Page 81 - Illustrated Pocket Dictionary of Chromatography

FILTER, INLET 77

filters (1) Porous materials that are used to remove particulates
from solvents, samples, and mobile phases. See individual filter type
for further discussion. (2) Used in spectrophotometers to restrict the
range of wavelengths transmitted to the sample.

It is important that one realizes that the material of construction for
the filter must be compatible with the solvent used. Also, the average
pore size in the filter, the porosity (how many pore/unit surface area),
and the total available surface area are important filter characteris-
tics. There are two basic types of spectral filters: band pass and cutoff.
A band-pass filter transmits a defined upper and lower value of wave-
lengths, whereas a cut-off filter transmits wavelengths either above or
below a set wavelength.
filter, inlet Removes particulate from the mobile phase before it
enters the instrument. In HPLC the inlet filter is typically a sintered
glass or porous stainless steel component that is attached to the end
to the inlet tube. This assembly then rests in the reservoir. Filters can
also be placed in a special housing above the reservoir. In this setup
the filter is often connected to a vacuum so that the solvent is both
filtered and degassed before it reaches the pump. In GC work the filter
is typically in line after the gas tank and removes particulates and any
aspirated oils, etc., before they reach the GC unit.

Stainless steel inlet filters. Left to right: female union, male union, nozzle-ended.
All tubing is wide-bore PTFE to facilitate flow to the pump head.