Page 137 - Tandem Techniques
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dispersion at flow rates more in line with those used in practice will be considered later.
The curves for tubes used with microbore columns operated at the their optimum flow rate are shown in
Figure 3.4. It is seen that because the optimum flow rate for microbore columns is much smaller than
that for standard columns, the tube dispersion is much less. In fact, even for the dead volume peak, a
tube length of 35 cm can be employed without seriously denigrating the column efficiency.
Nevertheless, the effect of the tube dispersion is only small for the microbore column when operated at
the optimum flow rate. Unfortunately, the optimum flow rate is rarely used in practice, as the analysis
time is too lengthy and at higher flow rates, the effect of tube dispersion becomes far more serious.
Figure 3.4
Graph of Standard Deviation of Dispersion from
Connecting Tubes against Length (Microbore Column)
The variance per unit length of an open tube at velocities significantly higher than the optimum is given
from equation (3.2) by
