Femtogram detection of perfluorocarbon tracers using capillary gas chromatography-electron-capture negative ion chemical ionisation mass spectrometry

An ultrasensitive and selective method has been developed for the detection of a range of perfluorocarbon tracers suitable for long-range atmospheric studies. Following direct injection onto a capillary column the perfluorocarbons are separated and detected using mass spectrometry with electron-capture negative ion chemical ionisation (ECNICI-MS) with methane as reagent gas and selected-ion monitoring. All nine perfluorocarbons tested underwent non-dissociative resonance electron capture to form the molecular anion which was the base peak in all cases. Using this technique, detection limits (signal-to-noise ratio of 2:1) of 3 and 2 fg were obtained for perfluoromethylcyclohexane and perfluoro-1,3-dimethylcyclohexane respectively. The corresponding detection limits using a conventional electron-capture detector were 8 and 9 fg respectively. In addition to increased sensitivity, the ECNICI-MS technique allows temperature programming for the simultaneous analysis of a range of perfluorocarbons and has superior selectivity being less prone to coeluting interferences. Furthermore the method is potentially one to two orders of magnitude more sensitive than the current gas chromatography-MS methods using 13C2H4 tracers.     

Detection of trace levels of triclopyr using capillary gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry

Triclopyr, after esterification, is shown to be a suitable candidate for detection by gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry forming a characteristic carboxylate anion which offers a high detection sensitivity. A detection limit of 70 fg reaching the ionizer is indicated. Low backgrounds and an absence of chemical interferences are shown for vegetation extracts, using a simple method of extraction and derivatisation. A similar behaviour is demonstrated for 2,4-D and 2,4,5-T.     

Detection of trace levels of thiodiglycol in blood, plasma and urine using gas chromatography-electron-capture negative-ion chemical ionisation mass spectrometry

A sensitive method has been developed for the detection and quantitative determination of thiodiglycol in blood, plasma and urine. Samples were extracted from Clin Elut columns and cleaned up on C18 Sep-Pak cartridges (blood, plasma) or Florisil Sep-Pak cartridges (urine). Tetradeuterothiodiglycol was added to the sample prior to extraction as internal standard. Thiodiglycol was converted to its bis-(pentafluorobenzoate) derivative and analysed by capillary gas chromatography-electron-capture negative-ion chemical ionisation mass spectrometry using selected ion monitoring. Levels of thiodiglycol down to 1 ng/ml (1 ppb) could be detected in 1-ml spiked blood and urine samples; calibration curves were linear over the range 5- or 10-100 ng/ml. Blood and urine samples from a number of control subjects were analysed for background levels of thiodiglycol. Concentrations up to 16 ng/ml were found in blood, but urine levels were below 1 ng/ml.     

Quantitative analysis of estrogens in human urine using gas chromatography/negative chemical ionisation mass spectrometry

A sensitive procedure for the determination of estrogens in urine has been developed, using enzymatic hydrolysis and ether extraction followed by capillary gas chromatography with negative chemical ionisation mass spectrometry (GC/NCI-MS) of the pentafluorobenzoyl derivatives. These derivatives were superior for GC/NCI-MS to trifluoroacetyl, heptafluorobutyl, pentadecafluorooctanoyl and perfluorotolyl derivatives, giving characteristic negative molecular ions as the base peak for each of the naturally occurring estrogens estrone, estradiol and estriol, and for the synthetic estrogen ethynylestradiol used in contraceptive pills. The method was also suitable for determination of some metabolites of estrone and estradiol. The specificity and sensitivity of the GC/NCI-MS method simplifies sample preparation. Recovery of spiked samples was in the range 84-101% for the natural estrogens based on additions to increase the concentration by 5 and 1 microg L(-1). The repeatability of the method was 1-8% for all estrogens.     

Determination of trace levels of pyrethroid metabolites in human urine by capillary gas chromatography-high resolution mass spectrometry with negative chemical ionization

Summary Applications of high-resolution gas chromatography and high-resolution mass spectrometry (GC-MS) for identification and quantitation of trace amounts of pyrethroid metabolites in human urine samples are demonstrated. The method covers the pyrethroid metabolitescis- andtrans-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropane carboxylic acid (cis- andtrans-DCCA),cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis-DBCA), 4-fluoro-3-phenoxybenzoic acid (FPBA), and 3-phenoxybenzoic acid (3-PBA). After acid-induced hydrolysis of urine samples and exhaustive solvent extraction, a carbodiimide-coupled esterification of the free carboxylic acids with hexafluoroisopropanol (HFIP) is applied. Identification of the derivatives formed is achieved by low-resolution electron-impact mass spectrometry (EIMS) using an ion-trap detector. Quantitation was by capillary gas chromatography—high-resolution mass spectrometry using negative chemical ionization (GC-NCIMS). 2-Phenoxybenzoic acid (2-PBA) served as internal standard. The limits of detection forcis- andtrans-DCCA,cis-DBCA, FPBA and 3-PBA were 0.03 μg L⁻¹ or below. The applicability of the presented method was tested on urine samples of persons exposed to low levels of pyrethroids.     

Determination of benzidine in urine using capillary gas chromatography and negative-ion chemical ionisation mass spectrometry

Summary A highly sensitive and specific gas chromatographic-mass spectrometric (GC-MS) assay for the determination of benzidine in urine is reported. It is based on the solvent extraction of the hydrolysed benzidine conjugates, together with the deuterium-labelled benzidine-d₈ added as an internal standard, and a two-phase derivatisation procedure using pentafluoropropionic anhydride (PFPA) in the presence of pyridine as the phase-transfer catalyst. The reaction is complete within 5 min at room temperature. The pentafluoropropyl derivatives are quantified through capillary column GC-MS using selected ion monitoring (SIM) in the negative-ion chemical ionisation mode (NICI). The lower limit of detection for benzidine was 0.5 g/l and the calibration plot showed linearity between 2 g/l and 200 g/l. The recovery of the analyte added to pooled urine was above 82%. Analysis of 20 urine samples from un-exposed persons and 20 urine specimens of workers employed in a polyurethane-making plant using this procedure showed no substances likely to manifest false positive results in the range of interest.     

Enantioselective trace analysis of amphetamine in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry

A method for the quantitative enantioselective analysis of amphetamine in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry (GC/NICI-MS) is presented. Five-fold deuterated analogues of both enantiomers were used as internal standard. Plasma sample preparation was performed by a rapid liquid-liquid extraction using n-hexane. Derivatization with (S)-(-)-N-(heptafluorobutyryl)prolyl chloride was accomplished directly in the n-hexane extract to avoid loss of amphetamine during sample concentration. The method was validated in the expected concentration range of 0.006 for a pharmacokinetic study. Calibration curves were linear within a range 0.006-50 ng/mL plasma. Precision and accuracy were acceptable over the entire calibration range. Baseline separation of the enantiomers was easily achieved on a 15-m nonchiral apolar column. The method is simple and robust, and has been applied to the batch analysis of amphetamine enantiomers.     

Fast analysis of decabrominated diphenyl ether using low-pressure gas chromatography-electron-capture negative ionization mass spectrometry

This paper reports the applicability of low-pressure gas chromatography-mass spectrometry operated in electron-capture negative ionization mode (LP-GC-ECNI-MS) for the analysis of decabrominated diphenyl ether (BDE-209). Particular attention was paid to find optimal injector and oven conditions for minimal thermal degradation of BDE-209. The analytical characteristics were compared for LP-GC columns (10 m x 0.53 mm) with different film thicknesses (d(f) 0.15 microm versus 0.25microm) and for a conventional GC column (15 m x 0.25 mm, 0.10 microm d(f)). Short residence times (6.5 and 9.8 min) of BDE-209 were found for the LP-GC systems with 0.15 and 0.25microm d(f), respectively, resulting in a low elution temperature and minimal degradation. Additionally, baseline separation of 22 polybrominated diphenyl ether (PBDE) congeners (major components of PBDE technical mixtures) was possible in less than 12 min using the LP-GC-ECNI-MS system with 0.15microm d(f). The optimized method was applied for the determination of PBDEs in Belgian indoor dust samples. The obtained concentrations of BDE-209 (range 8-292 ng/g dry weight) were in the same range or lower than concentrations in dust from other European countries.     

Analysis of human blood plasma triacylglycerols using capillary gas chromatography, silver ion thin-layer chromatographic fractionation and desorption chemical ionization mass spectrometry.

The identification and quantitation from pooled human plasma of over 50 molecular species of triacylglycerols, including 22 not previously reported, are reported. The triacylglycerols were first resolved by silver ion thin-layer chromatography into seven fractions, which were independently analysed by polarizable capillary gas chromatography and desorption chemical ionization mass spectrometry in the presence of an internal standard. The two methods gave similar values for the estimates of oligoenoic species, but the former method underestimated the polyenes (due mainly to significant losses caused by thermal degradation), and the latter method overestimated the saturates. The results show that an effective analysis of molecular species of plasma triacylglycerols cannot be obtained by either technique alone.     

Determination of 4,4'-methylenebis(2-chloroaniline) in urine using capillary gas chromatography and negative ion chemical ionization mass spectrometry.

A highly sensitive and specific gas chromatographic-mass spectrometric (GC-MS) assay for the determination of 4,4'-methylenebis(2-chloroaniline) (MBOCA) in urine is reported. It is based on the solvent extraction of the hydrolysed MBOCA conjugates, together with deuterium-labelled benzidine-d8 added as an internal standard, and a two-phase derivatization procedure involving use of pentafluoropropionic anhydride in the presence of ammonia as the phase-transfer catalyst. The reaction is complete within 2 min at room temperature. The pentafluoropropyl derivatives are determined by use of capillary column GC-MS with selected-ion monitoring in the negative ion chemical ionization mode. The lower limit of detection for MBOCA was 1 microgram dm-3 and the calibration graph showed linearity between 10 and 250 micrograms dm-3. The recovery of the analyte added to pooled urine was above 86%. Thirty urine specimens from workers employed in a polyurethane-producing plant were analysed for MBOCA by this method.     

Measurement of equilin and estrone in human plasma by capillary gas chromatography-negative ion chemical ionization mass spectrometry

A procedure is described for the analysis of the estrogens equilin and estrone in human plasma following oral administration of conjugated estrogen preparations. After enzymatic hydrolysis of the sulfate conjugates, plasma proteins are precipitated with methanol and the estrogens extracted into ethyl acetate. Derivatization with the reagent flophemesylamine converts equilin and estrone into volatile pentafluorophenyldimethylsilyl ethers ideally suited to capillary gas chromatography-negative ion chemical ionization mass spectrometry. Using a 15 meter dimethyl silicone bonded phase fused silica capillary column separation of the estrone and equilin derivatives is achieved within 9 minutes. Selected ion monitoring of the intense negative molecular ions enables levels of 1 ng.ml^?1 to be measured with coefficients of variation of 9.3 % and 14.2 % for estrone and equilin respectively. Plasma levels of the compounds are reported in two male volunteers up to 24 hours after dosing with 5 milligrams of Premarin?. (? Ayerst Laboratories Inc., New York, USA.).     

Analysis of trichothecene mycotoxins in human blood by capillary column gas chromatography-ammonia chemical ionization mass spectrometry

Capillary column gas chromatography-ammonia chemical ionization mass spectrometry was found to be an excellent technique for the trace detection and identification of underivatized trichothecene mycotoxins. Abundant (M + H)+ and/or (M + NH4)+ pseudo-molecular ions were observed for T-2 toxin, HT-2 toxin, T-2 triol, diacetoxyscirpenol, deoxynivalenol and verrucarol under the conditions developed. This method was successfully applied to the analysis of human blood samples spiked with mycotoxins in the 0-500 ng/g range during a recent interlaboratory exercise. T-2 toxin and diacetoxyscirpenol were detected in these samples in the 2-180 ng/g range. Detection limits of 0.7 and 3.6 ng/g for T-2 toxin and diacetoxyscirpenol, respectively, were possible owing to the specificity of the method.     

Detection of phenolalkylamines by capillary column gas chromatography-negative chemical ionization mass spectrometry

Twelve phenolalkylamines normally used in different pharmaceutical products were determined in urine from volunteers given a therapeutical dose of the drug. The urine extracts were first derivatized with perfluoro propionic or butyric anhydride, then detected by capillary gas chromatography-negative chemical ionization mass spectrometry. The method is highly sensitive and specific in the analysis of biological samples.     

Structural elucidation of monoterpene oxidation products by ion trap fragmentation using on-line atmospheric pressure chemical ionisation mass spectrometry in the negative ion mode.

Based on ion trap mass spectrometry, an on-line method is described which provides valuable information on the molecular composition of structurally complex organic aerosols. The investigated aerosols were generated from the gas-phase ozonolysis of various C(10)H(16)-terpenes (alpha-pinene, beta-pinene, 3-carene, sabinene, limonene), and directly introduced into the ion source of the mass spectrometer. Negative ion chemical ionisation at atmospheric pressure (APCI(-)) enabled the detection of multifunctional carboxylic acid products by combining inherent sensitivity and molecular weight information. Sequential low-energy collision-induced product ion fragmentation experiments (MS(n)) were performed in order to elucidate characteristic decomposition pathways of the compounds. Dicarboxylic acids, oxocarboxylic acids and hydroxyketocarboxylic acid products could be clearly distinguished by multistage on-line MS. Furthermore, sabinonic acid and two C(9)-ether compounds were tentatively identified for the first time by applying on-line APCI(-)-MS(n).     

Quantitative gas chromatographic/mass spectrometric analysis of morphine glucuronides in human plasma by negative ion chemical ionization mass spectrometry

A sensitive and specific method for the determination of morphine glucuronides in human plasma is presented. Morphine glucuronides, namely morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G), were extracted from plasma by solid-phase extraction on C(18) cartridges at pH 9.3 and derivatized to their pentafluorobenzyl ester trimethylsilyl ether derivatives. The compounds were measured by gas chromatography/negative ion chemical ionization mass spectrometry without any further purification. Using this detection mode, a diagnostic useful fragment ion at m/z 748 was obtained at high relative abundance for both target compounds. [(2)H(3)]-labeled morphine glucuronides were used as internal standards. Calibration graphs were calculated by polynomial fit within a range of 10-1280 and 15-1920 nmol l(-1) for the 6- and 3-glucuronide, respectively. At the limit of quantitation (LOQ), the inter-assay precision was 2.21% (M3G) and 2.23% (M6G) and the GC/MS assay variability was 1.8% (M3G) and 0.9% (M6G). The accuracy at the LOQ showed deviations of +4.92% (M3G) and +1.5% (M6G). The sample recovery after solid-phase extraction was 84.7% for both M3G and M6G. The method is rugged, rapid and robust and has been applied to the batch analysis of morphine glucuronides during pharmacokinetic profiling of the drugs.     

Quantitative analysis of memantine in human plasma by gas chromatography/negative ion chemical ionization/mass spectrometry

A sensitive and specific method for the determination of memantine in human plasma is presented. Memantine was extracted from plasma and derivatized to the pentafluorobenzoyl derivative in a one-step procedure avoiding any sample concentration steps. Amantadine was used as an internal standard. The compounds were measured by gas chromatography/negative ion chemical ionization mass spectrometry without any further processing. Using this detection mode, the fragment ions at m/z 353 and 325 were obtained at high relative abundance. Calibration graphs were linear over the range 0.117-30 ng ml(-1). At the limit of quantification (LOQ), the inter-assay precision was 2.00% and the intra-assay variability was 3.22%. The accuracy at the LOQ showed deviations of -1.42% (intra-assay) and -2.47% (inter-assay). The method is rugged, rapid and robust and was applied to the batch determination of memantine during pharmacokinetic profiling of the drug.     

Application of positive ion chemical ionisation and tandem mass spectrometry combined with gas chromatography to the trace level analysis of ethyl carbamate in bread

A rapid, sensitive and selective method has been developed and validated for the analysis of the contaminant ethyl carbamate (EC) in bread products at the part-per-billion level. The new procedure uses positive ion chemical ionisation (PICI) and tandem mass spectrometry (MS/MS), combined with gas chromatography (GC), on a 'bench-top' triple-quadrupole mass spectrometer. Ammonia was the PICI reagent gas of choice because of its ability to produce abundant [M+H]+ and [M+NH4]+ ions from EC and deuterium-labelled EC (LEC) used as an internal standard. For identification and quantification, selected reaction monitoring (SRM) was used to follow the precursor-to-product ion transitions of m/z 107 --> 90, m/z 107 --> 62 and m/z 90 --> 62 for EC, as well as m/z 112 --> 63 for the LEC internal standard. The limits of detection and quantification were 0.6 and 1.2 microg kg(-1), respectively, and the recovery of the method was 101 +/- 10% at 10 microg kg(-1) and 98 +/- 5% at 100 microg kg(-1). The precision of the method, established under conditions of intermediate reproducibility, did not exceed a relative standard deviation of 7%. The quantitative performance of the new GC/PICI-SRM procedure compared favourably with that of a reference method based on GC/MS and selected ion monitoring (correlation coefficient, r = 0.997). However, the new method had the advantages of reduced sample preparation time, improved sensitivity and unambiguous identification of EC at all concentrations. Application of the new method to the analysis of 50 UK breads showed that levels of EC ranged from 0.6 to 2.3 microg kg(-1) in retail products and from 3.1 to 12.2 microg kg(-1) for breads prepared using domestic breadmaking machines (dry weight basis). Toasting bread in a domestic toaster led to increases of between two- and three-fold in mean EC concentrations.     

Determination of trace levels of benzodiazepine in urine using capillary electrochromatography-time of flight mass spectrometry

This paper details a method for the separation and determination of ten benzodiazepines in urine using CEC-MS(TOF) and an hexyl acrylate-based porous monolith. The TOF mass spectrometer provides an exact mass of protonated benzodiazepines to three decimal places (1-6 ppm). This high selectivity along with the CEC separation, provides an effective method for the identification of benzodiazepines. Linearity is satisfactory for all compounds in the concentration range of 25-500 ng/mL for lorazepam and 12.5-500 ng/mL for the others. The RSDs are between 1.4-2.3% for retention times and 1.1-9.2% for relative areas. Using the monolithic stationary phase, a preconcentration step is achievable and permits an 75-140-fold improvement in sensitivity. This strategy permits the quantification of these drugs down to 1 ng/mL in urine. This method was used for the analysis of benzodiazepines in spiked urine samples.     

Detection of β-blocking drugs in urine by capillary column gas chromatography-negative ion chemical ionization mass spectrometry

β-Blocking drugs present in commercial pharmaceutical products are determined in present urine of volunteers between 4 and 24 hours after the administration of a therapeutical dose. The drugs are extracted, hydrolysed, derivatized with pentafluoropropionic anhydride, and analyzed by capillary gas chromatography and electron capture detection. Metabolite identification and drug confirmation is by capillary gas chromatography–negative ion chemical ionization mass spectrometry (GC-NICIMS). This method is very specific and a sensitivity below 1 ng/ml is obtained.