AS deals with e transfer transition of valence electron between electronic states

AAS

I0 I

CA

)/log(TlogA

εbC

吸收值與濃度呈線性關係

A ： absorbance

T ： transmittance

C ： conc.

ε ： absorpivity

b ： path length

hν hν

ΦL = k′Φ0C ΦL C Φ0

CA

)/log(TlogA

εbC

螢光源與入射光頂角成正比 , 且與濃度成正比

Light source

於 P0° 角看放出之螢光 (P0° 乃因有散射 )

激發態原子不穩定會降到 ground state, 而以光的形式放出 , 放出之光的強度與處於激發態的原子數目有關 ( 波茲曼係數 )

Ej

EijE

jjijiE

n

VnhA

Nj/Ni = Pj*e-ΔEi/kT/Pi

AFS

AES

Temperature effect on the atomic spectra Boltzmann equation

AA 吸收希望 atoms 在 ground state,

AES 溫度要高 , 在 excited state’s atoms or ions ↑.

Nj/N0 = gj/g0 * exp(ΔE/RT)

Spectral line intensity

Iem

λ

原子在 excited 愈多 , 強度愈高 ( 僅電流多點即可 )

當 conc. 很低時 ,conc. ↑ 或原子在 excited 增加 ,則 intensity 會增強 , 最後不再增強而變寬

變寬效應

∴ Iem C ( 但不會無限制增加 )

Sequential ICP-AES Instrumentation

Major Components of ICP-AES

Sample Delivery System - pump, nebulizer, spray chamber

Inductively Coupled Plasma - torch, RF generator

Spectrometer - Monochrometer, photomultiplier tube

Sample Delivery System

Concentric-tube pneumatic

nebulizer

Cross flow nebulizer

Nebulizer:

• converts sample to aerosol by a jet of gas (compressed Ar)

Common types:

•Pneumatic - concentric tube, cross flow

•Ultrasonic

Ultrasonic nebulizer with desolvation

Inductively Coupled Plasma

What is a Plasma?

•Plasma source provides atomization

•Plasma: “a gas-like phase of matter that consists of charged particles”

•ICP-AES plasma source is from the carrier gas

Typically argon is used

Drawback

• Solid and liquid samples must be prepared so that they can be easily evaporated and ionized by the instrument1

• ICP-AES is a destructive technique, but only a small bit of sample is necessary

• Sample introduction into the instrument: the thorn in the side of ICP-AES

Plasma

• Plasma source provides atomization

• Plasma: “a gas-like phase of matter that consists of charged particles”2

• ICP-AES plasma source is from the carrier gas

Inductively coupled plasma (ICP)…torch design…

Radiofrequency Generator

ICP torch

ICP temperatures

Detection

Radial Viewing

2 Types of Detection Positions:

1. Radial Viewing

2. Axial Viewing

Characteristics of the ICP 1. High Temp.

2. Long residence times.

3. High electron number densities(few

ionization interferences)

4. Free atoms formed in nearly chemically

inert environment.

5. Molecular species absent or present at low

levels.

6. Optical thin.

7. No electrodes.

8. No explosive gas.

How to perform Simultaneous Analysis

• Simultaneous analysis was carried out until

today by using:

– polychromators, which are Paschen-Runge

optics coupled to high sensitivity detectors

known as Photomultiplers (PMT)

– Echelle-Grating optics, coupled to Solid State

Detectors , (CCD, SCD & CID types), also

known as Charge Transfer Devices (CTD’s)

Detail of a Paschen-Runge optics with PMT detectors

Diffraction Grating

Optical Fibers

Photo multipliers

Grating

Rowland circle

Photographic Film

PhotomultiplierTubes

Entranceslit

Exit slits

Advantages:High light throughputWide spectral rangeFew optical componentsLow stray light levelRobust

XY

PMT

SCANNING + PMT

Optics and Detectors

Typical Echellogram

ICP optical emission spectrometryICP-OES

• Capable of true simultaneous multielement analysis

• Minimal chemical interferences

• Spectral interferences overcome with use of alternate lines or intensity corrections on either side of analytical line

• Axial and side-on viewing systems available

ICP-OES operation

• Variety of sample introduction approaches available (pneumatic nebulizer with ~ 1 mL/min uptake is most common)

• Sensitivities better than FAA and often comparable with GFAA when using axial viewing

• Varying degrees of automation available

Background Noise Sources

• Argon emission lines

• Carbon and silicon lines

• Oscillation by the plasma itself and oscillations caused during aerosol production and sample delivery

Such intensities are practically constant and easily recognized

Poor Detection Limits on Certain Trace Elements

• Examples of interferences include:• 40Ar16O on the determination of 56Fe

• 38ArH on the determination of 39K

• 40Ar on the determination of 40Ca

• 40Ar40Ar on the determination of 80Se

• Solution: the cold/cool plasma

Limits of DetectionDecrease in limits of detection over the course

of time using examples of Perkinelmer ICP emissionSpectrometers ICP/5000 (1980), Optima 3000 (1993),

Optima 3000 XL (1997)

All detection limits were determined by the blank method using the statistical factor K = 3 [concentrations in ppb]

1980 radial

1993 radial

1997 axial

As 193 150 50 5Cd 214 3 2 0.3Cr 267 5 2 0.2Ni 231 10 5 0.7Pb 220 50 10 0.8Zn 231 2 1 0.1

DCP

Inductively coupled plasma mass spectrometry

ICPMS

ICPMS characteristics

• “Simultaneous” multielemental analysis• 5-6 orders of magnitude in dynamic range(need

fewer standards for calibration)• ppt and even ppq LODs available• Isotopic information available• Spectral interferences occur and involve

polyatomic ions or isotopes of other elements• Interferences involving ion optics (e.g., “space

charge”) and ionization efficiency are unique to ICPMS