OPTIMIZATION OF METHODOLOGY FOR DETERMINATION OF THE FLUORIDE IN URINE
Improvement of the procedure for measuring the concentration of fluoride ions in urine samples in order to eliminate the interfering influences and improve the accuracy of the determination. Studies of samples for the content of fluoride ions were performed by an ion-selective method. A feature of the proposed technique is the elimination of the matrix effect in complex samples, which is achieved by adding to the standard buffer solution the disodium salt of ethylenediaminetetraacetic acid. This procedure increases the recovery rate by 10 % compared to the use of a standard buffer solution and provides a recovery level of 99.7 %. The correctness of the obtained results was estimated by the method of additives, which allowed to establish the optimal conditions for the analysis. The indicators of precision, reproducibility and accuracy of the fluoride-ion measurement method in urine samples were first determined. For the measuring range 0.19-40.00 mg/dm3, standard deviations calculated under repeatability and reproducibility conditions are 3.76 and 5.2 %, respectively. The measurement accuracy index does not exceed ± 11 %. To assess the possibility of using measurement results when implementing the methodology in the activity of a particular laboratory, the values of the limits of repeatability and reproducibility are calculated. The results of measurements of fluoride concentrations in the urine of patients with different fluoride loads are presented. The improved technique allows to make measurements in a range overlapping the measured levels in persons with different technogenic loads. Precision, reproducibility and accuracy of the improved methodology were calculated for the first time.