Standard Reference Material? 84L
Potassium Hydrogen Phthalate
KHC8H4O4
Acidimetric Primary Standard
This Standard Reference Material (SRM) is intended for use as an acidimetric primary standard. It consists of highly purified potassium hydrogen phthalate (KHP), KHC8H4O4. A unit of SRM 84L is supplied as crystalline material in a 60 g unit.
Certified Value: The certified value listed in Table 1 is the mass fraction of total acid (replaceable H+ ) expressed as KHP. A NIST certified value is a value for which NIST has the highest confidence in its accuracy in that all known or suspected sources of bias have been investigated or taken into account [1]. Table 1. Certified Value (a) for SRM 84L Potassium Hydrogen Phthalate 99.9934 % ? 0.0076 %
(a) The certified value is expressed as the value ? its expanded uncertainty, U. The expanded uncertainty is calculated as U = kuc, where k is the coverage factor and uc is the combined standard uncertainty calculated according to the ISO Guide [2]. The value of uc represents the combined uncertainty in the certified value, at the level of one standard deviation, and includes the replication uncertainty of the 30 titrations of the SRM and all sources of uncertainty inherent to the coulometric method. The value of k controls the approximate level of confidence associated with U. For this SRM, k = 2.04. This value corresponds to a level of confidence of approximately 95 %. The value of k is obtained from the Student’s t-distribution with effective degrees of freedom, νeff = 31.