Digital Designs and Scientific Hardware - Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs - page 219

FIGURE 6.62 The open-source colorimeter circuit schematic.
The schematic was developed at Frizing.org, 59 which is extremely useful for sharing your
electronic design schematics. It is clear from Figure 6.62 that the design does not come close
to need the full functionality of even the Arduino Uno and thus could be made even more in-
expensively. This is left for future researchers working on specialized projects because again
using the Arduino greatly accelerates the ability of the user to get a functioning device in a
short amount of time for a wide range of applications. The open-source colorimeter's irmware
was developed with the Arduino IDE by G. Anzalone and provides an easy-to-navigate hier-
archical menu system for selection of the device's functions.
Colorimetric methods are used to determine the concentration of dissolved species, relying
on the ability of many ionic species to absorb light of one or more specific wavelengths, fol-
lowingthe Beer-Lambert law shown in Eqn (6.1) :
(6.1)
where A is the absorbance (absorbance units), I is the intensity of light passing through un-
known, and I 0 is the intensity of light passing through the blank. The absorbance is related to
concentration as shown in Eqn (6.2) :
(6.2)
where a λ is the molar absorptivity of the species of interest at a certain wavelength ( λ ) of
light, b is the path length of light through solution, and c is the concentration of the analyte.
The design was evaluated using the closed reflux COD method [ 47 ] . The closed reflux color-
imetric method used for COD employs potassium dichromate (K 2 Cr 2 O 7 ) as oxidant, requires
only a small sample size, and produces minimal waste. A 2 ml aliquot is added to dichromate