Filtration particulate fractions

Filtration. To separate the dissolved from the particulate fraction filtration or centrifugation will be necessary. This causes a severe risk of contamination it is therefore often not carried out with open ocean samples, where the concentrations of suspended material are low. The presence of phytoplankton or a variable concentration of suspended matter affects the total concentration and a comparison of samples can thus become difficult. In speciation Studies the presence of particles may influence the results even more (complexation, adsorption), therefore filtration over acid washed membrane or screen filters in an appropriate filtration apparatus is recommended for all natural samples (Bewers et al., 1985). High pressure during filtration should be avoided ruptured (plankton-) cells will contribute organic matter, nutrients and trace metals to the solution. A pressure < 25 kPa is recommended (Florence and Batley, 1980). 

Samples with particulate matter may present quite serious problems, and it may be desirable to remove particles, for example, by centrifugation, and examine this fraction by procedures applicable to solid phases which are discussed in Section 2.2.5. Tangential-flow high-volume filtration systems have been used for analysis of particulate fractions (>0.45 jum) where the analytes occur in only low concentration (Broman et al. 1991). Attention has already been drawn to artifacts resulting from reactions with cyclohexene added as an inhibitor to dichloromethane. It has also been suggested that under basic conditions, Mn2+ in water samples may be oxidized to Mn(III or IV) which in turn oxidized phenolic constituents to quinones (Chen et al. 1991). Serious problems may arise if mercuric chloride is added as a preservative after collection of the samples (Foreman et al. 1992) since this has appreciable solubility in many organic solvents, and its use should therefore be avoided. 

A first example is shown on Fig. 12 for a treatment plant of a refinery (different from the one in Fig. 10), including a separator of hydrocarbons (API tank) and a sand filtration unit before a trickling filter. The raw wastewater composition is characterised by the presence of phenolic compounds with an absorption peak around 265 nm. The effect of the two pretreatment steps is evident on the particulate fraction (including the effect of emulsified hydrocarbons), but does not affect the dissolved matrix. This last is removed (at least the phenolic compounds) with the biological step, the effect of which is a removal of almost 90% of the TOC. At the end of the treatment, cooling water (pumped from the sea) is mixed with treated wastewater, explaining the nitrate dilution and the presence of chloride in the discharge. 

Collection of sea surface microlayer samples with a metallic screen and subsurface samples with Niskin bottles or bucket filtration through fibreglass filter Whatman GF/C extraction at pH 2 of large samples (20 or 1001) with chloroform extraction of the particulate fraction with CH3OH—CsH 1 1 TLC, GLC... 

For most particulates above 1 /xm in natural waters and wastewaters, the power-law coeflBcient appears to be greater than 3. Therefore, adequate removal of the particulate fraction by sedimentation or flotation requires a reduction in p by, for example, coagulation/flocculation, which shifts the major portion of particulate surface area and mass into size classes above about 30 /xm. If granular-media filtration is used as the particulate separation process, only particulate destabilization may be necessary to achieve desired removals. 

If only the soluble COD is desired, the sample should be coagulated with lanthanum chloride (Lads) and filtered through a 0.45 pm membrane to eliminate colloidal and particulate fractions. The filtrate can then be subjected to standard COD analyses. 

In total mercury determinations, filtration of seawater samples has been found to be a serious source of contamination (see also Chapter 2). Hierefore, filtration should only be considered in cases where the suspended particulate matter (SPM) needs to be investigated separately and/or when the particulate fraction of Hgr is >20% and expected to fluctuate strongly as, e.g., in estuaries and other coastal zones. 

Computer sensitivity studies show that hole size strongly affects the fraction of fission products released from the containment. The failure location determines mitigation due to release into another building in which condensation and particulate removal occur. The quantity released depends on the time of containment fails relative to reactor vessel failure. If containment integrity is maintained for several hours after core melt, then natural and engineered mechanisms (e.g., deposition, condensation, and filtration) can significantly reduce the quantity and radioactivity of the aerosols released to the atmosphere. 

When an ophthalmic ointment is manufactured, all raw material components must be rendered sterile before compounding unless the ointment contains an aqueous fraction that can be sterilized by heat, filtration, or ionizing radiation. The ointment base is sterilized by heat and appropriately filtered while molten to remove extraneous foreign particulate matter. It is then placed into a sterile steam-jacketed kettle to maintain the ointment in a molten state under aseptic conditions, and the previously sterilized active ingredients) and excipients are added aseptically. While still molten, the entire ointment may be passed through a previously sterilized colloid mill for adequate dispersion of the insoluble components. 

The simplest approach to the collection and subdivision of organic materials in seawater is to use some physical or chemical means of removing one fraction from solution or suspension. The techniques vary, from simple filtration to collect particulate matter, to chemical methods, such as solvent extraction and coprecipitation. With each of these methods, the analyst must know the efficiency of collection and exactly which fraction is being collected. Very often the fraction is defined by the method of collection two methods... 

Standing-Crop Particles. Standing-crop, noncolloidal, particulate matter was sampled by using two techniques 1, niskin casts followed by filtration onto track-etched filters and 2, serial sieve fractionation in-line with continuous-flow centrifugation, which enabled the collection of gram quantities of suspended particles. 

Our water-column sampling techniques include in-line filtration using an all-Teflon sampling device with quartz fiber filters (0.7- xm nominal size cutoff) to differentiate between dissolved and particulate phases (21). Particulate concentrations (nanograms per gram) and subsequent calculations of partitioning between particle and aqueous phases (log KD) are based on this particle size division. This fractionation scheme precludes direct estimates of colloidal influences on Hg transport. 

In the (aquatic) environment elements occur in particulate-, colloidal- and dissolved forms. These forms are usually distinguished by filtration or centrifugation. Traditionally, a 0.45 um (membrane)- filter separates the particulate from the dissolved forms. This may result in the passage of colloidal fractions through the filter, classifying colloidal matter incorrectly within the dissolved fraction. Although the interaction between dissolved and particulate (surface) fractions cannot be neglected, it is common in speciation studies to consider the "dissolved" fraction. The dissolved forms of trace elements are mainly present as ... 

Literature data on the distribution of trace elements amongst the different size fractions in natural freshwaters are summarised in Table 8.1. There is a striking paucity of data for the environmentally important elements Cu, Pb and Cd. Elements which have a low affinity for complexing sites on NOM are present predominandy in the low molecular weight fraction, e.g. Cs, Sr, V while those which specifically coordinate to particular functional groups in NOM, e.g. Ag, Cd, tend to be present in the particulate and colloidal fractions. A major difficulty when trying to compare the literature data is that operational and variable size limits are used, and that filtration, which may lead to drastic artefacts, is still largely used for size fractionation. 

Bovine serum albumin (BSA), fraction V, B-lactoglobulin, gum arabic, and alginic acid, low viscosity, were purchased from Sigma Chemical Co. (St. Louis, MO). The proteins were used without further purification. Aqueous solutions of gum arabic and alginic acid were filtered successively through cellulosic membrane filters of 5.0 fan and 0.45 fan pore size to remove insoluble particulate matter. The filtrate was frozen and lyophilized prior to use. 

The emission measurements during this testing included N0X, smoke, particulate and PNA. N0X was determined by a non-disper-sive infrared analyzer, and smoke by the Bacharach test. Both the particulates and PNA were sampled by a source assessment sampling system (SASS). The SASS system isokinetically samples a fraction of the stack gas and traps particulates in a series of cyclones, which classify the particulate by size. Final filtration is through a fiberglass filter mounted in an oven heated to 200°C to prevent condensation of acids. In this program, the cyclones were not used, since previous work (3) had shown the particulate from coal-derived fuel oils to be small, with an average diameter on the order of 0.4 /um. The PNA which is not deposited on the particulate is collected on XAD-2 resin after the gas has been cooled to 15-20°C. PNA analyses were carried out on a combined extract from the particulate, XAD-2 resin, other condensates in the system, and the solvent rinses used to clean the SASS system. 

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