2.3. Quality control
Quality control consisted of method blanks, blank spikes, matrix spikes, certified reference material, and blind duplicates. The average T-Hg concentration of hair certified reference material (NIES-13) was 4.30±0.17 μg/g (n=6), which was comparable with the certified value of 4.42±0.40 μg/g; the average Me-Hg concentration of 3.84±0.11 μg/g (n=5) was in good agreement with the certified value of 3.80±0.40 μg/g. The average T-Hg concentration of rice certified reference material (GBW10010) was 5.4±0.4 ng/g (n=8), which is comparable with the certified concentration of 5.3±0.5 ng/g. The recoveries from spiked samples ranged from 80.2% to 111% for Me-Hg in rice sample, and ranged from 98% to 103% for U-Hg. The relative standard deviation was lower than 5% for T-Hg in hair, urine and rice duplicate samples and was lower than 10% for Me-Hg in hair and rice duplicate samples (ranging from 0.8% to 9.9%).