Development and Validation of a QuEChERS-Based LC–MS/MS Method for Natamycin in Imported Agricultural Commodities in Korea

Natamycin is widely used in other countries for the postharvest treatment of agricultural commodities to prevent fungal growth. However, since no MRL has been set in Korea, natamycin residues are regulated under the Positive List System (PLS) with a uniform limit of 0.01 mg/kg, requiring the development of highly sensitive and reliable analytical methods. In this study, a QuEChERS-based analytical method was developed and validated for the quantification of natamycin in five agricultural commodities-soybean, mandarin, hulled rice, green pepper, and potato-using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Extraction using methanol with 3 g of MgSO₄ resulted in high recoveries without crystallization, and clean-up with MgSO₄ and C18 effectively reduced matrix interferences blow <50%. Natamycin was detected in all five matrices at 6.8 min without any interfering peaks. The MLOQ was determined at 0.01 mg/kg for all five matrices. The mean recoveries (82.2-115.4%) and %CV values (1.1-4.6%) values were within the acceptance criteria defined by the CODEX guidelines. Matrix effects were classified as "soft" for mandarin (|ME| < 20%) and "medium" for soybean, hulled rice, green pepper, and potato (20% ≤ |ME| < 50%). The analytical method for natamycin was validated as suitable for regulatory safety monitoring under the Korean PLS.