Sample screening systems in analytical chemistry

Speciation of inorganic lead and ionic alkyllead compounds by GC/MS in prescreened rainwaters

A simple and novel screening method for lead compounds in environmental waters is proposed. The analytes, in an acetic medium, are sorbed on a C60 fullerene column as diethyldithiocarbamate complexes and subsequently eluted with isobutyl methyl ketone (IBMK), the lead being determined by flame atomic absorption spectrometry. The screening method acts as filter and indicates whether the target analytes are present above or below the detection limit of the method (0.5 ng/mL), giving no false positives. Positive samples were speciated by GC/MS, using a flow system similar to that of the screening method. Lead(II) and ionic di- and trialkyllead are derivatized with a Grignard reagent. Both methods use similar chemical and flow variables except for the eluent, IBMK in the screening method and n-hexane in the speciation method. The GC/MS speciation method is very sensitive; it exhibits a linear range of 0.02-5 ng/mL, and detection limits of 1-4 ng/L are achieved. Also, its repeatibility, as RSD, is less than 6%. The method was applied to the speciation of Pb2+ and di- and trialkyllead in positive prescreened rainwater samples from three different urban areas.