Simultaneous Differential Determination of Inorganic Acid and Nitrate in DMF Solution by Nonaqueous Conductometric Titration with Sodium Tetrahydroborate

Generally the degree of electrolytic dissociation of an aqua (protic solvent) is larger than that of a nonaqueous solvent (aprotic solvent). And the electric conductivity of an inorganic salt dissolved in a nonaqueous solvent is smaller than in an aqueous solution. Therefore the differential of electric conductivity was conspicuous because electric conductivity when dissolved with a solute is low in a nonaqueous solvent. The differential determination by conductometric titration of mixed solution of inorganic salts was possible in a nonaqueous solvent such as N,N-dimethylformamide (DMF). The simultaneous differential determination of nitrate and inorganic acid in solution was conducted by nonaqueous conductometric titration with sodium tetrahydroborate (STHB) in DMF. Inflection points appeared on conductometric titration curves of nitrate and inorganic acid solution in DMF, and were due to differences in reactivity and acidity. The inflection points indicated concentrations of nitrate and inorganic acid simultaneously. STHB and Al(NO3)3 reacted at a mole ratio of 1:3, and Co(NO3)2 reacted at 1:2. It was considered that the reaction mole ratio of STHB and nitrate was fixed by the valence of the metal ion. In order to investigate the reaction mechanism, ions in the DMF solution and precipitates were identified during titration by fourier transformation infrared spectroscopy (FT-IR), inductive coupling plasma emission spectrometry (ICP-AES) and the X-ray diffraction method (XRD). 10 % water in the sample solution did not interfere with the titration. The determination limit was 0.01-0.005 mol dm-3 with this method.