I think there are two types that can’t be backflushed. One is that the sieve plates at both ends are not the same for backflushing operation, because the inlet side sieve plate has a larger aperture, which will be more resistant to solid particles. At least the blocking time will be relatively long. In this case, once backflushing may cause the loss of packing, resulting in a decrease in HPLC column efficiency. The other is that an HPLC column with a collapsed HPLC column head is not suitable for backflushing, because the HPLC column head collapses to leave space on the HPLC column head.
Backflushing will cause the HPLC column bed to move, loosening and redistributing the packing material, but do you think this kind of HPLC column can still be used? The collapse of the stigma means that there is a relatively large dead volume in front of the stigma. I am afraid that the peak shape has changed a long time ago. You can still expect to use such an HPLC column for analysis? So for this kind of column, it is meaningless to not recoil, Because it is already a waste pillar.
Let’s talk about why it is used in the forward direction. This is related to the direction of the column. As mentioned above, the HPLC column is filled in the direction opposite to the arrow on the HPLC column body. The packing at the bottom will be tighter (due to the high pressure the lower stainless steel tube will undergo slight deformation and increase its diameter.
After the HPLC column is installed, the stainless steel tube will return to its original shape. The packing in the HPLC column can support a certain pressure so that this pressure cannot be ruled out and will remain at the bottom of the chromatographic column. The result is the packing at the bottom will be tighter). If you open the sieve plate at the entrance of the new column, you will find that the packing will be about 1mm more.
Now that we know that it will protrude by 1mm after opening, it is not difficult to understand the necessity of forwarding use, because the loss of packing on the HPLC column header can be replenished in time (the loss of packing usually starts from the HPLC column head, mainly for The sample damages the composition of the column, and the damage caused by the mobile phase is often integral because the sample amount is small, but the amount of mobile phase is large), so that the HPLC column head will not collapse and cause dead volume.
There are two reasons for the advantages of backwashing. One is that solid particulate matter usually accumulates on the HPLC column head, which cannot be washed off by forwarding washing, while backwashing can more or less wash it down, delaying the increase in HPLC column pressure. time. The second is the accumulation of strongly retained substances on the HPLC column head. Forward flushing needs to wash the entire distance of the HPLC column bed. It is itself a strongly retained substance.
How long does it take to flush it down? Maybe flush one with pure methanol or acetonitrile It can’t be washed for hours, but it causes secondary pollution to the HPLC column bed; while backflushing only needs to wash a little distance on the HPLC column head, maybe less than 1cm in length, which is much easier than forwarding washing.