Sensor Current
Electrochemical reaction cells measure molecular oxygen permeating through barrier packaging materials by generating an electrical current directly proportional to gas flux. In coulometric oxygen transport testing, carrier gas sweeps oxygen molecules migrating across a barrier film into a catalytic sensor where every molecule reacts completely to yield four electrons. The resulting current establishes the absolute oxygen transmission rate under controlled temperature and relative humidity conditions.
Test Cell
Dual chamber sealed units isolate the dry or humidified test gas from the nitrogen carrier gas stream on opposite sides of a flat packaging specimen. Gas molecules dissolve into the polymer surface on the high-concentration side, diffuse across the film matrix driven by a concentration gradient, and desorb into the carrier gas on the lower surface. The sensor measures continuous microampere output until steady-state permeation is achieved, converting total charge passed per unit time into cubic centimeters per square meter per day.
Temperature stability inside the test cabinet remains critical because polymer chain mobility and gas solubility double for roughly every ten degree Celsius rise.
Transmission Limit
Barrier film performance degrades when physical pinholes or microcracks disrupt polymer orientation. Coulometric detection pinpoints minute gas leakage through thin coated papers or metallized films down to fractions of a cubic centimeter. Ambient humidity variations alter polymer swelling and alter oxygen diffusion rates in hydrophilic materials.
