Flow injection spectrophotometric determination of chloride ion in glacial acetic and monochloroacetic acids using o-nitroaniline with nitrite 

T. Yokoyama, K. Kuzume, E. Fukuda, T. Shimizu, S. Kuroda, T. Imagawa, Y. Ochi, D. Kawamoto, H. Sakae

The Sandmeyer reaction produces a chloro-compound due to the replacement of an aromatic diazonium ion, which is produced from an aromatic amine and nitrite ion to a chloride ion under acidic conditions with a copper(I) catalyst. Therefore, the reaction is expected to determine the chloride ions based on lowering the diazonium ion concentration, i.e., reducing its absorbance. Acetic acid is a frequently used acid solvent in many chemical plants. The purity of neat acetic acid, i.e., glacial acetic acid, affects the yields of many chemical reactions. It is, however, difficult to detect chloride impurities in glacial acetic acid by common anion chromatography using a conductivity detector or a UV absorption detector. Since acetic acid exhibits significant UV absorption and conductivity, the strong peak associated with acetate ions overlaps with that of chloride ions. It would also be useful to determine chloride ions in monochloroacetic acid because it produces chloride ions upon decomposition by photolysis and oxidation. A spectrophotometric flow injection analysis (FIA) method for chloride ions was newly designed and constructed based on the Sandmeyer reaction to overcome these difficulties in chloride ion determination. The optimum conditions were determined as follows: aromatic amine, o-nitroaniline; flow rate, 1.5 mL min-1; temperature, 90 ºC; measurement wavelength, 405 nm; o-nitroaniline, 0.20 mM; sodium nitrite, 0.20 mM; reaction coil length, 4 m; and granular copper metal column length, 15 cm. The detection and quantification limits for the chloride ion were 37 and 88 μM, respectively. The linear concentration range for the chloride ion was from 0.088 to 1.0 mM based on the coefficient of determination (r2 = 0.99). A relative standard deviation of 1.3% for peak heights was obtained for nine FIA measurements of 0.10 mM chloride ion. Good analytical performance was achieved under optimized conditions to determine chloride ion in glacial acteic acid. Although well-known spectrophotometric FIA methods for chloride ion use mercury(II) thiocyanate, the developed FIA could determine chloride ions without any harmful mercury compounds. This FIA was successfully applied to the determining chloride ions in a commercial batch of monochloroacetic acid without any large interference.

J. Flow  Injection Anal.

The Japanese Association for Flow Injection Analysis

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