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Wet Ashing Procedure for using HNO3+30%H202 for Determining P, K, Ca, Mg, Zn, Mn, Cu, Fe, S

Reagents

  1. CONCENTRATED NITRIC ACID - HN03
  2. 30% HYDROGEN PEROXIDE - H202 (stored in refrigerator)

Apparatus

  1. DIGESTION BLOCK
  2. 100 mL STRAIGHT DIGESTION TUBES - CALIBRATED AT 50 mL.
  3. SILICONE-RUBBER STOPPERS
  4. PIPET DISPENSERS
  5. TEST TUBES FOR ICP AUTOSAMPLER

Procedure

  1. Weigh 0.5000 + 0.0005 g into labeled 100 mL digestion tubes.
  2. 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.
  3. 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.
  4. Remove samples from block and let cool for a few minutes.
  5. 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.
  6. Heat for 1 h. Record ending heat time on board.
  7. Repeat steps 4-6.
  8. 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.
  9. Remove dry samples one by one from the block adding 10 mL of 1:10 HN03. Set samples in second rack under hood.
  10. Let samples cool for 15 minutes.
  11. Dilute to 50 mL with deionized water.
  12. Stopper and shake vigorously.
  13. Transfer aliquot to labeled ICP tubes.
  14. 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.

Quality Control

  1. 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.
  2. Save solution and run daily on ICP with standards and samples.
  3. Check ICP standards at midpoints and end of run.

References

  1. Jones & Case. Analyzing plant tissue samples.
  2. Jones, J. B., Wolf, B., and Mills, H. A. Plant Analysis Handbook. Micro-Macro Publishing, Inc. p.197.
  3. Plank, C. O. Plant Analysis Reference Procedures for the Southern Region of the United States. Southern Cooperative Series Bulletin 368, May 1992. p.9.