T

It is the combination of a highly effective mode of separation with a highly specific mode of detection which makes the cou- pling of capillary gas chromatography with mass spectrometry (HRGC-MS) appealing for trace organic analysis. The enormous possibilities offered by this system may, however, tempt the analyst to take too casual a view of the stringent requirements of good analytical work. The question arises: do we - sometimes - misuse the potential of GC-MS?

Clearly it is the nature of the problem which determines which part of the analytical process - separation or detec- tion - should be given priority in order to generate the necessary selectivity. No matter how specific a determination can be made by using a selective detector, such as the mass spectrometer, the basis of any advance analytical scheme for organic trace analysis is a problem-oriented set of non-discriminating separation steps.

Any multi-component/multi-matrix prob- lem in organic analytical chemistry requires first of all a strategy for reducing the number of and/or structuring the types of detectable compound. After sampling, the steps (1) extractionidissolution,

Do We Always Use Our Analytical

Tools in the Best Possible Way?

(2) removal of interfering matrix compo- nents (clean-up), and (3) preseparation by liquid chromatography into groups of related compounds are crucial for reducing the number of sample components to a level which is amenable to separation by gas chromatography. In particular, matrix depletion as the first step requires a well evaluated multi-functional separation scheme. Prior to detection the analyst should strive to bring the separation of the analytes from all other sample components to the highest possible level. In addition to being a sound analytical strategy, it helps in optimizing the performance of any detector, including a mass spectrometer.

If the aim is to obtain a complete picture of the complex pattern of compounds present

in a polluted sample, an optimized separa- tion, preferably constructed of modular units, must be selected prior to detection. If, however, only certain compounds with- in a complex mixture of pollutants are of interest, a simple clean-up combined with a highly selective mode of detection is a better choice. Without the selectivity and sensitivity of the electron-capture detector many of the environmental problems asso- ciated with halogenated compounds would not have been recognized as early as they were.

The potential specificity of the mass spec- trometric detector is, unfortunately, often used to compensate for sloppiness or inex- perience in dealing with an analytical problem: often the mass spectrometer is substituted for a sensible separation step. No analytical chemist worth his salt would use his detector as a waste dump for unwanted molecule. Any coin has two sides: let us continue to refine the combi- nation of separation and detection to the pinnacle of analytical art.

AT K. Ballschrniter

Journal of High Resolution Chromatography VOL. 14. JUNE 1991 365