The intensity of the reference gas peaks was controlled by adjusting the gas pressure of the reference gas within the system using the pressure regulator of the interface. At the same time, the sample inlet split on the LC-Isolink interface was opened while a 0.05 M H2SO4 eluent and 0.015 M VCl3 in 0.3 M HCl reducing agent were pumped at a rate of 200 mL min -1 each.