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15th Needle/Leaf Interlaboratory Comparison Test - 2012/2013
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15th Needle/Leaf Interlaboratory Comparison Test - 2012/2013
61 laboratories in 28 countries participated in the 15th Needle/Leaf Interlaboratory Test. A new system for qualification and re-qualification started with the 11th test in 2009. This system was enlarged after the manual update in 2010 to all ICP-Forests partners (see König et al. 2010, Rautio et al. 2010, Pitman et al. 2010). With the ring test report each participant received a qualification report. It has been decided to qualify the results of each parameter separately. If 50% or more (generally two, three or all four samples) of the results for this parameter for all the samples of the ring test are within the tolerable limits, the laboratory is qualified. Re-qualification is mandatory for all ICP-Forests laboratories, if monitoring results (foliage, litterfall, ground vegetation) will be submitted to PCC Hamburg in autumn 2013 from the vegetation period 2012.

New since the 14th Interlaboratory Test is the usage of maximum acceptable limits of quantification (LOQ). These limits are needed, because a lot of laboratories are using multi element methods (mostly ICP-AES) with a high LOQ for some elements. But for evaluating and classification of the monitoring samples real measured results and lower LOQ are needed. A task was given from the 12th Expert Panel Meeting Foliage and Litterfall (Tallinn 2011) to the Working Group QA/QC in Laboratories to fix this problem. Maximum acceptable LOQs for mandatory and optional parameters for foliage, litterfall and ground vegetation were discussed and accepted in the 3rd Lab-Head Meeting (Arcachon 2011).

In case of very low concentrations of copper, cadmium and lead in the interlaboratory comparison test samples, these results will be excluded from the evaluation (this happened for the lead result of sample 2). This procedure is needed to avoid wrong qualification results influenced by inaccurate measurements - and on the other hand there is no real need to detect these very low concentrations in real monitoring samples, because it gives no additional information of the nutrient status or of the pollution impact situation.

In general are the results of the 15th Needle/Leaf Interlaboratory Test better than the test before. But a high percentage of non tolerable results could be found for mandatory elements especially potassium (18.0 %), sulphur (13.9 %) and calcium (12.1 %). A clear recommendation to ICP-AES can be given and, where ICP-AES is not sensitive enough, ICP-AES with ultrasonic nebulizer, ICP-MS or Flameless AAS should be used. For nitrogen and carbon, element analyzers are the best choice, if a correct calibration is performed.

The following participating laboratories with a lower percentage of correct results (less than 80%) have bigger QC/QA-problems in their laboratory and with their method:
A57 (79.6%), F04 (78.6%), A43 (71.4%), A83 (66.7%), A62 (62.5%), F24 (53.6%) and A75 (50.0%).

Some laboratories failed with the same elements like in the last Needle/Leaf Interlaboratory Test:
A43 (K), A46 (K), A51 (P), A57 (Ca) and A75 (Ca, Mg, K). All of these laboratories had to check and validate their method or select a new method. If reference material is needed for this purpose FFCC can offer some material.

Figure 1: 15th Interlaboratory Comparison Test - Percentage of correct results

All laboratories are invited to participate in the re-qualification program and/or contact the Google group QA/QC in labs for additional help with their specific problems. 

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