DETERMINATION OF THE O-18 AND DEUTERIUM CONTENT OF FRUIT AND VEGETABLE JUICE WATER - AN EUROPEAN INTER-LABORATORY COMPARISON STUDY

Two inter-laboratory comparison studies were organised by a working group of the technical committee for the analysis of fruit and vegetable juices of the European Commission of Standardization (CEN/TC 174) on oxygen-18 and on deuterium determinations in fruit juice water. The oxygen-18 study was carried out by fifteen laboratories in six European countries. For this comparison, each laboratory received two randomly selected samples of 250 mi of orange and apple juice and one sample of 30 mi of GISP water from the International Atomic Energy Agency. Oxygen-18 determinations were performed according to the same experimental protocol but under different conditions (operator, spectrometer, period of time). The results were considered to be acceptable by specialists in the field of isotopic analysis: the repeatability (r) and reproducibility (R) obtained in this ring test were 0.32 parts per thousand and 0.43 parts per thousand, respectively, according to the ISO Standard 5725-1986. Twelve laboratories of five European countries participated in the deuterium determination and received two further randomly selected samples of 250 mi of orange and apple juice and one sample of 30 mi of demineralized water from one of the participating laboratories. The GISP water previously used for the oxygen-is comparison was also used as the fourth sample in the ring-test. Each participant performed the deuterium determination according to proposed protocols differing only by the reduction method (uranium or zinc). The results were not significantly different between the two modes and for this comparison study the r and R according to the ISO Standard 5725-1986 were equal to 3.6 parts per thousand and 7.6 parts per thousand, respectively, and were considered to be acceptable by the working group.