ESTIMATING THE UNCERTAINTY OF EUROPEAN POINT MEASUREMENTS - THE USE OF PROFICIENCY TEST-RESULTS

The European Point Measurement system for white sugar quality covers v isual appearance, solution colour and conductivity ash. In the present study the uncertainty of this important control measure was estimated using an experimental data set of 80 commercial white sugar analyses. They were supplied by the laboratories of French sugar manufacturers, participating in proficiency tests organized by the Institut de Reche rches de l'Industrie Sucriere (IRIS). These data are very characterist ic of French laboratories. Before the study, the only available result s from collaborative tests of validation were performed by a few exper t laboratories on a small number of samples, often long ago. For visua l appearance and solution colour, uncertainty was found to be independ ent of the mean level of the sample. It was equal to 1.08 EEC points ( 0.54 colour types) for visual appearance and 0.84 EEC points (0.11 ICU MSA Units) for solution colour. No significant differences were demons trated between grade 1 and grade 2 sugar. For conductivity ash, howeve r, the uncertainty was proportional to the ash content, and represente d 13.4% of the ash level. Although these values do not correspond well to the limits in the EU regulations, they do permit a laboratory to d efine realistic goals in terms of accuracy in its quality assurance pr ocedures.