AOAC SPIFAN Nutrients ERP Review (March 14, 2019)

Fluor-03 (Feb. 2019) FOR ERP USE ONLY DO NOT DISTRIBUTE

Possible anionic interferences for fluoride were checked by analyzing standard solutions of chloride, acetate, formate, and lactate separately and as mixed standard to check possible overlays with fluoride in the standards as well as in the samples. There was no overlapping observed and no influence of the fluoride peak height detected (see Figures 9 and 10).

Figure 9 Overlay of a 500 μg/kg fluoride check standard (green) with a 500 μg/kg mixed standard with fluoride, chloride, acetate, and lactate (pink). The peak heights of fluoride match for both standards, while none of the interfering peaks could be detected nearby.

Figure 10 Overlay of the SMPR 1849a (black); a 0.5 mg/kg mix standard with fluoride, chloride, acetate, formate, and lactate (pink); a mix standard with 10 μg/kg fluoride, and 0.5 mg/kg acetate, formate, and lactate (yellow), a 10 μg/kg fluoride standard (green), and a 5 μg/kg fluoride standard (blue). (b) Calibration. —Three independent calibration series with nine standards were run three times. The calibration standards were prepared from different analysts and analyzed at different days using the IC system with two different columns (see Annex A). Comparing the three calibrations (anions high and low) the RSD of the individual standard heights is less than 8% ( Table 7 ), while the RSD of the curve fit (quadratic, intercept = 0, all replicates included) is < 2%, i.e. 0.4% for anions low and 1.4% for anions high ( Figure 10 ). The correlation coefficient r 2 > 0.9999 for both correlations.

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