Separation of isotopic compounds by reversed‐phase liquid chromatography. Effect of pressure gradient on isotope separation by ionization control

Abstract

Abstract Isotope separation utilizing ionization control in reversed‐phase liquid chromatography was studied. Several organic acids and bases labeled with oxygen‐18 and nitrogen‐15 were successfully separated from unlabeled compounds by using either 6‐m microbore columns or recycle chromatography with short columns of conventional size. Differences in the separation factors for the same isotopic mixtures were observed between the two chromatographic systems, and attributed to the difference in the pressure gradient along the columns in the two systems. The steep pressure gradient existing in the short recycle columns resulted in an increase in the peak width and the separation factor for oxygen isotopic compounds, and a decrease in the peak width and the separation factor for nitrogen isotopic compounds.