Wet Ashing Procedure for using HNO3+30%H202 for Determining P, K, Ca, Mg, Zn, Mn, Cu, Fe, S
- CONCENTRATED NITRIC ACID - HN03
- 30% HYDROGEN PEROXIDE - H202 (stored in refrigerator)
- DIGESTION BLOCK
- 100 mL STRAIGHT DIGESTION TUBES - CALIBRATED AT 50 mL.
- SILICONE-RUBBER STOPPERS
- PIPET DISPENSERS
- TEST TUBES FOR ICP AUTOSAMPLER
- Weigh 0.5000 + 0.0005 g into labeled 100 mL digestion tubes.
- Under hood, add 5 mL conc. HNO3 rinsing down sides during the addition. Predigest samples for 30 min. by leaving under hood with no heat.
- Place digestion tubes on digestion block and heat at 125oC for 1 and 1/2 h. Make sure front and back shields are on rack. Close sash. Record ending heat time on board.
- Remove samples from block and let cool for a few minutes.
- Add 3 mL 30% H202 slowly to each sample rinsing down sides during the addition. Allow frothing to settle. Place tubes back on block. Close sash.
- Heat for 1 h. Record ending heat time on board.
- Repeat steps 4-6.
- Increase block temperature to 200oC. Heat for 1 h. Record ending heat time on board. This should bring the samples to dryness. If sample is still wet, heat a little longer.
- Remove dry samples one by one from the block adding 10 mL of 1:10 HN03. Set samples in second rack under hood.
- Let samples cool for 15 minutes.
- Dilute to 50 mL with deionized water.
- Stopper and shake vigorously.
- Transfer aliquot to labeled ICP tubes.
- For P, K, Ca, Mg, and S move decimal on ICP sheet two places to the left and record 2 decimals. For Zn, Cu, Mn, and Fe record values directly from ICP sheet with no decimals.
- Ash an NIST peach sample on Monday along with samples. Prior to use, the NIST peach sample is dried at 80oC and stored in the desiccator.
- Save solution and run daily on ICP with standards and samples.
- Check ICP standards at midpoints and end of run.
- Jones & Case. Analyzing plant tissue samples.
- Jones, J. B., Wolf, B., and Mills, H. A. Plant Analysis Handbook. Micro-Macro Publishing, Inc. p.197.
- Plank, C. O. Plant Analysis Reference Procedures for the Southern Region of the United States. Southern Cooperative Series Bulletin 368, May 1992. p.9.