Oxygen Transmission Rate Tester – Coulometric Sensor Method

The coulometric sensor responds only to oxygen, giving better selectivity, higher sensitivity and a lower detection limit (down to 0.01 for films), free from interference by other gases. The differential-pressure method suits work needing multi-gas switching or solubility/diffusion coefficients. If OTR is your core metric, coulometric is usually the better fit.

The coulometric sensor responds only to oxygen: permeated O₂ is reduced at the sensor, producing a current proportional to the amount present. The carrier gas transports that oxygen into the sensor, so it must itself be oxygen-free. Insufficient purity raises the baseline reading — the error is most pronounced on high-barrier materials, where transmission is already low, and can render results non-discriminating. It is the most easily overlooked precondition of this method.

It depends on the question you need answered. Film mode characterises the material itself (test area 50 cm² or 38.48 cm², resolution 0.01) — use it for material selection and incoming inspection. Container mode measures the finished bottle, pouch or tray directly (resolution 0.00005, range 0.00005–40), because forming, heat sealing and creasing all alter barrier performance: the same material can differ by more than an order of magnitude between flat film and a formed container. For shelf-life decisions and regulatory claims, test the finished container.

Choose by range and purpose. The gravimetric cup method is closest to the pharmacopoeia and ASTM E96 classic: a wide range, finished containers can be measured directly, but each run is long — best for compliance comparison and referee testing. The electrolytic method is an absolute coulometric method suited to low-transmission films and containers. The infrared (TDLAS) method responds fast and suits trace water vapour in high-barrier materials and high-throughput work. Pick the cup method when compliance leads, electrolytic or infrared when line efficiency leads.

The differential-pressure method creates a pressure difference across the specimen and tracks the pressure rise on the low-pressure side; one instrument measures oxygen, carbon dioxide, nitrogen and other non-toxic gases, making it the general-purpose choice. The equal-pressure method keeps both sides at the same pressure and uses a coulometric sensor for oxygen only, giving higher sensitivity for the extremely low OTR of high-barrier materials. Two rules: choose differential pressure when you need several gases, coulometric when you measure oxygen only and need the lowest detection limit.

Because the transmitted amount is extremely small, you must wait until permeation reaches steady state and the accumulated signal exceeds the instrument resolution; temperature and humidity equilibration and the system background (residual oxygen or water vapour) also take time. Practical ways to shorten it: raise the test temperature and note it in the report, reduce background and leaks, use a more sensitive sensor, and add parallel test chambers. No speed-up should compromise the steady-state criterion.

The effect is significant: conditions must match the method standard and be stated in the report. Higher temperature raises transmission; for hydrophilic materials, a change in relative humidity markedly changes both water vapour and oxygen transmission. This instrument controls 15–45 °C to ±0.3 °C and covers 35%–90% RH (some models also offer 0% RH). Before comparing data between laboratories, check that both used the same temperature and humidity.

Yes. Standard models ship as-is, while chamber count, specimen size, fixtures, temperature range and software modules (including the GMP Computerized System module) can be tailored to your SOP and URS. IQ/OQ/PQ validation documentation packages are available.

Standard models usually ship in 4–8 weeks; customised builds depend on the agreed scope. Instruments are packed in export wooden cases and can move by sea, air or rail. We supply proforma invoice, packing list and certificate of origin (CO / Form E), and work under EXW, FOB, CIF or DAP terms.

We provide remote installation guidance, bilingual (Chinese/English) manuals and video training; on-site commissioning by our engineers is available. Users can self-calibrate with standard weights, reference films or calibrated leak standards, and third-party calibration certificates can be supplied.

The instrument carries a 12-month warranty from acceptance plus lifetime maintenance support. Consumables (molecular sieve, desiccant, sealing grease, printer paper) are kept in long-term stock, and key components are international brands available worldwide. We respond to technical enquiries within 24 hours.

Yes. Every instrument lists its applicable standards on the specification page (ASTM, ISO, GB, YBB, Chinese Pharmacopoeia, USP, EP, JIS, DIN, TAPPI and more). The software outputs raw records and reports suitable for audit trails, with an optional GMP / FDA 21 CFR Part 11 compliance module.

The software ships with Chinese and English interfaces; other languages can be added on request. Data export is available over RS232, USB, Ethernet or Wi-Fi, and reports can be exported to Excel, PDF or structured files for LIMS integration.