Trace Enrichment and Chemical Derivatization in Liquid Chromatography; Problems and Potential in Environmental Analysis

Abstract

The importance of detection limits in the trace analysis of pollutants is well recognized. Very often selectivity is another criterion and in order to achieve this, a chromatographic separation step may be necessary. The attainable detection level will then also depend strongly on chromatographic parameters and particularly on the injection step. It has been observed in earlier work that relatively non-polar organics dissolved in a polar solvent such as water are concentrated upon injection onto commercial reversed phase material (C₈, C₁₈) into a small zone on top of the column. This concentrating effect can be adopted for trace enrichment of pollutants in aqueous samples. It permits the use of large injection volumes up to several hundred millilitres without serious band broadening. The disadvantage of such a procedure is that interferences are also concentrated and one has to trade selectivity for sensitivity. Some of this drawback can be eliminated by using column coupling and step gradient techniques and by combining these methods with chemical derivatization techniques in the post-column mode. With the proper choice of the post-column reaction, one can further improve the selectivity by choosing a more or less selective reagent. The use of a reagent with reasonable reaction kinetics and a good chromophore or fluorophore will greatly enhance the detection properties. All these concepts have been demonstrated with a few practical examples. The reproducibility of these techniques (usually below 4% rel. S.D.) permits good quantitation of pollutants.