Cloud point extraction of mercury with PONPE 7.5 prior to its determination in biological samples by ETAAS

Cloud point extraction (CPE) has been used for the pre-concentration of mercury, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by electrothermal atomic absorption spectrometry (ETAAS) using polyethyleneglycolmono-p-nonyphenylether (PONPE 7.5) as surfactant. The chemical variables affecting the separation step were optimized. Under the optimum conditions, i.e, pH 8.5, cloud point temperature 80 °C, 5-Br-PADAP = 4 × 10−5 mol L−1, PONPE 7.5 = 0.2%, sample volume = 1.0 mL, an enhancement factor of 22-fold was reached. The lower limit of detection (LOD) obtained under the optimal conditions was 0.01 μg L−1. The precision for 10 replicate determinations at 2.0 μg L−1 Hg was 4.0% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for mercury was linear with a correlation coefficient of 0.9994 at levels near the detection limits up to at least 16 μg L−1. The method was successfully applied to the determination of mercury in biological samples and in certified reference material (QC METAL LL3).