Detect Melamine With ELISA Assays

The measurement range required for these assays is ideally suited to the wavelength in which all photometers have an excellent degree of accuracy. The detection limits of the assays are highly dependent upon the accuracy and precision of these photometric readouts. As such, only marginal differences, too small to be significant, were observed between the LOD values. With both ELISA kits, concentrations of melamine below 10 µg/L are easily detected. Therefore, the ELISA assays are able to detect melamine levels to the same degree of accuracy as LC/MS/MS tests.

Determination of Melamine

The three different types of milk were spiked with pure melamine and analyzed using both ELISA kits. These measurements were taken using a range of different photometer types. The results from one of the photometers are shown in Table 2 (see p. 47). Results obtained from all other photometers were fully compliant with the results shown in Table 2.

The data shown illustrate how both assay kits show very similar activity, with <10% difference in recovery efficiencies. Additionally, both kits have a common tendency to slightly underestimate melamine concentrations in those samples with a high melamine concentration; however, this does not affect the usability of these assays, because all samples are still detected as strong, positive ones in the screening assay. Therefore, the results clearly show that ELISA assays are well suited for screening purposes, including the detection of melamine in an unknown milk sample.

Based on the above results, both of these tests can be used to detect melamine residuals accurately in dairy products. The assay sensitivity obtained is on par with that of mass spectroscopy analyses. ELISAs present a cost advantage when compared to chromatographic methods, however. This simple, high-throughput screening method enables large-scale screening of thousands of samples with low instrumentation costs and affordable running prices.

Although these assays have a slight inclination to underestimate the high melamine concentrations in milk samples, the level of sensitivity obtained is still well within acceptable levels for melamine screening when a qualitative yes/no answer is required. When these assays are used for screening, positive samples should still be confirmed subsequently using LC/MS/MS or GC/MS/MS methods to verify the exact quantity of melamine present.

Melamine residuals in milk can be detected in a fast (total assay time: approximately one hour) and cost-effective way to efficiently screen dairy products, ensuring that any contamination is quickly and easily identified. ■

Lampinen is a senior application scientist with Thermo Fisher Scientific. Reach her at [email protected].