Spectroscopy apparatuses oriented to the critical angle of the sample are described that detect the spectral characteristics of a sample. The apparatus includes an electromagnetic radiation source adapted to excite a sample with electromagnetic radiation introduced to a measurement site of the sample at a plurality of angles of incidence near a critical angle of the sample and a transmitting crystal in communication with the electromagnetic radiation source and the sample. The transmitting crystal may have a high refractive index adapted to reflect the electromagnetic radiation internally. The apparatus includes a reflector adapted to introduce the electromagnetic radiation to a measurement site of the sample at a plurality of angles of incidence near the critical angle between the transmitting crystal and sample. The apparatus includes a detector for detecting the electromagnetic radiation from the sample. Also, provided herein are methods, systems, and kits incorporating the peri-critical reflectance spectroscopy apparatus.