Analyssis of pharmaceutical substances by reaction gas chromatography/mass spectrometry

Derivatization of six pharmaceutical substances (catopril, metoclopramide, sotalol, hydrochlorothiazide, nalidixic acid, and stavudine) has been performed using five derivatizing reagents of different types; the derivatization has been followed by the GC/MS detection of the resultant products. The number of labile hydrogen atoms in the initial molecules substituted by the structural fragments of derivatizing reagents has been determined.     

Long-term stability of a gas chromatography/mass spectrometry system in quantitative gas analysis

A gas chromatograph/quadrupole mass spectrometer (GC/MS) system was used to supervise a test programme for evaluating the potential of a natural gas storage plant. The dispersion characteristics of a large nitrogen reservoir located in a tight sandstone formation 1600 m below sea level between claystones, was investigated by injection and withdrawal of 350 000 m³ nitrogen with argon as tracer gas. The GC/MS system was installed in a shed in an open field and operated under computer control continuously 24 h a day for three weeks; about 3000 analyses were done. The on-line results were in good agreement with those obtained from additional gas samples withdrawn every 4 h for independent quantitative gas analyses with a purpose-built mass spectrometer.     

Investigation of vancomycin and related substances by liquid chromatography/ion trap mass spectrometry

Liquid chromatography (LC) methods compatible with mass spectrometry (MS) that are suitable for impurity profiling of vancomycin mixtures have not been described in the literature. The mobile phases of the existing methods contain non-volatile additives and/or solvents that give problems in combination with MS. In this paper, a reversed-phase LC/tandem mass spectrometry method is described for the investigation of vancomycin and related substances. The LC method uses a Zorbax Extend C18 column (250 x 4.6 mm i.d.), 5 microm, and a mobile phase consisting of methanol, water and ammonium acetate solution (pH 9.0). This method allows us to separate vancomycin and its impurities. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an electrospray interface operated in the positive and negative ion modes. The LCQ is ideally suited for identification of impurities and related substances because it provides on-line LC/MSn capability, which allows efficient identification without time-consuming isolation and purification procedures. Using this method, the fragmentation of vancomycin and known derivatives was studied and the structures of six substances occurring in commercial samples were elucidated.     

Structure elucidation of four related substances in gramicidin with liquid chromatography/mass spectrometry

A selective reversed phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of related substances in commercial gramicidin samples. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an electrospray interface operated in the positive and the negative ion mode. The LCQ is ideally suited for identification of related substances because it provides on-line LC/MS(n) capability. Compared with UV detection the main advantage of this hyphenated LC/MS(n) technique is the efficient identification of novel related substances without time-consuming isolation and purification procedures. Using this method four novel related substances were separated and identified in a commercial sample.     

Determination of sulphonamides by electron-capture gas chromatography. Preparation and properties of perfluoroacyl and pentafluorobenzyl derivatives.

The derivatization of benzenesulphonamide, N-ethylbenzenesulphonamide and N-phenylbenzenesulphonamide with trifluoroacetic and heptafluorobutyric anhydride and pentafluorobenzyl bromide has been studied. A rapid quantitative acylation is obtained in benzene in the presence of trimethylamine. Pentafluorobenzylation is performed by the extractive alkylation technique using tetrabutylammonium as counter ion and methylene chloride as solvent. Less than 20 min are required for a quantitative derivatization. The derivatized sulphonamides have a hydrophobic character, making them very suitable for gas chromatography. Trifluoroacetylation and heptafluorobenzylation decreases it. The derivatives have a high electron-capture detector response (minimum detectable quantity, 1-2 X 10-minus 16 moles/sec). A standard curve is given for the determination of N-phenylbenzenesulphonamide as trifluoroacetyl derivative in the range 1.8-90 ng/ml.     

Combined use of gas chromatography and selected ion flow tube mass spectrometry for absolute trace gas quantification

The value of the gas chromatography (GC) and selected ion flow tube mass spectrometry (SIFT-MS) combination for the analysis of trace gases is demonstrated by the quantification of acetone in air samples using the three precursor ions available to SIFT-MS, viz. H3O+, NO+ and O2+, and by the separation of the isomers 1-propanol and 2-propanol, and their analysis using H3O+ precursor ions. It is shown that the GC/SIFT-MS combination allows for accurate trace gas quantification obviating the regular, time-consuming calibrations that are usually required for the more commonly used detectors of GC systems, and the positive identification of isomers in mixtures that is often challenging using SIFT-MS alone. Thus, the GC/SIFT-MS combination paves the way to more confident analyses of complex mixtures such as exhaled breath.     

Investigation of unknown related substances in commercial erythromycin samples with liquid chromatography/mass spectrometry

A selective reversed phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of erythromycin impurities and related substances in commercial erythromycin samples. Mass spectral data are acquired on a LCQ ion trap mass spectrometer equipped with an electrospray interface operated in positive ion mode. The LCQ is ideally suited for identification of impurities and related substances because it provides on-line LC/MS(n) capability. Compared with UV detection, this hyphenated LC/MS(n) technique provides as a main advantage efficient identification of novel substances without time-consuming isolation and purification procedures. Using this method four novel related substances were identified in commercial samples.     

A single glucose derivative suitable for gas chromatography/mass spectrometry and gas chromatography/combustion/isotope ratio mass spectrometry

The incorporation of stable isotopes improves the assessment of glucose metabolism and, with some researchers using two tracers, (2)H-glucose assessed by gas chromatography/mass spectrometry (GC/MS) and (13)C-glucose by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), a common derivative for both is advantageous. The most commonly used derivatives for GC/MS are inappropriate for GC/C/IRMS as additional functional groups dilute the label. We therefore considered the suitability of six derivatives for both GC/MS and GC/C/IRMS. Glucose alkylboronates were prepared by adding the appropriate alkylboronic acid (butyl- or methylboronic acid) in pyridine to desiccated glucose. The derivatisation was completed by reacting this with either (a) acetic anhydride or trifluoroacetic anhydride (acetate derivatives) or (b) bis(trimethylsilyl)trifluoroacetamide BSTFA (TMS derivatives). All six derivatives were assessed using GC/MS and (13)C GC/C/IRMS.Neither TMS derivative exhibited any signal intensity in the molecular ion, although a M-15 ion showed good agreement between experimental and theoretical data and, whilst still low in intensity, could be suitable for isotope work. Similarly, none of the acetate derivatives showed any intensity at the molecular ion although three key fragmentation series were identified. The most attractive sequence, initiated by the loss of 1,2 cyclic boronate, resulted in the main fragment ion of interest, m/z 240, corresponding to the fluorinated methylboronate derivate. Minimal carbon and hydrogen atoms are added to this derivative making it an excellent choice for stable isotope work, while proving suitable for analysis by both GC/MS and GC/C/IRMS.     

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.     

Identification of the related substances of tilmicosin by liquid chromatography/ion trap mass spectrometry

Structures of seven impurities of the veterinary drug tilmicosin have been elucidated by multiple fragmentation with ion trap tandem mass spectrometry. All related compounds possess the main lactone ring of tilmicosin. The differences in their structures are due to the hydroxyl, mycaminose, 3,5-dimethylpiperidine and mycinose groups connected to C(3), C(5), C(6), C(14) of the lactone ring, respectively. The following compounds of the impurity profile of tilmicosin were identified: B - tilmicosin with a hydroxyl group at C(3); C - tilmicosin without a methyl group at the N-atom connected to C(3) of the mycaminose ring; D - tilmicosin with a hydroxyl group at C(6) of the mycaminose ring; E - tilmicosin with a methoxy group at C(3), F - desmicosin; G - 20-dihydrodesmicosin; and H - tilmicosin without a mycaminose ring. Isomers of the compounds B, C, D, E and H were identified by their mass chromatograms and retention times. The concentrations of the impurities varied in the range of 0.1% to 2.9%.     

Novel, highly robust method of carbohydrate pre-purification by two-dimensional liquid chromatography prior to liquid chromatography/mass spectrometry or gas chromatography/mass spectrometry

We describe a novel two-dimensional liquid chromatography (2D-LC) method for fast and robust isolation and concentration of low abundant carbohydrates (sorbitol, glycerol) from biological matrices (plasma and urine). Off-line pre-purified fractions, enriched by analyte of interest, were analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS-MS). Initial 2D-LC automated sample pre-purification improved MS detection, eliminated matrix effects, and achieved high sensitivity (picogram detection limit) with a 6 min runtime and increased column lifetime. Using this method we have analyzed more than 1300 samples from biological matrices without column replacement.     

Reaction gas chromatography/mass spectrometry. 2—the use of catalytic on-line dehydrogenation for the investigation of alcohols by gas chromatography/mass spectrometry

A method for structure determination of aliphatic alcohols within mixtures is described. It involves the use of a vapour phase dehydrogenation micro-reactor (Cu, 300°C) located between the chromatographic column and the mass spectrometer or between the injection port and the column. Since primary and secondary alcohols are converted into corresponding carbonyl compounds, they can be readily differentiated from tertiary alcohols and dialkyl ethers. An examination of the mass spectra of alcohols and carbonyl compounds permits the determination of molecular mass, the location of hydroxyl group and the determination of branching at the β-carbon atom.     

Determination of erythromycin and related substances in commercial samples using liquid chromatography/ion trap mass spectrometry

A sensitive, precise and accurate quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the measurement of erythromycin A (EA) and related substances in commercial samples was developed and validated. The samples were chromatographed on a reversed-phase column with a polar endcapping and analyzed by ion trap tandem mass spectrometry in the multiple reaction monitoring (MRM) mode using positive electrospray ionization. The method showed high recovery (>or=98.82%), high sensitivity (lower limit of quantitation of 0.25 ng/mL for EA and less than 7.3 ng/mL for the related substances) and high precision (or=0.991) with a run time of only 13 min. The method was successfully applied to the determination of EA and related substances in commercial samples. Moreover, using the advanced data-dependent acquisition capability of the ion trap software two new unexpected EA related substances could be detected and possible structures for these substances were postulated.     

Negative-ion counting techniques for gas chromatography—mass spectrometry

Negative-ion counting techniques for gas chromatography—electron-impact ionization quadrupole mass spectrometry (g.c.—m.s.) are described. Signal-to-noise performance is good and data acquisition is fast. Digital processing of the negative ion signals is done with an ion-counting device and data acquisition with a multi-channel analyzer. The negative-ion mass spectra from g.c.—m.s. measurements are shown for a mixture of tetrachloro-methane, 1,2,2-trichloroethane and 1,1,2,2-tetrachloroethane.     

Simultaneous determination of psychotropic phenylalkylamine derivatives in human hair by gas chromatography/mass spectrometry

A gas chromatography/mass spectrometric (GC/MS) method was developed and validated for the determination of thirteen psychotropic phenylalkylamine derivatives (amphetamine; AP, phentermine; PT, methamphamine; MA, cathinone; Khat, methcathinone; MCAT, fenfluramine; FFA, desmethylselegiline; DSEL, 3,4-methylenedioxyamphetamine; MDA, 3,4-methylenedioxymethamphetamine; MDMA, 3,4-methylenedioxyethylamphetamine; MDEA, norketamine; NKT, mescaline; MES, 4-bromo-2,5-dimethoxyphenethylamine; 2CB) in human hair. Hair samples (20 mg) were washed with distilled water and acetone, cut into small fragments (<1 mm), and incubated in 0.25 M methanolic HCl under ultrasonication at 50 degrees C for 1 h. The resulting solutions were evaporated to dryness, derivatized using trifluoroacetic anhydride (TFAA) at 70 degrees C for 30 min, and analyzed by GC/MS. The linear ranges were 0.02-25.0 ng/mg for AP, PT, Khat, FFA, DSEL, MDMA, and 2CB; 0.05-25.0 ng/mg for MA, MCAT, and MES; 0.05-12.5 ng/mg for MDA; and 0.1-25.0 ng/mg for MDEA and NKT, with good correlation coefficients (r(2) > 0.9985). The intra-day, inter-day, and inter-person precisions were within 12.7%, 14.8%, and 16.8%, respectively. The intra-day, inter-day, and inter-person accuracies were between -10.7 and 13.4%, -12.7 and 11.6%, and -15.3 and 11.9%, respectively. The limits of quantifications (LOQs) for each compound were lower than 0.08 ng/mg. The recoveries were in the range of 76.7-95.6%. The method proved to be suitable for the simultaneous qualification and quantification of phenylalkylamine derivatives in hair specimens.     

Pyrolysis–gas chromatography mass spectrometry and field ionization mass spectrometry of polyquinones

Low- and high-molecular mass thermal decomposition products of five polyquinones with different linking aromatic structures have been analyzed by pyrolysis–gas chromatography and by direct (in-source) pyrolysis–field ionization mass spectrometry. The quantity of carboxyl groups present in the polymer is obtained by the amounts of carbon dioxide found by pyrolysis–gas chromatography. Assuming a radical thermal decomposition mechanism the distribution of ketoacidic and quinonoid segments along the macromolecular ladder could be estimated from the high-molecular mass products measured by pyrolysis–field ionization mass spectrometry. A random distribution of the two different segments was found for polyquinones with biphenylene and dibenzofuran subunits, while a structure built up of blocks of two or more identical segments was obtained for polyquinones with dibenzothiophene and diphenylmethane subunits. At the same time the anomalous structural moieties in the polyquinone ladders are also clarified with the help of the identification of the unexpected pyroysis products. Oxidated and bis-dibenzothiophene and bis-diphenylmethane subunits were found. The observed temperature dependence for the appearances of the thermal degradation products indicates that condensation and elimination reactions are taking place under the described pyrolysis conditions. Condensation in the ketoacidic segments forming new quinonoid segments proved to be important in the polymer which was a 100% poly(ketoacid), but negligible in the polyquinones containing ketoacidic segments up to 60%.     

毛细管气相色谱法测定细辛脑及有关物质

建立了细辛脑中相关杂质的气相色谱快速分析方法.色谱柱为HP-1石英毛细管柱(30 m×0.53 mm i.d.,1.5 μm),检测器为FID氢火焰离子化检测器,柱温185 ℃.能够明确的测定细辛脑中3种物质:β-细辛脑、2,4,5-三甲氧基苯甲醛、1-(2,4,5-三甲氧基苯基)-1-丙醇.细辛脑进样量在0.010～10.140 μg范围内线性关系良好,r=0.9995,方法平均回收率为99.5%(n=9),细辛脑的检出限为0.304 ng.该方法对细辛脑合成工艺优化和样品的质量控制均具有指导作用.