Observation, identi®cation and correction of structured molecular background by means of continuum source AASÐdetermination of selenium and arsenic in human urine

A high-resolution continuum source atomic absorption spectrometer based on a xenon short-arc lamp, a transversely heated graphite furnace module with longitudinal Zeeman option, a double eÂchelle monochromator and a linear array CCD detector was developed. The system allows the investigation and clari®cation of background correction problems in conventional AAS caused by atomic and molecular interferences during the atomization of samples with complex matrices. As an example, the determination of selenium at 196.026 nm and arsenic at 193.696 nm in undiluted human urine samples is demonstrated. The two species NO and PO responsible for the spectral interferences were identi®ed and successfully corrected for by means of a mathematical correction algorithm. From measurements of human urine reference materials (Lyphochek Urine Metals Control Level 1 No. 69011 and No. 69041; Bio-Rad, Anaheim, CA, USA), it was found that the analytical performance of this method is comparable to that of line source AA systems. For Se the determined element concentrations of 59¡3 and 79¡4 mg l, respectively, correspond well with the certi®ed values of 61¡12 and 73¡14 mg l, and for the LOD and the reproducibility values of 38 pg in the matrix and 3.5% were obtained, respectively. In the case of As, only NaCl and PO produced molecular structures and were corrected for. Again the measured concentration of 168¡6 mg l lies in the acceptable range of 154¡31 mg l given for the reference sample (Lyphochek Urine Metals Control Level 2 No. 69012; Bio-Rad) and the LOD was found to be 25 pg in presence of the undiluted human urine matrix.