Relative control optimization analysis

Coupled columns packed with different stationary phases can be used to optimize the analysis time (71, 75). In this approach the different columns are connected in a series or in parallel. liie sample mixture is first fractioned on a relatively short column. Subsequently the fractions of the partially separated mixture are separated on other columns containing the same or other stationary phases in order to obtain the individual components. Columns differing in length (number of theoretical plates), adsorptive strength or phase ratio (magnitude of specific surface area), and selectivity (nature of the stationary phase) can be employed, whereas, the eluent composition remains unchanged. Identification of the individual sample components via coupled column technique requires a careful optimization of each column and precise control of each switching step. 

If the analysis to be optimized involves a sample in which the relative peak areas are expected to be constant (for instance in a quality control situation), then a criterion may be used that is affected by the relative peak height (A), i.e. FO or Pv may be used. If this is not the case, then a criterion should be selected that does not vary with A ( Rs or S P or P"). This will avoid the very unattractive situation in which the location of the optimum is a function of the (quantitative) composition of the sample, so that in theory there may be different optimum conditions for every single sample ... 

The SIMS spectra are all obtained in the same way a molecular peak (high mass >100 amu peaks were preferred) characteristic of the investigated polymer sample is selected and the signal intensity is optimized by adjusting the first lens (extraction) potential. The time required for this procedure and the acquisition of one spectrum (160-10 amu) corresponds to a total ion dose less than 2.1013 ions/cm2. The relative peak intensities for the same polymer are perfectly reproducible from one analysis to another, indicating that a good control of the... 

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