comparison of aqua regia digestion with reflux systems...
TRANSCRIPT
Comparison of aqua regia digestion with refluxsystems (ICP Forests manual) with aqua regiadigestion with microwave system (part of the newDIN EN ISO norm)
Nils König(Based on evaluations of Kainz and Stange)
NW-FVA
Northwest German Forest
Research Station
Meeting of the heads of the labs7./8. September, Pallanza, Italy
Introduction:- The reference method for aqua regia extraction is the reflux method (DIN ISO
11466).- Some years ago it was discussed at the meeting of the Heads of the Labs also to
accept microwave digestion. Results from France (see later) and Germany (German forest ring test) showed, that for different elements the results arenot comparable.
- The reason is that the aqua regia extract is no total digestion; there is a residueafter extraction. With microwave systems you get different digestion ratesdepending on time and energy. Therefore it is difficult to get comparable resultbetween different microwave systems.
- Compared to the reflux system the microwave system leads to higher resultsfor different parameters like Na, K, Al, Cr and others.
- In 2014 the DIN ISO 11466 was canceled; the new aqua regia norm is DIN EN 16174. This norm allows both methods: reflux system and microwave system.
- We have to decide if we allow only the reflux system or both methods for thefuture!
- 273 Samples - 10 types of soil and humus- 22 Elements (As, B, Ba, Be, Cd, Co, Cr,
Cu, Hg, Li, Mn, Mo, Ni, Pb, Se, Sb, Sn, Sr, Tl, U, V, Zn)
- => 220 combinations Element/Soiltype
Soil types:- Fen peat- Humus layer- Sand- Loam- Loess (Ah, B)- Loess (eAh, Cc)- Haugh- Alluvial clay- Substrates of clay shale- Substrates of copper shale
Comparison of trace element analysis from aqa regia reflux- and microwavedigestion of 273 soil samples
Results of Regression anlysis:- 181 linear regressions, but only 16 of them with regression
coefficients between 0,95 and 1,05 - => 165 linear regressions with regression coefficients
between 0,18 and 1,39 - 18 quadratic or cubic regressions- 21 combinations with no regression
Cu
0,84
0,85
1,390,85
0,86
0,78
0,75
0,90
Humus layer
Substrates ofcopper shale
Substrates ofclay shale
loamsand
Alluvial clayHaughFen peat
Loess eAh, CcLoess (Ah, B)
Humus layerFen peatSandLoamLoess (Ah, B)Loess (eAh, Cc)HaughAlluvial claySubstrates of clayshaleSubstrates ofcopper shale
Pb
0,84
0,850,45
nonlinear
nonlinear
nonlinear
nonlinear1,18
nonlinear
Fen peatHumus layerSandLoamLoess (Ah, B)Loess (eAh, Cc)HaughAlluvial claySubstrates of clayshaleSubstrates ofcopper shale
Cd
0,80
0,09
0,63
0,80
0,67
0,86
Fen peatHumus layerSandLoamLoess (Ah, B)Loess (eAh, Cc)HaughAlluvial claySubstrates of clayshaleSubstrates ofcopper shale
Zn
0,80
0,840,90
0,90
Fen peatHumus layerSandLoamLoess (Ah, B)Loess (eAh, Cc)HaughAlluvial claySubstrates of clayshaleSubstrates ofcopper shale
Cr
0,58
0,48
0,72
0,56
0,72
0,670,66
0,720,66
0,83
Fen peatHumus layerSandLoamLoess (Ah, B)Loess (eAh, Cc)HaughAlluvial claySubstrates of clayshaleSubstrates ofcopper shale
Ni
0,76
0,78
0,86
0,83
0,87
0,74
0,83
Fen peatHumus layerSandLoamLoess (Ah, B)Loess (eAh, Cc)HaughAlluvial claySubstrates of clayshaleSubstrates ofcopper shale
Proposal:The results of the aqua regia digestion withreflux systems are not comparable with thoseof microwave systems.Therefore the method with reflux systemshould be the mandatory method for aquaregia digestion in the ICP Forests manual!