Abstract
Nano-silver coated silica gel was impregnated with ammonium pyrrolidine-dithiocarbamate (APDC) and used for the separation and preconcentration of lead prior to its determination by flame atomic absorption spectrometry. The silver coated silica gel was prepared by mixing slurried silica gel with solid silver nitrate and sodium boron hydride. The silver coated silica gel was then impregnated with ammonium pyrrolidine-dithiocarbamate. For enrichment/separation of the analyte, as an alternative to the conventional column technique, the housing of a syringe-mountable filter was filled with the sorbent and mounted to the tip of a 50 mL of syringe. In order to retain the analytes, the sample solution was drawn into the syringe and ejected back again by passing through the sorbent in the filter. The analyte on the sorbent was then eluted by drawing and ejected back an eluent. The effects of experimental conditions with regards to the amount of sorbent, pH of sample, concentration and kind of eluent, foreign ions, flow rates of sample and eluent on the recovery (retention and elution) of the analyte were investigated. All quantifications were performed with a flame atomic absorption spectrophotometer. The analyte was quantitatively retained at pH 7 and eluted with 3.0 M of HNO3 applying a 20 mL min-1 of drawing and discharging rates (flow rates) for sorption and elution steps with less than 10% of RSD. In order to increase the sample volume and thereby concentration factor, several portions of sample were successively drawn and ejected back through the sorbent but eluted only once. The limit of detection of the method for lead was 0.36 ng mL-1 according to 3 criteria (N=10). The validation of the proposed method was tested by using waste water certified reference materials and quantitative recoveries in the range of 95% confidence level were obtained. Finally, the presented method was used for the determination of lead in real water samples. The sorbent prepared is novel and its use in syringe mountable filter for enrichment/ separation is challenging.
Keywords: Silica gel, Lead, Nano sized silver, Atomic absorption spectrometry
7