Cleaning of Glassware

The success of a Pharmaceutical test analysis depends very much upon how effectively the glassware such as beakers, flasks, burettes, pipettes etc. is cleaned. It becomes more critical for certain microbiological assays, the pyrogen test and where small volumes of liquid are measured.

Following are the recommended ways to clean the glassware:
1. Hot Nitric Acid: For cleaning glassware, one of the most useful agents is hot nitric acid.

2. Chromic Acid Mixture:
Chromic Acid Mixture is used for cleaning of (removing organic matter from) glassware without heating.
Preparation of Chromic Acid Mixture:
a. Take a hard, borosilicate glass beaker.
b. Now dissolve 200 g of Sodium dichromate in about 100 ml of water.
c. Cool it in ice bath.
d. Wear safety glasses and add to it, slowly with continuous stirring, 1500 ml of sulphuric acid.
Storage:
a. The Chromic acid mixture must be stored in glass-stoppered bottles in a safe place, (because it is extremely corrosive and hygroscopic.)
b. Crystalline Chromic acid tends to separate from the mixture on standing and can be removed by decantation.
Precautions:
a. The glassware treated with Chromic acid mixture tends to adsorb it; therefore prolonged final rinsing with water is required.
b. Calibrated glassware, which is used for optical measurements, should never be cleaned with Chromic acid.
Discarding: Discard the Chromic acid mixture under continuous flowing water when turns green.

3. General Cleaning: For general cleaning of glassware, synthetic detergent solutions or alkaline cleansing agents such as trisodium phosphate may be used but these also require prolonged rinsing.

Note: All glassware should be finally rinsed with purified water before use.