Why do we mark direction on the HPLC columns?
In conventional use, the mobile phase has a specific flow direction in the column. For the old-fashioned columns, the filters and the structure in the inlet head and outlet head are different, like the pore diameter and the size of the filters. You have to use the column based on the direction. Otherwise, you can’t get the right result.
But in the new-fashioned columns, the structures and filters are the same at both ends. There are not as many restrictions on the packing process and the column usage as before.
For HPLC column suppliers like us, this direction is also the packing direction.
Is it possible to use the HPLC column in the opposite direction?
If you want to use the column in the opposite direction, that’s really okay in theory. Just make sure that the flow direction is the same for each test.
For the repeatability of application performance, each testing has to use the same direction. The results will be different in different directions. Because the properties of the two ends may change during use, like impurities content, resin fragments, blocked frit. Some columns will collapse at the inlet, because of the bad resin packing process. Some packing materials will break with many fragments. These fragments will block the frit.
We highly recommend you to use the column based with the direction shown on the label.
When to use the column in the opposite direction?
We generally use the column in the opposite direction when cleaning column after usage. The purpose is to clean the frits and the resin inside of the column.