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A new method for flow-injection analysis (FIA) for the determination of penicillins based on the extraction and spectrophotometric determination of ion associates with selected thiazine dyes (methylene blue, azure A, and azure B) is proposed. The reaction conditions (cdye = 2 × 10−4 mol l−1, cKCl = 1 mol l−1, pH ≅ 6, λ = 635 nm) were found. The factorial design has been carried out to determine the optimum flow conditions. A wide linear dynamic range of calibration curves (5.1–700 µg ml−1 for penicillin V with all dyes, R = 0.9985) and good repeatability (e.g., relative standard deviation [RSD] = 4.6–0.6% in this concentration range for the reaction with azure B) were found. The detection limit for penicillin V is 1.5 µg ml−1, and the determination limit is 5.1 µg ml−1. The maximum analysis rate is 35 samples per h. The practical samples of pharmaceutics were tested. There are no interferences from the additives in pharmaceutics.

A study has been made of the conditions for the reaction of heparin with thiazine dyes in both static and flow-through systems. Factorial design was used to determine the significance of the individual flow-through experimental parameters and their optimal values were found: at pH = 6, c dye = 8 × 10 −5 mol l −1 , the optimum overall flow rate (dye : buffer = 1 : 1) is of 4.2 ml min −1 , volume injected of 500 μl, reaction coil length of 20 cm. Methods were developed for the flow-through spectrophotometric determination of heparin. The concentration ranges of calibration curves are 0–10 and 0–12 μg ml −1 , respectively, for individual dyes, the limit of detection of about 0.1, limit of determination of about 0.3 μg ml −1 .