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.     

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.     

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 trichothecenes in human blood using capillary gas chromatography-electron-capture negative ion chemical ionisation mass spectrometry

A sensitive and selective method has been developed for the simultaneous detection in blood of eleven trichothecenes of widely varying polarity. The procedure involved precipitation of blood proteins with acetone followed by a clean-up using reversed-phase Sep-Pak C18 cartridges. The extracted trichothecenes were derivatised as their pentafluoropropionyl esters, separated using capillary gas chromatography and detected using electron-capture negative ion chemical ionisation with methane reagent gas and selected-ion monitoring. Optimum sensitivity and selectivity were obtained using low source temperatures (60 degrees C indicated) and high source pressures (1 Torr indicated). Detection limits on 1-ml blood samples were in the range 0.1-5 ppb. The method was readily adaptable to the detection of other trichothecenes. A protocol was used which minimised the risk of cross-contamination. The method was validated in collaborative studies by the successful analysis of 42 blood samples spiked and submitted blind by two independent laboratories for analysis.     

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.     

超高效液相色谱-串联质谱法检验腐败血中吗啡和6-单乙酰吗啡

采用改良的QuEChERS前处理方法，建立了同时检验腐败血中吗啡和6-单乙酰吗啡的超高效液相色谱-串联质谱（UPLC-MS/MS）方法。腐败血中加入乙腈-水（4：1，v/v）混合溶液、30 mg NaCl和60 mg MgSO₄盐析促进相分离，最后经25 mg N-丙基乙二胺（PSA）和25 mg MgSO₄净化。选用ZORBAX Eclipse Plus C₁₈色谱柱分离，0.01%（v/v）氨水和乙腈作为流动相进行梯度洗脱，电喷雾电离正离子（ESI⁺）模式扫描，多反应监测（MRM）模式检测。结果表明，吗啡和6-单乙酰吗啡在5~200 μg/L范围内线性关系良好，相关系数（r²）≥ 0.9957，检出限（S/N=3）均为1 μg/L，定量限（S/N=10）均为5 μg/L。3个加标水平（5、100和200 μg/L）下，吗啡和6-单乙酰吗啡的平均加标回收率分别为81.84%~103.44%和81.03%~104.46%，日内和日间精密度（RSD）均小于12%，基质效应为83.04%~107.61%。方法简便、灵敏、可靠，可实现腐败血中吗啡和6-单乙酰吗啡的快速定性定量检验。     

Identification of hydroxymethylpyrazines using mass spectrometry

Pyrazines are well‐known natural products that are present in bacterial odours and food flavouring agents and are used as insect pheromones. Recently, a number of hydroxymethylpyrazines have been identified as thynnine wasp pheromones and orchid semiochemicals that are essential for pollination in sexually deceptive plants. These compounds are present in low amounts in complex blends, making GC–MS (including high‐resolution techniques) the method of choice for their structure elucidation. We report the EI mass spectra for 14 representative compounds and have found that based on characteristic fragmentations, it is possible to distinguish between different positional isomers of hydroxymethylpyrazines. The presence or absence of either [M ? 17]⁺, [M ? 18]^+· or [M ? 19]⁺ fragment species provides characteristic information to allow the distinction between the different isomers. Considering the importance of pyrazines as a group of bioactive natural products, and the recent findings of biological activity for hydroxymethylpyrazines, our results presented here will aid the identification of these compounds in other biological systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of plant sterols in hexaploid and tetraploid wheats using gas chromatography with mass spectrometry

Free sterols from hexaploid and tetraploid free-threshing wheats (Triticum aestivum L. and T. durum Desf.) and from their respective hulled wheats (T. spelta L. and T. dicoccon Schrank) were analysed by gas chromatography with mass spectrometry. The qualitative analysis of sterols showed a similar pattern either between hexaploid (T. aestivum, T. spelta) and tetraploid (T. durum, T. dicoccon) wheats or between free-threshing (T. aestivum, T. durum) and hulled (T. spelta, T. dicoccon) wheats. However, quantitative differences were found between tetraploid and hexaploid wheats, in that free sterol amounts in tetraploid wheats were 40% higher than in hexaploid ones. The mass spectra of the sterols were classified into four groups, taking into account the structural features of rings A and B. Typical mass spectral fragmentations of the four classes, and additional evidence related to the side chain of each molecule, were investigated together with their chromatographic behaviour, allowing identification of all the detected sterols.     

Enhanced mass resolution tandem mass spectrometry method for 2,3,7,8-tetrachlorodibenzo-p-dioxin detection with ion trap mass spectrometry using high damping gas pressure

Damping gas flow was optimized for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) determination using ion trap mass spectrometer. A tandem mass spectrometry (MS-MS) method with better than unit-mass resolution (mass width, 0.3 u) was developed at a damping gas flow of 1.5 ml/min and a collision-induced dissociation (CID) voltage of 3.30 V. The relative standard deviation (R.S.D.) at the enhanced resolution was 2.9% in 24 h of consecutive injections. The detection limit was significantly improved because the efficiency of both precursor ion trapping and fragmentation increased with the damping gas flow. Product ion yield was 4.5 times higher and limit of detection was 3.2 times lower than at the default flow (0.3 ml/min and 1.65 V).     

Identification and differentiation of dragon's blood in works of art using gas chromatography/mass spectrometry

Dragon's blood is a common but non-specific name for red-coloured resins that are produced by various plants, particularly exudations from plant species belonging to the genera Dracaena and Daemonorops. Although dragon's blood is mentioned in historic sources as a colourant, it has hardly ever been identified in real artworks. This paper reports the identification and discrimination of dragon's blood produced by Dracaena cinnabari, Dracaena draco as well as Daemonorops draco and Daemonorops micracantha by means of gas chromatography/mass spectrometry (GC/MS) within the context of a routine analysis of binding media used in works of art. The detection of specific flavonoid marker compounds in both underivatised and methylated methanol extracts provided the first evidence for the use of dragon's blood from all four species in various works of art from the fifteenth to nineteenth centuries. Dragon's blood was mainly used as a red colourant in gold lacquers as well as translucent glazes and paints, e.g. in reverse-glass paintings (Hinterglasmalerei).     

Determination of chlorophenols in water samples using simultaneous dispersive liquid-liquid microextraction and derivatization followed by gas chromatography-electron-capture detection

Simultaneous dispersive liquid-liquid microextraction (DLLME) and derivatization combined with gas chromatography-electron-capture detection (GC-ECD) was used to determine chlorophenols (CPs) in water sample. In this derivatization/extraction method, 500 microL acetone (disperser solvent) containing 10.0 microL chlorobenzene (extraction solvent) and 50 microL acetic anhydride (derivatization reagent) was rapidly injected by syringe in 5.00 mL aqueous sample containing CPs (analytes) and K(2)CO(3) (0.5%, w/v). Within a few seconds the analytes derivatized and extracted at the same time. After centrifugation, 0.50 microL of sedimented phase containing enriched analytes was determined by GC-ECD. Some effective parameters on derivatization and extraction, such as extraction and disperser solvent type and their volume, amount of derivatization reagent, derivatization and extraction time, salt addition and amount of K(2)CO(3) were studied and optimized. Under the optimum conditions, enrichment factors and recoveries are in the range of 287-906 and 28.7-90.6%, respectively. The calibration graphs are linear in the range of 0.02-400 microg L(-1) and limit of detections (LODs) are in the range of 0.010-2.0 microg L(-1). The relative standard deviations (RSDs, for 200 microg L(-1) of MCPs, 100 microg L(-1) of DCPs, 4.00 microg L(-1) of TCPs, 2.00 microg L(-1) of TeCPs and PCP in water) with and without using internal standard are in the range of 0.6-4.7% (n=7) and 1.7-7.1% (n=7), respectively. The relative recoveries of well, tap and river water samples which have been spiked with different levels of CPs are 91.6-104.7, 80.8-117.9 and 83.3-101.3%, respectively. The obtained results show that simultaneous DLLME and derivatization combined with GC-ECD is a fast simple method for the determination of CPs in water samples.     

Identification of low molecular vaporizable components in silicone resins using gas chromatography/mass spectrometry

Silicone resins can be used as polymeric precursors in the production of ceramic materials. Cohydrolysis of mixtures of trimethylchlorosilane, methyldichlorosilane, vinylmethyldichlorosilane and phenyltrichlorosilane leads to the formation of especially suitable polysiloxanes, but also low-molar mass siloxanes are formed as undesired by-products. The structures of these by-products have been elucidated. Vaporizable components of the matrix have been isolated by distillation, separated using gas chromatography and identified by mass spectrometry in EI (electron impact ionization) and CI (chemical ionization with isobutane) mode. The EI mass spectra of the siloxane oligomers with different numbers of Si-H, Si-phenyl and Si-vinyl groups show characteristic fragments like Me₃Si⁺, ViMe₂Si⁺, Vi₂MeSi⁺, PhMe₂Si⁺, and Ph₂MeSi⁺, which give a first indication to the structure, but generally do not show molecular peaks. A reliable determination of the molar mass has been possible considering the CI-ions and CI-fragments [M+1]⁺, [M−1]⁺, [M−27]⁺ and [M−77]⁺, respectively. The compounds M₂D^Ph,OH and M₃T^Ph have been identified as main components of the investigated siloxane mixture. Besides, numerous linear compounds of the type M₂(D^H)n(D^Vi)_m and M₂T^Ph(D^H)_n(D^Vi)_m M as well as cyclic ones of the structure [MT^Ph(D^H)_n(D^Vi)_m] with n, m=0–3 have been indicated. Received: 3 March 1995/Revised: 25 March 1995/Accepted: 3 April 1995     

Identification of low molecular vaporizable components in silicone resins using gas chromatography/mass spectrometry

An experimental set-up for the detection of elemental chlorine in chlorinated hydrocarbons (CHCs) is described based on a miniaturized system, which could be used for on-line monitoring of chlorinated compounds. With an optimized time-resolved detection chlorine from CHCs like CCl₄ can be determined by Laser-Induced-Breakdown-Spectroscopy (LIBS) with g/g-detection limits in the gas phase. The application of a miniaturized Nd : YAG laser resulted only in a minor loss in performance, hence it could be used for designing a rugged and small on-line sensor. In addition, preliminary results for the detection of chlorine via the formation of CuCl in the plasma formed by focussing the laser on a copper surface are reported. Utilizing the luminescence of the CuCl D-system at 440 nm, a tenfold improvement in the detection limits was obtained. It appears that the formation of ad hoc selected, small molecules in a laser plasma could be a promising alternative for the selective and sensitive analysis of gaseous chlorinated and other species.     

Identification of iso- and n-propylphosphonates using liquid chromatography-tandem mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy

Organophosphorus nerve agents and their precursors, specifically listed in the schedules of chemicals in the Annex to the Chemical Weapons Convention (CWC), include analogues with C1-C3 alkyl groups on phosphorus. The Organisation for the Prohibition of Chemical Weapons (OPCW) requires designated laboratories to unequivocally identify isomeric propyl groups bonded to phosphorus in analytes that may be present in samples submitted for analysis. Homologous series of isomeric pairs of dialkyl iso- and n-propylphosphonates, alkyl iso- and n-propylphosphonochloridates, and alkyl iso- and n-propylphosphonofluoridates, have been analysed by liquid chromatography-ion trap tandem mass spectrometry and/or by gas chromatography-Fourier transform infrared spectroscopy. The results show that P-propyl isomers can be reliably differentiated by collision induced dissociation (CID) of selected fragment ions and by their infrared P=O stretching and C-H deformation frequencies.     

Trace analysis of trichlorobenzenes in fish by microwave-assisted extraction and gas chromatography-electron-capture detection

An analytical method consisting of extraction, clean-up, and analysis by gas chromatography-electron-capture detection (GC-ECD) was developed for the determination of trichlorobenzenes (TCBs) in fish samples. Two extraction methods, saponification and liquid-liquid extraction (S-LLE), and microwave-assisted extraction (MAE), were evaluated. In both cases, n-pentane was used as the extraction solvent. For S-LLE, the recoveries ranged from 66.6+/-9.1% for 1-bromo-4-chlorobenzene (4-BCB) to 93.5+/-4.9% for 1,2,4-trichlorobenzene (1,2,4-TCB). The recoveries were significantly lower, between 31.0+/-3.9% for 1,2,3-trichlorobenzene (1,2,3-TCB) and 52.3+/-3.0% for 1,3,5-trichlorobenzene (1,3,5-TCB), in the absence of fish. Proteins and glycerides of the fish tissue seemed to compete with TCBs for the base, and hence decreased their decomposition rate. In the case of MAE, the recoveries were highly dependent on the pressure applied during extraction. At 5 bar, much higher recoveries were obtained, from 66.7+/-15.6% for 4-BCB to 79.9+/-13.6% for 1,2,4-TCB, than at 1 bar. Sulfur formation was, however, observed at 5 bar, and interfered with the GC-ECD analysis of TCBs. Sulfur was adequately removed by copper powder treatment, which was shown not to affect the recovery of analytes. The recoveries of target analytes by S-LLE and MAE did not differ statistically (t-test, alpha = 0.01). Both methods were appropriate for the detection of TCBs at concentration levels typically observed in marine biota, i.e. approximately 1 ng/g. S-LLE was, however, more time consuming, and required larger volumes of high-purity organic solvents than MAE.     

Solid-phase extraction of fluoxetine and norfluoxetine from serum with gas chromatography-electron-capture detection

A rapid, selective, and sensitive method is described for the purification and analysis of fluoxetine and norfluoxetine using a solid-phase extraction column and gas chromatography-electron-capture detection. Linear quantitative response curves for fluoxetine and norfluoxetine are generated over a concentration range of 20-200 ng/ml. Overall extraction efficiency of the extraction procedure is found to be greater than 90% and greater than 75% with correlation coefficients of 0.997 and 0.993 for fluoxetine and norfluoxetine, respectively.     

Selective ultra-trace detection of NO and NO2 in complex gas mixtures using broad-bandwidth REMPI mass spectrometry

In this paper we demonstrate the feasibility of ultra-trace resonance enhanced multiphoton ionization (REMPI) detection employing a small broad-bandwidth solid state laser system. The results reported here are compared with measurements carried out with a conventional excimer pumped dye laser combination. Mass selected broad-bandwidth REMPI spectra for the environmentally relevant nitrogen oxides NO and NO2 are presented. Tunable broad-bandwidth laser radiation with a spectral resolution of > 10 cm(-1) in the wavelength range 560-400 nm was employed for the detection of NO2. For NO detection, the range 230-224 nm was covered. Laser radiation was generated using an optical parametric oscillator pumped by an unseeded Nd:YAG laser. A mobile time-of-flight mass spectrometer equipped with an atmospheric pressure laser ionization source allowed for mass selective parent ion detection at m/z 30 for NO and m/z 46 for NO2. The limit of detection was 10 pptV for NO and 20 pptV for NO2. A selectivity of > 2000 for both compounds with respect to N2O5, organic nitrates and NO2 in the case of NO is reported. An improved laser system currently under construction is expected to provide detection limits below pptv mixing ratios for both nitrogen oxides in a 20 s integration interval.     

Capillary gas chromatography and mass spectrometry detection of anabolic steroids II

High resolution gas chromatography-mass spectrometry has been used to detect anabolic steroids in urine. With fused silica capillary columns connected directly to mass spectrometer, the anabolic steroids could be detected after extraction, hydrolysis, and derivatization with a sensitivity better then 1 ppb. In vivo excretion and metabolism has been investigated for androstanolone, methandriol, oxymesterone, quindenione, and boldenone.