Determination of trace amounts of highly hydrophilic compounds in water by direct derivatization and gas chromatography — mass spectrometry

A new procedure has been developed to derivatize a large set of highly hydrophilic substances ((poly) hydroxy and/or (poly)carboxylic acids, glycols and dihydroxybenzenes) directly in water. The key element of the method is the derivatizing agent used, n-hexyl chloroformate, which proved to be much more effective than other alkyl and aryl chloroformates. Detection limits in the low μg/L range were found for most of the compounds studied, using positive ion chemical ionization mass spectrometry as the detection technique. Calibration curves exhibited a good linearity over 2–3 orders of magnitude, so that quantitative determinations were possible. Among the experimental parameters tested, it was found crucial to introduce the chloroformate slowly and under sonication. The whole derivatization procedure takes only 2–3 min from sample collection to injection into the gas chromatograph.     

改进的五氟苄基溴衍生化反应测定水中酚类化合物

建立了气相色谱-质谱法测定水中6种酚类化合物(2,6-二氯酚、2,4-二氯酚、2,4,6-三氯酚、2,4,5-三氯酚、2,3,4,6-四氯酚和五氯酚)的方法.样品经二氯甲烷-乙酸乙酯混合溶剂萃取后,用旋转蒸发浓缩至1 mL,加入五氟苄基溴进行改进版衍生化反应,产物用DB-5 mS毛细管柱分离,采用选择离子监测模式测定....     

Ultratrace determination of phosphorus in ultrapurified water by a slope comparison method

The analytical method for the determination of phosphorus in ultrapurified water was developed. Ultrapurified water was evaporated to concentrate phosphorus and the final sample volume for analysis was 10 ml. In 0.55 mol l⁻¹ HCl, orthophosphate forms molybdophosphate, and then the molybdophosphate forms ion associate with Malachite Green (MG), which can be collected on a tiny membrane filter (diameter: 5 mm, and effective filtering diameter: 2 mm). After the ion associate on the membrane filter is dissolved together with the membrane filter in 1 ml of methyl cellosolve (MC), the absorbance of MC solution is measured at 627 nm by a flow injection-spectrophotometric detection technique. When 10 ml of the sample solution was used for the procedures and absorbance measurement, the calibration graph is linear up to about 500 ng l⁻¹ of phosphorus and the detection limit was 8 ng l⁻¹ (S/N=3). For the determination of phosphorus in an ultrapurified water, 10-40 ml of sample solutions were transferred into poly(tetrafluoroethylene) (PTFE) beaker and evaporated to 5 ml or to dryness. To them, 0.003 mol l⁻¹ HCl was added to get 10 ml of final solution, which was used as sample. Phosphate is determined by comparing the slope of the varied sample volume after evaporation/concentration with a slope of the standard calibration graph (a slope comparison method: SCM). The SCM enables to evaluate the concentration of phosphate in ultrapurified waters more sensitively and accurately.     

Gas chromatographic-mass spectrometric determination of hydrophilic compounds in environmental water by solid-phase extraction with activated carbon fiber felt

Simple gas chromatographic-mass spectrometric determination of hydrophilic organic compounds in environmental water was developed. A cartridge containing activated carbon fiber felt was made by way of trial and was evaluated for solid-phase extraction of the compounds in water. The hydrophilic compounds investigated were acrylamide, N,N-dimethylacetamide, N,N-dimethylformamide, 1,4-dioxane, furfural, furfuryl alcohol, N-nitrosodiethylamine and N-nitrosodimethylamine. Overall recoveries were good (80-100%) from groundwater and river water. The relative standard deviations ranged from 4.5 to 16% for the target compounds. The minimum detectable concentrations were 0.02 to 0.03 microg/l. This method was successfully applied to several river water samples.     

Application of the novel 5-chloro-2,2,3,3,4,4,5,5-octafluoro-1-pentyl chloroformate derivatizing agent for the direct determination of highly polar water disinfection byproducts

A novel derivatizing agent, 5-chloro-2,2,3,3,4,4,5,5-octafluoropentyl chloroformate (ClOFPCF), was synthesized and tested as a reagent for direct water derivatization of highly polar and hydrophilic analytes. Its analytical performance satisfactorily compared to a perfluorinated chloroformate previously described, namely 2,2,3,3,4,4,5,5-octafluoropentyl chloroformate (OFPCF). The chemical properties (reactivity, selectivity, derivatization products, and their chromatographic and spectral features) for ClOFPCF were investigated using a set of 39 highly polar standard analytes, including, among others, hydroxylamine, malic and succinic acids, resorcinol, hydroxybenzaldehyde, and dihydroxybenzoic acid. Upon derivatization, the analytes were extracted from the aqueous solvent and analyzed by gas chromatography (GC)-mass spectrometry (MS) in the electron-capture negative ionization (ECNI) mode. Positive chemical ionization (PCI)-MS was used for confirming the molecular ions, which were virtually absent in the ECNI mass spectra. ClOFPCF showed good reaction efficiency, good chromatographic and spectroscopic properties (better than with OFPCF), good linearity in calibration curves, and low detection limits (0.3–1 μg/L). A unique feature of the derivatizations with ClOFPCF, and, in general, highly fluorinated chloroformates, is their effectiveness in reacting with carboxylic, hydroxylic, and aminic groups at once, forming multiply-substituted non-polar derivatives that can be easily extracted from the aqueous phase and determined by GC-ECNI-MS. The entire procedure from raw aqueous sample to ready-to-inject hexane solution of the derivatives requires less than 10 min. Another benefit of this procedure is that it produced stable derivatives, with optimal volatility for GC separation, and high electron affinity, which allows their detection as negative ions at trace level. In addition, their mass spectra exhibits chlorine isotopic patterns that clearly indicate how many polar hydrogens of the analyte undergo derivatization. Finally, derivatization with ClOFPCF was used successfully to identify 13 unknown highly polar disinfection byproducts (DBPs) in ozonated fulvic and humic acid aqueous solutions and in real ozonated drinking water.     

Ultratrace molybdenum determination in biological samples by graphite-furnace atomic-absorption spectrometry

A method is described for molybdenum determination in human serum at sub-ng/ml levels by graphite-furnace atomic-absorption spectrometry. Sample preparation involves a nitric acid digestion, chelation with benzohydroxamic acid and extraction into hexanol. A detection limit of 0.1 ng/ml and a characteristic concentration of 0.18 ng/ml for 1% absorption can be achieved. The effectiveness of the method has been demonstrated by analysis of unspiked and spiked human serum, standard reference materials, and comparison with the results obtained by inductively-coupled plasma atomic-emission spectroscopy.     

Rapid and highly sensitive determination of low-molecular-weight carbonyl compounds in drinking water and natural water by preconcentration HPLC with 2,4-dinitrophenylhydrazine.

The aim of this research was to develop a simple procedure for a highly sensitive determination of low-molecular-weight (LMW) carbonyl compounds in drinking water and natural water. We employed a preconcentration HPLC system with 2,4-dinitrophenylhydrazine (DNPH) for the determination of LMW carbonyl compounds. A C-18 reverse-phase preconcentration column was used instead of a sample loop at the sample injection valve. A 0.1 - 5.0 mL portion of the derivatized sample solution was injected with a gas-tight syringe, and a 15% acetonitrile aqueous solution was pushed through the preconcentration column to remove the unreacted excess DNPH, which caused serious interference in the determination of formaldehyde. The detection limits were 1 - 3 nM with a relative standard deviation of 2 - 5% for 20 nM standard solutions (n = 5). The calibration curves were essentially unaffected by coexisting sea salts. Applications to commercial mineral water, tap water, river water, pond water and seawater are presented.     

Gas chromatographic determination of phenol compounds with automatic extraction and derivatization

Two gas chromatographic procedures for the determination of a variety of substituted phenols in water samples are described. The phenols were extracted or extracted-derivatized by using a continuous liquid-liquid extraction-derivatization system and quantified with flame ionization detection. Ethyl acetate was found to be the most efficient solvent for phenols whereas n-hexane yielded essentially the same recoveries for derivatized phenols. Between 0.1 and 300 mg/l of the different phenols can be detected with a relative standard deviation 1.1 and 3.7%. The acetate esters of six phenols were formed by the direct addition of acetic anhydride to the organic extractant. The stable acetate esters thus formed were isolated by using a standard dimethyl polysiloxane gas chromatographic column.     

Ultratrace determination of mercury in water following EN and EPA standards using atomic fluorescence spectrometry

Chemical vapour generation has been used in combination with atomic fluorescence spectrometry to determine mercury at ultratrace concentrations down to 0.1 ng L^–1. A time-based injection of 1 mL of solution for measurement was sufficient to generate a steady-state detector response in the direct mode of measurement. The detection limit calculated from a ten-point calibration curve according to DIN 32645 was 0.26 ng L^–1. Instrument noise is limited by reflected radiation from the light source rather than by the dark current of the photomultiplier. The detection limit is directly influenced by the reagent blank which was 2 ng L^–1 in the experiments described. Focusing by amalgamation and subsequent thermal desorption generates a detector response which is about eight times higher in peak intensity and about twice as large in integrated intensity. The detection limit under these conditions is 0.09 ng L^–1 which can be further improved by preconcentration of larger volumes of solution for measurement. The cycle time for one individual reading is about 40 s without amalgamation and 125 s with amalgamation. The linear dynamic range of the system is five orders of magnitude with a single photomultiplier gain setting. The carry-over is less than 0.3% in direct measurement mode. Reference water samples and a surface water containing approximately 5 ng L^–1 were used to prove the validity of the method for real samples. Good accuracy and recoveries of 103% were calculated using the fast direct determination technique.     

Polar, hydrophilic compounds in drinking water produced from surface water. Determination by liquid chromatography-mass spectrometry.

Drinking water produced from surface water may contain many polar, hydrophilic compounds in spite of different treatment steps such as soil filtration, ozone treatment and activated carbon filtration. Little is known about these compounds. The objectives of this work were the detection and identification by means of tandem mass spectrometry (MS-MS) coupled on-line by a thermospray interface with liquid chromatography. Quantification is possible if standard compounds are available. The different compounds in the water extracts were not only separated by means of an analytical column but also using MS-MS after loop injection bypassing the analytical column. Molecular weight information in the loop spectra (overview spectra) and collisionally induced dissociation (CID) made possible the identification of some of these compounds which cannot be eliminated in the drinking water treatment process. Identification was not only done by interpretation of the recorded daughter- and parent-ion spectra but also by comparing them with a laboratory-made daughter-ion library of polar, hydrophilic pollutants. Direct mixture analysis using MS-MS allows the detection and identification of some of the pollutants if they reach the drinking water in the course of the surface water treatment process because of their biochemical and chemical persistence and/or non-sorbability during the soil or activated carbon filtration process. The proposed method for the analysis of water for polar, non-volatile and/or thermolabile organic substances is a quick, specific and powerful technique which makes it possible to detect and identify these substances without any chromatographic separation or derivatization     

Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol

A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO₄ and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO₄ and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of detection of 10 g 1^–1 foro-cresol and 30 g 1^–1 form-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absorbance wavelengths obtained for the reaction products of PAP witho-cresol (614 nm) andm-cresol (632 nm), both compounds can be simultaneously determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.     

Ultratrace analysis for trans,trans-muconic acid by electrophoric derivatization and capillary gas chromatography

A highly sensitive method is described for the determination of trans,trans-muconic acid (MA), a biomarker of benzene exposure. The method is based on the derivatization of MA with an electrophoric reagent, 2-(pentafluorophenoxy)ethyl-2-(piperidino)ethanesulfonate, using potassium carbonate and 18-crown-6 ether as reaction activators. The resulting pentafluorophenoxy derivative of MA was analyzed by capillary GC with an electron-capture detector (ECD). The lower quantitation limit of the method is attainable at 0.3 μM of MA with a detection limit of about 60 nM (S/N=3) (60 fmol per 1.0 μl injection). Application of the method to the analysis of MA in urine proved feasible.     

Ultratrace determination of adenine in the presence of copper by adsorptive stripping voltammetry

An electrochemical stripping procedure for ultra-trace measurements of adenine is described based on the adsorption of the adenine-copper complex on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found when using a 0.005 M NaOH solution containing 0.4 ppm of copper, an accumulation potential of -0.30 V, a scan rate of 100 mV s(-1) and a linear scan mode. There is a linear response to adenine concentration in the range of 0.1-1.0 ppb and the detection limit for 6 min accumulation time was of 4.0 ppt (3.0x10(-11) M). Proper conditions for measuring the adenine in presence of guanine, thymine and cytosine were also investigated. The method was applied for the determination of adenine in a sample of single-stranded calf thymus DNA.     

Synthesis,spectral properties,and solvatochromism of merocyanine dyes based on bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate

Di-, tetra-, and hexamethine merocyanines containing heterocyclic fragments with different electron-donor abilities have been synthesized on the basis of bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate. Their electronic absorption spectra in solvents with different polarities have been studied, and their electronic structure and electronic transitions have been analyzed by DFT and TDDFT quantum chemical calculations using B3LYP functional and 6-31G(d,p) basis set. The electronic structure of the synthesized merocyanines changes from neutral polyene to polymethine and dipolar polyene, depending on the electron-donor ability of the heterocyclic fragment, length of the polymethine chain, and solvent polarity. Therefore, these merocyanines display positive, negative, and reverse solvatochromism.     

Ultratrace determination of Bi in Greenland snow by laser excited atomic fluorescence spectrometry

The results of the first determination of Bi traces in snow samples from Greenland by laser excited atomic fluorescence spectrometry are presented. A limit of detection as low as 0.05 for one-color LEAFS technique is attained. Strong matrix interference in real snow samples was observed and some ways of reducing this are tested. The main source of background is molecular fluorescence of unidentified species. The measured Bi concentration in snow samples ranges within 0.07–0.6 .     

Solid phase microextraction procedure for the determination of alkylphenols in water by on-fiber derivatization with N-tert-butyl-dimethylsilyl-N-methyltrifluoroacetamide

The solid phase microextraction (SPME) technique with on-fiber derivatization was evaluated for the analysis of alkylphenols (APs), including 4-tert-octylphenol (4-t-OP), technical nonylphenol isomers (t-NPs) and 4-nonylphenol (4-NP), in water. The 85 μm polyacrylate (PA) fiber was used and a two-step sample preparation procedure was established. In the first step, water sample of 2 mL was placed in a 4 mL PTFE-capped glass vial. Headspace extraction of APs in water was then performed under 65 °C for 30 min with 800 rpm magnetic stirring and the addition of 5% of sodium chloride. In the second step, the SPME fiber was placed in another 4 mL vial, which contained 100 μL of N-tert-butyl-dimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) with 1% tert-butyl-dimethylchlorosilane (TBDMCS). Headspace extraction of MTBSTFA and on-fiber derivatization with APs were performed at 45 °C for 10 min. Gas chromatography/mass spectrometry (GC/MS) was used for the analysis of derivatives formed on-fiber. The adsorption-time profiles were also examined. The precision, accuracy and method detection limits (MDLs) for the analysis of all the APs were evaluated with spiked water samples, including detergent water, chlorinated tap water, and lake water. The relative standard deviations were all less than 10% and the accuracies were 100 ± 15%. With 2 mL of water sample, MDLs were in the range of 1.58-3.85 ng L⁻¹. Compared with other techniques, the study described here provided a simple, fast and reliable method for the analysis of APs in water.     

Simultaneous high-performance liquid chromatographic determination of catecholamine-related compounds by post-column derivatization involving coulometric oxidation followed by fluorescence reaction

A highly selective and sensitive high-performance liquid chromatographic method for the determination of catecholamines (norepinephrine, epinephrine and dopamine) and related compounds (L-DOPA, normetanephrine, metanephrine, 3-methoxytyramine, 3,4-dihydroxymandelic acid, 3,4-dihydroxyphenylacetic acid, homovanillic acid, vanillylmandelic acid, 3,4-dihydroxyphenylethylene glycol, 4-hydroxy-3-methoxyphenylethylene glycol and 4-hydroxy-3-methoxyphenylethanol) with a post-column technique involving coulometric oxidation followed by fluorescence derivatization is described. These compounds, 3,4-dihydroxybenzylamine and ferulic acid are separated within 35 min by ion-pair reversed-phase chromatography using acidic buffers (pH 3.1) with methanol-acetonitrile (3:2, v/v) gradient elution, and then oxidized by a commercial coulometric detector to the corresponding o-quinones, which are converted into fluorescent derivatives by reaction with 1,2-diphenylethylenediamine. The detection limits (signal-to-noise ratio = 3) on-column are 1.5-4 pmol for the two mandelic acids, 600 fmol for L-DOPA and 20-70 fmol for the others.     

Determination of major phenolic compounds in water by reversed-phase liquid chromatography after pre-column derivatization with benzoyl chloride

A simple reversed-phase LC method capable of detecting ng/ml quantities of phenolic compounds in water is described. Pre-column derivatization with benzoyl chloride is used for the separation and determination o-cresol, m-cresol, p-cresol, phenol, resorcinol, catechol and hydroquinone in water. The benzoyl derivatives formed within in 15 min, were extracted with dietyl ether, and then analyzed by liquid chromatography with UV detection at 232 nm. With a mobile phase of acetonitrile-tetrahydrofuran-water (54:6:40, v/v) the seven derivatives were eluted in 15 min. The detection limits were between 0.05 and 0.50 ng/ml for 50 ml of a standard water sample. The method was applied to the analysis of phenols in wine and river water. The recovery of the derivatives from pure water was 81-94% with relative standard deviations of 2.5-5.0%.