Liquid suspension filter standards

There are two basic laboratory methods for the preparation of filter standards--dust generation and the liquid suspension technique. Dust generation has a distinct advantage because of the ability to produce atmospheres similar to the workplace which can then be... 

Liquid samples may contain particles of solid material that need to be removed by filtration or centrifugation. The filter material must be chosen so that it does not adsorb analytes or contaminate the liquid. Some samples that are mostly liquid contain suspended solid material orange juice and liquid antacids are examples. In these types of samples, the liquid and its associated solids may need to be sampled for analysis without removing the solids. It may be difficult to obtain a representative sample from these suspensions a standard sampling procedure is needed to ensure that results can be compared from one day to the next. Liquid samples may consist of more than one layer because they contain two or more immiscible liquids. Examples include samples of oil and water from an oil spill at sea, oil and vinegar salad dressing, or cream at the top of a bottle of milk. The layers may need to be emulsified to provide a representative sample, but it may be more useful to sample each layer separately. 

Filter media efficiency tests are made using dilute suspensions of standard particles. A wide variety of test powders is available, in fine and coarse grades. Industrial users will tend to use a test mixture typical of the products of interest, e.g. yeast in the browing industry. In the gaseous field, both solid (sub-micron sodium chlorid crystals) and liquid particles (di-octyl phthalate dispersion) are used. 

Turbidity is caused by any solid material which is dissolved or suspended in a liquid. The intensity of light scattered by a sample is measured and compared with that measured for standard formazin suspensions, and expressed as nephelometric turbidity units (NTU). Colour is determined as the absorbance (measured spectrophotometrically at 400 nm) of the sample filtered through a 0.4S micron pore size membrane filter [12, 13]. 

Sadana and Gaonkar have simultaneously determined diloxanide furoate and tinidazole in pharmaceutical dosage form by gas liquid chromatography [37]. Powdered tablets or suspension formulations were dissolved in chloroform, the solution filtered, and then diluted to 25 mL with chloroform. The solution also contained metronidazole as an internal standard. A 600 nL aliquot was analyzed on a stainless steel column (1 m X 3.2 mm) containing 3% of OV-17 on Chlorosorb W-UP (100-120 mesh). The GC system was operated at 200°C, using nitrogen as the carrier gas (45 mL/min). Flame ionization detection was used to observe the analytes. 

Sampling procedures are often dependent on the method of sample preparation as well as the physical and chemical properties of the analyte For most analytes that are collected by the above method the usual procedure is to ash the filter in either a low temperature plasma asher or a muffle furnace, disperse the residue in a suitable liquid such as isopropanol using ultrasonic agitation, and filter the suspension through a silver membrane filter. In addition, if the internal standard method is used, the chosen standard must be added to the residue suspension prior to filtration ... 

Deltamethrin is extracted from the water-dispersible tablet sample with a mixture of dioxane and water. The suspension is further diluted five times with iso-octane and filtered. The deltamethrin content is determined by comparing the response of the sample with that of a deltamethrin standard by high-performance liquid chromatography (HPLC), using a Nucleosil column (or equivalent) and a mixture of dioxane and iso-octane as the mobile phase. 

Spectrex PC 50 Partascope vicw ei consists of a small, battery-operated "Black Box" which internally generates two parallel, scanning laser beams. Samples of water, oil or other liquid are introduced by beaker or bottle. Through Fraunhofer diffraction, particles in suspension, as small as 1 pm diameter, are made visible directly to the human eye. The two laser beams permit comparison of a sample with standards, or of pre- and post-filter samples. 

The suspension of an SPM sample in 100mL of CH2CI2 is sonicated for 15 min and filtered with a membrane that has a 0.1-pm pore size, the filtrate is evaporated, and the residue is resolved in acetonitrile [24]. The concentration of the chemicals in the SPM extracts is determined using a multicolumn high-performance liquid chromatography (HPLC)/spectrofluorometer/computer system. According to EQ = S([PAH]iEFi +. ..+ [PAH] EF ), the chemically derived induction equivalent (EQ) is calculated to standardize the biological effect of the chemical on the EROD capacity of the Flep G2 cells [25]. 

Efficient and rapid removal of solvent and antisolvent is a vital component of the successful MBPprocess. Once the precipitation has been completed (concurrently for continuous process and at the end of the solvent addition for the semi-batch process), the MBP is filtered from the suspension. This is generally performed by any of the standard filtration processes such as vacuum filtration ranging from Buchner funnel to Nutsche filter or centrifugal filter. Centrifugal filters are preferred for filtration of MBP suspension because of the particle size, the hydrogel nature of the polymer, and the effectiveness in solid/liquid separation... 

Freshly distilled phosphorus trichloride (87 mL, 1 mol), anhydrous ethyl ether (200 mL), and dry pyridine (81 mL, 1 mol) are mechanically stirred in a three-necked flask (1 L) under a dry argon atmosphere at-78°C. Distilled 3-hydroxypropionitrile (68 mL, 1 mol) in anhydrous ethyl ether is added dropwise over ca. 2 h to the cold mixture maintained at-78°C. The suspension is then allowed to warm to ambient temperature and stirred overnight under argon. The precipitate is filtered and washed with ethyl ether (100 mL). The filtrate is concentrated under reduced pressure, and the crude reaction product is fractionally distilled under vacuum affording 2-cyano-ethoxy-dichlorophosphine as a colorless liquid (bp 78°C at 0.6 mm Hg) in 55% yield (95 g, 0.55 mol) (12,18). ip-NMR (CDCI3) 178.8 ppm downfield from the external 80% H3PO4 standard (20). H NMR (CDCI3) 5 in ppm 2.7 (t, 2H) 4.4 (2t, 2H) relative to an internal tetramethylsilane standard (20). 

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