Abstract: The use of iodide in acidic medium as a reagent for the liquid chromatographic amperometric determination of non-volatile nitrosamines was investigated in a two-line flow injection manifold. The method was based on the decomposition of nitrosamines in warm acidic solution to yield nitrite and the electrochemical detection of the oxidation of nitrite with iodide. The FIA system allowed 20 µL of nitrite solution to be injected into a carrier stream (0.5 ml/min, water or water/acetonitrile, 1:3) which was then merged with a KI stream in 0.5 M H2SO4 (0.5 ml/min). The merged solution was passed through a heated reactor coil, a cooling coil and the flow-through detector cell containing Au electrodes at a potential of 0.2-0.3 V vs. SCE. A linear response was obtained for 0.5-5 mM nitrite with a reaction temperature of 50-60°C and an iodide concentration of 2 mM. The detection limit for nitrite was 10 pg in a 20 µL sample (0.1 µM). Compared with the use of Ce(IV) reagent, the proposed method achieved a higher sensitivity, a lower detection limit and comparable band broadening and tailing.

Abstract: Nitrite solution (30 µL) was injected into a carrier stream (0.5 ml/min) that then merged with a reagent stream of Ce(IV) solution in 0.5 M H2SO4 (0.5 ml/min) and passed through a 25-cm-long single-bead string reactor constructed from PTFE tubing (0.5 mm i.d.) containing 0.25-mm diameter glass beads followed by a three-dimensionally knitted PTFE delay tube (3 m x 0.5 mm), both enclosed in a thermostatically controlled chamber. The solution was passed via a tightly coiled water-cooled PTFE tube (1 m x 0.5 mm) to a detector comprising a 3 µL thin-layer rectangular-channel flow cell containing an Ag/AgCl/3 M NaCl reference electrode and two flat Au-disc working electrodes for the mono- or bi-amperometric determination at 1.4 V or a difference of 0.3 V, respectively, of the Ce(III) produced by the reduction of Ce(IV) by the nitrite. When the post-column reactor was used to determine nitrite in a carrier stream of aqueous 30% acetonitrile with reactor and delay coil temperature of 70°C the response was rectilinear from 1 to 10 µM-nitrite and the detection limit was 50 nM. It was shown that the presence of the reactor and delay tube had little effect on the standard deviation of the detected peaks and gave a more nearly Gaussian peak shape. The results showed that the system should be suitable for use in the LC determination of nitrosamines.