|How to prepare a foliage sample for the interlaboratory comparison test?|
Usually we need 4 kg of dry and powdered foliage per test and you want also some material left for using as a reference sample or for your method validation. So you had to collect a lot of material for this purpose. A rule of thumb is 4 kg dry leaves or needles are 8 kg fresh material without twigs.
The next step is drying the foliage material in an air circulation drying oven. The best temperature is 105°C; spruce needles needs at this temperature only 4-5 h for drying. There is no need for lower temperature (e.g. 70°C), because you must not avoid possible element losses like in the monitoring samples. You had to prepare a sample with a constant element concentration and you are not interested to know the exact element concentration in the original sample. Anyhow this higher temperature speeds up the drying process.
After drying you had to separate foliage from the twigs. So keep in mind, if you have enough twigs you can also use the twigs as a litterfall ringtest sample!
Foliage and twigs must be grind to a fine powder. You should use a contamination free mill for grinding. Especially the contamination with optional elements (Fe, Mn, Zn, Cd, Pb, Cu) should be avoided. If you have no proper mill you can submit the whole dry material like it is to FFCC.
If you want to take a part of this sample for your own purpose you had to homogenize the sample before you split the sample in two parts. A good and cheap equipment for this purpose is a big plastic box where you can fill in the whole sample. Steer carefully with a plastic or wooden spoon for minimum 30 minutes and try to include the outer part of the sample too then split the sample in two parts. The powdered sample (minimum amount 4 kg) should be packed in a contamination free PE-bottle, box or a strong plastic bag and should be submitted to:
Federal Research Centre for Forests/FFCC
Seckendorff Gudent Weg 8
A-1131 Vienna , Austria
Anyhow the sample must be homogenized once more in the laboratory of the Federal Research Centre for Forests before it can be used as a ringtest material.