An LED-based multi-sample absorbance spectrophotometer for chemistry and biochemistry

The instrument described in this article measures the absorbance of visible light (with wavelengths in the range of approximately 400 to 650 nm) by liquid samples, a method widely used for determining solute concentrations. To minimize the cost of the instrument, interchangeable light-emitting diodes (LEDs) are used as light sources. Transmitted light is detected using a photodiode device and the signals are processed using an Arduino microprocessor board. Measured absorbances are displayed on an LCD panel and can be transferred to another device via a USB interface. The instrument has measuring positions for up to six samples, each with a separate LED and detector, making it particularly well suited for parallel kinetic experiments with multiple samples. Because the spectrophotometer was designed with undergraduate laboratory courses in mind, it has a modular construction that allows for easy assembly and disassembly, so that students can be given an opportunity to assemble the instrument themselves. The device has a power requirement of only 0.4 W from a 5 V USB supply, making it practical for field studies or other applications where access to electric power is limited.