Automated gas chromatography/tandem mass spectrometry assay for tebufelone and a 13C,(18)O-labeled analog in plasma: applicabilityto absolute bioavailability determination

High-performance liquid chromatographic-tandem mass spectrometric evaluation and determination of stable isotope labeled analogs of rofecoxib in human plasma samples from oral bioavailability studies

A method for the simultaneous determination of a cyclooxygenase-2 inhibitor, 4-(4-methanesulfonylphenyl)-3-phenyl-5H-furan-2-one (rofecoxib, I) and [13C7]rofecoxib, (II), in human plasma has been developed to support the clinical oral bioavailability (BA) study of I. The method is based on high-performance liquid chromatography (HPLC) with atmospheric pressure chemical ionization tandem mass spectrometric (APCI-MS-MS) detection in the negative ionization mode using a heated nebulizer interface. Two different stable isotope labeled analogs of I were initially evaluated for their use as intravenous (i.v.) markers in the BA study. [13CD3]Rofecoxib was shown to be isotopically unstable in plasma and water containing solvent and an efficient deuterium exchange prevented its use in the study. On the other hand, the isotopic integrity of the subsequently synthesized [13C7]rofecoxib (II) was maintained, as expected, in plasma and other solvent systems. The results of these experiments clearly demonstrated the need for the careful evaluation of the isotopic integrity of the stable isotope labeled compound for the successful utilization of these compounds in BA studies and also as internal standards in the quantitative analysis of drugs in biological fluids. After liquid-liquid extraction of I, II, and internal standard (III) from plasma, the analytes were chromatographed on a narrow bore (100 mm x 3.0 mm) C18 analytical column, with mobile phase consisting of acetonitrile-water (1:1, v/v) at a flow-rate of 0.5 ml/min. The MS-MS detection was performed on a PE Sciex API III Plus tandem mass spectrometer operated in the selected reaction monitoring mode. The precursor-->product ion combinations of m/z 313-->257, 320-->292, and 327-->271 were used to quantify I, II, and III, respectively. The assay was validated in the concentration range of 0.1 to 100 ng/ml of plasma for both I and II. The precision of the assay (expressed as relative standard deviation) was less than 10% at all concentrations within the standard curve range, with adequate assay accuracy. The assay was utilized to support the clinical BA study in which oral doses of I were administered together with an i.v. dose of II to determine the oral BA of rofecoxib at 12.5- and 25-mg doses.

Simultaneous determination of unlabeled and carbon-13-labeled etoricoxib, a new cyclooxygenase-2 inhibitor, in human plasma using HPLC-MS/MS

A method for the simultaneous determination of etoricoxib and its carbon-13 analog ((13)C(6)-etoricoxib) from human plasma has been developed and used to support bioavailability studies. Plasma samples (0.5 mL) were extracted by using a 3M Empore 96-well plate (C(8)) and the resulting extracts were analyzed by using a PE-Sciex API-3000 HPLC-MS/MS with a heated nebulizer interface (500 degrees C). The method was validated with two different calibration curve ranges, one for etoricoxib (5 to 2500 ng/mL) determined in the presence of lower concentrations of (13)C(6)-etoricoxib (0.5 to 250 ng/mL), and a second curve for the quantitation of similar concentrations of both etoricoxib and (13)C(6)-etoricoxib (0.5 to 250 ng/mL). Extraction recoveries of etoricoxib, (13)C(6)-etoricoxib, and a methylated internal standard were >70% over the range of concentrations included in both calibration curves. Intraday precision and accuracy for the quantitation of etoricoxib were 7.8% relative standard deviation (RSD) or less and within 3.4% respectively over the range of 5 to 2500 ng/mL, and 10.8% RSD or less and within 4 % respectively over the range of 0.5 to 250 ng/mL. Within-batch precision and accuracy for the quantitation of (13)C(6)-etoricoxib over the range of 0.5 to 250 ng/mL were 8.3% RSD or less and within 2.3%, respectively. The validated assay was used in support of human clinical trials.

Hyphenated chromatographic methods for biomaterials

The improvement in hyphenated analytical techniques has significantly widened their applications to the analysis of biomaterials. In this article, we discuss recent advances in applications of hyphenated chromatographic techniques including capillary electrophoresis to the analyses of biological samples. As tools of separation, gas chromatography, high-performance liquid chromatography and capillary electrophoresis are considered with special emphasis on applications utilizing the hyphenation of these methods to mass spectrometry. Moreover, applications using other detection methods such as Fourier transform infrared spectroscopy hyphenated to gas chromatography and photodiode array detector combined with high-performance liquid chromatography or capillary electrophoresis are also discussed. Owing to their high sensitivity, luminescence-based detection systems such as laser-induced fluorescence and chemiluminescence are also included in this review.

Simultaneous determination of unlabeled and deuterium-labeled indinavir in human plasma by high-performance liquid chromatography with tandem mass spectrometric detection

A method for the simultaneous determination of indinavir and its hexadeuterated analog (d6-indinavir) in human plasma is described. Isolation of the analytes and internal standard from plasma was achieved via liquid-liquid extraction with methyl-t-butyl ether. The analytes were chromatographed under reversed-phase conditions on a BDS-Hypersil C8 column. A Sciex API III+ tandem mass spectrometer equipped with a turbo ion-spray interface was used as the detector. Multiple reaction monitoring using the parent-->product ion combinations of m/z 614-->465, 620-->471 and 654-->505 were used to quantify indinavir, d6-indinavir, and internal standard, respectively. The method was validated, using 1-mL aliquots of plasma, in the concentration range in plasma of 1 to 200 ng/mL. Precision of the assay, as measured by the coefficient of variation, ranged from 0.9 to 4.3% and 0.9 to 6.2% for indinavir and d6-indinavir, respectively. Indinavir assay accuracy ranged from 95.8 to 105.0% of nominal, whereas the accuracy of the assay for d6-indinavir ranged from 97.4 to 104.0% of nominal. The assay was used to support a clinical study in which the stable isotope technique was used to determine the bioavailability of indinavir.

Direct injection for high sample throughput capillary gas chromatographic-mass spectrometric bioanalysis

Because of the drawback of the relatively long analysis times inherent to temperature-programmed splitless injection capillary GC-MS, isothermal direct injection capillary GC-MS was investigated for quantitative bioanalysis. Using extracts from spiked plasma samples, we showed that high quality chromatography with a run time much shorter than that achievable with splitless injection can be achieved with direct injection. Sensitivity and other performance parameters were as good as or better than those of the splitless method. Since sample throughput is of great importance in laboratories that analyze thousands of biological samples, it is recommended that, when possible, splitless injection, which has traditionally been used in trace level GC-MS bioanalytical methods, be replaced by direct injection.

Rapid liquid chromatographic-mass spectrometric assay for oxymetazoline in whole rat blood

A rapid HPLC-electrospray mass spectrometric assay for the quantitation of oxymetazoline in whole rat blood has been developed. Sample preparation was a single liquid-liquid extraction after addition of a deuterated internal standard (IS) and pH adjustment. An aliquot of reconstituted extract was injected onto a narrow-bore octadecyl reversed-phase column at a flow-rate of 400 microliters/min. Using a 20:1 post-column split, 5% of the eluent was introduced into the mass spectrometer interface. Elution of the analyte and IS occurred in less than 2 min. This rapid separation was made possible because of the sample cleanup and the selectivity of the mass spectrometric detection. The [M+H]+ ions for oxymetazoline (m/z 261) and [2H9]oxymetazoline (m/z 270) were detected using selected ion monitoring. The linear range of the assay was 0.67-167 ng/g of blood and the limit of quantitation with a 0.30-g sample was 1.0 ng/g. The assay permitted the analysis of nine samples per hour with the requisite sensitivity and selectivity and was used to determine the blood pharmacokinetics of oxymetazoline in rats dosed via intravenous and intranasal routes.