An optical spectrometer module for analysing samples. The optical spectrometer module comprises two or more sample holders. Each sample holder is adapted to receive and reproducibly position a sample in fixed locations within the optical spectrometer module. Each sample holder is also adapted to receive a light beam to thereby enable a sample contained in the sample holder to be exposed to the received light beam. Each sample holder is further adapted to enable light transmitted through the sample holder to exit the sample holder. The optical spectrometer module also comprises two or more electro-thermal components. Each electro-thermal component is thermally coupled to a respective sample holder to control the temperature of the sample holder.