An investigation of column efficiency and the relationship to liquid phase distribution on ultra-low loaded glass bead gas chromatographic columns


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

Chemistry and Biochemistry



Date Submitted


Document Type





Gas chromatography



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