The increasing need for reliable analytical measurements in chemistry is a consequence of the impact of results on socio-economic or legal decisions, tack of reliability of analytical results, partly originates from the absence of a structured metrology system in chemistry. Ideally, such a metrology system should be able to allow to generate results traceable to the International System of units and to evaluate reliably the uncertainty, Most chemical measurements request long and complex procedures leading to physical or/and chemical treatments of samples forbidding a direct link to the kilogram or the mole. Only few analytical;methods can be proposed as:''primary methods" linking results directly to the fundamental units and often they cannot be used on real samples, To perform their task analytical chemists use secondary methods, validated and calibrated with reference materials, certified if possible. The way used to obtain secondary traceable-methods, to develop and use reference materials, and to evaluate the uncertainty of measurement results are described and discussed.

The influence of glycaemic control and diabetes characteristics on plasma concentrations of magnesium, zinc, copper, selenium, rubidium and bromine has been evaluated in 44 diabetics (30 insulin-dependent, 14 non insulin-dependent), and the results obtained were compared to those of 309 control subjects of the same mean age. Diabetics had reduced plasma magnesium concentrations (P less than 0.01) but normal erythrocyte magnesium levels. Plasma zinc and selenium concentrations were reduced, whereas those of copper were increased and those of bromine and rubidium were normal. Correlation between glycaemic control, evaluated by measurement of glycosylated haemoglobin levels, and each of the parameters studied was only demonstrated with magnesium in insulin-dependent diabetics (r = -0.561; P less than 0.02). No correlation was found with the other clinical or anthropometric characteristics of the diabetic patients studied. Diabetes seems to be associated with numerous abnormalities of plasma trace elements and magnesium, but the mechanism of these abnormalities has not yet been elucidated. A decrease in zinc and selenium concentrations and an increase in copper concentrations might be additional factors of atherogenicity.