UV-Vis Spectrophotometer Comparison

UV-Vis spectrophotometers are used routinely to determine the concentration of solution species from the measured absorbance of light in accordance with Beer’s Law. A study was undertaken to compare the quantitative performance of five different spectrophotometers and one colorimeter that have been recently acquired by the chemistry department. Knowledge of this information will aid in selecting between these instruments for different applications. Figures of merit were obtained for the determination of iron (III) concentrations using thiocyanate ion to produce a red colored complex. Standards were prepared from a 995 ppm iron(III) standard and analyzed simultaneously on each instrument. Absorbance was measured at 479 nm for each standard. All five spectrophotometers gave analytical sensitivities of 0.172±0.004 L/mg. As expected, the colorimeter had a lower analytical sensitivity, 0.117 L/mg, due to the use of broadband LED light source. The best linear dynamic range was observed for the Cary 300 research grade spectrophotometer: 0.005-24 ppm. The poorest limit of quantitation (low limit), 0.63 ppm, observed for the Spectronic 200. The poorest limit of linearity (upper limit) was 8 ppm (Vernier UV-Vis). Analytical sensitivities, detection limits and wavelength ranges were also compared.