In October 2006, the protocol of a new key comparison coordinated by the BIPM (BIPM.QM-K1, Ozone at ambient level) was distributed to potential participants. The first participant of the 2007-2008 cycle was the NIST in January 2007, with six other participants expected in 2007. An external audit of the Quality System established for the activities directly linked with the ozone photometer comparisons was successfully undertaken.
A study of systematic biases and measurement uncertainties in NIST standard reference photometers (SRPs) was published in Metrologia in October 2006, and led to the NIST establishing a "NIST SRP upgrade kit" in order to minimize the two major biases revealed by the study. BIPM-SRP32 was upgraded, and an installation procedure developed. The BIPM is now able to install upgrade kits for those participants in BIPM.QM-K1 maintaining a NIST SRP. A generalized least-square regression implemented in the ozone comparison software is described in an article written in collaboration with Dr W. Bremser (BAM) and submitted to Metrologia in May 2007.
The programme to develop a primary ozone photometer using a frequency-doubled laser as a light source has continued. The detector chain has been modified to use UV photodiodes, and the laser cooling system has been improved. Additional optical filters have been placed in the laser beam to reject the residual portion of the fundamental wavelength in the frequency-doubled beam. Initial measurements of ozone concentration performed with this first version of a laser-based SRP succeeded in measuring ozone mole fractions in dry air to within a few percent of the values determined by a mercury lamp-based SRP.
All measurements related to the BIPM coordinated study, CCQM-P73 (Comparison of nitrogen monoxide gas standards), were completed. Gravimetrically prepared NO standards in the range (30-70) µmol/mol from 11 NMIs were analyzed using two independent methods as well as Fourier transform infrared (FTIR) spectroscopy for impurity analysis. A reference value for the comparison was calculated from the most consistent set of gas standards, and it could be shown that in all but one case that impurity measurement problems were the cause of discrepancies of certified values from the reference value. The comparison draft B report was circulated in June 2007.
The BIPM's nitrogen dioxide gas standard dynamic facility was upgraded to include a nitrogen generator and new control and data acquisition software for the FTIR spectrometer. Studies of the consistency of nitrogen dioxide concentrations calculated from permeation rates and those measured by various analysers are currently underway, and comparisons with certified values in gas cylinders based on static gravimetry are planned. Following the request of the CCQM Gas Analysis Working Group, a planned future comparison of NO2 gas standards will be extended to include the comparison of spectroscopic methods for gas concentration determination.
The organic analysis programme has developed a facility for purity assessment and to organize comparisons of NMI's facilities for primary calibrator characterization, initially for analytes of interest to the laboratory medicine community. Refurbishment of a laboratory to provide an area for controlled gravimetric transfer of materials and the accurate preparation of calibration solutions was completed in 2007. The BIPM is coordinating subsequent rounds of the CCQM-P20 series of organic substance purity analysis comparisons: CCQM-P20.e for theophylline; and CCQM-P20.f for digoxin. For CCQM-P20.e the main focus has been the identification and quantification of theophylline and related compounds from the xanthine group. For CCQM-P20.f, methods for the determination of the steroid glycosides digoxin and digitoxin, and various related cardiac glycosides as well as their corresponding aglycones have been developed.
The fifth meeting of the Executive Committee of the JCTLM was held at the BIPM in December 2006, and the timetable for the approval of Cycle III nominations of higher order reference materials and reference measurement procedures, and of Cycle I nominations of laboratory reference measurement procedures was agreed. The construction of the internet-based searchable database for higher order reference materials and measurement methods/procedures approved by the JCTLM was completed and, the new website of the JCTLM database was launched in December 2006. From December 2006 to June 2007, the number of external connections to the JCTLM database website was, on average, 750 each month. The first list of reference measurement services offered by laboratories was published on the JCTLM website in June 2007. The JCTLM web application will be extended to include the reference measurement laboratory services as a searchable category to the database, and this will be available by the end of 2007.
Summary
