This method, which is applicable to determining the gas permeance of thepackaging materials or containers for 

pharmaceuticaluse,consists ofdifferential-pressure method and coulometric method. The differential-pressure method 

is only suitable for testing of the films or sheeting, and the coulometricmethod is only suitable for determining the

 oxygen gas permeance.

Method1 Differential-pressure method

The high-pressure chamber filled with about 0.1MPa of the test gas and thelow-pressure chamber of known volume 

are separated by the film or sheeting forpharmaceutical use. After being sealed by the test specimen, the low-pressurechamber 

is evacuated of all air by a vacuum pump. Then the pressure increment (AP)of the low-pressure chamber is measured by a 

manometer to determine the amount of gas passing through the test specimen from the high-pressure chamber to 

the low-pressure chamber as a function of time, but the initial period during which the gas transmission rate changes 

with the time should be excluded.

Apparatus and materials An apparatus for determining gas permeance by differential-pressure method mainly consists 

of the following parts:

Transmission cell The cell consists of an upper part and a lower part. When the test specimen is mounted, the upper 

part equipped with a gas inlet tube is the high-pressure chamber for containing the test gas, and the lower part is the 

low-pressure chamber for containing the permeated gas and determining:the difference in pressure before and after 

the gas permeation.

Manometric device The high-pressure chamber and the low-pressure chambershould be respectively equipped with a manometer. The 

manometer in thehigh-pressure chamber should be with a minimum sensitivity of 100 Pa, and that inthe low-pressure 

chamber should be with a minimum sensitivity of 5 Pa.

Vacuum pump The pump should be capable of producing a pressure lower than10 Pa in the lower-pressure chamber.

Test gas The purity of the test gas should not be less than 99.5%.

Procedure Choose three pieces of the test specimens, which should be ofuniform thickness and suitable size, and 

should be free from wrinkles, creases,pinholes and other defects. Mark the side of each specimen facing the test gas, 

andcondition the specimens at 23°C+2°C in a desiccator for more than 48 hours. Measurethe thickness at least five 

points of each specimen to the nearest 0.001 mm with asuitable gage, and take the arithmetic mean of the measurements, 

Mount the specimen,and carry out the test, Perform a pre-permeation experiment for 10 minutes to rejectthe nonlinear 

phase in the initial period of the test, and continue the test until thesteady permeation to be attained as the changes of 

pressure difference in the equalintervals of timeremain constant.

Testing instrument：Air permeability tester

Method 2Coulometric analysis method (Coulometric method)

The transmission cell is divided into two parts by the test specimen. Oxygen ispurged on one side, and the carrier gas

 of nitrogen is purged on the other side. Theoxygen passing through the specimen is transported by the nitrogen carrier 

gas intothe coulometric analyzer, where chemical reaction occurs to produce eleetrie voltage.which is proportional to 

the amount of oxygen flowing into the coulometricanalyzerper unit time.

Apparatus and materials An apparatus for determining gas permeance bycoulometric analysis method mainly consists 

of the following parts:

Transmission cell Consisting of two parts, the cell should be equipped withthermometric devices and assembled with suitable closures. 

The test area of thespecimens, generally between1-150 cm’, should be adapted according to the range ofvalues to be determined.

Carrier gas It normally could be nitrogen gas or a nitrogen-hydrogen hybrid gascontaining certain ratio of hydrogen.

Test gas The purity should not be less than 99.5%.

Coulometrie deteetor (Coulometer) The detector, sensitive to oxygen, with aconstant operation characteristic, could be

 used to measure the quantity of oxygentransmitted.

Procedure Choose three pieces of the test specimens, which should be ofuniform thickness and suitable size, and should be free from 

wrinkles, creases.pinholes and other defects. Mark the side of each specimen facing the test gas, andcondition the specimens 

at 23°C± 2°C in a desiccator for more than 48 hours.Measure the thickness at least five points of each specimen to the nearest 

0.001 mmwith a suitable gage, and take the arithmetic mean of the measurements. Place thespecimen into the transmission 

cell, and then perform the test, End the test when theoutput signals of the apparatus are steady for a period of time.