Capillary Chromatography - Heart Cutting 2

This application is quite different, however, as in this case, the technique is employed to improve the resolution of a complex sample not merely as a enrichment procedure. An example of this type of assay might be the measurement of the contaminant benzene in a complex hydrocarbon mixture such as gasoline or diesel fuel. Benzene is perceived as being toxic and carcinogenic and, as a consequence, its presence in a commercial produce must be monitored. Unfortunately in a multi-component hydrocarbon mixture a trace of benzene will be masked by other co-eluting substances with all types of stationary phase. It follows that the separation must be carried out employing two types of stationary phase, one dispersive and the other polar. The effect of this combination is depicted in figure 23.

This application is quite different, however, as in this case, the technique is employed to improve the resolution of a complex sample not merely as a enrichment procedure. An example of this type of assay might be the measurement of the contaminant benzene in a complex hydrocarbon mixture such as gasoline or diesel fuel. Benzene is perceived as being toxic and carcinogenic and, as a consequence, its presence in a commercial produce must be monitored. Unfortunately in a multi-component hydrocarbon mixture a trace of benzene will be masked by other co-eluting substances with all types of stationary phase. It follows that the separation must be carried out employing two types of stationary phase, one dispersive and the other polar. The effect of this combination is depicted in figure 23.

 

If the hydrocarbon sample is separated on a purely dispersive stationary phase (e.g. OV101, Column 1) the benzene will co-elute with the C7 isomers and be lost amongst a confusion small peaks. If the sample is trapped and re-run on a polar stationary phase (e.g., polyethyleneglycol of a Cyanopropyl, Column 2) then the dispersive C7 hydrocarbons will be rapidly eluted and the benzene will be relatively strongly retained and separated as a single peak as depicted diagramatically in figure 23. In this way the trace of benzene can easily be discerned form the bulk of the hydrocarbons. This type of heart cutting technique is probably the more popular and useful.

 

 

Figure 23. Heart Cutting for Improved Resolution