Hydrogen ion exponent



Definition in words

Negative decadic logarithm of the relative molal activity of hydrogen ion

Definition by equation

Systematic terms

pH of hydrogen ion in system 1

Result type

Logarithmic scale
  • Value sets are numerical values
  • Addition and subtraction are allowed (|a-b|=|c-d|; |a-b|≠|c-d|)
  • Division and multiplication are not allowed


Ferard G, Dybkaer R, Fuentes-Arderiu X. Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences : Recommendations 2016. 1 ed: Royal Society of Chemistry; 2016. 182 p.

Laboratory field


Clinical Chemistry


Example 1
Generic abbreviated
NPU02412 P(aB)—Hydrogen ion; pH(body temp.) = ?
Full result NPU02412 Plasma(arterial blood)—Hydrogen ion; pH(body temperature) = 7.46
Abbreviated result NPU02412 P(aB)—Hydrogen ion; pH(body temp.) = 7.46
Written expression The pH of Hydrogen ion in plasma from Mr. Smith’s arterial blood is [7.46]. The body temperature is 37.6 °C.

Reproduction and Fertility

Example 2
Generic abbreviated
NPU02414 SemP—Hydrogen ion; pH = ?
Full result NPU02414 Seminal Plasma—Hydrogen ion; pH = 7.3
Abbreviated result NPU02414 SemP—Hydrogen ion; pH = 7.3
Written expression The pH of Hydrogen ion in Mr. Smith’s Seminal plasma is [7.3].


NPU database, and
  • Kind-of-property

    • Nominal kind-of-property

    • Kind-of-quantity

      • Unitary kind-of-quantity

        • Logarithmic unitary kind-of-quantity

          • pH


  • Dybkaer R. Concept system on ‘quantity’: formation and terminology. Accredit Qual Assur. 2013;18(3):253-60.
  • Dybkaer R. ISO terminological analysis of the VIM3 concepts ‘quantity’ and ‘kind-of-quantity’. Metrologia. 2010;47(3):127-34.
Date Term Note
1996-01-01 pH Term established