The present invention discloses apparatuses and methods for non-invasive determination of attributes of human tissue by quantitative infrared spectroscopy. The embodiments of the present invention include subsystems optimized to contend with the complexities of the tissue measurements. The subsystems can include an illumination/modulation subsystem, a tissue sampling subsystem, a calibration maintenance subsystem, a data acquisition subsystem, and a computing subsystem. Embodiments of the present invention provide analyte property determination and identity determination or verification from the same spectroscopic information, making unauthorized use or misleading results less likely that in systems that include separate analyte and identity determinations. The invention can be used to prevent operation of automobiles or other equipment unless the operator has an acceptable alcohol concentration, and to limit operation of automobiles or other equipment to authorized individuals who are not intoxicated or drug-impaired.