Inlet Filters

[lgchrom]

What kind should I use for ion chromatography? Which do you suggest?

What about an in-line filter before the column? Would you recommend it? Would it be ok to use instead of a guard column?

[tom jupille]

Re the inlet filter, you can use either stainless steel or plastic. The porosity is generally somewhere in the 5 - 10 micron range; the idea is to screen out gross particulate contamination that gets in after the mobile phase has been prepared (and, presumably, filtered).

In-line filters and guard cartridges do different things:
- inlet filters take out particulate contamination
- guard cartridges take out chemical contamination.

The guard cartridge *will* also trap particles, but it's an expensive way to do it!

I'm a firm believer in in-line filters; they are cheap insurance. The utility of guard cartridges depends on your sample characteristics. It the samples are consistently and predictably clean, then a guard cartridge is unnecessary. I the samples are consistently and predictably dirty, then a guard cartridge is effective, but expensive (compared to better sample cleanup). Guard cartridges are most valuable where samples are unpredictable.

[HW Mueller]

I am one of those who always has a pre-column filter in line, but a cartridge only with "dirty" samples. I found the sieves (wire mesh) from VALCO the best for in line filtering as they can handle more junk before plugging, compared to frits.

[lmh]

Can I add a rider to Tom's reply about inlet filters versus guard columns?

In simple technologies such as C18, guard columns are incredibly cheap. In UK terms I know of two manufacturers whose guards come out at under £20 each. Given that a reasonable eppendorf-tube spin-filter can cost nearly £1, I can stop filtering and block my guard column with particulates once every 20 sample injections, and still break even on cost.

The reason for filtering a sample before running it is more to avoid down-time than to save cost on blocked guards.

My lab works with fairly clean samples, but we run a lot of things for which we have no pre-existing method in the lab, so we are attempting some sort of method set-up (and a bit of validation) at the same time as our client is developing their sample prep procedure. When I used to filter things, I often got complaints at the stage of method development that we might be losing the compound of interest by binding to the filter. Now I just spin everything and rely on the guard in the rare event that spinning isn't enough. Perhaps it's not very professional, but it removes one element of uncertainty from a method that's often being set up in a hurry.

In decisions like this, so much depends on the nature of the lab and its work...

[HW Mueller]

And I thought this chain pertained to in-line filters, not off-line.

I forgot to mention that my in-line filter sits ahead of the injection valve, so is a mobile phase filter. Even though it has a diameter of only about 3 mm it can last for many liters of mobile phase (a year of work or more was not unusual). The reason for doing this that the Rheodynes got plugged too often in spite of inlet frits in the mobile phase bottle. One could also clearly see that these in-line filters were doing their job since they did accumulate visible junk and did have resistance increase in time.

[lmh]

yes, I was aiming to comment only on Tom's bit about guards being an expensive alternative to an inline filter, but inadvertantly expanded the subject-matter...

Thanks for the tip about a solvent filter. Is this in addition to the usual inlet filters?

[tom jupille]

In decisions like this, so much depends on the nature of the lab and its work...

Exactly! (and then "common sense" from that).

[lgchrom]

The samples will be 90% drinking water. Not really dirty samples like suggested.

And regarding the cost of the guard, for ion chromatography it is not quite affordable..


Will the SS inlet filters affect cation determination? I thought that it could be a potential source of contamination.

[Bruce Hamilton]

Metal filters are a very bad idea for most ion chromatography, especially if you are using an all-polymer Ion chromatograph with alkaline eluents.

The essential difference between guard columns and filters is that the filters prevent insoluble particulates from passing through, whereas the guard columns also grab soluble gunk that will bind strongly to your (much more expensive ) column.

If you are confident that no binding gunk is present, then the guard columns may not be required, however given the expense of most ion chromatography columns, I'd use one. After all if the samples are clean the guard will last for many, many samples = cheap insurance.

If there is a lot of insoluble particulates that also require a filter, my first option would be to fix the sample preparation to remove the insoluble material ( eg centrifuge, filtration ), and I would use one of the cheap polymeric low volume, high-pressure, in-line filters from firms such as Upchurch as the insurance.

You can use a high pressure in-line filter to protect the guard with minimal adverse effects on chromatography, but if the samples are dirty, you would have to change it frequently, hence the preference for fixing the sample preparation.

The sample preparation could also involve a low-pressure, low cost, replaceable prefabricated filter on the injection loading/vial filling device.

I would not use sintered or mesh metal filters, as they have large surface areas, which assists metal dissolution into mobile phase., as well as binding of some ions.

[HAZMAT]

Biocompatible Titanium frits offer a favorable alternative to the typical 316 SS frits found in standard HPLC filters. Some IC methods or instruments require ZERO metals in the flowpath, but often that isn't the case.

Optimize Tech offers a wide variety of reservoir filters and inline or direct connect filters - all made in the USA. We also produce a couple of different filter types for handtight use at UHPLC pressures.

http://www.optimizetech.com/opti-shop/i ... ex&cPath=5

Call us if you want to learn more!
800.669.9015

/endplug

[Markus Laeubli, Metrohm]

Dear mariosapm

We are recommending in line filters to be used regardless the use of guard columns (which we recommend as well).
The inline filter is placed between the pump and the injector.
The filter material recommended is polymeric. Stainless steel does not make sense in a metalfree system. Biocompatible titanium might be good for bioLC applications. In IC I strongly recommend to avoid titanium as this material may absorb e.g fluoride. Which might give false low fluoride results.

We are using the 6.2821.120 Inline filter 2 µm. The 2 µm frit may be replaced as required. But you also may use other types (e.g. Upchurch etc.).