Chromatography Forum

Hi ,

I have my standard pesticide in prepared in pure water , when i filter just to see i found that it adsorbs on the PTFE filter disk . I may need huge a mount of sample to saturate the filter but does any one has any idea to overcome this adsoerption proplem without using this huge amount of discarded sample ( because imagine sometimes i need to test the adsorption in 2 ml of sample , how can i do that in smal a mount and making sure no filter adsorption accour ) ?

Any help will much appreciated

Centrifuge instead of filtering? (and put a stainless steel in-line filter in your system right after the injector to deal with any residual particulates)

Use Nylon or PVDF filters

Doe the pesticide have to be in pure water?

Thanks all

Tom
Do you have some figures to show this good technique because not sure if our poor lab has one like this ( Tom really gratefull for your always help )


pharmaguy

I found also Nylon filter adsorp my pesticide until 20 mls ( too much really )


HW Mueller

Yes my dear must be in pure water , but the filter doesn't matter if it is been washed with methanol .

Interestingly , if i wash the filter with 20 mls of my sample all the samples after that will not be adsorped , then i said ok lets just wash with 20 mls water without pesticide ( i feel like i heared the filter say walk from another door doN'T play with me i need the pesticide where is it !
)

Any idea as my method validation doesn't take centrifuge in the consideration ( also the the instrument is broken down hhhhh i feel like i am not in UK )

I once did a syringe filter validation for a drug assay, and discovered that different manufacturers of the same type of filter (i.e. nylon or PTFE) adsorbed the drug differently. Sometimes you can ask a vendor for a few free sample filters to try to see if their product works.

I was not hinting on washing the filter with methanol, I am thinking of increasing the solubility of your stuff by adding organic, or whatever, to the analyte solution, prior to filtering.

Any idea , because i still have this proplem what can i give the filter to saturated with things other than my sample ?

Oh my god i am stop right now

You can't add anything to the filter to saturate it. Its simply an absorption phenomenum: unpolar anlytes tend to stick to the unpolar filter surface instead of staying dissolved in the water. If there is enough analyte absorpted (filter saturated) an equilibrium is established between adsorpted and dissolved analyte.
"Saturating" your filter with an other unpolar layer of something will not prevent your analyte from adsorbing.
You will have to increase the "solvation power" of your solvent or have to decrease the "unpolar attractivness" of your filter material.