Of membrane filters

Improvements ia membrane technology, vahdation of membrane iategrity, and methods to extend filter usage should further improve the performance of membrane filters ia removal of viral particles. Methods to improve or extead filter life and iacrease flow rates by creating more complex flow patterns could possibly be the focus of the next generation of membrane filters designed to remove viral particles. 

Standard Pest Methodfor Determining Bacterial detention of Membrane Filters IJtili dforPiquid Filtrations ASTM F838-83, American Society for Testing and Materials, Philadelphia, Pa., 1983 reapproved 1988. 

In this work hybrid method is suggested to determine anionic surfactants in waters. It is based on preconcentration of anionic surfactants as their ion associates with cationic dyes on the membrane filter and measurement of colour intensity by solid-phase spectrophotometry method. Effect of different basic dyes, nature and hydrophobicity of anionic surfactants, size of membrane filter pores, filtration rate on sensitivity of their determination was studied. Various cationic dyes, such as Methylene Blue, Crystal Violet, Malachite Green, Rhodamine 6G, Safranin T, Acridine Yellow were used as counter ions. The difference in reflection between the blank and the sample was significant when Crystal Violet or Rhodamine 6G or Acridine Yellow were used. 

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. 

Although most particles, larger than a given pore size, are normally retained, many smaller particles (sometimes 10 - 1000 times smaller than the pore size) may also be retained. If above and within a pore depth filtration occurs (see Chapter 7.6 and Fig. 7.12) colloidal particles smaller than the pore size become attached to the larger particles. Furthermore the pore size distribution of membrane filters is often non-narrow. 

Manuals and bibliographies for use of membrane filters. Millipiore Corporation, Bedford, MA. 01730. 

Engelbrecht, D. Cahill, T.A. Feeney, P.J. "Electrostatic Effects on Gravimetric Analysis of Membrane Filters" APCA Journal, 1980, 30(4), 391. 

Osumi, M., Yamada, N., Toya, M. Bacterial retention mechanisms of membrane filters. J Pharm Sci Tech 50 30—34 (1996). 

American Society for Testing and Materials. Standard Test Method for Pore Size Characteristics of Membrane Filters for Use with Aerospace Fluids. ASTM F316-80, part 25. Philadelphia pp. 872-878 (1981). 

Figure 7.5 Apparatus for testing the microbial retention characteristics of membrane filters. The whole apparatus is sterilized, and initially the flask contains 140 mL of double-strength culture medium. The culture to be tested (100 mL) is passed through the filter with clamp 1 open and clamp 2 closed. The sides of the filter apparatus are washed with two 20 mL portions of sterile broth. Clamp 2 is then opened, the vacuum released, and clamp 1 closed. The filter apparatus is replaced by a sterile rubber stopper and the flask incubated. Absence of turbidity in the flask indicates that the filter has retained the test organism. From Brock [4]. Courtesy of Thomas D. Brock...

Figure 7.8 Correlation of P. diminuta microbial challenge and bubble point test data for a series of related membranes [6]. Reprinted from T.J. Leahy and M.J. Sullivan, Validation of Bacterial Retention Capabilities of Membrane Filters, Pharm. Technol. 2, 65 (1978) with permission from Pharmaceutical Technology, Eugene, OR...

T.J. Leahy and M.J. Sullivan, Validation of Bacterial Retention Capabilities of Membrane Filters, Pharm. Technol. 2, 65 (1978). 

The mineralization of suspended matter involves the decontamination of membrane filters with sediment using a mixture of hydrochloric and hydrofluoric acids, and the subsequent removal of silicon as volatile SiF4.33... 

The advantage of membrane filters is that particles do not become imbedded in the filter medium. Thus, individual particles are readily identifiable and characterized microscopically on the filter surfaces. Furthermore, certain kinds of chemical analysis, such as X-ray fluorescence analysis, readily can be done in situ with minimal effects of filter interference on the membrane substrates. 

ASTM E 1294-89 Standard test method for pore size characteristics of membrane filters using automated liquid porosimeter, ASTM International. 

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