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Plant Dry Ash/Acid Extraction for Ca, K, and Mg

Last revised July 22, 1997

Page contents (click to skip down):

* [Equipment]
* [Extractant solution]
* [Procedure]
* [Post-analysis calculations]


1) 30 ml high-form crucibles and caps

2) Scintillation vials and caps

3) Laundry marker and graphite pencil

4) Plant standard material, e.g. NBS 1572 citrus leaves

5) Reservoir bottle of deionized water (diH2O) with 20 ml repipettor

6) Stock bottle of extraction acid with 10 ml repipettor

Aqua regia extraction acid
1) in 400 ml cylinder, add

2) transfer to 1000 ml volumetric

3) bring to volume with diH2O

4) invert to mix; allow to stand; recheck volume

1) Dry sample 70 degrees C, 24 hours

2) Grind sample in Spex mill

3) Wash crucibles and caps in 10% HNO3 and muffle at 750 degrees C for 2 hours.

4) Label crucibles on bottom with graphite pencil

5) Weigh out ~0.5000 g of ground sample into each crucible using Mettler (four-place) balance. Record sample code and weight.

6) Place ~.5g samples in muffle furnace. Bring to ashing temperature (450 degrees C) slowly (90 minutes.) Ash for four hours. Allow crucibles to cool.

7) Set out as many scintillation vials as there are crucibles of ash to extract. Rinse extraction vials (sciltillation vials) with ~3ml of extraction acid. Transfer ash pellet to extraction vial with 10.0 ml extraction acid as follows:

8) Set out a second set of scintillation vials, as many as the first.

9) Consult the detailed atomic absorption method for each particular analyte. Determine the linear range of concentrations for the wavelength to be used and devise an appropriate sample dilution scheme.

10) Measure diluted extract by atomic absorption spectrophotometry. Calculate dry sample content from measured dilute extract value.

11) As recovery check, ash known NBS plant standards in parallel to unknowns.


Allen, S. E., et al. 1974.
Chemical Analysis of Ecological Materials. John Wiley and Sons, New York.

Jones, J. B. Jr., B. Wolf and H. A. Mills. 1990.
Organic matter destruction procedures. pp.195-6. In Plant Analysis Handbook. Micro-Macro Publishing, Inc., Athens, GA.

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