Interference of Humic Substances in the Spectrophotometric Determination of Bromate by Phenothiazines in Natural Waters

Abstract

The spectrophotometric method of bromate (BrO₃ ^?) determination by phenothiazines was applied to natural water samples and the interferences due to the presence of inorganic and humic substances were investigated. Common ions present in natural waters did not interfere and only the less abundant NO₂ ^? and Fe²⁺ exhibited strong interferences. Interferences of the two latter ions, if they existed, could be controlled and the method proved to be accurate and with a low detection limit. However, it was found that the presence of soluble humic substances resulted in positive interference, rendering the method unsuitable for bromate determination in natural waters and restricted its use in pure bromate solutions. This interference can be attributed to the electron acceptor groups invariably existing in the humic molecules. Since humic substances can remain in the water even after its ozonation, they will also contribute to a positive interference in bromate determination in potable waters.     

Bromate determination in water using chlorpromazine after correction of chlorinating agents and humic substances interference

The presence of soluble humic substances and chlorinating agents interfered positively with the spectrophotometric determination of bromate (BrO ₃ ⁻ ) using chlorpromazine. Removal of the soluble humic substances through their precipitation by a basic lead acetate (15.9 g/L Pb(CH₃COO)₂ · 3H₂O-4.7 g/L PbO) solution corrected their interference effectively. In addition, the use of NaHSO₃ at pH 5.1 ± 0.2 eliminated the interference of ClO ₂ ⁻ , Cl₂-OCl⁻, and Cl₂-NH₂Cl, when present in concentrations of up to 1.5, 3.5, and 3.5 mg/L, respectively. Thus, the spectrophometric method was rendered suitable for the direct bromate determination in natural, chlorinated, and ozonated waters, since the application to such samples resulted in the accurate and precise determination of bromate. The method’s detection limit was estimated as 1.6 μg BrO ₃ ⁻ /L and the linear range of the calibration curve was extended up to 700 μg BrO ₃ ⁻ /L. The method also gave results comparable to those obtained by the well-established ion chromatographic method and had the additional advantage of being simple, rapid, low cost, and suitable for brackish water. The text was submitted by the author in English.     

A new ionic strength adjustor for nitrate analysis in waters,soils and plants using ion-selective electrode

A new ionic strength adjustor, ISA (ISA-Pb) composed of 0.02M Pb(CH₃COO)₂–0.01M PbO–0.02M CH₃COOK–0.01M NH₂SO₃H, was tested for the rapid nitrate analysis of waters, soil and plant extracts by means of ion-selective electrode (ISE). It was found that nitrate can be determined accurately and precisely within the concentration range of 5 × 10^–2 M to 2 × 10^–6 M. The proposed ISA-Pb, with a pH of 6.8, controlled the interferences of Cl^–, HCO ₃ ^– , NO ₂ ^– , and organic anions effectively, and gave results comparable to those obtained by the commonly used ISA with Ag₂SO₄ (ISA-Ag) and to well established chemical methods as well. ISA-Pb is much cheaper than ISA-Ag, and can therefore economically replace the latter when ISE is used for nitrate determination.Part of the senior author's doctorate thesis