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Planar differential spiral sensor (PDSS) for permittivity measurement of liquid samples is proposed in this paper. The sensor comprises two ACS (Asymmetric Coplanar Strip) fed spiral sensors (AFSS) resonating at 2.4GHz for real time permittivity measurement. One sensor acts as reference sensor and other as measurement sensor. The AFSS is fabricated on FR4 substrate with dielectric constant 4.4, loss tangent 0.02 and thickness 1.6mm. The overall dimension of the AFSS is 10mm×9mm. The resonance of the sensor shifts to a lower frequency when immersed in liquid samples. The shift in resonant frequency and reflection coefficient is used to determine the relative permittivity (er) of liquid samples. The sensor is compact in size and the sensitivity is high compared with other reported sensors. The differential configuration of the sensor overcomes the limitation of cross sensitivity to ambient conditions, such as temperature and humidity. Adulteration of oil samples can also be detected as detailed in the paper. An equivalent circuit model of the sensor is also proposed. [ABSTRACT FROM AUTHOR]

Downsizing surface-enhanced Raman spectroscopy (SERS) within microfluidic devices has opened interesting perspectives for the development of low-cost and portable (bio)sensors for the optical analysis of liquid samples. Despite the research efforts, SERS-fluidic devices still rely either on the use of expensive bulky set-ups or on polymeric devices giving spurious background signals fabricated via expensive manufacturing processes. Here, polymeric platforms integrating fluidics and optics were fabricated with versatile designs allowing easy coupling with fiber-based Raman systems. For the first time, anti-fouling photocurable perfluoropolyether (PFPE) was explored for high-throughput SERS-integrating chip fabrication via replica molding of negative stamps obtained through standard and advanced fabrication processes. The PFPE devices comprised networks of channels for fluid handling and for optical fiber housing with multiple orientations. Embedded microfeatures were used to control the relative positioning of the fibers, thus guaranteeing the highest signal delivering and collection. The feasibility of PFPE devices as fiber-based SERS fluidic platforms was demonstrated through the straightforward acquisition of Raman-SERS spectra of a mixture of gold nanoparticles as SERS substrates with rhodamine 6G (Rh6G) at decreasing concentrations. In the presence of high-performing gold nanostars, the Rh6G signal was detectable at dilutions down to the nanomolar level even without tight focusing and working at low laser power—a key aspect for analyte detection in real-world biomedical and environmental applications. [ABSTRACT FROM AUTHOR]

The stable nitrogen isotope (15 N) analysis of ammonium (NH4+) and nitrate (NO3–) is widely used in ecological research, providing insights into N cycling and its underlying regulating mechanisms in both aquatic and terrestrial ecosystems. To date, a large number of methods have been developed for the preparation and measurement of 15 N abundance of NH4+ and NO3– in liquid environmental samples at either natural abundance or enriched levels. However, these methods are all subject to certain specific advantages and limitations, and ecologists might be looking for an efficient way to select the most suitable methods in face of shifting sampling and analytical conditions. Based on our extensive review of these 15 N analysis methods we developed a decision support tool (DST) to provide quick and proper guidance for environmental researchers in finding the optimal method for preparing their liquid samples for 15 N analysis in NH4+ or NO3–. The DST is a decision tree based on several key criteria that users need to take into account when choosing the preferred sample preparation method for their samples. The criteria concern: the sample matrix, the 15 N abundance and the concentration of the target N species, the contamination by other N-containing chemicals, the isotopic fractionation, the availability of equipment, concerns about toxicity of reagents, and the preparation time. This work links field-scale experiments and laboratory 15 N analysis. Potential applications of our decision trees include 15 N studies ranging from natural abundance to tracer level in a wide range of terrestrial, freshwater and marine ecosystems. [ABSTRACT FROM AUTHOR]

Abstract In this work, the combination of dispersive micro solid-phase extraction (DµSPE) with laser-induced breakdown spectroscopy (LIBS) was evaluated for simultaneous preconcentration and detection of Zn, Cd, Mn, Ni, Cr and Pb in aqueous samples. Two adsorbent materials were tested in the microextraction step, namely graphene oxide and activated carbon. In both cases, the microextraction process consisted in the dispersion of a small quantity of adsorbent in the sample solution containing the analytes. However, while the use of activated carbon required a previous chelation of the metals, this step was avoided with the use of graphene oxide. After extraction, the analytes retained in the adsorbents were analysed by LIBS. Several experimental factors affecting the extraction of the metals (adsorbent amount, pH and extraction time) were optimized by means of the traditional univariate approach. Under optimum microextraction conditions, the analytical features of the proposed DµSPE-LIBS methods were assessed, leading to limits of detection below 100 µg kg−1 and 50 µg kg−1 with the use of activated carbon and graphene oxide, respectively, as adsorbents in the DµSPE process. Trueness evaluation of the most sensitive procedure was carried out by spike and recovery experiments in a real sample of tap water, leading to recovery values in the range 98–110%. Graphical abstract fx1 Highlights • DµSPE-LIBS, using graphene oxide as sorbent, has been evaluated for the first time. • Several metals in liquid samples has been detected at µg Kg−1 level by LIBS. • Metal chelation step has been avoided with the use of graphene oxide. • Graphene oxide provides superior analytical capabilities than activated carbon. [ABSTRACT FROM AUTHOR]

A rapid and efficient Dispersive Liquid–Liquid Microextraction (DLLME) followed by Laser-Induced Breakdown Spectroscopy detection (LIBS) was evaluated for simultaneous determination of Cr, Cu, Mn, Ni and Zn in water samples. Metals in the samples were extracted with tetrachloromethane as pyrrolidinedithiocarbamate (APDC) complexes, using vortex agitation to achieve dispersion of the extractant solvent. Several DLLME experimental factors affecting extraction efficiency were optimized with a multivariate approach. Under optimum DLLME conditions, DLLME-LIBS method was found to be of about 4.0–5.5 times more sensitive than LIBS, achieving limits of detection of about 3.7–5.6 times lower. To assess accuracy of the proposed DLLME-LIBS procedure, a certified reference material of estuarine water was analyzed. [ABSTRACT FROM AUTHOR]

In-needle extraction was applied for preparation of aqueous samples. This technique was used for direct isolation of analytes from liquid samples which was achieved by forcing the flow of the sample through the sorbent layer: silica or polymer (styrene/divinylbenzene). Specially designed needle was packed with three different sorbents on which the analytes (phenol, p-benzoquinone, 4-chlorophenol, thymol and caffeine) were retained. Acceptable sampling conditions for direct analysis of liquid sample were selected. Experimental data collected from the series of liquid samples analysis made with use of in-needle device showed that the effectiveness of the system depends on various parameters such as breakthrough volume and the sorption capacity, effect of sampling flow rate, solvent effect on elution step, required volume of solvent for elution step. The optimal sampling flow rate was in range of 0.5-2 mL/min, the minimum volume of solvent was at 400 µL level. [ABSTRACT FROM AUTHOR]

The use of an in-needle technique for direct isolation of analytes from real liquid samples is a new proposal. The in-needle technique has been relatively seldom used for direct sampling of liquid matrix through the needle. In this work the in-needle technique has been applied for the determination of compounds evolved to artificial saliva from dental prosthetic materials. It has been shown that results from the experiment with in-needle device were at least comparable with those obtained with using well known solid phase extraction (SPE). It is worth to mention that in-needle extraction offers some advantages: lower consumption of solvent, shorter step-preparation time and reduced costs. The compounds released from prosthetic materials may affect the stability of tissue conditioners and limit their long-term use in the oral cavity. Examined soft dental materials have been found to be stable as minor amount of various species have been emitted from them. Results of the stability tests of soft dental materials with the use of in-needle device on sample preparation step enable their quick evaluation and estimations of their quality. [ABSTRACT FROM AUTHOR]

In situ ionic-liquid-dispersive liquid-liquid microextraction was introduced for extracting Sudan dyes from different liquid samples followed by detection using ultrafast liquid chromatography. The extraction and metathesis reaction can be performed simultaneously, the extraction time was shortened notably and higher enrichment factors can be obtained compared with traditional dispersive liquid-liquid microextraction. When the extraction was coupled with ultrafast liquid chromatography, a green, convenient, cheap, and efficient method for the determination of Sudan dyes was developed. The effects of various experimental factors, including type of extraction solvent, amount of 1-hexyl-3-methylimidazolium chloride, ratio of ammonium hexafluorophosphate to 1-hexyl-3-methylimidazolium chloride, pH value, salt concentration in sample solution, extraction time and centrifugation time were investigated and optimized for the extraction of four kinds of Sudan dyes. The limits of detection for Sudan I, II, III, and IV were 0.324, 0.299, 0.390, and 0.655 ng/mL, respectively. Recoveries obtained by analyzing the seven spiked samples were between 65.95 and 112.82%. The consumption of organic solvent (120 μL acetonitrile per sample) was very low, so it could be considered as a green analytical method. [ABSTRACT FROM AUTHOR]

A method for automatic qualitative classification of liquid samples based on their absorption spectrum in the ultraviolet, visible and near-infrared regions is presented. A fiber-optic setup has been employed for material characterization. A simple technique based on image matching is proposed to perform spectra comparison. This alternative implementation of conventional spectrum matching methodologies can be easily translated to hardware platforms thus improving the time response of the classification system. The proposed method does not make any assumption on the probability density function of the data and it is also capable of automatic outlier removal. “Spectral marks” based on the polar representation of the absorption spectra and their “optimized marks” improved by means of Principal Component Analysis have been implemented. Preliminary discrimination results have been obtained on the classification of different oil samples from seeds and olives. [ABSTRACT FROM PUBLISHER]

This article gives an overview of the state-of-the-art of multi-element and single-element preconcentration procedures prior to X-ray fluorescence (XRF) analysis of liquid samples. Many of these preconcentration methods were developed long ago and the purpose of this review is to present some new efficient variations of these methods and new techniques extending the possibilities of XRF for liquid solutions analysis. In addition, trends and future perspectives in this domain are also commented on and discussed in the last section of the review. [ABSTRACT FROM AUTHOR]

An improved and novel sample preparation method for 226Ra determination in liquid samples by isotope dilution inductively coupled plasma sector field mass spectrometry using laboratory-prepared 228Ra tracer has been developed. The procedure involves a selective preconcentration achieved by applying laboratory-prepared MnO2 resin followed by cation exchange chromatographic separation. In order to completely eliminate possible molecular interferences, medium mass resolution ( R = 4,000) combined with chemical separation was found to be a good compromise that enhanced the reliability of the method. The detection limit of 0.084 fg g−1 (3.1 mBq kg−1) achieved is comparable to that of the emanation method or alpha spectrometry and is suitable for low-level environmental measurements. The chemical recovery of the sample preparation method ranged from 72 to 94%. The proposed method enables a rapid, accurate and less labor-intensive approach to routine environmental 226Ra determination than the radioanalytical techniques conventionally applied. [ABSTRACT FROM AUTHOR]

Abstract: An easy and reproducible preparation of manganese dioxide impregnated resin of homogeneous particles has been described. The characteristics of radium, thorium, uranium and plutonium uptake (pH dependency, kinetic studies and matrix dependency) have been determined in batch mode. The resin due to its high efficiency for radium, uranium and thorium at neutral pH values can be an effective tool for radionuclide pre-concentration from liquid samples even with high dissolved solid content. [Copyright &y& Elsevier]

Abstract: This review intends to show analytical chemists a very little known application of ultrasound for sample preparation: that dealing with liquid samples. The influence of this type of energy on the development of chemical reactions (e.g. depolymerization, redox, esterification, alkylation, addition, ethylation of organometallic compounds, complex formation) and that on heterogeneous liquid–liquid processes (e.g. liquid–liquid extraction, homogenization, emulsification, liposome formation) deserves to be taken into consideration in the analytical laboratory in order to take profit from its versatile effects to improve, accelerate or make possible a given process. [Copyright &y& Elsevier]

Abstract: A review of the effects of ultrasound (US) on liquid–liquid extraction is here presented. The phenomena produced by US, particularly cavitation, influence in different ways mass transfer between two immiscible liquids. The nature of the donor and acceptor phases and the presence of a chemical reaction dramatically affect mass transfer. Discrete and continuous approaches for the development of US-assisted liquid–liquid extraction as well as their advantages and limitations are discussed as a function of the system under study. In depth research in this field is needed in order to establish the liquid–liquid systems which can benefit by application of this type of energy. [Copyright &y& Elsevier]

An analytical methodology based in the combination of Thin Film Microextraction with Laser-induced Breakdown Spectroscopy (TFME-LIBS) was investigated, for the first time, for detection of Cu, Cr, Ni and Pb in aqueous solutions. In this methodology, the analytes were extracted in a thin film of adsorbent material deposited on a solid support, which was introduced in the sample to analyse. After extraction, the analytes retained in the adsorbent were analysed by LIBS. In order to obtain adsorbent films useful for the microextraction step, two different experimental procedures for film generation, denoted as Drop Casting Deposition and Mould Deposition, were evaluated. In both cases, graphene oxide was used as adsorbent material. The mould deposition procedure was found to produce more homogeneous graphene oxide layers, leading to more uniform distribution of the adsorbed analytes on the graphene oxide surface. Experimental parameters affecting the TFME procedure, such as the adsorbent amount and extraction time, were studied. Under optimum microextraction conditions, the analytical figures of merit of the proposed TFME-LIBS method were evaluated, leading to limits of detection ranging from 41 μg kg−1 and 52 μg kg−1. Method trueness, evaluated from the analysis of a real sample of bottle water, led to recovery values about 70%, indicating the existence of strong matrix effects probably due to the presence of major cations in the bottle water. After 50% dilution of the sample with deionized water, recoveries values improved to 100%–108%. Image 1 • TFME-LIBS, using graphene oxide as adsorbent, has been evaluated for the first time. • Thin Film microextraction is an easily automated procedure reducing the sample handling. • Several metals in liquid samples has been detected at μg kg−1 level by LIBS. • Metal chelation step has been avoided with the use of graphene oxide. [ABSTRACT FROM AUTHOR]