Electrothermal atomic absorption spectrometric determination of cadmium and lead in traces in aquatic systems following flotation by two chromium(III) collectors

Abstract

A fast flotation method for determination of cadmium and lead in aquatic systems by two chromium(III) collectors is described. The first collector is a colloid precipitate of hydrated chromium(III) oxide, Cr₂O₃· xH₂O, while the second is a bulk chromium(III) pentamethylenedithiocarbamate, Cr(PMDTC)₃. Cadmium and lead present in water are incorporated into the collector mass at pH 7.5 by addition of 20 mg of Cr(III) and 0.4 mmol of pentamethyleneammonium pentamethylenedithiocarbamate, PMA-PMDTC, to 0.5 L water sample. A solid precipitate was separated from the processed water system by air bubbles. After dissolving with strong acid, the solution is tested by electrothermal atomic absorption spectrometry (ETAAS). The limit of detection for Cd by flotation/ETAAS method is 0.002 μg L^{− 1}, while for Pb is 0.04 μg L^{− 1}. The precision of the method is expressed as relative standard deviations ranging of 5.0% for Cd (concentration range from 0.1 to 0.5 μg L^{− 1}) and 4.25% for Pb (concentration range from 0.5 to 5 μg L^{− 1}). The characteristic mass (mass that gives an integrated absorbance of 0.0044 s) of 1.06 pg for Cd and 16.7 pg for Pb were obtained. The method was validated by the standard additions and by its application to the reference materials (Surface water-SPS-SW-1, River Thames Water-LGC-6019).

Keywords:

• Cadmium
• lead
• flotation
• hydrated chromium(III) oxide
• surfactant
• pentamethyleneammonium pentamethylenedithiocarbamate
• chromium(III) pentamethylenedithiocarbamate
• ETAAS