Development of a contactless conductivity detector cell for 1.6 mm OD (1/16th inch) HPLC tubing and micro-bore columns with on-column detection

A capacitively coupled contactless conductivity detector cell was designed and constructed suitable for standard HPLC 1.6 mm o.d. (1/16 ``) tubing and columns. Bode plots were acquired in order to determine the optimum input frequency for the new detector cell, with three feedback resistors of increasing resistance (1 M Omega, 3.3 M Omega and 4.7 M Omega) alternately fitted to maximize sensitivity. To evaluate the new detector geometry, a 190 mm x 0.381 mm i.d. (1.59 mm o.d.) column packed with Dionex OmniPac 8.5 mu m PAX-100 anion exchange resin was used, with an eluent of 0.5 mM sodium benzoate containing 2 methanol, pumped at 20 mu L min(-1), with detection taking place `on-column`. Standard analytical performance criteria were used to compare the test detector with a commercially available TraceDec (CD)-D-4 capillary ( 360 mu m o.d.) detector, with the new detector cell matching the performance of the commercial instrument in terms of linearity, sensitivity and reproducibility. In `on-column` detection mode, the detector cell could be moved during ( or between) chromatographic runs along the length of the packed column bed, to shorten the effective length of the column and thus reduce the retention time of strongly retained sample components, whilst maintaining the resolution of weakly retained components. In addition, the detector could also be applied to the evaluation of the stationary phase packing homogeneity by physically scanning the entire length of the micro-bore column with the moveable detector cell.