DETERMINATION OF LEAD IN BIOLOGICAL-MATERIALS BY MICROWAVE-ASSISTED MINERALIZATION AND FLOW-INJECTION ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

The design and operation of an on-line automated microwave-assisted mineralization and flow injection electrothermal atomic absorption spectrometric system for the determination of lead in biological materials are described. Certified reference materials were homogeneously dispersed in a 0.4% v/v Triton X-100 solution with an ultrasonic device. Mineralization of samples was accomplished with an HCl-HNO3 plug downstream in a PTFE coil located inside the microwave oven. A gas diffusion cell device allowed efficient degasification of mineralized samples. Precise volumes of the mineralized samples, collected in a capillary of a sampling arm assembly, were introduced by means of positive displacement with air through a time-based solenoid injector into the graphite furnace. The entire system was controlled by a computer, independent of the spectrometer. The spectrometer autosampler used for the introduction of the chemical modifier was pre-programmed to synchronize with the operation of the flow system. The linear range was from 0 to 70 mug l-1 of lead and the detection limit was 0.1 mug l-1 (0.8 pg). The agreement between observed and certified values was good, except for the botanical samples Olive Leaves and Pine Needles (with an average recovery of about 900%). The main advantage of the method is that in this totally closed system with on-line sample mineralization low and repeatable blanks were obtained, allowing the rapid determination (about ten samples per hour) of lead in various biological matrices with minimum exposure to the environment and minimum operator attention.