Simultaneous analysis of 16 metal ions by ion-pairing high-performance liquid chromatography-electrospray ionization tandem mass spectrometry

Metal ions can be analyzed by ESI-MS with chelating agents. However, matrix effect and the marginal difference in atomic weight of the isotopes of some metal ions make the analysis of a metal ion mixture not feasible. In this paper, we present the use of IP-HPLC in conjunction with a metal ion chelating agent to analyze the metal ion mixtures. Hydrophobic (+/-)-trans-1,2-cyclohexylenedinitrilotetraacetic acid (CDTA) was used to chelate 16 metal ions. The chelates were then separated by IP-HPLC followed by ESI-MS analysis. For IP-HPLC, different combinations of primary amines and their salts were employed as the ion-pairing reagent in eluent on a high-pH resistant C-18 column under basic conditions. For ESI-MS, Q-Exactive Focus system was used. Among the metal ions, the results indicated that Al3+ showed the lowest LOD (3.88 x 10(-3) mu M) while Zn2+ showed the highest (0.227 mu M). The sensitivity was close to that of ICP-AES. The coefficients of determination (R-2) were greater than 0.995 except for Sr2+ (R-2 = 0.9899), indicating the high accuracy of the method. Finally, this method was used to analyze the black soybean samples from two different sources. Eight metal ions were successfully identified with simultaneous detection of sugars, organic acids, and nucleotides.

Automated summary

In this paper, the use of IP-HPLC in conjunction with a metal ion chelating agent to analyze metal ion mixtures was presented. The method showed high sensitivity, close to that of ICP-AES, and high accuracy with coefficients of determination greater than 0.995.