AVALIAÇÃO DA QUALIDADE DO ARLA 32: USO DO NEGRO DE ERIOCROMO T COMO INDICADOR COLORIMÉTRICO PARA IDENTIFICAÇÃO DE ADULTERANTES

Abstract

The quality of Automotive NOx Reducing Agent Liquid (ARLA 32) is essential for the proper functioning of Selective Catalytic Reduction (SCR) systems. However, adulteration practices compromise its efficiency, increasing pollutant emissions and causing severe damage to catalysts. This study investigated the use of Eriochrome Black T (EBT) indicator as a rapid screening strategy to identify adulteration in the field. A total of 20 real samples were analyzed, including one commercial sample and 19 obtained from inspections, in addition to 13 simulated adulteration conditions at ratios of 1:1, 1:3, and 3:1. The indicator exhibited a blue color in solution and variations to lilac, purple, and pink tones in adulterated samples, reflecting the complexation of EBT with Ca²⁺ and Mg²⁺ ions present in non-demineralized water and agricultural urea. Refractometric analysis confirmed a high level of non-compliance in field samples, which corroborates the loss of quality. The colorimetric observations allowed a clear distinction between ARLA 32 and the different levels of adulteration simulated in the laboratory, with greater chromatic intensity observed in the more diluted samples. It is concluded that the proposed method demonstrates simplicity, low cost, and sensitivity, representing a promising alternative for rapid screening at inspection stations, contributing to the strengthening of quality control actions and to the reduction of vehicular emissions.