Page 136 - Tandem Techniques

Page 118

Figure 3.3
Graph of Standard Deviation of Dispersion from
Connecting Tubes against Length (Standard Short Column)
It is seen that for solutes eluted at the dead volume, a tube length of about 2 cm is the maximum that
can be tolerated. For solutes eluted at k'= 2, an extrapolated tube length of about 55 cm would be
acceptable, but this would require that the chromatographic system was adjusted so that all the solutes
of significance were eluted at (k') values greater than 2. Furthermore, the optimum column flow rate
was also set for a solute eluted at k'=2. In fact, all eluted peaks should be given the same priority, and so
it is clear that connecting tubes should be kept at an absolute minimum length, preferably less than 3
cm, and certainly less than 5 cm. Furthermore, the curves shown in Figure 3.3 assume that the column
is operated at an optimum velocity appropriate for the solutes of interest. In fact, the optimum velocity
is rarely used, because optimum columns are not usually designed for the specific analyses. It follows
that the flow rate employed will be considerably in excess of the optimum flow rate to avoid extended
elution times and long analyses. The effect of tube length on