Wet Ashing Procedure for Determining P, K, Ca, Mg, Zn, Mn, Cu, Fe, S using HN03 AND HCL04
(This procedure is not recommended for ICP analysis.)
- CONCENTRATED NITRIC ACID - HNO3
- 70% PERCHLORIC ACID - HCl04
- PERCHLORIC ACID FUME HOOD
- HOT PLATE*
- 150 mL BEAKERS
- WATCH GLASS COVERS
- 100 mL VOLUMETRIC FLASKS
- Weigh 1.000 g sample into 150 mL beakers.
- Add 10 mL conc. HNO3.
- Place beakers on hot plate and cover with watch glass covers and heat at 4.5 until all organic matter is digested - clear yellow. Remove watch glasses and continue to heat to reduce volume to near dryness (do not bring to dryness).
- Remove beakers from hot plate and add 5 mL of 70% HCl04.
- Return to hot plate and digest at 5.5 until white fumes appear and solution is clear (silicates will be in bottom). If S is to be determined, allow to fume a minimum of 1 1/2 h.
- Remove beakers from hot plate. While still under the hood add about 10 mL of dH20 to beakers to cool samples and stop fuming.
- Quantitatively transfer sample into 100 mL volumetric flask with dH2O - cool to room temperature.
- Dilute to volume, stopper and shake flasks.
- Allow silicates to settle and transfer aliquot to test tubes.
*The setting 4.5 on the hot plate corresponds to about 100oC, the setting 5.5 corresponds to about 200-250oC.
- Ellis, R. J., Jr., J. J. Hanway, G. Holmgren, D. R. Kenney, and O. W. Bidwell. Sampling and Analysis of Soils, Plants, Waste Waters, and Sludge-Suggested Standardization and Methodology. Agricultural Exp. Station, Kansas State University, Manhattan, Res. Pub. 170. North Central Regional Pub. 230.
- Haynes, R. J. 1980. A Comparison of Two Modified Kjeldahl Digestion Techniques for Multi-Element Plant Analysis with Conventional Wet and Dry Ashing Methods. Comm. in Soil Sci. and Plant Anal. 11(5): 459-467.