Preparation and certification of the new reference materials; plastics (disk form, JSAC 0621-0625) for determination of mercury using x-ray fluorescent analysis.

The Japan Society for Analytical Chemistry has developed some new plastic certified reference materials (CRMs) for the analysis of mercury in polyester disks using XRF analysis. These CRMs (named as JSAC 0621-0625) were prepared by casting polyesters including a toluene solution of organometallic compounds as a standard. Concentrations of the five levels of mercury ranged from 0 to 250 mg/kg. Homogeneity tests of prepared disks had shown excellent results. Interlaboratory comparison study for the certification was performed by 15 laboratory participants. The z-scores in robust statistical method was applied for the evaluation of outliers. The certified values were assigned after discarding outliers. The uncertainties of certified values were determined as the confidence levels of 95%.

Comparative study of robustness of statistical methods for laboratory proficiency testing.

A Monte Carlo approach has been applied to investigate the statistical properties of data analysis methods for proficiency testing, namely, the median-nIQR, Q-method, Algorithm A and Classical method. Simulations were carried out by using a population consisting of two normal distributions, a main population without bias and a sub-population with bias. The difference for robustness among the methods has been discussed. An actual PT for a dioxin isomer was well interpreted by using the population model employed in this study.