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Replicate gas-liquid chromatographic based specific retention volumes, activity coefficients, and interaction parameters of ten solutes with poly(dimethylsiloxane) (PDMS) solvent at 303 K are reported. The average relative standard deviation of the former (three GLC columns) is 0.82%. The values moreover compare favorably with those reported previously for four PDMS used commonly as stationary liquids in analytical GLC. Static-determined activity coefficients and interaction parameters are also reported and compared with the GLC results. The internal consistency of the former lies within ±1.2%, while the averages of these agree with the GLC values to within ±0.5%, thus providing validation of the latter. Previously reported discrepancies between static and GLC-based activity coefficients and interaction parameters with PDMS solvents are therefore attributed to experimental artifact rather than fundamental principle.

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There is today little question of the value of GLC retentions in quantitative analysis, and only minor dispute regarding the validity of the technique in qualitative identifications. In the latter instance, use is often made of some or other form of relative retention scheme [l] wherein instrumental variables tend to selfcancel. Of remaining concern, however, is the purity of the stationary liquid. For example, the most widely disseminated GLC data base is that of McReynolds [2] where, unfortunately, surfactants were employed in admixture with each solvent. These data must therefore be accorded some deliberation prior to attempts at correlation with others arising from pure-phase investigations.Squalane (2,6,10,15,19,23-hexamethyltetracosane) has to date been the most-studied (although perhaps not the most widely employed) of all GLC liquids, partly as a result of its ready availability and partly due to the fact that comparison of static with gas-chromatographic solute infinite-dilution activity coefficients was made with it early in the history of GC [3-51. These data moreover remain in part even today the basis of judgment of precision and accuracy of instruments employed for physicochemicalstudies [6][7][8].AsaresuIt,retentionsand Kovatsretention indices [9] for very many solutes have been reported over the years with squalane stationary phase [10][11][12], and correlations of these in addition made with compound boiling point and structure.Unfortunately, squalane is generally not suited for open-tubular (capillary) columns when used at temperatures of in excess of 100°C for prolonged periods of time. Alternative phases which provide elution on the basis predominantly of vapor pressure (Trouton's rule iS&,Tb-' -23.2cal m0l-l deg-l, whence In P i --23.3Tb (RT)-' + c) constitute the polydimethylsiloxanes (OV-1, OV-101, SP-2100, SE-30, and so on), which have the attendant advantages of even film formation on capillary walls, low volatility at 3OO0C, and moderate lifetime under continuous use. However, there exists a paucity of tabulation of retentions and retention indices of high accuracy with these phases. There is furthermore some question regarding the utility of such data in view of the potentially diverse distribution of chain molecular weight even of thesamematerialfromone batchtothe next fromagivensupplier.We have in contrast to the above found only minor differences in absolute retentions with these materials, and virtually no differences in relative retenti0ns.Thu.s. the choice of one overthe others as a standard reference phase becomes a matter of some subjectivity. We find for instance that column efficiency with all such phases at moderate temperature is satisfactory (9,000 effectiveplatespermeterforglasscolumnsofca.O.l-mmi.d.), but that the less viscous of these (OV-101, SP-2100) tend in small-i. d. tubes to coalesce (thus blocking the tube orifice) if subjected to severe temperature-gradient velocity (>lo O min-' heating or cooling). The choice of a general-purpose phase for open-tubular column...

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