Spectrophotofluorometric assay of Sulfaguanidine in Milk whey

The methylene blue fluorescence quenching and bromocresol purple spectrophotometric methods were applied to achieve the detection of sulfaguanidine in whey. The quenching of the fluorescence marker by sulfaguanidine in whey was used to elucidate the effect of the quencher on the Stern-Volmer quenching constant (K_SV) values. The interaction of methylene blue with sulfaguanidine increases in whey by 3 times compared to water (K_SV = 3 × 10³ M^-1 and K_SV = 1 × 10³ M^-1, respectively). The value of the Stern-Volmer quenching constant K_SV = 4 × 10⁴ M^-1 is the highest for quenching of whey fluorescence by bromocresol purple. The obtained results were applied as a spectral method for determining the concentration of sulfaguanidine in whey. Analytic emission (348, 430 and 700 nm) and absorption (259, 435 and 590 nm) wavelengths were used. The concentration for detecting sulfaguanidine in whey was 5 × 10^-7 M (0.01 mg/mL) which is an order of magnitude lower the limit of spectrophotometric method.