Flow-injection solid-phase spectrophotometry for the determination of zinc in pharmaceutical preparations

Abstract

A flow system exploiting solid-phase spectrophotometry is proposed for the determination of zinc in pharmaceutical preparations. The chromogenic reagent 1-(2-tiazolylazo)-2-naphthol (TAN) was immobilized on C18 bonded silica loaded into a homemade flow cell with 1 mm optical path and 78 mm2 cross section. The flow cell was designed in such a way that the sensitivity is enhanced and the attenuation of the radiation beam due to scattering and absorption by the solid material is minimized. The flow cell was placed in the spectrophotometer so that the radiation beam was focused on the overall surface containing the adsorbing material. Reagent immobilization was performed on-line and allowed to work for at least one month. Analyte reaction, retention and detection were performed simultaneously, followed by elution with hydrochloric acid. The apparent molar absorptivity was estimated as 2.02×105 l mol−1 cm−1 and the procedure allowed the determination of zinc in the 0.04–4.0 mg l−1 range with a coefficient of variation of 3.3% (n=10). A sample throughput of 45 determinations per hour and a detection limit of 10 μg l−1 (99.7% confidence level) were achieved. The results agreed at a 95% confidence level with those found by inductively coupled plasma atomic emission spectrometry.