Characterization of metal glycinate complexes by electrospray Q-TOF-MS/MS and their determination by capillary electrophoresis-ICP-MS: application to premix samples

A method was developed for the determination of metal complexes with glycine (glycinates, [M(Gly)(x)(H2O)(y)(SO4)(z)](n), where M denotes Zn, Cu, Mn and Fe) in premix samples used for the preparation of animal feeds enriched in essential trace elements. The method was based on the extraction of the glycinates with 10 mM ammonium acetate (pH 7.4) followed by their determination using capillary electrophoresis with ICP MS detection. The stability of the glycinates in solution was verified by electrospray TOF-MS. Each supplement was shown to be a mixture of complexes, with polymerization degrees ranging from n=1 to n=4 (depending on the metal), that were fully or partially dehydrated. The metal glycine complex moiety was found to be preserved during capillary electrophoresis. The detection limits, calculated as three times the standard deviation of the blank plus the blank, were between 0.05 and 0.2 mu g mL(-1) (as the metal), and the calibration curves were linear, allowing the analysis of premix samples. Repeatability for glycinate standards was below 12%, and analytical precision was typically within 15%.