Capacity of uncoated 0.53 mm id pre-columns for retaining sample liquid inthe presence of a solvent vapor exit

0.53 mm i.d. uncoated precolumns of about 10 m in length followed by a solv ent vapor exit have become a standard set-up for large volume on-column inj ection. It went unnoticed, however, that the introduction of a vapor exit r equires two modification of previous working guidelines. First, the capacit y of the precolumn to retain sample liquid is increased by a factor of 2.3- 3 as a result of the around 100 times higher carrier gas flow rate. Secondl y, it must be considered that this gain in retention of liquid is lost agai n upon closure of the exit: as the gas flow rate is reduced to a few mL/min , the layer of the residual sample liquid expands about 2.3-3 times. Hence, closure should occur late, and a section of the precolumn must be assigned for this secondary spreading.