Daniel P. Kirby

On-line liquid chromatography-mass spectrometry of ion pairs

Abstract An on-line continuous extraction interface between a high-performance liquid chromatograph and a mass spectrometer permits the operation of the chromatograph in the reversed-phase mode without compromising the performance of the spectrometer. Solutes are extracted into a volatile organic solvent which is then transported to the spectrometer by a moving-belt interface. A greatly simplified version of the original extraction interface is shown. In its new design the extractor operates on the principle of solvent rather than air segmentation, and much of the expensive peripheral equipment has been eliminated. Flow-rates of up to 1.0 ml/min each of aqueous (mobile) and organic (extracting) phases are easily accommodated in this on-line operation. We have examined the compatibility of ion-pair chromatography with the high-performance liquid chromatography-extraction-mass spectrometry combination, particularly in terms of the quality of solute spectra obtained and the volatility of the counter ions. The results presented here show that ion pairing and subsequent extraction are compatible with the on-line operation under both chemical ionization and electron impact conditions. Spectra are produced from the ion pairs which consist of the solute spectrum superimposed on but easily discerned through the spectrum of the counter ion. A rationale to explain the mass spectrometric observations is presented. The implication of these results for the analysis of ionic compounds by this technique is discussed.

Ion Pairing Techniques: Compatibility with On-Line Liquid Chromatography—Mass Spectrometry

The mass spectrometric properties of a series of model ion pairs were examined. In the cases studied it was possible to vaporize the ion pair consituents and to produce spectra corresponding to those of the unpaired materials. These findings offer a convenient means for derivatizing certain ionic compounds and demonstrate the feasibility of analyzing ionic species by on-line liquid chromatography-mass spectrometry.