High purity acids

Most of the phosphoms produced as the element is later converted to high purity phosphoric acid and phosphate compounds the remainder is used in direct chemical synthesis to produce high purity products. In contrast, phosphoric acid produced by the wet process is used in lower purity apphcations, especially in fertiliser and to a lesser degree in animal feed (see Feeds AND FEED ADDITIVES). More recendy, a small portion of wet acid is purified in a second process and then also used in high purity acid and phosphate compound apphcations. 

The popularity of MSA as an electrolyte in electrochemical appHcations has developed as a result of the following unique physical and chemical properties (/) exhibits low corrosivity and is easy to handle, (2) nonoxidizing, (7) manufacturing process yields a high purity acid, (4) exceptional electrical conductivity, (3) high solubiHty of metal salts permits broad appHcations, (6) MSA-based formulations are simpler, (7) biodegradable, and (8) highly stable to heat and electrical current. 

For example, the industrial preparation of mineral acids, such as sulfuric, hydrochloric and nitric, inevitably leads to them containing small concentrations of metals as impurities. If the acid is to be used purely as an acid in a simple reaction, the presence of small amounts of metals is probably unimportant. If, however, the acid is to be used to digest a sample for the determination of trace metals by atomic absorption spectrometry, then clearly the presence of metallic impurities in the acid may have a significant effect on the results. For this latter application, high-purity acids that are essentially metal-free are required. 

In addition, the residue of the digestion should be quantitatively dissolved in a small volume of high purity acid. The decomposition and accuracy of analytical data should be checked with the aid of certified reference materials. Possible contamination and losses of trace elements by absorption or volatilization should be avoided. 

High-purity acids, silicon, and other materials are essential for acceptable yields in the production of semiconductor devices. Contamination becomes a more and... 

The sample introduction system, sampler, skimmer, and ion optics can be sources of contamination that produces high ICP-MS blank signals so proper cleaning and maintenance are essential [369], Some have argued that no dilution or evaporation (for preconcentration) of high-purity acid samples should be used... 

The current analytical capabilities of ICP-MS provide a means to assess new low levels of contamination in the semiconductor industry [385]. Contamination in clean room air can be detected at very low levels. Dopant and trace metal contamination on semiconductor wafer surfaces can be monitored. Ultratrace metals in deionized water, high-purity acids, and other process chemicals can often be measured at concentrations less than 1 part per trillion. 

If a high-purity acid is desired, further purification steps such as solvent extraction, ion exchange, and carbon decolorization are used. 

In every analytical problem a unified approach must be taken to obtain results of satisfactory accuracy. Considerations of interferences due to contamination are of the utmost importance in the analysis of trace elements from air samples. In many cases attention must be given to selection of high-purity acids and other reagents, and particularly to the purity requirements for collection media such as filters. 

Kuehner, E.C., Alvarez, R., Paulsen, P.J., Murphy, T.J. Production and analysis of special high-purity acids purified by sub-boiling distillation. Anal. Chem. 44, 2050-2056 (1972)... 

Consider the case of determining alkaline and alkaline-earth concentrations. The catalyst samples where the matrix is alumina or a zeolite are reduced to a powder and dissolved in hydrochloric acid solution either by direct attack by high purity acids or after fusion with lithium metaborate. The choice of acids used to attack the samples depends both on their composition (alumina or aluminium silicate) and on the active elements present. Success of the method in forming a solution depends partly on the information available on the composition of the sample. If the presence of certain elements is not known, it may be necessary to test several methods prior to obtaining a satisfactory dissolution. 

Standards are prepared from high purity salts dissolved with high purity acids or can be obtained as commercial solutions with a certified element content. These solutions are then diluted in order to obtain the desired concentration levels in the elements and an identical acidity to that of the sample solutions with which they are compared. Multi-element standards can be manufactured by mixing single-element solutions taking care to assure compatibility of the chemical species so as not to produce precipitates. 

The analysis of semiconductor materials is illustrated in Tables II and III. Table II shows comparison of the Impurity content of a series of silicon samples. These materials are received as chunks (in the case of starting materials) or slices from a crystal. They are cut to the appropriate size and etched for cleaning with high purity acid. The figure Illustrates high sensitivity analysis of three polycry stall ine silicon samples with the -20 material showing natch higher aluminum content than the others. SSMS performs well in this type of comparative analysis. 

The size of the drop of solution in the cell, which determined the concentration of the absorbing species, was controlled by the heating effect of the infrared source lamp of the spectrophotometer and by the addition of dilute, high purity acid... 

J. R. Moody and E. S. Beary, Purified Reagents for Trace Metal Analysis, Talanta, 29 (1982), 1003. Describes sub-boiling preparation of high-purity acids. 

R. C. Richter, D. Link, and H. M. Kingston, On-Demand Production of High-Purity Acids in the Analytical Laboratory, Spectroscopy, 15(1) (2000) 38. Describes preparation using a commercial sub-boiling system. 

External calibration curves are prepared from solutions of known concentrations of the sample element. High-purity metals dissolved in high-purity acids are used to make the stock standard solution. For AAS, stock standard concentrations are either 1000 or... 

Spark ablation. Spark ablation solid sampling uses the same type of spark source already described. The function of the spark in this case is to vaporize the solid sample the ICP plasma can atomize any nonatomic vapor reaching it. Spark ablation is limited to the analysis of solids that conduct electricity. It is very useful for metals and alloys because it eliminates time-consuming sample dissolution and costly high-purity acids. 

It follows from the above that sulfonated hypercrosslinked polystyrene resins taken in the form should be able to eliminate trace metal cations from concentrated mineral acids much more efficiently than conventional cation exchanger [377], which could be exploited in the preparation of high-purity acids. 

The acids commonly nsed to dissolve or digest samples are hydrochloric acid (HCl), nitric acid (HNO3), and snlfnric acid (H2SO4). These acids may be used alone or in combination. The choice of acid or acid mix depends on the sample to be dissolved and the analytes to be measured. The purity of the acid must be chosen to match the level of analyte to be determined. Very-high-purity acids... 

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