Development of the ASTM Standard Practice for Estimating pH to Verify Status of Laboratory Samples D8294-21

Collaborative Efforts to Improve Environmental Monitoring
Oral Presentation

Prepared by C. Prokisch
MACHEREY-NAGEL, Valencienner Str. 11, Dueren, NRW, 52355, Germany

Contact Information: [email protected]; 020-421-9690


pH testing using test strips is widely applied and generally thought to not require explanation. Still, the ASTM “Standard practice for estimating pH to verify status of laboratory samples” contains aspects of pH testing that are counter intuitive and may have a significant impact on the daily routine. Strangely, the inherent error in pH testing is largest in unbuffered solutions around pH 7 – in the middle of the range where most other analytical methods show the smallest error bars.
Data will show, that it is well possible to reliably check sample conservation at pH 2 but that determining the pH of surface water at pH5-6 with good precision is often difficult.
The discussion in the development of the standard also revealed some other aspects that will be presented and explained.