Chromatography Chemical Ionization Mass Spectrometry Research Articles

Structure determination of organic aging products in lithium-ion battery electrolytes with gas chromatography chemical ionization mass spectrometry (GC-CI-MS)

For Gas Chromatography Chemical Ionization Mass Spectrometry (GC-CI-MS) method development, a standard lithium-ion battery (LIB) electrolyte was thermally aged at 95 °C for a faster generation of decomposition products.

A method for the identification and quantitation of hydraulic fluid contamination of turbine engine oils by gas chromatography–chemical ionisation mass spectrometry

ABSTRACTThe identification of aircraft hydraulic fluid contamination of turbine engine oils is difficult. Repeated field incidents of this type of cross contamination have led to the requirement to develop a method suitable for quantitation of such contamination. A gas chromatography–chemical ionisation mass spectrometry method for the determination of H‐537 hydraulic fluid contamination in turbine engine oil was developed and validated. The intraday and interday relative standard deviations of the standards were 3–7% and 5–9%, respectively. Mean recoveries of hydraulic fluid in turbine engine oil were 90–94%, and the calibration curve was linear with R2 = 0.999. Limits of detection and quantitation were 0.05% (w/w) and 0.5% (w/w), respectively. The method was successfully applied to laboratory degraded samples and field samples. Copyright © 2012 John Wiley & Sons, Ltd.

Dispersive micro-solid phase extraction combined with gas chromatography–chemical ionization mass spectrometry for the determination of N-nitrosamines in swimming pool water samples

A simple sample pretreatment technique, dispersive micro-solid phase extraction, was applied for the extraction of N-nitrosodimethylamine (NDMA) and other four N-nitrosamines (NAs) from samples of swimming pool water. The parameters affecting the extraction efficiency were systematically investigated. The best extraction conditions involved immersing 75 mg of carbon molecular sieve, Carboxen™ 1003 (as an adsorbent), in a 50-mL water sample (pH 7.0) containing 5% sodium chloride in a sample tube. After 20 min of extraction by vigorous shaking, the adsorbent was collected on a filter and the NAs desorbed by treatment with 150 μL of dichloromethane. A 10-μL aliquot was then directly determined by large-volume injection gas chromatography with chemical ionization mass spectrometry using the selected ion storage mode. The limits of quantitation were <0.9 ng/L. The precision for these analytes, as indicated by relative standard deviations, were <8% for both intra- and inter-day analyses. Accuracy, expressed as the mean extraction recovery, was between 62% and 109%. A preliminary analysis of swimming pool water samples revealed that NDMA was present in the highest concentration, in the range from n.d. to 100 ng/L.

An advanced method for the determination of carboxyl methyl esterase activity using gas chromatography–chemical ionization–mass spectrometry

We developed a quantitative method for the determination of methyl esterase activity, analyzing substrate specificity against three major signal molecules, jasmonic acid methyl ester (MeJA), salicylic acid methyl ester (MeSA), and indole-3-acetic acid methyl ester (MeIAA). We used a silylation reagent for chemical derivatization and used gas chromatography (GC)–mass spectroscopy in analyses, for high precision. To test this method, an Arabidopsis esterase gene, AtME8, was expressed in Escherichia coli, and then the kinetic parameters of the recombinant enzyme were determined for three substrates. Finally, this method was also applied to the direct quantification of phytohormones in petals from lilies and roses.

Determination of NG, NG-dimethyl- l-arginine, an endogenous NO synthase inhibitor, by gas chromatography–mass spectrometry

A fully validated gas chromatographic–mass spectrometric (GC–MS) method for the accurate and precise quantification of N G, N G-dimethyl- l-arginine (asymmetric dimethylarginine, ADMA), an endogenous inhibitor of the NO synthase, in cell culture supernatants and in small volumes of plasma is described. ADMA was concentrated by solid phase extraction and converted to its methyl ester pentafluoropropionic amide derivative. The derivatives were analyzed without any further purification. Using gas chromatography–chemical ionization mass spectrometry, fragment ions at m/ z 634 and m/ z 640 were obtained for ADMA and for N G, N G-[ 2H 6]-dimethyl- l-arginine ([ 2H 6]-ADMA) as internal standard, respectively. [ 2H 6]-ADMA was synthesized by reaction of l-ornithine fastened at bromcyan-agarose with dimethylamine. The limit of detection of the method was 2 fmol, while the limit of quantitation for cell culture supernatants was 0.05 μM. The method was validated in a concentration range of 0–1.2 μM in cell culture medium and 0–2 μM in 50 μl aliquots of human plasma. The precision was ≥97% and the accuracy was determined to be ≥94%. This method is fast, rugged and an alternative to high performance liquid chromatography (HPLC) analysis of ADMA in cell culture supernatants and small volumes of human plasma.

Derivatisation and gas chromatography–chemical ionisation mass spectrometry of selected synthetic and natural endocrine disruptive chemicals

Methods for ultra trace detection of endocrine disruptive chemicals (EDCs) are needed because of their low levels of impact. Twenty-one EDCs were selected, including 17β-estradiol, 17α-ethinylestradiol, 17β-testosterone and bisphenol A. Derivatisation with eight different fluorine containing compounds was examined. All EDCs could be derivatised automatedly (autosampler) with heptafluorobutyric acid (HFB) anhydride and trifluoroacetic acid (TFA) anhydride, respectively. The detection of these HFB and TFA derivatives in different chemical ionisation modes was studied. Fourteen different reagent gases, including methane, ammonia, acetone and water, were tested with the HFB and TFA derivatives in the negative chemical ionisation mode. Furthermore both types of derivatives were measured in positive chemical ionisation mode. Methane or water provide a good detection of all 21 TFA derivatives and create mass spectra with few fragmentation and characteristic mass peaks. This could serve as a basis for tandem or multiple mass spectrometric measurements.

Gas chromatographic–mass spectrometric determination of erythrocyte 3-deoxyglucosone in diabetic patients

To determine if the erythrocyte levels of 3-deoxyglucosone (3-DG) are increased in diabetic patients, and if they correlate with glycemic status, they were measured in diabetic patients without renal disease as well as in healthy subjects. The erythrocyte levels of 3-DG were measured by a selected ion monitoring method of gas chromatography–chemical ionization mass spectrometry using [ 13C 6]-3-DG as an internal standard. The erythrocyte levels of 3-DG were significantly higher in diabetic patients than in healthy subjects. The erythrocyte concentration of 3-DG was significantly and positively correlated with HbA1c ( r=0.84, P<0.001). However, no significant correlation could be found between erythrocyte 3-DG and age, onset age of diabetes, or duration of diabetes in our group of diabetic patients. In diabetes, the production of 3-DG in the erythrocytes is increased via the polyol pathway and/or the Maillard reaction due to hyperglycemia.

Rapid screening method for determination of Ecstasy and amphetamines in urine samples using gas chromatography–chemical ionisation mass spectrometry

The need for analytical screening tests more reliable and valid to detect amphetamine and related “designer drugs” in biological samples is becoming critical, due to the increasing diffusion of these drugs on the European illegal market. The most common screening procedures based on immunoassays suffer a number of limitations, including low sensitivity, lack of specificity and limited number of detectable substances. This paper describes a screening method based on gas-chromatography-mass–spectrometry (GC/MS) using positive chemical ionisation (PCI) detection. Methanol was used as reactant gas in the ionisation chamber. Molecular ions of different compounds were monitored, allowing a sensitivity of 5–10 ng/ml with high selectivity. The sensitivity of the method gives positive results in samples taken 48–72 h after intake of one dose of 50–100 mg. The method is simple and rapid. Sample preparation was limited to one liquid–liquid extraction, without any hydrolysis and derivatisation. Hydrolysis is critical to identify metabolites excreted as conjugates. Blank urine samples spiked with known amounts of amphetamine (AM), methylamphetamine (MA), methylenedioxyamphetamine (MDA), methylenedioxymethylamphetamine (MDMA), methylenedioxyethylamphetamine (MDEA) and methylenedioxyphenyl- N-methyl-2-butanamine (MBDB) were analysed. The method was successfully tested on real samples of urine from people, whose use of amphetamine was suspected, and results were compared with results obtained with immunoassays.

Investigation of combwax of honeybees with high-temperature gas chromatography and high-temperature gas chromatography–chemical ionization mass spectrometry: II: High-temperature gas chromatography–chemical ionization mass spectrometry

Crude combwax of six various honey bee species have been analyzed by high-temperature gas chromatography (HTGC)–chemical ionization mass spectrometry after a two-step silylation procedure. An optimized chromatographic procedure, described previously, enables the separation of high-molecular mass lipid compounds resulting in a characteristic fingerprint of the combwaxes of different honeybee species. The coupling of HTGC to mass spectrometry requires appropriate instrumentation in order to achieve sufficient sensitivity at high elution temperatures and avoid loss of chromatographic resolution. Chemical ionization was carried out using methane as reagent gas in order to determine the molecular mass of the individual compounds by means of abundant quasi molecular ions. To confirm the presence of unsaturated wax esters, ammonia was used as reagent gas. More than 80 lipid constituents were separated and characterized by their mass spectra. Representative chemical ionization mass spectra of individual compounds are presented. Both, HTGC–flame ionization detection data and the results of the HTGC–mass spectrometric investigations enabled a rapid profiling of the individual classes of compounds in crude combwaxes.

Investigation of combwax of honeybees with high-temperature gas chromatography and high-temperature gas chromatography–chemical ionization mass spectrometry: I. High-temperature gas chromatography

The combwaxes of the honeybee species Apis mellifera, Apis cerana, Apis dorsata, Apis laboriosa, Apis florea and Apis andreniformis have been examined by high-temperature gas chromatography. Combwax consists of a complex mixture of homologous neutral lipids. These compounds containing up to 64 carbons were chromatographed intact on a 10 m×0.2 mm high-temperature stable SOP-50-PFD (50%-diphenyl/50%-1H,1H,2H,2H-perfluorodecylmethylpolysiloxane)-coated Duran glass capillary column. The use of this stationary phase results in lower retention values and, at last, in lower thermal stress of the analytes. In order to minimize the discrimination effect due to adsorption and/or degradation, a two-step derivatization was performed resulting in the formation of tert.-butyldimethylsilyl esters of the long chain fatty acids and trimethylsilyl ethers of complex hydroxyesters, respectively. The derivatization procedure was optimized using a modification of the extended Donike test. In addition this test allows the quantification of the thermal stability of the derivatives performed. The derivatization procedure was applied for combwax analysis. More than 80 compounds were separated and their peak areas semiquantitatively exploited.

Gas chromatographic–mass spectrometric analysis of erythrocyte 3-deoxyglucosone in hemodialysis patients

The erythrocyte levels of 3-deoxyglucosone (3-DG) were measured by a selected ion monitoring method of gas chromatography–chemical ionization mass spectrometry using [13C6]-3-DG as an internal standard. Because the erythrocyte levels of 3-DG measured after deproteinization using ethanol were 18 times higher than those using ultrafiltration, we used ethanol deproteinization for measurement of total 3-DG in the erythrocytes. The concentration of 3-DG was significantly elevated in hemodialysis (HD) patients compared with healthy subjects. Although HD treatment could remove the erythrocyte 3-DG efficiently, its post-HD levels were still elevated compared with the healthy subjects.

Quantitative acylcarnitine profiling in fibroblasts using [U- 13C] palmitic acid: an improved tool for the diagnosis of fatty acid oxidation defects

A method was developed for the investigation of mitochondrial fatty acid β-oxidation in cultured fibroblasts. Monolayer cultures were incubated without foetal calf serum with commercially available [U- 13C] palmitic acid and l-carnitine for 96 h. The acylcarnitines produced by the cells were extracted from the cell suspension and analysed either by quantitative stable isotope dilution gas chromatography chemical ionization mass spectrometry, or by fast atom bombardment mass spectrometry. Characteristic acylcarnitine profiles were obtained for all the different enzyme deficiencies investigated, with the exception of carnitine palmitoyltransferase II deficiency and carnitine/acylcarnitine carrier deficiency which showed similar patterns. Comparison between this method and the 3H-myristate and 3H-palmitate tritium release assays revealed that the method described here is superior, allowing unequivocal identification of patients.

Identification of cyclopropene triacylglycerols by high-temperature gas chromatography and high-temperature gas chromatography-negative chemical ionization mass spectrometry

The seed oil of Choriosa speciosa, which is known to be rich in cyclopropene triacylglycerols, has been investigated by high-temperature gas chromatography using glass capillary columns coated with the stationary phase SOP-50 (50% diphenyl–50% dimethylpolysiloxane, methoxy terminated). Cyclopropene rings were characterized after a mild catalyzed hydrogenation procedure. The partial π-character of the resulting cyclopropane ring supports the separation of individual triacylglycerol species on the polarizable stationary phase. Characterization of the separated compounds was performed by negative chemical ionization–mass spectrometry with ammonia as reagent gas. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 223–229, 1999

Rapid characterization of artemether and its in vitro metabolites on incubation with bovine hemoglobin, rat blood and dog blood by capillary gas chromatography–chemical ionization mass spectrometry

A fast and sensitive analytical method was developed to characterize artemether and its metabolites in small amounts in body fluids. The extracts were derivatized with N-methyl- N-trimethylsilyltrifluoroacetamide, separated on an optimized capillary gas chromatographic system and identified by chemical ionization mass spectrometry by using ammonia as reagent gas. The analytical assay is demonstrated on samples extracted from bovine hemoglobin, rat blood and dog blood. Full mass spectra of artemether and three metabolites were obtained at a level of 1·10 −6 g/ml.

Determination of S-1 (combined drug of tegafur, 5-chloro-2,4-dihydroxypyridine and potassium oxonate) and 5-fluorouracil in human plasma and urine using high-performance liquid chromatography and gas chromatography-negative ion chemical ionization mass spectrometry.

A high-performance liquid chromatography (HPLC) and gas chromatography-negative ion chemical ionization mass spectrometry (GC-NICI-MS) method was developed for the analysis of the combined antitumor drug S-1 (tegafur, 5-chloro-2,4-dihydroxypyridine and potassium oxonate) and active metabolite 5-fluorouracil in human plasma and urine. Tegafur was fractionated from biological fluids by extraction with dichloromethane and analyzed by HPLC. 5-Fluorouracil and 5-chloro-2,4-dihydroxypyridine were extracted with ethyl acetate from the residual layer after extraction of tegafur, and converted to pentafluorobenzyl (PFB) derivatives. Potassium oxonate was cleaned up with an anion-exchange column (Bond Elut NH2). The extracted potassium oxonate was degraded to 5-azauracil and converted to PFB derivatives. The PFB derivatives were analyzed by GC-NICI-MS. A stable isotope was employed as the internal standard in the GC-NICI-MS analysis. The limits of quantitation of tegafur, 5-fluorouracil, 5-chloro-2,4-dihydroxypyridine and potassium oxonate in plasma were 10, 1, 2 and 1 ng/ml, respectively. The reproducibility of the analytical method according to the statistical coefficients is approximately 10%. The accuracy of the method is good; that is, the relative error is < 10%. The methods were applied to pharmacokinetic studies of S-1 in patients.

Quantitative analysis of plasma acylcarnitines using gas chromatography chemical ionization mass fragmentography.

A stable isotope dilution gas chromatography chemical ionization mass spectrometry (GC-CI-MS) method was developed for the quantitative profiling of plasma acylcarnitines. The clean-up procedure was comprised of a solid-phase cation exchange extraction using PRS-columns from which the acylcarnitines were eluted with a barium chloride solution. Isolated acylcarnitines were transformed into acyloxylactones and analyzed by positive GC-CI-MS using isobutane as reactant gas. The selected monitoring of a common ion at m/z [85]+ and the protonated molecular ion enabled a selective and sensitive detection of all C2-C18 acylcarnitines. An accurate quantitation was achieved by the use of stable isotope-labeled internal standards (C2-C18) and acylcarnitines could be analyzed in the sub-nanomolar range. Control values for C2-C18 acylcarnitines in plasma were established. Concentrations ranged from 0.02 micromol/L for C14-acylcarnitine to 4.90 micromol/L for C2-acylcarnitine. The diagnostic suitability of the method was demonstrated for patients with medium-chain acyl-CoA dehydrogenase deficiency and very long-chain acyl-CoA dehydrogenase deficiency.

Distinguishing Amphetamine, Methamphetamine and 3,4-Methylenedioxymethamphetamine from Other Sympathomimetic Amines After Rapid Derivatization with Propyl Chloroformate and Analysis by Gas Chromatography—Chemical Ionization Mass Spectrometry

Abstract Misidentification of ephedrine and pseudoephedrine as methamphetamine has been reported because of similar retention times of their derivatives in gas chromatography as well as very similar mass spectral fragmentation patterns in the conventional electron impact mode of analysis. Recently, a new derivatization of amphetamine and methamphetamine has been described using propyl chloroformate. The derivatization is easily accomplished at room temperature by adding the derivatizing reagent in the extraction solvent because the reagent is stable in the presence of water. The electron impact mass spectrum of derivatized methamphetamine (base peak, m/z 144, other peaks at m/z 102, 58) is similar to the electron impact mass spectrum of both derivatized pseudoephedrine (base peak, m/z 144, other peaks, m/z 102, 58), and ephedrine (base peak, m/z 144, other peaks, m/z 102, 58). Therefore, misidentification of ephedrine and pseudoephedrine as methamphetamine is possible even if this new derivatization technique is used with conventional gas chromatography/electron impact mass spectrometry. We demonstrated that by using chemical ionization mass spectrometry, this problem can be eliminated. In the chemical ionization, using methane as a reagent gas, derivatized methamphetamine showed a protonated molecular ion as a base peak at m/z 236 and other strong peaks at m/z 144 and 119, both derivatized ephedrine and pseudoephedrine showed a base peak at m/z 192 and another strong peak at m/z 148, thus differentiating them clearly from methamphetamine. Amphetamine also showed a protonated molecular ion at m/z 222 and other strong peaks at m/z 130 and 119, whereas phenylpropanolamine after derivatization with propyl chloroformate showed a base peak at m/z 220 and another strong peak at m/z 238, thus differentiating it from amphetamine. The designer drug 3,4-methylenedioxymethamphetamine (MDMA) showed a molecular ion at m/z 279 using electron impact, after derivatization with propyl chloroformate. Using chemical ionization, a relatively stronger protonated molecular ion at m/z 280 was observed. We conclude that using chemical ionization instead of conventional electron impact and propyl chloroformate derivatization, misidentification of ephedrine or pseudoephedrine as methamphetamine or phenylpropanolamine as amphetamine can be eliminated.

Direct analysis by electrospray ionization and matrix‐assisted laser desorption ionization mass spectrometry of standard and urinary acylcarnitines. Comparison with fast atom bombardment and gas chromatography chemical ionization mass spectrometry

AbstractA simple method using matrix‐assisted laser desorption ionization mass spectrometry (MALDI‐MS) is described for the characterization of acylcarnitines in standard solutions and urinary samples from controls and patients with β‐oxidation deficiency disorders. This mass spectrometric approach is compared with other techniques currently utilized for studying acylcarnitines: fast atom bombardment mass spectrometry (FABMS), gas chromatography/chemical ionization mass spectrometry (GC/CIMS) and electrospray ionization mass spectrometry (ESI‐MS). MALDI‐MS was found to compare favourably with the recently described ESI‐MS analysis of acylcarnitines. Both ESI‐MS and MALDI‐MS share the following advantages: (i) non‐requirement of a derivatization step; (ii) easy detection of acylcarnitine esters in standard preparations and urinary samples from human subjects; (iii) detection of fatty acid oxidation disorders from the urinary acylcarnitine profiles in patients suffering from medium‐chain acyl‐CoA dehydrogenase deficiency (MCADD), multiple acyl‐CoA dehydrogenase deficiency (MADD) and mitochondrial carnitine palmitoyltransferase type II (CPT II) deficiency; (iv) sensitivity comparable to FABMS and GC/CIMS, the two reference methods most widely utilized for routine detection of acylcarnitines; and (v) ability (like FABMS but in contrast with GC/CIMS) to detect long‐chain acylcarnitines, suggesting that these esters might have been previously underestimated in body fluids from patients with β‐oxidation deficiency disorders. MALDI‐MS, like ESI‐MS, provides a fast and sensitive method for determining carnitine and its esters, with the potential for routine application in neonatal screening for inherited metabolic disorders involving acylcarnitine metabolism.

Assay of zatebradine in plasma by fully automated sample clean-up, capillary gas chromatography and ammonia chemical ionisation mass spectrometry.

A method has been developed for the measurement of zatebradine (UL-FS 49), a heart-rate lowering drug, suitable for the treatment of stable angina pectoris. The method comprises a fully automated liquid-solid extraction using a Zymark Benchmate, a capillary gas chromatography and ammonia chemical ionisation (CI) mass spectrometry using hexadeuterated zatebradine for the internal standard. The assay has a mean between-batch imprecision of 4.9% and a mean inaccuracy of 1.5%. The calibration curve covers the range of 1-30 ng/ml. About 60 samples can be handled per day. The assay has been successfully applied to human pharmacokinetic studies.

Determination of l-α-acetylmethadol, l-α-noracetylmethadol and l-α-dinoracetylmethadol in plasma by gas chromatography—mass spectrometry

A method is described for the simultaneous determination of l-α-acetylmethadol (LAAM) and its N-demethylated metabolites, l-α-noracetylmethadol (norLAAM) and l-α-dinoracetylmethadol (dinorLAAM), in plasma by gas chromatography—chemical ionization mass spectrometry. Deuterated internal standards for each analyte serve as carriers and control for recovery during sample purification on a solid-phase extraction column (C 18), and subsequent separation and analysis on a DB-17 capillary column. With this method, we have determined levels of LAAM, norLAAM, and dinorLAAM in small volumes of plasma (100 μl). The limit of quantitation for all analytes was approximately 1.0 ng/g plasma and the limit of detection was approximately 0.5 ng/g plasma. An experimental application is also described where these analytes are quantitated in plasma obtained from rats before, during, and after chronic administration of LAAM-HCl. Since this technique affords a selective and sensitive means of detection of LAAM and its active, N-demethylated metabolites in small samples of blood, it may enable patient compliance to be more easily assessed by allowing samples to be collected by a simple finger-prick technique.