Potentiometry measures the potential difference between an indicator electrode in a solution and a reference electrode. This provides a quantitative non-destructive measurement of a liquid sample. A common electrode is the glass-membrane electrode used in a pH meter., but various indicator electrodes are designed for specifically for various solutions. The potentiostat is an unloved staple in most wet-labs in one form or another.
Metrohm provides a plethora of cheap screen-printed and interdigitated electrodes for your scientific studies or provisional perusal. You can make an open-source potentiostat with such electrodes for just $60, as detailed in a paper by Alar Ainla, Maral Mousavi, Maria-Nefeli Tsaloglou, Julia Redston, Jeffrey Bell, Teresa Fernández-Abedul, and George Whitesides (whew that’s a lot of names!) .
As has become the standard, the actually interesting information in this paper is hidden away in the supplementary information, which includes parts lists, circuit diagrams and most interestingly a comparison of open-source potentiostats.
For those of you who aren’t interested in using your potentiometer with a smartphone and prefer something less mobile, there is the $80 CheapStat, described in the paper written by Aaron A. Rowe,Andrew J. Bonham,Ryan J. White,Michael P. Zimmer,Ramsin J. Yadgar,Tony M. Hobza,Jim W. Honea,Ilan Ben-Yaacov,Kevin W. Plaxco.
Then for the extra price of a pizza there is the $90 DStat, complete with parts list, circuit diagrams, and instructions in the paper written by Michael Dryden ,Aaron Wheeler.
And finally there is the $100 potentiostat/galvanostat, complete with parts list, circuit diagrams, and instructions in the paper written by
Thomas Dobbelaere, Philippe Vereecken, and Christophe Detavernier.