Surface Glass Test

Surface Glass Test Procedure | Surface Glass Test USP | USP <660 Surface Glass Test |

Surface Glass Test : Determines hydrolytic resistance of inner surface; distinguishes between Type l and Type ll container with high hydrolytic resistance and Type lll containers with moderate hydrolytic resistance.

The Surface Glass Test combined with the Glass Grains 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.

Determination of The Filling Volume

The filling volume is the volume of Purified Water to be added to the container for the purpose of the test. For vials, bottles, cartridges, and syringes, the filling volume is 90% of the brimful capacity. For ampuls, it is the volume up to the height of the shoulder.

Vials and bottles: Select six dry vials or bottles from the sample lot, or their capacity exceeds 100 mL, and remove any dirt or debris. Weigh the empty containers with an accuracy of 0.1 g. Place the containers on a horizontal surface, and fill them with Purified Water to about the rim edge, avoiding overflow and the introduction of air bubbles. Adjust the liquid levels to the brimful line. Weigh the filled containers to obtain the mass of the water expressed to two decimal places, for containers having a nominal volume less than or equal to 30 mL, and expressed to one decimal place, for containers having a nominal volume greater than 30 ml. Calculate the mean value of the brimful capacity in mL, and multiply it by 0.9. This volume, expressed to one decimal place, is the filling volume for the particular container lot.

Cartridges and syringes: Select six dry syringes or cartridges, and seal the small opening (mouth of cartridges; Luer cone or staked needle of syringes), using an inert material. Determine the mean brimful capacity and filling volume according to Vials and Bottles.

Ampuls: Place at least six dry ampuls on a flat, horizontal surface, and fill them with Purified Water from a buret until the water reaches point A, where the body of the ampul starts to decrease to the shoulder of the ampul (see Figure 2). Read the capacities, expressed to two decimal places, and calculate the mean value. This volume, expressed to one decimal place, is the filling volume for the particular ampul lot. The filling volume may also be determined by weighing.


The determination is carried out on unused containers. The volumes of the test solution necessary for the final determination are shown in Table 5.

Table 5. Volume of Test Solution and Number of Titrations

Filling Volume (ml)Volume of Test Liquid for One Titration (ml)Number of Titrations
NMT 325.01
30 – 100100.02
NLT 1OO100.03


Cleaning: Remove any debris or dust. Shortly before the test. rinse each container carefully at least twice with Purified Water, refilled, and allow to stand. Immediately before testing, empty the containers; rinse once with Purified Water, then with carbon dioxide-free water; and allow to drain. Complete the cleaning procedure from the first rinsing within 20-30 min. Closed ampules may be warmed in a water bath or in an air oven at about 40° for approximately 2 min before opening to avoid container pressure when opening. Do not rinse before testing.

Filling and heating: The containers are filled with carbon dioxide-free water up to the filling volume. Containers in the form of cartridges or prefillable syringes are closed in a suitable manner with material that does not interfere with the test. Each container, including ampuls, shall be loosely capped with an inert material such as a dish of neutral glass or aluminum foil previously rinsed with Purified Water. Place the containers on the tray of the autoclave. Place the tray in an autoclave containing a quantity of water such that the tray remains clear of the water. Close the autoclave, and carry out autoclaving procedure steps 1-8 as described in the Glass Grains Test, except that the temperature is maintained at 121° ± 1° for 60 ± 1 min. If a water bath is used for cooling samples, take care that the water does not make contact with the loose foil caps to avoid contamination of the extraction solution. The extraction solutions are analyzed by titration according to the method described below.

Titration: Carry out the titration within 1 h of the removal of the containers from the autoclave. Combine the liquids obtained from the containers, and mix. Introduce the prescribed volume (see Table 5) into a conical flask. Transfer the same volume of carbon dioxide-free water, to be used as a blank, into a second similar flask. Add to each flask 0.05 mL of Methyl red solution for each 25 mL of liquid. Titrate the blank with 0.01 M hydrochloric acid. Titrate the test solution with the same acid until the color of the resulting solution is the same as that obtained for the blank. Subtract the value found for the blank titration from that found for the test solution, and express the results in mL of 0.01 M hydrochloric acid per 100 mL of test solution. Express titration values of less than 1.0 mL to two decimal places; express titration values of greater than or equal to 1.0 mL to one decimal place.


The results, or the average of the results if more than one titration is performed, are not greater than the values stated in Table 6.

Table 6. Limit Values for the Surface Glass Test

Filling Volume (ml)Maximum Volume of 0.01 M HCI per 100 mL of Test Solution (ml)
Types l and llType lll
NMT 12.020.0
1 – 21.817.6
2 – 31.616.1
3 – 51.313.2
5 – 101.010.2
10 – 200.808.1
20 – 500.606.1
50 – 1000.504.8
100 – 2000.403.8
200 – 5000.302.9
NLT 5000.202.2

Also read : Glass Vial Testing as Per USP

Also read : Glass Grains Test – USP