Marb's Lab Cooks Up an Antimony Electrode Arduino-Driven pH Meter From Scratch

Mononymous self-described "citizen scientist" Marb, of YouTube channel Marb's Lab, has demonstrated how to build your own pH meter for measuring acidity and alkalinity — provided you're confident with glassworking and have some antimony and a graphite crucible to hand.

"[This pH meter design] would be suitable for a lab on a chip," Marb says of his creation, "as it can be miniaturized. It has already been used in medicine as a gastric probe, to measure the pH value of stomach acid, [and] further applications in medicine would be to measure the pH value of blood or urine."

A traditional potentiometric pH mater has a reference electrode and a glass electrode, but Marb's build opts for a different design that swaps the glass electrode for antimony — known for its simplicity and reliability in harsh conditions, though with the caveat that it offers lower accuracy than traditional designs.

The move to antimony doesn't mean Marb's pH meter has no glass involved, though: building the gadget involves cutting tubes of borosilicate glass and rounding their ends, then melting antimony in a graphite crucible — to prevent the formation of antimony trioxide — before drawing it up into a glass tube. The reference electrode, made using a copper-copper(II) sulfate, is somewhat simpler, needing only a little epoxy to secure it in the tube before filling it with copper sulphate and sealing it with a potassium-nitrate-treated wooden dowel.

The electrodes are connected to an Arduino-compatible microcontroller, then calibrated with fluids of known pH value. "As the pH value also depends on temperature," Marb adds, "the PCB also has a connector for a[n Analog Devices] DS18B20 temperature sensor with a wide measuring range."

The project is documented in the video embedded above and on Marb's YouTube channel, complete with a schematic for the electronics.