Mixed cellulose ester filters

Collect asbestos on a special, 0.8 micrometer pore size, 25 mm diameter mixed cellulose ester filter, using a back-up pad. 

SRM 1876b is intended for use in evaluating transmission electron microscopy (TEM) techniques used to identify and count chrysotile fibers. This SRM consists of sections of mixed-cellulose-ester filters containing chrysotile fibers deposited by an aerosol generator. 

RM 8411 consists of a section of collapsed mixed-cellulose-ester filters with a high concentration (138 fibers/o.oi mm) of chrysotile and a medium concentration (43 fibers/o.oi mm) of amosite. It is intended for use in evaluating the technique used to identify and count asbestos fibers by TEM. 

Sampling and Analytical Precision and Accuracy. The accuracy of results obtained from a sampling and analytical method are determined by comparison with an independent method. The aerosols of phosphoric and sulfuric acids were collected on mixed cellulose ester filters (14 ) and analyzed by ion chromatography. Table V shows the collection efficiency of the 7-mm O.D./700-mg silica gel collection tubes with respect to the results obtained from filter samples, and the precision obtained from calculation of the pooled relative standard deviation. 

The first of the set is chlordane (Figure 2). In this case chlordane was collected primarily on the mixed-cellulose ester filter with about 10% collected on the sorbent. If the sampling device was only tested over the proposed sampling period, one hour in this case, vapor collected on the sorbent may not have been detected. Hence, extended sampling periods are necessary to realistically test collection efficiency of the individual sampling media in the train. Also, at higher temperatures and lower chlordane concentration, the fraction collected on the sorbent may be substantially increased. 

Prior to high-performance liquid chromatography (HPFC), samples were filtered through a 0.2-gm pore size mixed cellulose ester filter (Schleicher Schuell, Dassel, Germany). Buffer components such as acetic acid, citric acid, maleic acid, and succinic acid were separated on an Aminex HPX-87H (Bio-Rad, Hercules, CA) organic acid column at 65°C using a... 

These atomization techniques are used in NIOSH, AIHA, and APHA approved (recommended) methods (5-7). Although the purpose of this discussion is MS techniques, one must briefly consider collection of samples. The primary method of collecting metal dust samples and fume samples are 0.8 urn and 0.45 urn mixed cellulose ester filters. The filter is dissolved in acid or leached with dilute base, acid, or distilled water to give an analyte for MS analysis. A general procedure P CAM 173 (5), was developed by NIOSH for the analysis of metals. This method provides a starting point and standard of comparison for the analysis of metals. 

Chromium. Chromium is not an easily analyzed element because three distinct standards are listed by OSHA (Tables IV and V ). One standard exists for hexavalent chromium, chromic acid and chromates, another standard for soluble chromium compounds and chromous salts, and another standard for insoluble chromium compounds and chromium metal. The permissible amount of chromium in air decreases as the oxidation state increases. The analysis of chromium is further complicated by the multiplicity of NIOSH methods for chromium compounds. Hexavalent chromium shall be collected on PVC filters, although a criteria document for chromic acid (14) specifies mixed cellulose ester filters. The analytical method described in the hexavalent... 

MCEF Mixed cellulose ester membranes filter... 

An infrequently used method (in pharmaceutical research) for determining the UWL permeability involves measuring transport of molecules across a high-porosity microfilter that is not coated by a lipid. The molecules are able to diffuse freely in the water channels of the microfilter. The filter barrier prevents convective mixing between the donor and acceptor sides, and an UWL forms on each sides of the microfilter. Camenisch et al. [546] measured the effective permeabilities of a series of drug molecules in 96-well microtiter plate-filterplate (Millipore GVHP mixed cellulose ester, 0.22 pm pore) sandwich where the filters were not coated by a lipid. The permeabilities were nearly the same for all the molecules, as shown in Fig. 7.8a. Our analysis of their data, Fig. 7.8b, indicates / aq = 460 pm (sandwich stirred at 150 rpm). We have been able to confirm similar results in our laboratory with different microfilters, using the lipid-free method. 

Filter Methods. The filters most commonly used were mixed-cellulose ester (MCE), glass fiber (GF), and polytetrafluoroethyl-ene (PTFE). Glass fiber and PTFE filters were used almost... 

Use mixed cellulose ester or polycarbonate filter in the analysis. 

PTFE filter is used to remove boron-containing particulates. Use of mixed cellulose ester membrane prefilters is not recommended. 

Air samples of the workplace should be taken using calibrated sampling pumps with cassettes that contain either mixed cellulose ester (MCE) or polyvinyl chloride (PVC) filters. There may be a number of country-specific statutory sampling requirements. The guide shown in Table 16.1 provides an overview of the effectiveness of control measures. 

Figure 37-8 shows a Fiberglas sheet (2600x). Notice the irregular pore size. Figure 37-9 is a mixed cellulose ester membrane (lOOOx) with 0.45 pm pore size showing bacteria trapped on the surface. This is a popular size for filtering HPLC solutions. 

Filters For total particulate/aerosol sampling, the open- or close-faced 37 mm filter cassette is the most popular in many countries. A newer type of sampler for inhalable dust is the lOM sampler with a 25 mm filter. Many studies have shown that the lOM sampler provides the best reference for inhalable aerosol. Other samplers that are emerging for this purpose are Respicon, and the Button samplers. There are several types of filters commonly used for this purpose glass fiber, mixed cellulose ester fiber (MCE), and poly(vinyl chloride) (PVC) filters. They are selected based on their ability to collect material and their suitability for laboratory analysis. For example, PVC filters are normally used for gravimetric analysis and MCEs are used when a chemical analysis is needed followed by digestion or extraction. 

Membrane filters are used to remove particulates from samples and solvents prior to HPLC analysis and also for the preparation of liquid samples, where no solvent is used. Typical materials of construction for membrane filters are usually synthetic polymeric materials, although natural substances, such as cellulose, and inorganic materials, such as glass fibers, are also used acrylic copolymer, aluminum oxide, cellulose acetate, glass fiber, mixed cellulose esters, nitrocellulose, nylon, polycarbonate, polyester, polyether sulfone, polypropylene polysulfone, PTFE, PVC, etc. The compatibility of the polymeric material with the solvents used must be a great concern of their different chemical properties. 

Sampie assembly (The assembly is shown in Figure 3). Conductive filter holder consisting of a 25-mm diameter, 3-piece cassette having a 50-mm long electrically conductive extension cowl. Backup pad, 25-mm, cellulose. Membrane filter, mixed-cellulose ester (MCE), 25-mm, plain, white, 0.4-to 1.2- j,m pore size. 

Collection Procedure A known volume of air is drawn through a 37-mm diameter filter cassette containing a 0.8-tim mixed cellulose ester membrane filter (MCEF). 

This method describes the colledion of airborne elemental cadmium and cadmium compounds on 0.8- m mixed cellulose ester membrane filters and their subsequent analysis by either flame atomic absorption spectroscopy (AAS) or flameless atomic absorption spectroscopy using a heated graphite furnace atomizer (AAS-HGA). It is applicable for both TWA and Action Level TWA Permissible Exposure Level (PEL) measurements. The two atomic absorption analytical techniques included in the method do not differentiate between cadmium fume and cadmium dust samples. They also do not differentiate between elemental cadmium and its compounds. 

Airborne elemental cadmium and cadmium compounds are collected on a 0.8- i.m mixed cellulose ester membrane filter (MCEF). The air filter samples are digested with concentrated nitric acid to destroy the organic matrix and dissolve the cadmium analytes. After digestion, a small amount of concentrated hydrochloric add is added to help dissolve other metals which may be present. The samples are diluted to volume with deionized water and then aspirated into the oxidizing air/acetylene flame of an atomic absorption spectrophotometer for analysis of elemental cadmium. 

Previously, two OSHA sampling and analytical methods for cadmium were used concurrently (5.3., 5.4.). Both of these methods also required 0.8- xm mixed cellulose ester membrane filters for the collection of air samples. These cadmium air filter samples were analyzed by either flame atomic absorption spectroscopy (5.3.) or inductively coupled plasma/atomic emission spectroscopy (ICP-AES) (5.4.). Neither of these two analytical methods have adequate sensitivity for measuring workplace exposure to airborne cadmium at the new lower TWA and Action Level TWA PEL levels when consecutive samples are taken on one employee and the sample results need to be averaged with other samples to determine a single TWA. 

Filter cassette unit for air sampling A 37-mm diameter mixed cellulose ester membrane filter with a pore size of 0.8-nm contained in a 37-mm polystyrene two- or three-piece cassette filter holder (part no. MAWP 037 AO, Millipore Corp., Bedford, MA). The filter is supported with a cellulose backup pad. The cassette is sealed prior to use with a shrinkable gel band. 

Collection efficiencies of metallic fume and dust atmospheres on 0.8- i.m mixed cellulose ester membrane filters are well documented and have been shown to be excellent (5.11.). Since elemental cadmium and the cadmium component of cadmium compounds are nonvola-... 

Mixed cellulose ester (MCE) filters with nominal pore sizes between 0.1 and 0.22 xm are commonly used. Larger pore sizes must be avoided as they allow shorter fibers to penetrate too deeply for recovery [22]. Once MCE filters are dry, they are collapsed to a smooth transparent plastic using acetone or dimethyl formamide (DMF). While 0.22 xm pore MCE filters tend to filter larger volumes more quickly than 0.1 xm MCE filters, 5% etching in an oxygen plasma is generally required because some fibers can penetrate beyond retention by the apphed carbon film. This thin ( 20 ran) carbon coat is applied to the collapsed MCE sraface in a high vacuum (<10 Torr) evaporator to trap the exposed fibers. 

Particulates and aerosols are most often collected on filter media which are inserted into a plastic support cartridge. Several types of filter materials are available, including Teflon, PVC and mixed cellulose ester, all of which are porous materials. Others include glass, plastic, cellulose. 

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