Method for determining analyte type and/or concentration with a diffusion based metal oxide gas sensor

A method for determining a type and/or concentration of an analyte from a set of analytes comprising the steps of

• providing a measurement device having
• a housing,
• a cavity within said housing,
• a gas sensor comprising a metal-oxide sensing layer and a heater for heating the sensing layer, and
• a passage extending between the cavity and the outside of the housing,
• heating the metal-oxide sensing layer, thereby generating a condition where said analyte is catalytically decomposed with a reaction rate k at said metal-oxide sensing layer,
• taking at least two measurements on said metal oxide sensing layer indicative of a concentration of said analyte, wherein the measurements are taken
• during a phase where a concentration cAV of the analyte within the cavity is in a non-steady state,
• deriving at least one material parameter indicative of the analyte from said measurements, using the diffusion kinetics of the analyte through the passage and using the catalytic decomposition kinetics of the analyte at said metal-oxide sensing layer,
• wherein said at least two measurements are taken at different times during a phase where a concentration cAV of the electrolyte within the cavity is in a non-steady state and while the concentration cAV relaxes into an equilibrium state,
• wherein a ratio V/d is between 5 and 300 mm2, wherein
• V is a volume of said cavity and
• d is a diffusion constant depending on a geometry and design of said passage and describing the diffusion through said passage, with d being defined by
• R=−d·(cAV−cA0)·D,
• with R being a rate of diffusion of an analyte of diffusivity D, cAV is a gas concentration in said cavity and cA0 is a gas concentration outside said housing at said passage,
• wherein said at least two measurements are taken for different reaction rates k,
• further comprising a step of changing said reaction rate by heating a first region of the metal-oxide sensing layer and then heating a second region of the metal oxide sensing layer, with said first and said second region having different areas, and in particular wherein said first and said second regions are heated to the same temperature.