Fractionation methods gravimetric

Cleanup steps are an important component of infrared (IR)-based and gravimetric methods because these methods are very sensitive to nonpetroleum hydrocarbon interferences. Cleanup steps are not always a part of the petroleum analytical process, but when they are necessary, the goals of extract cleanup steps typically include one or more of the following (1) removal of nonpetroleum compounds, (2) isolation of a particular petroleum fraction, and (3) concentration of analytes of interest. 

The classical methods for detection and quantitation of racemization require analysis of the chiral purity of the product of a peptide-bond-forming reaction. For example, the Anderson test is used to explore a variety of reaction conditions for the coupling of Z-Gly-Phe-OH to H-Gly-OEt (Scheme 6). 9 The two possible enantiomeric tripeptides are separable by fractional crystallization, so that gravimetric analysis furnishes the racemization data. This procedure has a detection limit of 1-2% of the epimerized tripeptide. A modification by Kemp,1"1 utilizing 14C-labeled carboxy components, extends the detection limit by two to three orders of magnitude by an isotopic dilution procedure. The Young test 11 addresses the coupling of Bz-Leu-OH to H-Gly-OEt, and the extent of epimerization is determined by measurement of the specific rotation of the dipeptide product. 

Form of Reported Data. The mass of material leached can be determined either by any standard gravimetric method or, in the case of radioactive samples, by measurement of the radioactivity dissolved in the leaching medium. Since different ions are often leached at different rates, it is important to specify the ion when quoting leach rate results. To avoid confusion on this matter, it has been suggested( ) that long-term leaching results be reported as (fraction of A leached) (cm /g) day) , where A is the specific ion analyzed for. 

The method to realize mole fraction gravimetric preparation... 

By weighing the receptor cylinder, which has been selected and treated, before and after each introduction of component gas and by means of Eq. 2, we are able to get the mole fraction of each component. This method is known as gravimetric preparation. Since mass is one of the seven base quantities and the atomic or molecular weight M can be determined very precisely, the application of gravimetric preparation makes the value of quantity traceable to the mole, the SI base unit in chemistry. 

The experimental values reported for the differential vapor pressure, gravimetric sorption, and piezoelectric methods are the weight fraction of solvent in the polymer solution and the pressure of the solvent vapors in equilibrium with the polymer solution. Differential vapor pressure measurements are performed by adding a known amount of solvent to a weighed polymer sample and measuring the vapor pressure of the solvent over the polymer solution (Bawn et al., 1950). 

The quantitative amount of the tars was determined based on the contents of the 22 most abundant PAHs in the gas. The procedures of methods used for calibration and optimising the GC-MS is described elsewhere [9]. Content of the heavy fraction of the tars that could not be analysed with GC-MS, was determined by gravimetric methods. 

The methods used can be conveniently arranged into a number of categories (a) fractionation by precipitation (b) fractionation by distillation (c) separation by chromatographic techniques (d) chemical analysis by spectrophotometric techniques (infrared, ultraviolet, nuclear magnetic resource. X-ray fluorescence, emission, neutron activation), titrimetric and gravimetric techniques, and elemental analysis and (e) molecular weight analysis by mass spectrometry, vapor pressure osmometry, and size exclusion chromatography. 

In the following examples, HP7680 SFE instruments (Hewlett-Packard) were used. With these instruments, samples are input to the instrument via containers referred to as extraction thimbles. Extracted components are collected and concentrated on soUd traps. The temperature of the solid trap can be independently set for extraction and reconstitution steps in a method. The chemical functionahty (none to quite polar) of the trap is selected by the choice of the packing material. A reconstitution solvent is used to move extracted components from the solid trap to automatic liquid sampler vials (or to waste). Depending upon the appUcation, the vials are presented to a subsequent analytical instrument or possibly manipulated for a gravimetric assay. With this instrument implementation, samples are input and fractions of extracted components in hquid solvents in 2-mL vials are output with no manual intervention between input and output steps. 

The SFE conditions are shown in Table 2. In Table 2 note that the temperature of the solid trap is changed between the extraction and reconstitution steps. During the optimisation of the SFE method, it was observed that a higher temperature in the trap during reconstitution greatly improved the efficiency of that step and the overall sample preparation process - i.e., the solubility of the fat in the solvent was increased so that less reconstitution solvent was necessary, resulting in smaller fraction output volumes (one vial) and less time spent in reconstitution and subsequent blowdown for the gravimetric measurement. The final method incorporated all of the conditions of Table 2 and experiment Set 4 from Table 1. The combined pre-SFE sample manipulation process then yielded a 99 % recovery of a... 

ISO 11461 2001 Soil quality - Determination of soil water content as a volume fraction using coring sleeves - Gravimetric method. 

Deuteration has also been used as a gravimetric method for determining accessibility, the results for cotton being in exact agreement with those of Valentine. The linear relationship which exists between moisture sorption and the fraction of material found to be amorphous to infrared has been confirmed for thirteen different t5qies of cellulose, and it is suggested that a difference in the ratio of moisture regain to amorphous content between samples of cellulose I and cellulose II reflect differences in their sorption behavior and, hence, in the structure of their amorphous... 

While total organic matter is defined as arbitrary physical fractions (dissolved, particulate, and volatile), the recommended methods for their measurement are similar. An outline of the methods used for analysis of organic carbon in sea-water samples is shown in Fig. 7. Most of these methods are based on oxidation of organic matter to CO2 which is determined by volumetric, gravimetric, conductometric, titrimetric, or coulometric methods... 

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