Detection and quantification of dicyandiamide (DCD) adulteration in milk using infrared spectroscopy: A rapid and cost-effective screening approach

Abstract

Dicyandiamide (DCD) has been identified as a potential adulterant in milk. This study presents the development of a convenient, fast, and cost-effective FTIR-based screening method that considers both DCD tautomeric structures, given their relative stability in the ground state (with an energy difference of 288.68 kJ/mol between the two tautomers). The study identifies the 2200 cm−1 and 2160 cm−1 FTIR peaks of DCD as the most promising non-interfering peaks for calibration plots, effectively eliminating interference from the medium and possible adulterants. Density Functional Theory (DFT) studies using the B3LYP/6–31 G (d) method confirm that these two peaks correspond to N-C-N bond stretching in two DCD tautomers. Developed calibration plots for the 2160 cm−1 and 2200 cm−1 peak intensities and the integrated peak area versus DCD concentration show a strong positive linear relationship (2200 cm−1 = 0.9952, 2160 cm−1 = 0.9959, Area = 0.9981). This study highlights the utilization of the Area under the peak for both N-C-N stretching peaks, considering both tautomer structures. The novel FTIR-associated DCD detection method is grounded in simple linear regression theories and has been rigorously verified as an accurate, rapid, and cost-effective technique for screening DCD-adulterated milk samples using FTIR spectroscopy.