Determination of melamine in milk by fluorescence spectroscopy and second-order calibration.

Melamine is a compound commonly used in the manufacturing of plastic and flame retardant products, but due to its solubility on water and high nitrogen content, it is also used to adulterate milk to mask adulteration by dilution in protein content tests. This work proposes a quick method using excitation-emission matrix (EEM) fluorescence spectroscopy and second-order calibration methods (PARAFAC and U-PLS/RBL) for the identification and quantification of melamine in milk. The proposed method uses a single clean-up step with acetic acid, resulting in a quick, low-cost, and environmentally friendly procedure, in agreement with green chemistry principles. Both PARAFAC and U-PLS/RBL were capable of detecting melamine in milk above 120.6 and 146.5 ppm respectively, adequate for adulterations above 2% in volume, with RMSEPs of 68.6 and 81.9 ppm, respectively.

Oil spill in northeastern Brazil: Application of fluorescence spectroscopy and PARAFAC in the analysis of oil-related compounds.

Between November 2019 and February 2020, 53 water samples were collected along 430 km of coastline in northeastern Brazil, which was the location of an oil spill that occurred in August 2019. Synchronous fluorescence matrices (SFMs) were acquired to avoid regions affected by Raman Stokes scatterings and second harmonic signals, and then, the SFMs were converted into excitation-emission matrices (EEM) by shear transformation. The matrix coupled with parallel factor analysis (PARAFAC) was used in the study of fluorescent components present in the collected waters. A sample collected before the oil spill and another from Florianópolis-SC, 2000 km from the incident, were used as references for nonimpacted waters. In the postspill samples, 4 components were determined, with component 1 (λexc = 225 nm, λem = 475 nm) being associated with humic-like organic matter (terrestrial), component 2 (λexc = 230 nm, λem = 390 nm) being associated with humic-like organic matter (marine), component 3 (λexc = 225/295 nm, λem = 345 nm) being associated with dibenzothiophene-like components also observed in tests with crude oil samples, and component 4 (λexc = 220/280 nm, λem = 340 nm) being associated with a naphthalene-like substance. Principal component analysis (PCA) was performed on the PARAFAC scores. The distribution of samples along the 4 components was observed and compared with the reference samples.