Chromium, lead and cadmium in Danish milk products and cheese determined by Zeeman graphite furnace atomic absorption spectrometry after direct injection or pressurized ashing.

A method for the direct determination of chromium in homogeneous samples of milk and milk products is described. Minimum sample handling and prevention of contamination was given priority. After injection of the sample into the graphite furnace, the sample was ashed in a stream of oxygen at 650 degrees C and then further ashed at 1,100 degrees C with argon as the purge gas. Zeeman background correction was used in the atomisation step at 2,300 degrees C. The detection limit was 0.7 ng/g. Direct detection of chromium in milk, using only argon as purge gas, was inferior. Non-homogeneous and solid samples, e.g. yoghurt with fruit jam and cheese, were ashed under pressure with nitric acid before analysis. The same analytical principle as used for chromium was also used for the analysis of lead and cadmium in the samples. Analytical quality control was performed for both methods and the results are reported. The results for lead, cadmium and chromium in Danish milk and milk products were in the parts per billion or parts per trillion range and compare well with literature data. The intake of lead, cadmium and chromium from milk and milk products is less than 4% of the total Danish dietary intake of these elements. It is concluded that the contribution from milk and milk products to the total intake of lead and cadmium is toxicologically insignificant and that milk and milk products are only a minor source of the essential element chromium.