Change to Shorter Column
One way of making use of an existing LC system to easily achieve savings in solvents is to use a shorter column of the same internal diameter. For example, the analysis time is halved when the column length is halved as in the example below. If you simply switch over to a shorter column with the same packing material, separation will be impaired; however, it can be maintained by decreasing the packing material particle size from 5 µm to 2.2 µm.
(Reference: Technical Report No.1 " Prominence UFLC Next Generation High-throughput HPLC")
[Example of Shift over to Short Column]
Current column:150 mm (L) x 4.6 mm (I.D.)
(Shim-pack VP-ODS: particle size 5 µm)
New column:75 mm (L) x 4.6 mm (I.D.)
(Shim-pack XR-ODS: particle size 2.2 µm)
Analysis conditions:With gradient analysis, all of the programmed time settings are halved.
The delivery pump flow rate and the sample injection amount are not changed.
Gradient mixer:With gradient analysis, the mixer is changed to one with about half the capacity.
(In the case of a Shimadzu LC, the system mixer can be changed to a 0.5 mL mixer if it is already connected to a 1.7 mL mixer.)
Note, however, that this method cannot be applied to all peaks. In the case of peaks with relatively early elution or when there are many peaks, a conventional LC plus a shorter column combination leads to extra-column dispersion due to piping or the detection cell, which causes the number of theoretical plates to drop and impairs separation. If a method migration program (Please contact your Shimadzu local representative) is used for determining analysis conditions, you can judge whether appropriate migration is possible. When the type of filler differs from that of the column currently in use, differences in retention characteristics might cause the separation pattern to change.
If solvent savings cannot be sufficiently attained by merely halving the amount of consumed solvent, the analysis time can be shortened by changing the existing LC system according to "3-2) Higher Speed."