AAS原子光谱之波长大部分在UV范围.ppt

Atomic spectrometry,Atomic absorption spectrometry (AAS),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,h,h,h,wavelength selector,Photoelectric transducer,I,Signal processor and readout,AAS：,source lamp or laser,sample holder,h,h,h,wavelength selector,Photoelectric transducer,I,Signal processor and readout,AFS：,source and sample holder,h,h,wavelength selector,Photoelectric transducer,I,Signal processor and readout,AES:,AAS,I0,I,吸收值與濃度呈線性關係,A：absorbance T：transmittance C：conc. ：absorpivity b：path length,h,h,L = k0C L C I0,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,Ei,Nj/Ni = Pj*e-Ei/kT/Pi,Energy level diagrams for (a) atomic sodium and (b) magnesium Electronic state： Term symbol,C：1S2, 2S2, 2P2 term symbol 有 3P03P1 3P2 1D2 1S0,Na之ground state為,2S1/2,電子能階間之轉移,2P1/2 589.6 nm,2P3/2 589.0 nm,紅光,Mg+,類似,(但能階不同),I,h/2,h, (為linewidth),Atomic linewidth,Uncertainty effect (natural broadening) Doppler broadening Pressure broadening,如Na (5890) n = 2*10-5 nm,T = 2500K (與分子運動速度有關,而運動速度和溫度有關) D = kT/M D = 0.045 nm,T = 2500K flame/N2 L = 0.035 nm,分子會碰撞,使line變寬 (collisional),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),Linewidth (光譜解析之寬),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,AA吸收希望atoms在ground state, AES溫度要高,在excited states atoms or ions .,Nj/N0 = gj/g0 * exp(E/RT),Spectral line intensity,Iem,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 C (但不會無限制增加),一團原子,h,Detector,原子conc. ,高度 最後高度增加慢而變寬,emission,A/b,nif/b cm-2s,AES AAS,吸收效應小 (conc.低),濃度高時 (a = 0.0),atom cell (在高溫狀態較寬) 強度減弱大,Line source,I,line,continuous,I/I0,I /I0,Spectrometer之解析度 1-2 nm,原子吸收光譜要用line source,不用continuous source,log ni,log aL,0,Slope = 1,log ni,log aL,0,Slope = 1,Slope = 0,Slope = 1/2,原子吸收光譜,原子發射光譜,希望原子吸收光譜在ground state (T太高會在激發態而強度減弱),atomizer,Flame 火焰,Furnace 石墨,Sample放入之方法：,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 ,難度：標準品？,2600-3000K,要了解量的是原子 (Ag)n solution (Pb)n PbX (Au)n,Aerosol transport,Nebulization,Sample,spray,Precesed spray,desolvation,vaporization,A,霧化器,Sample溶液狀態為分子狀態,火焰會看到分子光譜 (分子光譜是continuous),Excited state vapor,h,h,h,*,*,*,Equilibration of vaporized species,Molecular vapor,Atomic vapor,Ionized atomic vapor + e-,水珠,nebulization,M+X-(aq),vaporization,MX,M + X,M+ + e-,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)* h + M(s),Hollow cathode lamp,內放1-5 torr的Ne或Ar,Emission原子發光,Ar+,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,MX,r. f. (radical frequency),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),Atom cell：,continuous： flame, plasma,noncontinuous： flame, plasma,Hollow Cathode Lamp,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),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,interferences,火焰最常偵測到此二情況,(Pb)n,org,Pb2+ 有機相中之Pb加HNO3變水溶液,NNO3,配一standard solution於AA量訊號得校正曲線,Signal,Conc.,y = mx + b,Ex. (Pd)n,accuracy?,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,Atomizer :2600-3000K,火焰叫 pre-mixer burner,溫度會高一點,Sample cell為5 cm,Sample cell較長,燃料： C2H2/air, C2H2/NO2,氣體為 laminar flow flame (較靜) 分子noise最小,火焰最常碰到 molecular,Continuous band Blackbody emission,Sample是被吸入 (干擾大,要擠入就較不會),石墨：物理干擾較少sample是擠入的,A = bc b：sample cell 之長度,火焰物理干擾有：viscosity, surface tension, Temp.,火焰化學干擾：Ca,CaO (MO),OH,MX,Ca,氧化成鹽類,再成原子狀態,高溫有還原性的東西,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,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,0.0044,A,B,Noise大,偵測極限小,S/N = 3,有同樣之sensitivity,然而noise不同則偵測極限有差別,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,原子吸收光譜必須知道,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),石墨爐,Graphite furnace,產生原子的效率,n: nebulization (5%) 在火燄內 efficition s: solvation v: vaporization a: atomization,T = nsva,樣品熱處理,1. flame：5 mL/min,10 L/min (gas),m,4 L/sec (5%en, 多數為廢液),100 L/min = 1.6 L/sec (到燃燒頭),Expand 10倍,樣品,5 mL/min,4 L sample/1.6L gas = 2.5*10-6,2. Furnace (石墨爐中),5 mL/2 mL = 2.5*10-3,石墨爐體積,石墨爐稀釋效應,相差1000倍,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.,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,100 80 60 40,相對吸收值 (%),設為灰化溫度,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,設為原子化溫度,灰化溫度,原子化溫度,std,Au3+,(Au)n 奈米,乃為最佳操作條件,t (),t (),0.50.40.30.20.10,1500 2000 2400 2700,Absorbance,慢慢升溫,很快加溫,(即要很快加溫, 所有power設定0秒才能達到最佳操作條件),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),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),MO(s) + C(s),M(l), M(g),M(g),M = Co, Cr, Cu, Fe, Mo, Ni, Pb, Sn, V,若有很多分子,則溫度會影響其產生之效率,GFAAS 2% 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) + O2,M = Al, Cd, Zn,石墨爐有特殊處理： 如CH4昇高溫 (pyrolytically-coated graphite) 何以要用平台 ( Lvov 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),平台,absorbance,t (時間) ,From wall,From platform,Tube temperature,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,Volatillization from the tube wall,absorbance,t (時間) ,Tube temperature,做實際樣品希望在第2節把其它基值皆燒掉,只剩MO(s),Matrix modification reduce or eliminate volatilization and vapor-phase interferences,溶化灰化溫度過程產生之干擾,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,高溫下,Pb,2200,1805,1600,1400,Matrix modifier 之作用 讓干擾物揮發快一點 讓分析物耐高溫一點,Absorbance,Time (s),0.5 0.40.30.20.10,A (Al3+),B (Al3+ + Mg),Mg