Solid Phase Dispersants

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

PLE pressurized liquid extraction, SPE solid phase extraction, UE ultrasonic extraction, DSPE dispersive solid phase extraction, SBSE stir bar sorptive extraction, TD-GC-MS thermal desorption-gas chromatography-mass spectrometry, LAS linear alkylbenzene sulfonates, CDEAs coconut diethanol amides, NPEOs nonylphenol ethoxylates, DP degradation products, SPC sulphenyl carboxylates, PCDD dibenzo-p-dioxins (PCDD), PCDF dibenzofurans, PCBs biphenyls... 

In spite of the large success of XRD in routine structural analysis of solids, this technique does present some limitations when applied to catalysis [1,9]. First, it can only detect crystalline phases, and fails to provide useful information on the amorphous or highly dispersed solid phases so common in catalysts [22], Second, due to its low sensitivity, the concentration of the crystalline phase in the sample needs to be reasonably high in order to be detected. Third, XRD probes bulk phases,... 

In matrix solid-phase dispersion (MSPD) the sample is mixed with a suitable powdered solid-phase until a homogeneous dry, free flowing powder is obtained with the sample dispersed over the entire material. A wide variety of solid-phase materials can be used, but for the non-ionic surfactants usually a reversed-phase C18 type of sorbent is applied. The mixture is subsequently (usually dry) packed into a glass column. Next, the analytes of interest are eluted with a suitable solvent or solvent mixture. The competition between reversed-phase hydrophobic chains in the dispersed solid-phase and the solvents results in separation of lipids from analytes. Separation of analytes and interfering substances can also be achieved if polarity differences are present. The MSPD technique has been proven to be successful for a variety of matrices and a wide range of compounds [43], thanks to its sequential extraction matrices analysed include fish tissues [44,45] as well as other diverse materials [46,47]. 

Usually, the typology of batch reactors also includes the semi-batch gas-liquid reactors, in which a gaseous phase is fed continuously in order to provide one of the reactants. A typical example is given by the reactors used both in different oxidative industrial processes and in the active sludge processes for the treatment of wastewater. It is possible to distinguish between the bubble columns (Fig. 7.1(c)), in which the gas rises undisturbed in the liquid phase, and the bubble stirred reactor, in which a mechanical mixer is added. Finally, the slurry reactors can be considered, in which the liquid phase contains a finely dispersed solid phase as well, which can act as a reactant or as a heterogeneous catalyst these reactors assume in general the features of Fig. 7.1(d). 

A suspension is a colloidal dispersion in which a solid is dispersed in a continuous liquid phase (Figure 1.6). The dispersed solid phase is sometimes referred to as the internal (disperse) phase and the continuous phase as the external phase. Suspensions may be either aqueous or non-aqueous. 

A liquid-phase resistance inside a dispersed solid phase such as cell floes, immobilized enzymes, etc. 

Su oemulsions are defined as a mixture of a dispersed solid phase and an emulsified oil phase in water as the continuous or bulk phase. The solid phase is a solid, water insoluble active ingredient, the oil phase a liquid pesticide in pure form or dissolved in a water insoluble solvent. The oil phase can sometimes also be an oil or adjuvant. Suspoemulsions are a relatively new formulation type as becomes evident by the fact that a FAO specification was established only as late as 1997. At the same time specific evaluation methods were officially published (CIPAC MT 180) [2]. 

Anastassiades, M., Lehotay, S.J., Stajnhaher, D., Schenck, F.J. Fast and easy multrresidue method employing acetonitrile extraction/partitioning and dispersive solid-phase extraction for the determination of pesticide residues in produce. J. AOAC InL 86(2), 412-431 (2003)... 

Spherical beads that can be expanded into foam under the influence of heat or steam are produced directly by suspension polymerization in the presence of blowing agent. The term suspension polymerization describes a process in which water-insoluble monomers are dispersed as liquid droplets with suspension stabilizer and vigorous stirring to produce polymer particles as a dispersed solid phase. Initiators used in suspension polymerization are oil-soluble. The polymerization takes place within the monomer droplets. The kinetic mechanism of the suspension process is considered to be a free radical, water-cooled microbulk polymerization [1]. 

Pesticides are extracted from grapes with acetonitrile using a singlephase extraction followed by liquid-liquid partitioning formed by addition of MgS04 and NaCl. Removal of residual water and clean up are performed simultaneously by using dispersive solid-phase extraction. The pesticide extract was analyzed by GC/MS. 

The chemical composition, structure, and, hence the properties of products with modified surface are determined both by observing the required sequence of operations, and chosen chemico-technological parameters of process the chemical nature of reagents (volatile and solid), temperature (in stages of preparation of surface, chemisorption and desorption), concentration of reagents (in gas phase and functional groups on surfaces of substrate), hydrodynamics of the process (rate of transport and removal of reagents, mobility or stationary condition of disperse solid phase). 

Suspension is connected with the presence of a dispersed solid phase, which is suspended ( whirled up ) in the liquid. The material system solid/liquid (S/L) is thus involved. Occasionally a gas is distributed and dispersed in the liquid at the same time, whereupon the material system concerned is a solid/liquid/gas (S/L/G) system. 

There is also a new form of SPE, called matrix dispersion solid-phase extraction, which uses the solid phase (silica and C-18) to grind the samples and prepare the analyte for extraction. The food product is incorporated into the pores of the 40-pm packing material in the grinding process, which is done in a mortar and pestle, and the packing material is then packed into a... 

This method is also referred to as the miscible-displacement or continuous-flow method. In this method a thin disk of dispersed solid phase is deposited on a porous membrane and placed in a holder. A pump is used to maintain a constant flow velocity of solution through the thin disk and a fraction collector is used to collect effluent aliquots. A diagram of the basic experimental setup is shown in Fig. 2-6. A thin disk is used in an attempt to minimize diffusion resistances in the solid phase. Disk thickness, disk hydraulic conductivity, and membrane permeability determine the range of flow velocities that are achievable. Dispersion of the solid phase is necessary so that the transit time for a solute molecule is the same at all points in the disk. However, the presence of varying particle sizes and hence pore sizes may produce nonuniform solute transit times (Skopp and McCallister, 1986). This is more likely to occur with whole soils than with clay-sized particles of soil constituents. Typically, 1- or 2-g samples are used in kinetic studies on soils with the thin disk method, but disk thicknesses have not been measured. In their study of the kinetics of phosphate and silicate retention by goethite, Miller et al. (1989) estimated the thickness of the goethite disk to be 80 /xm. 

Mass transfer processes are governed by the driving force difference in the chemical potentials, the physical proportions (mass transfer coefficient) of the substance, and the surface area (the interface between the phases to be separated). This is known from the basic transport equations of heat and mass transfer. A large surface area, therefore, favors separation processes. A suspension with a distribution of mainly small particles would feature a high interface area. There is, however, a limitation to the size of the disperse solid phase. This is due to the necessary liquid-solid separation at the end of the process, on the one hand, and the necessity of the disperse phase to move in different directions as the main flow direction of the continuous phase so that a maximum of the driving potential between the two phases can be maintained, on the other hand. 

This section discusses dispersive SPE, matrix solid phase dispersion, solid phase micro-extraction, micro-extraction by packed sorbent, stir-bar sorbent extraction, and the restricted-access materials. ... 

Fagerquist CK, Lightfleld AR, Lehotay SJ, Confirmatory and quantitative analysis of fS-lactam antibiotics in bovine kidney tissue by dispersive solid-phase extraction and liquid chromatography-tandem mass spectrometry. Anal. Chem. 2005 77 1473-1482. 

Suspension polymerization occurs in water with the liquid monomer dispersed by agitaliorL The polymer is produced as a dispersed solid phase fiom polymerization of initiator-containing, 10 to 500 pm droplets under kinetics that match those of the bulk reaction of the monomer (7). The suspension is stabilized by insoluble organic or inorganic solids, electrolytes to increase monomer-water interfacial tension, and water soluble polymers that increase aqueous viscosity. Suspension polymerization is commonly used to synthesize two polymers covered in this book, polystyrene and polyvinyl chloride. 

Matrix solid-phase dispersion (MSPD) is an SPE variant where samples are ground and mixed with a support. In the initial application, samples were placed in a disposable column previously packed with Florisil, which trapped the fat from the sample and allowed the compounds of interest to be eluted. This has successfully been applied to the determination of lipophilic pesticides from both fatty and non-fatty matrixes. Recently, an orthogonal technique, dispersive solid-phase extraction, for the isolation and analysis of a variety of pesticides on numerous food matrixes has been introduced. The technique is called QuEChERS, which stands for quick, easy, cheap, effective, rugged, and safe. The technique offers advantages in time and solvent usage since it uses approximately 10 ml of solvent per sample when compared to the potentially hundreds of milliliters of solvent used for more standard extraction and isolation protocols. It uses a combination of MgS04 and primary secondary amine (PSA) sorbent not only to remove water and non-target compounds, but also isolate the compounds of interest. 

Yang, R. Z, Wang, J. H., Wang, M. 1., Zhang, R., Lu, X. Y., and Liu, W. H. 2011. Dispersive solid-phase extraction cleanup combined with accelerated solvent extraction for the determination of carbamate pesticide residues in radix glycyrrhizae samples by UPLC-MS-MS. J. Chromatogr. Sci. 49 702-708. 

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