Determination of eperisone in human plasma by gas chromatography—mass spectrometry

A gas chromatographic—mass spectrometric method was developed to determine eperisone hydrochloride, 4′-ethyl-2-methyl-3-piperidinopropiophenone hydrochloride, in human plasma over the concentration range 0.2–40 ng/ml. Excellent sensitivity was achieved by selection of a favorable fragment ion, m/z 98, of eperisone and reduction of heat decomposition of eperisone by using a splitless injector and a shortened capillary column. The method described here allows the determination of plasma concentrations as low as 0.2 ng/ml, the concentration attained 6 h after a single oral administration of 50 mg. At eperisone hydrochloride concentrations higher than 0.5 ng/ml, the mean inter-day variation of accuracy of the assay was less than 12%.     

Determination of cyclophosphamide in urine by gas chromatography—mass spectrometry

A sensitive gas chromatographic method for the determination of cyclophosphamide in urine is presented. After liquid—liquid extraction with diethyl ether and derivatization with trifluoroacetic anhydride, cyclophosphamide was identified and quantified with mass spectrometry. The method is suitable for the determination of cyclophosphamide at concentrations of more than 0.25 ng/ml, which enables the uptake of cyclophosphamide during occupational activities, such as the preparation and administration of antineoplastic agents in hospitals, to be measured. Simple preparation makes the method appropriate for routine analysis.     

Determination of clofilium, a new antifibrillatory agent, in plasma by gas chromatography—mass spectrometry

A sensitive and selective method for the assay of the new quaternary amine antifibrillatory agent clofilium is described. Plasma samples were extracted with dichloromethane (98.5 ± 0.2% recovery) and analyzed by gas chromatography—mass spectrometry operating in the electron-impact mode. The method involves a Hofmann elimination of an N-alkyl radical from clofilium and the internal standard in the presence of a strong nucleophile in the injector of the gas chromatograph. The resulting tertiary amines are chromatographed and detected by selective ion monitoring. The ratio of the clofilium base peak (m/z 224) to the internal standard peak (m/z 210) was linear relative to the plasma clofilium concentration over the range of 25–1000 ng/ml plasma.     

Determination of 9α,11β-prostaglandin F2 in human urine and plasma by gas chromatography—mass spectrometry

Sensitive and specific assay methods for 9α,11β-prostaglandin F₂ (9α,11β-PGF₂) by gas chromatography—mass spectrometry with electron impact ionization are described. The mass spectrometric assay for 9α,11β-PGF₂ was based on the use of the methyl ester—dimethylisopropylsilyl ether derivative, and pentadeuterated PGF_2α as a convenient internal standard. The calibration graph for 9α,11β-PGF₂ was linear from 5 pg to 100 ng for both the standard and spiked biological samples. The limit of detection was 50 pg/ml for urine and 25 pg/ml for plasma (signal-to-noise RATIO = 2.3). The method was applied to the determination of 9α,11β-PGF₂ in urine and plasma samples from patients with bronchial asthma.     

Determination of plasma propofol levels using gas chromatography—mass spectrometry with selected-ion monitoring

Propofol (2,6-diisopropylphenol, I.C.I. 35 868) is a rapid-acting, intravenous anesthetic agent recently introduced for the induction and maintenance of general anesthesia. This paper describes a gas chromatographic—mass spectrometric procedure using selected-ion monitoring for the determination of plasma propofol levels. The drug and the internal standard (thymol) were extracted from plasma into diethyl ether—pentane, and derivatized to their trimethylsilyl derivatives before analysis. The reproducibility of the daily standard curves had coefficients of variation ranging from 2.7% to 10.2%. The precision of the assay yielded a coefficient of variation ranging from 4.5% to 5.6%, and the concentration means for the seeded control samples were found to be within −1.6% to +0.6% of the theoretical values for propofol. No interfering peaks have been observed in application of this procedure to either normal volunteer or patient samples. The minimum detectable level under the conditions described was 0.20 ng propofol/ml plasma. This assay and a high-performance liquid chromatographic assay with fluorescence detection were both used to measure plasma propofol concentrations in 89 human plasma samples, and the correlation between the two methods was excellent.     

Specific determination of plasma nicardipine hydrochloride levels by gas chromatography—mass spectrometry

A highly specific method for the determination of the plasma level of the potent vasodilator 2-(N-benzyl-N-methylamino)ethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine carboxylate hydrochloride (nicardipine hydrochloride) in rats, dogs and humans is described. N-d₃-Methyl derivative was added as an internal standard, then the plasma was extracted with diethyl ether and subjected to thin-layer chromatography (TLC) to remove the pyridine analogue, one of the drug's metabolites. The area corresponding to the unchanged drug was identified with simultaneously run N-d₇-benzyl derivative under UV light. The unchanged drug with a 1,4-dihydropyridine structure was oxidized with nitrous acid to its pyridine analogue, which was stable for gas chromatography, and subjected to mass spectrometry at m/e 134 (nicardipine) and m/e 137 (N-d₃-methyl derivative). The sensitivity limit was 5 ng ml⁻¹. The ratio of the unchanged drug to the value obtained by the method without TLC separation was 100% for rats and 80% for dogs and humans at almost all times investigated after dosing. These results demonstrate that in these species, the amount of pyridine analogue in plasma was very small compared with that of the parent drug.     

Determination of (-)-threo-chlorocitric acid in human plasma by gas chromatography—positive chemical-ionization mass spectrometry

A method is described for measuring (-)-threo-chlorocitric acid in human plasma. Plasma is acidified to pH 1 to minimize lactonization and a¹³C analogue of (-)-threo-chlorocitric acid is added as internal standard. The acidified plasma is then extracted with ethyl acetate containing 10% methanol. The ethyl acetate—methanol extract is back-extracted with acetate buffer (pH 5). This extract, following adjustment to pH 1, is reextracted with ethyl acetate. The residue after removal of the ethyl acetate is treated with ethereal diazomethane. The wet residue is reconstituted in ethyl acetate and a portion of this solution is analyzed by gas chromatography—chemical ionization mass spectrometry. The mass spectrometer is set to monitorm/z269 [MH⁺ of trimethylated (-)-threo-chlorocitric acid] andm/z270 [MH⁺ of trimethylated (-)-threo-[¹³C]chlorocitric acid] in the gas chromatographic effluent. Them/z/269 tom/z270 ion ratio in a sample containing an unknown amount of (-)-threo-chlorocitric acid is converted to an amount of compound using a calibration curve. The calibration curve is generated by analyzing control plasma spiked with various known amounts of (-)-threo-chlorocitric acid and a fixed amount of (-)-threo-[¹³C]chlorocitric acid. The limit of quantitation is 0.1–0.6 μg ml⁻¹, depending on the characteristics of the calibration curve generated with each set of samples. The precision (relative standard deviation) at a concentration of 2 μg ml⁻¹ is 3.3%.     

Determination of the anti-ulcer agent geranylgeranylacetone in serum by gas chromatography—mass spectrometry

A highly specific and sensitive method for the determination of the anti-ulcer drug geranylgeranylacetone (GGA) in human serum is described. The extract from serum with hexane was saponified with potassium hydroxide and subjected to silica gel column chromatography to remove interfering substances. GGA in the partially purified extract was then reacted with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and measured by selected ion monitoring using gas chromatography—mass spectrometry. A low detection limit (1 ng/ml) and high precision were obtained.     

Determination of 2-hydroxypropyl-γ-cyclodextrin in plasma of cynomolgus monkeys after oral administration by gas chromatography–mass spectrometry

This report describes a specific and highly sensitive gas chromatography–mass spectrometry (GC–MS) assay for the analysis of industrially produced 2-hydroxypropyl-γ-cyclodextrin, a heterogeneous mixture of homologues and isomers, in plasma of cynomolgus monkeys. Instead of analyzing the polysaccharide mixture as a whole, in a first step the HP-γ-cyclodextrin mixture, together with the internal standard (2,6-di-O-methyl-β-cyclodextrin), was deuteromethylated, and in a second step hydrolyzed with hydrochloric acid to the respective monosaccharides. The resulting reaction mixture was trimethylsilylated to 1,4-bis(O-trimethylsilyl)-2,3-bis-O-deuteromethyl-6-O-2′-deuteromethoxypropylglucose (representative for HP-γ-CD) and 1,4-bis-(O-trimethylsilyl)-bis-2,6-O-methyl-3-O-deuteromethylglucose (representative for the internal standard), respectively, and analyzed by GC–MS. The limit of quantification of this assay was 20 nmol/l.     

Determination of midazolam and two metabolites of midazolam in human plasma by gas chromatography—negative chemical-ionization mass spectrometry

A method is described for measuring midazolam, a new anesthesia induction agent and hypnotic, and its hydroxymethyl and desmethyl metabolites in human plasma. Deuterated analogues of each compound are added to plasma as internal standards. The compounds are extracted from plasma with benzene containing 20% 1, 2-dichloroethane and after removal of the extracting solvent are dissolved in a solution of bis-(trimethylsilyl)acetamide and acetonitrile. An aliquot of this solution is analyzed by gas chromatography—mass spectrometry with the mass spectrometer set to monitor in the gas chromatographic effluent the M$$$ ions of drug, metabolites and internal standards generated by methane electron-capture negative chemical ionization. For all three compounds, the limit of quantitation is 1 ng ml⁻¹, and the precision (relative standard deviation) at a concentration of 5 ng ml⁻¹ is less than 6%. Measurable amounts of the hydroxymethyl, but not the desmethyl, metabolite of midazolam could be found in the plasma of humans given either an intravenous or an oral dose of midazolam maleate.     

Determination of imidazobenzodiazepine-3-car☐amide, a new anxiolytic agent, in human plasma by gas chromatography—negative chemical-ionization mass spectrometry

A method is described for measuring imidazobenzodiazepine-3-car☐yamide, a new anxiolytic agent, in human plasma. A tetradeuterated analogue of the analyte is used as the internal standard. The drug and its internal standard are (1) extracted from plasma at pH 9 with benzene containing 20% 1, 2-dichloroethane, (2) derivatized with pentafluoropropionic anhydride in the presence of triethylamine and (3) the nitrile derivative of the analyte and internal standard are analyzed by gas chromatography (GC)—negative chemical-ionization mass spectrometry (CIMS) using methane as both GC carrier gas and CI reagent gas. The mass spectrometer is set to monitor the intense (M-HCl)⁻- ions of imidazobenzodiazepine-3-nitrile and its tetradeuterated analogue atm/z 316 andm/z 320, respectively. Quantitation of an experimental plasma sample is based on the comparison of them/z 316 tom/z 320 ion ratio in each sample to that obtained from the analyses of control plasma spiked with various amounts of the drug and a fixed amount of internal standard. The limit of quantitation of the method is approximately 100 pg ml⁻¹ of plasma and the precision (relative standard deviation) at a plasma concentration of 1 ng ml⁻¹ is 4%.     

Analysis of procarbazine and metabolites by gas chromatography—mass spectrometry

Twelve compounds representing procarbazine, seven metabolites, and an internal standard were analyzed by gas chromatography—mass spectrometry on a 3% OV-1 column. Procarbazine and four metabolites were derivatized with acetic anhydride.A sensitive, specific and quantitative assay was established by selected ion monitoring using a synthetic analogue of the drug as an internal standard. The limits of detection were approximately 1 ng/ml of plasma while the limits of quantitation were 10 ng/ml of plasma.Studies on the degradation of procarbazine - HCl in 0.05 M phosphate buffer (pH 7.4) were compared to in vivo studies. At 1 h after incubation of procarbazine - HCl in buffer, the azo and aldehyde metabolites were detected in the highest concentrations representing 27.2% and 20.3% of total drug and metabolites. In the in vivo studies, analyses of rat plasmas indicated that 1 h after an oral dose of procarbazine - HCl, the aldehyde metabolite represented 72% of the total drug and metabolites, and that relatively little of the azo metabolite was present.     

Determination of isoniazid and its hydrazino metabolites, acetylisoniazid, acetylhydrazine, and diacetylhydrazine in human plasma by gas chromatography—mass spectrometry

A gas chromatographic—mass spectrometric assay for isoniazid and its hydrazino metabolites in human plasma was developed. The trimethylsilyl derivatives of diacetylhydrazine and acetylisoniazid and of the benzaldehyde hydrazones of acetylhydrazine and isoniazid were separated on a 1% OV-17 column and quantitated by single ion monitoring using a LKB 9000 mass spectrometer. Deuterated analogues served as internal standards. The method is well suited for the determination of the hepatotoxic hydrazino metabolites of isoniazid in human plasma following an oral therapeutic dose of isoniazid.     

Determination of dioxopiperazine metabolites of quinapril in biological fluids by gas chromatography—mass spectrometry

The dioxopiperazine metabolites of quinapril in plasma and urine were extracted with hexane—dichloroethane (1:1) under acidic conditions. Following derivatization with pentafluorobenzyl bromide and purification of the desired reaction products using a column packed with silica gel, the metabolites were analysed separately by capillary column gas chromatography—electron-impact mass spectrometry with selected-ion monitoring. The limits of quantitation for the metabolites were 0.2 ng/ml in plasma and 1 ng/ml in urine. The limits of detection were 0.1 ng/ml in plasma and 0.5 ng/ml in urine, at a signal-to-noise ratio of > 3 and > 5, respectively. The proposed method is applicable to pharmacokinetic studies.     

Simplified assay for the quantification of 2,3-dinor-6-ketoprostaglandin F1α by gas chromatography—mass spectrometry

Endogenous prostacyclin production is best assessed by the measurement of its excreted metabolites, of which a major one is 2,3-dinor-6-ketoprostaglandin F_1α (2,3-dinor-6-keto-PGF_1α). Gas chromatographic—mass spectrometric (GC—MS) assays have been developed for this compound but are cumbersome and time-consuming. We now report a modified assay for the measurement of 2,3-dinor-6-keto-PGF_1α employing GC—MS in which sample preparation time is markedly shortened by replacing a number of extraction steps with reversed-phase column extraction and by modifying derivatization procedures. Precision of the assay is ± 5% and the accuracy is 98%. The lower limit of detection in urine is approximately 15 pg/mg creatinine. Normal urinary levels of this metabolite were found to be 141 ± 54 pg/mg creatinine (mean ± S.D.). Urinary excretion of 2,3-dinor-6-keto-PGF_1α is markedly altered in situations associated with abnormalities of prostacyclin generation when quantified using this assay. Thus, this assay provides a sensitive and accurate method to assess endogenous prostacyclin production and to further explore the role of this compound in human health and disease.     

Quantitation of propofol in whole blood by gas chromatography—mass spectrometry

A gas chromatographic—mass spectrometric assay, using selected-ion monitoring (GC-MS-SIM) with thymol as internal standard, was developed for quantitating propofol, an intravenous anaesthetic. The method described is rapid and sensitive for the determination of propofol in whole blood. The sensitivity of the present method is 10 ng/ml. The recovery of propofol added to human whole blood in the concentration range 10-10 000 ng/ml ranged between 95 and 100%. A single extraction procedure was used with chloroform-ethyl acetate. The assay allowed the detection of two metabolites formed during propofol metabolism: 2,6-diisopropyl-1,4-quinone and 2,6-diisopropyl-1,4-quinol.