Basic principles of atomic spectroscopyAAS

Slide 1 Vasiliy V Rosen, M Sc , ZBM Analytical Laboratory www rosen r8 org 2011 ATOMIC SPECTROSCOPY Absorption Spectroscopy AAS Emission Spectroscopy FES, ICP AES(OES) Mass Spectrometry ATOMIC SPECTRO.

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

www.rosen.r8.org

2011

ATOMIC SPECTROSCOPY

Absorption Spectroscopy:

AAS

Emission Spectroscopy: FES, ICP-AES(OES)

Mass Spectrometry

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)

FlameOptic Filter

NebulizerData 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

ATOMIC ABSORPTION SPECTROSCOPY (AAS)

Elements detectable by AA are highlighted in pink

ATOMIC ABSORPTION SPECTROSCOPY (AAS)

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

ATOMIC ABSORPTION SPECTROSCOPY (AAS)

I nductively C oupled P lasma

-A tomic E mission S pectrometry

ATOMIC EMISSION SPECTROSCOPY

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)

❑ 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);

After Spectro Gmbh, Germany

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

ICP-AES: OPTICS

After Spectro Gmbh, Germany

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)

❑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