Determination of melamine concentrations in dairy samples

A novel polymeric fluorescence sensor based on acrylated citric acid for detection of melamine adulteration: Application in milk powder

Melamine selective acrylate citric acid (ACA) based polymeric membrane sensor was prepared by radical polymerization method and the sensor was characterized. The sensor showed a selective fluorescent response to melamine (λ_ex/λ_em = 388/425 nm). The sensor response is linear in the concentration range of 3.96 × 10^-9 to 7.93 × 10^-8 mol L^-1, the optimum pH value is 6.0 and response time is less than 1 min. Limit of detection (LOD) and limit of quantification (LOQ) were calculated as 2.32 × 10^-10 mol L^-1 and as 7.74 × 10^-10 mol L^-1, respectively. The sensor showed great selectivity towards melamine in the presence of a large number of molecules and ions. The performance of sensor was also confirmed by determining of melamine in milk powder sample and the results were compared with HPLC results and acceptable results were obtained. As a conclusion, the results revealed that the proposed sensor is an interesting alternative for melamine determination.

Preconcentration of sulphonamides in bovine milk by the cloud point extraction method using smartphone-based digital images

Sulphonamides are a group of synthetic antibiotics used specially in veterinary medicine. Among the procedures employed in the sample preparation for sulphonamide determination are liquid-liquid extraction (LLE) and solid-phase extraction (SPE) that use large volumes of organic solvents. Hence, a clean procedure was developed based on preconcentration and cloud point extraction (CPE) without using organic solvents to quantify total sulphonamides in bovine milk. The procedure was optimized as follows: 2 mL of pre-cleaned milk sample, 2 mL of reagent solution and 1 mL of Triton X-114 7% (m/v) were added to a tube, heated in a water bath at 40 °C for 10 minutes and centrifuged at 2950 rcf for 20 minutes. Digital image acquisition was employed directly at the tube without removing the supernatant/aqueous phase. The linear response was observed between 10 and 400 μg L^-1 of total sulphonamides and described by the following equation: S = 2.50 + 0.0514C (μg L^-1) and R = 0.999. The LOD and the CV (n = 11) were estimated to be 10 μg L^-1 and 1.3%, respectively. The main interferents present at their usual concentrations in the sample did not interfere with the results. Spike and recovery tests of total sulphonamides were carried out in UHT and pasteurized milk with recovery values between 73 and 106% and the results obtained for this kind of sample were in agreement with those achieved by a high performance liquid chromatography (HPLC) procedure at the 95% confidence level. The analytical procedure presents an adequate sensitivity to determine total sulphonamides in bovine milk and does not require organic solvents, being aligned to the principles of green chemistry.

Melamine contamination in milk powder in Uruguay

Forty samples of milk powder purchased in Uruguay were analysed to assess melamine (MEL) levels. Trichloroacetic acid and acetonitrile were used to extract and precipitate milk proteins previously to clean up of the samples by solid-phase extraction and then were determined by liquid chromatography coupled to ultraviolet detection. The limit of detection (LOD) and limit of quantification (LOQ)of MEL were 0.006 and 0.019 mg kg^-1, respectively. Milk was fortified with MEL at three levels, producing average recoveries higher than 83.8%. The values for positive samples ranged from 0.017 to 0.082 mg kg^-1. Nine samples were positive. Three of them had concentrations between LOD and LOQ. The mean MEL contamination was 0.028 mg kg^-1. Consumption of milk powder containing these levels of MEL does not constitute a health risk for consumers.