Studies have shown that it is possible to detect and quantitate non-UV-absorbing ionic compounds by high-performance liquid chromatography (HPLC) by the addition of a UV-absorbing ion to the mobile phase with indirect photometric detection. The method is applicable to both organic and inorganic ions using ion-exchange1p2 and reversed-phase chromatography in the ion-pair mode3-g. Recent reports have shown that this method of detection can be extended to neutral species such as alcoholslo ketoneslOJ1 and monosaccharides12 using methylene blue in the solvent. The authdrs suggest in the latter cases that some form of "ion-pair" complex is involved in the perturbation of the eluate concentration of the methylene blue". More recently, it has been observed in this laboratory l3 that neutral molecules which absorb in UV light may be added to the chromatographic solvent to enable detection and quantitation of non-UV-absorbing neutral species such as aliphatic alcohols, ethers and esters by indirect photometric detection.
This paper reports a more detailed investigation of this phenomena using reversed-phase HPLC of Cs-and C4-alcohols as a model system.
EXPERIMENTAL
Reagents and materials
The alcohols used in this study were obtained from Ajax Chemicals (Sydney, Australia) and re-distilled prior to use. The benzamide (Hopkin & Williams, U.K.) and the uracil and theobromine (Sigma, U.S.A.) were all shown to be chromatographically pure by HPLC using the solvent system employed in the present study. The acetonitrile was HPLC grade (Ajax Chemicals).
Chromatographic equipment
The liquid chromatograph consisted of a pump and variable-wavelength detector (LC-3, Pye-Unicam, Cambridge, U.K.)