Pressurized fluid extraction of nonpolar pesticides and polar herbicides using in situ derivatization

Analysis of polar acidic herbicides has traditionally presented a challenge because of their strong adsorption to and ionic interactions with soil. One approach which has been successful for extraction of these polar compounds from soil is supercritical fluid extraction (SFE) coupled with in situ derivatization. This technique involves the addition of common derivatization reagents directly into the extraction chamber, where the acid herbicides are derivitized to extractable esters or ethers. This study describes the application of an in situ derivatization technique to pressurized fluid extraction (PFE) for the herbicides 2,4-D, 2,4,5-T, dicamba, silvex, trichlopyr, and bentazone. The efficiency of in situ derivatization PFE for these analytes is compared with a conventional basic extraction method followed by ex situ derivatization. The variables of temperature, pressure, static extraction time, and derivatization-reagent amount were optimized for recovery of these analytes from soil. Average recovery for these six analytes was 107% for in situ derivatization PFE from spiked sand, 93% for the same method from a high-concentration spiked soil (50 mg/kg), and 68% for the optimized in situ derivatization PFE method from low-concentration soil (0.5 mg/kg). The in situ derivatization PFE method has substantial advantages of simplicity of methodology and reduction in extraction time compared with the conventional technique. A second in situ derivatization PFE strategy was investigated using sodium EDTA in the extraction chamber for the extraction of 2,4-D from soil. Preliminary results demonstrate improved recovery with the use of Na4EDTA. Extraction efficiency of PFE for nonpolar organochlorine insecticides and slightly polar triazine herbicides from soil is also presented and compared with that of Soxhlet extraction.     

Acidic acetonitrile for cellular metabolome extraction from Escherichia coli

Cellular metabolome analysis by chromatography-mass spectrometry (MS) requires prior metabolite extraction. We examined a diversity of solvent systems for extraction of water-soluble metabolites from Escherichia coli. Quantitative yields of approximately 100 different metabolites were measured by liquid chromatography-tandem MS and displayed in clustered heat map format. Many metabolites, including most amino acids and components of central carbon metabolism, were adequately extracted by a broad spectrum of solvent mixtures. For nucleotide triphosphates, however, mixtures of acidic (0.1 M formic acid-containing) acetonitrile/water (80:20) or acetonitrile/methanol/water (40:40:20) gave superior triphosphate yields. Experiments involving isotopic tracers revealed that the improved triphosphate yields in the acidic acetonitrile were in part due to reduced triphosphate decomposition, which is a major problem when extracting with other solvent systems such as methanol/water. We recommend acidic solvent mixtures containing acetonitrile for extraction of the E. coli metabolome.     

Strategies for the analysis of polar solvents in liquid matrixes

Various approaches to the analysis of polar compounds in different matrixes by solid-phase microextraction (SPME) were studied. The analysis of polar analytes in nonpolar matrixes was performed with custom-made SPME fibers coated with Nafion perfluorinated resin. The sensitivity of this fiber in this type of analysis was better by 1 order of magnitude on average as compared to those of any of the commercially available fibers. The fiber was the most sensitive for the most polar of the compounds studied, i.e., methanol. Determination of methanol, ethanol, and 2-propanol in unleaded gasoline was illustrated. Except for methanol, the fiber did not perform very well in the analysis of alcohols in water. The fiber was capable of extracting water from benzene. SPME analysis of polar compounds in water was studied using aqueous solutions of acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), 2-propanol, 2-methyl-2-propanol, and tetrahydrofuran. Fibers coated with poly(dimethylsiloxane)/divinylbenzene yielded the highest sensitivity in this type of analysis. Low- or sub-ppb detection limits were obtained for all the analytes with FID detection when the samples were saturated with NaCl. Since fibers of this type extract analytes by adsorption rather than absorption, nonlinear responses were observed when all the analytes were allowed to equilibrate because of the limited number of adsorption sites on the surface of the coating and displacement of compounds with low distribution ratios by compounds with high distribution ratios (mainly MIBK). Two approaches allowed a significant improvement in linearity: extraction of a vigorously stirred sample for a short time, or extraction under static conditions for a time much shorter than that required for equilibration of all the analytes. In both cases the amount of MIBK extracted was significantly reduced, while the remaining analytes were affected to a much lesser degree. The sensitivity of acetone determination was greatly improved by in-solution derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride and extraction of the oxime formed.     

Global metabolic profiling of Escherichia coli cultures: an evaluation of methods for quenching and extraction of intracellular metabolites

Metabolomics and systems biology require the acquisition of reproducible, robust, reliable, and homogeneous biological data sets. Therefore, we developed and validated standard operating procedures (SOPs) for quenching and efficient extraction of metabolites from Escherichia coli to determine the best methods to approach global analysis of the metabolome. E. coli was grown in chemostat culture so that cellular metabolism could be held in reproducible, steady-state conditions under a range of precisely defined growth conditions, thus enabling sufficient replication of samples. The metabolome profiles were generated using gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS). We employed univariate and multivariate statistical analyses to determine the most suitable method. This investigation indicates that 60% cold (-48 degrees C) methanol solution is the most appropriate method to quench metabolism, and we recommend 100% methanol, also at -48 degrees C, with multiple freeze-thaw cycles for the extraction of metabolites. However, complementary extractions would be necessary for coverage of the entire complement of metabolites as detected by GC/TOF-MS. Finally, the observation that metabolite leakage was significant and measurable whichever quenching method is used indicates that methods should be incorporated into the experiment to facilitate the accurate quantification of intracellular metabolites.     

Fully automated dynamic in-syringe liquid-phase microextraction and on-column derivatization of carbamate pesticides with gas chromatography/mass spectrometric analysis

A new fully automated dynamic in-syringe liquid-phase microextraction (LPME) and on-column derivatization approach, with gas chromatography/mass spectrometric (GC/MS) analysis, was developed to determine carbamate pesticides from water samples. With the use of a CTC CombiPal autosampler and its associated Cycle Composer software, a sample preparation-GC/MS method was enabled that allowed sample extraction, extract injection, and analyte derivatization to be carried out completely automatically. Optimization of extraction parameters was carried out by orthogonal array design which required a minimum of 16 experiments; the entire set of experiments was performed completely automatically and consecutively without any human intervention. Low limits of detection ranging from 0.05 to 0.1 μg/L were achieved for the carbamates. Effective enrichment of the analytes at a low concentration of 0.01 mg/L was also achieved (enrichment factors of between 57 and 138). The precision of the optimized method was satisfactory, with relative standard deviations of <6.0% (n = 6). High relative recoveries of between 81 and 125% were obtained when the method was applied to the analysis of real water samples, indicating that the sample matrix had little effect on the developed method. This automated dynamic in-syringe LPME approach demonstrated the feasibility of a complete analytical system comprising sample preparation and GC/MS that might be operated onsite, fully automatically without human intervention.     

Stir bar sorptive extraction for the determination of ppq-level traces of organotin compounds in environmental samples with thermal desorption-capillary gas chromatography--ICP mass spectrometry

The extraction and preconcentration capabilities of a new extraction technique, stir bar sorptive extraction, were combined with the separation power of capillary gas chromatography (CGC) and the low limits of detection (LODs) of inductively coupled plasma mass spectrometry (ICPMS) for the determination of the organotin compounds tributyltin (TBuT) and triphenyltin (TPhT) in aqueous standard solutions, harbor water, and mussels (after digestion with tetramethylammonium hydroxide). Throughout, tripropyltin for TBuT and tricyclohexyltin for TPhT were used as internal standards to correct for variations in the derivatization and extraction efficiency. Calibration was accomplished by means of single standard addition. Derivatization to transform the trisubstituted compounds into sufficiently volatile compounds was carried out with sodium tetraethylborate. The compounds were extracted from their aqueous matrix using a stir bar of 1-cm length, coated with 55 microL of poly(dimethylsiloxane) (PDMS). After 15 min of extraction, the stir bar was desorbed in a thermal desorption unit at 290 degrees C for 15 min, during which the compounds were cold-trapped on a precolumn at -40 degrees C. Flash heating was used to rapidly transfer the compounds to the GC where they were separated on a capillary column with a PDMS coating. After separation, the compounds were transported to the ICP by means of a homemade heated (270 degrees C) transfer line. Monitoring of the 120Sn+ signal by ICPMS during the run of the GC provided extremely low LODs for TPhT in water: 0.1 pg L(-1) (procedure) and 10 fg L(-1) (instrumental) and a repeatability of 12% RSD (n = 10). In harbor water, concentrations of 200 pg L(-1) for TBuT and 22 pg L(-1) for TPhT were found. In fresh mussels, a concentration of 7.2 ng g(-1) (dry weight) TPhT was found. The accuracy of the method was checked by the determination of TPhT in CRM477 (mussel tissue) and comparison of the result to that of an analysis of the same material with a classical liquid/liquid extraction with isooctane.     

Improved tert-butyldimethylsilylation gas chromatographic/mass spectrometric detection of nerve gas hydrolysis products from soils by pretreatment of aqueous alkaline extraction and strong anion-exchange solid-phase extraction

In the analysis of tert-butyldimethylsilyl derivatives (IBDMS) of alkyl methylphosphonic acids (RMPA) and methylphosphonic acid (MPA), from soils by gas chromatography/mass spectrometry (GC/MS), the detection yields are generally low, due to the suppression of TBDMS derivatization by the soil matrix components and the adsorption of RMPA and MPA to the soils. An ion-exchange pretreatment of the aqueous soil extract can be used to overcome the former factor by removing interfering compounds. A pretreatment method is described for improving the detection yields due to the latter factor, using an alkaline extraction procedure. The recovery was estimated quantitatively using capillary electrophoresis. The soil samples tested included volcanogenous immature soils and showed a low aqueous extraction recovery and GC/MS detection yields. The inclusion of sodium hydroxide in the extraction solvent dramatically increased the recovery. Using a 0.1 M sodium hydroxide solution, the recovery was in excess of 68%. Interfering components were removed from the alkaline soil extract by solid-phase extraction of the acids on a silica-based strong anion exchanger. The alkaline soil extract was neutralized with hydrofluoric acid and applied to the cartridge in the fluoride form. After washing with water, MPA and RMPA could be eluted with methanolic ammonia nearly quantitatively. Using the established pretreatment method, MPA and RMPA were detected from all the soil samples in more than 67% yield.     

In situ derivatization/solid-phase microextraction: determination of polar aromatic amines

A solid-phase microextraction GC/MS method for the trace determination of a wide variety of polar aromatic amines in aqueous samples was developed. Prior to extraction the analytes were derivatized directly in the aqueous solution by diazotation and subsequent iodination in a one-pot reaction. The derivatives were extracted by direct-SPME using a PDMS/DVB fiber and analyzed by GC/MS in the full-scan mode. By diazotation/iodination, the polarity of the analytes was significantly decreased and as a consequence extraction yields were dramatically improved. The derivatization proved to be suitable for strongly deactivated aromatic amines and even the very polar diamino compounds can efficiently be enriched after derivatization. We investigated 18 anilines comprising a wide range of functional groups, which could be determined simultaneously. The method was thoroughly validated, and the precision at a concentration of 0.5 microg/L was 3.8-11% relative standard deviation for nonnitrated analytes using aniline-d(5) as internal standard and 3.7-10% for nitroaromatic amines without internal standard. The in situ derivatization/SPME/GC/MS method was calibrated over the whole analytical procedure and was linear over 2 orders of magnitude. Using 10-mL samples, detection limits of 2-13 ng/L were achieved for 15 of the 18 analytes. For two aminodinitrotoluene isomers and a diaminonitrotoluene, detection limits ranged from 27 to 38 ng/L. By allowing quantification at the 0.1 microg/L level, analysis of all target compounds meets EU drinking water regulations. The method provides high sensitivity, robustness, and high sample throughput by automation. Finally, the method was applied to various real water samples and in wastewater from a former ammunition plant the contents of several aromatic amines were quantified.     

Electrogenerated chemiluminescence detection of amino acids based on precolumn derivatization coupled with capillary electrophoresis separation

A novel method for highly sensitive detection of primary and secondary amino acids with selective derivatization using acetaldehyde as a new derivatization reagent was proposed by capillary electrophoresis (CE) coupled with electrogenerated chemiluminescence (ECL) of tris(2,2'-bipyridine)ruthenium(II). The precolumn derivatization of these amino acids with acetaldehyde was performed in aqueous solution at room temperature for 1 h. Upon optimized derivatization, the ECL intensities and detection sensitivities of the amino acids were significantly enhanced by 20-70 times. Using four amino acids, arginine, proline, valine, and leucine, as model compounds, their derivatives could be completely separated by CE and sensitively detected by ECL within 22 min. The linear ranges were 0.5-100 microM for arginine and proline and 5-1000 microM for valine and leucine with the detection limits of 1 x 10(-7) (0.5 fmol, arginine), 8 x 10(-8) (0.4 fmol, proline), 1 x 10(-6) (5 fmol, valine), and 1.6 x 10(-6) M (8 fmol, leucine) at a signal-to-noise ratio of 3. The derivatization reactions and ECL process of amino acids were also proposed based on in situ Fourier transform infrared and ultraviolet spectrometric analyses.     

Perfluorosulfonated ionomer-modified polyethylene. A material for simultaneous solid-phase enrichment and enhanced precolumn dansylation of C-21 ketosteroids in human serum

A new derivatization procedure has been developed where solid-phase catalysis is utilized to facilitate the formation of hydrazones in precolumn labeling of keto-containing compounds. This procedure has been implemented on a solid-phase enrichment and enhanced derivatization (SPEED) device, prepared from porous polyethylene that has been coated with Nafion and dansylhydrazine. The SPEED devices have been optimized using experimental design and characterized for dansylation of C-21 ketosteroids by multivariate data analysis, using progesterone as the model compound. The reaction temperature and the molar ratio between the steroid and the derivatization reagent were found to be the factors most strongly affecting the reaction. Faster reaction kinetics were achieved when the molar ratio between dansylhydrazine and the steroid was increased. Mass spectroscopic analysis showed that the four derivative peaks eluting when derivatized progesterone was separated on an octadecyl silica stationary phase were due to the syn and anti mono- and bis(hydrazones) formed in the reaction. Using optimal reaction conditions, the derivatives mainly constitute the syn and anti conformers of bis-derivatives. In contrast to solution-based acid catalysis, the SPEED device was remarkably insensitive to water in the reaction mixture. A sample volume of 400 microL was found to be the maximum, enabling sample enrichment prior derivatization. Using optimal experimental conditions, picomole amounts of ketosteroids could be derivatized in 10 min at room temperature. Analysis of spiked serum samples containing 0.4-2.0 nmol of progesterone showed overall recoveries of 52-63%. The corresponding 3delta detection limit was 1.3 pmol (n = 4, 100 microL injected), as estimated from calibration curve data.     

Analysis of pharmaceuticals in fish using liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) screening method has been developed targeting 23 pharmaceuticals and 2 metabolites with differing physicochemical properties in fish tissue. Reversed-phase separation of target compounds was achieved using a C18 column and a nonlinear gradient consisting of 0.1% (v/v) formic acid and methanol. Eluted analytes were introduced into the mass analyzer using positive or negative electrospray ionization, as appropriate. A variety of extraction solvents, differing in polarity, pH, or both, were investigated in order to assess recovery of target compounds from 1-g tissue homogenates. Among 10 solvents tested, a 1:1 mixture of 0.1 M aqueous acetic acid (pH 4) and methanol was identified as optimal, resulting in extraction recoveries for 24 of 25 compounds exceeding 60%. Tissue extracts were found to influence the LC-MS/MS response for several analytes. Consequently, matrix-matched calibration standards were employed to determine analyte concentrations in environmental samples. Statistically derived method detection limits were <6 ng/g for most analytes. The method was subsequently used to screen for target analytes in fish from an effluent-dominated stream. Diphenhydramine, diltiazem, carbamazepine, and norfluoxetine were detected in 11 of 11 environmental samples at concentrations ranging from 0.11 to 5.14 ng/g.     

Development, validation, and application of a method for quantification of methylmercury in biological marine materials using gas chromatography atomic emission detection

A gas chromatographic method was developed for the quantification of alkylmercury species using microwave-induced plasma atomic emission detection (GC-AED). The column conditioning and analyte derivatization required for previous methods were found to be unnecessary for stable, accurate, and sensitive element-specific detection using GC-AED. Chromatographic and detection parameters such as stationary phase type, stationary phase film thickness, GC column dimensions, helium mobile phase column head pressure, detector makeup gas flow rate, and detector reagent gas type and flow rate were found to significantly affect analyte response. The detection limit for the optimized GC-AED conditions was 0.8 pg (0.1 pg/s) of methylmercury chloride (as mercury). A solid-liquid extraction procedure with preparative gel permeation chromatography cleanup and GC-AED analysis was used to quantify methylmercury in a variety of complex matrix marine materials. The methylmercury quantification method was validated with four marine certified reference materials (CRMs). The method was then applied to 13 standard reference materials, CRMs, and control materials for which no certified reference values for methylmercury have been determined. Four National Institute of Standards and Technology Standard Reference Materials and one control material, which were analyzed using the GC-AED method, were also analyzed by two other laboratories using independent methods to further validate the method.     

微波辅助萃取/分光光度法快速测定抗菌纺织品中的三氯生

为了测定抗菌纺织品中三氯生的含量,本文以二氯甲烷为萃取溶剂,采用微波萃取技术萃取抗菌纺织品中的抗菌剂三氯生。萃取液蒸发至干后,用甲醇定容,然后以甲醇为参比溶液,在282nm波长下测定其吸光度,从而建立了一种测定抗菌纺织品中的抗菌剂三氯生的分光光度方法,并对萃取条件、方法的线性关系、精密度、回收率、检出限等进行了研究。三氯生在0.2-80mg/L范围内呈现良好的线性关系,线性相关系数为0.9998,回收率为91.98%-104.94%,相对标准偏差均小于6%,检出限为0.1mg/kg(S/N=3)。采用该方法对市售抗菌纺织品进行检测,发现部分抗菌纺织品中使用高含量的三氯生。     

Determination of anionic and nonionic surfactants, their degradation products, and endocrine-disrupting compounds in sewage sludge by liquid chromatography/mass spectrometry

A comprehensive analytical method based on reversed-phase liquid chromatography and mass spectrometry using both atmospheric pressure chemical ionization and electrospray ionization has been developed for the simultaneous determination of anionic and nonionic surfactants, their polar degradation products, and endocrine-disrupting compounds (EDCs) in sewage sludge. Extraction of target compounds, with recovery rates from 86% to nearly 100% for polyethoxylates and from 84 to 94% for polar degradation products, was achieved applying ultrasonic solvent extraction with a mixture of methanol/ dichloromethane (7:3, v/v). Cleanup of sample extracts was performed on octadecyl solid-phase extraction cartridges. Determination of less polar compounds: alcohol ethoxylates (AEOs), nonylphenol ethoxylates (NPEOs), coconut diethanol amides, poly(ethylene glycol)s, and phthalate esters was accomplished by reversed-phase LC-APCI-MS in positive ionization mode, while more polar compounds: nonylphenolcarboxylates, nonylphenol (NP), octylphenol, and bisphenol Awere analyzed by ion-pair LC-ESI-MS under negative ionization conditions. This protocol was successfully applied to the trace determination of anionic and nonionic surfactants, polar degradation products, and EDCs in sewage sludge collected from different sewage treatment plants. The analysis revealed the presence of NP at high concentration levels ranging from 25 to 600 mg/kg. Polyethoxylates (AEOs and NPEOs) were also found in all samples at parts-per-million levels (10-190 mg/kg AEOs and 2-135 mg/kg NPEOs, respectively).     

Low part per trillion determination of reactive alkanethiols in wastewater by in situ derivatization-solid-phase microextraction followed by GC/MS

A solid-phase microextraction (SPME) procedure for the simultaneous determination of volatile alkanethiols (i.e., methane-, ethane-, propanethiol) and dihydrogen sulfide in aqueous samples as stable thioethers followed by GC/MS determination was developed. Accordingly, N-ethylmaleimide as derivatization reagent in the aqueous phase was used for the first time, improving the analyte stability and method sensitivity in comparison to the determination of free forms. Thus, pH of the aqueous medium, reaction time, and derivatization reagent concentration have been evaluated, and the main parameters affecting the SPME process (i.e., coating selection, extraction mode and time profile, extraction and desorption temperatures) optimized. At the selected derivatization and extraction conditions, the proposed method provided no matrix effect either in the derivatization reaction or in the microextraction steps. RSD values were lower than 11% and LODs from 0.74 to 5.2 ng L(-1). The developed procedure was successfully applied to different water and wastewater samples, where dihydrogen sulfide and some of the target alkanethiols were identified at low-microgram per liter concentrations.     

Simultaneous preconcentration and determination of U(VI), Th(IV), Zr(IV) and Hf(IV) ions in aqueous samples using micelle-mediated extraction coupled to inductively coupled plasma-optical emission spectrometry

A simple cloud point extraction method followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for simultaneous preconcentration and determination of trace amounts of U(VI), Th(IV), Zr(IV) and Hf(IV) ions in aqueous samples. The metal ions in 50 ml of aqueous solution (containing 0.1 M sodium acetate, pH 6.0) were formed complexes with dibenzoylmethane (DBM). Then, Triton X-114 (0.2%, w/v) was added to the solution. By increasing the temperature of the solution up to 50 degrees C, a phase separation occurred. After centrifugation at 4000 rpm for 6 min, the surfactant-rich phase (sediment phase) was diluted with 1.0 ml of 20:80 (v/v) of methanol/1 M HNO(3). The metal ions were then determined using ICP-OES. Finally, the main factors affecting the cloud point extraction were evaluated and optimized. Under optimized conditions, enhancement factors in the range of 37.0-43.6 were obtained. The calibration graphs were linear in the range of 0.5-1500 microg l(-1) for Th and Zr, 0.5-500 microg l(-1) for Hf and 2.5-1240 microg l(-1) for U with correlation coefficients (r(2)) better than 0.9926. The detection limits were between 0.1 and 1.0 microg l(-1) and the R.S.D. values for seven replicates were lower than 6.1%.     

Separation and detection of siderophores produced by marine bacterioplankton using high-performance liquid chromatography with electrospray ionization mass spectrometry

High-performance liquid chromatography-electrospray ionization mass spectrometry was applied to the detection of the iron(III) complexes of the hydroxamate siderophores rhodotoluric acid, deferrioxamine B, and deferrichrome. Separation of the iron(III) complexes was obtained using a polystyrene-divinylbenzene stationary phase. The retention and responses of ferrioxamine and ferrichrome were optimal when a gradient elution program with methanol and 0.1% (v/v) formic acid as the mobile phases was used. These conditions were also suitable for the retention and separation of the uncomplexed ligands. Retention of iron(III) rhodotoluate was improved when formic acid was replaced by the ion-pairing reagent heptafluorobutyric acid (0.1%). Detection limits for the ferric complexes, defined as 3 SD of the lowest determined standard, were 26 nM for iron(III) rhodotoluate, 0.23 nM for ferrioxamine, and 0.40 nM for ferrichrome. A protocol for the solid-phase extraction of these hydroxamate siderophores from seawater was developed and applied to the extraction of siderophores from enriched incubated seawater samples.     

Systematic Evaluation of Extraction Methods for Multiplatform-Based Metabotyping: Application to the Fasciola hepatica Metabolome

Combining data from multiple analytical platforms is essential for comprehensive study of the molecular phenotype (metabotype) of a given biological sample. The metabolite profiles generated are intrinsically dependent on the analytical platforms, each requiring optimization of instrumental parameters, separation conditions, and sample extraction to deliver maximal biological information. An in-depth evaluation of extraction protocols for characterizing the metabolome of the hepatobiliary fluke Fasciola hepatica , using ultra performance liquid chromatography and capillary electrophoresis coupled with mass spectroscopy is presented. The spectrometric methods were characterized by performance, and metrics of merit were established, including precision, mass accuracy, selectivity, sensitivity, and platform stability. Although a core group of molecules was common to all methods, each platform contributed a unique set, whereby 142 metabolites out of 14,724 features were identified. A mixture design revealed that the chloroform:methanol:water proportion of 15:59:26 was globally the best composition for metabolite extraction across UPLC-MS and CE-MS platforms accommodating different columns and ionization modes. Despite the general assumption of the necessity of platform-adapted protocols for achieving effective metabotype characterization, we show that an appropriately designed single extraction procedure is able to fit the requirements of all technologies. This may constitute a paradigm shift in developing efficient protocols for high-throughput metabolite profiling with more-general analytical applicability.     

Development of a cloud-point extraction method for copper and nickel determination in food samples

A new, simple and versatile cloud-point extraction (CPE) methodology has been developed for the separation and preconcentration of copper and nickel. The metals in the initial aqueous solution were complexed with 2-(2'-benzothiazolylazo)-5-(N,N-diethyl)aminophenol (BDAP) and Triton X-114 was added as surfactant. Dilution of the surfactant-rich phase with acidified methanol was performed after phase separation, and the copper and nickel contents were measured by flame atomic absorption spectrometry. The variables affecting the cloud-point extraction were optimized using a Box-Behnken design. Under the optimum experimental conditions, enrichment factors of 29 and 25 were achieved for copper and nickel, respectively. The accuracy of the method was evaluated and confirmed by analysis of the followings certified reference materials: Apple Leaves, Spinach Leaves and Tomato Leaves. The limits of detection expressed to solid sample analysis were 0.1 microg g(-1) (Cu) and 0.4 microg g(-1) (Ni). The precision for 10 replicate measurements of 75 microg L(-1) Cu or Ni was 6.4 and 1.0, respectively. The method has been successfully applied to the analysis of food samples.     

Simultaneous determination of estrogenic short ethoxy chain nonylphenols and their acidic metabolites in water by an in-sample derivatization/solid-phase microextraction method

An in-sample derivatization headspace solid-phase microextraction method has been developed for the simultaneous determination of nonylphenol, nonylphenol mono- and diethoxylates (NP, NP1EO, NP2EO), and their acidic metabolites (NPlEC, NP2EC) in water. The analytical procedure involves derivatization of NPEOs and NPECs to their methyl ethers--esters with dimethyl sulfate/NaOH and further headspace (HS) solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) determination. Parameters affecting both derivatization efficiency and headspace SPME procedure, such as the selection of the SPME coating, derivatizationextraction time, temperature and ionic strength were optimized. The commercially available Carbowax-divinylbenzene (CW-DVB) fiber appears to be the most suitable for the simultaneous determination of both NPEOs-NPECs. Run-to-run precision of the in-sample derivatization/HS-SPME-GC/MS method gave relative standard deviations between 8 and 18%. The method was linear for NP over 2 orders of magnitude, and detection limits were compound dependent but ranged from 20 to 1500 ng/L. The SPME procedure was compared with a solid-phase extraction SPE-GC/MS method for the analysis of NPEOs-NPECs in water samples and good agreement was obtained. Therefore, in-sample derivatization HS-SPME-GC/MS can be used as a method for the simultaneous determination of short ethoxy chain nonylphenols and their acidic metabolites in water.