Membrane Filtration Methods

The purpose of a sterility test is to determine the probable sterility of a specific batch. The USP lists the procedural details for sterility testing and the sample sizes required [1], The USP official tests are the direct (or culture tube inoculation) method and the membrane filtration method. 

Biological fouling was monitored using the customary indicators of RO performance, including flux (productivity), salt passage, and bundle pressure drops (AP). In addition, the total bacteria count (TBC) of the RO feed water and the reject brine stream were also obtained using the membrane filtration method (Ref. 6). The increase in TBC between the feed and reject portions of the system had been found in the preliminary stages of... 

Since membrane filtration methods such as ultra filtration or nanofiltration can discriminate according to the size of a given molecule, they can easily be used to retain biocatalysts (which are macromolecules). For chemical catalysts additional procedures have to be applied mostly. Immobilization on a solid support is used... 

Total aerobic viable count per standard test method (provide reference number) using membrane filtration method. Sample 100 ml shall be filtrated and placed on low-nutrient content media, at 20 to 22°C for 5 days and observed for another 2 days. 

Microbial recovery studies of membrane filtration method challenged with less than 100 CPU of each organism listed in USP-25, EP-2002 and in-house microbial isolates. Two lots of (Product Name) (Batch Numbers) have been validated in triplicate for each organism. Validation mimicked the test proper in every detail, such as in the volumes of media used, quantities and dilutions of product and diluents. 

Standard Test Method (STM) , Membrane filtration method, using... 

Nuortila-Jokinen J, Kaipia L, Nystrbm M, Jahren S, and Rintala J. Internal purification of thermomechanical pulp clear filtrate with a combined biological and membrane filtration method a preliminary study. Sep. Sci. Techn. 1996 31(7) 941-952. 

In the membrane filtration method, the product samples are put aseptically into a volume of non-inhibitory diluent and then passed through a sterile 0.45 pm membrane filter (Fig. 1). The membrane is rinsed through with additional volumes of diluent, then aseptically cut in half. Half is transferred to a container of soybean casein digest medium (SCDM) and the other to fluid thioglycollate medium (FTM). 

Fig. 1 Generalized scheme for the Test for Sterility by the membrane filtration method.

Whichever variant of the membrane filtration method is used, SCDM is incubated at 20-25°C and the FTM at 30-35°C for 14 days. 

One liter in situ samples directly taken on-site, were concentrated by the membrane filtration method for enumerating nannoplankton. A measured volume of a well-mixed sample (20 -100 mL, depending on the number concentration of algae) was filtered at a constant suction rate through a membrane filter having a pore diameter of 0.45 um. The algae collected on the membrane were identified and counted by means of optical compound microscopy. If the identification after membrane filtration is too difficult as a result of alteration of cell shape, the above mentioned settling chamber technique is used. 

The USP describes two general methods for conducting the test the direct transfer, or direct inoculation, method and the membrane filtration method. As the name indicates, the direct inoculation method involves the aseptic transfer of a sample of test product solution into the sterility test growth medium. To use this method, it must first be demonstrated that the product solution itself does not inhibit the growth of typical indicator microorganisms specified in the USP method. It should be self-evident why it is important to perform testing to negate the chance of product inhibition of possible microbial contaminants, as this is the purpose of the sterility test. The direct inoculation method, while not theoretically complex, requires the utmost technical precision and aseptic manipulation techniques for proper execution. As a consequence of the repetitive motions involved, it is prone to human error. 

The membrane filtration method is specified by the USP to be used whenever the nature of the product permits. The direct transfer method should... 

The TAC can be conducted using a number of microbiological methods. These are the pour-plate, membrane filtration, and multiple tube methods. The TYMC is conducted by using either the pour-plate or membrane filtration method. The TAC for bioburden is performed by adding 10 g, 10 mL, or 10 units in SCD broth or lactose broth to make 100 mL. Aliquots of this sample preparation are transferred into four standard size (15 x 100 mm) Petri dishes. Into two of the plates 15-20 mL of molten SCD agar is poured, and into the other two the same volume of Sabouraud dextrose agar (SAB) agar is poured. 

Membrane filtration method. This method is widely used for water but has some applications for food examination. A certain volume of the water or diluted food sample is filtered through a membrane filter. The filter is placed on the surface of a solid medium (usually selective). After incubation for the selected time and temperature the bacteria retained on the surface of the membrane develop into visible colonies, from which a value for the number of cfp in the sample can be calculated. 

Control of dirt and other particles involves use of a membrane filtration method (ASTM D-2276, IP 216) in which the dirt retained by filtration of a sample through a cellulose membrane is expressed as weight per unit volume of the fuel. This test provides field quality control of dirt content and can be supplemented by a visual assessment of membrane appearance after test against color standards (ASTM D-3830). However, no direct relationship exists between particulate content weight and membrane color, and field experience is required to assess the results by either method. 

The tests used to determine the presence of indicator organisms fall into two groups, multiple tube methods and membrane filtration methods. 

Both multiple tube and membrane filtration methods are not only qualitative they are also quantitative, thus enabling an assessment to be made of the potential danger to health. 

It is obvious that the use of one membrane filtration method as a single separation technique cannot give comprehensive information on metal speciation in aqueous media. Combinations of UF with FFF, sedimentation, ion exchange, and liquid-liquid extraction are useful for the identification of the species of an element. However, membrane filtration itself is a rather powerful means if a number of membranes having different pore size are used for studying one sample. 

Because products that require sterilisation are often aqueous solutions, the initial microbiological contamination can easily be determined in the quality control laboratory by the membrane filtration method (see Sect. 19.6.3). 

Membrane Filtration Method The water sample (generally 100 mL) is filtered through a 0.45 xm (sometimes 0.22 xm) sterile filter thereby retaining the organisms on the filter surface. With face upward, the filter is then simply placed on the surface of a culture medium and incubated. Alternatively, before incubation, the filter may be placed on an absorbent pad that is sterile and saturated with broth. This method is suitable for examining relatively large volume of water with low turbidity [77]. The bacteria are also not heat-shocked in the process. However, the bacterial cells may be damaged due to excessive filtration pressure. 

Enumeration of Fecal Streptococci/Enterococci 4.8.3.1 Membrane Filtration Method... 

International Standard, ISO 7899-2 (2000). Water Quality—Detection and enumeration of intestinal enterococci—Part 2 Membrane Filtration Method. International Organization for Standardization, Geneva, Switzerland. 

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