1. Elemental analysis of foodstuff: sample preparation
and measurement techniques
Vasiliy V. Rosen, M.Sc., ZBM Laboratory
icpaes@gmail.com, www.rosen.r8.org
2. Introduction
What elements we determine in foodstuff and why?
Poisonous elements
3. Sample Preparation
• The sample has to be representative;
Sampling
danger of contamination.
• Homogenization / grinding; drying.
Danger of contamination and volatile
Sample
Pretreatment compounds loss.
• Sample preparation – different
Sample digestion methods.
Preparation
4. Sample Preparation
Microwave-
Dry Ashing Wet Ashing Assisted Digestion
The sample (0.5 g dry The sample (0.5 g dry wt.)
wt.) digested at 500 ° The sample (0.5 g dry
wt.) digested with digested with acid(s) in closed
C 4-6 h, then dissolved Teflon vessel in microwave
in acid(s) acid(s) in glass or Teflon
tube on the Hotplate or oven.
Digestion block
Advantages: cheap Advantages: No volatile
method; sample weight compounds lost (close digestion);
may be increased. Advantages: less loss contamination is minimized;
and contamination than digestion conditions are strong
in Dry Ashing Method; (temperature, acid and pressure);
high throughput. digestion is quick (about 30 min).
Disadvantages: loss of
volatile elements (Cl, As,
Se, Mo, Hg); Disadvantages: some acids
(cross)contamination; are extremely dangerous Disadvantages: expensive
formation of non-soluble (HClO4, HF); method is equipment; the throughput is
time-consuming. usually low.
silicates.
5. Sample Preparation
Wet Ashing: Instruments
Digestion Block
Microwave Laboratory
Oven “Ethos 1”
Teflon Vessel with Tº and pressure control
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6. Instrumentation
Atomic Spectrometry
Ion Emission
Atom Emission
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
7. 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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