|4th Needle/Leaf Interlaboratory Comparision Test 1999/2000|
State Environment Agency (LUA)
Wallneyer Str. 6 / D-45133 Essen
In co-operation with:
Austrian Federal Office and Research Centre for Forests, Vienna
The Finnish Forest Research Institute, Parkano
Bundesministerium f. Ernährung, Landwirtschaft und Forsten, Bonn
International co-operative Programme Forests of UN-ECE in collaboration with EU initialised a programme for intensive and continuous monitoring of forest ecosystems for Europe in order to realise a better understanding of air pollution processes. An important task in this field is the needle/leaf-analysis of trees, because they serve as bioindicators for nutrition state and damages.
Necessary is the harmonising and the improvement of analytical techniques. A high and comparable laboratory standard in all countries is indispensable for a European-wide survey of forest state. Important steps on this way have been the edition of the "Manual on methods and criteria for harmonised sampling, assessment, monitoring and analysis of the effects of air pollution on forests" (UN-ECE, Hamburg and Prague 1994) and the performance of the first European needle/leaf interlaboratory test on two certified standards (BCR 100-beech leaves and BCR 101 - spruce needles) with 24 laboratories from 21 countries, organised by France in 1993.
The intensive discussion of the forest foliar expert panel in As 1994 ended with the recommendation of a second test with 4 unknown samples (spruce, pine, oak) during the running level-II monitoring programme. It was organised by Germany in 1995/96 and subsequently discussed on expert panels in Vienna 1997. The expert panel in Vienna therefore decided on a complete repetition and authorised the Landesumweltamt North-Rhine-Westfalia (LUA) to organise another interlaboratory test on foliage every two years. The 3rd interlaboratory study with 5 unknown samples (spruce, pine, oak, beech) and its consequences for the analytical quality manegement were intensively discussed in Bonn 1999 and ended with a revision of Part IV "Sampling and analysis of needles and leaves" of the above mentioned manual.52 Laboratories from 29 European countries took part in the 4th Needle/Leaf Interlaboratory Test 1999/2000. In comparison to the 3rd test, the results show a distinct improvement of analysis quality at European laboratories working on the issue of forestry analysis. This improvement results, apart from a growing awareness of the problems of quality management, especially from the increased use of elemental analyzers and multi-element spectroscopes. These more and more replace classic analytical methods. Still the elements sodium and lead are as problematic as before. The evaluation of the applied methods indicates for some elements tendencies that should be taken into consideration in the revised manual:
Nitrogen:Analysis by Kjeldal methods results in distinctly lower values than analysis by elemental analyzers. This was to be expected in theory but had not shown so clearly in former ring tests. In future, elemental analyzers are to be used with preference.
Sulphur:The combination of nitric acid - pressure digestion with ICP-OES (inductively coupled plasma-optical emission spectroscopy) results in very homogenous results close to the overall lab mean and therefore has advantages over classic bariumchloride - methods.
Metals (in general):The 4th ringtest basically confirms the formerly detected tendency that closed digestion systems (nitric acid pressure digestion prior to nitric acid microwave digestion) produce greater comparability of the results than digestion in open systems. The combination with ICP-OES is the most favourable method.
Aluminium:Only a minority of laboratories have kept to the instructions given in the manual and used hydrofluoric acid for digestion. Whereas the results from the few laboratories that used both variants (with and without hydrofluoric acid) were clearly higher when using hydrofluoric acid, the differences disappeared when looking at the overall results. Seemingly digestion and/or determination are so faulty that the differences between the methods applied within one laboratory disappear among all participants. Because of that methodology has to be discussed again. But if the majority of the laboratories are not prepared to keep to the manual, aluminium should be cancelled from the list of "optional elements".
It is suggested to reduce the selection of recommended methods in favour of automatic methods. Sensible would be:
- C-N-S - elemental analyzers (for carbon, nitrogen, sulphur)
- nitric acid - digestion in closed systems (pressure bomb or microwave digestion) combined with ICP-OES or ICP-MS (inductively coupled plasma-mass spectroscopy)for sulphur, phosphorous and metals
- X-ray - spectroscopy: This has not proved to be as successful as the before mentioned methods because of higher determination limits but should be maintained and developed for a quick, automatic and non-destructive multi element method of analysis. (for sulphur, etc.)
Download (pdf-files):Report (256k)
Results (mandatory and optional elements) (386k)
Results (other elements) (21k)
Evaluation laboratory (216k)
Evaluation pretreatment methodes (218k)
Evaluation determination methodes (171k)