as deals with e transfer transition of valence electron between electronic states
DESCRIPTION
AS deals with e transfer transition of valence electron between electronic states. =. =. -. -. =. =. -. -. I. I. I. I. A. A. log. log. T. T. log(. log(. /. /. ). ). o. o. =. =. ε bC. ε bC. µ. µ. A. A. C. C. AAS. A : absorbance T : transmittance C : conc. - PowerPoint PPT PresentationTRANSCRIPT
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