This article outlines the method for cleaning glass apparatus with nitric acid.
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Description
Cleaning Glass Apparatus
Success in conducting many Pharmacopoeial assays and tests depends upon the utmost cleanliness of the glassware apparatus used. For example, the accuracy of the assays of heparin sodium and vitamin B12 activity, as well as the pyrogen and total organic carbon tests, are particularly dependent upon scrupulously clean glassware.
One effective method used in the past for cleaning glassware is the application of hot nitric acid. A second traditional method for removing organic matter that does not require heat is the use of a chromic acid–sulfuric acid mixture. However, the chromic acid wash is not recommended because of the hazardous and toxic nature of the material.
Several safer alternatives, including the use of cleansing agents, such as trisodium phosphate and synthetic detergents, have proven highly useful, but require prolonged rinsing. It may be useful to rinse with diluted nitric or sulfuric acid prior to rinsing with water. This operation will facilitate removal of residual alkaline material.
For optical measurements, special care is required for cleaning containers, but the use of both chromic acid and highly alkaline solutions should be avoided.
Effective removal of organic matter is very important for testing pharmaceutical waters. It has been demonstrated that an alkaline detergent with potassium hydroxide as the primary ingredient leaves the least amount of organic matter residuals. Heating in a muffle furnace produces comparable results and is the least labor-intensive procedure; however, it requires specialized equipment.
In all cases, it is important to verify that the cleaning procedure is appropriate for the particular test or assay being undertaken. This can be accomplished via blank runs, scientific judgments, residuals data from cleansing agent and detergent manufacturers, or other controls. Specifically, special care is required for cleaning containers for optical measurement applications; the use of highly alkaline and the no longer recommended chromic acid solutions should be avoided. Finally, a statement should be included in the cleaning protocol describing how the success of the cleaning procedure will be assessed.
