A least-squares fit to the data in Figure 2 shows that the
absorbance measurements made using the homemade spec-
Figure 1. Fully assembled spectrophotometer consisting of (A) LED,
(B) lens, (C) cuvette holder, (D) grating, (E) rotatable detector arm,
(F) photodiode, (G) digital multimeter, (H) hinge, and (I) power
supply for LED.
Figure 2. Absorbance at 590 nm recorded using basic bromothymol
blue solutions at various indicator concentrations. For each solution,
the absorbance measured using the homemade spectrophotometer is
plotted versus that measured with an Ocean Optics USB2000+
spectrophotometer. Circles represent absorbance measurements; the
line represents a least-squares fit.
Journal of Chemical Education Article
1433 dx.doi.org/10.1021/ed200829d | J. Chem. Educ. 2012, 89, 1432−1435
trophotometer are in close agreement with those made using
the Ocean Optics USB2000+ over the typical range of
absorbance measurements up to A ∼1. As is usual for
absorption spectrophotometry, it is desirable to keep
absorbance values within this range as measured signals
become comparable to the dark signal (i.e., become