Flow-injection determination of sulphite and assay of sulphite oxidase

Sulphite (1–80 × 10^?5 M) in formaldehyde-stabilized solutions is determined by injection into a flowing stream of pH 8.5 phosphate buffer, passing through a mini-column of sulphite oxidase immobilized on controlled-pore glass, with amperometric detection of the hydrogen peroxide produced. Sulphite oxidase (5–100 U l^?) is determined by injection into a flowing stream of formaldehyde-stabilized 2 × 10^?3 M sodium sulphite in pH 8.0 phosphate buffer; hydrogen peroxide is again monitored.     

Development and Validation of Kinetic Spectrophotometric Method for the Determination of Losartan Potassium in Pure and Commercial Tablets

A validated kinetic spectrophotometric method has been developed for the determination of losartan potassium in pure and dosage forms. The method is based on oxidation of the losartan potassium with alkaline potassium permanganate at room temperature (25 ± 1 °C). The reaction is followed spectrophotometrically by measuring the increase in absorbance with time at 603 nm, and the initial rate, fixed time (at 12.0 min) and equilibrium time (at 90.0 min) methods are adopted for constructing the calibration graphs. All the calibration graphs are linear in the concentration range of 7.5–60.0 μg mL^?1 and the calibration data resulted in the linear regression equations of n? = ?6.422 × 10^?7 + 1.173 × 10^?5 C, A =3.30 × 10^?4 + 5.28 × 10^?3 C and A = ?2.09 × 10^?2 + 1.05 × 10^?1 C for initial‐rate, fixed time and equilibrium time methods, respectively. The limits of detection for initial rate, fixed time and equilibrium time methods are 0.71, 0.21 and 0.19 μg mL^?1, respectively. The activation parameters such as E_a, ΔH^?, ΔS^?, and ΔG^? are also determined for the reaction and found to be 87.34 KJ mol^?1, 84.86 KJ mol^?1, 50.96 JK^?1 mol^?1 and ?15.10 KJ mol^?1, respectively. The variables are optimized and the proposed methods are validated as per ICH guidelines. The method has been applied successfully to the estimation of losartan potassium in commercial tablets. The performance of the proposed methods was judged by calculating paired t‐ and F‐ values. The analytical results of the proposed methods when compared with those of the reference method show no significant difference in accuracy and precision and have acceptable bias.     

Determination of cholesterol by flow injection analysis with immobilized cholesterol oxidase

The injected sample passes through a column of enzyme immobilized on controlled pore glass, at pH 7.0, and the hydrogen peroxide produced is detected amperometrically. As little as 0.2 μg of cholesterol can be detected. The method is applied to blood serum, wax-wool alcohol and an extract of butter.     

Determination of glucose in blood by flow injection analysis and an immobilized glucose oxidase column

A flow-injection system for glucose determination is described. Glucose oxidase is immobilized on controlled porosity glass (CPG) and used in a glass column (2.5 mm diameter × 2.5 cm). The hydrogen peroxide produced by the enzymatic reaction (? 1 × 10^?6 M) is detected by the current produced in a flow-through cell, with two platinum electrodes having a potential difference of 0.6 V. Glucose (0–20 mmol l^?1) can be determined in blood plasma either with a dialyser in the system or, better, by incorporating a column of copper(II) diethyldithiocarbamate on CPG before the enzyme column. The results compared well with those obtained by a conventional analyser system. The glucose oxidase column showed little change in activity over a 10-month period.     

Quantitative analysis of irbesartan in commercial dosage forms by kinetic spectrophotometry

The objective of this work is to develop a new kinetic spectrophotometric method for the determination of irbesartan in pharmaceutical formulations. The method is based on the reaction of carboxylic acid group of the oxidized irbesartan with a mixture of potassium iodate (KIO(3)) and iodide (KI) to form yellow colored triiodide ions in aqueous medium at 30+/-1 degrees C. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 352 nm. The initial-rate and fixed-time (DeltaA) methods are adopted for constructing the calibration curves, which were found to be linear over the concentration ranges of 10.0-60.0 and 7.5-60.0 microg ml(-1) respectively. The regression analysis of calibration data yielded the linear equations: rate=-2.138 x 10(-6)+1.058 x 10(-4)C and DeltaA=-3.75 x 10(-3)+3.25 x 10(-3)C for initial rate and fixed time (DeltaA) methods, respectively. The limit of detection for initial rate and fixed time methods are 0.21 and 2.40 mug ml(-1), respectively. The various activation parameters such as E(a), DeltaH++, DeltaS++ and DeltaG++ are also calculated for the reaction and found to be 70.95+/-0.43 kJ mol(-1), 68.48+/-0.21 kJ mol(-1), 16.54+/-0.24 J K(-1) mol(-1) and -4.94+/-0.07 kJ mol(-1), respectively. The proposed methods are optimized and validated as per the guidelines of International Conference on Harmonisation (U.S.A.). The point and interval hypothesis tests have been performed which indicate that there is no significant difference between the proposed methods and the reference method. The methods have been successfully applied to the determination of irbesartan in commercial dosage forms.     

Immobilized enzymes in clinical and biochemical analysis : Applications to the Simultaneous Determination of Acetylcholine and Choline and to Determination of Lipids

Uses of immobilized enzyme mini-columns in flow-injection systems are described Simultaneous determination of ? × 10^?5 M choline and acetylcholine is achieved by using acetylcholinesterase and choline oxidase columns. A home-made amperometric detector is used to detec the hydrogen peroxide produced enzymatically. An ion-exchange column is used on-line to remove interferences at the amperometric detector during analysis of blood and brain samples. Immobilization of the lipid enzymes phospholipase-C and -D is described. These enzymes are used for the determination of phospholipids. Total phospholipids (1– mM) are determined with a combination of phospholipase-D, lipase and glycerol-3-phosphate oxidase. All the methods described are simple and reproducible and the immobilized enzymes show good stability.     

Tests of significance using selected sample quantiles

Large sample tests of significance for the location parameter, the scale parameter, and quantiles for a location-scale family of distributions based on a few optimally chosen sample quantiles are considered.     

The kinetic determination of clinically significant enzymes in an automated flow-injection system with fluorescence detection

An automated flow-injection manifold is described for the kinetic determination of enzyme activities by a stopped-flow procedure with fluorescence detection. The linear calibration range for alkaline phosphatase is 0/2-250 U l^?1 with a precision of 2%; sample thoughput is 35/2-40 h^?1. Linear responses were also obtained for lipase (0/2-100 U l^?1), acethylcholinesterase (0/2-500 U l^?1) and chymotrypsin (0/2-200 U l^?1). The advantages of this approach to the determination of plasma enzyme activities include sensitivity and the small sample and reagent volumes needed.