Спектрофотометричне визначення фторидів у природних водах

Abstract

The interaction of fluoride ions with solutions of ionic aluminum associate with benzoylhydrazone of salicylic aldehyde (BHSA) and polymethine dye with astrafloxin FF (AF) in a solution, in the presence of starch was studied. It was demonstrated that fluorides destroy the ionic aluminum associate, which leads to the release of the dye (λmax = 538 nm) and the decrease in the intensity of light absorption of solutions at λmax = 588 nm. This was underlain as the basis for the spectrophotometric determination of fluoride ions. Under optimal conditions of interaction (pH 6.5-9.5; C(Al3+) = 2×10-5 mol/L; CBGSA = 2×10-4 mol/L; CAF = 2×10-5 mol/L; C(starch) = 0,01%) the chemical-analytical characteristics of the system for the spectrophotometric determination of fluoride ions were calculated: the limits of the linearity of the calibration plot 0.012-1.52 mg/L; regression equation for the calibration plot y = 0.7059x + 0.0335 (R2 = 0.9884), where x - concentration of fluorides, mg/L; limit of detection (LOD) – 3.6 μg/L, limit of quantitative determination (LOQ) – 11.8 μg/L. A sufficiently high selectivity of spectrophotometric determination of fluorides was shown. Determination of fluorides is not interfered with more than 2000-fold amounts of cations of alkaline and alkaline earth metals, sulfates, chlorides, nitrates, carbonates, phosphates and oxalates, 100-fold the amount of Cu(II), Cr(III), Mn(II), Co(II), Ni(II), Zn(II). The spectrophotometric determination of fluorides is hindered already by equal amounts of Boron compounds, Zr(IV), Th(IV) and Fe(III). The effect of Fe(III) is eliminated by ascorbic acid. On the basis of the conducted research, a new express method of spectrophotometric determination of fluoride ions in natural river waters which has satisfactory metrological characteristics was developed and tested. The proposed method has accuracy, relative standard deviation was 3.1-3.5%, it is simple in execution and fast, and all the necessary reagents and equipment are available. It is found that the content of fluorides in the river waters of Transcarpathia is small. Keywords: fluorides; natural waters; spectrophotometric determination; ion association pair.