Influence and Interference by Thymol added as a Biocide on the Analysis of Precipitation Samples

Abstract

Thymol (2-isopropyl-5-methyl phenol) is recommended for the preservation of precipitation samples to suppress the microbial activity and conversion of organic acids unless refrigeration can be used. However, the addition of thymol to precipitation samples influences and interferes with the analysis of samples. The pH value of dilute (10^-4M) KCl solution decreased when the amount of thymol added was more than 100 mg/100 ml dilute KCl solution. In contrast, the pH value increased when the amount of thymol added was less than 10 mg /100 ml precipitation sample. The absorbance in the colorimetric method (indophenol blue method for NH₄⁺analysis) was decreased by the addition of thymol. This result was probably caused by the competitive reaction of thymol and phenol through their similar chemical structures. The decrease in the absorbance was dependent on the amount of thymol added. Therefore, the indophenol blue method cannot be recommended for samples to which thymol is added before starting collection because it is impossible to add an appropriate amount of thymol.