Development and validation of a multigas optical sensor cell for the meat industry

Bacterial processes during shelf life of meat are of paramount importance for packaging, preservation and conservation of food. As those processes are linked with fermentation and production of some gaseous species, a sealed thermostatic test cell has been developed and fitted with optical gas sensor as a tool for microbiology and food researchers. The gas sensing instrument is able to detect ammonia and water vapour through a fiber coupled, Herriott multipass absorption cell used with a Distributed Feedback (DFB) laser operating around 1514nm in a Tunable Diode Laser Absorption Spectroscopy (TDLAS) setup. A software defined Wavelength Modulation Spectroscopy (WMS) was used together with a custom made fitting routine to discriminate ammonia and water vapour. A Non Dispersive Infrared (NDIR) instrument at 4260nm is also included in the gas path for carbon dioxide sensing. Headspace gas is sampled from the cooled thermostatic cell and circulated with a diaphragm pump through the sensing instrument while measurements are logged. The whole device consisting of electro optical sensors assemblies and circulation fittings has been integrated into a portable unit. Validation tests were performed at different temperatures with calibrated solutions of ammonia and water directly placed in the thermostatic cell. The results were compared with a reference electrochemical sensor and show that the multipass ammonia sensor is able to reach a resolution in the order of 100ppb with a time response of less than one minute.