Determination of melamine impurities by capillary zone electrophoresis with UV- and quadrupole time-of-flight mass spectrometric detection.

A method based on CZE coupled to quadrupole TOF MS (Q-TOF MS), which is suitable to analyze seven common melamine impurities is presented. MS compatible formic acid based BGEs with various concentrations of organic modifiers were investigated using UV detection to determine the best separation system regarding resolution and speed. The optimized BGE consisted of 350 mM formic acid with 10% ACN and migration times were <6 min. The detection limits were considerably improved when ESI MS was applied instead of UV detection. In addition the instrument allows quantification with good linearity and repeatability in the relevant concentration range. The analytical characteristics of the method were evaluated for melamine, guanylurea, diaminotriazine, ureidomelamine, guanlymelamine, melam, methylmelamine, and dimethylmelamine both with UV and MS detection. Several different melamine samples were analyzed und the determined impurity levels were in the range from 0.02 to 2.3%.