Reagent Grade Chemicals, Purity

Caffeine was obtained from Sigma Aldrich France (Saint Quentin Fallavier) as a reagent grade chemical (purity >99%). It was recrystallized twice in absolute ethanol to reach a higher purity. Commercial sucrose was also recrystallized in a pilot crystallizer in the laboratory to reach a surface tension above 73 mN/m, which is the evidence of the absence of traces of impurities, especially the surface active ones. Doubly distilled deionized water (FiPLC grade) was used to prepare the aqueous solutions. 

Note For this assay, use reagent-grade chemicals with the lowest practicable Sb, As, Bi, Cd, Cu, Pb, Hg, Ag, and Sn levels, and use only high-purity water and gases. Rinse all glass- and plasticware twice with 10% nitric acid and twice with 10% hydrochloric acid, and then rinse thoroughly with High-Purity Water. 

Acetone and n-propanol were Merck reagent-grade chemicals. SDS and sodium dodecylsulfate (SDOS) (Merck 99% pure) were used without purification, the limiting conductance at 298.15 K in water being the purity criterion (6) nDTMABr (Eastman Kodak) was recrystallized three times from pure acetone and dried 24 hr at 323 K before use. 

A high-quality chemical analysis reqnires reagents and solutions of known purity. A freshly opened bottle of a reagent-grade chemical can ordinarily be used with... 

Finally in the purity of reagent grade chemicals field there have been surprisingly few polarographic methods described. Thus in a preparation of 5,8-dihydrox)maphthoquinone about 20 per cent of the labelled substance< ) was found, and in a preparation of erythrose less than 5 per cent of the substance. In pyridoxal-5-phosphate preparation about 1-5 per cent of pyridoxal could be detected. These are only a few examples of compounds produced by well-known companies. It is doubtless that the specific properties of polarographic analysis would make the method very suitable as a control technique in this field. 

Purity of Reagent—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Atudytical Reagents of the American Chemical Society, where such specifications are available. ... 

Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended... 

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