Application of Gas Chromatographic Retention Indices to GC and GC–MS Identification with Variable Limits for Deviations Between Their Experimental and Reference Values

The potential of a new algorithm for comparing experimental and reference values of gas chromatographic retention indices (RIs) is discussed. This algorithm is designed to minimize significant elements of uncertainty typical of numerous contemporary recommendations, primarily, the fixed limiting values of permissible deviations between experimental and reference RI-values, ΔRI = (RI_ref - RI_exp). The algorithm proposed implies the calculation of deviations, ΔRI, for the most reliably identified constituents of multicomponent mixtures in different parts of chromatograms with known reference RI values, followed by calculation of coefficients of regression equations ΔRI = (RI_ref - RI_exp) = <i>a</i>RI_exp + <i>b</i> for both of the reduced sets of analytes. This equation allows for the recalculation of experimentally determined RIs into corrected values RI_corr = RI_exp + ΔRI, which means replacing the fixed "global" limits with data-dependent adaptive thresholds for different constituents of multicomponent samples. Such an algorithm makes it possible to use reference RI values for semi-standard nonpolar polydimethylsiloxane phases (with 5% phenyl groups and others) for the comparison with data determined with standard nonpolar polydimethylsiloxanes and vice versa, as well as to minimize the influence of possible erroneous reference RI data. It is applicable both to statistically processed reference data and to results of single measurements. Both of these kinds of reference data are known and presented in contemporary RI databases, e.g., in the NIST RI database.