Liquid sedimentation technique

Liquid Sedimentation Techniques for Measuring the Particle-Size Distribution of Primary Explosives , PATR 4387 (1972) 42) Anon, Stan-... 

These methods fall into two general classifications those using a liquid sedimentation technique, and those employing an air elutriation system. 

Soil, sediment, and dust samples were prepared in a similar way before analysis. After the pre-cleanup steps and homogenization, FRs were extracted from samples using different solid-liquid extraction techniques. The most commonly used technique was accelerated solvent extraction (ASE), which enables the fast extraction of samples using different solvents such as hexane and dichloromethane [98-100]. Other commonly used techniques for these samples were ultrawave-assisted extraction (UAE) [97], which also enabled quick extraction, and the more time-consuming but very efficient technique, Soxhlet extraction [96]. Some authors have also described less common techniques such as microSPE [95]. There is also information that many FRs that are no longer produced (mainly PCBs and PBDEs) are present in dusts, soils, and sediments in very high amounts, even 390 pg/g [98]. 

ISO/WD 13317-3 Determination of Particle Size Distribution by Gravitational Liquid Sedimentation Methods- Part 3 (1996) The X-ray Gravitational Technique, 360... 

Ultrasound extraction (sonication) is based on the conversion of AC current at 50/60 Hz into electrical energy at 20 kHz and its transformation in mechanical vibrations. Due to the cavity, microscopical vapor bubbles are formed and, after implosion, they produce strong shockwaves into the sample. For isolating the (semi)volatile organic compounds, the liquid-liquid ultrasound technique is applied to samples such as soils, sediments, coal, etc. The process is also useful for the biological materials destruction (Loconto, 2001). Sonication extraction is faster than Soxhlet extraction (30-60 min per sample) and allows extraction of a large amount of sample with a relatively low cost, but it still uses about as much solvent as Soxhlet extraction, is labor intensive, and filtration is required after extraction. 

A dynamic coupled-column liquid chromatographic technique was used to obtain aqueous solubility data on 11 aromatic hydrocarbons. The aqueous solubility at 25° C was determined for each compound. The precision of replicate solubility measurements was better than 3%. The variation of the solubility of each compound with temperature is expressed in the form of either a quadratic or cubic equation based on a least-squares fit of the solubility to temperature. These equations can be used to interpolate the solubility to within 2% of the experimentally measured values between 5° and 30°C. Enthalpies of solution (AHJ were then calculated from the values obtained and Setschenow constants were calculated from the effect of salinity on solubility. This system was also used to investigate the partitioning of PAHs between aqueous solutions and some sediment samples. 

Sedimentation methods are also useful in determining particle size distribution. Webb (28) describes the techniques employed in liquid sedimentation and gives data comparing the results with those obtained in mechanical screening. Sedimentation methods are particularly useful in measuring sub-sieve sizes. Air-elutriation methods (Roller, 29) are also useful, especially when used in connection with microscopic examination (Wiley, Deloney, and Denton, 30 Matheson, 31). 

Mouse livers were excised and homogenized with a Potter-Elvehjem homogenizer. The microsomal fraction was isolated by centrifuging the homogenate at 9000 x g for 15 min, to sediment nuclei, mitochondria, and membrane debris. The supernatant was centrifuged at 100,000 x g for 60 min to pellet microsomes. The microsomes were further purified by another centrifugation step to remove soluble proteins (e.g., hemoglobin). HCQ was incubated with the microsomes for 2 h. Then a liquid-liquid extraction technique was performed to recover HCQ and its metabolites. The molecules were separated by a commercial CE system with ultraviolet (UV) absorbance detection. 

The sedimentation technique is reliable for particle size determination when rf is in a size range of 2-50 pm. The falling rate of smaller particles is affected by Brownian motion resulting from collisions with the molecules of the liquid and other interactions between particles. Stokes law is valid only for laminar or streamline flow (i.e., when there is no turbulence). The Reynolds number (Re) is a measure of when the process transitions from turbulent to laminar flow ... 

A simple sedimentation technique, which readily lends itself to the determination of crystal size distribution in the range 1-50 pm, is the Andreasen pipette method. Although it is generally better to prepare a fresh suspension of the crystals under test in a suitable inert liquid, it is possible to classify crystals suspended in their own mother liquor. If the difference in density between the particles and suspending liquid is <0.5gcm special care must be taken to avoid convection currents. The method, briefly, is as follows (BS 3406/2, 1986). 

Pressurized liquid extraction (PLE) is also known as pressurized solvent extraction (PSE), enhanced solvent extraction (ESE), pressurized fluid extraction (PEE), or accelerated solvent extraction (ASE ) in the literature. PLE is considered an environmentally friendly extraction technique because it requires only small volumes of solvents. PLE was primarily used for the extraction of environmental samples, such as soils and sediments. Elevated temperatures (usually between 50 and 200 °C) and pressures (between 10 and 15 MPa) are used in closed vessels, which allow extractions to be completed in a very short time. High pressure allows the solvent to remain in its liquid state even at temperatures above its boiling point, and forces it into the matrix pores. High temperatures decrease the solvent viscosity and increase metabolite solubilization, the diffusion rate, and mass transfer kinetics, thus facilitating desorption of the analytes from the plant material. Most PLE applications reported in the literature employ the same organic solvents as those commonly used in conventional solid-liquid extraction techniques. When water is used as the extraction solvent, the technique is referred to as pressurized hot water extraction (PHWE). Extractions are carried out in stainless steel extraction cells of various volumes (typically 1-250 mL). One extraction cycle is generally applied for 5-20 min at temperatures ranging from 50 to 140 °C in the vast majority of applications. 

The dispersive liquid—liquid microextraction technique (DLLME) [16] has attracted much attention due to its simplicity and to the high enrichment factors that can be achieved. DLLME is a fast micro-extraction technique based on the use of a ternary mixture, composed by an aqueous phase, an organic phase (extractant) and an additional organic solvent also named as disperser solvent, which is miscible in both phases. The disperser is initially mixed with the extractant and then rapidly injected into the sample. By the fast dissolution of the disperser into the aqueous phase, the extractant is disrupted into small droplets enhancing the effective surface area of extraction. The separated extractant droplets are then sedimented at the bottom of the vial or float upon the aqueous sample-disperser phase, depending on the density of the extractant used. 

The axial dispersion of solids can be measured using a steady state diffusion sedimentation technique. This method was applied e.g. by Kato et al. [27] and recently by Brian and Dyer [59]. At zero liquid rates, if the particles are only suspended by the gas flow, a solid concentration profile will be established ... 

The 2eta potential (Fig. 8) is essentially the potential that can be measured at the surface of shear that forms if the sohd was to be moved relative to the surrounding ionic medium. Techniques for the measurement of the 2eta potentials of particles of various si2es are collectively known as electrokinetic potential measurement methods and include microelectrophoresis, streaming potential, sedimentation potential, and electro osmosis (19). A numerical value for 2eta potential from microelectrophoresis can be obtained to a first approximation from equation 2, where Tf = viscosity of the liquid, e = dielectric constant of the medium within the electrical double layer, = electrophoretic velocity, and E = electric field. 

The liquid chromatography - tandem mass spectrometry (LC/MS/MS) technique was proposed for the determination of corticosteroids in plasma and cerebrospinal fluid (CSF, liquor) of children with leucosis. Preliminai y sample prepai ation included the sedimentation of proteins, spinning and solid-phase extraction. MS detection was performed by scanning selected ions, with three chai acteristic ions for every corticosteroids. The limit of detection was found 80 pg/ml of plasma. 

There are a large number of processes in the chemical industries that handle a variety of suspensions of solid particles in liquids. The application of filtration techniques for the separation of these heterogeneous systems is sometimes very costly. If, however, the discrete phase of the suspension largely contains settleable particles, the separation can be effected by the operation of sedimentation. The process of sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening,... 

Stability may be inherent or induced. In the latter case, the original system is in a condition of metastable or neutral eouilibrium. External influences which induce instability in a dispersion on standing are changes in temperature, volume, concentration, chemical composition, and sediment volume. Applied external influences consist of shear, introduction of a third component, and compaction of the sediment. Interfacial energy between solid and liquid must be minimized, if a dispersion is to be truly stable. Two complementary stabilizing techniques are ionic and steric protection of the dispersed phase. The most fruitful approach to the prediction of physical stability is by electrical methods. Sediment volumes bear a close relation to repulsion of particles for each other. 

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