atomic spectroscopy basics (2012)

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

[email protected], www.rosen.r8.org

2012

mailto:[email protected]

INTRODUCTION

ספקטרוסקופיה בליעה

Absorption Spectroscopy:

AAS

ספקטרוסקופיה פליטה

Emission Spectroscopy:

FES, ICP-AES(OES)

ספקטרוסקופיה מסה

Mass 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

INTRODUCTION

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

INTRODUCTION

SAMPLE PREPARATION

Drying

Grinding

Dry or Wet Acid

Digestion

Process Goal Problems

Sample stabilization,

homogenization and

accurate weighing

facilitation

Sample homogenization,

organic matter reduction

facilitation

Organic matter destruction,

solid material dissolution

Thermal

decomposition and

reduction in dry

weight

Pollution by metals

from the mill parts

Analyte loss,

contamination, not

complete solid

dissolution

SAMPLE PREPARATION EQUIPMENT

Most samples have to be prepared for analysis on ICP, FF and AA. Solid samples are

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

Hot Plate

Microwave-assisted Digestion

Digestion Block


Microwave Laboratory Oven “Ethos One”

and Teflon vessels


“Ethos One”: Temperature and Pressure control


“Ethos One”: “Vent-and-Reseal” technology


“Ethos One”: Digestion profile

6 samples

0

50

100

150

200

250

0.00 0.05 0.10 0.15 0.20 0.25

Time (minutes)

Te

mp

era

ture

(°C

)

0

200

400

600

800

1000

1200

Po

we

r (w

att)

Cd, 1 mg/L, in weak acid

Cd, 1 mg/L, in base

11

MATRIX

Analyte concentrations are equal, but intensities are different

MATRIX

The elements that are stable/soluble in HNO3

MATRIX

The elements that are stable/soluble in HCl

MATRIX

The elements that are stable/soluble in H2SO4

MATRIX

HNO3

HCl

H2SO4

QC PROCEDURES

Replicates – method precision * evaluation.

Spike – addition of the known concentration of

analyte to the sample at the preparation step. The

evaluation of the preparation quality and matrix effect.

Matrix matching – preparation of the calibration

standards in the same matrix as the samples.

Standard Reference Material preparation and

analysis for method accuracy ** evaluation.

*Precision is how close the measured values are to each other.

**Accuracy is how close a measured value is to the actual (true) value.

Internal standard – addition of the element that

sample does not contain (Y, Sc) in known

concentration. The evaluation of the matrix effect.

QC PROCEDURES

SRM 1570a Spinach Leaves Elemental Analysis

Method precision Method accuracy

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, Cs and Ca).


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.


Operation principle of AAS

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

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

solids).

Detector – photomultiplier.

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

ICP SPECTROMETER

Main Systems

ICP-AES: SAMPLE INTRODUCTION SYSTEM

Nebulizer (cross-flow)

Spray Chamber

Argon Supply

To Waste

Torch with Plasma

Sample

Solution

Entrance

ICP-AES: NEBULIZER

Cross-flow nebulizer Modified-Lichte nebulizer

Burgener nebulizer

ICP-AES: NEBULIZER

aerosol

ICP-AES: NEBULIZER

Modified Lichte Nebulizer

aerosol

ICP-AES: NEBULIZER

aerosol

ICP-AES: TORCH

Auxiliary

Argon Flow

Coolant

Argon Flow

Nebulizer

Argon Flow

ICP-AES: TORCH

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)

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: OPTICS

ICP-AES: BACKGROUND CORRECTION

Background Correction

Position 1

Background Correction

Position 2

Linear Function Approximation

ICP-AES: BACKGROUND CORRECTION

Linear Function

Approximation

Polynomial Function

Approximation

ICP-AES: SPECTRAL INTERFERENCES

Sulfur in plant sample Boron in plant sample

Sulfur in standard

(10 mg/L)

Boron in plant sample

Boron in standard

(1 mg/L)

Sulfur spectral interference on Boron line 182.6 nm


Iron spectral

interference on

Boron lines 249.7

and 208.8 nm

Fe 25 ppm

B 0.1 ppm

Fe 25 ppm


Mn 10 ppm

Au 1 ppm

Manganese spectral interference on Gold lines 242.7 mn

Numerical Data

ICP-AES: CALIBRATION CURVE

ICP-MS: BASICS

Cones sample the center

portion of the ion beam

(+)

(+) (+) (+)

Electrostatic lens

focuses the beam

into the slit

Shadow stop blocks

the photons

ICP-MS: BASICS

Quadropole mass filter can

separate up to 2400 amu (atomic

mass units) per second by switching

alternating voltages applied to

opposite pairs of the rod

ICP-MS: BASICS

ICP-AES (MS), 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)

ZBM LABORATORY WEBSITE

http://departments.agri.huji.ac.il/zabam/




atomic spectroscopy basics (2012)

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