Fast quantitative determination of melamine and its derivatives by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

A simple, sensitive and fast method for the determination of melamine and its derivatives in milk powder using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was developed. Neither time-consuming sample preparation, nor special target plates, or other extra equipment are necessary. The common matrix sinapinic acid (SA) was used with a dried-droplet preparation. Detection limits (signal-to-noise (S/N) ratio = 3) for standard solutions of melamine, ammeline and cyanuric acid were 10, 25 and 10 µg/L, respectively. The limit of quantification (LOQ) for melamine was 25 µg/L and excellent linearity (R(2): 0.9990) was maintained over the range of 10-2000 µg/L. Ammeline and cyanuric acid were analyzed with an LOQ of 50 µg/L and also excellent linearity (R(2): 0.9997 and R(2): 0.9998). Good accuracy and precision were obtained for all concentrations within the range of the standard curve. The developed method was successfully used for the determination of melamine, ammeline and cyanuric acid in milk powder samples with a simple sample preparation. The LOQ of melamine was 0.5 µg/g. Ammeline and cyanuric acid were detectable at 0.5 and 5 µg/g. This method showed excellent accuracy, precision and linearity and significantly reduces the needed analysis time, as only approximately 10 s/sample measuring time is required. To the authors' knowledge, this is the first published method to quantify melamine and derivatives by MALDI-TOF-MS.