Abstract
A comparison (CCQM-3) of the concentration of the compound (pp'-dichlorodiphenyl) dichloroethylene (pp'-DDE) in 2,2,4-trimethyl pentane solvent by national laboratories using isotope dilution mass spectrometry has been completed. Two levels of sample solution were provided within the range 0.05 µg g-1 to 5 µg g-1. A discussion on the choice of compound for this comparison is given. The purity of the pp-DDE material used was determined using gas chromatography, differential scanning calorimetry and high-performance liquid chromatography. Details of the preparation of the comparison solutions are given, including choice of containers and septum seals to prevent solvent evaporation. Full results of the comparison are given. Good agreement was obtained between laboratories at both concentration levels, with a majority of participants achieving a result within 1% of the reference values. There was a lack of consistency in the calculation of the overall uncertainty, therefore a typical example of a measurement uncertainty estimation for this comparison is given. Brief details of calibration procedures in IDMS are also given.