pH - Dynamic NPU Manual



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
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