Applicability of Pressurized Liquid Extraction for Melamine Analysis in Pet Foods with High-Performance Liquid Chromatography with Diode Array Detection

A pressurized liquid extraction (PLE) method was developed for melamine analysis in pet foods. The PLE method which utilized an accelerated solvent extraction (ASE®) system was also compared with sonication and polytron extraction methods. The parameters for the optimized PLE method were temperature (75 °C for wet pet food, 125 °C for dry pet food), pressure (1,500 psi), static time (10 min), flush volume (40%), purge time (1 min), and number of cycles (1). Recoveries obtained by PLE method were significantly higher (P ≤ 0.05) than those of sonication and polytron methods for dry pet food samples. For the analysis of adulterated pet foods, PLE resulted in the highest melamine content followed by sonication and polytron. Using PLE, samples fortified with melamine at 2.5 and 100 mg kg−1 resulted in recoveries ranging from 55% to 90% for wet samples and from 90% to 116% for dry samples. Low recovery rate from wet samples at low spike level (2.5 mg kg−1) may have been caused by co-aggregation of polysaccharide and protein with melamine due to low pH during solid-phase extraction cleanup. Limit of detection and limit of quantification values were 0.5 (mg kg−1) and 1.0 (mg kg−1) for dry samples. Overall, PLE had the best extraction efficiency compared to sonication and polytron, proving PLE to be a useful tool for melamine analysis of pet foods.