For simultaneous assay of nitrite and nitrate, sample zone is split in the holding coil (A) and its 200 mcrL portion send into the column. Next the remaining (100 mcrL) portion in the holding coil is reacted with Gries reagent in holding coil, and sent to flowcell, yielding the first peak for nitrite.
The nitrate formed in the Cd column is then retrieved (as 100 mcrL) portion into the holding coil, yielding, after reaction with Gries reagent, the second peak, which is the sum of nitrate and nitrite.
Injecting separate nitrite, nitrate (200 ppB N) samples yields separate traces, which when overlaid (B), reveal that the column efficiency is close to 100%, since the peaks of nitrite and nitrate are of the same height.
When sample containing mixture of nitrite, nitrate (each 100 ppB N) is injected (blue trace C) the first peak corresponding to nitrite is half of the second peak corresponding to mixture of nitrate and nitrite. Series of samples containing an increasing concentration of nitrite and constant concentration of nitrate (100 ppB N) injected in duplicate (D), shows how well this dual channel analyzer resolves samples of varying concentrations, without any carryover at a rate of 110 assay results per hour.