In an infrared analysis instrument, a fiber optic probe, designed to be inserted into a particulate sample, is formed from distal ends of transmitting and receiving optic fibers. The distal ends of the transmitting fibers are located centrally in the probe and the distal ends of the receiving fibers are formed in a ring around the distal ends of the transmitting fibers. The distal ends of the receiving fibers are set back from the distal ends of the transmitting fibers. The receiving fibers carrying diffusely scattered light reflected from and transmitted through the particulate sample to a spectrophotometer housing containing fixed grating and an array of silicon photodetectors arranged to detect the spectrum dispersed by the grating in the range of 500 to 1100 nm.