Mechanised flow system for on-line microwave digestion of food samples with off-line catalytic spectrophotometric determination of cobalt at ng l(-1)levels

A mechanised system for on-line slurry food sample digestion was developed and an off-line cobalt determination was performed. The stabilised slurry s ample was introduced into an air carrier stream until reaching the digestio n coils located inside a household microwave oven. Software written in Visu al Basic 3.0 was developed to permit the transport of the slurry samples an d the programming of the microwave oven and also the control of the mineral ization valve. The proposed system was optimized for determination of cobal t in certified samples such as mussels, bovine liver and fish and also unce rtified fish samples. The digestion parameters were established as 3 mol l( -1) HNO3 for mussels, 3 mol l(-1) HNO3 plus 0.16% v/v H2O2 for bovine liver and 12 mol l(-1) HNO3 for fish employing maximum power for 5 min of microw ave actuation. In the subsequent spectrophotometric method for the catalyti c determination of cobalt, the Tiron and hydrogen peroxide concentrations w ere 1.8 x 10(-3) and 3.0 x 10(-4) mol l(-1), respectively, and the sample r esidence time was 300 s as determined by an optimisation process. The propo sed method features a linear range from 10 to 200 ng l(-1) Co (r > 0.996) w ith detection and quantification limits of 1.7 and 5.5 ng l(-1) Co, respect ively. The precision, expressed as RSD, was 2.4% (n = 12) for repeatability and 5.2% (n = 10) for reproducibility and the accuracy of the proposed met hod was assessed by using certified samples and an alternative technique (E TAAS).