Precise Zn isotopic ratio measurements of human red blood cell and hair samples by multiple collector ICP mass spectrometry

Precise Zn-66/Zn-64 and Zn-68/Zn-64 isotopic ratios of biochemical samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). In order to eliminate the mass spectrometric interferences on Zn isotopes (e.g., Ni-64+ and Ba-136(2+)), we chemically purified the analyte using an ion chromatographic technique. The resulting precisions of the Zn-66/Zn-64 and Zn-68/Zn-64 ratio measurements were 0.05 parts per thousand and 0.10 parts per thousand (2SD), respectively, which were enough to detect the isotopic variation of Zn in nature. Red blood cell (RBC) samples were collected from five volunteers (four males and one female), including a series of 12 RBC samples from one person through monthly-based sampling over a year. These were analyzed to test possible seasonal changes and variations in Zn-66/Zn-64 and Zn-68/Zn-64 ratios among the individuals. The Zn-66/Zn-64 and Zn-68/Zn-64 ratios for a series of 12 RBC samples collected over a year were 0.43 parts per thousand and 0.83 parts per thousand higher than the values of highly purified Zn metal (JMC Zn), and no seasonal change could be found. The Zn-66/Zn-64 and Zn-68/Zn-64 ratios for RBC samples collected from five volunteers did not vary significantly. In order to investigate Zn isotopic heterogeneity in a human body, Zn isotopic ratios of a hair sample collected from one of the volunteers was also analyzed. The Zn-66/Zn-64 and Zn-68/Zn-64 ratios for the hair sample were 0.59 parts per thousand and 1.14 parts per thousand lower than the mean value of RBC samples. This result demonstrates that detectable isotopic fractionation occurs in the human body. The data obtained here suggest that the isotopic ratios of trace metals could provide new information about transportation of metal elements in vivo.