In September 2008 almost 52,000 infants in China suffered urinary problems from consumption of melamine contaminated baby-formulas and some other dairy products (WHO, 2009). By the end of November 2008 almost 300,000 infants were affected and six deaths have been confirmed by the Chinese Ministry of Health. A low level of melamine contamination was also found in other non-dairy products made in China such as biscuits, candies and even coffee drinks. Reportedly more than 90% of ingested melamine is excreted with urine within 24 hours (Mast et al., 1983) without any adverse health issues; however, if melamine exceeds a certain threshold, it forms crystals in urine that grow into stones (calculi) in kidneys, ureter or bladder.
In light of the melamine crisis, the FDA increased sampling and analysis of imported milk-derived ingredients and products. Recently, the government also set a threshold of 1 µg/mL for melamine in infant formula, making it critical to have a low level melamine detection method. There are several analytical techniques that could be used to detect and quantify melamine:
|Technique||Selectivity / Sensitivity||Quantification Limits (range), µg/g||Notes|
|Enzyme-linked immunosorbent assay (ELISA)||Low/Low||0.1 - 25||For detection only|
|Gas Chromatography – Mass Spectrometry (GC-MS)||Medium/Medium||0.05 - 10||Should be be used as a confirmatory and/or a screening method due to their medium selectivity|
|High-Performance Liquid Chromatography – ultraviolet / diode array detection (HPLC-UV/DAD)||Low/Low||0.05 - 65||Could be used for confirmation if validated for the matrices.|
|High-Performance Liquid Chromatography – tandem mass spectrometry (HPLC-MS/MS)||High/High||0.025 - 6||Screening and confirmation at trace levels|
|Gas Chromatography – tandem mass spectrometry (GC-MS/MS)||High/High||0.002 - 5||Screening and confirmation at trace levels|
The HPLC-UV method has become the most popular method as the high cost of maintenance and operation of GC-MS, HPLC-MS and tandem mass spectrometry limit their practical use outside of specialized testing labs. However, the existing melamine HPLC methods require acetonitrile which has significantly increased in price due to the worldwide shortage caused by the global economic crisis. That’s where Venkatasami and Sowa (2010) come to the rescue. The scientists report the first known acetonitrile-free reverse-phase HPLC melamine detection method.
The analytical method uses 0.10% TFA/methanol (90:10) as the eluent and exhibits decent linearity (r>0.999) from 1.0 to 80 µg/mL with the limit of detection (LOD) 0.1 µg/mL and the limit of quantification (LOQ) 0.2 µg/mL. The method’s analysis time of ~6 min per sample in acetonitrile-free mobile phase as well as its simplicity makes it very attractive for use in production facilites.