Determination of cadmium, lead and copper in milk and milk powder by means of flow potentiometric stripping analysis

A flow potentiometric stripping analysis procedure for the determination of cadmium, lead and copper in milk and milk powder samples is described. The instrumental arrangement consists of a glassy-carbon thin-layer cell through which six different solutions may be drawn by means of a peristaltic pump and magnetically operated valves. The glassy-carbon electrode is pre-coated with a film of mercury which can be employed for several analytical runs. The sample, diluted five-fold with Suprapur hydrochloric acid, is electrolysed for 0.5–4 min prior to stripping in Suprapur hydrochloric acid. Pump-rate, electrolysis time and potential, opening and closing of inlet valves and digital evaluation of stripping times are controlled automatically by the computer. The analytical results agree satisfactorily with the certified values for three milk powder reference samples. The detection limit for cadmium, lead and copper in milk samples after 4, 1 and 0.5 min of pre-electrolysis is 0.8, 4 and 8 μg l. , respectively. An analytical procedure for the determination of lead in samples containing high concentrations of tin is described.