Total fluorine analysis in solid samples by instrumental neutron activation analysis coupled with the internal standard method

Instrumental neutron activation analysis (INAA) is a valuable technique for quantifying F; however, it is associated with significant measurement uncertainty, which can be reduced by combining INAA with the internal standard method. In this study, known amounts of Sc were added to both samples and calibration standards to compensate for variations in the fluence rates of the irradiated neutrons and measurements of the γ-rays. The ^46mSc produced during neutron irradiation was used as the internal standard. Data were collected using two approaches: a single irradiation for 5 s followed by a 10 s γ-ray measurement, and a cyclic method involving five repetitions of the single irradiation and γ-ray measurements. Normalization of the counting rate using the internal standard effectively eliminated day-to-day variations, and a reliable relationship was established between the normalized signal and the amount of F. The proposed method produced a robust and highly linear calibration plot, enabling the accurate quantification of the mass fraction of F. The analytical performance of the proposed method was validated using certified reference materials before using it to quantify the mass fraction of F in commercially available synthetic polymer resins. The cyclic irradiation method, which required approximately 30 min for measurement, yielded a lower expanded uncertainty in the mass fraction of F compared with the single irradiation method, in which measurements were completed within 30 s. Consequently, the single irradiation method was more suitable for screening, whereas the cyclic irradiation method was more suitable for the precise quantification of F.