Elemental Analysis of Plants using ICP-OES(2023)

The fundamentals of elemental analysis pertaining to plant materials will be elucidated. The lecture will delve into the intricacies of the sampling process, sample pre-treatment, and the preparation of plant material samples for subsequent analysis via ICP.

1. Dr Vasiliy V. Rosen
[email protected]
The Plasma Spectrochemistry Laboratory
The Scientific Service Core Facility
The Faculty of Agriculture
The Hebrew University of Jerusalem
July 4, 2023
Elemental analysis of plant material by
ICP-OES/MS

2. AGENDA
Introduction to ICP-OES/MS:
Principles and Instrumentation

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

4. The levels of major elements and micronutrients in mature
leaf tissue (after Munson R., 1997)
4

5. Sampling
Decontamination
Drying
Grinding
Non-representative sample
Remained surface pollutants
Loss of volatile compounds
and weight
Contamination by mill blades
(Fe, Ni, Cr, Mo…)
ProcedureDanger
Storage
Contamination by wrong
package(Sn from can; B, Si,
etc – from Pyrex Glass)
Sample
naming
Complicated names lead to
human mistake

6. Dry Ashing
Equipment
Porcelain or platinum crucible
Electric or microwave muffle

7. Open Wet Digestion
Hot-block open
digestion
Digestion on aluminum block in glass tubes with HNO3

8. Oven cavity
Rotor
Teflon vessel
Closed Microwave-assisted Wet Digestion

9. Closed digestionOpen digestion
Max. temperature 200 – 300 °CMax. temperature limited by
solution boiling point
Low acid consumptionHigh acid consumption
Lower sample weightHigher sample weight
No loss of volatile elementsLoss of volatile elements (Hg, I)
Risk of contamination from
digestion vessels
Risk of contamination from air and
cross-contamination
Digestion duration: 15-60 minDigestion duration: 2 – 15 h (or
even more)

10. Matrices and Matrix Effect
HNO3 HCl
HF
https://www.inorganicventures.com/

11. Cd, 1 mg/L, in weak acid
Cd, 1 mg/L, in base
Analyte concentrations are equal, but intensities are different
Matrices and Matrix Effect

12. Dry Ashing
The sample (0.5 g dry
wt.) digested at 500 °
C 4-6 h, then
dissolved in acid(s)
Advantages: cheap
method; sample
weight may be
increased.
Disadvantages: loss of
volatile elements (Cl, As,
Se, Mo, Hg); (cross)-
contamination; formation
of non-soluble silicates.
Wet Digestion
(Hot-Block)
The sample (0.5 g dry
wt.) digested with
acid(s) in glass or
Teflon tube on the
Hotplate or Digestion
block
Advantages: less loss
and contamination than
in Dry Ashing Method;
high throughput.
Disadvantages: some
acids are extremely
dangerous (HClO4, HF);
method is time-consuming.
Wet Digestion with
Microwave Oven
The sample (0.5 g dry wt.)
digested with acid(s) in closed
Teflon vessel in microwave
oven.
Advantages: No volatile
compounds lost (closed
digestion); contamination is
minimized; digestion conditions
are strong (temperature, acid
and pressure); digestion is quick
(about 30 min).
Disadvantages: expensive
equipment; the throughput is
usually low.

13. Introduction to ICP-OES/MS: Principles and Instrumentation
This is how AI thinks the ICP instrument looks like

14. ICP-OES
720/725, Agilent
USA
Arcos, Spectro,
Germany
Analytik Jena,
Germany
iCAP 7000 Plus,
Thermo Scientific
USA
Optima,
Perkin-Elmer, USA
ICPE 9800,
Shimadzu, Japan
Introduction to ICP-OES/MS: Principles and Instrumentation
This is what the ICP-OES really looks

15. The Plasma Spectrochemistry (ICP) Lab
1989
1994
2007
2007
2018
Radial, Sequential Axial, Simultaneous
Axial, Simultaneous
Axial, Simultaneous
Radial, Simultaneous
Dual-view,
Sequential
Mass-Spectrometer (ICP-MS)
Introduction to ICP-OES/MS: Principles and Instrumentation

16. Ernest
Rutherford
(1871 – 1937)
Niels Bohr
(1885 – 1962)
Introduction to ICP-OES/MS: Principles and Instrumentation

17. Introduction to ICP-OES/MS: Principles and Instrumentation
This is how AI perceives the
appearance of the argon
plasma
This is what the
argon plasma really
looks like

18. Energy absorption
by ground-state
atoms
Atomic Absorption
(AA, GFAA)
Singly charged
ion formation
ICP-MS
Energy emission by
excited atoms and
ions
Adapted from Boss and Freeden, 1997
Flame photometry,
ICP-OES
Introduction to ICP-OES/MS: Principles and Instrumentation
sampling
disposal
argon
argon
argon

19. T, °C of the excitation source
Instrument LOQ
Low High
High Low
Introduction to ICP-OES/MS: Principles and Instrumentation

20. Introduction to ICP-OES/MS: Principles and Instrumentation

21. Introduction to ICP-OES/MS: Principles and Instrumentation
ICP-OES vs MS :
Adjustment
Ion Optics
Scan settings
Element selection
ICP-OES

22. ICP-OES: Cd 224 nm
LOQ 0.2 µg/L (ppb)
Introduction to ICP-OES/MS: Principles and Instrumentation
RSD = 3.91 %
RSD = 0.76 %
LOQ 0.0054
µg/L (ppb)

23. Fresh animal liver,
digested in HNO
3
(0.5 g in 25 mL)
Introduction to ICP-OES/MS: Principles and Instrumentation

24. Method Advantages Method Limitations
❑ Multi-element ❑ Adjustment of measurement
conditions; Spectral
Interference
❑ High sensitivity = Low
LOQ
❑ Sample preparation
❑ Wide linear dynamic
range
❑ Matrix effect and Spectral
Interference
Introduction to ICP-OES/MS: Principles and Instrumentation

25. ❖Objects: soil, plants, waters,
tissues, food, and drinks
❖Nutrient analysis
❖Trace elements analysis (including
toxic elements)
❖ Food authentication (geographical
origin through mineral profiling
and/or isotope ratio analysis)
❖Speciation (HPLC+ICP-MS)
Introduction to ICP-OES/MS: Principles and Instrumentation

26. Brown seaweeds (Kombu and Wakame) display a greater capacity to accumulate total As and iodine than the red
seaweed (Nori)
Rosen, Shimshoni, et al, 2023 (unpublished)
Introduction to ICP-OES/MS: Principles and Instrumentation

27. Quality Control in ICP-OES/MS analysis
(after Munson R., 1997)
Ycps = a*Xmg/L+b
The slope isa measure of sensitivity:
how much the signal changes for a
change in concentration.
Ycps = a*Xmg/L+b
a
CaKCuPbCr

28. Quality Control in ICP-OES/MS analysis
Concentration Units

29. Accuracy is how close a
measured value is to theactual
(true) value.
Precision is how close the measured
values areto each other.
Quality Control in ICP-OES/MS analysis
LOQ is the lowest concentration at
which a measurement is quantitatively
meaningful (Mitra, 2003)
LOD is the concentration at
which we can decide whether an
element is present or not
(Thomsen, 2003)

30. Quality Control in ICP-OES/MS analysis
The combined uncertainty Uc in analytical
measurement is a single numerical value that
represents the total estimation of uncertainty,
taking into account various sources of error and
variability associated with the measurement process.
Uncertainty
Uexp = Uc*k, k is coverage factor
(appr. 2 for CI=95%)

31. Take home message
•Choose your spectrometry
technique/instrument based
on your research goals.
•Always remember the sample
pre-treatment and preparation
steps.
•Check the reliability of your
analysis