PubMed · 11510857
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C M Harris. 2001-08-01. LED source becomes a sensor.. https://doi.org/10.1021/ac012492j
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An adaptation of the HPLC method previously described for the simultaneous assay of amprenavir, ritonavir, indinavir, saquinavir, nelfinavir and efavirenz after solid-phase extraction is proposed here for the separate analysis of the newer PI lopinavir (LPV) and the NNRTI nevirapine (NVP). After viral inactivation by heat (60 degrees C for 60 min), plasma (600 microl), with clozapine added as internal standard, is diluted 1+1 with phosphate buffer pH 7 and subjected to a solid-phase extraction on a C(18) cartridge. Matrix components are eliminated with 2 x 500 microl of a solution of 0.1% H(3)PO(4) neutralised with NaOH to pH 7. LPV and NVP are eluted with 3 x 500 microl MeOH. The resulting eluate is evaporated under nitrogen at room temperature and is reconstituted in 100 microl MeOH 50%. A 40-microl volume is injected onto a Nucleosil 100, 5 microm C(18) AB column. LPV and NVP are analysed separately using a gradient elution program with solvents constituted of MeCN and phosphate buffer adjusted to pH 5.07 and containing 0.02% sodium heptanesulfonate. LPV and NVP are detected by UV at 201 and 282 nm, respectively. The calibration curves are linear up to 10 microg/ml. The mean absolute recovery of LPV and NVP is 91% and 88%, respectively. The method is precise with mean inter-day C.V.s within 2.1-6.6% and 0.9-1.7% for LPV and NVP, and accurate (range of inter-day deviations -1.1 to +2.4%, and -1.9 to +0.8%, for LPV and NVP, respectively). The method has been validated and is currently applied to the monitoring of LPV and NVP in HIV patients, and has been notably applied in a study aimed at assessing the extent of transplacental passage of nevirapine and PIs, notably lopinavir, at the time of delivery in pregnant HIV-infected women.
We have developed a simultaneous quantification method for prostaglandin (PG) E(2), PGD(2), PGF(2 alpha), 8-epi-PGF(2 alpha), 6-keto-PGF(1 alpha) and thromboxane (TX) B(2). Using [3,3,4,4-(2)H(4)]PGE(2), [3,3,4,4-(2)H(4)]PGD(2), [3,3,4,4-(2)H(4)]8-epi-PGF(2 alpha), [3,3,4,4-(2)H(4)]PGF(2 alpha), [3,3,4,4-(2)H(4)]6-keto-PGF(1 alpha) and [18,18,19,19-(2)H(4)]TXB(2) as internal standards (I.S.), the eicosanoids and their I.S. were simultaneously extracted by solid-phase extraction from cell-cultured medium, derivatized to methyl ester/methoxim/tert.-butyldimethylsilyl ether derivatives and analyzed using gas chromatography-mass spectrometry in the selected ion monitoring mode. The accuracy for the added eicosanoids ranged from 92 to 113%, and coefficients of variation ranged from 0.1 to 12.2%. Increased eicosanoids in RAW264.7 and U937 cells stimulated by lipopolysaccharide were suppressed by NS-398 and indometacin. This simultaneous quantification method can be applied routinely for assaying eicosanoids in vitro.
When the assumption of homoscedasticity is not met for analytical data, a simple and effective way to counteract the greater influence of the greater concentrations on the fitted regression line is to use weighted least squares linear regression (WLSLR). The purpose of the present paper is to stress the relevance of weighting schemes for linear regression analysis and to show how this approach can be useful in the bioanalytical field. The steps to be taken in the study of the linear calibration approach are described. The application of weighting schemes was shown by using a high-performance liquid chromatography method for the determination of lamotrigine in biological fluids as a practical example. By using the WLSLR, the accuracy of the analytical method was improved at the lower end of the calibration curve. Bioanalytical methods data analysis was improved by using the WLSLR procedure.