STUDIES ON SYSTEM PERFORMANCE AND SENSITIVITY IN ION CHROMATOGRAPHY

Improvements in HPLC instrumentation, suppressor technology and ion-exchange columns have occurred over the past several years to the point where an ion chromatograph can now be configured for anion analysis using a considerable variety of hardware, suppressor and column combinations. A number of parameters, including hardware configuration, effect of temperature, column type and suppressor device, were studied with a view toward optimizing the performance of an ion chromatographic (IC) system. It was found that dual-piston, reciprocating pumps used with few-pressure pulse dampeners significantly reduced baseline noise for both suppressed and non-suppressed conductivity detector combinations, while column temperature control proved essential in order to achieve routine sub-ppb detectability in non-suppressed IC. In general, the use of suppressed IC resulted in lower detection limits than non-suppressed IC when using the same columns and hardware. Of the columns studied, the methacrylate-based HR column was found to give the best overall separation selectivity when using a carbonate-bicarbonate eluent and suppressed conductivity detection. The majority of column and suppressor combinations evaluated gave acceptable performance, although some gave less than satisfactory results. Also, some combinations resulted in lower than expected analytical results, particularly for chloride, when quantitated using single-point calibration. In addition to the use of commercially available suppressor devices, there is also a large number of high-capacity cation exchangers which can be used as suppressors and these columns, in some instances, may offer equivalent (or superior) performance compared to the commercial devices.