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). <EOS>