• Dartmouth Trace Element Analysis Core Facility, Departments of Earth Sciences and Chemistry, Dartmouth College, 6105 Sherman Fairchild Hall, Hanover, NH, 03755, USA. Stefan.sturup@dartmouth.edu

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on 76Se, 77Se, and 78Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H2 gas. We developed a novel simple optimization routine for the H2 gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H2 flow was 2.9 mL min-1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO3 and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 microg L-1 for 76Se and 78Se and 0.13 microg L-1 for 77Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 microg L-1 and the range was 73.4-305.5 microg L-1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145+/-3 microg L-1 (n=36) and the certified value of 136+/-9 microg L-1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911+/-75 microg L-1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920+/-60 microg L-1.