Abstract

A sequential injection analysis (SIA) spectrophotometric method for the determination of trace amount of mercury (II) with pyrogallol red (PGR) was described. The method was based on the measurement of absorbance of the mercury (II)–PGR complex, yielding a light yellow-coloured product at pH 9.0 with absorption maximum at 370 nm. The SIA parameters affecting the signal response were optimised in order to obtain the better sensitivity and minimum reagent consumption. The linear range for determination of mercury (II) was over the range of 0.1–2.0 mg L⁻ ¹. The limit of detection and limit of quantification, calculated following IUPAC were 0.06 and 0.10 mg L⁻¹, respectively. The repeatability was 1.25% (n = 10) for 0.5 mg L⁻¹ of mercury (II). The proposed method was successfully applied to determine the mercury (II) in commercial cosmetics, local Thai traditional medicines and water samples with a sampling rate of 40 h⁻¹. Results obtained were in justifiable agreement with those obtained by the official ICP-MS method at the 95% confidence level.