Plate Theory and Extensions - Experimental Examination of Dead Volume Measurement > Page 35

Experimental Examination of Dead Volume Measurement

Alhedai et al. (11) critically examined a commercially available reverse phase column packing, Zorbax C8, and measured some of the individual volumes included in equation (39). The exclusion characteristics of the interstitial cavities were obtained by measuring the retention volumes of salts having different molar volumes. The salts were ionically excluded from the pores of the packing and, thus, only penetrated the interstitial cavities as they passed through the column. The results are shown as a curve relating retention volume against ion volume in Figure 6.

Courtesy of the Analyst (ref.11)


Figure 6. Graph of Retention Volume of a Series of Ions against Their Ionic Volume


The retention volume decreases linearly as the ion volume increases. It should be pointed out that the retention i not related to the charge on the ion. The intercept of the curve on the retention volume axis gives a value for the total interstitial volume of the column, which differs only slightly from the retention volume of sodium nitrate. Thus, the retention volume of sodium nitrate would give a close approximation to the interstitial volume of the column. The slope of the curve shown in Figure 6 clearly indicates the exclusion properties of the interstitial volume are significant.