42 general 357 filtering

Filtration. Any type of clarification is foUowed by filtration through leaf-type vertical or horizontal pressure filters. Carbonatated Hquors, containing calcium carbonate, may require addition of diatomaceous earth as a filter precoat. Phosphatated Hquors are generally filtered with the addition of diatomaceous earth as precoat and body feed. 

A significant proportion of products are solids that are separated from a reaction mixture by filtration and centrifugation and purified by crystallization. Recently, more sophisticated techniques for purification (e.g. HPLC) have come in use but crystallization still remains the predominant method. In order to separate solid/liquid mixtures, centrifuges and plane filters (nutches) are u.sed. Generally, filters and centrifuges are operated batchwise. No specific... 

Injections and infusion fluids must be manufactured in a manner that will minimize or eliminate extraneous particulate matter. Parenteral solutions are generally filtered through 0.22 pm membrane filters to achieve sterility and remove particulate matter. Prefiltration through a coarser filter is often necessary to maintain adequate flow rates, or to prevent clogging of the filters during large-scale manufacturing. A talc or carbon filtration aid (or other filter aids) may also be necessary. If talc is used, it should be pretreated with a dilute acid solution to remove surface alkali and metals. 

In cases where water is turbid, samples are generally filtered through glass fiber Alters (GEE) prior to percolation through sorbents. This step recovers waterborne particulates and microorganisms with average diameters >0.7 pm, which are analyzed separately. However, chemicals associated with colloid-sized particulates and DOC are not removed by GFFs. 

In many cases, sample extracts are generally filtered, dried with desiccant, and concentrated before analysis. Concentration of the extract may allow for lower sample detection limits. Frequently, sample extracts must be concentrated to obtain detection limits low enough to meet regulatory action limits. 

Orthogonal signal correction (OSC) This method explicitly uses y (property or analyte) information in calibration data to develop a general filter for removing any y-irrelevant variation in any subsequent x data [118]. As such, if this y-irrelevant variation includes inter-instrument effects, then this method performs some degree of calibration transfer. The OSC model does not exphcitly handle x axis shifts, but in principle can handle these to some extent. It has also been shown that the piecewise (wavelength-localized) version of this method (POSC) can be effective in some cases [119]. 

Dielectric resonators are extensively used in mobile communications technology. As far as selectivity and temperature drift are concerned the requirements for hand-held units are far less demanding than for those used in the base stations, and for the more general filter applications. For example, for... 

Particles greater than 10 /mi are generally filtered out by the vibrissae at the nostrils. 

Cut filter membranes to 22 X 23 cm and treat according to the vendor s instruction. Generally, filters are labeled in permanent ink with the KP number, A vector used, and the name of target species. First, soak filters in distilled water followed by soaking in a solution of 1 MNaCl. Blot the filters dry on Whatman 3MM paper to remove excess moisture just prior to use. 

After diazotisation is completed the liquid is allowed to run into an alkaline solution of the phenol or its sulphonic acid, care being taken that the mixture remains alkaline. After some time the dyestuff is salted out, and is generally filtered through a filter-press. The combination of diazo-compounds with amines is somewhat more complicated. Some of these, for instance metaphenylenediamine, combine with diazo-compounds in neutral aqueous solutions while others, like diphenylamine, are dissolved in alcohol, and a concentrated solution of the diazo-compound gradually added. In the manufacture of amidoazobenzene and all compounds in which an intermediate formation of a diazo-amido-compound takes place, a large excess of the amine has to be employed, to hold the diazoamido-compound formed in solution. 

Bromba and Ziegler have defined a general filter with weighting elements defined by the form... 

Filtration and centrifugation both have been commonly employed to separate the saturated solution from the solute phase. Filtration is easily accomplished, but filter sorption can be a significant source of error. Generally, filter sorption is more significant for hydrophobic and poorly soluble compounds, and obviously it is directly proportional to the filter surface area. Typically, pre-rinsing the filter with a few milliliters of the saturated solution can remedy the problem. Flowever, in some extreme cases where the solubility of the compound is very low, a much larger volume may be needed to saturate the filter adsorption sites. 

Leonard [97] defined a generalized filter as a convolution integraH ... 

Exponential filtering, a fast procedure, is equivalent to RC-tjq>e analog filtering. It must be used with great care, because it involves a lag in the curve which can cause errors in the case of overlapping peaks. The general filtering formula is... 

Generally, filtering respiratory devices are only to be used when the oxygen content of ambient air is at least above 17%. 

Shukla, A., Peter, M., and Hoffmann, L., Analysis of positron lifetime spectra using quantified maximum entropy and a general filter, Nucl. Instrum. Methods Phys. Res. A, 335, 310-317 (1993). 

Soluble solid samples are dissolved in a suitable solvent, usually deuterated, for analysis. A typical sample size is 2-3 mg dissolved in 0.5 mL of solvent. Some solid polymer samples may be run under liquid conditions, that is, without MAS, by soaking the solid in solvent and allowing it to swell. This gives enough fluidity to the sample that it behaves as a liquid with respect to the NMR experiment. Other solid samples must be run in an instrument equipped with MAS, as has been discussed. Sample solutions are generally filtered through alumina to remove any particles. 

Generally, filter fluorimeters are more sensitive than those with monochromators. However, they lack scaiming options and hence cannot be used for investigations related to molecular structure. Nevertheless, for a number of routine analyses filter instruments are quite satisfactory. If a filter fluorimeter is used, the excitation filter should be a narrow band filter (+5nm) centred at 325 nm. On the emission side, a wide band pass filter ( 10-20 nm) centred at 420 nm should be used. Scanning fluorimeters should have excitation and emission monochromators with slit widths of 5 nm or smaller. 

In general, filter aid filtration should be used only for systems that meet two key requirements. First, the desired product is the filtrate, not the cake. Second, the filter aid is acceptable in the filter cake or the filter cake can be easily repulped and refiltered to remove the filter aid. In addition, the particle-settling rate should be less than 0.012 m/min and the particle concentration lower than 0.1 wt% (< 0.3% for rotary drum precoat). 

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