Title: Digital colorimetric determination of chlorides in water using gas extraction and methyl orange
Abstract: The current article presents a sensitive and selective method for the quantitative determination of chlorides in water based on the oxidation of potassium permanganate in sulfuric acid, gas extraction of the formed chlorine and subsequent digital colorimetric determination using the reactive indicator paper impregnated with methyl orange. A simple and affordable installation is described that makes it possible to realize this combination and carry out the determination without the sample preparation. The high selectivity of this technique is ensured by the fact that the reaction of the formed chlorine with methyl orange is carried out outside the analyzed solution. The method for preparing the reactive indicator paper with a uniform and reproducible distribution of the reagent is proposed. Conditions providing the completeness of chlorides oxidation and reproducible extraction of the resulting chlorine from the test solution are selected. The method of digital colorimetry using scanning and color images processing is recommended for the quantitative determination. The green coordinate G in the RGB system is chosen as the most sensitive and promising analytical signal. Exponential and linear calibration functions and their equations are presented. The limit of detection was 0.004 mg·L -1 , and the concentration range was 0.1-1.5 mg·L -1 . The time of single determination was 25 minutes. The technique was successfully tested for the analysis of the Don River water. The developed method of analysis is simple in execution, available, and does not require any expensive reagents or equipment. Therefore, the method can be recommended for the monitoring studies. Keywords: chlorides, selective detection, dynamic gas extraction, digital colorimetry DOI: http://dx.doi.org/10.15826/analitika.2017.21.3.007 1,2 M.O. Gorbunova, 1 Е . М . Bayan, 1 A.V. Shevchenko, 2 M.S. Kulyaginova 1 Southern Federal University, Zorge st., 7, 344090, Rostov-on-Don, Russian Federation 2 Rostov State Medical University of the Ministry of Healthcare of Russian Federation, Nakhichevansky lane, 29, 344022, Rostov-on-Don, Russian Federation