Method / Description Acid-Digestion


Analytical balance
Ventilated hood (suitable for acidic smoke)
Hot plate with temperature control
Savillex PTFE-vessels (15 cm3)
Volumetric flask (glass); 25 cm3
Various PE-beakers
PE-bottles (30 cm3) cleaned with HNO3

HF (40%); suprapur
HClO4 (60%); p.A.
HNO3 (65%); suprapur
Aqua bidest. (Milli-Q-quality)
Certificated soil standard (i.e. MAG-I)

The Savillex vessels are cleaned mechanically with a soft tissue (don`t scratch! ), then filled with 5 cm3 of pure water and 3 cm3 of HNO3, closed tight  and heated for 4 hours at 140 °C.
Open the vessels carefully, rinse thoroughly with pure water, cover them with a Kimwipe and let them dry in the oven.

The samples and the standard have to be dried (at least 24 hours at 65°C) and homogenized. Weigh 100 mg of each sample into a Savillex vessel (write down the exact weight!). Moisten the sample with a few drops of pure water. Do the same with the standard (twice).
For the blank fill a few drops of pure water into a savillex vessel (twice).
Pipette 2 cm3 HF, 2 cm3 HNO3 and 3 cm3 HClO4 into each vessel filled with sample. Close them tight and heat them for 8 hours at 185 °C.
Take the vessels from the hot plate, let cool and open them carefully. Put the open vessels back on the hot plate (190 °C) and let the acids smoke off until the samples are almost dry (right time: sample looks like a matt, viscous drop of rubber). Put the lids on the hotplate too, to boil away acid residues. Then add 1 cm3 of HNO3 and smoke off the acid again. Now take the vessels off the hotplate, add 5 cm3 of pure water and 1 cm3 of HNO3. Close them tight and heat them again for 2 hours at 140 °C.

Heat the vessels at 60-70 °C and transfer the clear digestion solution into a volumetric flask (25 cm3). Rinse vessels and lids thoroughly with pure water and pour it all into the volumetric flask. Fill up with pure water to the line measure and mix well. Pour a few cm3 of this solution into an acid-cleaned PE-bottle (30 cm3) and rinse the bottle with it. Do this twice. Then fill the rest of the sample solution into the bottle.
Clean the savillex vessels again according to 1.).

Samples can be measured with ICP-AES for the following parameters:
Na, K, Fe, Mn, Mg, Al; Sr, Ca, Ba, Li, Ti, Cr, Mo, Ni, Zn, Cu, V

This method is modified after the original method of Heinrich & Hermann (Praktikum der analytischen Geochemie; Springer-Lehrbuch).