Automated method for the solid phase extraction of tetracyclines in wastewater followed by fluorimetric determination.

This work presents a multisyringe flow injection analysis (MSFIA) system for the automatic extraction and determination of tetracyclines in wastewater samples. The sample was adjusted with Na2EDTA buffer before solid-phase extraction with an Oasis HLB column used for the analyte preconcentration. The europium (Eu3+)-based and citrate-mediated method (using Tris-HCl buffer) was selected for the fluorimetric analysis (λexc/em = 400/612 nm). For fluorescence detection, a low-cost system consisting of an USB 2000 CCD detector and a 3D-printed support that holds a LED light source was used. Under optimized conditions, the proposed method provided low limits of detection (9.4 µg L-1) and quantification (31 µg L-1), and good values for intra-day (<4 %) and inter-day precisions (<6 %). Recoveries of spiked TCs in wastewater samples ranged from 87 to 106 %. The results of this work were in good agreement with the measurements obtained by liquid chromatography coupled to a fluorescence detector.

Determination of dissolved nickel in natural waters using a rapid microplate fluorescence assay method.

A new microplate analytical procedure is described for the determination of nickel (Ni2+) ions in natural water samples. A lophine analogue fluorescent sensor was synthesized and a spectral study showed a selective fluorescence quenching effect of chemical sensor by Ni2+ under optimized conditions. Density functional theory (DFT) calculations confirmed the formation of a Ni(II)L3 complex obtained by the Job plot. The calculations showed that the fluorescence emission peak of L collapses due to the distortion of L in the complex. The simple and fast microplate procedure allowed us to quantify Ni2+ with a linear response from 1.6 to 40 µg L-1 and a quantification limit of 5.4 µg L-1 without the need of a preconcentration step. The optimized procedure using high-throughput microplate assay has been applied for the determination of Ni2+ in natural water samples with good analytical performances.

Multisyringe Flow Injection Analysis of Tropomyosin Allergens in Shellfish Samples.

This paper presents the development and the application of a multisyringe flow injection analysis system for the fluorimetric determination of the major heat-stable known allergen in shrimp, rPen a 1 (tropomyosin). This muscle protein, made up of 284 amino acids, is the main allergen in crustaceans and can be hydrolyzed by microwave in hydrochloric acid medium to produce glutamic acid, the major amino acid in the protein. Glutamic acid can then be quantified specifically by thermal conversion into pyroglutamic acid followed by chemical derivatization of the pyroglutamic acid formed by an analytical protocol based on an OPA-NAC reagent. Pyroglutamic acid can thus be quantified between 1 and 100 µM in less than 15 min with a detection limit of 1.3 µM. The method has been validated by measurements on real samples demonstrating that the response increases with the increase in the tropomyosin content or with the increase in the mass of the shrimp sample.

Sub-ppb mercury detection in real environmental samples with an improved rhodamine-based detection system.

A new procedure is described for the determination of Hg2+ ions in water samples. A Rhodamine based fluorescent sensor was synthesized and the experimental conditions were specifically optimized for application to environmental samples, which requires low detection limits and high selectivity in competitive experiments with realistic concentrations of other metal ions. Incorporation of a Rhodamine-6G fluorophore to a previously described sensor and optimization of the buffer system (detection with acetic acid at pH 5.25) enabled significant enhancement of the sensitivity (detection limit = 0.27 µg L-1) and selectivity. The optimized procedure using high-throughput microplates has been applied to tap and river waters with good results.

Development of an automated system for the analysis of inorganic chloramines in swimming pools via multi-syringe chromatography and photometric detection with ABTS.

Inorganic chloramines are disinfection by-products resulting from the unwanted reaction between chlorine used as disinfectant in swimming pools and nitrogenous compounds brought by bathers. This parameter (total chloramines or combined chlorine) is currently measured on site by a colorimetric method that does not allow to measure only inorganic chloramines. In this paper, a multi-syringe chromatography system combined with a post column derivatization is applied for the first time for the specific detection of the three individual inorganic chloramines (monochloramine, dichloramine and trichloramine). These latter ones are separated using a low-pressure monolithic C18 column, and separately detected after a post-column reaction with the chromogenic reagent ABTS (2,2'-azino-bis-(3-ethyl-benzothiazoline)-6-sulfonic acid-diammonium salt). Development of two ABTS reagents provides discrimination of chlorine and monochloramine that are not separated on the column. Optimization of the experimental conditions enables determination of inorganic chloramines with very good detection limits (around 10 µg eq.Cl2 L-1) without interferences from other chlorinated compounds such as organic chloramines or free available chlorine. The validation of the whole procedure has been successfully applied to real swimming pools samples.

Modified 3D-printed device for mercury determination in waters.

3D printing technology is increasingly used in flow analysis, to develop low cost and tailor-made devices. The possibility of grafting specific molecules onto 3D printed parts offers new perspectives for the development of flow systems. In this study, a MPFS system including a dicarboxylate 1,5-diphenyl-3-thiocarbazone grafted 3D-printed device has been developed for mercury determination. For this purpose, the surface of 3D-printed cuboids was first modified with amine functional groups and then grafted with dicarboxylate 1,5-diphenyl-3-thiocarbazone. This new grafted device resulted in selective mercury preconcentration with extraction and elution yields higher than 90% even at high sampling flow rates. The detection can then be carried out in two ways: a direct detection of mercury extracted onto 3D-printed grafted cuboids by atomic absorption spectrophotometry after amalgam on gold or a detection of mercury in solution after elution with l-cysteine by spectrophotometry or cold vapour atomic absorption spectrometry.

3D-printed lab-on-valve for fluorescent determination of cadmium and lead in water.

In recent years, the development of 3D printing in flow analysis has allowed the creation of new systems with various applications. Up to now, 3D printing was mainly used for the manufacture of small units such as flow detection cells, preconcentration units or mixing systems. In the present study, a new 3D printed lab-on-valve system was developed to selectively quantify lead and cadmium in water. Different technologies were compared for lab-on-valve 3D printing. Printed test units have shown that stereolithography or digital light processing are satisfactory techniques for creating complex lab-on-valve units. The lab-on-valve system was composed of two columns, eight peripheral ports and a central port, and a coil integrating baffles to increase mixing possibilities. A selective extraction of lead was first carried out by TrisKem Pb™ Resin column. Then, cadmium not retained on the first column was extracted on a second column of Amberlite® IR 120 resin. In a following step, lead and cadmium were eluted with ammonium oxalate and potassium iodide, respectively. Finally, the two metals were sequentially detected by the same Rhod-5N™ fluorescent reagent. This 3D printed lab-on-valve flow system allowed us to quantify lead and cadmium with a linear response from 0.2 to 15 µg L-1 and detection limits of 0.17 and 0.20 µg L-1 for lead and cadmium, respectively, which seems adapted for natural water analysis.

3D-printed flow system for determination of lead in natural waters.

The development of 3D printing in recent years opens up a vast array of possibilities in the field of flow analysis. In the present study, a new 3D-printed flow system has been developed for the selective spectrophotometric determination of lead in natural waters. This system was composed of three 3D-printed units (sample treatment, mixing coil and detection) that might have been assembled without any tubing to form a complete flow system. Lead was determined in a two-step procedure. A preconcentration of lead was first carried out on TrisKem Pb Resin located in a 3D-printed column reservoir closed by a tapped screw. This resin showed a high extraction selectivity for lead over many tested potential interfering metals. In a second step, lead was eluted by ammonium oxalate in presence of 4-(2-pyridylazo)-resorcinol (PAR), and spectrophotometrically detected at 520nm. The optimized flow system has exhibited a linear response from 3 to 120µgL-1. Detection limit, coefficient of variation and sampling rate were evaluated at 2.7µgL-1, 5.4% (n=6) and 4 sampleh-1, respectively. This flow system stands out by its fully 3D design, portability and simplicity for low cost analysis of lead in natural waters.

Β-hydroxymyristic acid as a chemical marker to detect endotoxins in dialysis water.

An analytical chemical method has been developed for determination of ß-hydroxymyristic acid (ß-HMA), a component of lipopolysaccharides (LPSs/endotoxins) in dialysis water. In our investigation, the ß-HMA component was used as a chemical marker for endotoxin presence in dialysis water because it is available in the molecular subunit (lipid A) and responsible for toxicity. It is the most abundant saturated fatty acid in that subunit. The developed method is based on fluorescence derivatization with 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ). A high-performance liquid chromatographic separation of the ß-HMA derivative was achieved using an octadecyl silica column in gradient elution. A wide dynamic range of ß-HMA was tested and a calibration curve was constructed with accuracy of 90% and variability of less than 10%. The limits of detection and quantification obtained were 2 and 5µM, respectively. The developed method was applied to detect endotoxins in dialysis water by alkaline hydrolysis of LPS using NaOH (0.25M) at 60°C for 2h. After hydrolysis, free acid was detected as its NBD-PZ derivative using high-performance liquid chromatography/mass spectrometry (HPLC/MS). Good recovery rates ranging from 98 to 105% were obtained for ß-HMA in dialysis water.

Development of a simple fluorescence-based microplate method for the high-throughput analysis of proline in wine samples.

This paper presents a simple, accurate and multi-sample method for the determination of proline in wines thanks to a 96-well microplate technique. Proline is the most abundant amino acid in wine and is an important parameter related to wine characteristics or maturation processes of grape. In the current study, an improved application of the general method based on sodium hypochlorite oxidation and o-phthaldialdehyde (OPA)-thiol spectrofluorometric detection is described. The main interfering compounds for specific proline detection in wines are strongly reduced by selective reaction with OPA in a preliminary step under well-defined pH conditions. Application of the protocol after a 500-fold dilution of wine samples provides a working range between 0.02 and 2.90gL(-1), with a limit of detection of 7.50mgL(-1). Comparison and validation on real wine samples by ion-exchange chromatography prove that this procedure yields accurate results. Simplicity of the protocol used, with no need for centrifugation or filtration, organic solvents or high temperature enables its full implementation in plastic microplates and efficient application for routine analysis of proline in wines.

Individual volatile fatty acids determination by chromogenic derivatization coupled to multi-syringe chromatography.

In this paper, a new multisyringe chromatography (MSC) system is proposed for a simple and accurate measurement of individual 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 the separation of VFA derivatives on an Onyx C18 monolithic column (25 mm × 4.6mm i.d.). Chromatographic separation conditions have been investigated and were found to be optimal with a mixture of acetonitrile and formic acid 0.1% (ratio 35/65), providing good separation of C2-C5 VFA in 8 min. Optimization of the derivatization reaction was also carried out with special attention paid to the buffering capacity of the reaction medium, so as to be able to deal with samples of various characteristics in terms of alkalinity or of VFA concentration range. Individual VFA could be quantified between 0.05-2.5 g L(-1) with LOD of 0.01-0.02 g L(-1). Overall procedure time was about 18 min for one analytical cycle, which fulfils the requirement of real-time monitoring of an anaerobic digester. Validation of the system developed has been assessed by application of the procedure to sludge samples from various origins, and comparative results with gas chromatography analyses showed satisfactory correlation (R²>0.98).

On-line analysis of volatile fatty acids in anaerobic treatment processes.

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.

Alternative spectrofluorimetric determination of short-chain volatile fatty acids in aqueous samples.

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. This 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.

Toward a synthetically useful stereoselective C-H amination of hydrocarbons.

Reaction between a sulfur(VI) compound and an iodine(III) oxidant in the presence of a catalytic quantity (<=3 mol %) of a rhodium(II) catalyst leads to the formation of a chiral metallanitrene of unprecedented reactivity. The latter allows intermolecular C-H amination to proceed in very high yields up to 92% and excellent diastereoselectivities up to 99% with C-H bond containing starting materials as the limiting component. The scope of this C-H functionalization includes benzylic and allylic substrates as well as alkanes. Secondary positions react preferentially, but insertion into activated primary C-H bonds or sterically accessible tertiary sites is also possible. Cooperative effects between the nitrene precursor and the chiral catalyst at the origin of these good results have also been applied to kinetic resolution of racemic sulfonimidamide. This methodology paves the way to the use of Csp3-H bonds as synthetic precursors for the introduction of a nitrogen functionality into selected positions.

Sulfonimidamides: efficient chiral iminoiodane precursors for diastereoselective copper-catalyzed aziridination of olefins.

N-(p-Toluenesulfonyl)-p-toluenesulfonimidamide reacts with iodosylbenzene to afford in situ a chiral iminoiodane. The latter gives, in the presence of a copper(I) catalyst, a nitrene that is very efficiently transferred under stoichiometric conditions to a variety of alkenes with diastereoselectivities up to 60%. [reaction: see text]