Elemental analysis of foodstuff: sample preparation

and measurement techniques

Vasiliy V. Rosen, M.Sc., ZBM Laboratory

.org8, www.rosen.ricpaes@gmail.com

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://