Fourier Transform Infrared Spectrometric Determination of Alkyl Chain Conformation on Chemically Bonded Reversed-Phase Liquid Chromatography Packings

Article abstract of DOI:10.1021/ac00258a021

A series of dimethyl-n-alkyl bonded phase sorbent ranging in length from C₁ to C₂₂ have been prepared and studied by use of Fourier transform infrared spectrometry (FT-IR).Spectra have been produced for each of the bonded phases, and comparisons are made to the corresponding silane reagents.By use of assignments reported for nonplanar conformations of normal alkanes, the supramolecular structure of these bonded phase systems is examined.The presence of absorption bands at 1341, 1354, and 1367 cm^-1 in the bonded phase spectra confirms that bonded alkyl chains are bent, i. e., a significant fraction of the carbon-carbon bonds are in the "gauche" configuration.The degree of conformational disorder in chemically bonded stationary phases is shown to be comparable to that observed in the corresponding n-alkane liquids at room temperature and above.Phase transitions for the bonded phases are not observed at temperatures near or below the melting points of alkane and silane reagents of comparable length.Instead, the bonded phase chains are seen to retain a notable degree of disorder at low temperature.Finally, the effect of mobile phase environment on chain conformation is examined for a range of deuterated water/methanol mixtures varying from 70percent to 100percent methanol.Evidence is presented that in this range the mobile phase effects a significant increase in the order of the stationary phase.