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A rapid, precise and specific hydrophilic interaction chromatography (HILIC) combined with postcolumn derivatization using o -phthaldialdehyde and fluorescence detection was developed and validated for the determination of selected pharmaceutically active thiols. The analysis was carried out on a Diol HILIC column using a mobile phase consisting of acetonitrile and solution of 10 mmol/L citric acid adjusted with 1-propylamine to pH 5.5 in ratio 75:25 (v/v) for separation of cysteine and homocysteine and in ratio 85:15 (v/v) for separation of N -acetyl- l -cysteine and captopril. The postcolumn derivatization reaction was performed at room temperature using reagent (5 mmol/L OPA in 0.05 mol/L 4- (2-hydroxyethyl) piperazine-1-ethanesulfonic acid at pH 7) delivered at the flow rate of 0.3 mL/min. Fluorescence detection was carried out at excitation and emission wavelength of 345 nm and 450 nm, respectively. The effect of chromatographic conditions including acetonitrile content, salt concentration in the mobile phase and mobile phase pH on the retention of tested thiols was investigated. The postcolumn reaction conditions such as reaction temperature, derivatization reagent flow rate, o -phthaldialdehyde concentration and derivatization reagent pH were deeply studied. The developed method was validated in terms of linearity, accuracy, precision and selectivity according to the International Conference on Harmonisation guidelines. The HILIC method was successfully applied for the analysis of commercially available samples of pharmaceutically active thiols such as captopril, N -acetyl- l -cysteine (NAC) and cysteine. [ABSTRACT FROM AUTHOR]

This is the first study to employ a reaction flow (RF) HPLC column of a short 5 cm length to identify antioxidants in a variety of complex samples represented by tea, utilising simultaneous multiplexed detection techniques. The detection responses included: underivatised UV at 280 nm, underivatised fluorescence detection (FLD) and a post column derivatisation (PCD) colorimetric response for antioxidants via the ferric reducing antioxidant power (FRAP) assay. Both similarities and differences in the chromatograms obtained using the three detection modes highlight the power of multiplexed detection. The main findings from the bioactive profiling include: the Fruit of the Forest tea contains the lowest level of antioxidants and is clearly distinct from the other three teas which are based on Camellia sinensis . The antioxidants detected in the green tea and the two black teas are similar. The green tea contains a higher concentration of the two main antioxidants that eluted at 4.0 and 5.7 min. The simplicity of sample analysis and chemical profiling using RF columns and selective detection was the focus of this study via the analysis of antioxidants in tea using the FRAP reagent. The main advantage of RF-PCD is the ability to split flows for simultaneous detection with minimal post column dead volume contributions, making peak matching between detectors much easier. To date, few studies exploit the power of RF-PCD multiplexed detection to differentiate and identify bioactive compounds in various complex samples. Applications of the approach developed in this study may include antioxidant screening and profiling of natural products, foods and beverages. [ABSTRACT FROM AUTHOR]

The coupling of high performance liquid chromatography (HPLC) with post column derivatisation (HPLC-PCD) will increase the sensitivity of an instrument to the target molecule, improve specificity by selective derivatisation to remove potential interferences from the matrix, and be cost-effective; all these factors may well prove that PCD is an alternative to existing techniques for routine analysis. Calcidiol (25(OH)D) concentrations are used in the determination of vitamin D deficiency in humans, and there is growing interest and demand in its analysis with some controversy surrounding the sensitivity and specificity of its detection. 25(OH)D analysis is currently performed using either competitive binding assays or HPLC analysis, coupled with detection by a variety of means, such as, UV–Vis absorption, electrochemical or mass spectroscopy (MS) detection. HPLC coupled with MS (HPLC-MS) detection is the gold standard for 25(OH)D analysis due to its sensitivity and selectivity compared to all other techniques, however, its utility is limited by its high cost. This article reviews the current status of HPLC based techniques in the detection of 25(OH)D (and its metabolites), and further explores the use of HPLC-PCD. [ABSTRACT FROM AUTHOR]

The retention behavior of primary aliphatic amines (homologous series of aliphatic alkyl amines and cycloalkyl amines) and positional isomers of alkylamines in the hydrophilic interaction chromatography mode was studied. The study was carried out on a TSKgel Amide-80 column followed by postcolumn derivatization with fluorescence detection to describe the retention mechanism of tested compounds. The effect of chromatographic conditions including column temperature, acetonitrile content in the mobile phase, mobile phase pH (ranging from 3.5 to 6.8), and salt concentration in the mobile phase was investigated. The final mobile phase consisted of acetonitrile and solution of 20 mM potassium formate pH 3.5 in ratio 80:20 v/v. The analyses were carried out at mobile phase flow rate of 1.0 mL/min and the column temperature of 20°C. The developed method was fully validated in terms of linearity, sensitivity (limit of detection and limit of quantification), accuracy, and precision according to International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines. The proposed new methods were proved to be highly sensitive, simple, and rapid, and were successfully applied to the determinations of isopropylamine, cyclohexylamine, and cyclopropylamine in relevant active pharmaceutical ingredients. [ABSTRACT FROM AUTHOR]

An in-line size-exclusion (SE) ultra-high-performance liquid chromatography (UHPLC)- 5,5-dithio-bis-(2-nitrobenzoic acid) (DTNB) method to quantify thiols in monoclonal antibodies (mAb) when manufacturing antibody-drug conjugates (ADCs) was developed. The mAbs are separated on an SE-UHPLC column and monitored with a UV detector at a wavelength of 280 nm. Eluents are channeled into a reaction coil and mixed with DTNB to form 5-thio-2-nitrobenzoic acid (TNB). Thiol concentration is calculated using absorption at 412 nm. Using optimized conditions, partially reduced mAbs can be separated from low-molecular weight contaminants and undergo the DTNB reaction. The standard curve of L-cysteine had good linearity between 100 and 1000 μM. The selectivity, linearity, repeatability, and robustness of this method were evaluated. The calculated free-SH:protein ratios of partially reduced mAbs were consistent between in-line SE-UHPLC-DTNB and conventional methods. The SE-UHPLC-DTNB method showed time- and temperature-dependent changes in the free-SH:protein ratio of mAbs during reduction. The changes in drug-antibody ratio (DAR) of ADCs during the conjugation reaction were also evaluated. This method is an inexpensive and versatile alternative to conventional methods of estimating the free-SH:protein ratio of mAbs and the DAR of ADCs. This method also minimizes assay time. [ABSTRACT FROM AUTHOR]

A postcolumn fluorescence reaction system for the high-performance liquid chromatographic (HPLC) determination of tetrodotoxin in the silver-cheeked toadfishLagocephalus sceleratusis discussed theoretically and investigated experimentally. Ion-pair chromatography with volatile ammonium perfluoroheptanoate was used for the separation of tetrodotoxin and 4,9-anhydrotetrodotoxin. The postcolumn reaction was based on the tetrodotoxin conversion to a quinazoline fluorescent compound under strong alkaline conditions. All postcolumn parameters were optimized that affected the sensitivity, dispersion, and stability. Helically coiled and knitted open tubular reactors composed of polyetheretherketone were constructed and characterized in detail. The performance of these reactors was evaluated on the basis of sensitivity and dispersion. Their optimal design is reported. The knitted reactors were more efficient than the relevant helically coiled reactors when higher reaction times are required. A 1500-µL polyetheretherketone knitted coil with 0.010″ internal diameter was optimum exhibiting higher pressure tolerances than Teflon coils. The HPLC postcolumn reaction method was evaluated in terms of linearity, sensitivity, accuracy, precision, and ruggedness. The linear dynamic ranges for tetrodotoxin and 4,9-anhydrotetrodotoxin were 40–3000 and 80–3000 ppb, respectively. The limits of detection and quantification were 12 and 41 ppb, respectively, for tetrodotoxin and 26 and 85 ppb, respectively, for 4,9-anhydrotetrodotoxin. The accuracy was evaluated by recovery measurements and the values for tetrodotoxin were between 90.7 and 93.6%. The use of a volatile perfuorocarboxylic acid as an ion-pair reagent allows confirmation of analytes in sample matrix by liquid chromatography tandem mass spectrometry using identical mobile phase conditions. [ABSTRACT FROM PUBLISHER]

Background/aim: Autism is a heterogeneous neurodevelopmental disorder. This study aimed to assess the clinical significance of amino acid profile assay in autism using cation-exchange chromatography with ninhydrin postcolumn derivatization. Materials and methods: This study included 42 autistic children and 26 apparently healthy children. All participants were subjected to the assay of plasma amino acids (essential, nonessential, and nonstandard) using cation-exchange chromatography with postcolumn derivatization by ninhydrin. Results: The levels of most of the essential amino acids were significantly lower in autistic children than controls. As regards nonessential amino acids, significantly lower levels for plasma cysteine, tyrosine, and serine and significantly higher levels for plasma glutamic acid were recorded in autistic children than controls. Finally, the autistic group demonstrated significantly lower levels of α-aminoadipic acid, carnosine, and β-alanine and significantly higher levels of hydroxyproline, phosphoserine, β-amino-isobutyric acid, and ammonia as compared to controls. Conclusion: The study revealed that autistic children exhibit distinct alterations in the plasma levels of some amino acids, which can in turn participate in the disease etiology and can be applied as a diagnostic tool for early detection of autism. [ABSTRACT FROM AUTHOR]

An HPLC method with postcolumn derivatization was developed and validated for the determination of theanine content in tea dietary ingredients and supplements. A variety of common commercially available supplement forms such as powders, liquid tinctures, tablets, softgels, and gelcaps, as well as three National Institute of Standards and Technology Camellia sinensis Standard Reference Materials were investigated in the study. A simple extraction procedure using citrate buffer at pH 2.2 allowed for the analysis of theanine without additional cleanup or concentration steps, even at low ppm levels. Theanine was separated from other naturally occurring amino acids using a cation-exchange column and detected using a UV-Vis detector after derivatization with ninhydrin reagent. A single-laboratory validation demonstrated that specificity, accuracy, precision, and other method performance parameters have met the requirements set for theanine analysis by the AOAC Stakeholder Panel on Dietary Supplements. [ABSTRACT FROM AUTHOR]

The study's objectives were to evaluate a method for the determination of aflatoxins (AFs) in the Brazilian peanut confection "Paçoca" and to apply the method in investigating AF concentrations in Paçoca marketed in São Paulo State throughout 2013. Results of another survey conducted between 1994 and 2002 with another method were also reported. The current method consists of immunoaffinity column cleanup, LC with postcolumn derivatization for AF fluorescence enhancement, and fluorescence determination for the toxins. The mean recovery and mean RSDr values were 88.6 and 7.9%, respectively. The LODs for aflatoxin B1, aflatoxin B2, aflatoxin G1, and aflatoxin G2 were 0.04, 0.01, 0.02, and 0.01 ng/g; and the LOQs were 0.15, 0.04, 0.07, and 0.04 ng/g, respectively. Results of the two survey studies indicate that the contamination of AFs in Paçoca remains a public health problem. In the 2013 survey, 71 of 100 samples (71%) had AFs contamination ranging from 0.3 to 41.8 ng/g, with 12 samples (12%) containing >20 ng/g of the toxins, whereas in the 1994-2002 survey, 73 of 150 samples (51%) had AFs contamination ranging from 9 to 1439 ng/g with 65 samples (45%) containing levels >20 ng/g. [ABSTRACT FROM AUTHOR]

The amino alcohols in l-valinol were effectively separated and quantified using hydrophilic interaction chromatography with fluorescence detection. The influence of the mobile phase (salt type, buffer concentration, and pH) on retention was studied. A column TSKgel amide and mobile phase consisting of 10 mM acetate buffer pH 4.0 and acetonitrile (20:80, v/v) provided well -separated symmetric peaks of analytes. Fluorescence detection was performed using postcolumn derivatization with o-phtaldialdehyde/2-mercaptoethanol at an excitation and emission wavelength of 345 and 450 nm, respectively. Simple sample pretreatment and very high sensitivity represent the main advantages of the developed method. After validation, the method was successfully applied to the analysis of commercial samples of l-valinol. [ABSTRACT FROM AUTHOR]

This normal-phase HPLC method with postcolumn reduction and fluorescence detection allows for the quantitative determination of trans vitamin K1 in infant, pediatric, and adult nutritionals. Vitamin K1 is extracted from products with iso-octane after precipitation of proteins and release of lipids with methanol. Prepared samples are injected onto a silica HPLC column where cis and trans vitamin K1 are separated with an iso-octane-isopropanol mobile phase. The column eluent is mixed with a dilute ethanolic solution of zinc chloride, sodium acetate, and acetic acid, and vitamin K1 is reduced to a fluorescent derivative in a zinc reactor column. The resulting hydroquinone is then detected by fluorescence at an excitation wavelength of 245 nm and an emission wavelength of 440 nm. During a single-laboratory validation of this method, repeatability and intermediate precision ranged from 0.6 to 3.5% RSD and 1.1 to 6.0% RSD, respectively. Mean overspike recoveries ranged from 91.9 to 106%. The method demonstrated good linearity over a standard range of approximately 2-90 µg/L trans vitamin K1 with r² averaging 0.99995 and average calibration errors of <1%. LOQ and LOD in ready-to-feed nutritionals were estimated to be 0.03 and 0.09 µg/100 g, respectively. The method met AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals Standard Method Performance Requirements® and was approved as a first action method at the 2015 AOAC Mid-Year Meeting. [ABSTRACT FROM AUTHOR]

The usefulness of terbium oxide nanoparticles (Tb 4 O 7 NPs) as post-column derivatizing reagent for the liquid chromatographic determination of residues of quinolone antibiotics in milk samples has been studied. Seven quinolones of veterinary use have been chosen as model analytes to develop this method. The derivatization step is based on the formation of luminescent chelates of quinolones with Tb 4 O 7 NPs, which are monitored at λ ex = 340 nm and λ em = 545 nm. Another relevant feature of the method is that the use of a 10-cm column and a ternary mixture of methanol, acetonitrile and acetic acid as mobile phase in gradient elution mode allow the chromatographic separation of the quinolones in about 13 min, whereas previously described chromatographic methods require about 20 min. The dynamic ranges of the calibration graphs and limits of detection are, respectively: 65–900 ng mL −1 and 35 ng mL −1 for marbofloxacin, 7.2–900 ng mL −1 and 2.5 ng mL −1 for ciprofloxacin, 6–900 ng mL −1 and 2 ng mL −1 for danofloxacin, 50–900 ng mL −1 and 20 ng mL −1 for enrofloxacin, 35–900 ng mL −1 and 12 ng mL −1 for sarafloxacin, 5–900 ng mL −1 and 2 ng mL −1 for oxolinic acid, and 7–900 ng mL −1 and 2.5 ng mL −1 for flumequine. The precision, established at two concentration levels of each analyte and expressed as the percentage of the relative standard deviation is in the range of 1.9–8.1% using standards, and of 3.4–10.7% in the presence of milk samples. The method has been satisfactorily applied to the analysis of skimmed, semi-skimmed and whole milk samples, with recoveries ranging from 89.0 to 106.5%. [ABSTRACT FROM AUTHOR]

The aim of the present work was to improve and validate the HPLC-CUPRAC postcolumn method for the evaluation of active antioxidant markers from the acetonic extracts of Ginkgo biloba leaves. Improvement of the HPLC online assay was performed by evaluating the suitable loop temperature, the reaction loop length, and the impact of flow rate. Separation of the analytes was performed by the HPLC method on an ACE C18 analytical column using a gradient elution program. The separated antioxidant markers in the extracts reacted with copper(II)-neocuproine (Cu(II)-Nc) reagent in the postcolumn reaction coil. The reagent was reduced by antioxidants to the copper(I)-neocuproine (Cu(I)-Nc) chelate with a maximum absorption at 450 nm. Validation experiments confirmed sufficient precision, sensitivity, and effectiveness of the corresponding method, which could be used for further evaluations of active antioxidant compounds in similar plant materials. [ABSTRACT FROM AUTHOR]

Hydrodynamic chromatography – inductively coupled plasma mass spectrometry (HDC-ICP-MS) is a technique that is widely used in the size-characterisation of nanoparticles. In this work, a system was modified to facilitate the injection of NIST-traceable standards into the post-column effluent, which then allowed the response from an eluting nanoparticle to be quantified against the response from the post-column standards. Combining the simultaneously acquired particle sizing data and mass concentration data allowed accurate quantification of the particle number concentration to be made in a single analytical run. This unique single-method approach was successfully validated against a nanoparticle system which had previously been characterised in a number of recent peer-reviewed publications. In addition to this, its robustness was assessed using extracts from a study investigating the fate of nanoparticles in sewage sludge, and found to provide much improved data compared to what might have been achieved using an external calibration approach. With in-vial limits of detection of 2 and 10 ng ml−1 for titanium and silver respectively, it is insufficient for use with environmental waters, but is foreseen as being useful in screening nanoparticle production processes, or in the characterisation of higher concentration materials. As this instrumental configuration is likely to be of use to researchers involved in the general area of quantitative trace element speciation, detailed description of construction of the interface is given as ESI. [ABSTRACT FROM AUTHOR]

Three mixer designs, a back-flow tee mixer (BT), an end-blocked membrane tee mixer (EMT), and a tubular membrane mixer (TM), were fabricated and compared to three commercially available mixers, Visco-Jet Micro mixer (VJM) and HS binary tee mixer with 2 and 10 μL volume (HS-2 and HS-10) mixing cartridges. Internal volumes ranged from 8.3 to 20.3 μL. Performance characteristics were evaluated by the Villermaux-Dushman reaction, noise in baseline conductance upon mixing an electrolyte solution with water, and dispersion/relative dispersion of an injected solute. No single characteristic would uniquely qualify a particular device. In typical postcolumn use when a small reagent flow is added to a principal flow stream using a low-pulsation high-end chromatographic pump, with the worst of these mixers, imperfect mixing accounted for 99.6% of the observed noise. EMT, BT, and TM with asymmetric inlets provided better mixing performances relative to VJM, HS-2, and HS-10 with symmetric inlet ports, especially when the secondary liquid flow rate was much lower than the principal stream-flow rate. Dispersion per unit residence time was singularly large for HS-2. Based on its mixing efficiency and small dispersion, the BT design was found to be the best for practicing postcolumn reaction. As an illustrative application, this was then used to introduce electrogenerated LiOH in a suppressed ion chromatography system to perform sensitive detection of weak acids in a second dimension. [ABSTRACT FROM AUTHOR]

The article presents a study on the use of high-performance liquid chromatography (HPLC) with bromocresol green postcolumn reaction to determine human mercaptalbumin (HMA) and human non-mercaptalbumin (HNA). The study performs HPLC separation for HMA and HNA in serum. Result shows that HMA and HNA were separated in less than 30 minutes using isocratic elution and weak anion exchange columns, suggesting the reliability of the method.

To increase detection sensitivity in liquid chromatography, a generic post-column refocusing strategy has been developed to enrich (target) analytes prior to detection. In this strategy, after separation on the analytical column, the analytes are led to a trap column preferably containing a stationary phase with strong retentive properties ( e.g. silica C 30 ). They are then eluted using a strong solvent in a backward-elution mode. A first key element of the proposed strategy is that the trapping time should be at least equal to the time the front of the remobilization solvent needs to cover the entire length of the trap column, divided by the ratio of the flow rates used for trapping and remobilization. This condition is independent of the retention properties of the analytes in the trapping and remobilization solvent. Another essential element is the addition of a third solvent (isopropanol in the present case) to the remobilization solvent to overcome viscous-fingering effects caused by the viscosity difference between the trap and the remobilization solvents. The potential of the proposed post-column refocusing strategy is demonstrated for an isocratic separation of KI ( t 0 marker), an antibiotic (sulfamethazine), and acetophenone as a case study. Using optimized remobilization conditions a maximum signal-enhancement factor of 8 was achieved. Higher enhancement factors using a remobilization solvent with slightly higher elution strength were prohibited by disturbances of the UV background signal. [ABSTRACT FROM AUTHOR]

Highlights: [•] Compared with reported method, sensitivity was significantly enhanced. [•] Rapid determination of six flavonoids in rat plasma within 5min. [•] Improved peak shape by the reduction of longitudinal diffusion. [•] Post-column mobile phase adjustment was systematically discussed and validated. [•] Eliminate the contradiction between LC and MS in negative ESI mode. [ABSTRACT FROM AUTHOR]

The main biogenic amines in foods are histamine, tryptamin, cadaverin, putrescin, spermin, and spermidin. The samples of pork, beef, and poultry were extracted with 0.6 mol · l−1perchloric acid and extract was filtered. Histamine, cadaverine, putrescine, and tyramine were determined by reverse-phase HPLC using a C18stationary phase column. Acetate buffer with water (pH 4.5) and acetate buffer with acetonitrile (45/55v/v) was used as a mobile phase, the flow-rate was 1 mL · min−1. The post column derivatization technique with OPT buffer (phthaldialdehyde buffer) as derivatization agent and the fluorescence detector at 330 nm and 465 nm as excitation and emission wavelengths was used. Limit of detection for biogenic amines was 0.2 mg · kg−1and limit of quantification was 0.5 mg · kg−1. The method was useful over a wide concentration range of biogenic amines. The concentrations from 0.5 to 1 000 mg · kg−1of histamine, tyramine, putrescine, and cadaverine in pork, beef, and poultry could be detected easily without any noticed disadvantage. Concentrations of biogenic amines were determined in pork, beef, and poultry and concentrations were increased depending on temperature and time. Concentrations of cadaverine and putrescine were highest for ground meat stored at 24°C after 10 days. Highest influence of temperature on production of biogenic amines was found in poultry samples. The concentrations of tyramine, putrescine and histamine were higher than 100 mg · kg−1and the concentration of cadaverine was more than 400 mg · kg−1. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chromatographic methods to detect effectively adulterants in roasted coffee. [•] Two distinct methods and HPLC systems were evaluated for the same samples set. [•] PCA distinguished the same predominant/characteristic carbohydrate for each matrix. [ABSTRACT FROM AUTHOR]

Highlights: [•] An effective and economic PCI-IS method for MEs correction in LC–ESI-MS. [•] PCI-IS could effectively correct MEs in urine specimens. [•] PCI-IS method resolved the drawbacks of traditional internal standard method. [ABSTRACT FROM AUTHOR]

Highlights: [•] A UFLC–MS method was developed to determination of arenobufagin in rat plasma. [•] A post-column switching valve was applied to reduce the matrix effect. [•] The method successfully applied to pharmacokinetic study of arenobufagin in rat plasma. [Copyright &y& Elsevier]

A challenge for capillary LC (c LC) is fraction collection and the manipulation of fractions from microscale columns. An emerging approach is the use of segmented flow or droplet technology to perform such tasks. In this work, a fraction collection and postcolumn reaction system based on segmented flow was developed for the gradient c LC of proteins. In the system, column effluent and immiscible oil are pumped into separate arms of a tee resulting in regular fractions of effluent segmented by oil. Fractions were generated at 1 Hz corresponding to 5 nL volumes. The fraction collection rate was high enough to generate over 30 fractions per peak and preserve chromatographic resolution achieved for a five-protein test mixture. The resulting fractions could be stored and subsequently derivatized for fluorescence detection by pumping them into a second tee where naphthalene dicarboxyaldehyde, a fluorogenic reagent, was pumped into a second arm and added to each fraction. Proteins were derivatized within the droplets enabling postcolumn fluorescence detection of the proteins. The experiments demonstrate that fraction collection from c LC by segmented flow can be extended to proteins. Further, they illustrate a potential workflow for protein analysis based on postcolumn derivatization for fluorescence detection. [ABSTRACT FROM AUTHOR]

Highlights: [•] Parallel segmented flow chromatography was applied to columns packed with shell particles. [•] Short 4.6mm×30mm columns packed with sub-3μm particles are not radially equilibrated. [•] PSFC at the column outlet improves the overall efficiency by a factor of nearly two. [•] The sensitivity of weakly retained compounds increase by 25% when applying PSFC. [•] Post-column band broadening should be minimized for best gradient elution performance. [ABSTRACT FROM AUTHOR]

The application of isotope dilution in high performance liquid chromatography (HPLC) and inductively-coupled plasma mass spectrometry (ICP-MS) represents an important tool for elemental speciation analysis. Currently commercially available software deals only with one type of HPLC-ID-ICP-MS measurement comprising an addition of isotope-enriched species into the sample before HPLC separation, that is, species-specific isotope dilution. However, there is another possibility: species-unspecific isotope dilution, which is, unfortunately, not easily employed by common software. In this method, the isotope enriched solution containing common inorganic compound of the analyzed element is added to the sample after HPLC separation. Here a novel software system addresses this problem. The most important features of the computer program include easy operation, data adjustment by smoothing, detector dead-time correction, mass discrimination correction, background correction, integration of peak area and ID enumeration, processing of multi-elemental analyses, a choice of various isotopes, and a database of isotope abundances. The reliability of the software was demonstrated by processing of artificial chromatographic data and real chromatograms of standard reference materials containing mercury species and mixtures of selenium species. [ABSTRACT FROM AUTHOR]

Amino acid analysis (AAA) has always presented an analytical challenge in terms of sample preparation, separation, and detection. Because of the vast number of amino acids, various separation methods have been applied taking into consideration the large differences in their chemical structures, which span from nonpolar to highly polar side chains. Numerous separation methods have been developed in the past 60 years, and impressive achievements have been made in the fields of separation, derivatization, and detection of amino acids (AAs). Among the separation methods, liquid chromatography (LC) prevailed in the AAA field using either pre-column or post-column labeling techniques in order to improve either separation of AAs or selectivity and sensitivity of AAA. Of the two approaches, the post-column technique is a more rugged and reproducible method and provides excellent AAs separation relatively free from interferences. This review considers current separations combined with post-column labeling techniques for AAA, comparison with the pre-column methods, and the strategies used to develop effective post-column methodology. The focus of the article is on LC methods coupled with post-column labeling techniques and studying the reactions to achieve optimum post-column derivatization (PCD) conditions in order to increase sensitivity and selectivity using various types of detectors (UV-Vis, fluorescence, electrochemical etc.) and illustrating the versatility of the PCD methods for practical analysis. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] One of the very first combinations of HILIC with post-column derivatization. [•] GSH is determined at the low micromolar level in wines without matrix effect. [•] Excess of sulfite preservation reagent does not affect the analysis. [ABSTRACT FROM AUTHOR]

Abstract: Despite their potential carcinogenicity and probable formation during water disinfection processes, little is known about the occurrence of other nitro(so) compounds than a few specific N-nitroso compounds such as N-nitrosodimethylamine (NDMA). An analytical method was developed to monitor various nitro(so) compounds including N-nitrosamines based on the Griess colorimetric determination of nitrite generated by UV-254 nm photolysis of nitro(so) compounds after separation by HPLC (HPLC-Post Column UV photolysis/Griess reaction (HPLC-PCUV)). To differentiate N-nitro(so) compounds (i.e. UV-labile) from other nitro(so) and N-containing compounds (i.e. UV-resistant), a pre-treatment was established by photolyzing solid-phase extracted samples at 254 nm (1000 mJ/cm2) and thus removing N-nitro(so) compounds selectively. Considering a 1000-fold concentration factor and extraction efficiencies (57–83%) during solid phase extraction, the method detection limits ranged from 4 to 28 ng/L for dimethylnitramine and eight N-nitrosamines (EPA 8270 nine nitrosamines mixture except for N-nitrosodiphenylamine). For four pool waters, the UV-resistant groups accounted for more than 78% of the estimated total concentration of nitro(so) and other N-containing compounds (6.1–48.6 nM). Only one unknown UV-labile compound was detected in one pool water (2.0–7.9 nM). NDMA was most frequently detected and N-nitrosodipropylamine (NDPA) and N-nitrosodibutylamine (NDBA) were additionally detected in one pool water. Chloramination of a secondary wastewater effluent with NDMA (0.2 nM) and UV-resistant compounds (7.9 nM) from a pilot-scale municipal wastewater treatment plant led to a significant formation of not only unidentified UV-resistant compounds (67.8 nM) and UV-labile compounds (14.6 nM), but also identified nitrosamines such as NDMA (4.3 nM), N-nitrosopiperidine (1.8 nM), NDPA (0.5 nM), and NDBA (0.5 nM). Overall, the novel HPLC-PCUV system is a powerful screening tool for the detection of (un)known N-nitro(so) as well as other nitro(so) and UV-induced nitrite-producing compounds. [Copyright &y& Elsevier]

Recent studies suggest that cyanate (OCN-) is a potentially important source of reduced nitrogen (N) available to support the growth of aquatic microbes and, thus, may play a role in aquatic N cycling. However, aquatic OCN- distributions have not been previously described because of the lack of a suitable assay for measuring OCN- concentrations in natural waters. Previous methods were designed to quantify OCN- in aqueous samples with much higher reduced N concentrations (micromolar levels) than those likely to be found in natural waters (nanomolar levels). We have developed a method to quantify OCN- in dilute, saline environments. In the method described here, OCN- in aqueous solution reacts with 2-aminobenzoic acid to produce a highly fluorescent derivative, 2,4-quinazolinedione, which is then quantified using high performance liquid chromatography. Derivatization conditions were optimized to simultaneously minimize the reagent blank and maximize 2,4-quinazolinedione formation (>90% reaction yield) in estuarine and seawater matrices. A limit of detection (LOD) of 0.4 nM was achieved with only minor matrix effects. We applied this method to measure OCN- concentrations in estuarine and seawater samples from the Chesapeake Bay and coastal waters from the mid-Atlantic region. OCN- concentrations ranged from 0.9 to 41 nM. We determined that OCN- concentrations were stable in 0.2 μm filtered seawater samples stored at -80 °C for up to nine months. [ABSTRACT FROM AUTHOR]

Highlights: [•] We developed a method for analyzing the C-toxin content in single Alexandrium tamarense cells. [•] With this HPLC-FL method, we could measure 1fmol of C2 with S/N=2. [•] Clonal heterogeneity within the toxic strain ranged from <1fmol to 700fmolcell−1. [•] This is the first to demonstrate definitively that PSP content varies on a cell-by-cell basis. [Copyright &y& Elsevier]

A simple and sensitive analytical method based on ultrasound-assisted solid–liquid extraction and immunoaffinity column clean-up coupled with high performance liquid chromatography and on-line post-column photochemical derivatization-fluorescence detection (USLE-IAC-HPLC-PCD-FLD) has been developed for simultaneous multi-mycotoxin determination of aflatoxins B1, B2, G1, G2 (AFB1, AFB2, AFG1, AFG2) and ochratoxin A (OTA) in 13 edible and medicinal nutmeg samples marketed in China. AFs and OTA were extracted from nutmeg samples by ultrasonication using a methanol : water (80 : 20, v/v) solution, followed by an IAC clean-up step. Different USL extraction conditions, pre-processing ways for nutmeg sample and clean-up columns for mycotoxins, as well as HPLC-PCD-FLD parameters (mobile phase, column temperature, elution procedure, excitation and emission wavelengths) were optimized. This method, which was appraised for analyzing nutmeg samples, showed satisfactory results with reference to limits of detection (LODs) (from 0.02 to 0.25 μg kg−1), limits of quantification (LOQs) (from 0.06 to 0.8 μg kg−1), linear ranges (up to 30 ng mL−1 for AFB1, AFG1 and OTA and 9 ng mL−1 for AFB2 and AFG2), intra- and inter-day variability (all ＜2%) and average recoveries (from 79.6 to 90.8% for AFs and from 93.6 to 97.3% for OTA, respectively). The results of the application of developed method in nutmeg samples have elucidated that four samples were detected with contamination of AFs and one with OTA. AFB1 was the most frequently found mycotoxin in 30.8% of nutmeg samples at contamination levels of 0.73–16.31 μg kg−1. At least two different mycotoxins were co-occurred in three samples, and three AFs were simultaneously detected in one sample. [ABSTRACT FROM AUTHOR]