Studies have been made of column efficiencies, extra-column effects, the liquid phase mass transfer term (C_l), and liquid phase distribution at ultra-low liquid loadings on glass bead gas-liquid chromatographic columns. The advantages of using lightly loaded columns are described in detail along with a critical evaluation of the limitations of this liquid phase reduction ad infinitum. Theories have been presented by Giddings^22,23,25,30,32 which predict the mass transfer term (C_l) as a function of two extreme liquid phase distributions. The first equation assumes 100% "capillary" liquid held at the glass bead contact points and represents a very inefficient column. This prediction is known to be valid for normal loaded columns in the 1.0 to 0.1 liquid percentage range^35,48. The second equation assumes a uniform liquid "adsorption" film around the glass bead which represents a very efficient condition. This equation has never been experimentally verified, but Hawkes^48 and Giddings^35 suggest that this condition is approached when the liquid phase is reduced and that a uniform film exists at loadings less than approximately 0.04%. The results of this research show that although a uniform film is approached with liquid load reduction, it is never reached, even at loadings as low as 0.004%. Data show that the capillary liquid assumption is valid for glass bead columns with liquid loadings greater than 0.05%, but fails to predict the proper efficiency term at the lower loadings. Two important transitions occur at about 0.03% liquid loading: (1) C_l ceases to decrease significantly with a liquid load reduction, and (2) C_l ceases to be the predominant (plate height controlling) efficiency parameter. Reductions below 0.03% do little to improve column efficiency and may cause adverse effects such as decreased resolution, increased adsorption, and a shorter column life. Data collected before and after some apparatus and procedure changes indicate the importance of minimizing extraneous peak broadening sources. It is suggested that a large amount of the literature is in error because of apathy in this area. The results suggest that a reduction in liquid load is an excellent method of increasing the column efficiency and reducing the analysis (sample retention) time.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





Gas chromatography



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Chemistry Commons