0.05 and 0.6 ng L−1, for just 10 mL of water sample. An original and spiked river water sample was also analyzed, and relative recoveries of 75–116% were achieved. Based on these analytical performance characteristics, and compared with other published methods, the present method can be considered as the most sensitive wholly automated approach for determination of taste and odor compounds in water.

Characterising microplastics based on spectroscopic measurements is one key step of many studies that analyse the fate of microplastics in the environment. Over the years, many potential sources of error were identified, which can be seen by the implementation of anti-contamination protocols, measuring laboratory blanks or using less aggressive chemicals for sample purification. However, the identification process itself in the meaning of a traceable and transparent documentation is hard to find in many research studies. Unfortunately, this can make it difficult to estimate if the presented results are representative and reproducible, as the evaluation process during microplastics identification depends dramatically on the performed data treatment. To increase the awareness of this often neglected topic, this article reviews suitable data preprocessing and evaluation methods for microplastics identification based on spectroscopic measurements and will recommend a practical workflow or check list that can easily be used for further research studies.

The drugs used for treatment during chemotherapy are manufactured individually for each patient in specialised pharmacies. Thorough quality control to confirm the identity of the delivered active pharmaceutical ingredient and the final concentration of the prepared application solution is not standardized yet except for optical or gravimetric testing. However, solution stability problems, counterfeit drugs, and erroneous or deliberate underdosage may occur and negatively influence the quality of the product and could cause severe health risks for the patient. To take a step towards analytical quality control, an on-site analytical instrument using Raman and UV absorption spectroscopy was employed and the results were compared to high-performance liquid chromatography coupled to diode array detection. Within the scope of the technology evaluation, the uncertainty of measurement was determined for the analysis of the five frequently used cytostatic drugs 5-fluorouracil, cyclophosphamide, gemcitabine, irinotecan and paclitaxel. The Raman/UV technique (2.0–3.2% uncertainty of measurement; level of confidence: 95%) achieves a combined uncertainty of measurement comparable to HPLC-DAD (1.7–3.2% uncertainty of measurement; level of confidence: 95%) for the substances 5-fluorouracil, cyclophosphamide and gemcitabine. However, the uncertainty of measurement for the substances irinotecan and paclitaxel is three times higher when the Raman/UV technique is used. This is due to the fact that the Raman/UV technique analyses the undiluted sample; therefore, the sample has a higher viscosity and tendency to foam. Out of 136 patient-specific preparations analysed within this study, 96% had a deviation of less than 10% from the target content.

Complete characterization and quantification of monoclonal antibodies often rely on enzymatic digestion with trypsin. In order to accelerate and automate this frequently performed sample preparation step, immobilized enzyme reactors (IMER) compatible with standard HPLC systems were used. This allows an automated online approach in all analytical laboratories. We were able to demonstrate that the required digestion time for the model monoclonal antibody rituximab could be reduced to 20 min. Nevertheless, a previous denaturation of the protein is required, which also needs 20 min. Recoveries were determined at various concentrations and were 100% ± 1% at 100 ng on column, 96% ± 7% at 250 ng on column and 98% ± 2% at 450 ng on column. Despite these good recoveries, complete digestion was not achieved, resulting in a poorer limit of quantification. This is 50 ng on column under optimized IMER conditions, whereas an offline digest on the same system achieved 0.3 ng on column. Furthermore, our work revealed that TRIS buffers, when used with an IMER system, led to alteration of the peptides and induced modifications in the peptides. Therefore, the addition of TRIS should be avoided when working at elevated temperatures of about 60 °C. Nevertheless, our results have shown that the recovery is not significantly influenced whether TRIS is used or not (recovery: 96 ± 7% with TRIS vs. 100 ± 9% without TRIS).

The presence and the concentration of taste and odor compounds are important parameters of drinking water quality. They have extremely low odor thresholds that requires their determination at levels below the capabilities of the analytical instrumentation, unless an enrichment process is added to the procedure. Several variations of solid- and liquid-phase (micro)extraction techniques have been developed to improve the classical approaches, in terms of lower sample volumes, less solid or liquid extraction phases, automatization, and enhanced analytical figures of merit. The present review covers the articles on development and application of such sample preparation techniques, prior to chromatographic analysis, for determination of taste and odor compounds in aqueous media, published over the range of 2005−2020. The most frequently observed compounds have been classified and discussed in three groups of (i) geosmin and 2-methylisoborneol, (ii) methoxypyrazine derivatives, and (iii) haloanisoles, and miscellaneous compounds have been collected in a single category.

Collision cross section (CCS, ω) values determined by ion mobility mass spectrometry (IM-MS) provide the study of ion shape in the gas phase and use of these as further identification criteria in analytical approaches. Databases of CCS values for a variety of molecules determined by different instrument types are available. In this study, the comparability of CCS values determined by a drift tube ion mobility mass spectrometer (DTIM-MS) and a traveling wave ion mobility mass spectrometer (TWIM-MS) was investigated to test if a common database could be used across IM techniques. A total of 124 substances were measured with both systems and CCS values of [M + H]⁺ and [M + Na]⁺ adducts were compared. Deviations

Water analysis has been an important area since the beginning of analytical chemistry. The focus though has shifted substantially: from minerals and the main constituents of water in the time of Carl Remigius Fresenius to a multitude of, in particular, organic compounds at concentrations down to the sub-nanogram per liter level nowadays. This was possible only because of numerous innovations in instrumentation in recent decades, drivers of which are briefly discussed. In addition to the high demands on sensitivity, high throughput by automation and short analysis times are major requirements. In this article, some recent developments in the chemical analysis of organic micropollutants (OMPs) are presented. These include the analysis of priority pollutants in whole water samples, extension of the analytical window, in particular to encompass highly polar compounds, the trend toward more than one separation dimension before mass spectrometric detection, and ways of coping with unknown analytes by suspect and nontarget screening approaches involving high-resolution mass spectrometry. Furthermore, beyond gathering reliable concentration data for many OMPs, the question of the relevance of such data for the aquatic system under scrutiny is becoming ever more important. To that end, effect-based analytics can be used and may become part of future routine monitoring, mostly with a focus on adverse effects of OMPs in specific test systems mimicking environmental impacts. Despite advances in the field of water analysis in recent years, there are still many challenges for further analytical research. Graphical abstract Recent trends in water analysis of organic micropollutants that open new opportunities in future water monitoring. HRMS high-resolution mass spectrometry, PMOC persistent mobile organic compounds.

Rationale The defined origin of food products is nowadays often seen as a marker of quality. Stontium (Sr) isotope ratio determination can be used to verify the origin of such food products and it has thus become an important technique. Wine samples in particular are often investigated using this technique. Sr isotopic ratio measurements are often disturbed by isobaric Rb interference, making a separation procedure necessary. In this investigation a very simple and effective procedure for the separation of Rb+ and Sr2+ ions for Sr isotope ratio determination in mineral water and wine samples was developed. Methods The classical Sr-carbonate precipitation reaction for the separation of Sr2+ ions from highly soluble Rb+ ions was used. For liquid samples, such as mineral water or wine, a prior digestion is not required. This sample preparation procedure was successfully applied for Sr isotope measurements on a widely available quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) device in combination with the Concentration-Gradient-Method (CGM). Results The separation achieved Sr/Rb concentration ratios of 50,000 to 150,000 in water and wine samples. The addition of Ca2+ ions to co-precipitate with the traces of Sr improved the Rb separation and the reproducibility of isotope ratio determination to an uncertainty of ±0.4 ‰ (single standard deviation). This sample preparation approach achieved 2 to 6 times better Rb separation than the commonly applied ion-exchange resin materials. Conclusions The quality of the separation is only limited by the number of precipitation repetitions. Moreover, the applicability of quadrupole-based ICP-MS for the characterisation of samples with respect to their origin by means of Sr isotope ratio determination was demonstrated.

In-tube extraction is a full automated enrichment technique that consists of a stainless-steel needle, packed with sorbent material for the extraction of volatile and semivolatile compounds. In principle, all particulate sorbents used for enrichment in air or headspace analysis can be used. However, the selection of the sorbents is merely based on empirical considerations rather than on experimental data, which is caused by a lack of knowledge about the relevant physicochemical properties of the sorbent. Especially, the knowledge of hydrostatic, advective, diffusive, and dispersion mechanisms in addition to sorption enthalpies are important for combined transport and sorption models. To provide these missing parameters, we developed and evaluated a method in which an ordinary in-tube extraction needle was employed directly as column for sorbent characterization by inverse gas chromatography. As probe compounds, benzene, ethyl acetate, and 3-methyl-1-butanol were used to determine thermodynamic parameters such as sorption enthalpy, partitioning constant between the solid and gas phase, and kinetic parameters such as the diffusion coefficient, dispersion coefficient, and apparent permeability, exemplarily. As sorbent, three commercially available phases were characterized to demonstrate the applicability of the method.

Free available chlorine (FAC) is the most widely used chemical for disinfection and in secondary disinfection; a minimum chlorine residual must be present in the distribution system. FAC can also be formed as an impurity in ClO2 production as well as a secondary oxidant in the ClO2 application, which has to be monitored. In this study, a new method is developed based on the reaction of FAC with glycine in which the amine group selectively scavenges FAC and the N-chloroglycine formed can be measured by ion chromatography with conductivity detector (IC-CD). Utilizing IC for N-chloroglycine measurement allows this method to be incorporated into routine monitoring of drinking water anions. For improving the sensitivity, IC was coupled with post-column reaction and UV detection (IC-PCR-UV), which was based on iodide oxidation by N-chloroglycine resulting in triiodide. The method performance was quantified by comparison of the results with the N,N-diethyl-p-phenylenediamine (DPD) method due to the unavailability of an N-chloroglycine standard. The N-chloroglycine method showed limits of quantification (LOQ) of 24 μg L−1 Cl2 and 13 μg L−1 Cl2 for IC-CD and IC-PCR-UV, respectively. These values were lower than those of DPD achieved in this research and in ultrapure water. Measurement of FAC in the drinking water matrix showed comparable robustness and sensitivity with statistically equivalent concentration that translated to recoveries of 102% for IC-CD and 105% for IC-PCR-UV. Repeatability and reproducibility performance were enhanced in the order of DPD, IC-CD, and IC-PCR-UV. Measurement of intrinsic FAC in the ClO2 application revealed that the N-chloroglycine method performed considerably better in such a system where different oxidant species (ClO2, FAC, chlorite, etc.) were present.

Many gas chromatography-flame ionization detection (GC/FID) studies are dealing with response behavior of analytes such as alcohols and alkanes. Studies in the field of liquid chromatography (LC)/FID mainly focused on volatile analytes. In contrast, studies on LC/FID by conveyor type interface covered high molecular weight non-volatile biopolymers, whereby no response factors were calculated. With this study, we fill the gap and present response factors of volatile and non-volatile analytes by LC/FID in terms of flow injection (FIA) measurements of the single compounds without an analytical separation by an LC column. In the present study, 56 different compounds such as carboxylic acids, N-heterocycles, halogenated acids, pharmaceuticals, and other compounds were investigated. In some cases, the obtained response factor data confirmed aspects known from GC/FID studies. But this study also disproves several assumptions done in previous response studies as well as the prediction models based upon the experimental data and literature. Especially the response factors and effective carbon number (ECN) values of structural isomers such as pyrazine, pyridazine, and pyrimidine are assumed to be equal in current response prediction models. Contradictory to these assumptions, the experimental response factors and ECN values of, e.g., the structural isomers pyrazine (RFExp = 0.59; ECNExp = 3.66), pyridazine (RFExp = 0.66; ECNExp = 4.1), and pyrimidine (RFExp = 0.63; ECNExp = 3.93) reveal different experimental response factors and ECN than proposed by response factor prediction models (RFExp = 0.64; ECNExp = 4). Graphical abstract Graphical abstract.

The use of liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) has steadily increased in many application fields ranging from metabolomics to environmental science. HRMS data are frequently used for nontarget screening (NTS), i.e., the search for compounds that are not previously known and where no reference substances are available. However, the large quantity of data produced by NTS analytical workflows makes data interpretation and time-dependent monitoring of samples very sophisticated and necessitates exploiting chemometric data processing techniques. Consequently, in this study, a prioritization method to handle time series in nontarget data was established. As proof of concept, industrial wastewater was investigated. As routine industrial wastewater analyses monitor the occurrence of a limited number of targeted water contaminants, NTS provides the opportunity to detect also unknown trace organic compounds (TrOCs) that are not in the focus of routine target analysis. The developed prioritization method enables reducing raw data and including identification of prioritized unknown contaminants. To that end, a five-month time series for industrial wastewaters was utilized, analyzed by liquid chromatography-time-of-flight mass spectrometry (LC-qTOF-MS), and evaluated by NTS. Following peak detection, alignment, grouping, and blank subtraction, 3303 features were obtained of wastewater treatment plant (WWTP) influent samples. Subsequently, two complementary ways for exploratory time trend detection and feature prioritization are proposed. Therefore, following a prefiltering step, featurewise principal component analysis (PCA) and groupwise PCA (GPCA) of the matrix (temporal wise) were used to annotate trends of relevant wastewater contaminants. With sparse factorization of data matrices using GPCA, groups of correlated features/mass fragments or adducts were detected, recovered, and prioritized. Similarities and differences in the chemical composition of wastewater samples were observed over time to reveal hidden factors accounting for the structure of the data. The detected features were reduced to 130 relevant time trends related to TrOCs for identification. Exemplarily, as proof of concept, one nontarget pollutant was identified as

Within this study, a novel liquid chromatography (LC)/flame ionization detector (FID) interface was improved. In contrast to previously published interface concepts, the main nebulizer body and the transfer capillary was made of stainless steel. Previously reported problems such as blocking of the transfer capillary were investigated. The simple design of the here presented nebulizer interface allows a convenient handling and the exchangeability of all nebulizer parts targets fast maintenance during routine analysis. A significant advantage is the capability to implement the novel interface into most common gas chromatography (GC)/FID systems. The effects of the instrumental parameters such as backpressure, gas flow, distance between nebulizer nozzle and FID collector or FID temperature on the signal were analyzed and optimized. The influence of the nebulizer material on flame stability and capillary blockage, a well-known problem of former coupling systems, was investigated, too. Finally, the novel interface was validated for the analysis of selected compounds known from literature. Obtained results for chromatographic separation of the alcohols propanol, butanol, pentanol and hexanol, used within previous studies in the field of LC/FID coupling are shown. Limits of detection (LODs), sensitivity and linearity found within this work are compared with LC/FID interfaces developed in the past.

The field of high-resolution mass spectrometry has undergone a rapid progress in the last years due to instrumental improvements leading to a higher sensitivity and selectivity of instruments. A variety of qualitative screening approaches, summarized as nontarget screening, have been introduced and have successfully extended the environmental monitoring of organic micropollutants. Several automated data processing workflows have been developed to handle the immense amount of data that are recorded in short time frames by these methods. Most data processing workflows include similar steps, but underlying algorithms and implementation of different processing steps vary. In this study the consistency of data processing with different software tools was investigated. For this purpose, the same raw data files were processed with the software packages MZmine2, enviMass, Compound Discoverer, and XCMS online and resulting feature lists were compared. Results show a low coherence between different processing tools, as overlap of features between all four programs was around 10%, and for each software between 40% and 55% of features did not match with any other program. The implementation of replicate and blank filter was identified as one of the sources of observed divergences. However, there is a need for a better understanding and user instructions on the influence of different algorithms and settings on feature extraction and following filtering steps. In future studies it would be of interest to investigate how final data interpretation is influenced by different processing software. With this work we want to encourage more awareness on data processing as a crucial step in the workflow of nontarget screening.

Extraction of adamantanes and diamantanes from petroleum source rock using nonionic surfactant was investigated and the optimum conditions for yields of the diamondoids were determined. The conventionally used accelerated solvent extraction method was compared to an innovative microwave-assisted nonionic surfactant extraction (MANSE). A three-level full factorial design of experiment (DoE) was adopted for the optimization of MANSE, involving solvent concentration, extraction temperature as well as extraction time. In-tube extraction (ITEX-2) using TENAX TA as sorbent in combination with gas chromatography-mass spectrometry (GC-MS) was used to determine the diamondoids in the extract. The results revealed that solvent concentration, extraction temperature and time have significant effects on extraction yields of the diamondoids. 0.04 M was the optimum surfactant concentration for extraction of both, adamantane and diamantane. The highest yields of the diamondoids were obtained at extraction temperature of 80 °C. The optimum extraction time for both adamantane and diamantane was 10 min. In comparison with the accelerated solvent extraction method, the results showed that MANSE is more efficient. This study has revealed that MANSE is a robust and efficient environmentally benign sample preparation method for geochemical evaluation of petroleum source rock.

Suspect and non-target screening based on the use of high-resolution mass spectrometry (HRMS) has become more common in water analysis over the past years. However, this only yields lists of features or suspects without quantitative information. To expand the use of HRMS data to a quantitative screening, we have developed and validated a simple and fast method for more than 140 micropollutants using ultra high-performance liquid chromatography coupled to traveling wave ion mobility quadrupole time-of-flight mass spectrometry (UPLC-IM-Q-TOF-MS). Positive findings from suspect and non-target screening can be prioritized and identified by reference standards. The quantitative screening is then performed by additional measurement of calibration standards. This is carried out by means of direct injection and external calibration, without consideration of matrix effects. For all substances, limits of quantification (LOQs) of less or equal than 100 ng/L are achieved. The calibration is carried out in a range of 100 to 1000 ng/L and the results are reported as concentration ranges, in which the concentration of the analyte in the sample is to be expected. All substances were evaluated using quadratic regressions. For the verification of the accuracy, different water matrices (drinking water, groundwater, and surface water) were spiked with five concentration levels (50 ng/L, 300 ng/L, 500 ng/L, 800 ng/L, and 2000 ng/L) and indicate that for the drinking water and groundwater sample, 97% correct assignments were found, whereas for the surface water sample, 88% correct assignments were achieved. A comparative study of water samples of various matrices was accomplished using the quantitative screening analysis method and validated target methods by means of three UPLC tandem mass spectrometry (MS/MS) methods and two gas chromatography (GC) coupled to MS and MS/MS methods. A total of 510 data could be compared, which showed a good match of both approaches in more than 80% of the results. As an alternative strategy for the monitoring of water samples by UPLC-IM-Q-TOF-MS, this method provides quantitative information about target components, besides tentatively or identified substances from suspect or non-target screening. Depending on the resulting concentration range and reporting requirements, validated target methods can be further used for the previously detected targets. Graphical abstract.

The injection volume and the associated column volume overload is one of the most common issues in miniaturized chromatography. The injection volume should not exceed 10% of the effective column volume. A further reduction of the injection volume leads to an increase in chromatographic efficiency. However, the signal intensity must be above a certain threshold to generate a chromatographic peak that can be detected. Therefore, the injection volume has to be optimized to reach the ideal balance between chromatographic efficiency and sensitivity. This study examined the general influence of the injection volume for both isocratic and gradient elution, depending on the retention factor and peak standard deviation. For this purpose, substances of different polarity were selected to represent a broad elution spectrum. Besides the model analyte naphthalene, these were mainly pharmaceuticals. For all measurements a microbore column with an ID of 300 µm and packed with 1.9 μm fully porous particles was used. For isocratic elution, the injection volume was varied between 4 and 16% of the effective column volume. The retention factors were adjusted between 2 and 10. For gradient elution, the injection volume was varied between 4 and 160% of the effective column volume. The observed effects were further investigated using the gradient kinetic plot theory. In isocratic elution, a loss in plate height up to 50% was observed for components that elute near the void time. A significant reduction of the chromatographic efficiency was noticed up to a retention factor of 4. In gradient elution, a reduction in peak capacity could only be observed if the injection volume exceeded 40% of the effective column volume. For some substances, only a slight loss in peak capacity was noticed even with a volume overload of 160%.

Rationale Bulk stable isotope analysis (BSIA) of dissolved matter (e.g. dissolved organic carbon, total nitrogen bound (TNb), etc.) is of particular importance since this pool is a prime conduit in the cycling of N and C. Studying the two elemental pools is of importance, as transformation and transport processes of N and C are inextricably linked in all biologically mediated systems. No system able to analyze natural abundance stable carbon and nitrogen isotope composition in aqueous samples (without offline sample preparation) and simultaneously has been reported so far. Extension of the high-temperature combustion (HTC) system, to be capable of measuring TNb stable nitrogen isotope composition, is described in this study. Methods To extend the TOC analyzer to be capable of measuring TNb, modifications from the HTC high-performance liquid chromatography/isotope ratio mass spectrometry (HPLC/IRMS) interface were implemented and expanded. A reduction reactor for conversion of NOx into N2 was implemented into the new developed system. The extension addresses mainly the development of the focusing unit for nitrogen and a degassing device for online separation of TNb from molecular nitrogen (N2) prior to injection. Results The proof of principle of the system was demonstrated with different compound solutions. In this initial testing, the δ15NAIR-N2 values of the tested compounds were determined with precision and trueness of typically ≤0.5‰. Good results (u ≤ 0.5‰) could be achieved down to a TNb concentration of 40 mgN/L and acceptable results (u ≤ 1.0‰) down to 5 mgN/L. In addition, the development resulted in the first system reported to be suitable for simultaneous and direct δ13C and δ15N BSIA of aqueous samples. Conclusions The development resulted in the first system shown to be suitable for both δ13C and δ15N direct BSIA in aqueous samples. This system could open up new possibilities in SIA-based research fields. Copyright © 2016 John Wiley & Sons, Ltd.

The efficiency of miniaturized liquid chromatography columns with inner diameters between 200 and 300 μm has been investigated using a dedicated micro-liquid chromatography system. Fully porous, core-shell and monolithic commercially available stationary phases were compared applying van Deemter and kinetic plot analysis. The sub-2 μm fully porous as well as the 2.7 μm core-shell particle packed columns showed superior efficiency and similar values for the minimum reduced plate heights (2.56-2.69) before correction for extra-column contribution compared to normal-bore columns. Moreover, the influence of extra-column contribution was investigated to demonstrate the difference between apparent and intrinsic efficiency by replacing the column by a zero dead volume union to determine the band spreading caused by the system. It was demonstrated that 72% of the intrinsic efficiency could be reached. The results of the kinetic plot analysis indicate the superior performance of the sub-2 μm fully porous particle packed column for ultra-fast liquid chromatography.

Sterol analysis of edible oils and fats is important in authenticity control. The gas chromatographic determination of the sterol distribution and total content is described by ISO norm 12228. Extraction, purification, and detection of the sterols are time-consuming and error-prone. Collaborative trials prove this regularly. Purification by thin-layer chromatography (TLC) and robust GC determination of all mentioned sterols is not straightforward. Therefore, a fully automated LC-GC-FID method was developed to facilitate the determination of sterols. The only manual step left was to weigh the sample into an autosampler vial. Saponification and extraction were performed by an autosampler while purification, separation, and detection were accomplished by online coupled normal-phase LC-GC-FID. Interlacing of sample preparation and analysis allowed an average sample throughput of one sample per hour. The obtained quantitative results were fully comparable with the ISO method with one apparent exception. In the case of sunflower oils, an additional unknown sterol was detected generally missed by ISO 12228. The reason was found in the omission of sterol silylation before subjection to GC-FID. The derivatization reaction changed the retention time and hid this compound behind a major sterol. The compound could be identified as 14-methyl fecosterol. Its structure was elucidated by GC-MS and ensured by HPLC and GC retention times. Finally, validation of the designed method confirmed its suitability for routine environments.

The presence of organic micropollutants and their transformation products (TPs) from biotic and abiotic processes in aquatic environments is receiving intense public and scientific attention. Yet a suitable sample preparation method that would enable extraction and enrichment of a wide range of such compounds from water is missing. The focus of this paper was to develop an enhanced solid phase extraction (SPE) protocol which enabled isolation of parent compounds and low molecular weight transformation products (that are produced after treatment of water with ozone) from different water matrices. Ten SPE sorbents were evaluated with regard to their ability to extract acidic, neutral, and basic compounds from water at several pH values. Highest recoveries (91-99 %) for all analytes in pure water were obtained by combining strong anion and cation exchangers of two manufacturers in a tandem mode without pH adjustment. Tandem Oasis (MAX+MCX) was finally applied to extract the spiked analytes from tap water, surface water, and several wastewater samples. The efficiency of the used SPE procedure was examined using an optimized liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method using multiple reaction monitoring (MRM) mode. The occurrence of some of the investigated TPs in environmental water matrices was proven for the first time in this study. Method quantification limits (MQLs) for all compounds ranged from 3.7 to 15.3 ng/L in all matrices. Recoveries (%RE) were between 90 and 110 %. Intraday and interday precision, expressed as relative standard deviation, varied from 0.7 to 5.9 % and 1.8 to 10.3 %, respectively. Matrix effect (%ME) evaluation demonstrated that even complex sample matrices did not show significant ion suppression or enhancement. The applicability of the method was shown during two sampling campaigns at Ruhr river and a wastewater treatment plant (WWTP) equipped with an ozonation step after regular biological treatment. The parent compounds were found in all water matrices at concentrations ranging between low nanogram per liter and low microgram per liter. Concentration levels of the detected TPs were in the lower nanogram per liter range. Their concentrations increased after ozonation of treated wastewater but decreased substantially after a polishing biological treatment in the final effluent and in the receiving surface water; thus demonstrating that occurrence at critical concentrations in aquatic ecosystems is rather unlikely.

RATIONALE In aqueous samples compound-specific stable isotope analysis (CSIA) plays an important role. No direct method (without sample preparation) for stable nitrogen isotope analysis (δ(15) N SIA) of non-volatile compounds is known yet. The development of a novel HPLC/IRMS interface based on high-temperature combustion (HTC) for both δ(13) C and δ(15) N CSIA and its proof of principle are described in this study. METHODS To hyphenate high-performance liquid chromatography (HPLC) with isotope ratio mass spectrometry (IRMS) a modified high-temperature combustion total organic carbon analyzer (HTC TOC) was used. A system to handle a continuously large amount of water (three-step drying system), favorable carrier and reaction gas mix and flow, an efficient high-temperature-based oxidation and subsequent reduction system and a collimated beam transfer system were the main requirements to achieve the necessary performance. RESULTS The proof of principle with caffeine solutions of the system succeeded. In this initial testing, both δ(13) C and δ(15) N values of tested compounds were determined with precision and trueness of ≤0.5 ‰. Further tests resulted in lower working limit values of 3.5 μgC for δ(13) C SIA and 20 μgN for δ(15) N SIA, considering an accuracy of ±0.5 ‰ as acceptable. CONCLUSIONS The development of a novel HPLC/IRMS interface resulted in the first system reported to be suitable for both δ(13) C and δ(15) N direct CSIA of non-volatile compounds. This highly efficient system will probably open up new possibilities in SIA-based research fields. Copyright © 2016 John Wiley & Sons, Ltd.

Environmental pollution issues, such as the impact of wastewater treatment plants (WWTPs) to contaminate the recipient waters, are multivariate problems in which several variables with varying correlation values contribute. Chemometrics-based methods can play a critical role to study the occurrence and fate of contaminants of emerging concern (CECs) in an environmental pollution question. This study performed nontarget screening (NTS) with liquid chromatography-high resolution mass spectrometry (LC-HRMS) for the investigation of pollution patterns of river water samples affected by the effluent of a WWTP (upstream/downstream) at three sampling times. The complex data sets collected in a designed experiment were analyzed using the ROIMCR approach, using data selection from MS regions of interest (ROI). Then, multivariate curve resolution alternating least-squares (MCR-ALS) was applied for simultaneous resolution of 18 upstream/downstream river water samples. The resolved and cleaned matrix of peak areas were subjected to group-wise ANOVA-simultaneous component analysis (GASCA) for interpretation of the variations induced by location and time factors in a sparse principal component analysis way and to uncover the groups of pollutants co-occurring in the environment. The resolved groups of significant features based on sampling site factor were compared with the prioritized features using partial least squares-discriminant analysis (PLS-DA) least squares-discriminant analysis ures using partial least-squares-discriminant analysis (PLS-DA). Here, we focused on the environmental relevance of groups of compounds with significant variations for a few tentatively identified contaminants. This study clearly shows that employing complementary chemometric tools for NTS can improve the current knowledge on exposure trends of CECs in water bodies for further investigation.

In the present work, a very sensitive and fully automated direct immersion PAL SPME Arrow procedure, coupled with GC–MS, has been developed and validated for determination of nine phosphorus flame retardants in different types of water samples (river, drinking and rainwater). PDMS/DVB was selected among three commercially available SPME Arrows (PDMS/DVB, DVB/PDMS/CWR and PDMS/CWR), since it resulted in the best sensitivity. The important experimental parameters were optimized via a central composite design response surface methodology and as result, extraction time of 65 min, extraction temperature of 80 °C and added salt concentration of 19% (w/v), were selected as the optimum values. The optimized method showed linear response over the calibration range (2 – 500 ng L−1), with R2-values higher than 0.9937. The precision (RSD%) measured by replicate analyses (n = 7) was estimated at 2 and 100 ng L−1 and was less than 29% and 21%, respectively. The LOQ of PAL SPME Arrow, calculated as S/N = 10, was between 0.2 and 1.2 ng L−1 (for triphenyl phosphate and tris-(1‑chloro‑2-propyl) phosphate, respectively) with extraction efficiencies between 5.9 and 31% (for tris-(1,3-dichloro-2-propyl) phosphate and tri-n‑butyl phosphate, respectively). To assess the performance of the developed technique for real samples, two river water samples, tap water from two regions and a rainwater sample were analyzed. Most of the target analytes were observed in the river samples with concentrations of 1.0 – 250 ng L−1 and the obtained recoveries at 50 ng L−1 ranged between 60 and 107%. Considering the figures of merit of the optimized method, PAL SPME Arrow-GC–MS showed to be the most sensitive analytical approach for determination of phosphorus flame retardants in water, with satisfying precision and accuracy, compared with conventional SPME-NPD, LLE-GC–MS and SPE-LC-MS/MS.

Several attempts to combine high performance liquid chromatography (HPLC) with flame ionization detection (FID) have been made since the 1960s. Elaborated systems were developed to overcome problems such as detector overload by use of organic solvents in HPLC or transfer of non-volatile analytes into FID. Almost twenty years after the first successful applications by solvent evaporation based techniques, subcritical water high temperature liquid chromatography opened the door for novel approaches to combine HPLC with FID. Direct coupling without pre-evaporation steps of signal disturbing organic solvents became possible and new instrumental developments resulted in capillary jet interface systems. These systems are suitable for a broad range of volatile and non-volatile analytes, which led to a significant increase of publications. This review discusses the most important developments of LC/FID coupling and summarizes its field of applications.

Microextraction techniques have been proven to provide similar or better results in terms of sensitivity and reproducibility in comparison to liquid-liquid extraction (LLE) and solid-phase extraction (SPE). Furthermore, the high time efficiency and decreased workload leads to a higher sample throughput. In this review the state of the art of some of these techniques, namely solid-phase microextraction (SPME), stir-bar sorptive extraction (SBSE), solid-phase dynamic extraction (SPDE), in-tube extraction-dynamic headspace (ITEX-DHS) and PAL SPME Arrow is shown. Furthermore, their benefits and drawbacks are discussed, together with their applicability to the analysis of water samples. To that end, the latest publications of microextraction techniques for a selection of regulated compound classes (chlorophenols (CPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides, short-chained chlorinated paraffins (SCCPs) and volatile organic compounds (VOCs)) are compared. Finally, a guideline for choosing the best microextraction technique for different analytical needs is described.

In the past, the main focus of flame ionization detector (FID) response studies was set on investigations of gas chromatography (GC) relevant analytes such as aliphatic hydrocarbons and selected functional groups. Only a few data are available for liquid chromatography (LC)/FID responses. Within this research paper, we present the FID response factors for a LC/FID system with an aqueous eluent as mobile phase. The study focus on the most common analytes of LC/FID studies in the past as well as several compounds that are not directly GC compatible because of their polarity. Furthermore, the range of substances was extended to isomers, poly-alcohols, and sugars to obtain more detailed information of the influence of hydroxyl groups on the recorded response. The data show a group-specific correlation of response factors with a correlation coefficient (R2) for, e.g., alcohols and ketones of 0.99. Constant contribution factors of functional groups as mentioned in several GC/FID response studies and prediction models were observed to a limited extent. Interactions of sugar analytes with water showed that transfer of GC/FID to LC/FID data cannot be done in general. The underlying mechanisms revealed several new aspects, which have to be taken into account for future response prediction models, especially of small molecules. Interactions between eluent and analytes show that LC/FID response prediction is more complex and requires more than simple addition of functional group contributions.