Chromatography-negative Ion Chemical Ionization-mass Spectrometry Research Articles

Confirmation of clorsulon residues in cattle kidney by capillary gas chromatography—negative-ion chemical-ionization mass spectrometry

A confirmatory assay for residues of the anthelmintic agent clorsulon [4-amino-6-(trichloroethenyl)-1,3-benzenedisulfonamide] in cattle kidney tissue has been developed. The assay involves isolation of a drug-containing fraction by solvent extraction, methylation of the analyte, and fused-silica capillary column gas chromatography—negative-ion chemical-ionization mass spectrometry of the pentamethyl derivative of clorsulon. The intensities of four negative ions [ m/z 406 and 408 (trichloro species) and m/z 413 and 415 (dichloro species)] are monitored. Confirmation of the presence of drug in an analyte requires that all four ions appear at the appropriate retention time with their intensity ratios within 10–15% of those arising from analysis of the reference standard, methylated clorsulon; the lower limit of detection is 3 ppb. Quantification of the drug is based on the intensity of the m/z 406 ion. Identification and quantification of residues by the gas chromatographic—mass spectrometric assay gave results in good agreement with those obtained with an electron-capture gas chromatographic assay.

Purification and quantitative analysis of urinary prostanoids in human and in rat by packed and capillary gas chromatography—negative-ion chemical-ionization mass spectrometry

We describe a method for the quantitative analysis of prostaglandin (PG) E 2 and the major urinary metabolites PGI 2 and thromboxane (Tx) A 2 in human and in rat by combined gas chromatography and negative-ion chemical-ionization mass spectrometry. The procedure is based on the sequential use of small columns with distinct properties combined with a thin-layer chromatography step, for the extraction and the purification of urinary prostaglandins. The compounds are then analysed as their pentafluorobenzyl ester-O-methyloxime-trimethylsilyl ether derivatives, using either packed or capillary columns. Deuterated analogues are used as internal standards. The method was established by using tritiated prostaglandins covering the extremes of polarity in order to optimize the recovery of prostanoids as well as the quality of the chromatograms and spectra. The overall recovery was 24%. Standard curves were obtained by the same procedure and found to be reproducible, with a maximal day-to-day variation of ±5%. The relatively simple approach required for the sequential extraction and purification of prostaglandins on small columns of distinct properties, combined with the highly specific and highly sensitive method of detection, places this procedure among the most reliable method for measuring urinary prostanoids in both humans and animals. In addition, the procedure is faster than classical approaches and necessitates smaller amounts of samples and solvents.

Long-lived enzymatic metabolites of thromboxane B 2 in the human circulation

Thromboxane A 2, a potent vasoconstrictor and platelet agonist, is an evanescent cyclooxygenase product of arachidonic acid. Assessment of thromboxane biosynthesis commonly relies upon analysis of the stable but biologically inactive hydration product, thromboxane B 2. However, measurement of this compound in plasma is readily confounded by platelet activation ex vivo. We have identified 11-dehydro-thromboxane B 2, 11-dehydro-13,14-dihydro-15-keto-thromboxane B 2, and 2,3-dinor-thromboxane B 2 as enzymatic products of infused thromboxane B 2 in the human circulation. Biosynthesis of deuterated standards permitted the development of quantitative analyses for these compounds, employing capillary gas chromatography-negative ion chemical ionization-mass spectrometry. We thus established that the postinfusion half-lives of 11-dehydrothromboxane B 2 and the keto-dihydro metabolite approximated 1 hour, while that of the dinor metabolite ranged from 15 to 17 min. Combined analysis of short- and long-lived enzymatic metabolites of thromboxane B 2 promises to bypass the problem of ex vivo platelet activation and enhance the likelihood of relating a discreet clinical event to an alteration in the biosynthesis of thromboxane A 2 in the human circulation.

Incorporation of2H from2H2O into ABA in Tomato Shoots: Evidence for a Large Pool of Precursors

Incorporation of²H from²H₂O into ABA in Tomato Shoots: Evidence for a Large Pool of Precursors

Determination of ketocyclazocine in human plasma by gas chromatography—negative-ion chemical-ionization mass spectrometry

Determination of ketocyclazocine in human plasma by gas chromatography—negative-ion chemical-ionization mass spectrometry

Sensitive determination of tyrosine metabolites, p-hydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenyl-acetic acid and 4-hydroxy-3-methoxymandelic acid, by gas chromatography—negative-ion chemical-ionization mass spectrometry : Application to a stable isotope-labelled tracer experiment to investigate their metabolism in man

A method has been established for studying the dynamic metabolism of tyrosine to its metabolites in humans using a deuterium-labelled amino acid. Phenylalanine-d 5 was administered orally to human subjects (5 mg/kg) and the levels of p-hydroxyphenylacetic acid-d 4, 4-hydroxy-3-methoxyphenylacetic acid-d 3, and 4-hydroxy-3-methoxymandelic acid-d 3 excreted into urine every hour were determined by gas chromatography—negative-ion chemical-ionization mass spectrometry. This method was also applied to some patients with depression and it was possible to detect a slight alteration in the excretion of some compounds compared with the control.

Determination of acetyltrimoprostil and its metabolite trimoprostil in human or dog plasma by gas chromatography—negative-ion chemical ionization mass spectrometry

A sensitive and specific procedure is described for the determination of the antisecretory prostaglandin acetyltrimoprostil and its metabolite trimoprostil in human or dog plasma using gas chromatography—negative-ion chemical ionization mass spectrometry (GC—NICI- MS). Trideuterated analogues of both compounds are added to plasma as the internal standards. The plasma is extracted at pH 7.3 with benzene—dichloromethane (9:1), and the residue of the organic extract is reacted at room temperature with pentafluorobenzyl bromide in the presence of 18-crown-6-ether and potassium acetate. The derivatives are reconstituted in heptane, and appropriate aliquots are analyzed by GC—NICI-MS with selected-ion monitoring of the intense (M - C 6F 5CH 2) − fragment ions of acetyltrimoprostil ( m/ z 419), trimoprostil ( m/ z 377), and their respective trideuterated analogues ( m/ z 422 and m/ z 380, respectively). Quantitation of an experimental plasma sample is based on a comparison of the m/ z 419 versus m/ z 422 and m/ z 377 versus m/ z 380 ion ratios in each sample to that obtained from the analysis of drug-free plasma fortified with various amounts of both protio compounds, and a fixed amount of each trideuterated internal standard. The limit of quantitation of the assay for human plasma is 0.2 ng ml −1 with mean relative standard deviations at this concentration of 15.5% and 9.7% for acetyltrimoprostil and trimoprostil, respectively.

Determination of low plasma concentrations of 3-methoxy-4-hydroxyphenylethylene glycol using gas chromatography—negative-ion chemical ionization mass spectrometry

Gas chromatography—negative-ion chemical ionization mass spectrometry (GC—NICI-MS) allowed the detection of extremely low plasma concentrations of 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG). Glucuronide and sulphate conjugates of MHPG were determined after enzymatic hydrolysis of plasma with β-glucuronidase—arylsulphatase. A 1-ml plasma sample was extracted at the pH of the hydrolysis (pH 4.8) with ethyl acetate, and the dry extract was derivatized with pentafluoropropionic anhydride in ethyl acetate. After evaporation of the solvent, the residue was dissolved in benzene and an aliquot was analysed by GC—NICI-MS. A trideuterated analogue of MHPG was used as an internal standard. Negative-ion chemical ionization of the pentafluoropropionyl derivatives was carried out using ammonia. The ion—molecule adducts at m/e 766 and 785 (MHPG) and m/e 769 and 788 (internal standard) were formed from the pentafluoropropionyl derivatives with the ions of m/e 163 (CF 3,CF 2,COO −) and m/e 144 (loss of fluorine from m/e 163). The concentrations of the ions of m/e 163 and 144 play a major role in the sensitivity and precision of this technique, which allows the detection of free MHPG plasma concentrations as low as 100 pg/ml in routine analysis.

Assay methods for 6-keto-prostaglandin F 1α in human urine : Comparison of chromatographic techniques with radioimmunoassay and gas chromatography—negative-ion chemical-ionization mass spectrometry

6-Keto-prostaglandin F 1α (6-keto-PGF 1α) in human urine is considered to be a reflection of renal prostacyclin production. Because of the large amounts of unidentified eicosanoid metabolites in urine that may potentially bind to 6-keto-PGF 1α antisera, most radioimmunoassays include chromatographic purification of urine. A comparison of chromatographic techniques and of antisera to 6-keto-PGF 1α for the assay of human urine is described. Gas chromatography—negative-ion chemical-ionization mass spectrometry (GC—NICI-MS) was used as the reference method. Radioimmunoassays were performed with each of four antisera combined with each of three chromatographic purification systems (silicic acid, Sephadex LH-20, reversed-phase high-performance liquid chromatography). There was marked variability in the results; however, there was at least one chromatographic method for each antiserum that yielded results comparable to GC—NICI-MS. Direct radioimmunoassay of urine without chromatography yielded markedly elevated and variable results for the four antisera. In contrast, the four antisera gave very similar results with direct assay of media from isolated perfused organs. Thus, for the radioimmunoassay of 6-keto-PGF 1α in human urine, each antiserum is sensitive to different contaminants in urine and must be individually matched to a chromatographic purification system.

Determination of nilvadipine in human plasma by capillary column gas chromatography—negative-ion chemical-ionization mass spectrometry

A highly sensitive and specific method for the determination of nilvadipine, a new dihydropyridine calcium antagonist, in human plasma is described. A deuterated analogue of nilvadipine is added to the plasma as an internal standard. The agent and its internal standard are extracted at pH 9 from the plasma into a benzene— n-hexane (1:1) mixture. The extract is analysed by fused-silica capillary column gas chromatography—negative-ion chemical-ionization mass spectrometry with methane as the reagent gas. The mass spectrometer is set to monitor the negative molecular ions of the agent and internal standard. Quantitation is possible down to 0.01 ng/ml using 1 ml of plasma. The coefficients of variation of the method are 6.4 and 2.1% at the 0.01 and 0.1 ng/ml levels, respectively. Plasma levels obtained with this method are given for four healthy volunteers who had received a 6-mg oral dose of nilvadipine.

Quantitation of cibenzoline in human plasma by gas chromatography—negative-ion chemical-ionization mass spectrometry

Quantitation of cibenzoline in human plasma by gas chromatography—negative-ion chemical-ionization mass spectrometry