Influence of storage of plant samples on their chemical composition

The possible variation in chemical composition of dried plant samples stored for many years under different storage conditions was investigated. Certified reference samples stored for 20 years under laboratory conditions showed no changes for almost all elements under study. Samples from a continuous interlaboratory exchange programme for dried plant material showed constant composition during storage independent of the way the samples were stored. In some cases it could be shown that the results changed due to improvement of analytical techniques.