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A set of experimental designs was applied to develop and validate a spectrophotometric method using derivative transformation coupled with zero-crossing methodology for the quantification of darifenacin hydrobromide in extended-release tablet form. In the presence of the matricial interference, a central composite (face-centered) design was necessary to reach the best condition without interference in the quantification. The optimal system was confirmed using the function named Derringer's desirability to assess high precision and low quantification limit. The best condition pointed was the first order to derivative transformation, Δλ = 4, scale factor 150, scanning speed 280 nm/s and anulation point in 239.4 nm as wavelength. From these parameters it was possible to perform the method validation resulting in R = 0.999, concentration ranging from 0.10 to 2.50 μg/mL, recovery 98.65% and mean precision 97.67% (RSD = 0.0136). Additionally, robustness was assessed by a Plackett-Burman design, and no significant variability was obtained. The spectrophotometric method was compared with high-performance liquid chromatography method, resulting in no significant difference between the methods. [ABSTRACT FROM AUTHOR]

This paper describes the validation of an HPLC method for the assay of a green tea brew. The method employs a RP-18 column with water:methanol:ethyl acetate elution and UV detection at 280 nm. Specificity was evaluated using a photodiode array detector. The validation data showed that the assay is specific, accurate, precise, and reproducible for determination of six catechins and caffeine simultaneously. The response was linear over a range of 37–185 μg mL−1 for caffeine, 99–500 μg mL−1 for (−)-epigallocatechin (EGC), 20–100 μg mL−1 for (+)-catechin (C), 30–150 μg mL−1 for (−)-epicatechin (EC), 150–800 μg mL−1 for (−)-epigallocatechin gallate (EGCG), 20–105 μg mL−1 for (−)-gallocatechin gallate (GCG) and 40–205 μg mL−1 for (−)-epicatechin gallate (ECG) ( r > 0.9999 for all compounds). The range of recoveries was 96.12–110.48% according to substances. The RSD values for intra- and inter-day precision studies were <2.07 and <6.65%, respectively. The composition of samples assayed suggests that the summer is the best season for extract a major content of EGCG and caffeine. This assay can be readily utilized as quality controlled method for major green tea compounds. [ABSTRACT FROM AUTHOR]

This study describes the development and full validation of a stability-indicating HPLC method to quantify ritonavir (RTV) and lopinavir (LPV) in soft gelatin capsules. The method uses a LiChrospher® 100 RP-18 (250 mm × 4.6 mm, 5 µm, Merck) column and isocratic elution. The mobile phase consisted of a mixture of acetonitrile-water-methanol (53:37:10, v/v/v), pumped at a flow-rate of 1.0 mL min−1 and UV detection at 210 nm using a photodiode array detector. LPV and RTV were exposed to thermal, photolytic, hydrolytic and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. The response was linear over a range of 40-360 µg mL−1 for LPV and 10–90 µg mL−1 for RTV ( r > 0,999 for both drugs). The mean recoveries were 99.46 and 100.81% for LPV and RTV, respectively. The RSD values for intra- and inter-day precision studies were < 0.70% for both drugs. Degradation studies showed that lopinavir is stable in thermal, alkaline and oxidative conditions, while ritonavir degraded under these conditions. The method was found to be stability-indicating and can be used for the routine analysis of the association LPV/RTV in soft gelatin capsules. [ABSTRACT FROM AUTHOR]