Sample oxidizing acids

Bromine is used as an analytical reagent to determine the amount of unsaturation in organic compounds because carbon—carbon double bonds add bromine quantitatively, and for phenols which add bromine in the ortho and para positions. Standard bromine is added in excess and the amount unreacted is deterrnined by an indirect iodine titration. Bromine is also used to oxidize several elements, such as T1(I) to T1(III). Excess bromine is removed by adding phenol. Bromine plus an acid, such as nitric and/or hydrochloric, provides an oxidizing acid mixture usefiil in dissolving metal or mineral samples prior to analysis for sulfur. 

Similar results were obtained when carbon was oxidized in liquid medium. Carbon in aqueous suspension is attacked by many oxidizing agents, e.g., permanganate (49-32), chromate (52-54), hypochlorite (52, 55), persulfate (52, 56, 57), and bromate ions (52, 56, 57) chlorine (49), dilute nitric acid (52,58), and concentrated nitric acid (28). The neutralization behavior against the four bases used in Table I was studied with a few samples oxidized in liquid medium (45, 46). The same ratio was observed as with the oxygen-treated carbons, except that twice the amount of groups reacting with sodium bicarbonate was found (Table III). 

Organic samples are usually mineralized to render them soluble in water and to eliminate possible interference from the matrix (for example through adsorption on the electrode surface). Mineralization can be carried out by heating with strong oxidizing acids, by fusion with alkalis or by combustion in an oxygen atmosphere [142]. Blood samples must be treated with heparin if they are not immediately analysed and the content of O2 and CO2 must be carefully maintained otherwise the dissociation equiUbrium of calcium is shifted [78,96]. 

Several people in the 18th and 19th centuries attempted to produce a pure form of zinc oxide for medical purposes. They were unaware that their samples contained cadmium, which at that time was an unknown element. In 1817 Friedrich Strohmeyer (1776—1835), a German chemist, analyzed a zinc compound (calamine) he believed contained zinc oxide (ZnO). However, what he really found was zinc carbonate (ZnCO ), which, though at first unknown to him, contained some cadmium. Strohmeyer then treated his sample with acids until all the zinc was dissolved and thus removed. He then heated the residue with carbon black, resulting in a small ingot of soft, bluish-white metal that proved to be a new element—cadmium. Strohmeyer is given credit for the discovery of cadmium. 

Phosphorus analysis is usually best accomplished via oxidative acid digestion (H2S04/ HC104) of the samples, followed by colorimetric estimation of the phosphorus as phos-phomolybdovanadate.8... 

Another major difference between the tar sand bitumen and the petroleum residues is suggested in Table IV. In all the petroleum samples, the base content is higher than the acid content. In the P. R. Spring sample, the acids are higher than the bases. This could indicate the differences in oxidation, maturation, or origin for the tar sand bitumen as compared with crude oils. In addition, the acid content may often have important effects on recovery processes, such as those which rely on caustic flooding. 

In a further method, sample digests are prepared according to method 1(c) of the Analytical Methods Committee [ 100] using precautions described subsequently [101]. The resulting 100 ml of digest, which is in normally 5% v/v sulfuric acid, should not be colourless and should contain any suspended solids. At the same time, prepare two reagent blanks from the volume of acid used in sample oxidation. 

Normally, for determination in biological samples, the sample is digested in an oxidizing acid mixture followed by atomic spectrometric determination. Organotin can be extracted from biological samples and determined by atomic spectrometric methods or gas chromatography, usually after derivatization. 

Calibration standards are made from a soluble mercury salt, such as, mercuric chloride. The standard solutions are analyzed first prior to the sample, following acid digestion, oxidation, and reduction, as described above. A standard calibration curve is constructed by plotting absorbance vs. concentrations of Hg (or mg Hg). The concentration of Hg in the sample is then determined by comparing the absorbance with that in the calibration curve. 

Biota samples usually are processed by dissolution in strong oxidizing acids or by dry combustion. In combustion, carbonaceous matter is removed at elevated temperatures as carbon dioxide and water in the presence of oxygen (air). Alternatively, some materials may be macerated with enzymes or in basic solution. Whatever process is used, the most important point in selecting... 

In general molybdenum disulphide is chemically very inert. It is resistant to attack by most acids, except aqua regia and hot concentrated sulphuric, nitric and possibly hydrochloric acids. Whereas most metals form salts when attacked by acids, molybdenum has no such tendency, and the product of acid attack is normally molybdenum trioxide. The same appears to be true of the disulphide, and the limited attack by acids can be considered more as a form of oxidation. There is considerable variation in the resistance of different samples to acid attack, and the reactions involved may therefore be primarily those of contaminants rather than of the molybdenum disulphide itself. 

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