Frequently Asked Questions

You can easily verify the distributor pricing online by logging in to your account. Not sure how to do it? Watch this video.

Watch this video tutorial on how to create your account.

Yes, we are able to ship to most countries in the world.

cellQART^® inserts are polyester (polyethylene terephthalate) track-etch membrane. This difference will likely influence how they grow. We recommend testing different seeding densities that are higher and lower than your current method and proceed in the direction of improved results.

Our transparent membranes are better suited for phase contrast and live monitoring.

Either of our transparent or translucent membranes can be used for fluorescent analysis.

Q: What’s the best way to concentrate large sample volumes in one go?

A: Concentrating medium to high volume samples can be time-consuming and costly in the laboratory setting. Happily, there are dedicated solutions for concentrating samples with initial volumes in the 0.1 - 5 L range, without having to resort to the process scale systems that require large mounting systems and high CAPEX investment. Vivaflow® cross flow devices are the most robust, lab scale dedicated devices and are offerred with two membrane options: PES or Hydrosart®. There is a choice of single use (Vivaflow® 50) or multi-use (Vivaflow® 50R and 200) options to meet both economical and contamination prevention requirements. The high surface area, thin channel, flip flow recirculation design results in 50x concentration of 1L samples in just 30 minutes. Similarly, initial sample volumes up to 5 L can be concentrated in under 75 minutes. Near total recovery of the concentrate is achieved with a single buffer rinse.

Q: How can I reduce protein degradation during concentration?

A: Incorrect buffer compositions and high shear stresses can commonly cause degradation during concentration. Likewise, the more linear the protein shape, the greater the adverse effects on structure caused by high relative centrifugal forces. In such cases, reducing the centrifuge speed to around half of the maximum RCF is a good starting point for process optimization. For globular molecules which are prone to aggregation, it is good practice to use a device which has a minimum sample capacity close to your starting volume. This generally ensures a higher membrane surface area, reducing the potential for blockages which can contribute to increased stress on the sample.

Note, however, that theincreased membrane area also represents an increase in the overall internal surface area of the device which is in contact with the sample, both of which can result in higher non-specific adsorption. Non-specific adsorption may also be more pronounced where the membrane material in use is not the optimal choice for the target molecule, or where the target is considered to be “sticky”. Laboratory crossflow cassettes, such as Vivaflow®, feature flow paths which carry the sample parallel to the membrane, further minimizing shear stresses in comparison to centrifugal devices. It should be noted that conventional stirred cell devices apply relatively high shear stresses on the sample. Finally, when the optimal buffer conditions (pH and composition) have been determined, these can be maintained or adjusted during concentration, using diafiltration for sequential or simultaneous buffer exchange or desalting. Buffer exchange is simplified with the Vivaflow® diafiltration reservoir and Vivaspin® 20 diafiltration cups, which ensure that even with increasing target molecule concentrations, the correct buffer balance is maintained or adjusted, as needed.

Q:  Which ultrafiltration method is best suited for virus concentration?

A: Viruses and viral vectors are in growing demand in therapeutics, vaccine and regenerative medicine applications. In general, the principles of device, membrane and MWCO selection are the same as with proteins and other biomolecules, unless there are specific considerations for your viral target. The rule of thumb is to choose a molecular weight cut-off (MWCO) close to one third the molecular weight of your target.

In the case of viruses where diameter is a more relevant measure of size, we provide a handy table to help you find the most appropriate MWCO (see Table A.). For example, concentration time and recovery for Lentivirus, with a diameter of ~90 nm, is typically optimal with a 300 kDa MWCO ultrafiltration membrane. A 100 kDa MWCO also provides good results, though with a compromise on process speed. Membrane properties should also be considered, as they may have an impact on recoveries. For instance, Hydrosart® and regenerated cellulose (RC) have no net charge at pH 7, whereas PES has a slight negative charge. These MWCO and membrane material considerations have been tested at Sartorius using Ambr® Crossflow. The results showed that optimal concentration of Lentivirus from a 15 mL sample was achieved with a 300 kDa MWCO Hydrosart® membrane, closely followed by 100 kDa PES. It is good practice to test and qualify the device, membrane and MWCO independently for each target molecule.

Q. What is the maximum temperature for the different filter membranes?
A. The maximum operating temperatures for Sterlitech filter membranes are listed below.

• Sterlitech Silver Metal - 427°C
• Sterlitech Ceramic - 350°C
• Sterlitech Polycarbonate Track Etch - 140°C
• Sterlitech Polyester - 140°C
• Sterlitech Nitrocellulose (MCE) - 130°C
• Sterlitech Nylon - 180°C
• Sterlitech Polyethersulfone (PES) - *130°C
• Sterlitech Polypropylene - 82°C
• Sterlitech Cellulose Acetate - 135°C
• Sterlitech PTFE (Laminated) - 130°C
• Sterlitech PTFE (Unlaminated) - 260°C
• Sterlitech PVC Data not available

*5.0um and 8.0um - max temp is 180°C

The pores of microporous membrane filters act as small capillaries.  When hydrophilic membranes come into contact with water, capillary action associated with surface tension forces causes the water to spontaneously enter and fill the pores.  In this manner, the membranes are easily wetted and allow the bulk flow of water through the pores.  Once wetted, hydrophilic membranes will not allow the bulk flow of air or other gasses, unless they are applied at pressures greater than the membrane’s bubble point.

Hydrophilic membrane filters are typically used with water and aqueous solutions.  They can also be used with compatible non-aqueous fluids.  Hydrophilic membrane filters are typically not used for air, gas or vent filtration since the filters would block flow if inadvertently wetted, by condensation for example.

When hydrophobic membranes come into contact with water, surface tension forces act to repel the water from the pores.  Water will not enter the pores and the membranes will act as a barrier to water flow, unless the water is applied at pressures greater than the membrane’s water entry pressure.  Low surface tension fluids, such as alcohols, can spontaneously enter and fill the pores of hydrophobic membranes.  Once all the air in the pores is displaced, there are no longer any surface tension forces and water can easily enter the pores, displace the low surface tension fluid, and pass through the membrane.  The membrane will then allow bulk flow of water for as long as the pore remain water filled.  If the membrane is allowed to dry (i.e. air enters the pores), then it must be pre-wet with a low surface tension fluid again prior to use with water.

Hydrophobic membrane filters are typically used with compatible non-aqueous fluids.  They are also commonly used as air, gas, or vent filters.  Hydrophobic membrane filters are sometimes used with water or aqueous solutions; and, in these applications, they must first be prewet with a low surface tension, water miscible fluid prior to use.

Q. What is the difference between nominal and absolute pore size ratings?

Nominal pore size ratings are provided as a general indication of filter retention.  It is understood that some quantity of particles greater than, and equal to, the nominal pore size ratings will pass through the filters into the filtrate.  Some manufactures may associate nominal pore size ratings with percentage filtration efficiencies. Nominal pore size ratings vary from manufacturer to manufacturer and, consequently, are not necessarily equivalent. Filters from different manufactures with similar nominal pore size ratings may not actually exhibit similar retention characteristics.

Absolute pore size ratings are typically based on retention studies performed using challenge suspensions of standard microorganism cultures or particles of known size. Absolute pore size ratings represent the size of the smallest microorganisms or particles completely retained during these studies. Absolute pore size ratings are almost always correlated to bubble point specifications that are used for quality control during membrane manufacturing. For the most part, absolute pore size ratings, especially those based on microbial retention, are comparable from manufacturer to manufacturer. There is more uncertainty for absolute pore size ratings based on particle retention studies, especially for pore size ratings <0.2µm, since there are no standard methods for these studies.

Regardless of pore size ratings, it is important to understand that application conditions do influence particle retention. Even filters with absolute pore size ratings can be operated in conditions that will allow unexpectedly sized particles to pass.

A. There is no predetermined shelf life for the silver membrane. The filters should be stored sealed in the original packaging until needed.  Over time, silver compounds may form on the surface of the membrane.  Any resulting surface discoloration is essentially cosmetic and does not affect filter performance.

Q. What if my membrane is slightly discolored?

A. Although the silver metal membrane is 99.97% pure silver, the formation of extraneous compounds is possible over time. For example, silver can become tarnished, especially when the environment contains certain emissions as described below. To minimize contamination of the membrane, leave it in sealed packs. Silver compounds may form on the surface which are primarily cosmetic imperfections and do not affect the pore structure or membrane filtration performance. Examples of colored compounds that can form on the surface of the silver metal membrane are:

• Ag₂S (black)
• Agl (yellow)
• Ag₃PO₄ (yellow)
• Ag₂CrO₄ (dark red)
• AgCl (dark brown)
• Ag₂O (dark brown)
• AgBr (light yellow)

The most common compounds that form on the silver metal membrane are Ag2S and AgCl. AgCl is a photosensitive salt that can be removed by flushing the membrane with an ammonia solution. Typically, just a brief soak or dip in the ammonia solution will dissolve AgCl. Ag2S is a very stable compound and is very difficult to remove from the membrane without altering the structure. A flush with methyl or ethyl alcohol can be used to remove some of the other compounds.

These compounds should not be confused with the natural grayish white appearance of the silver metal membrane surface. This appearance is due to the microporous structure of the media which reflects light in a manner different than polished silver. The slight difference in color between the two sides of the membrane is due to the manufacturing process and is most noticeable on 3 and 5 micron pores sizes.

Q. What NIOSH Standards are Silver Membranes specified for?

A. National Institute for Occupational Safety and Health (NIOSH) - used for industrial hygiene in foundries, glass plants, quarries, mines, ceramic manufacturing - Methods using 0.45 µm, 25 mm:

N6011 (Bromine & Chlorine) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/6011.pdf
N7500 (Silica, Crystalline) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/7500.pdf
N7501 (Silica, Amorphous) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/7501.pdf
N7504 (Vanadium Oxide) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/7504.pdf
N7505 (Lead Sulfide) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/7505.pdf
N7506 (Boron Carbide) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/7506.pdf
N9000 (Asbestos, Crysotile) - http://www.cdc.gov/niosh/docs/2003-154/pdfs/9000.pdf

Aluminum oxide is free of organic extractables and leachables and shows minimum adsorption.

Unfortunately, we are unable to supply the aluminum oxide membrane filters with custom diameters. Please contact us at [email protected] to inquire about alternatives.

Yes, the Sterlitech aluminum oxide membrane filters can be used as alternatives for the Whatman Anodisc filters. Our alumina filters do not have perimeter support rings, so somewhat greater care must be taken when handling the filters to avoid damage.

Sterlitech Cellulose Acetate (CA) membranes are made from cellulose diacetate. These membrane filters also have an integral nonwoven polyester (polyethylene terephthalate) support layer. When evaluating application compatibility, both materials should be considered.

Not including the polyester support layer, the Cellulose Acetate (CA) membrane filters are composed entirely of cellulose acetate polymer.  There may, however, still be a small amount of residual lignin present. 

Cellulose acetate (CA) membrane filters are one of the lowest protein binding filters available. They will generally have greater throughput with proteinaceous solutions when compared to other membrane filters. CA membrane filters are ideal for filtration of protein and enzyme solutions, tissue culture media and serums, biological fluids, and similar applications where maximum recovery of protein is critical.

CA membranes are manufactured with an integral nonwoven polyester support layer resulting in a dimensionally stable strong membrane that is easier to handle and resistant to curling. The filters have superior resistance to tearing and can withstand steam sterilization up to 135°C. They are suitable for use at elevated temperatures.

CA membranes are hydrophilic and readily wet in water and aqueous solutions. They have good chemical resistance and can be used with low molecular weight alcohols. 

Ceramic membranes are composed of a matrix of zirconium oxide and titanium dioxide. These rigid, inert inorganic filters have superior chemical and thermal resistance. They can be operated at temperatures that would destroy conventional polymer membranes, up to 350°C. These attributes are uniquely suited to applications where the filters are subjected to repeated regeneration with chemical and high temperature cleanings.

The ceramic membrane filters are only available with 47mm and 90mm diameters. You may want to consider other inorganic membranes, such as alumina oxide or silver, for applications requiring different diameters.

The ceramic membrane disk filters are considerably thicker than conventional membrane disk filters and will not fit in conventional disk filter holders.  The ceramic membrane disk
filters must be used with the specially designed holders offered here.

Glass Fiber Filters are exhibit high operating temperatures and are particularly economical for use as a pre-filter.

The acrylic (PMA) resin binder significantly improves the wet strength of the glass fiber filters. Resin bonded glass fiber filters are easier to handle and are resistant to fiber shedding. When evaluating application compatibility, it is important to consider the acrylic (PMA) resin.  

DOP is an abbreviation for dioctyl phthalate.  Aerosol particles made with DOP have a very uniform size of 0.3µm and are used to characterize air filter retention.  For example, DOP particles are used in ASTM D2986-95a, Standard Practice for
Evaluation of Air Assay Media by the Monodisperse DOP (Dioctyl Phthalate) Smoke
Test.

MCE membranes feature fast flow rates, a high protein binding capacity, and great thermal stability, making them a staple for many environmental and biological laboratories. Furthermore, they are available as presterilized, individually wrapped membranes, and can include a gridded pattern for quantifying microbial growth.

Unfortunately, in most instances, we are unable to supply the MCE membrane filters with custom diameters. Please inquire with your Sterlitech sales representative about alternatives.

Sterile mixed cellulose esters (MCE) membrane filters are used in vast quantities for microbiological studies across many industries and are manufactured in very high volumes to accommodate this demand.  Economies of scale and process automation allow the sterile MCE membrane filters to be offered at lower pack costs compared to non-sterile MCE membrane filters.  Non-sterile MCE filters are used much less frequently, necessitating less efficient, smaller volume manufacturing runs and packaging methods.  Consequently, the non-sterile MCE membrane filters have intrinsically greater manufacturing costs and must be offered at higher prices.

Nylon Membranes exhibit high protein binding, solvent resistance, and dimensional stability due to support by inert polyester.

The Sterlitech nylon membrane filters are constructed of nylon 66 polymer. Nylon 66 in inherently hydrophilic, nontoxic, and has good resistance to organic solvents. These membrane filters also have an integral nonwoven polyester (polyethylene terephthalate) support layer. When evaluating application compatibility, both materials should be considered.

We have a Chemical Compatibility Chart that you can use for reference.

PAN Membranes combine excellent selectivity, high flow rates and low pressure requirements for use. 

The polyacrylonitrile (PAN) membrane filters are absolute rated at 0.2µm and are bacterially retentive with typical 6 log reduction value (LRV). This level of retention can be expected to meet EPA standards for safe drinking water with respect to microorganisms. It is important to realize that the integrity of the combined filter holder and disk filter assembly must be considered in critical applications.

No, the PAN membrane filters cannot withstand autoclave sterilization. The fiters can be sanitized with hot water at 90C water for 30min or by soak in ethanol.

Q. What is a Polycarbonate or Polyester Track Etch filter membrane?

A. These types of filter membranes are precise, two-dimensional micro porous screens with straight through, cylindrical pores.

As in the case of other screen-type filters, particle capture takes place only on the surface, therefore there is more accurate separation cut-off. The precision cylindrical pores of Track Etch membranes have the most accurate size cut-off of any membrane. In depth filters, particles get caught throughout the torturous paths within the matrix as well as on the surface of the membrane.

Track Etch filters are also very thin (between 6 - 15 microns thick) but very durable (can withstand over 3,000 psi when properly supported).   They range in color from opaque to almost transparent and black.

Q. What are the benefits of using Sterlitech Polycarbonate or Polyester filter membranes?

A. Sterlitech Polycarbonate Track Etch (PCTE) and Polyester Track Etch (PETE) filters offer the lowest, non-specific binding of any filter membrane. The capture of samples occurs on a flat, glass-like smooth surface with an even distribution of particles captured on a single plane, simplifying microscopic and SEM examination of samples captured on the surface of the membrane.

• Sterlitech Track Etch filter membranes are manufactured and produced under class 100 condition during critical manufacturing steps. Therefore, the membrane is free of contaminants and pyrogens.
• Sterlitech PCTE and PETE membranes offer very low extractables. Both PCTE and PETE membranes are integral, plastic films, therefore, there is no sloughing or particle shedding.
• Sterlitech PCTE and PETE membranes are biologically inert. 
• Both filter membranes offer excellent chemical resistance and thermal stability, with PETE offering a higher chemical resistance.

Q. Will Sterlitech Track Etch filter membranes keep liquid behind the filter and let gases pass through?

A. PVP-Free Polycarbonate membranes have a water contact angle of approximately 90° and will not spontaneously wet out with liquids that have a surface tension equivalent to or greater than water (1 dyne). Due to the low water contact angle, polycarbonate membranes do not make effective vent filters. Low differential pressures will allow liquid water to break through the pores. We recommend membranes with a higher water entry pressure such as Hydrophobic PTFE, Hydrophobic Polyethylene, and Oleophobic Polyester for venting applications. Effective vent filters will allow permeation of gasses, while blocking liquid from entering the pores. Water vapor and other gases will pass through a hydrophobic vent membrane.

PEEK Membranes exhibit outstanding resistance to almost any known organic solvent, as they consist of pure PEEK (no sulfonation or similar). 

The polyether ether ketone (PEEK) membrane filters are hydrophobic. However, they tend to have lower water entry pressures than other common hydrophobic membrane filters such as PTFE, polypropylene, and polyvinylidene difluoride (PVDF).

Yes, the polyether ether ketone (PEEK) membrane filters may be purchased with diameters other than 25 and 47mm.  Please contact [email protected] to inquire about availability and pricing.

PES Membranes are low protein binding, PES membrane filters are ideal for tissue culture media sterilization, life science and microbiology fluid applications. 

The polyethersulfone (PES) membrane filters have asymmetrical pore structure. The pore structure varies within the thickness of the membrane such that the largest openings occur on one side and the smallest openings occur on the opposite side. When viewing the membrane with reflected light at low incidence angles, each side has a somewhat different visual appearance. The side with the largest pores will appear more dull or matte than the side with the smallest pores. With a little bit of experience, most users can easily identify the sides. For optimal throughput, the PES membrane filters should be oriented so that side with the largest pores (the duller side) is facing upstream. For applications involving microscopic analyses of captured particles or microbes, the user may choose to orient the filter so that the side with the smallest pores (the shinier side) is facing upstream. This orientation may reduce throughput but it improves the likelihood of capturing particles of interest on the surface of the membrane instead of within the pore structure.

The polyethersulfone (PES) membranes used in the Sterlitech membrane filters have asymmetric pore structure.  The pore structure varies within the thickness of the membrane such that the largest openings occur on one side and the smallest openings occur on the opposite side.  When viewing the membrane with reflected light at low incidence angles, each side has a somewhat different visual appearance.  The side with the largest pores will appear more dull (or matte) than the side with the smallest pores
(which will appear shinier).  With a little bit of experience, most users can easily identify the sides.  The membranes can be used with either surface oriented upstream without affecting retention.  However, orienting the dull side upstream increases total throughput
while orienting the shiny side upstream allows for better analyses of the retained particles.

It is possible to estimate the pore diameter of polyester track-etch (PETE) membranes from SEM images. In fact, this is how the pore size is characterized during manufacturing for most of the track-etch membranes. However, it is important to understand that there are calibration and performance variations between different SEMs. There is a good likelihood that a user’s results will not correlate to the manufacturing results that were used to characterize the membrane.

The Sterlitech polyester track-etch (PETE) membranes are made of polyethylene terephthalate.

Hydrophobic membrane filters are necessary for applications where the membrane is used to retain liquid water while allowing gases to pass through. Hydrophobic PCTE membranes typically have insufficient water entry pressures for these applications and will allow liquid water to pass at pressures lower than required. Hydrophobic PTFE and PETE membrane filters have the highest water entry pressures for membrane filters and are commonly used for these applications.

Q. What is the thickness of the polypropylene membranes?

A. The thicknesses of our polypropylene membranes are:

• 0.1um polypropylene: 75-110um
• 0.2um polypropylene: 140-180um
• 0.45um polypropylene: 140-180um

PP Membranes exhibit good hydrophobicity and can be considered in applications that don't require the chemical compatability of PTFE. 

You can find the current specifications for the Polypropylene (PP) membrane filters at https://www.sterlitech.com/polypropylene-membrane-filters.html.  Click the "Application/Specification" tab near the middle of the page and scroll down as necessary.

PTFE Membranes are extremely hydrophobic and exhibit superior chemical compatability with agressive solutions. 

The Advantec unlaminated PTFE hydrophilic membrane filters are not permanently hydrophilic. Once wetted, they will become hydrophobic if allowed to dry. Also, they will become hydrophobic if autoclave sterilized or otherwise exposed to temperatures >100°C.

A. The Smooth PTFE side should face towards the feed solution or liquid ingress.

Q. Are Sterlitech Syringe Filters certified pyrogen free?

A. No, we do not perform pyrogen tests on our filters.

Q.  What are the maximum filtration volumes for the 17mm and 30mm syringe filters?

A.  The 17mm and 30mm syringe filters offer greater filtration volume than smaller filters.

• 17 - 12ml
• 17 with glass fiber prefilter - 20ml
• 30 - 120ml
• 30 with glass fiber prefilter - 180ml

Q. What is the maximum operating temperature for the 17mm and 30mm syringe filters?

A.  The 17mm and 30mm syringe filters have a polypropylene housing, which allows them to withstand higher temperatures than an acrylic housing.  The 17mm and 30mm's have a maximum operating temperature of 180°C.  They are also able to be autoclaved.

This video shows the difference between Novamem PVDF20 membranes and the separator papers used in packaging.

The brown color observed here is typical for this particular material, and is likely a result of the heat history and chemical effects in the manufacturing process. The separator papers used will be white, or in some cases light blue.

We have a Chemical Compatibility Chart that you can use for reference.

Q. How is the performance of a filter measured?

A. Design and material selection determines the performance of a filter. Three important measures of filter performance are flow rate, throughput and bubblepoint, defined as follows:

Flow Rate: Determines the volume of liquid or air that will flow through the filter at a fixed pressure and temperature. This is usually displayed as ml/minute/cm^2.

Throughput: Describes the dirt handling capacity of a filter. Namely, how long the liquid will continue to flow through the membrane before the membrane clogs. The lower the flow rate and throughput, the longer it takes the researcher to complete the analysis.

Bubble point: A test to determine the integrity and pore size of a filter. The differential pressure at which a steady stream of gas bubbles is emitted from a wetted filter under specific test conditions. The bubble point test measures the largest pore. Bubble point is generally determined using water or an alcohol (methanol or isopropynol) and is displayed as PSI.

Q. What variables affect the performance of a filter?

A. Viscosity: The viscosity of a liquid determines its resistance to flow; the higher the viscosity, the lower the flow rate and the higher the differential pressure required to achieve a given flow rate.

Porosity: The flow rate of a membrane is directly proportional to the porosity of a membrane, eg. the more pores, the higher the flow rate.

Filter Area: The larger the filter area, the faster the flow rate at a given pressure differential and the larger the expected filter throughput volume prior to "clogging for a given solution."

Q. How are pore sizes rated?

A. A pore size rating is determined by the diameter of the particle that it can be expected to retain with a defined, high degree of efficiency. The rating is stated in nominal or absolute terms.

Q. What are the differences between the crossflow test cells and the Sterlitech HP4750 stirred cell?

A. The Sepa CF, CF042, and CF016 test cells operate in true crossflow mode and have both concentrate and permeate streams. Depending on system design and the fluid being processed, they are operated with user selected pressure and flow parameters and allow for continuous testing and sampling.The HP4750 stirred cell is an enclosed batch system with a maximum feed volume of 300mL that is typically pressured with compressed gas. Stirred cells are operated in normal flow mode and do not have a concentrate stream. Stir bar action is used to simulate cross flow near the membrane surface.

Cross flow velocity limits for commercially available spiral wound elements depend on the element construction limits, recommended maximum pressure drop in an element, and feed characteristics.  The recommended values could be obtained form the manufacturers. Please contact Sterlitech for more information.

Most importantly, flat sheet membranes should be kept wet after use. Control biological growth by adding 0.5% solution of formaldehyde, sodium metabisulfite, or use deionized water and change it out at least once a week. If you use sodium metabisulfite we recommend changing it out every three months since it is a little weaker than formaldehyde.

It is not uncommon for the foulant spacer to leave an imprint on the membrane and, in most cases, is not a cause for concern.

However, it is important to verify that the foulant spacer (or the foulant spacer and shim combination) is not thicker than the feed channel. If too thick of a foulant spacer is used, then it may cause damage to the membrane.

The Reynolds number is a dimensionless number that is related to the ratio of inertial forces to viscous forces experienced by a fluid for given flow conditions. The Reynolds number can be used to predict whether flow conditions result in a laminar or turbulent flow.

In theory, the cross section area of the test cell feed channel can be used to calculate the Reynolds number for the feed flow. In practice, it is very difficult to calculate the Reynolds number because of the complex geometry of the foulant spacer occupying the feed channel. There are empirical methods to estimate the Reynolds number by characterizing the relationship between feed flow and differential pressure.

Please contact us at [email protected] if you need assistance.

Q. How do I distinguish between the low foulant (34ml) feed spacer and the high foulant (68ml) feed spacer when I hold them in my hands?

A. The low foulant has smaller squares and bends slightly easier.  It feels lighter.  It is not stiff like the medium foulant.  The high foulant spacer has corragated ridges in it like cardboard.  No holes.

Q. How do I store used flat sheet crossflow membranes?

A. Used flat sheet membranes must always remain wet, including during storage.  Membranes that are allowed to dry will irreversibly lose water permeability.  To prevent microbial growth, the membranes can be stored in a 0.5% solution of formaldehyde.  Alternatively, the membranes can be stored in a 1.0% solution of sodium metabisulfite (SMBS).  To maintain efficacy, the SMBS solution should be replaced monthly.  Or the membranes can be stored in UPDI water that is replaced weekly.

Q. The Flat Sheet Membranes appear dry in their packaging. How do I pre-wet them? Do I need to do this?

A. Yes, you need to pre-wet the membranes. The best procedure is to place them in a dry holder and allow them to wet from the inlet side first. It may be best to perform this operation with water or a buffer, then dispose of the first rinse, and introduce the process fluid. This prevents any wetting agents or preservatives from mixing with the process solution.

Prior to use, the membranes should be stored in a climate controlled environment, away from sunlight and heat, while sealed in the original packaging. We recommend using the membranes as soon as practical after receiving them. However, most of the flat sheet membranes may be stored for up to one year without affecting performance. The exceptions are the GE cellulose acetate membranes (CE and CK) and the Aquaporin FO membrane which should be used within 6 months.

Yes, you may cut the membrane to fit in your stirred cell. You can use the support disk from the stirred cell as a template.  

Any conventional magnetic stir plate will work. Sterlitech recommend the Scilogex MS7-H550-Pro. The large 7in square ceramic base provides a good foundation for the stirred cells while the digital display ensures precise repeatable control of the stirring function.

The user must completely release the pressure before opening a stirred cell. The HP4750 and HP4750X stirred cells do not have integrated pressure relief valves, but Sterlitech does offer an accessory bleed valve for purchase which can be attached to the regulator's outlet to the high pressure hose upstream of the stirred cell. https://www.sterlitech.com/pressure-relief-bleed-valve-2500-psig-1155893.html . The bleed valve can be slowly opened to release pressure when necessary for sample removal or refilling.

The polymeric stirred cells have integrated pressure relief valves. These valves can simply be opened to release the pressure when necessary.

No, cellQART^® products include only the inserts.  We do offer well plates sold separately:

• 6-Well Glass Bottom Plates (SKU P06G-1.5-20-F)
• 12-Well Glass Bottom Plates (SKU P12G-1.5-14-F)
• 24-Well Glass Bottom Plates (SKU P24G-1.5-13-F) 

Yes, cellQART^® inserts are designed to be compatible with standard 6-well, 12-well and 24-well plates.  Their patented hanging design ensures optimal well placement while still allowing good pipetting access.

No, the Rocker vacuum pumps should not be moved while operating. Turn of the pump and open the inlet to atmosphere before moving it. Moving an operating Rocker 300 or 400 series pump will cause the Prote protection device within the inlet filter to close.

No, the Rocker vacuum pumps must be resting on a level, flat surface during operation. Operating the Rocker 300 or 400 series pumps while not level will cause the Prote protection device within the inlet filter to close.

The Rocker 800 vacuum pump is commonly used for high flow applications, such as vacuum ovens, where a moisture trap is not required. If you require a high flow vacuum pump with moisture trap, then you should order the Rocker 801 vacuum pump.

https://www.sterlitech.com/rocker-801-oil-free-vacuum-pump.html

Some of the benefits of reverse osmosis water are:

• Free of water contaminants
• Produced with minimal energy required
• Available with just a tap of a button
• Free of minerals found in hard water
• Cost-effective compared to purchasing bottled water
• Better-tasting

The RO purified water from the Y7 counter top water filtration system registered a pH of 7.5 to 9.5. The test was conducted by Ravenna Global SELLER on December 25, 2020.

Unfortunately, the UV light in the Y7 cannot be replaced but it should be fully operational for 3 to 5 years from first use. The water purifier UV light indicator on the smart touchscreen display panel lights up during sterilization.