For all applications of organic analysis, which includes areas of critical economic and social importance such as environmental, clinical, pharmaceutical, food safety, primary produce and forensic testing, among many others, pure compounds are the ultimate source of higher-order metrological traceability. Access to pure organic compounds and calibration solutions prepared from these materials, where the analyte mass fraction content has been assigned appropriately, is an essential element in the delivery of reliable, comparable measurements. The standard uncertainty associated with these value assignments establishes the baseline level of uncertainty achievable for any organic measurement procedure.
The BIPM coordinates an ongoing series of comparisons to support and benchmark NMI technical capabilities for content assignment of pure compounds and calibration solutions. It has established a dedicated laboratory facility to support these activities, which are essential for realizing traceability and high accuracy chemical measurements. The comparisons run by the BIPM are an integral component of the CCQM and the Organic Analysis Working Group (CCQM-OAWG) overall strategy to enable National Measurement Institutes (NMIs) to demonstrate their measurement capabilities in the area of organic analysis, and their basis for metrological traceability.
The BIPM has been the coordinating laboratory for the CCQM-K55 series of comparisons related to organic substance purity determination and will coordinate the follow-on CCQM-K148 series targeting capabilities in the same areas. The scope of the comparisons coordinated by the BIPM also includes the CCQM-K78 series the mass fraction assignment of organic analytes present in a multi-component calibration solution.
In recent years the BIPM has coordinated the following comparisons for purity assignment:
For each participant and each class of impurity in each study, plots are prepared to show the extent of agreement, within their stated uncertainties, of a participant's reported result with the reference values. This provides a mechanism for the demonstration of the robustness of an individual NMI's capability for organic purity assignment.
The CCQM small organic comparisons coordinated by the BIPM extend to mass fraction assignments for organic compounds of relative molecular weight in the range 100 Da to 1000 Da.
- Westwood S., Choteau T., Daireaux A., Josephs R.D., Wielgosz R.I., Mass balance method for the SI value assignment of the purity of organic compounds, Anal. Chem., 2013, 85, 3118-3126
- Westwood S. et al., An international comparison of mass fraction purity assignment of theophylline: CCQM Pilot Study CCQM-P20.e (Theophylline), 2009 Metrologia 46 Tech. Suppl. 08019
- Westwood S. et al., An international comparison of mass fraction purity assignment of digoxin: CCQM Pilot Study CCQM-P20.f (Digoxin), 2011 Metrologia 48 Tech. Suppl. 08013
- Westwood S. et al., Final report on key comparison CCQM-K55.a (Estradiol): An international comparison of mass fraction purity assignment of estradiol, 2012 Metrologia 49 Tech. Suppl. 08009
- Westwood S. et al., Final report on key comparison CCQM-K55.b (Aldrin): An international comparison of mass fraction purity assignment of aldrin, 2012 Metrologia 49 Tech. Suppl. 08014
- Westwood S. et al., Final report on key comparison CCQM-K55.c (L-(+)-Valine): Characterization of organic substances for chemical purity, 2014 Metrologia 51 Tech. Suppl. 08010
- CCQM-K55.d: Purity assessment of high purity organic materials: Folic Acid, Draft A report in progress