# Potentiostat

This is a revision from September 06, 2013 08:16. View all revisions

### Background

Potentiostats are commonly used to test for the presence (via electrical activity) of particular compounds and microbes in solution, and thus have applications in environmental monitoring, food and drug testing, and many other areas. Typically, potentiostats are used in a research or industrial laboratory context for these purposes, and most commercially-available potentiostats are very expensive ($1000 is on the “cheap” side). There have been several initiatives in the last decade that have focused on designing cheaper alternatives; and when investigating technologies related to water quality assessment. Our aim here is to build on these efforts, and leverage the experise of the open hardware community in order to build a very accessible, and capable, device. Possible applications include: • Tracking heavy metal concentrations in waterways. Various industrial processes used in the US and abroad can lead to the contamination of water with heavy metals that are dangerous to humans, like mercury and arsenic. An inexpensive, battery-powered potentiostat -- communicating over the cellular network, perhaps, or merely recording locally to an SD card -- might be able to track relative fluctuations in the concentrations of these metals, making monitoring these contaminants easier. • A low-cost ‘field lab’ for evaluating water samples. An inexpensive potentiostat, when used according to the proper protocols, might be used to indicate absolute concentrations of heavy metals in water. This could allow citizens and organizations who can’t afford to send water samples to an expensive, bonded laboratory to do their own testing -- particularly relevant in a developing-world context. • Education. Electrochemistry is an important part of many high school, college, and graduate chemistry curricula; an inexpensive potentiostat could render these curricula more accessible to educational institutions that don’t have the budget for the more expensive commercial versions. • Research. Making an easily-hackable, programmable, and extensible potentiostat platform, based on a widely-used and well-supported technologies like the Arduino and the Raspberry Pi, could allow for novel electrochemistry applications in the laboratory; when a device that once cost$2000 and didn’t “play nice” with other hardware and software suddenly becomes available for under \$200, and can be integrated with easy-to-use, open source software and hardware, researchers will likely dream up new approaches to open research problems -- and higher-throughput approaches in already-established research areas.

### Details

Reference for the above "Adder Potentiostat" circuit: Bard, Allen J., and Faulkner, Larry R. Chap. 15: Electrochemical Instrumentation. Electrochemical Methods: Fundamentals and Applications, 2nd ed. John Wiley & Sons, Inc., 2001. pp. 632-658

A potentiostat is essentially a three terminal analog feedback control circuit that does its best to maintain a fixed voltage between the Working Electrode (WE) and Reference Electrode (RE) while sourcing current from the Counter Electrode (CE), perhaps within an electrochemical cell having load resistances that may change over time. In 3-probe electrochemical experiments, often the CE and WE are made of electrochemically inert conductive materials (we are using graphite, like from pencils, but platinum and gold are popular). The RE is typically a contraption designed to have a well-defined and stable electrochemical potential - an inexpensive one can be made from a piece of silver wire dipped in bleach; the Ag (metal) / AgCl (sparingly water soluble salt) couple electrode is sequestered in a glass tube with a saturated potassium chloride solution, which is fitted with a porous separator to allow ion exchange with the cell. Now by hooking up a power source the energy of electrons in the working electrode can raised and lowered with respect to the reference. Electrons can be made to hop onto certain chemical species, reducing them, or they can be pulled off, oxidizing them -- - the voltages (w.r.t. the RE) and currents at which reductions and oxidations happen can be measured, revealing information about the energies and concentrations of the analytes.

• 8/5/2013: Craig Versek of PVOS has been building off a fully-fledged, open potentiostat design by Jack Summers. Craig is aiming to implement programmable current ranges. In this design, a CMOS analog multiplexer will switch out one of 5 standard current sense resistors (with room for 8 total), which are trimmer rheostats tuned to 250, 2.5k 25.0k 250k and 2.50M Ohms well within 0.5% margin of error.

### Uses

• Assess arsenic, cyanide, other contaminants / toxins in water
• Educational
• Identifying toxins / ingredients in foodstuffs

### Development

• olm-pstat - repository for the PLOTS/PVOS Open Lab Monitor potentiostat peripheral
• source code from Jack Summers' DIY potentiostat

OHS2013_potentiostat_poster.svg

OHS2013_potentiostat_poster.pdf