Ampoule Sealing Methods

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AMPOULES SEALING

DEFINITION: Ampoules are small, flask shaped, hermetically sealed glass containers that contain a sterile medicinal liquids intended for hypodermic injection either subcutaneously, intramuscularly or intravenously [1].

HISTORY: Ampoule was invented in 1886 by a French pharmacist Stanislas Limousin. It Was invented in a response to a need by physicians to conserve their stocks of injectable solutions that had become difficult to transport and also deteriorated rapidly due to development of moulds [1].

CONTAINERS AND CONTENTS [2]:

Ampoules are commonly made of glass and some are also made of plastic. It consists of various sterile liquids and powders. The chemicals sold in ampoules may be:

  • Injectable pharmaceuticals

  • Air sensitive reagents (like tetrakis palladium)

  • Hygroscopic materials (like deuterated solvents and trifluoromethanesulfonic acid etc)

  • Analytical standards

The filled ampoules should be sealed as soon as possible to prevent contamination.

SEALING OF AMPOULES [2,3]:

Ampuls are generally sealed at the neck portion using an open flame. The seal is opened by snapping off the neck causing a clean break without any extra glass shards.

The sealing of ampuls is done in two ways. They are:

  • Tip seals

  • Pull seals

TIP SEALS:

This type of seal is also called as a BEAD seal as melting the glass at tip of the neck of an ampul forms a bead that closes the opening.

In order to produce a uniform bead, heat should be applied to the neck of an ampul evenly on all sides. This can be done by using burners on either side of a stationary ampoule or by rotating the ampoule in a single flame. For complete closure of the opening by a bead the flame temperature and the intervals at which heat is applied should be properly monitored.

Excessive heating may result in expansion of gases within the ampul leading to a bubble formation whereas insufficient heating will result in a leaker which is an incompletely sealed ampul with an open capillary through the centre of the bead.

Tip seals are generally used for liquid samples.

PULL SEALS:

Pull seals are made by heating the neck of the ampul below the tip. The ampoule is rotated in the flame of a single burner and when the glass softens the tip is held with forceps or other mechanical devices and pulled away quickly from the body of the ampul, which continues to rotate.

The small capillary tube formed is thus closed by twisting the neck.

Pull sealing is a slow process but is more reliable than tip sealing.

Pull sealing is used for ampuls containing powder and those that need a wide opening.

Wetting of the necks at the time of filling can cause their fracture during sealing. Wet necks also increase the frequency of bubble formation and in case of an organic product this may even lead to carbon deposition.

To prevent decomposition of a product, it is necessary to displace the air in the space above the product in an ampoule with an inert gas.

Gases such as nitrogen or carbon dioxide are introduced as a steam into the ampul before or after filling. Immediately the ampoule is sealed so that the gas does not diffuse out.

PRECAUTIONS [3]:

  • The heating with high temperature gas oxygen flame must be even and carefully controlled to avoid distortion of the seal.

  • Excessive heating of air and gases in the neck causes expansion against soft glass with the formation of fragile bubbles at the point of seal.

  • With some sensitive products it may be necessary to close the ampuls with pull seals to prevent combustion products of the flame from entering the ampul at the time of sealing, as might occur with tip sealing.

REFERENCES:

[1] James Swarbrick. Encyclopedia of Pharmaceutical Technology, Third edition, Informa healthcare, volume 2, Page-949.

[2] Remington-The Science and Practice of Pharmacy, 21st edition, Volume 1, Page-825.

[3]The theory and practice of Industrial pharmacy, Third edition, Varghese publishing house, Page- 671.

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Author: P.V.ABHIGNA

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