The Kjeldahl method and four classic spectrophotometric methods (Biuret, Lowry, Bradford and Markwell) were applied to evaluate the protein content of samples of UHT whole milk deliberately adulterated with melamine, ammonium sulphate or urea, which can be used to defraud milk protein and whey contents. Compared with the Kjeldahl method, the response of the spectrophotometric methods was unaffected by the addition of the nitrogen compounds to milk or whey. The methods of Bradford and Markwell were most robust and did not exhibit interference subject to composition. However, the simultaneous interpretation of results obtained using these methods with those obtained using the Kjeldahl method indicated the addition of nitrogen-rich compounds to milk and/or whey. Therefore, this work suggests a combination of results of Kjeldahl and spectrophotometric methods should be used to screen for milk adulteration by these compounds.

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A derivação fotoquímica é proposta como abordagem para induzir fluorescência intensa (412/465 nm) da eritromicina. Parâmetros experimentais importantes como o tempo de irradiação com UV e tipo e concentração de ácido usado para tratar a solução de analito foram ajustadas. Limites de detecção e quantificação de 0,025e 0,085 µg mL -1 foram obtidos com resposta linear até 200 µg mL -1 . O procedimento é seletivo em relação a antibióticos aminoglicosídicos (canamicina, gentamicina e amicacina). O método foi testado em formulações farmacêuticas e em uma vacina contendo eritromicina como conservante, com recuperações do analito entre 98 e 105%.Photochemical derivatization was proposed to enable intense fluorescence (412/465 nm) from erythromycin. Crucial experimental parameters such as type and concentration of the acid used to treat analyte solutions and UV irradiation time were adjusted. Limits of detection and quantification of 0.025 and 0.085 µg mL -1 were achieved with linear range up to 200 µg mL -1 . The procedure was selective towards the presence of aminoglycoside antibiotics (kanamycin, gentamycin and amikacin). The method was tested using pharmaceutical formulations and one vaccine composition containing erythromycin as a preservative component, with analyte recoveries between 98 and 105%.

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