The Variability of Dry-Mass Correction for Certified Reference Materials

Abstract

A realistic or an acceptable level of variability that can be expected between laboratories when reporting dry-mass corrections for candidate reference materials is not known. The proper use of solid certified reference materials (CRMs) necessitates a dry mass correction so the elemental composition can be reported as a mass of analyte per unit dry mass of sample.

The water content of seven, biological and environmental, certified reference materials (Measurements and Testing Programme, formerly the BCR) was studied as a function of time, each in seven micro-environments ranging from 15 to 94-percent relative humidity. For the determination of water in these different relative humidity environments, one CRM was observed to have a reproducibility as high as 23-percent (α = 0.05). This degree of variability suggests reproducibility consistently less than 10-percent (α = 0.05), as observed in interlaboratory campaigns to certify candidate reference materials, represents acceptable between laboratory variability.

Key Words:

• Dry-mass correction
• humidity
• reference material
• variability
• water