Measurement and Uncertainty of Residual Inorganic Content by Micro-ROI Analysis for Certification of Reference Materials
Authors: Ryan Carrell, HuaHua Jian, Kevin Gates, Isil Dilek, Uma Sreenivasan
Presented at Pittcon, Orlando, FL, March 2010
Abstract
Certified reference materials for pharmaceutical, forensic/toxicology, clinical/diagnostic and environmental applications require thorough characterization. Understanding the traceability and uncertainty of the reference materials is critical for laboratories seeking to ensure compliance with ISO/IEC 17025. The purity of a reference material cannot be reliably stated in terms of chromatographic purity alone. Residual impurities such as water, solvent, and inorganic impurities must be considered when using reference materials for quantitative applications. Residual inorganic content is typically determined through residue on ignition techniques such as sulfated ash. USP <281> Residue on Ignition (ROI) requires large sample sizes of several grams. Reference materials, particularly impurities, metabolites, and stable labeled materials may not be available in large quantities. Residue on Ignition using micro-analytical techniques (micro-ROI) have been developed for measurement of residual inorganic content using small samples sizes. Uncertainty of this technique was evaluated along with its impact on the overall uncertainty of the reference material.