Filtration and Physical Properties of SPI-Pore™ Polycarbonate
Membrane Filters
No one discloses more about our membrane filters than SPI!
SPI Pore membranes have cylindrical, "straight through" pores, normal with
in is +/- 34° to the surface. This even and also random distribution
contributes to uniform sample deposition over the entire membrane filter
surface.
Because of the two step manufacturing process, SPI Pore Polycarbonate
Membrane Filters can be made in a wide range of pore sizes and pore
densities. Standard pore sizes range from 0.01 µm to 14 µm.
Non-standard pore sizes are available, as are also non-standard pore
densities, but in order to get anything approaching acceptable economics,
one has to be prepared to place a substantial order because of the high
set up costs to make that first non-standard membrane.
Just tell us your requirements and
let us see what we might even have on hand from previous runs that might be
closer to what you need (but in just limited quantities while that supply
lasts).
SEM photos show that the actual pore diameters are quite close in agreement
with the nominal pore size stated for that product. However, in practice,
actual pore diameters can vary from +0% to -20% of the rated (e.g. nominal)
pore size. The pore density (pores/cm2) of standard SPI Pore
Polycarbonate Membrane Filters is selected for each pore diameter to
provide the best combination of strength and flow rates.
Shinny vs. "matte" side of the SPI Pore Polycarbonate Membrane Filter:
The peak-to-valley distance on the "matte" side is less than 0.3 µm.
On the shiny side, the peak-to-valley distance is less than 0.1 µm.
This is an ideal surface on which to collect and analyze samples for light,
confocal, or any other kind of imaging device that would be visualizing
captured particles on the substrate membrane filter.
All particles larger than the actual pore size are captured on the membrane
surface. This "absolute" surface retention makes it possible to determine
the amount and type of particles in either liquids or gases - quantitatively
by analysis. Due to the sieving action of the cylindrical pores in the
SPI Pore Polycarbonate Membrane Filter products, particles can be separated
into various size ranges by serial filtration through membranes with
successively smaller pore sizes.
The SPI Pore Polycarbonate
Membrane Filters can also be
in a critical point dryer, making it possible for fragile biological
samples to be dried (for SEM examination, for instance) without being
exposed to drying artifacts from surface tension forces.
Acid resistance:
SPI-Pore and Nuclepore polycarbonate track etch membrane filters are indeed
acid resistant.
Physical Properties of SPI-Pore™ Polycarbonate Membrane Filters
Thickness 6-14 µm
Variation of thickness within same pack +/- 5%
Refractive Indices Birefringent at 1.584 and 1.625
Nominal tare weight 1.0 mg/cm2
Variation of tare weight within same pack +/- 5%
Water adsorption (%wt. gain 24 hr immersion) 0.24%
Residual Ash Weight average 0.92 micrograms/cm2
Specific Gravity 0.94-0.97
Tensile Strength <3000 psi (207 bar)
Autoclavable Yes
Leachables Negligible
Wetting Characteristics Hydrophilic
(can be made all or partially hydrophobic)
Wetting Agent Polyvinyl pyrrolidone (PVP)
Brust strength, minimum 10 psi (0.7 bar)
Migration of Filter Media Zero
Maximum Service Temperature 140°C (280°F)
Optical Properties Translucent with slight green tinge
(except the black membranes for epiflourescense work)
SPI-Pore™ Polycarbonate Membrane Filters are free of contaminants. And
to assure the absence of such unwanted and distracting particles on the
surface of the filter, of particular importance in epifluorescent microscopy
and other critical analytical procedures, SPI-Pore membranes are produced
under Class 100 conditions in critical manufacturing steps. This includes
packaging in a late technology vertical laminar flow Class 100 clean room.
Low Absorption and Adsorption:
SPI-Pore Polycarbonate Membrane Filters exhibit extremely low adsorption
and adsorption losses, varying from 3 to 6%. This binding is also
non-specific, important when filtering critical solutions. In comparison,
tortuous pore cellulosic filters adsorb from 40-65% depending on the
molecule.
Non-hydroscopic:
Since SPI-Pore Polycarbonate Membrane Filters are non-hygroscopic, they
are particularly well suited for gravimetric analysis. They do not require
drying when used directly out of the package. If they are wet, they can be
dried rapidly and they will not pick up moisture from the air during
weighing.
In addition, fluid absorption is minimal. For example, samples immersed in
water for 24 hours have an average weight gain of only 0.24%. SPI-Pore
Polycarbonate Membrane Filter membranes also will not generally absorb
components from fluid solutions.
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Saturday October 11, 2008
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