Application of crown ether coated piezoelectric crystal as a detector for ion chromatography

Abstract

A reusable and sensitive piezoelectric quartz crystal detector was developed for the detection of either cations or anions in ion chromatography. The quartz crystal electrode coated with crown ether (sym-dibenzo-16-crown-5-oxydodecanic acid) was prepared and was found to give the best results in terms of stability, sensitivity and reproducibility. Linear frequency (voltage) responses on a 10 MHz AT-cut crystal for ions were found on the range 0.1–5 × 10^–5 mol l^–1. Variations of the crystal frequencies were converted to voltage using a TC 9400 chip. Polystyrene–poly(divinyl benzene) with cryptand [2,2] as an anchoring group was synthesized and applied as a bifunctional ion chromatographic packing material for the separation of both cations and anions. The crown ether coated piezoelectric crystal detector with detection limits of 2 × 10^–5(1 × 10^–10 mol)–5 × 10^–5 mol l^–1(2.5 × 10^–10 mol) for various ions showed a similar detection limit to that of a commercial conductivity detector in ion chromatography. The effects of solvents, reproducibility of responses and competitiveness with respect to a commercial conductivity detector were also investigated.