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Filters
Before HPLC-MS analysis your sample will need to be filtered. Typically two sorts of filter
are used, spin-through filters and syringe tip filters. We use the latter because they are
cheaper. In either case various filter materials are available. The list below is not exhaustive
but includes the ones we use. For some, spectra of leaching peaks are available, but
please note that these spectra are very anecdotal: they are mostly taken from odd blank runs
and do not necessarily reflect the true quality of the filter membranes, as they may contain
other contaminants from other sources.
Squirting a solvent through a filter gives it intimate contact with a big surface area of plastic, so a plastic that is problematic in a filter membrane may not be such a serious problem in a pipette tip.
| Nylon |
Nylon is hydrophilic so it's suitable for aqueous samples as well as those in most other
solvents. In our experience it does tend to leach some
new masses
into the sample in small
quantities. It can bind some solutes more than alternatives such as polypropylene.
|
| Polypropylene |
Hydrophilic polypropylene is also described as suitable for samples in most solvents. It is
reckoned to bind solutes less than nylon. I'm not convinced it's leach-free.
|
| PVDF |
PVDF is polyvinylidine difluoride, and again suitable for both aqueous and nonaqueous samples.
It doesn't bind things much.
|
| PTFE |
Poly(tetrafluoroethylene), very inert and non-binding, best for nonaqueous samples because
it is hydrophobic. It can be made hydrophobic by wetting with alcohol and flushing with water,
a useful technique if you have an aqueous sample that is too acidic or too caustic to put
through other filters.
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