Atomic Spectroscopy: Basic Principles and Instruments

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

www.rosen.r8.org

2011

ATOMIC SPECTROSCOPY:BASIC PRINCIPLES AND INSTRUMENTS

ATOMIC SPECTROSCOPY

Absorption Spectroscopy:

AAS

Emission Spectroscopy:

FES, ICP-AES(OES)

Mass Spectrometry

ATOMIC SPECTROSCOPY

After Boss. C.B. and Freden K.J. Concepts, Instrumentation and Techniques in

Inductively Coupled Plasma Optical Emission Spectrometry. 1997

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

ATOMIC SPECTROSCOPY

After Skoog D. Fundamentals of Analytical Chemistry, 2004, p. 844

Nebulizer converts the solution into a spray

Flame (or Plasma) causes the solvent to evaporate, leaving dry aerosol particles, then volatilizes the particles,

producing atomic, molecular and ionic species

FLAME EMISSION SPECTROSCOPY (FES)

Propane-butane flame ( 2000 – 3000 º C);

Optical filter is used to monitor for the selected emission wavelength

produced by the analyte;

Suitable for elements with low excitation energy (Na, K, Li, Rb and Ca).

FLAME EMISSION SPECTROSCOPY (FES)

Flame

Optic Filter

Nebulizer

Data Display

Flame Photometer M-410 (Sherwood Scientific, UK)

ATOMIC ABSORPTION SPECTROSCOPY (AAS)

Gases mixture flame (1800 – 4500 º C): air-propane, air-acetylene etc. ;

Atomic absorption spectrometry quantifies the absorption of ground state atoms in the

gaseous state ;

The atoms absorb ultraviolet or visible light and make transitions to higher electronic

energy levels . The analyte concentration is determined from the amount of absorption.


Elements detectable by AA are highlighted in pink


After G.Ma and G.W. Gonzales, http://www.cee.vt.edu

Operation principle of AAS

Light source – hollow cathode lamp. Each element has its own unique lamp.

Atomic cell – flame (gas mixture) or graphite furnance (accepts solutions, slurries, or

even solids).

Detector – photomultiplier.

http://www.cee.vt.edu/

ICP-AES

Inductively Coupled Plasma -

Atomic Emission Spectrometry

ATOMIC EMISSION SPECTROSCOPY

ICP-AES

Basics

Atomic emission spectroscopy measures the intensity of

light emitted by atoms or ions of the elements of interest at

specific wavelengths;

Inductively Coupled Plasma spectrometers use emission

spectroscopy to detect and quantify elements in a sample;

ICP-AES uses the argon plasma (6000-10000º C) for

atomization and excitation of the sample atoms;

ICP-AES determines approximately all of the elements

except gases and some non-metals (C, N, F, O, H).

ICP-AES SPECTROMETER ARCOS

Schematic diagram of the processes in the ICP

After Spectro Gmbh, Germany

ICP SPECTROMETER

Main Systems

Sample Introduction System: to deliver the sample solution to the plasma.

Consists of pump, nebulizer and spray chamber.

Plasma: to generate the signal. Plasma is forming in the torch from gas

argon.

Optics: to measure the signal.

Computer with appropriate software: for controlling the instrument and

measuring process.

ICP-AES: SAMPLE INTRODUCTION SYSTEM

Nebulizer (cross-flow)Spray Chamber

Argon Supply

To Waste

Torch with Plasma

Sample

Solution

Entrance

After Manning T.J. and Grow W.P., 1997

Inductively Coupled Plasma Source

A plasma is a hot, partially ionized

gas. It contains relatively high

concentrations of ions and electrons.

Argon ions, once formed in a plasma, are

capable of absorbing sufficient power from

an external source to maintain the

temperature at a level at which further

ionization sustains the plasma indefinitely.

The plasma temperature is about 10 000 K.

ICP-AES: PLASMA

Inductively Coupled Plasma Source

ICP-AES: PLASMA

ICP-AES: RADIAL (SOP) AND AXIAL (EOP)

SOP: Side-on-Plasma EOP: End-on-Plasma

more suitable for hard matrices (concentrated samples);

alkali metals (Na, K, Li) calibration is more linear;

less spectral interferences;

lower sensitivity (Limit-of-Detection is higher);

more suitable for light matrices;

alkali metals (Na, K, Li) calibration is less linear;

more spectral interferences;

higher sensitivity (Limit-of-Detection is lower);


ICP-AES: RADIAL (SOP) AND AXIAL (EOP)

ICP-AES: OPTICS


ICP-AES: SAMPLE PREPARATION

Most samples have to be prepared for analysis by ICP. Solid samples are solubilized.

Organic matter is "mineralized" i.e. converted to inorganic compounds.

Hot Plate

Microwave-assisted Digestion

Digestion Block

ICP-AES: CALIBRATION CURVE

ICP-AES: SPECTRAL INTERFERENCES

Au (gold) peak on 242.795 nm

ICP-AES: SPECTRAL INTERFERENCES

Au (gold) peak on 242.795 nm is

interfered by Mn 242.794 nm

Au (gold) peak on 267.595 nm is free

of Mn interference!

ICP-AES, FES AND AAS: APPLICATION

Clinical Analysis: metals in biological fluids (blood, urine);

Environmental Analysis: trace metals and other elements in waters, soils, plants,

composts and sludges;

Pharmaceuticals: traces of catalysts used; traces of poison metals (Cd, Pb etc);

Industry: trace metal analysis in raw materials; noble metals determination.

Forensic science: gunshot powder residue analysis, toxicological examination

( e.g., thallium (Tl) determination)

REFERENCES

Boss, C.B. and Freden, K.J. Concepts, Instrumentation and Techniques in Inductively

Coupled Plasma Optical Emission Spectrometry. 1997

Skoog, D. Fundamentals of Analytical Chemistry, 2004

Ma, G. and Gonzales, G.B. Flame Atomic Absorption Spectrometry.

http://www.cee.vt.edu

Manning T.J. and Grow W.P. Inductively Coupled Plasma Atomic Emission

Spectrometry. The Chemical Educator, v.1. N 2. 1997.

Lecture by Dr. Mordechay Shoenfeld, “ICP-AES”, Course 71106, Faculty of

Agriculture, HUJI. 2010.

http://www.cee.vt.edu/

Atomic Spectroscopy: Basic Principles and Instruments

Education

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