General Considerations

Let us start with our existing knowledge of the analysis of organic micropollutants.

What were the main stages of the analytical determination?

Answer

(i) Extraction of the analyte.

(ii) Separation from interfering compounds by chromatography.

(iii) Concentration.

(iv) Analytical separation and determination by gas chromatography, for chlorinated compounds by using either an electron capture detector or mass spectrometric detector.

You should revise Section 4.2 if you have not remembered these steps.

We must now consider modifications to the method to analyse ng l-1 rather than ^g l-1 concentrations. There would appear to be two routes, as follows:

1. Increasing the overall concentration factor in the pretreatment stages.

2. Increasing the detection sensitivity.

There may be room for a small improvement in overall sensitivity by method 1 but this will be insufficient on its own. Note, for instance, the final extract volume (1 ml) given earlier in the DDT analytical method in Section 4.2. There could be at least a 10-fold reduction in this volume, with a corresponding increase in sensitivity. The possibility of increasing the sample size is limited by physical considerations of handling large samples under clean conditions. A disadvantage of this method is that any impurities carried through the extraction scheme will also tend to concentrate. Method 2 could lead to a more substantial increase in overall sensitivity, particularly if selective detection of the desired analyte is included.

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