Determination of cadmium, copper and lead in environmental samples. An evaluation of flow injection on-line sorbent extraction for flame atomic absorption spectrometry

A flow injection on-line sorbent extraction system was studied in conjunction with flame atomic absorption spectrometry to determine cadmium, copper and lead in digest solutions of solid environmental samples using octadecyl functional groups (C₁₈) bonded silica gel as sorbent with diethylammonium-N,N-diethyldithiocarbamate (DDDC) or ammonium diethyldithiophosphate (DDPA) as complexing agent and methanol as eluent. Using DDDC as complexing agent, citric acid was used as masking agent for iron and manganese. The complexing agent DDPA selectively extracts cadmium, copper and lead at pH values 1 to 3. Using DDPA as complexing agent with citric acid at pH 1.0, the results of the analysis of five environmental standard reference materials, including coal fly ash (CRM 038), calcareous loam soil (CRM 141), lake sediment (CRM 280), river sediment (CRM 320) and estuarine sediment (CRM 277) after digestion were in good agreement with the certified values except cadmium in the river sediment with a very high iron content. With a 20-s sample loading at 8.7 ml min^-1, detection limits (3σ) were 0.8, 1.4 and 10.0 μg l^-1 respectively for cadmium, copper and lead.