An improved residual oxygen detection method by using axis-sectional multi-reflection within optical-length-limited pharmaceutical vials

In-situ and accurate residual oxygen concentration detection in glass vials is an urgent topic in the pharmaceutical manufacturing industry, as the headspace oxygen would render the inner drug composition spoiled. In this paper, an oxygen detection method is designed based on wavelength-modulated tunable diode laser absorption spectroscopy (TDLAS-WMS). To be specific, a concept of coating the outer surface of the vial with a high-reflection silver ring film is firstly proposed, which assists the laser to achieve Axis-Sectional MultiReflection (ASMR) in the narrow space of the vial to break through the optical path limitation of traditional Direct-Transmission (DT) detection method. We abbreviate ASMR with the reflection number of n as n-ASMR. The experimental results prove 2/4/6/8-ASMR performs better stability and detection limit of 0.058%/0.054%/ 0.058%/0.046% with the integrate time of 28.9s/14.6s/4.76s/5.60s, compared with 0.22% for DT with 33.8s. Specially, 2-ASMR performs great application potential for its best ability to resist angle change.