We could turn this question around and ask why do other suppliers filter their HPLC solvents to 0.2 microns?

Certainly, instrument manufacturers recommended that users filter their solvents as otherwise particulate matter can have a bad effect on analytical performance through clogging of columns. Furthermore, pumps can be damaged and the additional wear and tear of the instrument can lead to expensive servicing and downtimes.

But many suppliers of HPLC solvents are just that. That is, they supply rather than manufacture. They take the solvents from the international market, test for suitability, then package into the user bottle of typically 2½ litres. International producers of tonnage quantities of solvents do not really take account of particulates in their processes. The process of distribution and handling also introduces impurities, including particulates. So really, rather than being a virtue, it becomes a necessity to filter during bottle filling.

In contrast, at ROMIL, all our solvents specified for HPLC (in the ROMIL-SpS™ and ROMIL-UpS™ ranges) are further purified by distillation by ourselves. No one else. The distillation process effectively removes any particulates that have accrued from the prime producer and down through the distribution chain. Our end-user container filling is done direct from the distillation receiver. We do not transfer to intermediate vessels. The end product is as pure as we can make it. Not only in chemical impurities, but also physical impurities such as particulates. Filtering does not make our solvents any purer. So we don't do it, and neither have we done it since we started in 1983.

What we do however, is distil and fill under inert nitrogen. This has a clear beneficial effect in that it displaces dissolved oxygen which can lead to baseline instability and interfere with some detector systems. Oxygen can also reduce the optical properties of the solvent in the far UV region. So many users prefer to just degas the solvent (with helium) and thereby avoid bubbles forming in the solvent line.

Nevertheless, that does not mean that users should not filter their solvents. Addition of salts and buffers to the mobile phase is a significant source of particulates. And general handling in the laboratory just adds to this. So a filtration accessory is a prudent measure, wherever users buy their solvent from.

So next time your supplier tells you that they filter their HPLC solvents as a sales benefit, just ask them, why?