text: Also see the web portals given in the references.\n\nA beam of infra-red light is produced and split into two separate beams. One is passed through the sample, the other passed through a reference which is often the substance the sample is dissolved in. The beams are both reflected back towards a detector, however first they pass through a splitter which quickly alternates which of the two beams enters the detector. The two signals are then compared and a printout is obtained.\n\nA reference is used for two reasons:\n\nThis prevents fluctuations in the output of the source affecting the data \nThis allows the effects of the solvent to be cancelled out (the reference is usually a pure form of the solvent the sample is in)