Abstract: The invention relates to a method for measurement and monitoring of analytes, for example ketones, particularly but not exclusively acetone in human or other mammalian breath. The invention also relates to apparatus for use in performance of the method. The present invention uses a spectroscopic technique known as CELIF which is a direct combination of the well-established and powerful laser-spectroscopic techniques cavity ring-down spectroscopy and laser-induced fluorescence. The method utilises a flow body to control a flow of sample gas through a laser beam.

Abstract: Apparatuses and methods are provided for quantifying an analyte in a gas or liquid phase. A light source with an emission spectrum overlapping an absorption of the analyte, and a pair of reflective mirrors located on an optical axis to form an optical cavity can be included. An off-axis photon detector can be configured as a fluorescence detector and located off the cavity axis and arranged to provide a first signal in response to fluorescence within the cavity. An axial photon detector can be located axially, and external, to the cavity and arranged to provide a second signal. The portion of the apparatus including the light source, the cavity, and the axial photon detector can be configured with a cavity-enhanced absorption spectrometer, and the portion of the apparatus including the off-axis photon detector can be configured with a cavity-enhanced laser-induced fluorescence (CELIF) spectrophotometer.

Abstract: Apparatuses and methods are provided for quantifying an analyte in a gas or liquid phase. A light source with an emission spectrum overlapping an absorption of the analyte, and a pair of reflective mirrors located on an optical axis to form an optical cavity can be included. An off-axis photon detector can be configured as a fluorescence detector and located off the cavity axis and arranged to provide a first signal in response to fluorescence within the cavity. An axial photon detector can be located axially, and external, to the cavity and arranged to provide a second signal. The portion of the apparatus including the light source, the cavity, and the axial photon detector can be configured with a cavity-enhanced absorption spectrometer, and the portion of the apparatus including the off-axis photon detector can be configured with a cavity-enhanced laser-induced fluorescence (CELIF) spectrophotometer.