The analysis of thiocarbamides by gas chromatography/negative-ion chemical-ionization mass spectrometry.

Thiocarbamides were converted to their di-N-pentafluorobenzyl (PFB) derivatives and analysed by gas chromatography/negative-ion chemical-ionization mass spectrometry with methane as reagent gas. The PFB derivatives of the 2-thiouracils gave mass spectra in which the ion current was carried largely by an ion arising from [M-PFB]-. The derivative was used in the determination of the uptake and metabolism of thiocarbamides by cultures of melanoma cells.     

Determination of fatty acid amides as trimethylsilyl derivatives by gas chromatography with mass spectrometric detection.

Fatty acid amides are a newly emerging class of compounds with biological activity. The amides are formed enzymatically in vivo. Analysis of fatty acid amides has been accomplished by gas chromatography coupled with mass spectrometry. Fatty acid amides required derivatization prior to analysis at high temperatures due to thermal instability. Trimethylsilylation of fatty acid amides has been accomplished under optimum reaction conditions. The limit of detection for the silylated amides is approximately 1 pmol, with the lowest detected level being 700 fmol for the lauramide derivative. Quantitation of fatty acid amide derivatives can be accomplished by monitoring m/z 59 or m/z M-71, the only two major fragments formed in the ion trap mass spectrometer with electron impact ionization. The smaller fragment is the result of a newly reported, McLafferty-type rearrangement; M-71 resulted from loss of an n-pentyl fragment. Either peak gave four-five orders of magnitude linear dynamic range. Numerous trimethylsilylamides from C7 to C20 were separated under standard conditions. Elution was linear with the number of carbons and was systematically affected by the number and position of the double bonds.     

Determination of halogenated mono-alcohols and diols in water by gas chromatography with electron-capture detection

We have developed an analytical method for the detection of halogenated alcohols in water with particular focus on 3-chloro-1,2-propanediol and 3-bromo-1,2-propanediol. In this method the target analytes are extracted from water, derivatized with heptafluorobutyric anhydride, and then analyzed with gas chromatography with electron-capture detection. The effects of water, pH and seawater constituents on the method were investigated. Method detection limits for a 5 ml aqueous sample ranged from 0.14 microg l(-1) for 2-bromo-1,3-propanediol to 1.7 microg l(-1) for 1,3-dichloro-2-propanol (1,3DCP).     

Determination of fungicides in natural waters using solid-phase microextraction and gas chromatography coupled with electron-capture and mass spectrometric detection

This study develops a method for the analysis of seven fungicides in environmental waters, using solid-phase microextraction (SPME). The analyzed compounds--dicloran, chlorothalonil, vinclozolin, dichlofluanid, captan, folpet and captafol--belong to different classes of chemical compound (chloroanilines, sulphamides, phthalimides and oxazolidines) and are used mainly in agriculture and as antifouling paints. Their determination was carried out by gas chromatography with electron-capture and mass spectrometric detection. To perform SPME, four types of fibre have been assayed and compared: polyacrylate (85 microm), polydimethylsiloxane (100 and 30 microm), carbowax-divinylbenzene (CW-DVB 65 microm) and polydimethylsiloxane-divinylbenzene (65 microm). The main parameters affecting the SPME process such as pH, salt additives, methanol content, memory effect, stirring rate and adsorption-time profile were studied. The method was developed using spiked natural waters such as ground water, sea water, river water and lake water in a concentration range of 0.1-10 microg/l. Limits of detection of studied compounds were determined in the range of 1-60 ng/l, by using electron-capture and mass spectrometric detectors. The recoveries of all fungicides were in relatively high levels (70.0-124.4%) and the average R2 values of the calibration curves were above 0.990 for all the analytes. The SPME conditions were finally optimized in order to obtain the maximum sensitivity. The potential of the proposed method was realized by applying it to the trace-level screening determination of fungicides and antifouling compounds in sea water samples originating from various Greek marinas.     

Sample preparation methods to analyze fipronil in honey by gas chromatography with electron-capture and mass spectrometric detection

Several sample preparation methods have been assayed to analyze residues of fipronil in honey. After diluting the honey, liquid-liquid extraction (LLE) with organic solvents, and solid-phase extraction (SPE) on commercial cartridges or Florisil-packed column have been tested at three concentration levels: 0.01, 0.1 and 1 mg/kg. LLE with n-hexane or SPE on a Florisil column resulted to be the most suitable procedures to analyze fipronil at trace concentrations. Fipronil was quantified by gas chromatography (GC) with electron-capture detection (ECD) or mass spectrometric (MS) detection after conventional or matrix-matched calibration. The detection limit of fipronil in honey samples was below 1 microg/kg. The degradation of fipronil in honey has also been studied, being identified three minor degradation products in the extracts.     

Determination of halogenated hydrocarbons by combined use of neutron activation analysis and capillary gas chromatography with electron-capture detection

Results obtained by the two techniques are compared. Two standard mixtures, one containing, HCB, DDT, DDE and DDD and the other chloro-, dichloro- and bromocyme, were at a halogen concentration of about 20, 2 and 0.2 mg l^?1. The neutron activation method gave an average recovery of 4% (relative standard deviation, 12%) based on 24 measurements for chlorine. For bromine, the figures were 99% and 11%, respectively. Volatile chlorinated organics pose a particular problem because they may evaporate during analysis. Investigations with chloroform as model substance, indicate that when sealed ampoules are used, the average recovery is 84% (r.s.d., 6%).     

Improved analysis of volatile halogenated hydrocarbons in water by purge-and-trap with gas chromatography and mass spectrometric detection

An analytical system composed of a purge-and-trap injection system coupled to gas chromatography with mass spectrometric detection (PTI-GC-MS) specific for the analysis of volatile chlorinated hydrocarbons (VCHCs) (chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) and trihalomethanes (THMs) (chloroform; bromodichloromethane; dibromochloromethane; bromoform) in water was optimised. Samples were purged and trapped in a cold trap (-100 degrees C) fed with liquid nitrogen (cryo-concentration). In order to make this method suitable also for only slightly contaminated waters, some modifications were made to PTI sample introduction, in order to avoid any air intake into the system. PTI, GC and MS conditions were optimised for halogenated compound analysis and limits of detection (LOD) were evaluated. The proposed method allows analysis of samples whose concentrations range from microg/L to ng/L. It is, therefore, applicable to drinking waters, in analyses required by law, and to slightly contaminated aqueous matrices, such as those found in remote areas, in environmental monitoring. Moreover, by changing cold trap temperature, even sparkling mineral waters can be analysed, thus avoiding CO2 interference during the cryo-concentration phase. Our method has been successfully used on real samples: tap water, mineral water and Antarctic snow.     

Determination of pesticide residues in peaches by using gas chromatography and mass spectrometric detection

ABSTRACT

A multi-residue method using selected ion monitoring mode GC-MSD has been developed for the quantitative analysis of 30 widely used pesticides in fresh peaches produced in Swat Malakand, Pakistan. The planned methodology involved a sample extraction procedure using liquid-liquid partition with acetonitrile followed by a clean-up step based on solid-phase extraction (SPE). Method validation was performed in accordance with European Union guidelines. The European Union criteria (recovery 70–120%, RSD <20%) were met for majority of pesticides. For most of the pesticides, signal-to-noise ratios were good and background-corrected mass spectra often contained sufficient diagnostic to enable identity and confirmation. The limits of quantification (LOQs) were in the range 0.01–1.0 mg/kg. The above method was successfully applied to the analysis of peach samples (n = 30) from the field. Pesticide concentration in real peach samples was compared with the maximum residue levels (MRLs). Pesticide residues were detected in 73% of the peach samples. Most frequent residues were metalaxyl, α-cypermethrin, azoxystrobin, dimethoate, tebuconazol, λ-cyhalothrin and spiromesifin in peach samples.     

Determination of natural and synthetic estrogens in water by gas chromatography with mass spectrometric detection

A procedure for the determination of six natural and synthetic estrogens (diethylstilbestrol, estrone, 17beta-estradiol, mestranol, 17alpha-ethinylestradiol and estriol) in water samples is described. Samples, up to 2000 ml, were concentrated using Oasis HLB solid-phase extraction cartridges. Analytes were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide and determined by GC-MS or GC-MS-MS. The reactivity of several silylation reagents versus aliphatic and aromatic hydroxyl groups contained in the structure of the selected analytes was evaluated. Influence of parameters such as sample pH, nature of the water samples and derivatization conditions on the performance of the whole analytical procedure was systematically studied. Under optimal conditions, quantification limits between 1 and 3 ng/l were achieved for the determination of the considered estrogens in sewage water.     

Determination of methanol in cosmetics by headspace and multidimensional gas chromatography with mass spectrometric detection

A novel, reliable, and robust analytical method using headspace and multidimensional GC coupled to MS was successfully developed for determining the methanol content in cosmetics. The methanol was quantitatively analyzed and confirmed by heart-cutting multidimensional GC and mass selective detection in full scan mode. The average recovery was 99.8% with an RSD of 4.3%; the LOQ was 5 mg/kg. The proposed method showed good accuracy and precision while minimizing erroneous results due to false positives compared with conventional single-column GC analysis.     

Comparative study of sample preparation procedures to determine fipronil in pollen by gas chromatography with mass spectrometric and electron-capture detection

Several sample preparation methods have been assayed to analyze residues of fipronil in pollen at trace concentrations. Extraction with organic solvents, solid-phase extraction on either commercial cartridges or a Florisil-packed column and a matrix solid-phase dispersion, also with Florisil as a dispersing agent, have been tested. Determination of fipronil in the extracts has been carried out by GC with electron-capture and mass spectrometric detection. An extraction with acetonitrile followed by a clean-up on ODS or polymeric cartridges was the most suitable procedure to obtain acceptable recoveries and relatively simple chromatograms. The matrix-effects observed in the quantification can be corrected with a matrix-matched calibration.     

Determination of busulfan in human plasma by gas chromatography with electron-capture detection

A simple and highly sensitive gas chromatographic method has been developed for the determination of busulfan in human plasma. After extraction of plasma specimens (clinical or spiked) with ethyl acetate, busulfan and the internal standard [1,8-bis(methanesulfonyloxy)octane] were derivatized with 2,3,5,6-tetrafluorothiophenol to yield compounds monitored by a 63Ni electron-capture detector. Sample recoveries from extraction and derivatization were greater than 78 and 91%, respectively. The limit of quantitation was 0.01 microgram/ml (0.04 microM) in 1 ml of plasma with a linear relationship over the 0.01-1.0 micrograms/ml (0.04-4 microM) concentration range. The method has been applied to analyze the plasma versus time profile of busulfan in human subjects following administration of an oral dose of 4 mg/kg per day as a marrow ablative chemotherapy for bone marrow transplantation.     

Determination of toxaphene enantiomers by comprehensive two-dimensional gas chromatography with electron-capture detection

Comprehensive two-dimensional gas chromatography with micro electron-capture detection (GC x GC-microECD) has been evaluated for the enantioseparation of five chiral toxaphenes typically found in real-life samples (Parlar 26, 32, 40, 44 and 50). From the two enantioselective beta-cyclodextrin-based columns evaluated as first dimension column, BGB-176SE and BGB-172, the latter provided the best results and was further combined with three non-enantioselective columns in the second dimension: HT-8, BPX-50 and Supelcowax-10. The combination BGB-172 x BPX-50 was finally selected because it provided a complete separation among all enantiomers. A satisfactory repeatability and reproducibility of the retention times in both the first and the second dimension were observed for all target compounds (RSDs below 0.8%, n = 4). Linear responses in the tested range of 10-200 pg/microl and limits of detection in the range of 2-6 pg/microl were obtained. The repeatability and reproducibility at a concentration of 100 pg/microl, evaluated as the RSDs calculated for the enantiomeric fraction (EF), was better than 11% (n = 4) in all instances. The feasibility of the method developed for real-life analyses was illustrated by the determination of the enantiomeric ratios and concentration levels of the test compounds in four commercial fish oil samples. These results were compared to those obtained by heart-cut multidimensional gas chromatography using the same enantioselective column.     

Determination of ultramicro amounts of selenium by gas chromatography with electron-capture detection

Formation of piazselenols by the reaction of Se(IV) with 1,2-diaminobenzene and its derivatives, followed by solvent extraction and gas chromatography with electron-capture detection, provides the most sensitive means of determining selenium. By suitable chemical manipulation, the method can be used for Se(-II), Se(O), Se(IV) and Se(VI). Applications to a wide variety of samples are reviewed.     

Simplified pesticide multiresidue analysis in virgin olive oil by gas chromatography with thermoionic specific, electron-capture and mass spectrometric detection

In the present work, an analytical multiresidue method has been developed for the analysis of 32 organochlorine, organophosphorus and organonitrogen pesticides at microg kg(-1) levels in virgin olive oil. The method consists of the extraction of the pesticides with acetonitrile saturated in n-hexane followed by a clean-up process based on gel permeation chromatography (GPC) with ethyl acetate-ciclohexane (1:1) as mobile phase to separate the low-molecular mass pesticides from the high-molecular mass fat constituents of the oil. The target compounds were determined in the final extract by gas chromatography (GC) using thermoionic specific (TSD) and electron-capture (ECD) detection. In the case of positive samples, the amounts found were confirmed by GC-MS/MS, being the results in good agreement. Recoveries and RSDs (n = 10) values were 91-124% and 1-8% (GC-ECD), 82-100% and 9-20% (GC-TSD), and 89-105% and 4-14% (GC-MS/MS), respectively. The three proposed methods were applied to samples collected directly in two olive mills located in the Jaén province (Spain). Specifically, 24 samples of virgin olive oil were collected. The most frequently pesticide residues found were the herbicides terbuthylazine and diuron and endosulfan sulfate, a degradation product of the insecticide endosulfan. The herbicide concentration was higher in those oil samples obtained from olives which were collected from the ground after they had fallen down than in those oil samples from olives harvested directly from the tree. The GC-MS/MS developed method was also applied to the analysis of an olive oil sample from a proficiency test spiked with organochlorine pesticides and all the values obtained were within the specified "satisfactory" range.     

Determination of anabolic steroids by gas chromatography/negative-ion chemical ionization mass spectrometry and gas chromatography/negative-ion chemical ionization tandem mass spectrometry with heptafluorobutyric anhydride derivatization

A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemical ionization (NCI) and tandem mass spectrometry (MS/MS) for the determination of eight anabolic steroids in human urine. Eight anabolic steroids were derivatized by heptafluorobutyric anhydride (HFBA), and were determined using GC/NCI-MS and GC/NCI-MS/MS. The linear correlation coefficients for calibration in NCI-MS/MS were in the range 0.9880-0.9988. This method of derivatization with HFBA for use with GC/NCI was useful in determinations of 19-norandrosterone, boldenone, 19-noretiocholanolone, 2-methylandrosterone, nandrolone, 1-methyleneandrosterone, 1-methylandrosterone, 4-dihydroboldenone and mesterolone. The detection limits of this procedure were 5-20 ppb at a signal-to-noise (S/N) ratio of 3.     

Determination of fluvalinate residues in beeswax by gas chromatography with electron-capture detection

A simple, rapid, and accurate method is described for the determination of residual fluvalinate in beeswax. The procedure consists of partitioning on a disposable column of diatomaceous earth (Extrelut), followed by chromatographic cleanup on a Florisil cartridge. The final extract is analyzed by capillary gas chromatography with electron-capture detection (GC-ECD). Briefly, wax samples were dissolved in n-hexane, and the solutions were sonicated and transferred to Extrelut columns. The fluvalinate was extracted with acetonitrile, and a portion of the extract was cleaned up on a Florisil cartridge. The fluvalinate was eluted with diethyl ether-n-hexane (1 + 1) and directly determined by GC-ECD. Recoveries from wax samples spiked at 5 fortification levels (100-1500 microg/kg) ranged from 77.4 to 87.3%, with coefficients of variation of 5.12-8.31%. The overall recovery of the method was 81.4 +/- 3.2%, and the limit of determination was 100 microg/kg.     

Determination of pesticide residues in lettuce by gas chromatography with electron-capture detection

A sensitive, rapid, and simple multiresidue method for the simultaneous determination of 19 pesticides in different varieties of lettuce (Lactuca sativum) was developed. Lettuce samples were extracted by homogenization with acetone and partitioned into ethyl acetate-cyclohexane. Subsequent sample cleanup was not needed. Final determination was made by capillary gas chromatography (GC) with electron-capture detection (ECD). Confirmation analysis of pesticides was performed by GC coupled with mass spectrometry in the selected ion monitoring mode. The average recovery by the GC-ECD method obtained for these compounds varied from 66.4 to 119.2% with relative standard deviations < 7.7%. The GC-ECD method has good linearity, and the detection limit for the pesticides studied varied from 0.1 to 3.8 microg/kg. The proposed method was used to determine pesticide levels in different types of lettuce grown in soils from experimental fields.     

Pesticide trace analysis using solid-phase extraction and gas chromatography with electron-capture and tandem mass spectrometric detection in water samples

Gas chromatography (GC) with electron-capture detection (ECD), mass spectrometry (MS) and tandem mass spectrometry (MS-MS) were employed for the identification of 12 pesticides in water samples. For this purpose, a solid-phase extraction procedure with C18 cartridges was used, optimising the breakthrough volume and the saturation concentration. In GC-MS-MS, the lowest detectable concentrations for the pesticides were between 2 and 26 ng l(-1), recoveries ranged from 70 to 133% in water samples spiked at 100 ng l(-1) and the relative standard deviations were in the range 5.3 to 17.4%. The proposed analytical methodology was applied to analyse pesticides in wetland samples from Almería (Spain).