An optical chemical analyser system comprising an optical chemical analyser and a vessel, wherein the optical chemical analyser comprises: a source of a first amount of radiation, an optics module configured to direct the first amount of radiation such that it is incident on or passes through a target at a target location, the optics module further being configured to receive a second amount of Raman scattered radiation from the target and direct the second amount of radiation to a Spatial Interference Fourier Transform (SIFT) module, the SIFT module including a first dispersive element and a second dispersive element, the SIFT module being configured such that a portion of the second amount of radiation is received by the first dispersive element and interferes with a portion of the second amount of radiation received by the second dispersive element to form an interference pattern; the SIFT module further comprising a detector configured to capture an image of at least a portion of the interference pattern and produce a detector signal based on the captured image; and a processor configured to receive the detector signal from the detector and perform a Fourier transform on the detector signal to thereby obtain a frequency spectrum of the second amount of radiation and process the frequency spectrum of the second amount of radiation and thereby identify the presence or absence of a substance in the target and/or determine a concentration of a substance in the target, wherein the target is a fluid and the fluid is contained in the vessel and the optical chemical analyser is configured to be located exterior to the vessel, characterized in that the fluid is held within the vessel at a pressure of above about 2 x 10 5 Pa (2 atmospheres). a source of a first amount of radiation, an optics module configured to direct the first amount of radiation such that it is incident on or passes through a target at a target location, the optics module further being configured to receive a second amount of Raman scattered radiation from the target and direct the second amount of radiation to a Spatial Interference Fourier Transform (SIFT) module, the SIFT module including a first dispersive element and a second dispersive element, the SIFT module being configured such that a portion of the second amount of radiation is received by the first dispersive element and interferes with a portion of the second amount of radiation received by the second dispersive element to form an interference pattern; the SIFT module further comprising a detector configured to capture an image of at least a portion of the interference pattern and produce a detector signal based on the captured image; and a processor configured to receive the detector signal from the detector and perform a Fourier transform on the detector signal to thereby obtain a frequency spectrum of the second amount of radiation and process the frequency spectrum of the second amount of radiation and thereby identify the presence or absence of a substance in the target and/or determine a concentration of a substance in the target, wherein the target is a fluid and the fluid is contained in the vessel and the optical chemical analyser is configured to be located exterior to the vessel, characterized in that the fluid is held within the vessel at a pressure of above about 2 x 10 5 Pa (2 atmospheres).