Determination of Roxithromycin Residues in Milk by UV-1200 Spectrophotometry - Master's thesis - Dissertation

Determination of Roxithromycin Residues in Milk Using Spectrophotometry

This experiment demonstrates the spectrophotometric method for detecting roxithromycin residues in milk. Key terms: spectrophotometry, milk, roxithromycin, analytical instrument, UV-1300. The main objective is to master the use of a UV spectrophotometer to analyze the concentration of roxithromycin in milk samples. Roxithromycin, a derivative of erythromycin, reacts with concentrated HCl in glacial acetic acid and forms a colored compound that absorbs maximally at 486 nm when reacted with p-dimethylaminobenzaldehyde. By comparing the absorbance with standard solutions, quantitative analysis can be performed through colorimetry. The instruments used include the UV-1300 spectrophotometer, centrifuge, and ultrasonic cleaner. Reagents such as glacial acetic acid, HCl, 95% ethanol, and p-dimethylaminobenzaldehyde were used. A standard solution of roxithromycin (0.8 mg/mL) was prepared in 95% ethanol, and fresh milk samples (2–3 types, 50 mL each) were tested. The procedure involved sample extraction by dissolving 1.00 g of milk in 10 mL of 95% ethanol, followed by sonication and centrifugation. For determination, standard solutions were prepared and measured at 486 nm to create a calibration curve. The sample extract was then analyzed using the same method, and the concentration of roxithromycin was calculated using the formula: x = cV/m, where x is the content in mg/kg, c is the concentration in μg/mL, m is the mass of the sample in grams, and V is the volume of the extract in mL. It is important to adjust the amount of sample based on the expected concentration of roxithromycin. Proper handling of reagents and accurate measurements are crucial for reliable results. This method offers a simple and effective way to detect antibiotic residues in dairy products, ensuring food safety and quality control. Keywords: spectrophotometry, milk, roxithromycin, analytical instrument, UV-1300.