Extra Column Dispersion - Dispersion in Unions and Stainless Steel Frits > Page 35

The peak from the straight tube (0.25 mm I.D.) is grossly asymmetrical and has an excessively wide base. Both the width and asymmetry are significantly reduced using an 0.18 mm I.D. tube but some serious asymmetry still persists. It would appear that the low dispersion serpentine tubing is the most satisfactory alternative to straight tube.


Dispersion in Unions and Stainless Steel Frits

Depending on their design, unions can also be a significant source of extra column dispersion. Instrument manufacturers have been aware of the problem of union dispersion and, as a consequence, have designed low dead volume unions which are now generally available. Actual data reporting the extent of the dispersion that takes place in such unions does not, however, appear to be readily available. Scott and Simpson also measured the relative dispersion that occurred in normal, low dead volume unions and drilled-out unions. Drilled-out unions allow the ends of the connecting tubes to butt against one another, or against the frit of a microbore column and thus reduce the union volume dead volume to virtually zero. The design of low dead volume and drilled out unions are depicted in figure 15.

Figure 15. The Design of Low Dead Volume and Drilled Out Unions