EQUIPMENT

1. ICP Emission Spectrograph
2. Autosampler
3. Digital Dilutor

REAGENTS

1. 3N Hydrochloric Acid: Dilute 250 mL of concentrated hydrochloric acid to 1 liter using deionized water and mix well.
2. Nitric Acid: HNO₃

STANDARDS

1. Stock Solutions: Use 1000 ppm certified, NIST traceable, plasma grade standards for the 16 listed elements.
2. Instrument Calibration Standards:
   1. WAT 1 - deionized water
   2. WAT 2 - Mn, Fe, Al, B, Cu, Zn, Na, Pb, Cd, Ni, Cr, Mo - Pipet 10 mL of stock solution of each element into a 1 liter volumetric flask. Add 5 mL of nitric acid. Dilute to volume with deionized water and mix well.
   3. PLN2 - P, K, Ca, Mg - Pipet the designated mL of stock solution into a 1 liter volumetric flask. Add 5 mL of nitric acid. Dilute to volume with deionized water and mix well.

      Element	Stock Solution mL	Final Concentration ppm	Instrument Readout %
      P	10	10	1.00
      K	50	50	5.00
      Ca	20	20	2.00
      Mg	10	10	1.00

3. Instrument Calibration Verification Standards:
   1. A second set of calibration standards obtained from a different manufacturer.

SAMPLE PREPARATION

1. Dry Ash
   1. Weigh 1g sample into a 10 mL glazed, high-form porcelain crucible.
   2. Ash in a muffle furnace for 4 hours at 500 C.
   3. Let cool and add 5 mL of 3N HCI.
   4. Place on a hot plate and boil gently for 5 minutes.
   5. Let cool and transfer to a 100 mL volumetric flask. Dilute to volume with deionized water and mix well. Use this solution for the analysis of Mn, Fe, Al, B, Cu, Zn, Na, Pb, Cd, Ni, Cr and Mo.
   6. Dilute the solution obtained in 1e. one to ten with deionized water using a digital dilutor. Use this solution for the analysis of P, K, Ca and Mg.

ICP PROCEDURE

1. Set up and operate the ICP Emission Spectrograph in accordance with manufacturer's specifications.
2. Mn, Fe, Al, B, Cu, Zn, Na, Pb, Cd, Ni, Cr, Mo analysis.
   1. Choose PLANT from the method menu.
   2. Calibrate the instrument using WAT1 and WAT2 instrument calibration standards.
   3. Analyze the sample digests obtained in 1e. of the sample preparation section.
3. P, K, Ca, Mg analysis.
   1. Choose PLANTDIL from the method menu.
   2. Calibrate the instrument using WAT1 and PLN2 instrument calibration standards.
   3. Analyze the digests obtained in 1f. of the sample preparation section.

QUALITY CONTROL

1. Following calibration, analyze one high instrument calibration standard, one instrument calibration verification standard and one quality control sample.
   1. Instrument Calibration Standard: Values must be within 3% of the known value for K and Mo. All other elements must be within 2% of the known value.
   2. Instrument Calibration Verification Standard: Values must be within 10% of the certified values.
   3. Quality Control Sample: Values for all elements must be within limits established by the Extension chemist.
2. Analyze a high instrument calibration standard after each tenth sample and at the end of the set of samples.
   1. Values must be within 8% of the known values.
   2. If any of the values are greater than 8% from the known values recalibrate the instrument and begin sample analysis from the last "good" instrument calibration standard.
3. Prepare one duplicate sample for each 10 samples. If the set contains less than 10 samples, prepare one duplicate per set.
   1. Results on the duplicate sample should agree within 20% of the average value of the two samples.

REFERENCES

1. Isaac, R.A. and W.C. Johnson, 1985, Elemental Analysis of Plant Tissue by Plasma Emission Spectroscopy: Collaborative Study. JAOAC. 68(3), pp 499-505.
2. AOAC Official Method 985.01, in Official Methods of Analysis of AOAC International, 16th edition, Volume I Chapter 3, p. 4.
3. AOAC Official Method 968.08 D(a), in Official Methods of Analysis of AOAC International, 16th edition, Volume I Chapter 4, p. 23.