Analytical methods plasma assays

Kobylinska et al. [62] described a high performance liquid chromatographic analytical method for the determination of miconazole in human plasma using solid-phase extraction. The method uses a solid-phase extraction as the sample preparation step. The assay procedure is sensitive enough to measure concentrations of miconazole for 8 h in a pharmacokinetic study of Mikonazol tablets and Daktarin tablets in human volunteers. The pharmacokinetics of the two formulations was equivalent. 

Extensive literature reviews (554, 555) have indicated that almost all reported analytical methods for the analysis of diuretics employ liquid chromatography. Most of these methods are limited, however, to assaying diuretics in urine and plasma. With the exception of a liquid chromatographic method for the determination of furosemide, another one for chlormethiazide, and a third method for chlorothiazide and hydrochlorothiazide residues in bovine milk, no chromato-... 

A rapid, sensitive, and enantioselective LC-MS-MS method using deuterium-labeled IS was developed and evaluated for the simultaneous quantitative determination of donepezil enantiomers in human plasma without interconversion during clean-up process and measurement [37]. The use of an avidin column allowed the separation of donepezil enantiomers, which were specifically detected by MS-MS without interference from its metabolites and plasma constituents. Evaluation of this assay method shows that samples can be assayed with acceptable accuracy and precision within the range from 0.0206 to 51.6 ng/ml for both R-donepezil and S-donepezil. This analytical method was applied to the simultaneous quantitation of donepezil enantiomers in human plasma. 

The procedure for GLC analysis gave a lower limit for quantitation of 1 in plasma of approximately 1 ng/ml from twice the standard deviation (0.32 ng) obtained for the amount of 1 recovered from 2.25 ng in 2 ml of plasma. Similarly, the procedure for radiochemical analysis gave a lower limit of approximately 0.2 ng/ml from twice the standard deviation (0.084 ng). A statistical analysis of the apparent differences between the tetrahydrocannabinol assays at a given time from both analytical methods showed no significance. 

Wade et al. reported the use of a novel statistical approach for the comparison of analytical methods to measure angiotensin converting enzyme [peptidyl-dipeptidase A] activity, and to measure enalaprilat and benazeprilat [8]. Two methods were used to measure peptidyl-dipeptidase A, namely hippuryl histidyl leucine (HHL-method) [9], and inhibitor binding assay (IBA method) [10]. Three methods were used to measure enalaprilat, namely a radioimmunoassay (RIA) method [11], the HHL method, and the IBA method. Three methods were used to measure benazeprilat (then active metabolite of benazepril) in human plasma, namely gas chromatography-mass spectrometry (GC-MS method) [12], the HHL method, and the IBA method, and were statistically compared. First, the methods were compared by the paired t test or analysis of variance, depending on whether two or three different methods were under comparison. Secondly, the squared coefficients of variation of the... 

Dietary constituents or drugs can either cause direct analytical interference in assays or influence the physiological processes that determine plasma and urinary levels of catecholamines and catecholamine metabolites. In the former circumstances, the interference can be highly variable depending on the particular measurement method. In the latter circumstances, interference is usually of a more general nature and independent of the measurement method (Table 29-6). 

Elements in an immunoassay that could impact its robustness include incubation temperatures, light exposure (enzyme-linked immunosorbent assay, ELISA), and different lots of matrix (plasma, serum CSF). The ruggedness of the analytical method can be tested by implementing changes to the analysts, different instruments, batch size, and the day, time, or other environment factors otherwise should not greatly impact the consistency of the assay. 

Many problems have existed with analytical methods of the determination of aluminium, and have been detailed by Cornells and Schutyser in a review of analytical problems related to these assays (Cornells and Schutyser, 1984). This review included data published since 1974 on aluminium in serum (or plasma) and urine of normal healthy individuals. In one group, 19 mean values of serum aluminium were listed for their respective normal range studies. These mean values ranged from 2.1-4.2 normal mean concentrations ranging from 72 to 1460 //g/L although obvious interferences were present in these methods. The literature survey of Cornelis and Schu-... 

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