Comparative separation procedures

The NAA measurements on the paper samples were made at the Breazeale Nuclear Reactor Facility at the Pennsylvania State University with a TRIGA Mark III reactor at a flux of about 1013 n/cm2-sec. Samples were irradiated from 2 to 20 min and counted for 2000 sec, after a 90 min decay time for Ba and a 60 hr decay for Sb, Analyses were performed instrumentally, without radiochemical separation, using a 35cm3 coaxial Ge-Li detector and a 4096-channel pulse height analyzer. With these procedures, detection limits for Ba and Sb were 0.02ug and 0.001 ug, respectively. These sensitivities are comparable to those obtained by GA s radiochemical separation procedure, and are made possible by the use of the higher neutron output from the more powerful reactor and in combination with the higher resolution solid state detector... 

When the separation procedures described in detail above are unsatisfactory for the separation of a mixture of organic compounds, purely physical methods may be employed. Thus a mixture of volatile liquids may be fractionally distilled (compare Section 2.26) or a mixture of non-volatile solids may frequently be separated by making use of the differences in solubilities in inert solvents. The progress of such separations may be monitored by application of the various chromatographic techniques detailed in Section 2.31, or indeed these techniques may be employed on the preparative scale for effecting the separation itself (e.g. flash chromatography, p. 217). The techniques of counter current distribution, fractional crystallisation or fractional sublimation (Section 2.21) may also be employed where appropriate. 

Several investigators have reported a particle concentration effect associated with the sorption of hydrophobic solutes. The decrease in the amount sorbed with increasing particle concentration is most pronounced for compounds characterized by large partitioning (Kd > 1000 mL/g). O Conner and Connolly (1980) reported observations that linear partition coefficients are inversely dependent upon the concentration of the solids in the system. Voice et al. (1983) also observed a significant increase in sorption as the solids concentration decreased and attributed it to the presence of microparticles contributed by the solids and not removed from suspension in the separation procedure. This suggests that sorption coefficients produced in studies using different techniques are not necessarily comparable. 

IHH TABLE 4 Comparative Features between the Separation Procedures Used in the Preparative HPLC Purification of Polypeptides and Proteins with Alternative Approaches and Typical Purification Factor Ranges and Time Required per Unit Operation... 

Figure 4 shows tnat charging a mixture of ethylene and propylene at 400 psig and increasing temperature from 400-600°F, propylene reacts before ethylene. At one "window" conversion of propylene is 95%, compared to 5% for ethylene thus, providing a separation procedure for the two monomers. Ethylene finally converts also, at a higher temperature. 

Formation of Asphaltenes in Straight-Reduced Asphalt. The straight-reduced 125-penetration asphalt (SR-125) has been separated into fractions using two separation procedures illustrated in Figures 2 and 3. The results of the separations are compared in Figure 5. The comparison of the amounts of fractions generated from the asphaltene-free (maltene) portion of SR-125 asphalt (Method 1) and acid- and base-free portion of SR-125 asphalt (Method 2) by chromatography on alumina shows that the amounts of saturates plus aromatics-1, often called oils, remain constant (53 wt %). Differences can be observed in the amounts of polar fractions (resins) defined as aromatics-2 and aromatics-3. The prior separation of acids and bases directly from the asphalt... 

Separating a whole sample of a coal liquid or shale oil into classes poses special problems since these materials contain high concentrations of heteroatomic species compared with natural petroleums. Many of these compounds are quite polar and can cause emulsification, precipitation, and may even react to produce artifactual compounds at some stage during a separation procedure. Many liquid chromatographic techniques have been useful in class separations and analyses of petroleums. More often, these have been applied to particular analytical scale operations with fossil-derived liquids. The most common applications are for aromatic-aliphatic and molecular weight types of separations. 

For multiplex measurements, when compared to fluorescence, SERRS also offers significant advantages. In multiplex measurements fluorescence has the disadvantage that the electronic spectra produced are broad (typically 50 to lOOnm full width at half maximum) and therefore overlap so that the technique is limited to the simultaneous measurement of around four dye labels [69, 77]. In contrast, SERRS uses the vibrational Raman spectrum of the label as a spectroscopic molecular fingerprint As a result the information content of the spectra is much higher and, because the vibrational bands are much narrower (about 1 nm full width at half maximum), spectral overlap is much less of a problem. Thus using SERRS it is possible to readily identify the components of a mixture without extensive separation procedures [78] and it has been estimated in the literature that simultaneous measurement with up to 30 SE(R)RS labels should be possible [79]. 

Preparation Procedures of Asymmetric Membranes. The development of the first asymmetric phase inversion membranes was a major breakthrough in the development of ultrafiltration and reverse osmosis. These membranes were made from cellulose acetate and yielded fluxes 10 to 100 times higher than symmetric structures with comparable separation characteristics. Asymmetric phase inversion membranes can be prepared from cellulose acetate and many other polymers by the following general preparation procedure 27... 

The first application of on-line dialysis to a flow system seems to be that made by Skeggs [ 1 ] in his pioneering work on segmented continuous flow analysis. The first report on using on-line dialysis in a non-segmented flow system was that made by Kadish and Hall [2], whereas Hansen and Ruzicka [3] were the first to report such applications in FIA. Despite its early implementation in HA, apyplications of on-line dialysis in this field have been rather few compared to other separation techniques, and mostly dedicated to the analysis of blood serum. This may be due to the fact that dialysis is a slow separation procedure compared to the speed of most FI procedures, and the dialysis efficiencies are usually quite low. 

Note that we intentionally used different subscripts than before (1 and 2 instead of s and /) because now separation into slow and fast coordinates is different. Figure 9.24 compares numerically exact rate constant fci2 as a function of rj = T2/T1 against VTST results and our simple spectrum separation procedure. The agreement is quite reasonable, which makes us believe... 

Resins are the materials which remain oil soluble after asphaltenes are precipitated in n-pentane or n-heptane, but are adsorbed on to surface-active material such as silica gel. They are a comparatively little known fraction (52, 53). Their composition is very much dependent on the separation procedure. The resin molecule is structiually similar to, but smaller than the asphaltene molecule and appears to be a good solvent for asphaltenes (17, 19). Because of its dispersion function for asphaltenes, researchers (35,36, 53, 54) started to note over recent years the influence of resins on the stability of water-in-crude emulsions. 

The flowmeter was calibrated by two separate procedures. The meter readings were recorded, and at the same time the gas passing through the flowmeter was collected and measured during a known time interval. This volume of gas collected was then compared with the volume found by integrating the nominal... 

Both and C are pure p emitters without associated y transition, with their beta maximum energies amounting to 0.02 and 0.2 MeV, respectively. This means that their determination requires careful separation from virtually all other radionuclides prior to radiation measurement taking into account that their activity concentrations in irradiated nuclear fuel are small compared to that of the other fission products, only expensive separation procedures will lead to reliable results. Often these procedures are further complicated by the requirement that different chemical forms of the radionuclides have to determined in parallel (e. g. HT— HTO, C02- " C0- CH4). In such cases one additionally has to take care that no change from one chemical state to another occurs during the analytical procedure. 

It was observed that organically bound phosphorus is completely decomposed to phosphate when oxidized with persulphate in an alkaline medium. Furthermore, more than 60 % of condensed phosphates are hydrolyzed. As concentrations of polyphosphates are negligible in most natural waters, a simultaneous oxidation procedure for organic phosphorus and nitrogen compounds has been developed by Korolejf (1977). Valderrama (1981) compared the procedure with former methods using separate determinations. In the simultaneous oxidation, the pH of the reaction starts at ca. 9.7 and ends at 4-5. These conditions are obtained by a boric acid-NaOH system. In seawater samples no precipitation is formed when the oxidation mixture is added. At elevated temperatures a precipitation is formed, which, however, dissolves as oxidation proceeds. 

One of the exceptional advantages of the isotope dilution technique compared with other methods is that a ratio (isotope ratio, R) is measured, whereas in all other analytical methods the amount of analyte needs to be measured, such that non-quantitative recovery during the sample pretreatment needs to be corrected for. For IDMS analysis, on the other hand, once the isotope dilution step has taken place, the recovery does not need to be known. This is because, for example, subsequent chemical separation procedures will usually not change the isotope ratio of the isotope-diluted sample to a significant extent. From this, it follows that sample loss does not affect the analytical result in IDMS analysis. An important precondition for successful element determination via isotope dilution is an equilibration of the sample and spike as early as possible in the analytical procedure. This prerequisite is best fulfilled in the case of solutions. Solid samples therefore need to be completely digested and thereby equilibrated with the spike, usually added in the form of an aqueous solution. If the analyte and the spike in the isotope-diluted solution are not equilibrated and exist in different chemical forms, sample preparation steps such as chromatographic separation will fractionate the analyte from the spike and the corresponding isotope ratio measurements will produce incorrect results. 

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