Page 109 - Illustrated Pocket Dictionary of Chromatography

106 INNER DIAMETER (ID)

Inner diameter (in.) Radius (cm) Volume of 10cm section (mL)
0.004 0.00508 0.81
0.007 0.00889 2.48
0.01 0.0127 5.07
0.02 0.0254 20.3
0.04 0.0508 81.1

Note that the use of about 4in. of 0.01-in. ID tubing leads to an equiv-
alent added extra-column volume as a sample injection of 5mL! Keep
the lengths of all connecting tubing after the injector and before the
detector as short as possible. In HPLC connector tubing, the choice
of ID is dictated by use. For tubing before the pump, it is usually a
large ID on the order of 0.02in. The tubing is meant to provide unre-
stricted flow from the pump. PTFE is frequently used because of its
chemical resistivity, flexibility, and ease of use. From the pump to the
injector, large-ID stainless steel is used. Once again, the tubing is used
to provide an unrestricted flow from the pump to the injector.
However, in this case the tubing must be able to withstand high pres-
sures (>4000psi) and so stainless steel is often used. For the connec-

Left to right: 1mm-, 2mm- and 4.6-mm inner diameter HPLC column tubing. All are
1
constructed from stainless steel and are /4in. in outer diameter.