1. Plant Mineral
Analysis
The Hebrew University of Jerusalem
Faculty of Agricultural, Food and Environmental Quality Sciences
Rehovot, Israel
Vasiliy V. Rosen, M.Sc., ZBM Laboratory
icpaes@gmail.com, www.rosen.r8.org 1

2. 1. Introduction
After Jones and Case, 1990 2

3. Introduction
What do we analyze when
we are analyzing plants?
 Essential elements (major elements
and micronutrients)
 Toxic elements
3

4. Introduction
The role of chemical elements in plants
(adopted from Munson R., 1997, and Macnicol R., 1984)
Essential
Major Micronutrients Toxic
Carbon (C) Boron (B), Silver (Ag)
Oxygen (O) Chlorine (Cl) Aluminium (Al)
Hydrogen (H) Copper (Cu) Arsenic (As)
Iron (Fe) Barium (Ba)
Nitrogen (N) Manganese (Mn) Berillium (Be)
Phosphorus (P) Molybdenum (Mo) Cadmium (Cd)
Potassium (K) Zinc (Zn) Mercury (Hg)
Nickel (Ni) Lead (Pb)
Sodium (Na) Cobalt (Co) Lithium (Li)
Silica (Si) Chromium (Cr)
Calcium (Ca) Selenium (Se) And all
Magnesium (Mg) Vanadium (V) micronutrients at
Sulfur (S) critical
concentration
4

5. Introduction
The levels of major elements and micronutrients in mature
leaf tissue (after Munson R., 1997)
5

6. Introduction
Concentration Units
Major Elements
% of dry weight
grams per kilogram (g/kg)
Micronutrients and Toxic Elements
parts per million (ppm) = 10-6 = mg/kg
parts per billion (ppb) = 10-9 = µg/kg
6

7. 2. Analytical
Chemistry Basics
Qualitative and quantitative analysis
Calibration and matrix
Limit of Detection and Limit of Quantitation
Accuracy and Precision
7

8. Analytical Chemistry Basics
Qualitative and
Quantitative Analysis
ICP : ATOMIC EMISSION SPECTROMETRY
AS QUALITATIVE ANALYSIS
Is there the analyte in the
sample?
Qualitative
Analysis
If yes, which one?
ICP: ATOMIC EMISSION SPECTROMETRY
AS QUANTITATIVE ANALYSIS
How much analyte is Quantitative Unknown Sample
there? Analysis
8

9. Analytical Chemistry Basics
Calibration Curve
The calibration curve is a plot of detector response as a function of concentration
(after Munson R., 1997)
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10. Analytical Chemistry Basics
Matrix
Cd, 1 mg/L, in weak acid
Cd, 1 mg/L, in base
Analyte concentrations are equal, but intensities are different
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11. Analytical Chemistry Basics
Limit of Limit of
Detection Quantitation
LOD is the concentration at which LOQ is the lowest concentration at
we can decide whether an element which a measurement is
is present or not (Thomsen, 2003) quantitatively meaningful (Mitra,
2003)
LOQ = 10*SDblank
LOD = 3*SDblank or
LOQ = 3.3*LOD
11

12. Analytical Chemistry Basics
Accuracy and Precision
Accuracy is how close a Precision is how close the
measured value is to measured values are to each
the actual (true) value. other.
after http://www.mathsisfun.com12

13. 3. Plant Samples
Pretreatment
Sampling Procedure
Decontamination
Drying
Grinding
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14. Plant Samples Pretreatment
Sampling Procedure
What to sample?
Mature leaves exposed to full
sunlight just below the growing
tip on main branches or stems are
usually preferred (Jones B., 2003)
How much material to sample?
Depending on plant and
investigation goal – usually tens
(20-100) leaves or small plants
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15. Plant Samples Pretreatment
Sampling Procedure
What DO NOT sample?
After Jones B., 2003
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16. Plant Samples Pretreatment
Decontamination
Contaminants Washing procedure
 Soil and dust particles: Fe, Al, Si  Tap water
and Mg. Calcareous soils – Ca.  Detergent solution , non-phosphate
 Liquide fungicides – Cu. (0.1 to 0.3%)
 Nutrition solution (fertilizer) –  Weak acid (HNO3 1%) – optional
NPK, essential elements.  Deionized water
 Investigator’s fingers - Cl
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17. Plant Samples Pretreatment
Drying
 Put washed fresh samples in paper bag (or envelope). Do not use plastic
bag since plastic retains moisture, thus accelerating respiration and decay.
 Refrigerate (4-5º C) or air-dry the fresh samples if delivery time to
laboratory is more than 12 h.
Fresh plant samples should be dried at 65-80º C in a ventilated oven at least
24 h (usually 2-3 days) to stop the enzymatic activity. Higher drying
temperature can affect the dry weight.
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18. Plant Samples Pretreatment
Grinding:particle size reduction
 Different types of mills are available: Jaw, Rotor, Cutting, Knife, Mortar,
Discs, Planetary Ball mills.
 Material used: stainless steel, Zr2O, agate, porcelain.
 Possible contaminants: Fe, Zn, Al, Na .
Planetary Ball Mill Rotor Mill 18

19. Plant Samples Pretreatment
Grinding: particle size units
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20. 4. Sample
Preparation
Techniques
Dry Ashing
Wet Ashing, Microwave-assisted acid digestion
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21. Sample Preparation Techniques
Dry Ashing
 Analytes: B, Ca, Cu, Fe, Mg, Mn, P (but wet ashing is more recommended), K, Na, Zn.
 Procedure: 500 mg of dry sample digested in porcelain crucible in muffle
oven during 4-6 h at 500º C . The ash dissolved in 1 N HCl.
 Element determination: AAS, ICP-AES, UV-VIS (B, P).
 Possible problems: easily volatilized elements are lost (Cl, S, As, Hg, Se);
boron (B) may be also volatilized; insoluble silicates are formed and decreased
recovery of other constituents, mainly trace elements; ashing temperature higher
than 500º C may decrease recovery of Al, B, Cu, Fe, K, Mn.
After Miller, 1998
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22. Sample Preparation Techniques
Dry Ashing: Tips and Tricks
 If an ashing aid is needed, add either 5 mL HNO3, or 5 mL 7% Mg(NO3)2*6H2O
prior to muffel digestion. Dry on a hotplate and then digest.
 To prevent Cl loss do the following: mix the sample with lime (CaO, ¼ of the
sample weight) and deionized water to make a thin paste. Dry the mixture, digest at
500º C, dissolve ash with HNO3 or H2SO4 (not HCl !!!)
 The following acid mixtures may be used for ash dissolution: 300 mL HCl and
100 mL HNO3 in 1000 mL deionized water; Aqua Regia (concentrated HNO3 :HCL
1:3), HNO3 alone (less corrosive for for metal parts of analytical instruments).
After Piper, 1950; Jones, 2001; personal experience
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23. Sample Preparation Techniques
Wet Ashing
 Analytes: B (teflon vessels only), Ca, Cu, Fe, Mg, Mn, Mo, P, K, Se, Na, S, Zn,
trace elements.
 Procedure: 500 mg of dry sample digested with some combination of four
acids: HNO3, HCl, H2SO4 and HClO4, with optional addition of H2O2. Digestion
is carried out in beakers on hot plate, in glass tubes on block, in open or closed
teflon vessels in microwave oven.
 Element determination: AAS, ICP-AES, UV-VIS ( P, S).
 Possible problems: HClO4 may react with organic material and result in an
explosion; in low Ca tissues CaSO4 may precipitate when H2SO4 is used;
contamination with B and Si when glass digestion tubes are used; contamination
with elements adsorbed by teflon.
After Piper, 1950; Jones, 2001; Miller,
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1998; personal experience

24. Sample Preparation Techniques
Wet Ashing: Instruments
Digestion Block
Microwave Laboratory
Oven “Ethos 1”
Teflon Vessel with Tº and pressure control
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25. Sample Preparation Techniques
Wet Ashing: Tips and Tricks
 Samples with added acid(s) should be predigested at room temperature overnight
to avoid violent reaction at the start of heating. This is especially important for closed
microwave-assisted digestion.
 H2O2 often contains Sn (tin) as a stabilizer. Do not use H2O2 if Sn is analyte.
 Wet ashing on block has a high throughput, but closed vessel microwave-assisted
digestion demonstrates less element loss and contaminations, and it is less time-
consuming.
 Increase sample weight for the determination of trace metals (Cd, Cr, Ba etc) to 1 g.
Add internal standard (element that does not exist in your samples, Y or Sc) at the
start of digestion to control preparation process quality.
After Jones, 2001; Miller, 1998; personal
experience
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26. 5. Instrumentation
used in plant
analysis
X-ray fluorescence spectroscopy (XRF)
Atomic absorption spectroscopy (AA)
Flame Emission Spectrometry (Flame Photometry)
ICP-AES/MS
UV-VIS Spectrophotometry
Elemental Analyzer, Chloride Analyzer, Ion
Selective Electrodes etc.
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27. Instrumentation
XRF: X-Ray Fluorescence Spectroscopy
 Principle: Excitation of the sample by an X-ray source,
secondary radiation measurement.
 Elements: with atomic number >8.
 LOD: 100 mg/kg for major elements (light) and 1 mg/kg
for traces (heavy).
 Sample Preparation: drying, fine grinding and pressing.
 Advantages: simple sample preparation; low cost;
portable instrument.
 Disadvantages: spectral interferences; method is matrix-
dependent.
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28. Instrumentation
AAS: Atomic Absorption Spectroscopy
 Principle: quantifies the absorption of ground state atoms in the
gaseous phase; the analyte concentration is determined by optics from
the amount of light absorption.
Elements: all the metals.
 LOD: some µg/L (ppb), less than 1 ppb – with graphite furnace.
 Sample Preparation: dry and wet digestion methods.
 Advantages: highly specific for an element; minimum spectral
interferences; low-cost gases used (air+acetylene).
 Disadvantages: ionization enhancement of the signal for elements
easily ionized when operating in the absorption mode, especially Na and
K; matrix interferences caused by viscosity or specific gravity
differences between sample and reference standard; elements analyzed
one at a time.
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29. Instrumentation
Flame Emission Spectroscopy (Flame Photometry)
 Principle: excitation of ground-state atoms by propane-
butane flame (2000-3000 ºC), electron loss by analyte atom,
when electron is recaptured, emission light of characteristic
wavelength is emitted.
 Elements: Na and K; Li, Rb, Cs, Ca.
 LOD: about 0.1-0.5 mg/L.
 Sample Preparation: dry and wet digestion methods.
 Advantages: simple, quick and inexpensive analysis; wide
dynamic range (0-100 mg/L); ideal for elements with low
excitation potential (Na and K)
 Disadvantages: only some elements may be determined;
elements analyzed one at a time.
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30. Instrumentation
ICP-AES: Inductively Coupled Plasma Atomic Emission
Spectrometry
 Principle: electrons of excited atoms return to their ground-state and emit electromagnetic
radiation (light) at the wavelengths that are characteristic of the atoms that are excited. Argon
plasma is the source of excitation (about 10 000 K).
 Elements: all the elements except gases and some non-metals (C, N, F, O, H).
 LOD: some µg/L (ppb), less than 1 ppb – with MS detector (ICP-MS technology).
 Sample Preparation: dry and wet digestion methods.
 Advantages: minimum chemical interferences; four to six orders of magnitude in linearity
of intensity versus concentration; multielement capabilities; rapid analysis; accurate and
precise analysis; detection limits equal to or better than AAS for many elements.
 Disadvantages: occurrence of spectral interferences; use of argon gas which can be
expensive; instrument is relatively expensive to purchase.
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31. Instrumentation
UV-VIS Spectrophotometry
Principle
Instrument
b
Applications:
 Kjeldal digestion for total N: determination of NH4 and P in digestate;
 Mo and B after dry or wet ashing;
NO3 in water extracts;
Metals: Cu, Fe, Mg, Mn and Zn determination.
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32. Instrumentation
Just a few words about….
Elemental Analyzer Chloride Analyzer Ion-selective Electrode
Elements: C,H,N,S,O. Elements: Cl Elements: K+, Cl-, NO3-
Digests finely grinded dry Titrates Cl- with Ag2+. Measures an electrical
samples. Readout range: 10-999 potential on the ion
mg Cl/L exchanger that is selective
to analyte ion.
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33. Last but not least…
First Law of Laboratory Work:
Hot glass looks exactly the same as cold glass
Thank you for your attention
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