Applications of xanthene derivatives in analytical chemistry. Part LVII. Spectrophotometric determination of minocycline using gallium and Eosin
A spectrophotometric method for the determination of micro-amounts of minocycline (MINO) as a tetracycline derivative in weakly acidic media is proposed. It is based on the formation of a ternary complex between Eosin (sodium 2,4,5,7-tetrabromofluorescein), gallium and MINO in the presence of poly(vinyl alcohol). Under optimum conditions, minocycline hydrochloride (MINO.HCl) was determined in the range 0–40 µg in 10 ml of solution at 545 nm. The apparent molar absorptivity of MINO.HCl was 1.1 × 105 l mol–1 cm–1 with a Sandell sensitivity of 0.0047 µg cm–2 MINO.HCl. The method was applied to the determination of MINO.HCl in pharmaceutical preparations.