Solid-phase extraction—Thermal desorption—Gas chromatography with mass selective detection for the determination of drugs in urine

Summary Solid-phase extraction (SPE) was combined with thermal desorption (TD) and gas chromatographic (GC) analysis to determine drugs in urine. The extrattion was performed inside a fritted GC liner using about 5 mg TENAX that was inserted into the liner on top of the frit. After extraction, the liner was placed into the injector of the GC and the analytes were thermally desorbed by using a programmed-temperature vaporiser. Several sorbent materials were investigated for the applicability of SPETD-GC analysis. TENAX proved to be the most suitable sorbent, since hardly any interferences were observed and acceptable absolute recoveries (73 and 74%) were obtained for lidocaine and diazepam. A mass selective detector (MSD) in the selected ion monitoring mode allowed detection of lidocaine and diazepam down to 0.5 ng·mL⁻¹ using 50μL urine. The use of only 5 mg of extraction material allowed rapid extraction, while a 10 m GC column provided a fast chromatographic system. As a results, the total analysis time was less than 20 min, including 5 min for drying the TENAX and 5 min for thermal desorption. Thus, SPETD-GC-MS appears to be a powerful tool for the rapid analysis of biological samples.     

The role of self-protonation under direct GC-MS determination of amphetamine hydrochloride

Summary We studied the possibility of direct GC-MS determination of amphetamine hydrochloride. In order to avoid the double peak we determined the optimal injector temperature (260°C) and heating rate (40°C min⁻¹). In the direct analysis of amphetamine hydrochloride containing samples, calibration for fragmentm/z=59 (originating from amphetaminium ion fragmentation; the calibrating agent is amphetamine hydrochloride) gave better results than calibration form/z=44 (derived from both free amphetamine and amphetaminium ion; calibration agents were amphetamine or amphetamine hydrochloride). We also compared the mass spectra of amphetamine and amphetamine hydrochloride taken by ion-trap GC-MS. The fragmentation path was cleavage of the C-C bond at benzyl position for the free base or between the phenyl group and the aliphatic moiety, in the case of free base and amphetaminium ion, respectively.     

Determination of bisphenol-a and related compounds in human saliva by gas chromatography—mass spectrometry

Summary A simple and sensitive method for the determination of trace amounts of bisphenol-A (BPA), bisphenol-A diglycidyl dimethacrylate (bis-GMA), bisphenol-A dimethacrylate (bis-DMA) and triethyleneglycol dimethacrylate (TEGDMA) in human saliva is proposed. These materials are used in dental restorations, as composites and sealants, and are sometimes detected in human saliva after dental treatment. The proposed method involves protein precipitation using acetonitrile followed by acidification, evaporation of the solvent and dissolution with dichloromethane prior to injection into a GC-MS. Thermal derivatization in the injection system was used for the identification and quantification of bis-GMA. Clean-up is not necessary using SIM mode. Bisphenol-F (BPF) was used as internal standard. The linear range was 15 to 1000 μg·L⁻¹ for BPA, 50 to 10 000 μg·L⁻¹ for bis-GMA, 50 to 1000 μg·L⁻¹ for bis-DMA and 1 to 100 μg·L⁻¹ for TEGDMA. The detection limits were 3,15,10 and 0.3 μg·L⁻¹ for BPA, bis-GMA, bis-DMA and TEGD-MA, respectively. Validation of the proposed method was carried out by using the standard addition methodology. Samples of 10 mL of human saliva collected 1 h after dental treatment were analysed in order to assess the applicability of the method to detect and quantify such compounds originated from methacrylic resins used in odontological treatment.     

Impurity Profiling of a Nonsteroidal Analgesic Drug by Capillary Electrochromatography

Summary The pesticides lindane, vinclozolin, aldrin, p,p′DDE, o,p′DDT, p,p′DDT, methoxychlor, kepone and mirex, which are classifed as endocrine disrupters, have been analysed. This was conducted within an extensive hospital-based epidemiological study that includes surgically treated breast cancer patients and a matching group of women with no sign of estrogenic-dependent disease. Patients were from the Hospital Torrecardenas and living in agricultural areas of Almería (Spain). The results from the analysis of 100 serum samples were performed by gas chromatography (GC) with electron capture detection (ECD) and tandem mass spectrometry (MS-MS) detection mode. Performance characteristics, such as linearity, detection limit (LOD) and quantitation limit (LOQ), together with an estimate of measurement uncertainty (using validation data) is presented for each pesticide, in both chromatographic methods. The results obtained were compared. The advantage of MS-MS over ECD to determine endocrine disrupting compounds in complex matrix was also shown. p,p′DDE was the most frequently encountered pesticide, as well as the one found at higher concentration level. p,p′DDT was found in eight samples. Lindane was detected at low concentration level. While vinclozolin, aldrin, methoxychlor, kepone, o,p′DDT and mirex were absent in all samples analysed.     

Gas chromatography–mass spectrometric identification of iodine species arising from photo-chemical vapor generation

Ultraviolet irradiation of aqueous solutions of iodide/iodate ion containing low molecular weight organic acids generates volatile iodine species that are amenable to detection by atomic spectrometry. In the presence of formic, acetic or propionic acids, photo-chemical generation results in the formation of HI, methyl- and ethyl-iodide respectively, the latter two products being directly identified by gas chromatography–mass spectrometry. Deuterium and ¹³C-labeled reagents were employed to elucidate the provenance of the alkyl group. Use of ¹³CH₃–COOH produced ¹³CH₃–I; deuterated acetic acid (D₃C-COOD) resulted in the formation of CD₃–I. These observations indicate direct transfer of the alkyl group from the carboxylic acid to iodide, consistent with the suggestion that the mechanism of synthesis involves radical induced reactions.     

Capillary gas chromatographic — Mass spectrometric determination of iprodione in chicory and leek

Summary A capillary GC/MS method is presented for the analysis of iprodione (CAS registry number 36734-19-7) in chicory and in leek. Preliminary extraction was carried out using methanol, and the extracts were cleaned up using two liquid-liquid extractions and Bakerbond SPE Florisil? cartridges. The eluates were evaporated to dryness under reduced pressure, and the residues dissolved in hexane. Iprodione was then monitored by capillary Gas Chromatography, with Mass Spectrometric Detection, in the selective ion mode at m/z 314. Recoveries of 89 % to 108 % were obtained for chicory and leek fortified at 100 and 500 μg kg⁻¹. The proposed method of analysis has a detection limit of 2 μg kg⁻¹ for chicory and 4 μg kg⁻¹ for leek.     

Application of LC and GC hyphenated with mass spectrometry as tool for characterization of unknown derivatives of isoflavonoids

Polyphenols belonging to the class of secondary metabolites of plants and microorganisms play an important role as bioactive food constituents as well as contaminants. Structure elucidation of polyphenols in plant extracts or polyphenol metabolites, especially those arising during biotransformation, still represents a challenge for analytical chemistry. Various approaches have been proposed to utilize fragmentation reactions in connection with mass spectrometry (MS) for structural considerations on polyphenolic targets. We compiled and applied specific liquid chromatography (LC)–electrospray ionization in positive mode [ESI(+)]–tandem MS (MS/MS) and gas chromatography (GC)–(electron impact, EI)–MS/MS fragmentation reactions with a special focus on the analysis of isoflavones, whereby this technique was also found to be extendable to determine further polyphenols. For ESI(+)-MS the basic retro-Diels–Alder (rDA) fragmentation offers information about the substitution pattern in the A- and B-rings of flavonoids and the elimination of a protonated 4-methylenecyclohexa-2,5-dienone (m/z = 107) fragment can be used as a diagnostic tool for many isoflavanones. For GC-(EI)-MS/MS analysis after derivatization of the analytes to their trimethylsilyl ethers, the elimination of methyl radicals, tetramethylsilane groups or the combined loss of two methyl groups can be shown to be specific for certain substitution patterns in polyphenols. The applicability of the fragmentation reactions presented is demonstrated exemplarily for three derivatives of the isoflavone irilone. With the help of these fragmentation reactions of the two MS techniques combined, a reliable identification of polyphenols is possible. Especially in such cases where NMR cannot be utilized owing to low analyte amounts being available or prior to purification, valuable information can be obtained. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Ronald Maul and Nils Helge Schebb contributed equally to this work.     

Solid-phase microextraction coupled with gas chromatography and gas chromatography—Mass spectrometry for public health pesticides analysis

Summary Public health pesticides in two-component mixed solutions were analyzed using solid-phase microextraction (SPME) coupled with gas chromatography (GC) and gas chromatography—mass spectrometry (GC-MS). The two-component mixed solutions used were allethrin mixed with cyfluthrin, cypermethrin mixed with tetramethrin, and transfluthrin mixed with cyfluthrin. Quantitative SPME-GC and SPME-GC-MS analyses using calibration and standard addition methods were evaluated. Using SPME pretreatment saved several tens to hundreds of mL of organic solvent. Quantitative analyses of the SPME-GC and SPME-GC-MS using the calibration and standard addition methods showed promise for simple, fast, and solventless public health pesticide analysis.     

Enhanced extraction of polychlorinated organic compounds from soil samples by fluidized-bed extraction (FBE)

Summary The extraction and determination of polychlorinated organic compounds, like hexachlorobenzene, pentachlorobenzene, octachlorostyrene and polychlorinated biphenyls in soils and solid wastes continues to be a subject for study. In this work Soxhlet extraction and a new extraction technique, fluidized-bed extraction, have been compared. The extraction of polychlorinated organic compounds by this technique has been optimized using experiemental design procedures. The variation of the number of extraction cycles, composition of extraction solvent (mixtures ofn-hexane-acetone) and the holding time after reaching the heating temperature were considering as experimental variables to generate a surface response design. Gas chromatography with mass spectrometric detection was used to determine levels of the analytes in the extracts. Extraction and analysis of a certified reference material (BCR CRM 392) showed the applicability of the method.     

Analysis of volatile compounds of rosemary honey. Comparison of different extraction techniques

Summary The analysis of the volatile fraction from honey requires the sugar matrix to be separated prior to the analysis by GC-MS. In this study, three extraction techniques, simultaneous extraction-distillation, liquid-liquid extraction and solid-phase extraction, were compared to the extraction of the volatile compounds of a rosemary honey. Analysis of these fractions by gas chromatography—mass spectrometry enabled the tentative identification of up to 122 volatile compounds (alcohols, ketones, aldehydes, acids, esters, terpenes, hydrocarbons, phenol, furan and pyran compounds). SDE extracts were rich in terpenes and esters, while the other two techniques avoided the formation of artefacts due to heating the sample.     

Continuous solid-phase extraction and gas chromatography–mass spectrometry determination of pharmaceuticals and hormones in water samples

A semi-automatic flow-based method for the simultaneous determination of 9 pharmaceuticals and 3 hormones in water samples in a single analytical run is proposed. The analytes were retained on a solid-phase extraction sorbent column and 1 μL of the eluate analysed by gas chromatography in combination with electron impact ionization mass spectrometry in the SIM mode. The sorbent used, Oasis-HLB, provided near-quantitative recovery of all analytes. The proposed method was validated with quite good analytical results including low limits of detection (0.01–0.06 ng L⁻¹ for 100 mL of water) and good linearity (r² > 0.993) throughout the studied concentration ranges. The method provided good accuracy (recoveries of 85–103%) and precision (between- and within-day RSD values less than 7%) in the determination of the pharmaceuticals and hormones in tap, river, pond, well, swimming pool and wastewater.     

Extraction of wood compounds by use of subcritical fluids

Summary A study of the extraction of oak wood compounds with subcritical water-ethanol mixtures as extractants, with an ethanol content between 0 and 60%, is reported. Identification and characterization of the extracted compounds were achieved by spectrophotometry and by gas chromatography with either flame ionization or mass spectrometric detection. Extraction was performed statically by use of a single cycle or repeated cycles. All variables affecting the extraction process were studied and optimized. Extraction time and temperature were 60 min and 200°C, respectively. Comparison of the extract thus obtained with commercial extracts showed the former to be rich in compounds characteristic of the commercial extracts. The method also enables manipulation of extract composition by changing the temperature and the water/ethanol ratio used. It is faster than traditional procedures for obtaining wood extracts.     

Gas chromatographic/mass spectrometric determination of mono- and dioctyltinchloride in aqueous solutions and biological samples

Summary A gas chromatographic/mass spectrometric method is described for the determination of mono- and dioctyltinchloride (MOTC and DOTC). Quantitative extraction from aqueous solutions was obtained with diethyl ether at pH=2. Several derivatization methods were tested. Grignard butylation in closed systems was most efficient. In the selected ion monitoring mode, the detection limits were 5 ng/ml for MOTC and 50 ng/ml for DOTC with a mean coefficient of variation of approximately 15%. Calibrations from different matrices were performed, e.g. from water, hepatocyte suspensions, urine and feces. The water solubility of DOTC was determined as 0.7 mg/l.     

Candidate reference method: Determination of valproic acid in serum by isotope-dilution mass spectrometry

Summary A method has been developed for the determination of valproic acid, without derivatization, in human serum by isotope-dilution mass spectrometry using labelled 2-propyl[3,3,3-d₃] valeric[5,5,5-d₃] acid as internal standard for accurate quantification of the concentration of valproic acid in the sample. After acidification, the analyte and internal standard are extracted withn-hexane. The amounts of valproic acid in the serum are calculated from the isotope ratio of valproic acid to labelled valproic acid, which is measured by electron impact (EI) and chemical ionization (CI) selected ion monitoring (SIM). The concentrations of valproic acid in sera measured using isotope-dilution mass spectrometry are compared with results from gas-liquid chromatography (GLC) and fluorescence polarization immunoassay (FPIA). The accuracy, precision and recovery of the GC-MS methods are discussed. The coefficient of variation determined from duplicate samples was less than 1.5%. The detection limit was 10 ng mL⁻¹ at a signal-to-noise ratio of 3:1. Part of this work was presented at the Kongre? der Deutschen Gesellschaft für Laboratoriumsmedizin, Berlin, 1994.     

Determination of metoprolol enantiomers in human urine by GC-MS using (−)-α-methoxy-α-(trifluoromethyl)phenylacetyl chloride as a chiral derivatizing agent

Summary A method for the assay of R-(+)- and S-(−)- metoprolol in human urine has been developed using gas chromatography-mass spectrometry. The method involved purification by liquid-liquid extraction and derivatization with N-methyl-N-(trimethylsilyl)trifluoroacetamide to form an O-silyl ether, followed by subsequent chiral derivatization with (−)-α-methoxy-α-(trifluoromethyl)phenylacetyl chloride to form diastereomeric amide. The reaction was rapid and the diastereomeric derivatives were well resolved. Quantitation was performed by selected-ion monitoring of fragment ions of the diastereomers in electron impact ionization mode. No racemization was found during the reaction. The detection limit was 0.5 ng·mL⁻¹. The intra-day variation ranged between 0.38 and 7.86% in relation to the measured concentration and inter-day variation was 2.26–8.06%. The method has been applied to the determination of R-(+)-and S-(−)- metoprolol in human urine from healthy volunteers dosed with racemic metoprolol tartrate.     

An evaluation of microwave-assisted derivatization procedures using hyphenated mass spectrometric techniques

The potential of microwave-assisted derivatization techniques in systematic toxicological analysis using gas chromatography coupled with mass spectrometry (GC–MS) was evaluated. Special emphasis was placed on the use of dedicated microwave reactors incorporating online temperature and pressure control. The use of such equipment allowed a detailed analysis of several microwave-assisted derivatization protocols comparing the efficiency of microwave and conventional heating methods utilizing a combination of GC–MS and liquid chromatography coupled with mass detection (LC–MS and LC–MS/MS) techniques. These studies revealed that for standard derivatization protocols such as acetylation (exemplified for codeine and morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) a reaction time of 5 min at 100 °C in a microwave reactor was sufficient to allow for an effective derivatization. Control experiments using standard operating procedures (30 min at 60 °C conventional heating) indicated that the faster derivatization under microwave irradiation is a consequence of the higher reaction temperatures that can rapidly be attained in a sealed vessel and the more efficient heat transfer to the reaction mixture applying direct in core microwave dielectric heating. The results suggest that microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

Analysis of deprenyl metabolites in some body compartments of rats using GC-MSD

Summary Deprenyl metabolites were analyzed in various organs of rats after chronic oral treatment. The investigation was carried out by gas chromatography combined with MSD after derivatization of the metabolites. When (−)-deprenyl (selegiline) was administered to rats higher ratios of methamphetamine to amphetamine were found in the kidney, and the heart at 1 and 5 h after treatment, than after (+)-deprenyl administration. Both deprenyl and its demethylated metabolite were also detected; however, their level was generally lower than that of either methamphetamine or amphetamine. Coadministration of verapamil with selegiline did not essentially alter the major metabolic pathway of deprenyl metabolism.     

Headspace solid phase microextraction in the determination of pesticides in water samples from the Okavango Delta with gas chromatography-electron capture detection and time-of-flight mass spectrometry

Headspace solid phase microextraction (HS-SPME) was optimized for the analysis of pesticides with gas chromatography electron capture detection (GC-ECD) and high-resolution mass spectrometry. Factors influencing the extraction efficiency such as fiber type, extraction mode and temperature, effect of ionic strength, stirring and extraction time were evaluated. The lowest pesticide concentrations that could be detected in spiked aliquots after HS-SPME–GC-ECD ranged from 0.0005 to 0.0032 μg L^{− 1}. Consequently hexachlorobenzene, trans-chlordane, 4,4′-DDD and 4,4′-DDE were detected in water samples after HS-SPME at concentrations ranging from 2.4 to 61.4 μg L^{− 1} that are much higher than the 0.1 μg L^{− 1} maximum limit of individual organochlorine pesticides in drinking water set by the European Community Directive. The same samples were cleaned with ISOLUTE C₁₈ SPE sorbent with an optimal acetone/n-hexane (1:1 v/v) mixture for the elution of analytes. No pesticides were detected after SPE clean-up and pre-concentration. Precision for both methods was satisfactory with relative standard deviations less than 20%. This work demonstrated the superiority of HS-SPME as a sample clean-up and pre-concentration technique for pesticides in water samples as well as the need to identify and control point sources of pesticides.     

Determination of 2-isopropyl thioxanthone and 2-ethylhexyl-4-dimethylaminobenzoate in milk: comparison of gas and liquid chromatography with mass spectrometry

Liquid chromatography–tandem mass spectrometry (LC-MS/MS) and gas chromatography–mass spectrometry (GC-MS) have been compared for the analysis of 2-isopropyl thioxanthone (ITX) and 2-ethylhexyl-4-dimethylaminobenzoate (EHDAB). Pressurized liquid extraction (PLE) was applied for the extraction of ITX and EHDAB from milk and milk-based beverages. Samples were homogenized with sea sand and anhydrous sodium sulfate, and were extracted with ethyl acetate at 100 °C and 10.3 × 10⁶ Pa in one cycle of 10 min at 90% flush. Both, GC-MS and LC-MS/MS were suitable to determine these photoinitiators in the PLE extracts, providing appropriate identification and quantification. The recoveries obtained ranged from 70 to 99% for ITX and from 70 to 95% for EHDAB. These recoveries were equal as those obtained by a conventional liquid–liquid partitioning with acetonitrile and tert-butyl methyl ether–hexane. The quantification limits using GC-MS, based on a signal-to-noise ratio of 10, were 0.5 μg/L for ITX and 1 μg/L for EHDAB. The repeatability of the method, as indicated by the relative standard deviations, was within the range 0.9–16.1%. The same parameters calculated using LC-MS/MS result in quantification limits of 0.1 μg/L for ITX and 0.02 μg/L for EHDAB and repeatability within the range 5.2–19.4%. These results pointed out that both techniques are appropriate to determine these compounds in food samples. The method was applied to milk and milk-based beverages from different supermarkets. The ITX and EHDAB contents ranged from 2.5 to 325 μg/L and from 8 to 126 μg/L, respectively. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A simple approach to on-line oxidative pyrolysis-capillary gas chromatography—Mass spectrometry

Summary A simple and robust approach to on-line oxidative pyrolysis-capillary gas chromatographymass spectrometry (OxPYR-CGC-MS) analysis is presented. Only minor adaptations on a conventional filament pyrolysis unit are required. Air is introduced into the pyrolyzer through a bypass-valve during pyrolysis and the degradation products are focused in a cryo-cooled programmed temperature vaporization (PTV) injector. Before GC analysis, the system is switched back to helium and after equilibration PTV injection is carried out. The potential of the system is illustrated with normal and oxidative pyrolyses of polystyrene (PS) and polyethylene (PE).