Impurity analyses removal

In the case of soil analysis, a 2.0cm i.d.x30cm column is used. Stones, roots and other gross impurities were removed, and the soil was reduced to a size between 30 and 60 mesh. 20g of soil was packed into the column between two glass wool plugs. Insecticides were desorbed from the soil by passing small volumes of acetone toluene (1 1) through the column at a rate... 

These phosphates and silicates form a slag. Thus, all the impurities are removed from the molten iron in a period of 7 to 8 h. Near the end of the period of treatment, samples of the molten iron are removed, solidified, and sent to the laboratory for accurate and rapid quantitative analysis. On the basis of information supplied by the laboratory, it becomes possible to calculate accurately the quantity of spiegeleisen which must be added in order to produce a steel of the desired composition. Thereafter,... 

A small amount of nitrotriazolo-diaminotriazine was also formed when preparing triazolyl-tetrazinyl-aminotriazine sodium. The impurity was removed by filtration when the reaction product mixture of Step 2 was dissolved in warm water. H-NMR and elemental analysis data for this compound supplied by the author. 

As a third option, impurities appearing in the reference chromatographic method may be isolated using analytical (under overloaded conditions) or semi-prep chromatography and then identified by MS and/or NMR. Mobile-phase components should be removed prior to analysis. Removal of mobile-phase components may entail evaporation, liquid-liquid extraction, freeze-drying, or solid-phase extraction. Identification by MS should be attempted first because its high sensitivity requires only small sample amounts. The less sensitive NMR requires the isolation of greater amounts of the impurity. An alternative to this approach is the use of LC-MS or LC-NMR. 

All sample types are amenable to SPE with suitable handling solids, liquids, semisolids, etc. Solid-phase extraction is extensively used in sample preparation, as it offers a fast, safe, and convenient means for subsequent analysis by chromatographic techniques [HPLC, thin-layer chromatography (TLC), GC, etc.]. The major benefit is that it requires less solvent than conventional LLE methods. Impurities are removed and the analytes are... 

Preferred bentonite clays are those whose chief constituent is mont-morillonite, a mineral of the composition corresponding to the empirical formula, 4Si02-Al203 H20. The principal sources of raw clay for the manufacture of the presently most widely used natural catalyst (Filtrol Corporation) are deposits in Arizona and Mississippi. The clay from these deposits contains appreciable amounts of impurities, principally CaO, MgO, and Fe203, which replace part of the A1203 in the ideal montmorillonite structure. The catalyst is prepared by leaching the raw clay with dilute sulfuric acid until about half of the alumina and associated impurities is removed. The resulting product is then washed, partially dried, and extruded into pellets, after which it is activated by calcination. A typical analysis of the finished catalyst is as follows (Mills, 12). 

Should the chromatogram remain seriously disturbed because of impurities not removed during the cleanup, the analysis results will be, at best, an approximation. Recourse to a mass spectrometer coupled with a high-performance computer system, which might remove the Interference, could then be considered. Use of a more efficient column in an aim to obtain a better discrimination between PCBs and impurities could also be considered. 

Alumina can be used for cleanup of extracts during analysis of nonionic surfactants. A great many ionic and polar nonionic impurities are removed by this treatment (107). Typically, impurities are eluted from the alumina with 50 50 hexane/methylene chloride, followed by elution of the surfactants with 100 1 methylene chloiide/methanol. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

When working with a solid sample, it often is necessary to bring the analyte into solution by dissolving the sample in a suitable solvent. Any solid impurities that remain are removed by filtration before continuing with the analysis. 

After dissolving the sample in a beaker, remove any solid impurities by filtering a portion of the solution containing the analyte. Collect and discard the first several milliliters of solution before collecting a sample of approximately 5 mL for further analysis. 

Faradaic currents due to impurities can usually be minimized by carefully preparing the sample. For example, one important impurity is dissolved O2, which is reduced first to H2O2 and then to H2O. Dissolved O2 is removed by bubbling an inert gas such as N2 through the sample before the analysis. 

The distribution of impurities over a flat sihcon surface can be measured by autoradiography or by scanning the surface using any of the methods appropriate for trace impurity detection (see Trace and residue analysis). Depth measurements can be made by combining any of the above measurements with the repeated removal of thin layers of sihcon, either by wet etching, plasma etching, or sputtering. Care must be taken, however, to ensure that the material removal method does not contaminate the sihcon surface. 

Preparation. It was first prepd in an impure form by Hantzsch who isolated a ciyst solid when anhyd nitric and perchloric acids were mixed. He reported the solid to be 0N(0H)2+.C104 (Ref 2), but later work by Goddard and coworkers showed this solid to be a mixt of nitronium perchlorate and perchloric ac mono-hydrate (Ref 4). It is best prepd by distilling anhyd perchloric ac onto an excess of dry dinitrogen pentoxide at -80°, the mixt allowed to warm to room temp, and the mixt pumped under vacuum for 2 days to remove volatiles. The residue was shown by analysis to be a mixt of 89 mole % nitronium perchlorate and 11 mole %... 

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