Talanro, Vol. 40, No. 10, pp. IWI-1549, 1993 Printed in Great Britain. All rights reserved 0039-9140/93 s6.00 + 0.00 Copyright 0 1993 Pcrgamon Pms8 Ltd THE GAS-LIQUID CHROMATOGRAPHIC STATIONARY PHASE PROPERTIES OF LIQUID ORGANIC SALTS: ANOMALOUS SELECTIVITY VARIATION WHEN EMPLOYING THE ROHRSCHNEIDER/McREYNOLDS SYSTEM RAUL MORALES,* CARLQS BLANCOt and KENNETH G. zyxwvutsrqponmlkjihgfedcbaZYXWV FURTONS Department of Chemistry, Florida International University, University Park, Miami, FL 33199, U.S.A. (Received 14 July 1992. Revised 14 April 1993. Accepted 20 April 1993) Summary-The liquid organic salts studied here have wide stable liquid temperature ranges and act as efficient, highly selective gas-liquid chromatographic stationary phases. The effect of carbon number on the gas-liquid chromatographic stationary phase properties of this series of tetra-n-butylammonimn n-alkylsulfonate salts was evaluated by the well-known Rohrschneider/McReynolds system. Several problems arose when attempting to characterize these polar liquid organic salts employing this system. The specific retention volumes for the polar selectivity probes were generally not affected by an increase in the carbon number for the series studied here. However, the specific retention volumes for the n-alkane retention index markers increased dramatically as the anion carbon number was increased. ‘Ihe overall effect was a net decrease in the calculated McReynolds constants with increasing carbon number, although the true selectivity of the different stationary phases remained constant. Additionally, the specific retention volumes of the basic test probe, pyridine, showed large erratic variations and, in some cases, was not recovered from the columns. The results suggest the possibility of on-column chemical reactions occurring with some of these salts, and an alternative test probe, 2,bdimethylpyridine (lutidine) is proposed to eliminate this problem. As McReynolds constants are presently the most commonly used parameters for predicting retention and gas chromatographic stationary phase selection, it is important that workers are aware of the inherent limitations of this scheme. Organic molten salts (OMS), also referred to as liquid organic salts (LOS) are a unique class of highly polar, selective solvents which make efficient, thermally stable gas chromatographic stationary phases.’ Liquid organic salts exhibit unique selectivity compared to conventional polymeric nonionic liquid phases presently used. These salts exhibit unusually strong orientation and proton donor/acceptor intermolecular interactions, and also possess inter-ionic forces, such as ion-dipole interactions, absent in mol- ecular liquids. Retention of a solute in gas-liquid chromatography (GLC) is deter- mined from the sum total of all interactions in the liquid stationary phase. The magnitude of individual intermolecular interactions is com- monly described as the stationary phase selectiv- *United States Drug Enforcement Administration, South- east Laboratory, 5205 NW 84th Avenue, Miami, FL 33166, U.S.A. tKonik Instruments, 6065 NW 167 Street STE B-20, Miami, FL 330159969, U.S.A. 3Author to whom correspondence should be addressed. ity; whereas, the extent of all possible intermolecular interactions for the stationary phase represents the stationary phase polarity. Therein lies the problem with conventional po- larity/selectivity schemes. There are few test solutes (also called probes) which exhibit, and, therefore, test for, only one intermolecular interaction. Likewise, it is impossible to devise a single test probe which can test for all possible intermolecular interactions. Generally, polarity/selectivity schemes are based on a relative measure of retention for several solutes which test for the dominant intermolecular interactions and a sum of all of the probes acts as an estimate of the stationary phase polarity. Although there are obvious defi- ciencies with such an empirical approach, con- temporary knowledge of solution interactions is inadequate to calculate all forces involved for complex molecules. There have been numerous approaches to estimating the polarity/selectivity of stationary phases including the calculation of the reluctance of a stationary phase to retain non-polar solutes such as hydrocarbons, as 1541