AS deals with e transfer transition of valence electron between electronic states
AAS
I0
A：absorbance
I
A = - log T = - log( I / I )
T：transmittance
= εbC
C：conc.
o
AC
吸收值與濃度呈線性關係
b：path length
AFS
Light source
於P0°角看放出之螢
光 (P0°乃因有散射)
ε：absorpivity
hν
ΦL = k′Φ0C ΦL  C  Φ0
hν
螢光源與入射光頂角成
正比,且與濃度成正比
AES
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
Ei
 E = A ji h ji n jV
E  n j
Nj/Ni = Pj*e-ΔEi/kT/Pi
Temperature effect on the atomic spectra Boltzmann equation
Nj/N0 = gj/g0 * exp(ΔE/RT)
AA吸收希望atoms在ground state,
AES溫度要高,在excited state’s atoms or ions ↑.
Spectral line intensity
原子在excited愈多,強度愈高 (僅電流多點即可)
Iem
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
λ
∴Iem  C (但不會無限制增加)
Sequential ICP-AES
Instrumentation
Major Components of ICPAES
Sample Delivery System - pump, nebulizer,
spray chamber
Inductively Coupled Plasma - torch, RF generator
Spectrometer - Monochrometer, photomultiplier tube
Sample Delivery
System
Nebulizer:
Concentric-tube
pneumatic
nebulizer
• converts sample to
aerosol by a jet of gas
(compressed Ar)
Common types:
•Pneumatic - concentric
tube, cross flow
Cross flow nebulizer
•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
2 Types of Detection
Positions:
1. Radial Viewing
2. Axial Viewing
Radial
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
Optical Fibers
Photo multipliers
Diffraction
Grating
Advantages:
Grating
Rowland circle
Entrance
slit
High light throughput
Wide spectral range
Few optical components
Low stray light level
Robust
Exit slits
Photomultiplier
Tubes
Photographic Film
X
Y
PMT
SCANNING + PMT
Optics and Detectors
Typical Echellogram
ICP optical emission spectrometry
ICP-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 Detection
Decrease in limits of detection over the course
of time using examples of Perkinelmer ICP emission
Spectrometers 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]
As 193
Cd 214
Cr 267
Ni 231
Pb 220
Zn 231
1980
radial
150
3
5
10
50
2
1993
radial
50
2
2
5
10
1
1997
axial
5
0.3
0.2
0.7
0.8
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