Demonstration of a novel ion-exchange column for pre-concentration of silver ions in optical emission spectroscopy utilizing a liquid-sampling atmospheric pressure glow discharge microplasma

Abstract

A novel, small-volume, strong cation-exchange column has been employed as an on-line pre-concentrator for samples introduced to the liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma. The column stationary phase was synthesized by a unique microwave-assisted grafting of sulfonic acid groups onto nylon 6 capillary-channeled polymer (C-CP) fibers. The column material is robust with respect to attack in acidic sample media, with high permeability that obviates the need to use a high-pressure liquid chromatography pump. The column-loading flow rate, sample-load volume, and sample concentration were studied to demonstrate the utility of the column in improving the limits of detection (LOD) of silver in nitrate/nitric acid solutions. The eluted analyte signal intensity was found to be unaffected by column-loading flow rates from 100 to 800 μL min⁻¹. When signal intensity was plotted against increasing sample-loading volumes and load concentrations, good linearity was observed (R² = 0.9939 and 0.9999). Overall, implementation of this novel column provides enhanced analytical performance for the LS-APGD-OES source with very minimal added experimental complexity. This is a key aspect as the microplasma is implemented on field-deployable platforms. It is imagined that the same fiber format could be easily adapted to larger size scales such as common to inductively-coupled plasma sources.