Comparison of three methods for detection of melamine in compost and soil

Recent product recalls and food safety incidents due to melamine (MM) adulteration or contamination have caused a worldwide food security concern. This has led to many methods being developed to detect MM in foods, but few methods haves been reported that can rapidly and reliably measure MM in environmental samples. To meet this need, a high performance liquid chromatography (HPLC) with UV detection method, an enzyme-linked immunosorbent assay (ELISA) test kit, and an enzyme-linked rapid colorimetric assay (RCA) test kit were evaluated for their ability to accurately measure MM concentrations in compost and soil samples. All three methods accurately detected MM concentrations if no MM degradation products, such as ammeline (AMN), ammelide (AMD) and cyanuric acid (CA), were present in an aqueous sample. In the presence of these MM degradation products, the HPLC yielded more accurate concentrations than the ELISA method and there was no significant (P>0.05) difference between the HPLC and RCA methods. However, if samples were purified by SPE or prepared with blocking buffer, the ELISA method accurately measured MM concentrations, even in the presence of the MM degradation products. The HPLC method generally outperformed the RCA method for measuring MM in soil extracts but gave similar results for compost extracts. The number of samples that can be analyzed by the ELISA and RCA methods in a 24-hour time period is much greater than by the HPLC method. Thus the RCA method would seem to be a good screening method for measuring MM in compost and soil samples and the results obtained could then be confirmed by the HPLC method. The HPLC method, however, also allows simultaneous measurement of MM and its degradation products of AMD, AMN and CA.