Flame atomic absorption spectrometry with flow-injection on-line adsorption preconcentration using a knotted reactor for cadmium determination in aqueous samples

A knotted reactor flow injection on-line preconcentration system coupled to a flame atomic absorption spectrometer (FAAS) was developed for the direct determination of cadmium in aqueous samples. Diethyldithiocarbamate was used to complex the analyte and then, it was adsorbed on the walls of a knotted reactor (KR) made from PTFE tubing. All the FI and chemical variables were optimized. The complex elution was performed on-line using ethanol. The sample loading time and flow rate were set at 60 s and 6 mL/min, respectively. An enhancement factor of 33 was achieved, resulting in a sampling frequency (h(-1)) of 30. The limit of detection was 3.44 mug/L. The accuracy of the method was tested by the analysis of three certified reference materials (Certified Aqueous Standard 7878, Reference Water TM-24 and Trace Elements in Water 1643d). The results obtained are within the certified ranges at a 95% confidence level and a good precision was also achieved (<2.7%, n=6). The proposed procedure was applied to the Cd determination in rain and sea water samples.