A simplified micromethod for fluoride analysis

A simplified method for the determination ionic fluoride (F−) concentrations in microvolume samples using a F−-selective electrode is described. Portions (20 μl) of a series of F− standard solutions (1000–0.4 parts/109 F−) were placed between the surface of the F− electrode and the surface of a reference electrode mounted end to end with the aid of a steel holder. In this position the two surfaces were used as an analysis chamber, retaining the sample by surface tension without the use of sleeves or other devices. The precision of the results and the absolute detection limit of the modified method were determined. The analytical performance of this set-up was tested by comparing the results with those obtained from the conventional method. The regression between the modified-method data and the conventional-technique data showed a strong correlation (R2=0.993) between the results obtained using the two techniques. In the range of F− concentrations from 1000 and 0.48 parts/109. the precision of the results (coefficient of variation) was of 5–6%, improving to 0.9% at 0.9 parts/109 level.