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Selecting and handling reagents and other chemicals in analytical Chemistry laboratory




The purity of reagents has an important bearing on the accuracy attained in any analysis. It is, therefore, essential that the quality of a reagent be consistent with its intended use.

Classifying Chemicals

A. Reagent Grade

** Reagent-grade chemicals conform to the minimum standards set forth by the Reagent Chemical Committee of the American Chemical Society (ACS) and are used whenever possible in analytical work.

** Some suppliers label their products with the maximum limits of impurity allowed by the ACS specifications while others print actual concentrations for the various impurities.

B. Primary-Standard Grade

** The qualities required of a primary standard, in addition to extraordinary purity, will be discussed in the following lessons.

** Primary standard reagents have been carefully analyzed by the supplier, and the results are printed on the container label.

** The National Institute of Standards and Technology (NIST) is an excellent source for primary standards. This agency also prepares and sells reference standards, which are complex substances that have been exhaustively analyzed.

Note: The National Institute of Standards and Technology (NIST) is the current name of what was formerly the National Bureau of Standards.

C. Special-Purpose Reagent Chemicals

** Chemicals that have been prepared for a specific application are also available. Included among these are solvents for spectrophotometry and high-performance liquid chromatography.

** Information pertinent to the intended use is supplied with these reagents.

** Data provided with a spectrophotometric solvent, for example, might include its absorbance at selected wavelengths and its ultraviolet cutoff wavelength.

Rules for Handling Reagents and Solutions

** A high-quality chemical analysis requires reagents and solutions of known purity.

** A freshly opened bottle of a reagent-grade chemical can usually be used with confidence. Whether this same confidence is justified when the bottle is half empty depends entirely on the way it has been handled after being opened.

** We observe the following rules to prevent the accidental contamination of reagents and solutions:

(1) Select the best grade of chemical available for analytical work. Whenever possible, pick the smallest bottle that is sufficient to do the job.

(2) Replace the top of every container immediately after removing reagent. Do not rely on someone else to do so.

(3) Hold the stoppers of reagent bottles between your fingers. Never set a stopper on a desk top.

(4) Unless specifically directed otherwise, never return any excess reagent to a bottle. The money saved by returning excesses is seldom worth the risk of contaminating the entire bottle.

(5) Unless directed otherwise, never insert spatulas, spoons, or knives into a bottle that contains a solid chemical. Instead, shake the capped bottle vigorously or tap it gently against a wooden table to break up an encrustation. Then pour out the desired quantity. These measures are occasionally ineffective, and in such cases a clean porcelain spoon should be used.

(6) Keep the reagent shelf and the laboratory balance clean and neat. Clean up any spills immediately.

(7) Follow local regulations concerning the disposal of surplus reagents and solutions.

Reference: Fundamentals of analytical chemistry / Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch. (ninth edition) , 2014 . USA



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