Hydrophilic Filter Research Articles

A cost-effective plate-based sample preparation for antibody N-glycan analysis

During early cell line and process development of therapeutic antibodies, a cost-effective high-throughput approach to characterize the N-linked glycans is highly desired given that a large number of samples need to be analyzed. Using commercially available, low cost 96-well plates, we developed a practical procedure to prepare fluorescently labeled N-linked glycans for both qualitative and quantitative analysis by mass spectrometry (MS) and ultrahigh performance liquid chromatography (UPLC). Antibody samples were continuously denatured, reduced, and deglycosylated in a single 96-well hydrophobic membrane filter plate. Subsequently, released glycans were fluorescently labeled in a collection plate, and cleaned-up using a hydrophilic membrane filter plate. Carried out entirely in ready-to-use 96-well plates with simple buffer systems, this procedure requires less than 90min to finish. We applied the optimized procedure to examine the N-linked glycosylation of trastuzumab and were able to quantify ten major N-linked glycans. The results from different amounts of starting materials (10–200μg) were highly similar and showed the robustness of this procedure. Compared to other methods, this new procedure is simple to implement, economically more affordable, and could be very valuable for early screenings of antibody development.

Rapid analysis of 28 primary aromatic amines in aqueous food simulants by high performance liquid chromatographytandem mass spectrometry

A novel method for rapid analysis of the migration amounts of 28 primary aromatic amines (PAAs) in aqueous food simulants (10% ethanol, 30 g/L acetic acid and 20% ethanol aqueous solution) was developed using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). After the migration test, the soaking solution was cooled down from 100 degrees C, vortexed, filtered through a hydrophilic polytetrafluoroethylene filter with a disposable syringe, and then the filtrate was analyzed by HPLC-MS/MS. A Zorbax SB-Phenyl column (250 mm x 4.6 mm, 5 microm) was selected for chromatography. The mobile phase consisted of water and 0.1% formic acid-25% acetonitrile-methanol solution with gradient elution. The 28 PAAs in aqueous food simulants were detected by tandem mass spectrometer operated in positive electrospray ionization (ESI+) and multiple reaction monitoring (MRM) mode. The limits of quantification for the 28 PAAs were between 0.002 microg/L and 10 microg/L. The linearity of the method was good with correlation coefficients (r2) greater than 0.995 over the concentration range from 5 microg/L or 10 microg/L to 100 microg/L. The average recoveries of the 28 PAAs were between 76.6% and 114% with the relative standard deviations between 1.53% and 8.97% at the levels of 10, 20, and 40 microg/L. The method shows rapid pretreatment, the lower limits of quantification, good recoveries and accuracies, and meets the requirement of European Union (EU) No 10/2011 regulation for the specific migration of PAAs. The method has been applied to analyze the 28 PAAs in different aqueous food simulants from the migration test of 30 batches of food contact material samples exported to EU.

Tangential Flow Ultrafiltration: A "Green" Method for the Size Selection and Concentration of Colloidal Silver Nanoparticles

Nowadays, AgNPs are extensively used in the manufacture of consumer products,(1) water disinfectants,(2) therapeutics,(1, 3) and biomedical devices(4) due to their powerful antimicrobial properties.(3-6) These nanoparticle applications are strongly influenced by the AgNP size and aggregation state. Many challenges exist in the controlled fabrication(7) and size-based isolation(4,8) of unfunctionalized, homogenous AgNPs that are free from chemically aggressive capping/stabilizing agents or organic solvents.(7-13) Limitations emerge from the toxicity of reagents, high costs or reduced efficiency of the AgNP synthesis or isolation methods (e.g., centrifugation, size-dependent solubility, size-exclusion chromatography, etc.).(10,14-18) To overcome this, we recently showed that TFU permits greater control over the size, concentration and aggregation state of Creighton AgNPs (300 ml of 15.3 μg ml(-1) down to 10 ml of 198.7 μg ml(-1)) than conventional methods of isolation such as ultracentrifugation.(19) TFU is a recirculation method commonly used for the weight-based isolation of proteins, viruses and cells.(20,21) Briefly, the liquid sample is passed through a series of hollow fiber membranes with pore size ranging from 1,000 kD to 10 kD. Smaller suspended or dissolved constituents in the sample will pass through the porous barrier together with the solvent (filtrate), while the larger constituents are retained (retentate). TFU may be considered a "green" method as it neither damages the sample nor requires additional solvent to eliminate toxic excess reagents and byproducts. Furthermore, TFU may be applied to a large variety of nanoparticles as both hydrophobic and hydrophilic filters are available. The two main objectives of this study were: 1) to illustrate the experimental aspects of the TFU approach through an invited video experience and 2) to demonstrate the feasibility of the TFU method for larger volumes of colloidal nanoparticles and smaller volumes of retentate. First, unfuctionalized AgNPs (4 L, 15.2 μg ml(-1)) were synthesized using the well-established Creighton method(22,23) by the reduction of AgNO3 with NaBH4. AgNP polydispersity was then minimized via a 3-step TFU using a 50-nm filter (460 cm(2)) to remove AgNPs and AgNP-aggregates larger than 50 nm, followed by two 100-kD (200 cm(2) and 20 cm(2)) filters to concentrate the AgNPs. Representative samples were characterized using transmission electron microscopy, UV-Vis absorption spectrophotometry, Raman spectroscopy, and inductively coupled plasma optical emission spectroscopy. The final retentate consisted of highly concentrated (4 ml, 8,539.9 μg ml(-1)) yet lowly aggregated and homogeneous AgNPs of 1-20 nm in diameter. This corresponds to a silver concentration yield of about 62%.

Cellulose-based material with amphiphobicity to inhibit bacterial adhesion by surface modification

Amphiphobic cellulose-based material was prepared by functional surface modification of nanofibres of a natural cellulose substance (e.g., commercial filter paper). The filter paper was firstly etched by alkaline solution to enhance the surface roughness, and then ultrathin titania films were deposited onto the cellulose nanofibre surfaces of the etched filter paper by a facile surface sol–gel process. A 1H,1H,2H,2H-perfluorooctyl trimethoxysilane (PFOTMS) monolayer was further self-assembled onto the titania ultrathin film pre-coated cellulose nanofibres. Due to the rough morphology of the etched filter paper and the low surface energy coating with PFOTMS monolayers, the naturally hydrophilic filter paper is converted into an amphiphobic material with both superhydrophobicity and high oleophobicity, which effectively inhibits the adhesion of bacteria such as lysogenic E. coli.

Determination of chromium(VI) in black, green and herbal teas

Speciation analysis of black, green and herbal teas was carried out by treating the samples with 0.1M Na2CO3 to determine total Cr(VI) and acid digestion (of tea samples in a microwave) was applied to determine the total chromium concentrations by graphite furnace atomic absorption spectrometry (GF-AAS). The Cr(VI) content that could be consumed per unit cup of tea was determined by soaking the leaf or tea bag (or infusion) in 200mL boiled water and the solution was filtered through a PDVF 0.45μm hydrophilic filter prior analysis by GF-AAS.Results of the investigation showed that concentration of total Cr(VI) in black teas varied between 0.03 and 3.15μgg−1(with an average of 1.07±1.14μgg−1), in green tea ranged between 0.03 and 0.14μgg−1 (with an average of 0.09±0.034μgg−1) and that in herbal tea was below the limit of detection (LOD) thereby indicating that Cr(VI) levels increase in the order of herbal tea, green tea and black tea. It was also found that up to 17.5μgL−1 of Cr(VI) could be consumed per unit cup of black tea (200mL) when standard tea bag (2.0g) or 2.0g leaf was used for the preparation of tea. Similarly, black teas were found to contain higher total Cr content (0.28–14.0μgg−1 with an average of 4.38±4.23μgg−1) than green (0.22–0.95μgg−1 with an average of 0.70±0.29μgg−1) and herbal teas (0.68–1.24μgg−1 with an average of 0.95±0.27μgg−1).

Are Dialysis Devices Usable as Ozone Gas Exchangers?

A study aimed to compare the efficiency of the ozone transfer of four hydrophilic dialysis filters, and one hydrophobic gas-exchange device (GED) has been performed. Obviously, the former should be specifically used only for dialysis. Unfortunately, some clinicians incautiously use them as GEDs. It has been shown that: (i) dialysis filters present a wide range of gas-exchange yield (from 0 up to 70%), often related to variability according to the treatment time; (ii) by scanning microscopy, it has been noticed that hollow fibers are somewhat altered by ozone; and (iii) because their constitutive materials may not be ozone-resistant, they may release toxic compounds harmful for the patients. On the contrary, the appropriate GED is ozone-transfer efficient, is ozone-resistant, and is suitable for blood autotransfusion and ozonation.

Interactions of Trace Metals with Hydrogels and Filter Membranes Used in DET and DGT Techniques

Equilibrium partitioning of trace metals between bulk solution and hydrogels/filter was studied. Under some conditions, trace metal concentrations were higher in the hydrogels or filter membranes compared to bulk solution (enrichment). In synthetic soft water, enrichment of cationic trace metals in polyacrylamide hydrogels decreased with increasing trace metal concentration. Enrichment was little affected by Ca and Mg in the concentration range typically encountered in natural freshwaters, indicating high affinity but low capacity binding of trace metals to solid structure in polyacrylamide gels. The apparent binding strength decreased in the sequence: Cu > Pb > Ni approximately to Cd approximately to Co and a low concentration of cationic Cu eliminated enrichment of weakly binding trace metal cations. The polyacrylamide gels also had an affinity for fulvic acid and/or its trace metal complexes. Enrichment of cationic Cd in agarose gel and hydrophilic polyethersulfone filter was independent of concentration (10 nM to 5 microM) but decreased with increasing Ca/ Mg concentration and ionic strength, suggesting that it is mainly due to electrostatic interactions. However, Cu and Pb were enriched even after equilibration in seawater, indicating that these metals additionally bind to sites within the agarose gel and filter. Compared to the polyacrylamide gels, agarose gel had a lower affinity for metal-fulvic complexes. Potential biases in measurements made with the diffusive equilibration in thin-films (DET) technique, identified by this work, are discussed.

Influence of different purification techniques on triamcinolone yield and particle size spectrum

To systematically investigate the common purification techniques for commercially available triamcinolone acetonide preparations and the influence of different filter parameters on final yield, reproducibility and particle size spectrum. Two non-filter techniques using either sedimentation or centrifugation, and two different filter techniques were tested. Filters with different characteristics were investigated with the pore size ranging from 0.1 to 5.0 microm, and the filter diameter ranging from 4 to 30 mm. Only sterile standard syringe filters with low adsorptive characteristics (hydrophilic cellulose filter membranes) for pharmaceutical use were employed. For quantification, triamcinolone acetonide was dissolved in 60% methanol and measured spectrophotometrically at 239 nm. The crystal size spectrum was determined using a particle size analyzer that combines electronic pulse area analysis and resistance measurement. Depending on the purification technique used the resulting triamcinolone doses differed significantly. While the centrifugation method achieved purification without relevant loss, the sedimentation method yielded only 28.7% compared to the original commercial suspension, and in addition, the predictability was low (range 8.1-17.2 mg). With filter techniques high and consistent doses with a good reproducibility were achieved, but results were highly dependent on the filter characteristics. The final triamcinolone amount inversely correlated with the filter diameter due to a uniform loss of crystalline particles. In contrast, enlarging the pore size caused a substantial shift in the particle size spectrum due to a selective loss of small crystalline particles. The most common purification techniques vary notably in regard to final triamcinolone doses, reproducibility and particle size spectrum. The appropriate choice of the filter parameters seems to be more important than assumed, as pore size and filter diameter substantially influence both the final TA doses and the particle size of the TA crystals.

A hybrid poly(dimethylsiloxane) microsystem for on-chip whole blood filtration optimized for steroid screening

Miniaturized biochemical devices in glass, silicon and polymer materials are starting to find their way from the academic laboratories to real-life applications. However, most attention has been given to miniaturize the downstream functions of various microfluidic systems, leaving the sample introduction and preparation steps to more conventional, bulkier solutions. For point-of-care diagnostics in particular, it becomes crucial to be able to handle complex human samples in a miniaturized format.In this work, we report on a microsystem for on-chip sample preparation that is able to remove blood cells from whole blood. The hybrid system consists of a commercially available membrane filter incorporated into a poly(dimethylsiloxane) (PDMS) casted device. Membrane materials were evaluated on the bases of low nonspecific adsorption of free and protein-bound testosterone as analyte substance. The hybrid system including a hydrophilic polypropylene filter successfully removed blood cells from diluted human whole blood. Surface oxidation was sufficient to make the plasma filtrate flow through the membrane filter and the channel system by capillary force alone and thus no external pumping source was needed.

Versatile Gas/Particle Ion Chromatograph

A new, compact gas/particle ion chromatograph has been developed for measuring ionic constituents in PM2.5 (particulate matter of aerodynamic diameter < or = 2.5 microm) and water-soluble ionogenic gases. The instrument has separate sampling channels for gases and particles. In one, a membrane denuder collects soluble gases for preconcentration and analysis. In the other, a cyclone removes larger particles, a membrane denuder removes soluble gases, and a continuously wetted hydrophilic filter collects particles. A single, multiport, syringe pump handles liquid transport, and one conductivity detector measures anions and ammonium for both channels. Electrodialytically generated gradient hydroxide eluent permits 20 min chromatographic runs. Gas/particle samples are each collected for 40 min, butthe sampling intervals are staggered by 20 min. Liquid samples from the gas denuder and particle collector are aspirated and preconcentrated on sequential cation and anion concentrators and transferred respectively to an ammonia transfer device and an anion separation column. The flow configuration results in an ammonium peak before anion peaks in the chromatogram. The system measures ammonia, organic acids (such as acetic, formic, and oxalic acids), HCl, HONO, SO2, HNO3, and the corresponding ions in the aerosol phase. Low ng/m3 to sub-ng/m3 limits of detection (LODs) are attained for most common gases and particulate constituents, the LODs for gaseous SO2 to NH3 range, for example, from sub parts per trillion by volume (sub-pptv) to approximately 5 pptv.

Continuous Collection of Soluble Atmospheric Particles with a Wetted Hydrophilic Filter

Approximately one-third of the area (14-mm diameter of a 25-mm diameter) of a 5-microm uniform pore size polycarbonate filter is continuously wetted by a 0.25 mL/min water mist. The water forms a continuous thin film on the filter and percolates through it. The flowing water substantially reduces the effective pore size of the filter. At the operational air sampling flow rate of 1.5 standard liters per minute, such a particle collector (PC) efficiently captures particles down to very small size. As determined by fluorescein-tagged NaCl aerosol generated by a vibrating orifice aerosol generator, the capture efficiency was 97.7+% for particle aerodynamic diameters ranging from 0.28 to 3.88 microm. Further, 55.3 and 80.3% of 25- and 100-nm (NH4)2SO4 particles generated by size classification with a differential mobility analyzer were respectively collected by the device. The PC is integrally coupled with a liquid collection reservoir. The liquid effluent from the wetted filter collector, bearing the soluble components of the aerosol, can be continuously collected or periodically withdrawn. The latter strategy permits the use of a robust syringe pump for the purpose. Coupled with a PM2.5 cyclone inlet and a membrane-based parallel plate denuder at the front end and an ion chromatograph at the back end, the PC readily operated for at least 4-week periods without filter replacement or any other maintenance.

Role of Chloride Ions in Modulation of the Interaction between von Willebrand Factor and ADAMTS-13

The degradation of von Willebrand factor (VWF) depends on the activity of a zinc protease (referred to as ADAMTS-13), which cleaves VWF at the Tyr(1605)-Met(1606) peptide bond. Little information is available on the physiological mechanisms involved in regulation of AD-AMTS-13 activity. In this study, the role of ions on the ADAMTS-13/VWF interaction was investigated. In the presence of 1.5 m urea, the protease cleaved multimeric VWF in the absence of NaCl at pH 8.00 and 37 degrees C, with an apparent k(cat)/K(m) congruent with 3.4 x 10(4) M(-1) s(-1), but this value decreased by approximately 10-fold in the presence of 0.15 M NaCl. Using several monovalent salts, the inhibitory effect was attributed mostly to anions, whose potency was inversely related to the corresponding Jones-Dole viscosity B coefficients (ClO(4)(-) > Cl(-) > F(-)). The specific inhibitory effect of anions was due to their binding to VWF, which caused a conformational change responsible for quenching the intrinsic fluorescence of the protein and reducing tyrosine exposition to bulk solvent. Ristocetin binding to VWF could reduce the apparent affinity and reverse the inhibitory effect of chloride. We hypothesize that, after secretion into the extracellular compartment, VWF is bound by chloride ions abundantly present in this milieu, becoming unavailable to proteolysis by AD-AMTS-13. Shear forces, which facilitate GpIbalpha binding (this effect being artificially obtained by ristocetin), can reverse the inhibitory effect of chloride, whose concentration gradient across the cell membrane may represent a simple but efficient strategy to regulate the enzymatic activity of ADAMTS-13.

Patents

High-strength asymmetric cellulose membranes Membrane for the treatment of waste lubricants Cross-linked polymer blend membrane Ceramic membrane Gas chromatograph calibration Sugar preparation Crosslinked sulphonated polyimide films Graft copolymer membranes Water supply system Hydrophilic polymers Ion-conducting membrane Polymerization reactors Water purification cartridge Self-contained water filter with zeolites Multiple-well sequencing plate Semi-permeable composite membrane Membrane body Down-hole gas separation system Microfabricated nanopore device for sustained release of therapeutics Apparatus and method for cleaning membrane filtration modules

Selecting Filter Membranes for measuring DOC and UV254

Seventeen filter membranes produced from eight membrane materials by four major manufacturers were evaluated for dissolved organic carbon (DOC) and ultraviolet (UV254) absorbance measurements and thus for specific UV absorbance determinations. Hydrophilic polyethersulfone filters from two manufacturers and a hydrophilic polypropylene filter were the best options among the filters tested for complying with the US Environmental Protection Agency's Disinfectants/Disinfection By‐products Rule. These filters should be rinsed with a minimum of 30 mL distilled and deionized water/cm2 filter surface area (e.g., 500 mL on a 47mm disc filter) prior to use. During sample filtration, an initial 25 mL of the filtrate on a 47‐mm filter must be wasted before samples for DOC and UV254 measurements are collected to minimize the impact of dissolved organic matter (DOM) losses to filter membranes. Other filters were not recommended because of one or a combination of the following factors: (1) they did not have an absolute pore size of 0.45‐μm, (2) they exhibited higher degrees of organic carbon leaching and were more difficult to render clean, and/or (3) they showed significant DOM uptake. Before a filter for DOC and UV254 measurements is selected, it is essential to conduct filtered blank experiments and to demonstrate that there is no gain or loss of DOC and UV254 during filtration. It is also important to recognize that there may be significant lot‐to‐lot variations in the levels of contamination on filters.

Plasma assisted hydrophobic coatings on porous materials: influence of plasma parameters

Cellulose-based filter paper was plasma treated for hydrophobicity and the permeation of the coating investigated. A five-layer stack of filter paper was the model porous medium and perfluoromethylcyclohexane (PFMCH) was the model monomer used in this study. Water-drop-absorption time (time needed for certain size droplet of water to be completely absorbed) was recorded as a measure of coating effectiveness. Video contact angle measurements were used to evaluate surface hydrophobicity and x-ray photoelectron spectroscopy was used to analyse the surface chemistry of each surface in the stack. It is clear that the outer surface of normally hydrophilic filter paper can easily be made hydrophobic by treatment with PFMCH plasma. By adjusting plasma power, pressure and time, a filter paper can be treated to have one side hydrophobic (water repellent) and the other side hydrophilic (water absorbent). The control of coating penetration into inner layers needs more careful study: it is seen that plasma permeation depends to a small extent on plasma power, negligible extent on background pressure, but to a very large extent on treatment time. During initial deposition, both, the water-drop-absorption rate and the contact angle, have exponential relationships with plasma time. It is shown that CF2 and CF3 functional groups are related to hydrophobic behaviour and that the contact angle and water-absorption time can be correlated to the total fluorine concentration on the surface. A very small amount of surface F is needed for hydrophobic behaviour.

A comparative study of artificial membrane permeability assay for high throughput profiling of drug absorption potential

Artificial membrane permeability measurement is a potentially high throughput and low cost alternative for in vitro assessment of drug absorption potential. It will be an ideal screening/profiling tool in the lead generation program of drug discovery research if it is proven to be generally applicable for classifying drug absorption potential and is advantageous over other in vitro or in silico methods. This study provides an in-depth evaluation of the method in close comparison to Caco-2, Log D, Log P, polar surface area (PSA), and quantitative structure-property relationship (QSPR) predictions using a large and diverse compound set. It showed that the accuracy of using artificial membrane permeability in assessing drug absorption is comparable to Caco-2, but significantly better than Log P, Log D, PSA, and QSPR predictions. This study also explored the artificial membrane composition by adopting a hydrophilic filter membrane for artificial membrane (lecithin–dodecane) support. The use of hydrophilic filter membrane increased the rate of permeation significantly and reduced the transport time to 2 h or less as compared with over 10 h when a hydrophobic filter membrane is used.

Ultrasonic extraction and field-portable anodic stripping voltammetric measurement of lead in dust wipe samples

Dust wipe samples were subjected to ultrasonic extraction (UE) in diluted nitric acid, and then analyzed for lead content using field-portable anodic stripping voltammetry (ASV). Recoveries of lead were determined from wipe materials which were spiked with certified reference materials (CRMs) containing known quantities of lead. Four different wipe materials and four different CRMs were tested, with and without filtration of aliquots of sample extract through 0.45 μm hydrophilic polytetrafluoroethylene filters. The CRMs consisted of paint, soil, particulate, and dust matrices. Wipe materials were chosen from those which have been found to meet the performance aspects of an ASTM standard specification. UE/ASV experiments were carried out in accordance with newly published ASTM procedures for on-site extraction and electroanalysis. Recoveries were found to vary for different wipe materials and CRMs. For several CRMs, quantitative (80–120%) recoveries for UE/ASV were observed for one wipe material whether filtration was used or not, while other wipe materials required filtration for quantitative recovery. In the case of one wipe material which contained detergents, quantitative recoveries could not be achieved whether filtration was used or not. The total analysis time for a sample set of 6–12 samples was 60–90 min, including extraction time and sample manipulation. The results of this work have provided information on the choice of wipe materials that can be used for quantitative lead measurements by UE/ASV in materials that are representative of sources of lead in surface dust.

Degradation of antiproteinases, complement and fibronectin in chronic leg ulcers.

It has been proposed that excessive and uncontrolled proteolytic activity is an important pathogenetic factor for chronic wounds. Identification of molecules that either control or reflect proteolysis in wounds may prove to be useful in determining wound healing activity. In this study wound fluid was sampled under a polyurethane dressing or on hydrophilic glass filters. Multiple chronic wound fluid components were identified; viz. the previously described alpha2-macroglobulin, alpha1-antitrypsin and fibronectin, as well as "novel" wound fluid molecules such as complement factor C3, inter-alpha-inhibitor, kininogen, IgG, IgA, C-reactive protein, tetranectin, orosomucoid and ceruloplasmin. There appeared to be a highly variable degradation of alpha1-antitrypsin in the wounds; furthermore, the activation of C3 appeared to correlate with the appearance of fibronectin breakdown products. In wound fluid, inter-alpha-inhibitor was degraded. The influence of the sampling procedures was studied. It was shown that contact phase activation must be taken into account in the study of molecules (such as kininogens) activated by hydrophilic charged surfaces.

Validation of filter sterilisation in autoclaves

Filter cartridges for sterilising filtration are often sterilised by autoclavation. Although this process should be fully validated, not all process parameters are always considered. In this paper, the influence of positioning and packaging on the F 0 121°C-values at the coldest spot of the filter was investigated in the Sealkleen® and Kleenpak® housings with hydrophilic and hydrophobic filters (Pall Process Filtration Ltd., Portsmouth, UK). A temperature mapping of the assembled filters was performed and it was shown that the coldest spot was located at the sterile side at the top of the filter. The vertical position with the non-sterile side down showed the highest F 0 121°C-values at the coldest spot. The use of biological indicators confirmed this finding. Different packaging methods with medical paper had no significant influence on F 0 121°C-values for the Kleenpak® filter. The hydrophilic Sealkleen® showed significantly lower F 0 121°C-values in the open filter compared to the filter closed at the sterile side, while the hydrophobic Sealkleen® showed significantly lower F 0 121°C-values for the filter in a bag compared to the open filter and the sterile side-closed filter

Latex Sphere Retention by Microporous Membranes in Liquid Filtration

An experimental study of particulate matter retention by microporous membranes during liquid filtration has been conducted using 0.1, 0.22, 0.45, and 0.65-μm-rated hydrophilic and hydrophobic membrane filters. Retention measurements have been made with polystyrene latex spheres using an automated filter test system and a laser particle counter to measure the upstream and downstream particle concentration. Particle filtration during loading tests was found to begin with a sieving dominant regime followed by a transition regime and a cake filtration regime as particles accumulate inside the filter pores and on the filter surface. For latex sphere sizes equal to the nominal pore size of the filter, the initial filter efficiencies ranged from 97 to 99.9 percent. Complete retention (&amp;gt;99.9999999 percent) was achieved for a range of particle sizes two to three times the rated pore sizes of the filter. With the addition of a surfactant to the liquid, the retention was found to be lowered as a result of enhanced particle passage through the filter due to modified surface adsorption and steric stabilization. It was found that particle retention by sieving with the addition of surfactant provided the "worst-case" test for filter performance.