Atomic Spectroscopy: Basic Principles and Instruments
-
Upload
vasiliy-rosen-phd -
Category
Education
-
view
47.103 -
download
6
description
Transcript of 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.
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)
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);
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)
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.