Trace metal analysis of natural waters and biological samples by axial inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) with flow injection on-line adsorption preconcentration using a knotted reactor

Traces of Cu, Ni, Sb, Co, Ag, Cd, Mo, In and Pb in biological materials and natural water samples were determined by axial inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) with ultrasonic nebulization a fter flow injection (FI) on-line sorption/preconcentration in a knotted rea ctor (KR). The ability to collect complete mass spectra at a high frequency (more than 20 000 complete mass spectra per second) makes ICP-TOFMS nearly ideal for the detection of FI (transient) signals. The analytes were compl exed with ammonium pyrrolidinedithiocarbamate (APDC) from acidic solutions in the flow system and sorbed onto the KR. The relatively small volume of m ethanol used as eluent, along with the employment of an ultrasonic nebulize r (USN) with membrane desolvation, minimizes the problems produced by the i ntroduction of organic solvents into the plasma. Using a preconcentration t ime of 120 s and a sample flow rate of 2.8 ml min(-1) an enhancement factor of 5 to 70 was achieved. The detection limits (3 sigma) varied from 0.5 ng l(-1) for Sb to 26 ng l(-1) for Pb. The precision (RSD) for 11 replicate d eterminations of 0.2 mu g l(-1) of each analyte was better than 5%. The acc uracy of the method was demonstrated by the analysis of four certified refe rence materials: a synthetic freshwater (NIST SRM 1643d), a natural filtere d coastal water (NRCC CASS-3) and two biological materials (BCR CRM 422 Cod muscle and BCR CRM 278R Mussel tissue) and by recovery measurements on spi ked samples.