EFFECT OF SOLUTION pH VALUE ON THE CHELATION STRUCTURE OF ZINC ACEXAMATE BY ELECTROSPRAY IONIZATION MASS SPECTROMETRY

AIM　To study the effect of solution pH value on the chelation structure of zinc acexamate. METHODS　A series of samples at different solution pH values were prepared by 10% HCl or 1 mol.L^-1 NH3.H2O. Then API/TOFMS with electrospray ion source was applied to assay the samples. The nitrogen curtain gas and nebulizer gas were adjusted to a constant flow rate of 0.6 μL.min^-1 and 2 μL.min^-1 respectively. Samples were infused into the electrospray interface using a 500 μL syringe pump at a flow rate of 5 μL.min^-1. Mass spectra were acquired in positive ion modes by scanning over the range of m/z 100～1 000. RESULTS The chelation structure of zinc acexamate is stable at pH 2.54 and it can be easy to form the ion (M+ZnY)⁺ (Y=CH₃CONH(CH₂)₅COO^-) and (2M+Na)⁺ in this condition. CONCLUSION　The drug is an effective antiulcer agent. It may decrease the acidity of stomach juice, and form a polymer to protect the ulcer.