The tubing and valve passageways of the HPLC system are very narrow and clogs can result from using solutions which have not been properly filtered. Columns are expensive and will also clog up with particulate matter causing increased back pressure and/or changes in retention times. Running clean, particulate free HPLC grade solvents through your chromatograph is a basic maintenance requirement. High grade chromatography solvents (and ultra pure water) are often pre-filtered through 0.2 micron filters by the manufacturer to meet their grade for use in chromatographic systems. However, there are times when you also prepare (mix) your own mobile phases using theses solvents with or without chemical reagents and additives. When you prepare mobile phase using these reagent grade chemicals or additives you should also take the extra time to filter the final mixture through a 0.2 micron glass or steel filter prior to use. This helps to insure that you start with as clean a solution as possible. *This is a critical procedure to follow with buffer solutions. When using aqueous solutions, possible bacterial and algae growth can occur so remember to date the solutions and dispose of them after a suitable time period (Make up only what you will use in one week). Do not re-filter these solutions and then use them again.
HPLC Solvent Inlet Filters:
Most HPLC manufacturer's supply solvent inlet filters on the lines which draw solvent into the pump head. To protect the pump and components downstream, these lines often incorporate a filter. These solvent pre-filters are usually made from plastic (PEEK or PEAK), glass or stainless steel. Their porosity is typically ten or twenty microns. A smaller porosity could be used, but it would restrict the lines ability to draw up fresh solvent into the pump head at the required flow rate so a compromise in pore size is necessary. The filter is primarily designed to stop the pump from drawing up any large particles or debris which could cause damage to the system and is NOT used to filter the solution (as mentioned above, the solutions used should be pre-filtered). These filters can clog up over time and so should be monitored for restrictions. Stainless steel filters can be cleaned using sonication and heat. Plastic filters should usually be replaced with new ones. Glass filters, which are often made of sintered glass, can be washed, but should never be sonicated to clean them as this can cause the glass to fracture and plug them up even worse. When in doubt, replace them with new filters. Filters used with clean organic solvents often last for many years. Filters which are used with aqueous solutions last for shorter times due to build up of undesirable biological matter.
- Another way in which you can insure a clean source of liquid for your HPLC system is to make sure that your mobile phase reservoir bottles are clean and free of dirt and dust during use. Keep them covered. Always wipe off any dust and debris from the solvent bottles before you uncap them and pour them into another container (much of the dust in the mobile phase comes from dirt that falls into the bottles). Instead of 'topping-off' bottles, replace them with clean bottles containing new solution.