Simple, accurate solid-state diode photometer for use in measuring oxygen saturation of whole blood.

A small, easily-built photometer is described, in which a solid-state light-emitting diode is used as the light source and a phototransistor as the detector. The detector response is kept constant by modulating the diode intensity in proportion to the absorption characteristics of the sample being analyzed. Linearity and stability are good, even with turbid solutions (drift is <0.00 1 absorbance unit per hour). A typical application of this photometer is the continuous measurement of the percentage of oxyhemoglobin (0 to 100 %) in blood. For hemoglobin concentrations from 3 to 18 g/dI, the relation between oxyhemoglobin as estimated with this diode photometer and by a galvanic method (LEX-02-CON) was: S02 % LED = 0.993 So2 % LEX + 0.69; r = 0.9975; n = 129; S,,, = 1.59.