Purity of reagents

Fe and Fe solutions should be used immediately after preparation. If Fe solutions are allowed to stand, some nucleation of goethite can take place, even at room temperature. If Al-substituted goethite is being prepared, for example, the presence of such seed crystals of goethite in an aged Fe solution will prevent a imiformly substituted product from being obtained. Aged Fe° solutions will, of course, be partly oxidized. 

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Voltaic cells 64. 504 Voltammetry 7, 591 anodic stripping, 621 concentration step, 621 mercury drop electrode, 623 mercury film electrode, 623 peak breadth, 622 peak current, 622 peak potential, 622 purity of reagents, 624 voltammogram, 622 D. of lead in tap water, 625 Volume distribution coefficient 196 Volume of 1 g of water at various temperatures, (T) 87... 

The line of thought elaborated in this paper continues to be useful for assessing functionally the purity of reagents and solvents and the effectiveness of purification procedures and the warning against spurious correlations remains topical. 

Gaseous sample introduction into an ICP-MS presents different problems. Owing to its extremely sensitive nature, Dean et al. [13] introduced the sample as the gaseous hydride by a flow-injection approach. This was reasonably effective because lower volumes of samples and reagents were in use. They utibzed nitric acid as a carrier stream to prevent the formation of argon chloride species in the plasma. Argon chloride has the same mass as arsenic which is mono-isotopic, and this severely bmits arsenic determination. An additional problem was that the sensitivity was extremely dependent on the purity of reagents. 

Mercury(II) forms either coordination complexes or organometallic complexes with olefins, depending on the reaction conditions 19, 34). In solutions of suitable pH and purity of reagents the following equilibria are established ... 

Both the detection limit and the limit of quantification, as defined, are often not very stable characteristics of an analytical method, because the blank signal and the signal generated by the very low concentrations of the analyte are frequently dependent on certain analytical parameters, including the purity of reagents, sample matrices, environmental conditions, instrumentation, and the analysts themselves. Sensitivity is a measure of the ability of an analytical method to discriminate between small differences in analyte concentration. It is defined as the analyte signal per unit concentration of the analyte. Despite the apparent simplicity of the sensitivity concept, a degree of confusion surrounds its use. This confusion stems from the perception that the sensitivity of a method is the same as the limit of detection. 

This arrangement would be very satisfactory if there were no gaps or errors in the original publications. Unfortunately, there are many gaps and some discrepancies in most of the papers. The tests are simple but numerous (1035 for a 46-liquid list). Discrepancies may arise through differences in the purity of reagents, especially water content, which is very important. 

Materials. Palladium acetate was prepared by oxidizing palladium black in acetic acid by 02 or by nitric acid (20). Material from nitric acid oxidation was crystallized five times or more before use, or more often, was purified by the following procedure. Finely powdered palladium acetate was made into a paste with sulfuric acid and digested at 140°-150°C for 30 min. Palladium (II) was thus converted into palladium sulfate, and crucial impurities were destroyed. Palladium sulfate was dissolved in water. After the sulfuric acid was neutralized, the addition of excess acetic acid precipitated purified palladium acetate. Oxi-dizable impurities were removed from acetic acid by repeated fractionation from CrOa and KMn04 solutions. Olefins were treated with alumina before use to remove peroxides. The reproducibility of the rate data was used as a test of the purity of reagents since the results were erratic when inadequate precautions had been taken. 

From a general survey of the literature it appears that the most common causes of poor yields in the Friedel-Crafts cyclization of acid chlorides are (a) reaction conditions which are too drastic, and (b) reagents of inadequate purity. The optimum conditions are those which are mild but still sufficient to complete cyclization. An apparent necessity for heating the reaction mixture in order to induce cyclization may be due, in part, to insufficient purity of reagents. The vital effect of the presence of impurities on the Friedel-Crafts reaction is fairly well known,62 63 but the advantage of mild conditions has not been generally appreciated. 

In most cases, sample preparation includes several stages, such as drying, homogenization and mineralization. Some of these steps, as performed in the laboratory, may be the source of contamination phenomena, essentially due to the type of vessels and purity of reagents used. They become more and more troublesome as the concentrations to be determined decrease. 

Use the highest purity of reagents and acids, including the water used for sample dilution. 

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