Analysis of Fluorine in Drinking Water by ICP-QMS/QMS with an Octupole Reaction Cell

The analysis of fluorine was carried out by measuring BaF⁺ ions with an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS). After optimization, a radio frequency power of 1300 W was found to benefit for the production of BaF⁺ ions while suppressing the production of BaOH₃⁺ ions. After optimization of the reaction cell gas, it was found that the best performance for measuring BaF⁺ could be achieved at a flow rate of O₂ in the range from 0.65 to 0.75 mL min^-1. The signal intensity of BaF⁺ depended linearly on the concentration of Ba when it was not higher than 100 mg kg^-1. The co-existence of metallic cations, such as Na in the sample, might suppress the generation of BaF⁺ ions in the plasma, while anions might not cause such a kind of interferences. The background equivalent concentration (BEC) and the lower detection limit (LDL) of fluorine were 0.4 and 0.06 mg kg^-1, respectively, by adjusting the samples to a 10 mg kg^-1 Ba matrix. The concentration of fluorine in a certified reference material (ERM-CA015a) was determined with the present method, for which the observed value was (1.36 ± 0.05)mg kg^-1, which agreed with the certified value (1.3 ± 0.1)mg kg^-1, where both values were shown as (mean value ± expanded uncertainty) with a coverage factor of (k = 2) for calculating the expanded uncertainty giving a level of confidence of approximately 95%. The present method was applied to the analysis of a tap water sample collected in the laboratory, for which the results of recovery tests gave a recovery around 100% with good reproducibility.