On-line microwave sample pretreatment for the determination of mercury in water and urine by flow-injection cold-vapour atomic absorption spectrometry

Abstract

A system for on-line treatment of liquid samples in a microwave oven and determination of mercury by cold-vapour atomic absorption spectrometry was designed and evaluated. The system consisted of an atomic absorption spectrometer, equipped with a mercury-hydride system and amalgamation accessory, a flow-injection system, an autosampler and a mircowave digestor. Urine and environmental water samples were stabilized with potassium dichromate-nitric acid and were mixed with a bromination reagent. The recoveries of eight mercury compounds from aqueous solutions and five compounds from dilute urine were studied. At an applied microwave power of 75 W, the recoveries of mercury(II) nitrate, methylmercury chloride, amidomercury chloride, phenylmercury chloride and diphenylmercury were between 92 and 102% for 1 + 2-diluted urine without amalgamation and between 94 and 111% for 1 + 5-diluted urine with amalgamation, respectively. The sample throughput was 30–40 h −1 without amalgamation and 24 h −1 in the amalgamation mode. Good agreement with certificate values was obtained for urine samples. A limit of detection (3σ) of 10 ng l −1 was obtained using 10-ml sample volumes of environmental waters (river, lake, rain) and the amalgamation technique. The results compared well with those from an external laboratory with correlation coefficients of 0.9302 and 0.9028 ( n = 22) for integrated absorbance and peak-height absorbance, respectively.