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Atomic absorption spectrometry (AAS). Atomic spectrometry. Atomic fluorescence spectrometry (AFS). Atomic emission spectrometry (AES). 原子光譜之波長大部分在 UV 範圍. hν. source lamp or heated solid . sample holder. hν. wavelength selector. hν. Photoelectric transducer. I.

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slide2

Atomic absorption spectrometry (AAS)

Atomic spectrometry

Atomic fluorescence spectrometry (AFS)

Atomic emission spectrometry (AES)

原子光譜之波長大部分在UV範圍

source lamp or

heated solid

sample

holder

wavelength

selector

Photoelectric

transducer

I

Signal processor

and readout

AAS:

sample

holder

wavelength

selector

Photoelectric

transducer

I

Signal processor

and readout

AFS:

source lamp or

laser

sourceand

sample holder

wavelength

selector

Photoelectric

transducer

I

Signal processor

and readout

AES:

slide4

=

=

-

-

=

=

-

-

I

I

I

I

A

A

log

log

T

T

log(

log(

/

/

)

)

o

o

=

=

εbC

εbC

µ

µ

A

A

C

C

AAS

A:absorbance

T:transmittance

C:conc.

ε:absorpivity

b:path length

I0

I

吸收值與濃度呈線性關係

Light source

於P0°角看放出之螢光 (P0°乃因有散射)

ΦL = k′Φ0C ΦL C  I0

螢光源與入射光頂角成正比,且與濃度成正比

激發太原子不穩定會降到ground state,而以光的形式放出,放出之光與到底有多少分子激發態有關 (波茲曼係數)

Ej

Nj/Ni = Pj*e-ΔEi/kT/Pi

Ei

slide5

2S + 1

L

J

Energy level diagrams for (a) atomic sodium and (b) magnesium

Electronic state: Term symbol

C:1S2, 2S2, 2P2

term symbol 有 3P0<3P1<3P2<1D2<1S0

電子能階間之轉移

2S1/2

2P1/2 589.6 nm

Na之ground state為

紅光

2P3/2 589.0 nm

類似,(但能階不同)

Mg+

slide7

Linewidth (光譜解析之寬)

I

Δλ (為linewidth)

h/2

h

λ

  • 如Na (5890Å) Δλn = 2*10-5 nm
  • Uncertainty effect (natural broadening)
  • Doppler broadening
  • Pressure broadening
  • T = 2500°K
  • (與分子運動速度有關,而運動速度和溫度有關)
  • ΔνD = k√T/√M ΔλD = 0.045 nm

Atomic linewidth

分子會碰撞,使line變寬

(collisional)

  • T = 2500°K flame/N2ΔλL = 0.035 nm

∴如要使line狹窄, 則P愈低, T愈低愈好

如HCL ~ 0.002 nm (∵HCL其壓力、溫度偏低,操作時可用手摸)

(Hollow Cathode Lamp)

slide8

∴原子的光譜溫度很重要, ∵1. 會影響line之寬度. 2. 會影響原子分佈

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

分子在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

∴Iem C (但不會無限制增加)

λ

slide10

原子conc. ↑,高度↑ ∴最後高度增加慢而變寬

一團原子

Detector

emission

吸收效應小 (conc.低)

濃度高時 (a = 0.0)

A/b

nif/b cm-2s

atom cell (∵在高溫狀態∴較寬) 強度減弱大

  • AES
  • AAS

I

line

continuous

Line source

I/I0

I ′ /I0′

λ

Spectrometer之解析度 1-2 nm

∴原子吸收光譜要用line source,不用continuous source

slide11

Slope = 1/2

Slope = 0

0

0

log aL

log aL

Slope = 1

Slope = 1

log ni

log ni

原子發射光譜

原子吸收光譜

希望原子吸收光譜在ground state (T太高會在激發態而強度減弱)

Flame 火焰

atomizer

Furnace 石墨

噴霧器

超音波

石墨爐 (才能做固體sample) 2600 ℃

雷射

Spark (電弧) (才能做固體)

火焰:1700 - 3150 ℃

Sample放入之方法:

難度:標準品?

2600-3000°K

slide16

A

Sample溶液狀態為分子狀態

要了解量的是原子

(Ag)n solution

(Pb)n PbX (Au)n

vaporization

desolvation

Precesed spray

Aerosol

transport

spray

Nebulization

火焰會看到分子光譜 (∵分子光譜是continuous)

霧化器

Sample

slide17

Excited state vapor

*

*

*

Equilibration of vaporized species

Molecular vapor

Ionized atomic vapor + e-

Atomic vapor

nebulization

vaporization

M+X-(aq)

水珠

MX

M + X

M+ + e-

slide18

Hollow cathode lamp

內放1-5 torr的Ne或Ar

Ar + e- → Ar+ + e2-電子去撞擊Ar,帶Ar+去撞擊金屬,產生游離

M(s)→ M(g)* → hν + M(s)

Ar+

Emission原子發光

EDL:electroless discharge lamp for volatile element As, Se, Fe, Ge, Hg

乃加高溫激發到激發態,然後產生emission

有些金屬在低溫時即會揮發, ∴用EDL因此把鹽類放在球裏面,產生radicla frequency,用source加溫激發

(∵鹽類易吸收radical frequency,可耐久)

MX

r. f. (radical frequency)

continuous: flame, plasma

Atom cell:

noncontinuous: flame, plasma

slide20

影響定量之物理干擾 (乃sample之物理狀態)及化學干擾和光譜干擾,才能做校正曲線用

  • Phy. int. viscosity, surface tension, Temp.
  • Chem. int. continuous band, blackbody emission
  • Spectral int. 分子寬光譜之干擾 (∵分子會吸收OH, CN,CO)

interferences

火焰最常偵測到此二情況

NNO3

(Pb)n,org

Pb2+ 有機相中之Pb加HNO3變水溶液

slide21

配一standard solution於AA量訊號得校正曲線

Signal

y = mx + b

Ex. (Pd)n

Conc.

Standard (H2O) 乃standard是在純水中,然而sample不是

Nano-Pd為標準品, ∴做standard最容易是做水溶液

accuracy?

slide22

Atomizer :2600-3000°K

Sample cell較長

Sample cell為5 cm

燃料: C2H2/air, C2H2/NO2

溫度會高一點

火焰叫 pre-mixer burner

氣體為 laminar flow flame (較靜)分子noise最小

A = εbc b:sample cell 之長度

火焰最常碰到 molecular

  • Continuous band
  • Blackbody emission

石墨:物理干擾較少∵sample是擠入的

Sample是被吸入 (干擾大,要擠入就較不會)

slide23

火焰物理干擾有:viscosity, surface tension, Temp.

火焰化學干擾:Ca

氧化成鹽類,再成原子狀態

高溫有還原性的東西

.OH

CaO (MO)

Ca

MX

要打斷溫度低一點即可

若裡面含Al,則成Ca-O-Al.其比CaO更難打斷變成Ca, 此為化學干擾

要打斷溫度要高,而高溫火焰要用C2H2/NO2笑氣 (先在C2H2/air下,再切到C2H2/NO2)

另加稀土元素,如La3+,則會搶Ca-O-Al的Ca,形成La-O-Al,抑制化學干擾

∴化學干擾可加些試劑抑制 如:有些加PO43-

Ti, Al, Zr, W, P refractory element

MO其氧化物很穩定,要很高之溫度才能打斷, 要用C2H2/N2O

∴做這些元素盡量用emission.若用absorption則需高溫,必須要用笑氣,否則測不到訊號

slide24

Sensitivity:1% Abs特性濃度 (1%之吸收值0.0044)

對Flame而言叫‵characteristic conc.′

ETA而言叫‵characteristic mass′

Detection limit

Noise大,偵測極限小

0.0044

S/N = 3

A

B

有同樣之sensitivity,然而noise不同則偵測極限有差別

slide25

Walsh/Australia , Alkemade/Holland

  • 1st commercial AAS
  • 1965 H2O/C2H2 flame,
  • 1970 ETA-AAS (Graphite furnace AAS)
  • 1971 Zeeman-background correction
  • 1975 ICP-AES
  • 1977 Constant temperature graphite furnace
  • 1978 Platform atomization
  • 1983 Smith-Hieftje background correction
  • 1984 STPE (Stabilized temp. platform furnace)
  • 1990 Horizontally heated graphite furnace

避免雜訊 ∴用premixed burner則2000多℃,會有溫度梯度, ∴外面又一層火燄

原子吸收光譜之火燄

如本生燈

slide26

Light source (line)

  • Atomization (原子化)
  • Atom spectrum + molecular spectra
  • (分子光譜之吸收會造成分子吸收, ∴會有干擾問題)

原子吸收光譜必須知道

石墨爐

Graphite furnace

n: nebulization (5%) 在火燄內 efficition

s: solvation

v: vaporization

a: atomization

εT = εnβsβvβa

產生原子的效率

slide32

εm

樣品熱處理

1. flame:5 mL/min

4 µL/sec (5%en, 多數為廢液)

10 L/min (gas)

100 L/min = 1.6 L/sec(到燃燒頭)

Expand 10倍

樣品

5 mL/min

4 µL sample/1.6L gas = 2.5*10-6

2. Furnace (石墨爐中)

5 mL/2 mL = 2.5*10-3

石墨爐稀釋效應

相差1000倍

石墨爐體積

Atom density 1000 (在atom density是火焰的100倍)

Molecular density 1000 (在分子 density是火焰的100倍)

∴matrix effect 特別嚴重

How to reduce or eliminate the matrix effect for furnace AAS is the most important task for accurate determination of real samples.

slide33

石墨爐原子吸收光譜之加熱程序分五個階段

Temp. program

在灰化及原子化的溫度是最重要的

slide34

設為原子化溫度

設為灰化溫度

100

80

60

40

相對吸收值 (%)

固定原子化溫度,改變灰化溫度,找到下降前最高點

固定灰化溫度,改變原子化溫度

灰化溫度

原子化溫度

乃為最佳操作條件

t (℃)

std

Au3+

(Au)n奈米

(即要很快加溫, ∴所有power設定0秒才能達到最佳操作條件)

0.50.40.30.20.10

很快加溫

Absorbance

慢慢升溫

t (℃)

1500 2000 2400 2700

slide35

I0

I

AA操作要 STPE

∴設定

  • Fast heating rate
  • Gas stop (∵會有稀釋效應)
  • Pyrolytically Coated platform
  • Matrix, modifier 種類

absorbance

Gas flow rate (mL/min)

高溫是氧化態存在,然石墨提供一還原環境

孔洞太多會吸 (∴把CH4通高溫裂解)

火焰希望是還原性火燄,石墨有還原作用 (一般燃燒為氧化下方能產生高溫)

slide36

火焰希望是還原性火燄,石墨有還原作用 (一般燃燒為氧化下方能產生高溫)

Atomization mechanism

  • Reduction of solid oxide on graphite surface (可幫助產生原子狀態)

½ M(g)

∵MO(s) + C(s)

M(l)

M(g)

若有很多分子,則溫度會影響其產生之效率

M = Co, Cr, Cu, Fe, Mo, Ni, Pb, Sn, V

∴GFAAS2% HNO3(∵MO要在氧化態存在才易氣化)

Flame AAS HCl

配standard要保持在酸性下. ∵玻璃Si會吸附金屬,變成MX. →不會產生氫氧化物沉澱

  • Thermal decomposition of solid oxide

MO(s)

M(g) + ½ O2

M = Al, Cd, Zn

slide37

石墨爐有特殊處理: 如CH4昇高溫 (pyrolytically-coated graphite)

何以要用平台 ( L’vov platform)?

平台的加熱方式與石墨爐的tube不同

透過電子加熱 (內外溫度不同)

Tube temperature

平台

From wall

absorbance

From platform

t (時間) →

平台壁溫度profile與石墨爐溫度不同

平台非靠電加熱而是靠熱傳導加熱 (∵溫度愈低愈有化學干擾)

平台提供讓sample加熱delay.當sample加熱要原子化時,石墨爐溫度已穩定下來,

則訊號會比較高,干擾較小

slide38

The interfering concomitant become more volatile

  • 如海水 NaCl + NH4NO3 NaNO3 + NH4Cl
  • m. p. 1079°K decomp. decomp.
  • b. p. 1691 483 653 789
  • Analyte is converted to less volatile form

Tube temperature

Volatillization from the tube wall

absorbance

做實際樣品希望在第2節把其它基值皆燒掉,只剩MO(s)

t (時間) →

Matrix modification reduce or eliminate volatilization and vapor-phase interferences

溶化灰化溫度過程產生之干擾

∴高溫下

Pb

2200℃

1805℃

1600℃

1400℃

讓分析物變較不容易揮發 (則可提高ashing溫度)

∴做AA把溫度設定好, matrix modifier找好即可做

slide39

B (Al3+ + Mg)

  • Matrix modifier 之作用
  • 讓干擾物揮發快一點
  • 讓分析物耐高溫一點

A (Al3+)

Mg為加Mg(NO3)2,做為基質修正

Absorbance

0.5 0.40.30.20.10

A,B積分面積一樣

加0.3 M HNO3

2 µg Pd

Time (s)

Al3+

Al3++ Mg(NO3)2

濃度一樣

4 µg Mo

20 µg Ni

較晚出來,表分析物更穩定

Pure Sb standard

1.4 M HNO3

一般認為,是以Al-Mg合金或couple狀態存在 (表面分析,但ppb較難)

Thermal pretreatment temperature

Matrix modifier (NH4)NO3 Ni(NO3)2

Mg(NO3)2 Mo(NO3)2

Pd(NO3)2 (耐高溫) 例如 Pb, Cd加Pd2+成合金,可使揮發性好一點

slide40

未添加基質修飾劑

相對吸收值 (%)

100

80

60

40

添加基質修飾劑

灰化溫度 (℃)

當把奈米加熱到500 ℃以上會死掉

600 700 800 900 1000 1100

通常原子吸收光譜之干擾有分子之吸收

CaOH 發射

光譜干擾

CaOH 吸收

Ba

slide41

4. Interferences

  • phy. Interference
  • chemical interference
  • spectral interference
  • 5. Effective background correction 有效背景校正
  • 背景有兩個特性
    • Continuous background emission
    • Band type molecular absorption
    • (分子吸收很廣)
slide50

Self-reversal

λ0

Low HCL Current

(Background + Analyte) Signal

High HCL Current

Background Signal

λ1

λ2

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