elemen analysis of foodstuff
DESCRIPTION
TRANSCRIPT
Elemental analysis of foodstuff: sample preparation
and measurement techniques
Vasiliy V. Rosen, M.Sc., ZBM Laboratory
.org8, [email protected]
What elements we determine in foodstuff and why?
Poisonous elements
Introduction
Sample Preparation
Sampling
• The sample has to be representative; danger of contamination.
Sample Pretreatment
• Homogenization / grinding; drying. Danger of contamination and volatile compounds loss.
Sample Preparation
• Sample preparation – different digestion methods.
Sample Preparation
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 Ashing
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.
Microwave-Assisted Digestion
The sample (0.5 g dry wt.) digested with acid(s) in closed
Teflon vessel in microwave oven.
Advantages: No volatile compounds lost (close 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.
Sample Preparation
Wet Ashing: Instruments Digestion Block
Microwave Laboratory
Oven “Ethos 1”
Teflon Vessel with Tº and pressure control
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Atomic Spectrometry
E – energy difference between two levels;
h – Plank’s constant, 6.626068 × 10-34 m2kg/s;
c – speed of light, 299 792 458 m/s;
λ – wavelenght, nm
Ion Emission
Atom Emission
Instrumentation
Instrumentation
ICP-AES: Inductively Coupled Plasma Atomic Emission
Spectrometer
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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ICP-AES Arcos
Atomic Spectrometry
Absorption Spectrometry:
Atomic Absorption Spectrometer
Emission Spectrometry:
Flame Photometer, ICP-AES(OES)
Mass Spectrometry: ICP-MS
ZBM Laboratory Website
/departments.agri.huji.ac.il/zabamhttp://