Ultraviolet-Visible and Infrared Spectrophotometry
The earliest routine application of molecular absorption spectroscopy, which dates to the 1830s, was colorimetry, in which visible light was absorbed by a sample. The concentration of analyte was determined visually by comparing the sample’s color to that of a set of standards using Nessler tubes, or by using an instrument called a colorimeter. The development of visi- ble absorption spectroscopy as a routine analytical technique was limited by the te- dious nature of making visual color comparisons. Furthermore, although infrared radiation was discovered in 1800 and ultraviolet radiation in 1801, their use in opti- cal molecular absorption spectroscopy was limited by the lack of a convenient means for detecting the radiation. During the 1930s and 1940s, advances in elec- tronics resulted in the introduction of photoelectric transducers for ultraviolet and visible radiation, and thermocouples for infrared radiation. As a result, “modern” instrumentation for absorption spectroscopy routinely became available in the 1940s. Progress in these fields has been rapid ever since.