Chemicals standard reagents

Reagent-Grade Chemicals. Potassium dichromate is an important analytical standard, and other chromium chemicals, in reagent grades, find considerable laboratory use (90,91). This use, though small, is most important in wet analyses. 

Labelling is a very important feature of laboratory management. Properly designed and used labels ensure that the identity and status of reagents, chemical standards, apparatus and equipment are always clear to users. There are various requirements that the label on a container should satisfy ... 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

Tetracyanoethylene (TONE), 1,3,5-trinitrobenzene (TNB), ra-dinitro-benzene, nitrobenzene, naphthalene, and anthracene were all laboratory chemical grade reagents and were purified by standard procedures. Pery-lene from Rutgerswerke-Aktiengesellschaft was used as received. Benzene (AR) was stored over active silica-alumina and filtered before use. Solutions of the adsorbates in benzene were 10 XM for TONE and TNB and 5 X 10 3M for naphthalene, anthracene, and perylene. 

An advantage of the technique is the use of an electrical standard to replace chemical standards and the problems associated with their preparation and stability. The coulometric titration also permits the generation of reagents such as copper(I) or bromine, which are difficult to employ as standard solution, or others such as silver(II) or chlorine, which are virtually impossible to use in any other way. A disadvantage of the coulometric titration is its lack of specificity. 

N-acetyl (4,5,6,7,8,9-l c) neuraminic acid was obtained from Amersham, U.S.A. All other chemicals were reagent grade. Purified glycolipid standards and reagents for GLC analysis were kind gifts from Dr. Samar Kundu, Albert Einstein College. 

As many abbreviations are used in this book, a separate list of abbreviations has been added, see front and back endpapers. Concerning abbreviations for chemicals and reagents we adhered to the Standard List of Abbreviations , published in J. Org. Chem., Vol. 68, No. 1, 1998, p. 19A. 

In the model system, the reaction has been kept as simple as possible by investigating self-assembly in a solution containing a single surfactant. The surfactants sodium p-6-tridecylbenzenesulphonate (6-SLABS) and sodium p-7-tridecylbenzenesulphonate (7-SLABS) (Fig. 19.1(a) and 19.1(b)) were pure samples obtained as a gift from Dr. Peter Garrett of Unilever, Port Sunlight Laboratory, UK. All other chemicals were standard reagents and were used without further purification. 

Primary standard — (in titrimetry) A highly purified and chemically stable reagent that can be dissolved in the solvent of choice to serve as reference material for the -> titration of a proper analyte. A primary standard reagent must react rapidly, completely, and stoichiomet-rically with the analyte, as well as having a reasonably large molar mass [i]. 

Reference Materials, Chemical Standards and Reagents which covers a wide variety of terms associated with standards and reagents used during an analysis, including calibration solutions prepared by the analyst. 

Reagents and solvents—use chemical formulae for standard reagents and solvents, but not when the name is shorter or more precise. 

Titrations are among the most accurate of all analytical procedures. In a titration, the analyte reacts with a standardized reagent (the titrant) in a reaction of known stoichiometry. Usually the amount of titrant is varied until chemical equivalence is reached, as indicated by the color change of a chemical indicator or by the change in an instrument response. The amount of the standardized reagent needed to achieve chemical equivalence can then be related to the amount of analyte present. The titration is thus a type of chemical comparison. 

Titrations are widely used in analytical chemistry to determine acids, bases, oxidants, reductants, metal ions, proteins, and many other species. Titrations are based on a reaction between the analyte and a standard reagent known as the titrant. The reaction is of known and reproducible stoichiometry. The volume, or the mass, of the titrant needed to react essentially completely with the analyte is determined and used to obtain the quantity of analyte. A volume-based titration is shown in this figure, in which the standard solution is added from a buret, and the reaction occurs in the Erlenmeyer flask. In some titrations, known as coulometric titrations, the quantity of charge needed to completely consume the analyte is obtained. In any titration, the point of chemical equivalence, experimentally called the end point, is signaled by an indicator color change or a change in an instrumental response. 

Like all titrations, neutralization titrations depend on a chemical reaction between the analyte and a standard reagent. The point of chemical equivalence is indicated by a chemical indicator or an instrumental method. The discussion here focuses on the types of standard solutions and the chemical indicators that are used for neutralization titrations. 

All chemicals were reagent grade, and the solutions were prepared with high-purity water from a Millipore system. The pH measurements were carried out with a combined glass electrode (Metrohm) standardized with pH-buffer solutions (Merck). The lepidocrocite suspensions were prepared according to the procedure developed by Brauer (21) by oxidation of a FeCL2 solution with NaNOa as the oxidant, in presence of hexamethylenetetramine at 60 °C for 3 h. To remove excess chloride, the lepidocrocite suspensions were washed sev-... 

Other standards. Reagents and chemicals that are commercially available at high purity that have been characterized by the vendor can be suitable for standard materials. Sufficient documentation should be provided by the vendor prior to use. 

Boyle refocused the study of chemistry in two important ways. First, he shifted attention away from questions surrounding the source and history of a material to its identity and purity. Second, he redirected the interest in desired byproducts to an examination of the chemical reaction itself In doing this, Boyle promoted the use of chemical identity tests and a control arm in an experiment. Among the measures of identity and purity were color, specific gravity, crystal shape, flame tests, solubifity, precipitates, and reaction to standardized reagents. In these ways, Boyle helped frame the important questions for succeeding chemists until the seminal work of Antoine-Laurent Lavoisier, see also Alchemy. 

The value obtained for cr is an estimate of the precision of the method. If an analyst sets up a new analytical procedure and carries out 20 determinations of a standard sample, the precision obtained is called the short-term precision of the method. This is the optimum value of cr because it was obtained from analyses run at the same time by the same analyst, using the same instrumentation and the same chemicals and reagents. In practice the shortterm precision data may be too optimistic. Routine analyses may be carried out for many years in a lab, such as the determination of Na and K in serum in a hospital laboratory. Different analysts, different chemicals and reagents, and even different instmmentation may be used. The analysis of a standard sample should be carried out on a regular basis (daily, weekly, etc.) and these results compiled on a regular basis. Over several months or a year, the long-term precision of the method can be calculated from these compiled results. This is a more realistic measure of the reliability of the analytical results obtained on a continuing basis from that laboratory. 

In the few examples of such reactions reported, side-chain functionalities appear to undergo typical chemical transformations by standard reagents, with no unusual reactivity or constraints... 

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