1. A method for measuring concentrations of species present at at least one point during a separation process operating as a simulated moving bed (SMB) reactor, or a hybrid separation operating as a simulated moving bed (SMB) separation and a further crystallization, said method employing:an immersion probe placed at a point of the reactor or at a point located on a stream entering or leaving said reactor (termed the measurement point),
a thermocouple placed at a distance between an immersed end of the probe and the thermocouple which is at most 30 cm from the measurement point,
a sampling point downstream of the measurement point for analysis by a reference analytical technique during a calibration step,in a manner such as to provide, a Raman spectrum and a temperature simultaneously for each measurement point, said method comprising:a) calibration by inline acquisition of Raman spectra for different mixtures covering a range of concentrations of the species which are to be measured and under temperature and pressure conditions which are representative of an industrial unit and sampling, simultaneously in situ at the sampling point, of moving mixture for analysis by a reference technique, enabling one or more mathematical model(s) to be constructed per constituent as a function of its content;
b) analysis by inline signal processing of the Raman spectrum obtained at each measurement point by means of a chemometric mathematical method employing the or said models constructed during the calibration for each constituent, taking into account the temperature (Tspl) at the measurement point under consideration as well as the range of concentrations Cj of the species present at said measurement point, in order to obtain the concentration Ci of each species present, in which, for each of a) and b), the acquisition of each Raman spectrum is carried out by:
sending a monochromatic signal through a first optical fibre connected to the immersion probe, originating from a laser source with a wavelength of 785 nm plus or minus 1 nm,
retrieving, through a second optical fibre also connected to the immersion probe, a signal corresponding to the Raman effect termed the Raman signal, which is sent to a spectrometer,
retrieving the Raman spectrum of the signal under consideration at the output from the spectrometer.