Frequently Asked Questions about MicroSolv Syringe Filters
- Sometimes I see extra peaks in my samples and sometimes I do not using the same filter. Do you have any ideas?
- Which membrane is best for aqueous buffers?
- I use normal phase chromatography, which filter do you recommend?
- Which solvents should I avoid with Nylon?
- Are the MicroSolv Filters sterile?
- Will I see any differences in my chromatography if I use your filters?
- What is a “steady state” for filters?
- Will I protect my columns from samples that permanently adsorb to them by using a syringe filter?
- What is an extractable?
- What materials are the 100 pack filter boxes made from?
- What is the maximum sample volume for a 25mm filter?
- If I use one filter for many samples will I get carry over?
- Can I make the PTFE filter more hydrophilic?
- What product traceability does MicroSolv provide for its syringe filters? Do you retain samples from each lot?
- What is the main use for Regenerated Cellulose Syringe Filters?
- Are the MicroSolv Syringe Filter Membranes supported in the plastic device?
- Can I autoclave the MicroSolv 25mm PTFE Syringe Filters?
- Are MicroSolv Syringe Filters bidirectional in their flow?
1. Sometimes I see extra peaks in my samples and sometimes I do not using the same
filter. Do you have any ideas? [top]
Yes, the “proper” way to use any syringe filter is to dispose of the first few milliliters that comes from the
filter. If there are any extractables or if there is going to be any adsorption to the membrane, it will happen
in the first few mls. This is called bringing the filter to a “steady state” (see explanation below). This may be
causing your differences. For 25mm devices you should not use the first 2-5 mls and for the 4mm device, you
should discard of the first 0.5ml.
2. Which membrane is best for aqueous buffers? [top]
The best membrane is a difficult question to answer as it depends on your sample that you are filtering and the
solvent is it dissolved in. For most HPLC and Dissolution testing, hydrophilic Nylon membranes are generally used
because they are durable, compatible with most aqueous solvents including water and have the lowest extractables
with aqueous solvents. The best way to determine if Nylon is compatible is to try them with your sample. You
should analyze your sample (if possible) with and without filtering. There should be no change in your analysis.
3. I use normal phase chromatography, which filter do you recommend? [top]
PTFE is the best for use with organic solvents.
4. Which solvents should I avoid with Nylon? [top]
Aldehydes and strong acids such as hydrochloric and nitric.
5. Are the MicroSolv Filters sterile? [top]
No, but on special order we can supply our filters in individual blister packs and can be sterilized. Depending
on the membrane, the sterilization could be autoclaving or radiation.
6. Will I see any differences in my chromatography if I use your filters? [top]
If you use proper techniques, you should not see any differences in your chromatography, CE or UV testing.
Filters only protect your equipment and columns.
7. What is a “steady state” for filters? [top]
A filter could have charged sites on it or a small amount of extractables. Most manufacturers, including
MicroSolv, produce filters with the lowest extractables possible. If these extractables are soluble in the
solvent you are using, you should see them only in the first few milliliters. This aliquot should be discarded.
If your filter has charges on it and it adsorbs your analyte, once all the charged sites are taken up (normally
in the first few milliliters), no more adsorption will take place and the concentrations of your filtrate will
remain constant. This is called “the steady state”.
8. Will I protect my columns from samples that permanently adsorb to them by using a
syringe filter? [top]
No, some people get confused on the purpose of syringe filters. They are not chemical filters, only particulate
filters and only remove un-dissolved particles from your filtrate. If anything is dissolved in your solvent, and
once the filter is at a steady state, it should not adsorb anything. It will only exclude particles that are
larger then the pore size rating of the filter.
9. What is an extractable? [top]
An extractable is any chemical that is present in your sample after filtering that was not there before and the
source is the filter. Most of the time, the membrane is the soruce but once in a while, it could be the
polypropylene housing depending on the solvent you are using.
10. What materials are the 100 pack filter boxes made from? [top]
The boxes are made of rigid, polystyrene that is an approved FDA plastic for food storage.
11. What is the maximum sample volume for a 25mm filter? [top]
You can use up to 100ml in a single 25mm syringe filter is you are using an aqueous solvent and your sample is
not cloudy. However, the best way to determine if the filter should be replaced is when you get either a very
fast drop in back pressure or a constant rise in back pressure. Both indicate it is time to replace them.
12. If I use one filter for many samples will I get carry over? [top]
You will most likely get some kind of carry over. It is not recommended to use one filter for more than one
13. Can I make the PTFE filter more hydrophilic? [top]
Yes, if you are wiling to introduce Methanol into your method. For a 25mm device, if you use 15-20mls of methanol
as a blank filtrate, the membrane will give you less back pressure after that for aqueous samples. This is due to
“wetting” the membrane with Methanol allowing more aqueous solvents to pass through it with less back pressure.
14. What product traceability does MicroSolv provide for its syringe filters? Do you retain samples from each lot? [top]
All syringe filters have lot numbers which can be followed to complete traceability to the raw materials used in
manufacturing the filters. We have a mandatory 3 year archive time of samples and lot analysis.
15. What is the main use for Regenerated Cellulose Syringe Filters? [top]
The main use for Regenerated Cellulose filters is for protein solutions. Due to the very low binding of proteins to
the membrane, these filters are an excellent choice for HPLC, CE, or instrumental analysis.
16. Are the MicroSolv Syringe Filter Membranes supported in the plastic device? [top]
The PTFE (Teflon) syringe filter membranes are backed with a polypropylene support all the others including
Nylon, Regenerated Cellulose, Cellulose Acetate and PVDF are not.
17. Can I autoclave the MicroSolv 25mm PTFE Syringe Filters? [top]
Yes, under conditions of 121 C for a maximum of 15minutes, the PTFE filters can be autoclaved. Maximum operating
temperature (continuous) we suggest that you do not exceed 80 C to maintain optimum performance.
18. Are MicroSolv Syringe Filters bidirectional in their flow? [top]
Yes, all the filters are bidirectional except PTFE and those that have pre-filters for aqueous solutions. Although
in a syringe filter format the flow in two directions may not be equivalent because of the filter design. In organic
solvent all the filters are bidirectional.