An oxygen concentration measuring device is provided for determining an oxygen concentration of a gas in a sample volume. The device includes an optical device configured for irradiating the sample volume containing oxygen with a first UV radiation intensity, at least one wavelength of which is close to a spectral absorption line of oxygen, a magnetic field generator configured for applying a magnetic field at the sample volume, and a UV light detector configured for measuring a second UV radiation intensity coming from the sample volume. The oxygen concentration in the sample volume is determined on the basis of the applied magnetic field and the measured second UV radiation intensity.