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Biomedical subjects

S J Gaskell

Publications and source records attributed to S J Gaskell.

At least 73 records · Page 4Linked to original sources
PubMed1989

Quantitation of leukotriene B4 in human serum by negative ion gas chromatography-mass spectrometry.

Leukotriene B4 (LTB4) is a potent chemotactic agent formed via the 5-lipoxygenase pathway from arachidonic acid. To understand the role LTB4 plays in several pathological processes it is essential that endogenous concentrations of LTB4 be accurately quantitated. We have developed a method based on electron capture negative ion mass spectrometry for the analysis of LTB4 in serum at low picogram per milliliter concentrations. Blood is collected into the 5-lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) to suppress ex vivo formation. Serum is isolated, equilibrated with the internal standard [2H4]LTB4, and extracted using octadecyl-silica (C-18) cartridges. After conversion of the carboxylic acids to their pentafluorobenzyl esters the extract is purified by straight-phase HPLC. Gas chromatographic-mass spectrometric analysis is accomplished on the tert-butyldimethylsilyl ether derivatives using dual-selected ion monitoring of m/z 431 and 435. These ions correspond to loss of tert-butyldimethylsilanol from the (M-PFB)- ion of endogenous and [2H4]LTB4, respectively. The concentration of LTB4 in human serum samples was 10.0 +/- 4.0 pg/ml (n = 5). The assay exhibited satisfactory precision, with an intraassay coefficient of variation of 17% and a high degree of accuracy. The concentration of LTB4 in serum collected with (NDGA) was less than 10% of that observed in blood collected without the lipoxygenase inhibitor. Ex vivo formation can therefore be a major obstacle in assessing circulating levels of LTB4.

Chromatography, High Pressure Liquid↗
PubMed1988

Characterization of glutathione conjugates by fast atom bombardment/tandem mass spectrometry.

The collisionally activated decomposition of [M + H]+ ions, generated by fast atom bombardment (FAB) of glutathione conjugates, has been studied by tandem mass spectrometry (MS/MS) using hybrid sector/quadrupole instruments. Abundant fragments of diagnostic utility were present in the daughter ion spectra. Common fragmentation modes were observed but their relative importance was strongly dependent on the nature of the conjugated species. As an example of a general approach to the characterization of glutathione conjugates in biological samples, the acetaminophen-glutathione conjugate was identified in rat bile, following coadministration of (2H0)- and (2H3)acetaminophen, using the experimental sequence: (i) conventional FAB mass spectrometric analysis, (ii) MS/MS using constant neutral loss (129 u) scanning to identify parent ions corresponding to glutathione conjugates, (iii) MS/MS to yield daughter ion spectra of parents so identified and corresponding to (2H0)- and (2H3)-labeled conjugates.

Animals↗
PubMed1988

Evaluation of the quantitative analysis of a steroid sulphate using fast atom bombardment and tandem mass spectrometry.

Dehydroepiandrosterone sulphate (DHAS) has been quantified in human blood serum by fast atom bombardment (FAB)/tandem mass spectrometry of immunoadsorption extracts. FAB of DHAS yielded abundant ions corresponding to the intact steroid sulphate; these were selected by a double-focusing mass spectrometer prior to collisionally activated decomposition in a quadrupole collision cell and mass analysis by a quadrupole mass filter. [HSO4]- (m/z 97) was the sole prominent daughter ion. For quadrupole mass filter was set to transmit m/z 97 and a narrow-range magnet scan yielded a spectrum of parents, including m/z 367 and 369, corresponding to DHAS and the (2H2)-analogue (used as internal standard), respectively. Serum concentrations by this procedure were in good agreement with data obtained by gas chromatographic/mass spectrometric analyses of DHA heptafluorobutyrate, formed by direct derivatization of the steroid sulphate.

Adult↗
PubMed1988

Collisionally activated decomposition of modified peptides using a tandem hybrid instrument.

Analyses are described of small peptides and related compounds using a tandem hybrid mass spectrometer of BEQQ geometry. Collisionally activated decomposition of [M + H]+ ions, generated by fast atom bombardment, was performed in the radio frequency (rf)-only quadrupole. Interpretation of fragmentation was greatly facilitated by analysis of labeled analogs, obtained by 18O exchange of carboxyl oxygens. N-Acetylation was also valuable although significant changes in fragmentation resulted from derivatization. Daughter ion spectra of [M + H]+ ions of angiotensin III showed diagnostic fragmentations throughout the peptide chain.

Angiotensin III↗
PubMed1988

Selected reaction monitoring during gas chromatography/mass spectrometry of eicosanoids.

Gas chromatography/electron capture negative ion mass spectrometry of eicosanoids, as pentafluorobenzyl (PFB) ester, methyl oxime (where applicable), trimethylsilyl (TMS) ether derivatives, is reported using a double-focusing instrument of trisector configuration. Sub-picogram detection limits were observed for prostaglandins E1, E2 and F2 alpha during selected ion monitoring (SIM) of [M-PFB]- ions. Selected reaction monitoring (SRM) of [M-PFB]-----[M-PFB-TMSOH]-, occurring in the first field-free region, was of modest sensitivity, reflecting the stability of the [M-PFB]- ions. The leukotriene B4 (LTB4) derivative was successfully analyzed by SIM at the low-picogram level. In this instance, the fragmentation [M-PFB]-----[M-PFB-TMSOH] occurred in high yield in the first field-free region. The advantageous improvement in selectivity of detection that may be achieved with SRM was evident during the analysis of a serum extract for LTB4.

Chromatography, High Pressure Liquid↗
PubMed1987

Determination of serum cortisol by thermospray liquid chromatography/mass spectrometry: comparison with gas chromatography/mass spectrometry.

The determination of serum cortisol by thermospray liquid chromatography/mass spectrometry (LC/MS) has been assessed. The method incorporates stable isotope dilution and immunoadsorption extraction. [M + H]+ ions are monitored during LC/MS. The within-assay reproducibility is satisfactory (coefficient of variation 7% at a concentration of 190 ng ml-1), though inferior to that achieved with the (more lengthy) procedure of gas chromatography/mass spectrometry (GC/MS). Satisfactory agreement between LC/MS (y) and GC/MS (x) data was observed (y = 0.934x + 12.4 ng ml-1; r = 0.968; n = 14). It is concluded that the generation of precise reference data for the assessment of routine cortisol assays is at present better achieved by GC/MS. LC/MS, however, provides satisfactory quantitative data via a more simple and rapid method.

Chromatography, Liquid↗
PubMed1986

Quantification of progesterone in human saliva.

A procedure for the quantification of progesterone in saliva has been developed, using gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring of the 3-enol heptafluorobutyrate derivative. (2H2)Progesterone is used as internal standard. The detection limit (c. 10 pg ml-1) is sufficiently low to permit the determination of the steroid in the saliva of adolescent girls. Assessment of the procedure indicated good assay linearity and excellent accuracy in the determination of progesterone added to saliva. Comparison of GC/MS and radioimmunoassay data showed good agreement, substantiating earlier immunoassay evidence for the occurrence of episodic increases in salivary progesterone concentrations in perimenarcheal girls.

Adolescent↗
PubMed1986

Gas chromatography-mass spectrometric analysis of salivary testosterone with reference to diethylstilboestrol-treated prostatic cancer patients.

Testosterone has been quantified in saliva by gas chromatography-mass spectrometry with selected ion monitoring of the t-butyldimethylsilyl ether (TBDMS) of the oxime derivative. High specificity of instrumental analysis has been complemented by immunoadsorption for extraction of the analyte. The sensitivity of the detection is approx. 4 pmol/l and the precision of quantification is 3.4% CV for a value of 160 pmol/l and 11% for a value of 25 pmol/l. Female subjects had salivary concentrations of testosterone of 14-52 pmol/l, while testosterone was not detected in the saliva of prostatic cancer patients treated with diethylstilboestrol (DES).

Adolescent↗
PubMed1986

Mass-spectrometric determination of serum cortisol: comparison of data from two independent laboratories.

Isotope dilution and mass spectrometry were used in two independent laboratories to determine cortisol in 15 plasma and serum pools used in the British and German national schemes for the external quality assessment of routine assays. For the concentration range 240-700 nmol/L, differences between the data obtained by the two laboratories were generally less than 4% but were approximately 7% in two instances. The discrepancies are nevertheless small in comparison with the bias observed for many routine assays.

Gas Chromatography-Mass Spectrometry↗
PubMed1985

Gaseous acidity and basicity scales as guides to chemical ionization in reversed-phase liquid chromatography-mass spectrometry with direct liquid introduction.

During direct liquid introduction (DLI) liquid chromatography-mass spectrometry (LC-MS), the detectability of acetone is shown to be predictable, based on consideration of the gas-phase acidities and basicities of solvents methanol and acetonitrile and modifiers formic acid and ammonium formate. Consequently, ion formation in DLI LC-MS resembles gas-phase chemical ionization processes; since the order of acidities is altered in solution, solution ionization must be much less important than gas-phase. Ion populations could be predicted on the basis of gas-phase proton affinities and acidities: acetone could be detected in all solvent mixture by positive ions, but it was not readily detected by negative ions when acid was also present. In solvents without additives it was always detected.

Acetonitriles↗
PubMed1985

Dual metastable peak monitoring: application to the analysis of oestradiol-17 beta as the bis (tert-butyldimethylsilyl) ether.

A new approach to dual metastable peak monitoring has been developed, based on synchronous switching of the accelerating voltage and electric sector voltage of a double-focusing mass spectrometer. The technique has been applied to the determination of oestradiol-17beta as the bis(tert-butyldimethylsilyl) ether, using the 2H3 analogue as internal standard. The detection limit was approximately 5 pg during monitoring of the [M]+ X----[M-C4H9]+ fragmentation. Analyses of plasma extracts indicated that greater selectivity of detection was achieved during metastable peak monitoring than during high resolution (8000) selected ion monitoring of the parent ion.

Estradiol↗