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| Appearance of the pores in the SPI-Pore™ PCTE membrane filters |
Corrosion cast of a typical SPI-Pore™ PCTE membrane filter showing the spatial arrangement of the pores. |
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Available Products:
Disc filters
- Black Membranes (SPI Pore only)
- Epifluorescence Microscopy
- Grease Coated Membrane Filters
- Membrane Filter Holders
- Standard White Membranes (SPI-Pore and Whatman/GE™)
- PVP-Free Membranes for Chemotaxis
Sheet format
- 8" x 10" White Membrane Material, Cut Sheets
Why Polycarbonate Membrane Filters?
Ordinary depth-type membrane filters contain tortuous pores that capture
particles via random entrapment. The result being some fraction of particles in the interior (interstices) of the membrane filter making them
unavailable for observation on the surface by LM or SEM.
In contrast, polycarbonate filters contain uniform, cylindrical pores preferentially etched into the membrane,
allowing for an even distribution of a collected sample in one plane across the entire exposed membrane surface.
Hence all samples are captured on a flat, smooth, glass-like surface. The precisely sized pores in a very narrow
distribution ensure accurate separation or fractionation of samples by size.
Contaminant-free, these microporous screens are biologically inert, offer
excellent chemical resistance, thermal stability, superior strength and negligible adsorption of filtrate.
These factors combined with the unique filtration capabilities of the polycarbonate membranes make it a clear preference for a number of EM
and LM applications including: Airborne Particulate Analysis (such as asbestos) Chemotaxis, Cytology,
Histology, Paleontology, Parenterals and Water Analysis for asbestos and other suspended inorganics.
The color of the most commonly purchased form of the product is white but in some situations the
black form of the product is preferred.
The
filtration and physical properties of PC membrane filters
make them fairly unique and set them apart from membrane filters of other
compositions giving them in many instance unique performance advantages.
Chemical Compatibility of PCTE membranes:
The membranes are surprisingly resistant to a number of organic solvents and inorganic liquids.
Caution some solvents will instantly dissolve PCTE membranes and you should
consult our solvent resistance information for more detail.
Fluorescence characteristics
All PCTE membrane filters, irrespective of the manufacturer are made from a polycarbonate that contains fluorescent pigmentation
in the raw material. This most
important and unique raw material is not available without this pigmentation
system.
Birefringence:
All polycarbonate membrane filters, exhibit some amount of birefringence because polycarbonate crystallizes and has a crystalline texture. In
a polarizing microscope, the individual crystallites show up as a fine "pepper" like appearance.
Maximum use temperature:
The polymer starts to soften at approximately 150°C and will melt at 240°C. If your requirements involve work at higher
temperatures, we recommend using either a)
Anopore®
aluminum oxide membrane filters or
b)
SPI-Pore™ Silver Membrane Filters.
Do the membranes have a charge?
The polycarbonate track etch membranes do not have an inherent positive or negative charge. They do act in the same way as the
dielectric film in a capacitor and static electricity will build up on it.
This static charge will cause the membrane to act as if it has a charge but this charge is not a property of the membrane; it is the result of
the environment in which the membrane has been exposed.
The Zerostat®
antistatic gun has proven effective in terms of neutralizing any charge that
might build up on a membrane.
SPI-Pore™ Polycarbonate Membrane Filters
SPI-Pore polycarbonate membrane filters are
manufactured
using unique proprietary manufacturing technology and also meet or exceed
industry standards for
high-grade polycarbonate membranes on all property levels:
- Capture of particulates on a flat, smooth, almost glass-like surface
with complete uniform distribution across the membrane surface.
- Precise pore sizing and narrow size distribution, not possible
with any other filtration media system.
- Completely non-hygroscopic, resulting in virtually no off-gassing
in vacuum systems.
- Exceptionally low tare weight.
- Low trace element levels, making polycarbonate an ideal substrate
when EDS is contemplated.
- Optically transparent (most pore sizes) when wet, otherwise the filter tends
to be white if not also opaque.
- Durable and high strength.
- Low extractables
- Nonstaining, providing exceptional background at both LM and SEM
levels.
- Biologically inert
- Same outstanding chemical resistance and thermal stability normally
associated with polycarbonate.
- Pore densities not to exceed 10%.
- Wet samples collected on these membrane filters can be critical point
dried in a critical point dryer.
Membrane characterization:
A large amount of information about the physical characteristics of the
SPI-Pore track etch polycarbonate membrane filters is described here.
SPI-Pore vs. Whatman/GE™ Polycarbonate Track Etch Membrane Filters
Since there is only one manufacturer in the
world of the special liquid monomer from which the polycarbonate film material is made, the two brands of membrane filters are similar.
But because different manufacturing processes are used different thicknesses of base
material film are needed. For most pore sizes the membrane thickness the SPI-Pore membranes is thinner than the Whatman/GE™ brand.
This has important implications on flow rates.
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Tuesday February 09, 2010
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