Preparative Chromatography - Sample Mass Overload > Page 17


These complex effects are best illustrated by experiment. The effect of mass overload was also investigated by Scott and Kucera (3) and the same column was used for mass overload experiments as that employed in the volume overload experiment. In the investigation of mass over load, the sample volume was kept constant at 200 ml, and a mixture of benzene, toluene and anthracene was placed on the column, the mass of benzene being increased progressively from 180 mg to 16.9 mg. An example of three of the chromatograms obtained are shown in figure 7. A chromatogram of the reference sample is shown on the left of figure 7 and contained 180 mg of benzene, 9 mg of naphthalene and 0.3 mg of anthracene. The mass of naphthalene and anthracene was kept at 9.0 mg and 0.3 mg respectively for all samples so only the benzene was overloaded. The mass of benzene was increased to 8.1 mg and then to 16.9 mg. Simple visual inspection of the chromatograms indicate that as the mass of solute is increased, the benzene peak has broadened, and become asymmetrical, which will be a direct result of the adsorption isotherm entering the non-linear region. The peak distortion resulting from mass overload is quite clear and it should be noted that, although the retention times of naphthalene and anthracene are both reduced with increased load, the peaks remain relatively symmetrical.

After, J. Chromatogr., Ref. (3).


Figure 7. An Experimental Example of Mass Overload.