No abstract

No abstract

No abstract

No abstract

Two simple and accurate spectrophotometric methods for determination of timolol and enalapril maleate are described. The first method is based on chelate formation with palladium(II) chloride in buffered medium. The second method is based on the formation of the colored complex between palladium(II), eosin, and the two cited drugs using methylcellulose as surfactant to increase the solubility and intensity of the formed complexes. Under optimum conditions the complexes showed maximum absorption at 369.4 nm and 362.8 nm for timolol and enalapril maleate, respectively, in the first method and 552.2 and 550.6 nm for the second method. Apparent molar absorptivities were 1.8 x 10(3) and 1.3 x 10(3) and Sandell's sensitivities were 5.9 x 10(-4) and 2.7 x 10(-4) for timolol and enalapril maleate in the first method; in the second method molar absorptivities were 2.8 x 10(4) and 1.1 x 10(4) while Sandell's constants were 9.1 x 10(-3) and 2.3 x 10(-3) for timolol and enalapril maleate. The solutions of the complexes obeyed Beer's law in the concentration ranges 20-200 micro g mL(-1) and 50-300 micro g mL(-1) for timolol and enalapril maleate, respectively. In the second method, because the reaction was more sensitive the ranges were reduced to 1.6-16 micro g mL(-1) for timolol 8-56 micro g mL(-1) for enalapril maleate. The proposed methods were applied to the determination of the two drugs in their pharmaceutical formulation.

A simple, sensitive and rapid liquid-liquid extraction method for the analysis of nicotinic acid (niacin) and its labeled internal standard nicotinic acid-d4 (niacin-d4) in human plasma was developed and validated. The analyte and its internal standard were isolated from acidified plasma using a single liquid-liquid extraction procedure with methyl-t-butyl ether. The extracted samples were analyzed by liquid chromatography-tandem mass spectrometry in positive electrospray ionization mode with multiple reaction monitoring. The calibration curves were linear in the measured range between 5 and 1000 ng/mL and the limit of detection was calculated as 122 pg/mL. The method required 250 microL of human plasma and the total run time between injections was 3.5 min. Matrix effects were assessed by post-column infusion experiments, phospholipids monitoring and post-extraction addition experiments. The extraction of phospholipids and niacin from plasma was studied under acidic, neutral and basic conditions. Acidic conditions were optimal for both the recovery of niacin and the removal of phospholipids; the degree of matrix effects for niacin was determined to be 2.5%. It was concluded that effective removal of matrix components can overcome low recovery issues associated with liquid-liquid extractions of polar analytes.

No abstract

No abstract