The accuracy of your measurement is in direct relation to the accuracy
of the pH buffer solution you use to calibrate your pH tester.
A pH measurement is no better than the buffers used for calibration.
are aqueous solutions with well defined pH values. A buffer solution
contains chemicals that will maintain a constant pH regardless of
additions of small quantities of acids or bases i.e. it must have a
buffering capacity. This is where the term buffer originates from.
Buffers can be classified in three categories. The main difference between the different types of buffers is the accuracy.
Commercial buffers, or so-called technical buffers, are solutions for practical use and the type of buffers you use for regular pH measurements.
Typical accuracy for a technical buffer is ±0.05 pH units.
Standard buffer solutions, also called secondary reference buffers, are buffers used as standards for precision measurements and in the manufacture of technical buffer solutions. To be called a standard buffer the buffer has to be produced according to a formula provided by a national standards laboratory, as for example the National Institute of Standards and Technology (NIST) in USA.
Standard buffer solutions have accuracies better than ±0.005 pH units between 0°C and 60°C (32°F and 140°F).
Standard buffers are more susceptible to accidental contamination and dilution than technical buffers. A technical buffer has a higher buffer capacity and is a more robust calibration solution compared to a standard buffer.
Primary reference buffer
Primary reference buffers show the lowest uncertainty in pH values, ±0.003. However, they are not available commercially and are used mainly in metrological institutes.
able to talk about the accuracy of your pH measurement or your pH
calibration solution, you need to understand the concept of traceability.