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At least 181 records · Page 10Linked to original sources
PubMed2000

Gas chromatography/negative ion chemical ionization mass spectrometry and liquid chromatography/electrospray ionization tandem mass spectrometry quantitative profiling of N-acetylcysteine conjugates of valproic acid in urine: application in drug metabolism studies in humans.

We report a GC/NICI-MS assay and a LC/ESI-MS/MS assay for the analysis of N-acetylcysteine (NAC) conjugates of (E)-2,4-diene VPA (NAC I and NAC II) identified in humans. The assay also includes the analysis of the NAC conjugate of 4,5-epoxy VPA (NAC III), an identified metabolite in rats treated with 4-ene VPA for its use in metabolic studies in animals. The highly sensitive GC/MS assay was designed to monitor selectively the diagnostic and most abundant [M - 181](-) fragment anion of the di-PFB derivatives of NAC I, NAC II, and NAC IV, the internal standard (IS) and the PFB derivative of NAC III. The higher selectivity of LC/MS/MS methodology was the basis for an assay which could identify and quantitate the underivatized conjugates simultaneously using MRM of the diagnostic ions m/z 130 and 123 arising from the CID of their protonated molecular ions [MH](+). The GC/MS assay employed liquid-liquid extraction whereas the LC/MS/MS assay used a solid-phase extraction procedure. Linearity ranges of the calibration curves were 0.10-5.0microg ml(-1) by GC/MS and 0.10-1.0microg ml(-1) by LC/MS/MS for NAC I, NAC II and NAC III (r(2) = 0.999 or better). Both assays were validated for NAC I and NAC II and provided good inter- and intra-assay precision and accuracy for NAC I and NAC II. The LOQ by LC/MS/MS was 0.1microg ml(-1), representing 1 ng of NAC I and NAC II. The same LOQ (0.1microg ml(-1)) was observed by GC/MS and was equivalent to 100 pg of each metabolite. NAC III was detected at concentrations as low as 0.01 microg ml(-1) by both methods. The total urinary excretion of the NAC conjugates in four patients on VPA therapy was determined to be 0.004-0.088% of a VPA dose by GC/MS and 0.004-0. 109% of a VPA dose by LC/MS/MS.

Acetylcysteine↗
PubMed1999

Serum ionized magnesium and calcium in women after menopause: inverse relation of estrogen with ionized magnesium.

OBJECTIVE: To study the serum concentrations of the sex steroid hormones and free divalent cations Mg2+ and Ca2+ in healthy women at or past menopause and to compare them with the serum concentrations of healthy, cycling women of child-bearing age at different stages of the menstrual cycle. DESIGN: Controlled clinical study. SETTING: An academic medical center. PATIENT(S): Women of varying age and duration of menopause, and healthy, cycling women. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Serum levels of the sex steroids (estrogen, progesterone, and testosterone) and of Ca2+ and Mg2+ were measured in menopausal and postmenopausal women, and in healthy, cycling women at five different stages of the menstrual cycle. RESULT(S): The Mg2+ and total Mg levels of the postmenopausal women were inversely related to the serum level of estrogen and were similar to the levels present during the early follicular phase of healthy women of child-bearing age. The Ca2+ level was unrelated to the sex steroid hormones present, but it was increased compared with that of younger women in both the follicular phase and the luteal phase. CONCLUSION(S): Serum levels of Mg2+ and total Mg were inversely correlated with the estrogen concentration in menopausal women. Serum levels of Ca2+ were significantly elevated in menopausal women compared with younger women, but the ratio of Ca2+ to Mg2+, a measure of cardiovascular problems, was not elevated in the postmenopausal women.

Aged↗
PubMed1999

Evaluation of volatile eluents and electrolytes for high-performance liquid chromatography-electrospray ionization mass spectrometry and capillary electrophoresis-electrospray ionization mass spectrometry of proteins. I. Liquid chromatography.

Proteins ranging in molecular mass from 14,000 to 80,000 were analyzed by reversed-phase high-performance liquid chromatography-electrospray mass spectrometry (RP-HPLC-ESI-MS) using 60 x 1.0 mm I.D. microbore-columns packed with 2.3 microns highly crosslinked, octadecylated poly(styrene-divinylbenzene) particles. Proteins were eluted at temperatures of 80-90 degrees C with gradients of acetonitrile in 0.10-0.50% aqueous solutions of trifluoroacetic acid, formic acid or acetic acid. Substitution of trifluoroacetic acid, the most commonly used mobile phase additive for RP-HPLC, by formic acid resulted in a 35-160-fold improvement in analyte detectability at the cost of an only 32-104% increase in peak width at half height of eluting chromatographic peaks. The lower limits of detection for carbonic anhydrase (M(r) 29,022.7) in full scan and selected ion monitoring mode were 37 and 2.3 fmol, respectively. Measurement of protein masses by RP-HPLC-ESI-MS was accurate and highly reproducible with maximum mass deviations of 0.025% and relative standard deviations of less than 0.011%. Calibration plots of peak area versus concentration allowed the reliable quantitation of proteins in a concentration range of 0.010-1.0 mg/ml. Finally, the optimized method was applied to the separation, identification and quantification of proteins in real samples such as commercial protein preparations, monoclonal antibody fragments, allergen extracts and whey drinks.

Chromatography, High Pressure Liquid↗