原子光谱之波长大部分在UV范围

1、Atomic spectrometryAtomic 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 orheated solid sample holderhhhwavelength selectorPhotoelectric transducerISignal processor and readoutAAS：source lamp orlaser sample holderhhhwav

2、elength selectorPhotoelectric transducerISignal processor and readoutAFS：source and sample holderhhwavelength selectorPhotoelectric transducerISignal processor and readoutAES:AASI0ICA)/log(TlogA=-=-=bCoII吸收值與濃度呈線性關係A：absorbanceT：transmittanceC：conc.：absorpivityb：path lengthhhL = k0C L C I0CA)/log(Tl

3、ogA=-=-=bCoII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)EjEijEjjijiEnVnhA=Nj/Ni = Pj*e-Ei/kT/PiEnergy level diagrams for (a) atomic sodium and (b) magnesiumElectronic state： Term symbolL2S + 1JC：1S2, 2S2, 2P2term symbol 有 3P03P1 3P2

4、1D2 1S0Na之ground state為2S1/2電子能階間之轉移2P1/2 589.6 nm2P3/2 589.0 nm紅光Mg+類似,(但能階不同)Ih/2h (為linewidth)Atomic linewidthUncertainty effect (natural broadening)Doppler broadening Pressure broadening如Na (5890) n = 2*10-5 nmT = 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 nmT = 2500K flame/N2 L = 0.035 nm分子

5、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 equationAA吸收希望atoms在ground state,AES溫度要高,在excited states atoms or ions .Nj/N0 = gj/g0

6、* 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hDetector原子conc. ,高度 最後高度增加慢而變寬emissionA/bnif/b cm-2sa)AESb)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 sourceIlinecontinuousI/I0I /I0Spectro

7、meter之解析度 1-2 nm原子吸收光譜要用line source,不用continuous sourcelog nilog aL0Slope = 1log nilog aL0Slope = 1Slope = 0Slope = 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)atomizerFlame 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

8、 solution(Pb)n PbX (Au)nAerosol transportNebulizationSamplesprayPrecesed spraydesolvationvaporizationA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 vaporhhh*Equilibration of vaporized speciesMolecular vaporAtomic vaporIonized atomic vapor + e-水珠nebulizationM+X-(aq)vaporizationMXM + XM+

9、+ 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ArEmission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emissionMXr. 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

10、radical frequency,可耐久) Atom cell：continuous： flame, plasmanoncontinuous： flame, plasmaHollow Cathode LampPhy. int. viscosity, surface tension, Temp.Chem. int. continuous band, blackbody emissionSpectral 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

11、況(Pb)n,orgPb2+ 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SignalConc.y = mx + bEx. (Pd)n球Xylene150 ppm水241 ppm六角Xylene225 ppm水441 ppm 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 cmSample cell較長燃料：

12、C2H2/air, C2H2/NO2氣體為 laminar flow flame (較靜) 分子noise最小火焰最常碰到 molecularContinuous bandBlackbody emissionSample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：CaCaO (MO)OHMXCa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

13、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化學干擾可加些試劑抑制 如：有些加如：有些加PO43-Ti, Al, Zr, W, P refractory elementMO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 ch

14、aracteristic conc. ETA而言叫 characteristic massDetection limit0.0044ABNoise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1995 Walsh/Australia , Alkemade/Holland1960 1st commercial AAS1965 H2O/C2H2 flame,1970 ETA-AAS (Graphite furnace AAS)1971 Zeeman-background correction1975 ICP-AES 1977 Constant tem

15、perature graphite furnace1978 Platform atomization1983 Smith-Hieftje background correction1984 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1.Light source (line)2.Atomization (原子化)3.Atom spectrum +

16、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 efficitions: solvationv: vaporizationa: atomizationT = nsva樣品熱處理 1. flame：5 mL/min10 L/min (gas)m4 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/min4 L sample/1.6L gas = 2.5*10-62. Furnac

17、e (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

18、段T ()Ramp time (sec)Hold time (sec)Gas flow (mL/min)1.乾燥Dryin灰化Ashing5501035150 於此把不該有的燒掉 (以免在原子化產生冒煙而影響光譜)3.原子化Atomization19000 (最快的加溫速度)50 (保持不動,在此為2 mL)4.清洗Clearing2600 (石墨爐最高溫度)141505.冷卻cooling2015150Temp. program在灰化及原子化的溫度是最重要的100806040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

19、變原子化溫度設為原子化溫度灰化溫度原子化溫度stdAu3+(Au)n 奈米乃為最佳操作條件t ()t ()0.50.40.30.20.101500 2000 2400 2700Absorbance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1.Fast heating rate2.Gas stop (會有稀釋效應)3.Pyrolytically Coated platform4.Matrix, modifier 種類absorbanceGas flow rate (mL/min)高溫是氧化態存在,然石墨提供一還原環境I0I孔洞太多會吸孔

20、洞太多會吸 (把把CH4通高溫裂解通高溫裂解)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 a)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s

21、tandard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b)Thermal decomposition of solid oxideMO(s)M(g) + O2M = 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absorbancet (時間) From wallFrom platformTube temperature平台壁溫度profile與石墨爐溫度不同 平台非靠電加熱而

22、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 wallabsorbancet (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1)The interfering concomitant become more volatile 如海水 NaCl + NH4NO3 NaNO3 + NH4Cl m. p. 1079K decomp. decomp. b. p. 1691 483 653 7892)Analyte is converted to less volatile form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Pb2200180516001400Matrix modifier 之作用1.讓干擾物揮發快一點2.讓分析物耐