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Long-chain fatty acids (LCFA) are commonly found in lipid-rich wastewaters and are a key factor to monitor the anaerobic digesters. A new simple, fast, precise, and suitable method for routine analysis of LCFA is proposed. The system involves in-syringe-magnetic stirring-assisted dispersive liquid-liquid microextraction (DLLME) prior to gas chromatography-mass spectrometry (GC-MS) without a derivatization process. Calibration curves were prepared in an ethanol solution (R2 ≥ 0.996), which was also useful as disperser solvent. Hexane was chosen as the extraction solvent. Several parameters (pH, ionic strength, extraction solvent volume, stirring time) were optimized in multivariate and univariate studies. Limits of detection (LODs) were found in the range 0.01–0.05 mg L−1 and good precision inter-day (RSDs≤7.9%) and intra-day (RSDs≤4.4%) were obtained. The method was applied to quantify LCFA in supernatants of anaerobic digesters and olive mill wastewaters (OMW). Palmitic, stearic, and oleic acids were the most abundant fatty acid in the analyzed samples and the relative recoveries for all of them were between 81 and 113%.

This work review shows a description of non-chromatographic and chromatographic procedures proposed for speciation analysis of antimony employing hydride generation (HG) coupled to atomic fluorescence spectrometry (AFS) in environmental matrices, including details of HG-AFS as the detection technique. Non-chromatographic procedures have been developed based on the determination of total antimony after a pre-reduction step. The main reductant agents used are discussed. Antimony(III) has been quantified in the presence of a masking agent. The most used are citrate and 8-hydroquinoline. Chromatographic procedures have been established utilizing High-Performance Liquid Chromatography (HPLC). Advantages and drawbacks of the main extracting agents and mobile phases employed in these procedures have been discussed. Also, alternatives to improve the method sensitivity during the determination of antimony(V) and its organic compounds by HPLC-HG-AFS are presented. Speciation procedures involving preconcentration steps have allowed methods with high sensitivity. Tables evidencing applications of non-chromatographic and chromatographic procedures in speciation studies of environmental samples are also shown. Advantages of automated and flow systems for antimony speciation studies are also highlighted.

A Multi-Syringe Flow Injection Analysis (MSFIA) fluorometric system based on a 3D printing device hosting a CCD detector has been designed for the determination of quinine in soft drinks. A LED controlled by an electronic circuit was used as a radiation source. The entire system is connected to two USB outputs of a computer. The AutoAnalysis program has been used for data acquisition and treatment. The results are more accurate and precise than those obtained with a manual method using a conventional spectrofluorometer. This developed system is a viable alternative to reduce the consumption of reagents, the impact on the environment and reduce measurement costs.

A simple potentiometric chip-based multipumping flow system (MPFS) has been developed for the simultaneous determination of fluoride, chloride, pH, and redox potential in water samples. The proposed system was developed by using a poly(methyl methacrylate) chip microfluidic-conductor using the advantages of flow techniques with potentiometric detection. For this purpose, an automatic system has been designed and built by optimizing the variables involved in the process, such as: pH, ionic strength, stirring and sample volume. This system was applied successfully to water samples getting a versatile system with an analysis frequency of 12 samples per hour. Good correlation between chloride and fluoride concentration measured with ISE and ionic chromatography technique suggests satisfactory reliability of the system.

International audience; 15 The present paper reports the development and the application of a microplate assay for the fast 16 and individual determination of thiols and sulfides. The method is based on the reaction of ethyl 17 propiolate with thiols and sulfides, yielding thioacrylates absorbing in the UV range. 18 Thioacrylate generated by derivation of sulfide with EP presents a bathochromic shift of 19 maximal absorbance wavelength of 16 nm compared to thioacrylates formed with thiols. EP 20 concentration, reaction time and derivatization pH were carefully optimized in order to 21 separately quantify thiols and sulfides using a spectral deconvolution procedure in 15 minutes. 22 The detection limits were 0.6 and 2.8 µM (63.7 and 92.4 µg.L-1) for mercaptopropionic acid 23 (used as reference thiol compound for calibration) and dissolved hydrogen sulfide respectively. 24 Non-thiol sulfur compounds (methionine, sulfates and sulfites) or other nucleophile compound 25 did not display any interference in the determination of MPA or sulfides. Interference from 26 metals was suppressed with application of a reduction step with TCEP and DTPA. Finally, the 27 method has been successfully applied to the analysis of raw and treated wastewater. 28 29

Dietary supplements may contain heavy metals with the property of bioaccumulation in humans. The aim of this research was to validate and apply two analytical methods to determine Pb, As, Cr, and Hg in dietary supplements by Total Reflection X-ray Fluorescence Spectroscopy (TXRF). Methods validation was conducted through a multivariate analysis using a central composite design (CCD) and a desirability function. Critical values for each study variable were established. The TXRF_DS_1 method was proposed for Pb, As, and Cr determinations, while the TXRF_DS_2 was established for Hg analysis. The digestion method with an acid mixture (HNO3 + HCl + H2O2) was used to break down the organic material of dietary supplements. A solution of 10 μg L−1 Ga was used as an internal standard. Excellent analytical performance was obtained as LODs of 0.59, 0.41, 0.57, and 0.75 μg L−1 and LOQs of 1.95, 1.35, 1.90, and 2.50 μgL −1 for Pb, As, Cr, and Hg, respectively. Calibration curves showed a good linearity for all elements (R2>0.999). Excellent accuracy and precision in measurements (% RSD) was achieved. The real and spiked samples analysis demonstrated the applicability of the TXRF technique (percentage recovery 91–108%). Besides, two samples were analyzed in a comparison study between the TXRF_DS_1 method and the ICP-OES method. The results obtained showed good agreement between both techniques. The TXRF technique allows the analysis of toxic heavy metals in dietary supplements, which are marketed in a wide variety of presentations.

Volatile fatty acids (VFAs) are key parameters to monitor anaerobic digestion processes. Thus, a fast, simple and precise determination of these analytes is necessary for a timely characterization of the biological processes present in municipal solid waste and wastewater treatment plants. In this work, an automated method for the extraction and preconcentration of VFAs, based on dispersive liquid-liquid microextraction with magnetic stirring in syringe, and gas chromatography with flame ionization detector for the separation and detection, is described. The effect of parameters such as the type and volume of extraction solvent, pH, salting out effect and stirring time, was studied using a multivariate and univariate experimental design. Extraction and preconcentration were performed simultaneously using tert-butyl methyl ether (TBME) as the extraction solvent, after stirring 100 s at a constant rate. The detection limits were in the range of 0.1 - 1.3 mg L-1 and a good linearity was observed up to 1000 mg L-1 of the studied VFAs, with a range of R2 between 0.9997 and 0.9999. The intra and interday precision expressed as relative standard deviation (n= 5) varied between 0.7 and 2.4% and between 1.7 and 7.0%, respectively. Subsequently, the developed method was successfully applied to evaluate the presence of VFAs in wastewater samples from anaerobic treatments and an average relative recovery of 102% was obtained.

The spectrophotometric determination of uranium (VI) has been developed using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). This reaction has been adapted to apply a multisyringe flow injection analysis (MSFIA) system with spectrophotometric detection. The ternary complex of uranium (VI)-(Br-PADAP)-F has been measured at 578 nm. The procedure was optimized using univariate method and two-level full factorial. Four variables (concentrations of Br-PADAP, CyDTA, NaF and sample volume) were regarded as factors in the extraction optimization. Results of the two-level full factorial design, showed that only two factors (concentration of Br-PADAP and CyDTA) are statistically significant. The calibration curve is linear over the range 0.3–5 mg L−1 uranium (VI) with a relative standard deviation of 4.0% (1 mg L−1 uranium (VI), n = 10). The recoveries of uranium in water samples were between 80 and 102%.

In this work, the automation of a catalytic spectrophotometric method for the determination of molybdenum is presented. For this purpose, a multisyringe flow injection system was coupled to an integrated microconduit that we have called “chip”. Reagents and sample were simultaneously dispensed to the chip where complete mixing, heating, and measurement were carried out. The spectrophotometric method is based on the oxidation of 4-amino-3-hydroxy-naphthalenesulphonic acid (AHNA) by hydrogen peroxide catalyzed by Mo (VI). Absorbance of the reaction product was measured at 465 nm. Two optical fibers were used to conduct the light, one from the source to the chip, and the other from the output of the cell to the spectrophotometer. The detection cell was incorporated in the thermostated zone of the chip. The initial rate method, at controlled temperature, was employed to determine the Mo (VI) concentration. The estimated precision was 3.7%, with the working range of 4.0–40 µg L−1 of Mo (VI), and the limit of detection of 1.2 µg L−1 of Mo (VI). The system was successfully applied to water samples and pharmaceutical products with a sampling throughput of 20 injections h−1.

In this work, we present an automated catalytic spectrophotometric method for determination of Mn(II) by using a multisyringe burette coupled to a chip microfluidic-conductor (Chip-MSFIA). The reaction is based on the catalytic effect of Mn(II) on the auto-oxidation reaction of succinimidedioxime (SIDO). Reagents and the sample were simultaneously dispensed to the chip for their complete mixing, heating, and measurement. The absorbance of the reaction product was measured at 700 nm. The product concentration could be determined by the fixed-time and the initial rate method under optimum conditions (temperature 35 °C, 4.70 mmol L−1 SIDO, and 0.60 mol L−1 NaOH). Both fixed-time and initial rate methods have been developed, with the fixed-time method giving higher reproducibility and a wider working range. Therefore it was selected for Mn(II) samples in the working range of 1–20 μg L−1 of Mn(II). The estimated precision was 0.67% (5 μg L−1, n = 15) and the limit of detection of Mn(II) was 0.33 μg L−1. The proposed method is highly sensitive, selective, and simple for trace Mn(II) determination without extraction and separation steps. The system was successfully applied to water samples with an injection throughput of 22 injections h−1.

The present paper proposes the use of a multi-syringe flow injection analysis (MSFIA) system for the determination of Cd in natural water by cold vapour atomic absorption spectrometry (CV-AAS). The chemical and physical conditions for vapour generation were investigated and optimized using multivariate optimization methodology. Some complexing reagents were tested as additives to increase the analytical signal. Thiourea showed a positive effect, whereas L-cysteine reduced the signal of Cd. The method allows the direct determination of Cd, i.e. without sample pre-concentration, with limits of detection and quantification of 5.8 and 19.3 ng L−1, respectively, and employing external calibration technique. The precision expressed as a relative standard deviation varied between 1.4% and 2.9% for two levels of cadmium (0.25 and 2.5 μg L−1). Using 2 mL of sample volume, an injection throughput of 87 h−1 was achieved. The accuracy was confirmed by the analysis of a certified reference sample of seawater (CASS-4) furnished by National Research Council of Canada and addition/recovery tests, obtaining recoveries between 94% and 101%. The method was satisfactorily applied for the determination of Cd in seawater and ground water samples from Mallorca, Spain.

An automatic integrated system implementing a catalytic spectrophotometric method for vanadium determination is presented. Thus, a multisyringe flow injection system (MSFIA) was coupled to a monolithic flow microconduit, called chip (CHIP-MSFIA). All reagents and samples were simultaneously propelled into the chip to achieve complete mixing, heating, and measurement inside it. This catalytic spectrophotometric method is based on the oxidation of gallic acid with bromate catalyzed by V(V). The reaction was followed by measuring the absorbance change at 384 nm. The incorporation of the detection cell inside the thermostatic zone of the chip allows two kinetic–catalytic determination methods: initial rate and fixed time methods. A critical comparison between these two methods at a controlled temperature is presented. Under optimized conditions, the determination of V(V) was performed in the range 0.24–75 μg L−1 achieving limits of detection of 0.33 and 0.24 μg L−1 for fixed-time and initial rate methods, respectively. Relative standard deviations were between 1% and 4%. Finally, the initial rate method was successfully applied to determine the V(V) concentration in natural and waste water samples. Good recoveries were obtained varying from 94% to 102%. Results were compared with those obtained by the reference method (ICP-AES), in order to confirm the accuracy of the CHIP-MSFIA method. Additionally, a certified reference material was satisfactorily analyzed.

In this work a fully automated catalytic–spectrophotometric method for determination of copper at trace levels using a multisyringe flow injection system (MSFIA) and a multipumping flow system (MPFS) coupled to a micro-chip (Chip–MSFIA–MPFS) is presented. The reaction is based on the catalytic effect of Cu(II) on the oxidation of the in situ reduced form of 2,6-dichlorophenolindophenol (DCPI)r, by hydrogen peroxide. Due to the importance of the mixing order of the reagents, a new design of the chip is proposed. DCPI, ascorbic acid and buffer are first propelled to mix in the front section of the chip using MPFS. Then this reagent mixture, together with hydrogen peroxide and the sample, is simultaneously dispensed to the rear section of the chip by using a multisyringe for mixing, heating and absorbance measurement of the product at 600 nm. The optimum conditions are 0.9 mmol L−1 DCPI, 3.6 mmol L−1 ascorbic acid, 0.8 mol L−1 ammonium chloride buffer, pH 10.5, and 0.3 mol L−1 H2O2. The proposed system is simple, rapid, selective and sensitive. We can determine trace levels of Cu(II) at room temperature (25 °C). The main analytical characteristics of the proposed method are a detection limit of 0.12 μg L−1 of Cu(II), a working range of 0.4–35.0 μg L−1 of Cu(II), and a relative standard deviation of 0.79% (10 μg L−1 Cu(II), n = 15). The system was successfully applied to water samples, certified reference materials (CRMs) of river and waste water, acid digested multivitamins and animal tissues with a sample throughput of 31 injections h−1.

In this paper, an on-line spectrofluorimetric system is proposed for a simple, rapid and accurate measurement of volatile fatty acids (VFA) in anaerobic treatment processes. The determination method is based on the derivatization of VFA with N-(1-naphthyl)ethylenediamine (EDAN) followed by a spectrofluorimetric detection of the corresponding amide. The analytical procedure is automated with a flow analysis technique, coupling multisyringe (MSFIA) and multi-pumping (MPFS) methods. Operative conditions have been investigated with a special attention paid to the activation and amidation steps and to the liquid-liquid extraction of the derivatized final product. Fluorescence intensities (lambda(em)=335 nm, lambda(ex)=395 nm) were found to be proportional to the concentration of VFA, expressed as acetic equivalent, in the range 19-1000 mg L(-1), with a detection limit (3sigma) of 5.1 mg L(-1). Our results showed a good selectivity for VFA as compared to other organic and inorganic compounds usually found in sewage sludges. Validation of the on-line system developed has been assessed by application of the procedure to aqueous samples originating from sewage sludge treatment plants. The results were in good agreement with ion chromatography measurements.

International audience; This paper presents a simple, accurate and multi-sample method for the determination of volatile fatty acids (VFAs) thanks to a 96-well microplate technique. A procedure using an activating reagent of the carboxylic function (water-soluble carbodiimide EDC) and a fluorescent amino labeling reagent (N-(1-naphthyl)ethylenediamine, EDAN) allows the formation of an isoindole derivative that needs to be separated from initial fluorescent amine for efficient VFAs determination. Isolation of these fluorescent VFA-derivatives was carried out by use of the fluorescent quenching of EDAN with o-phthaldialdehyde (OPA). Quenching was most efficient at pH around 7 and by heating at 40 degrees C within the microplate reader. This optimized procedure has been applied to various carboxylic acids and other organic compounds, demonstrating that VFA exhibit the highest fluorescence responses with homogeneous results for the main ones (acetic, propionic and butyric acid, all mass concentration expressed as acetic acid equivalents). This protocol was calibrated against acetic acid and determination of VFA was thus possible in the range 3.9-2000 mg L-1 (acetic acid equivalents). Subsequent application to real samples (sewage sludges or anaerobically digested samples) and comparison to gas chromatography analyses gave accurate results, proving the great potential of our high-throughput microplate-based technique for the analysis of VFA. (C) 2011 Elsevier B.V. All rights reserved.

Correspondance auteur: Boudenne J.L. E-mail: jean-luc.boudenne@univ-provence.fr; International audience; This paper presents a simple, rapid, and accurate method suitable for on-site measurement of short-chain volatile fatty acids (SCFA) in various environmental samples. This fluorimetric method involves a derivatization step of SCFA with N-(1-naphthyl)ethylenediamine (EDAN) and allows determination of acetic, butyric, propionic, valeric, lactic, succinic, and p-hydroxybenzoic acids in approximatively 10 min. To evaluate specificity and accuracy of the method, both laboratory-made waters and real samples ranging from wastewater plant and river to soils and composts have been tested. Good accuracy and correlation (r(2) = 0.9887) with HPIC determination have been obtained. The potential interference effect has been taken into account with compounds like humic substances, alcohols, amines, aldehydes, and metallic ions. Ibis method seems thus well designed for the determination of total SCFA in waters, in the range 0.84-500 mg/L. Because this method seems well suited for following of anaerobic treatment, it has been calibrated versus acetic acid-equivalent