Microwave method for preparing erythrocytes for measurement of zinc concentration and zinc stable isotope enrichment.

A microwave digestion method to prepare human erythrocytes for measurement of Zn concentration by atomic absorption spectrophotometry and stable isotope enrichment by mass spectrometry is described. Also described is a process for purifying digested erythrocyte samples enriched with Zn stable isotope for analysis by fast atom bombardment mass spectrometry. Microwave digestion was investigated as a way to increase sample throughput by replacing a more time-consuming conventional oven ashing/hot plate wet digestion method. Pooled red blood cells and NIST bovine liver standard reference material were digested by the two different methods and zinc recoveries compared by atomic absorption spectrophotometry. Microwave and conventional methods yielded 11.7 +/- 0.1 and 11.7 +/- 0.2 micrograms/g (wet wt), respectively, for the pooled erythrocytes, and Zn recovery from NIST bovine liver standard (certified 123 +/- 8 micrograms/g) was 128.2 +/- 1.2 and 127.4 +/- 1.3 micrograms/g, p > or = 0.282, respectively. Microwave digestion improved the processing of erythrocytes for atomic absorption spectrophotometry and mass spectrometry by reducing digestion time from 1 week to 2 h. In addition, a procedure for purifying digested erythrocyte samples by either extraction and ion-exchange chromatography in preparation for mass spectrometry analysis of Zn stable isotope enrichment is outlined.