Solids mixing sampling

IR spectra can be recorded on a sample regardless of its physical state—solid liquid gas or dissolved m some solvent The spectrum m Eigure 13 31 was taken on the neat sample meaning the pure liquid A drop or two of hexane was placed between two sodium chloride disks through which the IR beam is passed Solids may be dis solved m a suitable solvent such as carbon tetrachloride or chloroform More commonly though a solid sample is mixed with potassium bromide and the mixture pressed into a thin wafer which is placed m the path of the IR beam... 

A standard testing procedure for solids-mixing equipment is available (Ref. 1). This contains details and references pertaining to sampling from solids mixtures for both batch and continuous mixing. 

A new technique has been developed to analyze a- and (3-endosulfan concentrations in human urine (Vidal et al. 1998). Samples are mixed with a buffer solution and then passed through solid phase extraction cartridges for analysis using gas chromatography-tandem mass spectrometry (GC-MS-MS). 

Figure 38. Experimental solids mixing data and model predictions—0.254 m jet, Set Point 3, Sampling Port A.

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]. 

To investigate the effect of ratio of solution volume to mass of solid and adsorption of metal ions 0.5 g resin samples were mixed 25-75 mL of aqueous solution of the constant initial concentration of metal ions (50 ag/mL Pb +). The pH was adjusted to 4 for adsorption of Pb +. The flasks with their contents were stirred for 4 h. 

Quantitative FT-IR Analysis. Selected samples of the liquefaction products, total product, the chloroform extracts, the asphaltenes, and the solid residues were analyzed as KBr pellets by FT-IR. The methods employed for quantitative analysis have been described previously (14-17). Measured amounts of sample are mixed with measured amounts of KBr, so that spectra are reported in absorbance units/mg of sample in a 1.33 cm pellet. A spectral thesis routine was used to obtain peak areas for individual functional groups and previously determined absorbtivities (17) were employed to obtain the reported percentages of each functional group. 

The development of matrix-assisted laser desorption ionization (MAEDI) has advanced the entire field of mass spectrometry. To use this ionization method, the sample is mixed into a matrix that absorbs the laser wavelength extremely well (approximately 10,000 1 matrix analyte) and the mixture is placed on a solid substrate. Absorption of the laser causes the matrix to explode, ejecting the intact, nonvolatile molecules of interest into the gas phase. Proton exchange or alkali metal attachment occurs in the gas plume and the ionized species can be detected. 

Solid samples that have a sufficient vapour pressure at 300 °C are deposited on the tip of a heated metal probe which is then inserted into the instrument through a vacuum lock. With some ionisation methods, the solid sample is mixed with a liquid matrix (e.g. glycerol or benzoic acid). 

Most flame spectrometers use a premix burner, such as that in Figure 21-5, in which fuel, oxidant, and sample are mixed before introduction into the flame. Sample solution is drawn into the pneumatic nebulizer by the rapid flow of oxidant (usually air) past the tip of the sample capillary. Liquid breaks into a fine mist as it leaves the capillary. The spray is directed against a glass bead, upon which the droplets break into smaller particles. The formation of small droplets is termed nebulization. A fine suspension of liquid (or solid) particles in a gas is called an aerosol. The nebulizer creates an aerosol from the liquid sample. The mist, oxi-... 

Once a bulk sample is selected, a laboratory sample must be prepared for analysis (Figure 28-2). A coarse solid sample should be ground and mixed so that the laboratory sample has the same composition as the bulk sample. Solids are typically dried at 110°C at atmospheric pressure to remove adsorbed water prior to analysis. Temperature-sensitive samples may simply be stored in an environment that brings them to a constant, reproducible moisture level. 

Edible oils are easily dissolved in benzene, but if a solid food is to be analyzed, the sample should be well ground first. A portion is accurately weighed, to which a known volume of benzene is added. The sample is mixed, centrifuged, and a 5.0-ml aliquot of this extract is used for the analysis. 

The pressed-salt method has attained wide application in studies of the infrared spectra of solids. In this method the solid sample is mixed with a powdered halide salt such as KI or KBr and the mixture is pressed into a disk at high pressures 53-55). This method reduces scattering because solid-gas interfaces are replaced by solid-salt interfaces. When this method is used,-the particle size of the solid is not of critical importance and most ordinary silica or alumina catalysts can be used without the necessity of any particle-size separation. Although it is simple experimentally, the pressed-salt method will probably never attain a major importance in catalytic work, because once the sample is embedded in the salt, it cannot be subjected to further treatment. 

Solid-phase extraction (SPE) it is widely accepted as an alternative extraction/clean up method [39]. SPE has been used for the extraction of PCBs in various types of human milk. Milk powder and evaporated milk were constituted with water prior to extraction. The milk sample was mixed with 5mL of water and 10 mL of methanol and sonicated, followed by passing the sample through the column. 

Mixed Gas Plasmas. Water loading can be reduced by a desolvation system (condenser or membrane separator) only if the vast majority of the water can be removed. One way to eliminate the introduction of water into the plasma during measurement of the analyte signals is with electrothermal vaporization, laser ablation, or other direct solid sampling techniques. Mixed gas plasmas,... 

Liquid Samples Use fine quartz sand that passes a No. 40, but not a No. 60, sieve and that has been prepared by digestion with hydrochloric acid, washed acid free, dried, and ignited. Mix 30.0 g of the prepared sand, accurately weighed, with 1.5 to 2.0 g of sample, accurately weighed, and dry to constant weight at 60° under reduced pressure (50 mm Hg). Record the final weight of the sand plus the sample solids. Calculate the percent total solids as follows ... 

Bader et al. (1988) used common salt as a solid tracer, which was injected into a flowing catalyst bed. Solids samples, withdrawn downstream of tracer injection, were leached with water and the salt concentration determined by electrical conductivity of the solution. Their results indicated substantial solids backmixing. Li et al. (1991) observed solids mixing in a fast fluidized bed combustor by using raw coal as a tracer, which was injected into the ash bed. Their results also showed that near-perfect mixing prevailed. Similar experiments was also conducted by Chesonis et al. (1991) in a cold model. 

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