Correlation coefficients of solute relative retentions for pairs of modified cyclodextrins: evaluation of selectivity by differently responding gas chromatographic stationary phases.

ABSTRACT

Relative retention times versus the n-undecane for ten diverse probe solutes from volatile oils are scatterplotted between pairs of modified cyclodextrin (CD) phases. If the resulting line of best fit has a very high correlation coefficient (r), then the two CDs are behaving similarly and will not give different results. A low value of r between two CD phases indicates they behave contrastingly enough to give different analyses. Presuming a laboratory wants three differently behaving commercial CDs, twelve are considered in this way to find the optimum three pairings (each showing r to be less than 0.800 with an average of less than 0.700). These requirements are met by Chiraldex G-DA (gamma-dipentyl) and A-PH (alpha-hydroxypropyl, dimethyl) with Beta-Dex 225 (beta-diacetyl, butyldimethylsilyl) capillaries. Solutes that fall close to the line of fit between two of the phases are undergoing "normal" transient CD molecular interaction with both. They may then show extra retention with the third phase on the other two plots, which suggests close solute-guest/CD-host molecular fit. Another possibility is that this third modified CD may behave merely as a normal non-CD phase to such a solute (shown by the rejection of it) with a lower retention than is normal. Hierarchical cluster analysis seems unreliable to indicate CD-phase relationships.