Glass Grains Test – USP

Glass Grains Test Procedure | Glass Grains Test USP |

What is Glass Grains Test ?

Glass Grains Test Distinguishes Type I borosilicate glass from Type II and lll soda-lime-silica glass.

The Glass Grains Test combined with the Surface Glass Test for hydrolytic resistance determines the glass type. The hydrolytic resistance is determined by the quantity of alkali released from the glass under the conditions specified.

Glass Grains Test is performed to ensure the safety and quality of glass containers used for storing pharmaceuticals and other sensitive materials. This helps prevent potential contamination of the stored substances and ensures the integrity of the packaging throughout its intended use.

Sample Preparation

Rinse the containers to be tested with Purified Water, and dry in the oven. Wrap at least three of the glass articles in clean paper, and crush to produce two samples of about 100 g each in pieces NMT 30 mm across. Place in the mortar 30-40 g of the pieces between 10 and 30 mm across taken from one of the samples, insert the pestle, and strike it heavily with the hammer once only. Alternatively, transfer samples into a ball mill-breaker, add the balls, and crush the glass. Transfer the contents of the mortar or ball mill to the coarsest sieve (No. 25) of the set. Repeat the operation until all fragments have been transferred to the sieve. Shake the set of sieves for a short time by hand, and remove the glass that remains on sieves No. 25 and No. 40. Submit these portions to further fracture, repeating the operation until about 10 g of glass remains on sieve No. 25. Reject this portion and the portion that passes through sieve No. 50. Reassemble the set of sieves, and shake for 5 min. Transfer to a weighing bottle the glass grains that passed through sieve No. 40 and are retained on sieve No. 50. Repeat the crushing and sieving procedure with the second glass sample until two samples of grains are obtained, each of which weighs more than 10 g.

Spread each sample on a piece of clean glazed paper, and remove any Iron particles by passing the magnet over them. Transfer each sample into a beaker for cleaning Aad 30 mL of acetone to the grains using suitable means such as a rubber-tipped or plastic-coated glass rod. After scouring the grains, allow to settle and decant as much acetone as possible. Add another 30 mL of acetone, swirl, decant, and add a new portion of acetone. Fill the bath of the ultrasonic vessel with water at room temperature, then place the beaker in the rack, and immerse it until the level of the acetone is at the level of the water; apply the ultrasound for 1 min. Swirl the beaker, allow to settle, and decant the acetone as completely as possible; then repeat the ultrasonic cleaning operation. If a fine turbidity persists. repeat the ultrasonic cleaning aha acetone washing until the solution remans clear; Swirl, and decant the acetone. dry the grains, first by putting the beaker on a warm plate, then by heating at 140° for 20 min n a drying oven. Transfer the dried grains from each beaker into separate weighing bottles, insert the stoppers, and cool in a desiccator.


Filling and heating: Weigh 10.00 g of the cleaned and dried grans into two separate conical flasks. Pipet 50 ml of carbon dioxide-free Purified Water into each of the conical flasks (test solutions). Pipet 50 ml of carbon dioxide-free Purified Water into a third conical flask that will serve as a blank. distribute the grains evenly over the flat bases of the flasks by shaking gently. Close the flasks with neutral glass dishes or aluminum foil rinsed with Purified Water or with inverted beakers so that the inner surfaces of the beakers fit snugly down onto the top rims of the flasks. Place all three flasks in the autoclave containing the water at ambient temperature, and ensure that they are held above the level of the water in the vessel. Carry out the following operations:

  • 1. Insert the end of a calibrated thermometric device in a filled container through a hole of approximately the diameter of the thermocouple and connect it to an external measuring device If the container is too small to insert a thermocouple, apply a thermocouple in a suitable, similar container. Alternatively, use the internal thermometer of the autoclave.
  • 2. Close the autoclave door or lid securely but leave the vent-cock open.
  • 3. Start automatic recording of the temperature versus time. and heat the autoclave at a regular rate such that steam issues vigorously from the vent-cock after 20-30 min, and maintain a vigorous evolution of steam for a further 10 min. For autoclaves using a steam generator, it s not necessary to maintained temperature for 10 min at 100°.
  • 4. Close the vent-cock; and raise-the temperature from 100° to 121° at a rate of 1°/ min within 20-22 min.
  • 5. Maintain the temperature at 121° ± 1° for 30 ± 1 min from the time when the holding temperature is reached.
  • 6. Cool down to 100° at a rate of 0.8°/min, venting to prevent formation of a vacuum, within 40-44 min.
  • 7. Do not open the autoclave until it has cooled to 95°.
  • 8. Remove the hot samples from the autoclave using appropriate safety precautions, and cool the samples cautiously down to room temperature within 30 min, avoiding thermal shock.


To each of the three flasks add 0.05 mL of methyl red solution. Titrate the blank solution immediately with 0.02 M hydrochloric acid, then titrate the test solutions until the color matches that obtained with the blank solution. Subtract the titration volume for the blank solution from that for the test solutions. Calculate the mean value of the results in ml of 0.02 M hydrochloric acid per g of the sample. Repeat the test if the highest and lowest observed values differ by more than the permissible range given in Table 3.

Table 3. Permissible Range for Valuer Obtained

Mean of the values Obtained for the Consumption of Hydrochloric Add Solution per g of Glass Grains (mL/g)Permissible Range of the Valuer obtained
NMT 0.1025 % of the mean
0.10 – 0.2020 % of the mean
NLT 0.2010 % of the mean

[NOTE-Where necessary to obtain a sharp endpoint, decant the clear solution into a separate 250-mL flask. Rinse the grains by swirling with three 15-mL portions of carbon dioxide-free water, and add the washings to the main solution. Add 0.05 mL of the Methyl red solution. Titrate, and calculate as before. In this case also add 45 mL of carbon dioxide-free Purified Water and 0.05 mL of Methyl red solution to the blank solution.]


The volume does not exceed the values indicated in Table 4.

Table 4. Test Limits far Glass Grains Test

Filling Volume (mL)Maximum Volume of 0.02 M HCl per g of Test Glass (mL)
Type lType ll and lll

Also read : Glass Vial Testing as Per USP-Containers-Glass