TOC Determination in Phosphoric Acid by UV Digestion Application Note · multi N/C UV HS

Introduction

Phosphoric acid is used in many industries, for example, in the production of fertilizers and detergents or in food industries as a preservative in beverages or as an antioxidant in meat products. The monitoring of impurities in phosphoric acid is crucial for these kinds of applications. In addition to other parameters, the TOC is used as a sum parameter in quality control that addresses the whole range of contamination by organic impurities.

There are two very common approaches that can be applied for TOC determination in liquid aqueous matrices: catalytic high temperature combustion and wet chemical digestion promoted by UV light and additional chemical oxidants.

Wet chemical UV digestion is the principle of choice for very aggressive matrices, such as concentrated phosphoric acid or other mineral acids (except hydrochloric acid). While the phosphoric acid may quickly damage the combustion tube and catalyst in catalytic combustion TOC methods, the big advantage of UV digestion is a minimum of maintenance and wear of the TOC system. The oxidation power of the multi N/C® UV HS that was used for these measurements is very high due to its high-power, long-life UV reactor. Hence, a complete oxidation of the organic compounds inside the sample is ensured.