pH Electrode

This microelectrode is a miniaturized conventional pH electrode based on selective diffusion of protons through pH glass, and the determination of potentials between the internal electrolyte and a reference electrode. The reference electrode can be either external (separate sensor) or internal (same principle as the redox sensor shown below).

Image of a redox electrode with and without an internal reference. The same principle applies to a pH sensor.

The pH microelectrode is useful for several applications. One example is determination of pH microgradients which have evolved from biological or chemical activity. The figure above shows in-situ measurements of pH microgradients in a deep-sea sediment done with a deep-sea lander equipped with pH microelectrodes.

The pH microelectrode is also very useful in the field of corrosion research.

• Thomas, R.C. 1978. Ion-selective intracellular microelectrodes; how to make them and use them. Academic Press, London
• Revsbech, N.P. and Jørgensen, B.B. 1986. Microelectrodes: Their use in microbial ecology. In Marshall, K. C. (ed.) "Advances in microbial ecology" vol 9, p. 293-352. Plenum New York
• Gundersen, J.K., Jørgensen, B.B., Larsen, E., and Jannasch, H.W. 1992. Mats of giant sulphur bacteria on deep-sea sediments due to fluctuating hydrothermal flow. Nature 360: 454-455
  

pH sensor specifications

Note: BNC connections are discontinued as of August 1. 2010. Adapters are available from Unisense to support compatibility to legacy sensors and instrumentation.

		Standard	Options	Extra price for option selection
Glass electrodes	Outside tip dimensions (diameter x length of sensitive pH glass)	PH-10 (10-19 x 100-150µm) PH-25 (20-30 x 150-250µm) PH-50 (40-60 x 200-300µm) PH-100 (90-110 x 250-400µm) PH-500 (400-600 x 400-800µm)	100-400 µm	20%
	Diameter 20mm from tip	< 2mm	< 1mm	10%
	Diameter 50mm from tip	8mm	< 2mm	20%
Needle electrodes	Needle length	50mm	see below	see below
	Needle diameter	1.1mm	see below	see below
	Position of sensing tip	Exposed
All electrodes	Total length	150-200mm	70-350mm	20-50%
	Shaft diameter	8mm	6-20mm	20%
	Shaft protection diameter*	11mm	Can be omitted	-
	Cabling etc.
	Cable	Co-axial, 3mm
	Cable length	1.5-2m	0-5m	5%
	Connector	LEMO	BNC**	-
	In situ mini connectors***	No	Yes
	Characteristics
	Internal reference	No	Yes**** (not pH-N)	30%
	Water proof	Yes
	Temperature range	-10o-60o
	Temperature range tip	-10o-90o
	Guaranteed life time	3 months
	Expected life time	> 6 months
	Spatial resolution	about 150-250 µm (PH-500 about 500 µm)
	Range	pH 4-10 (linear 4-9)
	Detection limit	0.1 pH unit
	Response time (90%)	< 10s (from pH 7 to pH 4)
	Response	Log linear