Through the course of a PBL-based instrumental analysis laboratory, a double-beam visible spectrophotometer was designed, built, calibrated, and tested against common analytes. The instrument was built using commercially available optics and included the construction and calibration of a diffraction-grating monochromator using a computer-modulated stepper motor for wavelength selection. Sample and lens holders were designed using CAD software and constructed with a 3D printer, and all circuitry was built in-house. A National Instruments USB 6008 provided ADC of the dual photodiode output (sample and reference), as well as digital control of a stepper motor used to control and select the wavelength transmitted through the cells. The monochromator was calibrated against an OceanOptics RedTide USB photodiode array spectrophotometer and the calibration used with the student-designed LabVIEW program for absorbance analysis. Inorganic copper and cobalt salts provided initial samples for testing and comparison, as well as analytical figures of merit. The instrument provided similar results as the commercially available OceanOptics spectrophotometer, with 1 nm wavelength resolution.

Student designed and built visible spectrophotometer

248th National Meeting (2014)

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