Membrane filter technique

Another standard test, which is much simpler and more convenient, is the membrane filter technique. A suitable volume of sample is filtered through a sterile, 0.45-p.m membrane filter. The filter is placed in a petri dish containing a specific growth medium (M-Endo nutrient broth, M-Endo medium) and incubated for 24 h at 35°C. If after this time the colonies show the characteristic green sheen, this is taken as positive evidence for the presence of the coliform group (see Water, sewage). 

A membrane filter technique can also be used to determine the presence of fecal coliforms, and this procedure is said to be 93% accurate (20). A sample is passed through a membrane filter, and this filter is placed in a petri dish containing an enriched lactose medium. The dishes are incubated at... 

Elmholt, S. and A. Kj oiler (1987). Measurement of the Length of Fungal Hyphae by the Membrane Filter Technique as a Method for Comparing Fungal Occurrence in Cultivated Field Siols. Soil Biol. Biochem 19 (6) 679-682. 

The maximum contaminant levels for coliform bacteria are applicable to community and noncommunity water systems (Shelton, 1989). Two methods are used to measure coliform bacteria in water. One is the membrane filter technique and the other is the fermentation tube method. For details, see Shelton (1989). 

Quantitative tests. In some situations, actual enumeration of the number of organisms present may be necessary. This is the case, for example, for limitations imposed on a discharge permit. Generally, two methods are used to enumerate conforms the membrane-filter technique and the multiple-tube technique. 

Solution Using the criterion of 20 to 80 as the most vahd count in a membrane-filter technique, the results of the 10- and 500-mL portions can be excluded in the calculation. 

Based on average of two consecutive days 5 TU Membrane filter technique not to exceed 1/100 mL on monthly basis not to exceed 4/100 mL of coliforms in more than one sample in fewer than 20 samples per month on an individual sample basis not to exceed 4/100 mL of coliforms in more than 5% of sample in more than 20 samples per month on an individual basis. 

Pang TW, Schonfeld-Starr FA, Patel K. 1989. An improved membrane filter technique for evaluation of asbestos fibers. Am Ind Hyg Assoc J 50 174-180. 

Initially, the membrane-filter technique (Gillespie and Spiegelman,... 

Membrane filter technique. Water is filtered through a 0.45-p.m sterile filter which is then placed in a culture medium and incubated at 35°C for 24 h. The growth of visible colonies on the filter indicates the number of bacteria present. 

The complex formation of polycations with RNA, analyzed by the membrane filter technique in association with the assay of viral RNA infectivity, can be used to study the influence of biologically active substances like carcinogens, viral inhibitors, or heavy metal ions on nucleic acid-protein interaction. 

Filtration Technique. A measured quantity of sample water is filtered through the membrane filter. The filter is dried, cut and sections placed on microscope slides. The filter sections are rendered transparent by a drop of immersion oil. The slides are examined to identify the microorganisms listed below ... 

Membrane filtration is the technique reeommended by most pharmacopoeias and involves filtration of fluids through a sterile membrane filter (pore size = 0.45 im), any microorganism present being retained on the surfaee of the filter. After washing in situ, the filter is divided aseptically and portions transferred to suitable culture media which are then incubated at the appropriate temperature for the required period of time. Water-soluble solids can be dissolved in a suitable diluent and processed in this way. 

Until this point, the sample preparation techniques under discussion have relied upon differences in polarity to separate the analyte and the sample matrix in contrast, ultraflltration and on-line dialysis rely upon differences in molecular size between the analyte and matrix components to effect a separation. In ultrafiltration, a centrifugal force is applied across a membrane filter which has a molecular weight cut-off intended to isolate the analyte from larger matrix components. Furusawa incorporated an ultrafiltration step into his separation of sulfadimethoxine from chicken tissue extracts. Some cleanup of the sample extract may be necessary prior to ultrafiltration, or the ultrafiltration membranes can become clogged and ineffective. Also, one must ensure that the choice of membrane filter for ultrafiltration is appropriate in terms of both the molecular weight cut-off and compatibility with the extraction solvent used. 

The second important piece in the process development is the separation scheme. Several methods were suggested, such as decanting, water extraction or fractional distillation, use of hydrocyclones, hydrophobic membrane filters, etc. In the early work at EBC, many of its patents refer to facilitating catalyst separation via immobilization, although no mention is given on how activity was impacted by that immobilization. Furthermore, there were no details on how immobilization was achieved and which were the preferred means and techniques. 

Southern blotting Technique used to identify and locate DNA sequences which are complementary to another piece of DNA called probe using electrophorectic gels for separation of DNA and membrane filters with radiolabelled complementary probes. 

As discussed previously, the technique of microfiltration is effectively utilized to remove whole cells or cell debris from solution. Membrane filters employed in the microfiltration process generally have pore diameters ranging from 0.1 to 10 pm. Such pores, while retaining whole cells and large particulate matter, fail to retain most macromolecular components, such as proteins. In the case of ultrafiltration membranes, pore diameters normally range from 1 to 20 nm. These pores are sufficiently small to retain proteins of low molecular mass. Ultrafiltration membranes with molecular mass cut-off points ranging from 1 to 300 kDa are commercially available. Membranes with molecular mass cut-off points of 3,10, 30, 50, and 100 kDa are most commonly used. 

Drever JI. Preparation of oriented clay mineral specimens for X-ray diffraction analysis by a filter-membrane peel technique. Am. Mineral. 1973 58 553-554. 

It must also be emphasized that the major mass of a heterodispersed aerosol may be contained in a few relatively large particles, since the mass of a particle is proportional to the cube of its diameter. Therefore, the particle-size distribution and the concentration of the drug particles in the exposure atmosphere should be sampled using a cascade impactor or membrane filter sampling technique, monitored using an optical or laser particle-size analyzer, and analyzed using optical or electron microscopy techniques. 

There is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

Rotating diffusion cells These techniques bring the two phases in contact at the surface of a rotating membrane filter having well characterized hydrodynamics. 

V is the kinematic viscosity. The organic phase inside the membrane is considered at rest, and the membrane thickness and porosity control the diffusion rate. The major drawbacks of this technique are difficulties in well characterizing the thickness and porosity of the membrane filter, in utilizing really thin filters (less than 10 cm), and that, although the hydrodynamics inside the rotating cyhnder can be assimilated to those of a rotating disk, no studies have conclusively shown that the flows inside and outside the cylinder are the same. 

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