자외선 가시선 분광광도법 Ultraviolet-Visible Spectrometry

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1 Spectrometry ( 분광법 ) Spectrometry is the study of the interaction of electromagnetic radiation (EMR) with matter; and its applications There are many types of spectrometry UV-Visible Molecular Absorption Infrared Fluorescence Atomic Absorption/Emission X-Ray Absorption/Emission Mass

2 Five basic components of an optical instrument 1. Light source ( 광원 ) 2. Sample holder 3. Wavelength selector ( 파장선택기 ) 4. Detector or transducer ( 검출기 ) 5. Signal processor ( 신호변환기 ) The orientation between these components varies with the type of technique (absorption, emission, etc.)

3 2 장. Ultraviolet-Visible Spectrometry 자외선가시선분광광도법은광전자 ( 입자 ) 를흡수하는발색단 (chromophore) 기의존재를이용하여분석 180 ~ 780nm 영역 10~380, 200~380nm, 380~780, 780~300,000nm < 200nm 진공자외선, 진공상태기기조작. 분자내에너지와광에너지상호작용이용 흡수 ( 광 ) 정도가물질의성질 ( 정성 ) 과양 ( 정량 ) 에비례

4 흡수 ( 특정한작용기의존재유무에기인 ) 전자전이 ground 기저상태 excited 들뜬 / 여기상태 일반적불포화결합 (=, ) 화합물이 uv-vis 영역에서빛흡수 불포화결합포함하고있는작용기 =chromophore 발색단 빛흡수 ( 매우선택적 ), 상이한발색단, 상이한파장에서최대흡광 ( 분자속의한작은원자단에속하는전자가들뜨기때문 ), 상이한파장, 흡수되는빛의양에도차이 Absorption commonly occurs with many organic molecules metals metal-organic complexes

5 Concentration (c) 분자흡광 = 용액의 transmittance T 와 absorbance A 측정 주요점 : 흡광도와농도의선형비례관계 A = abc =εbc = log (P o /P) = -log (T) Beer s Law T %T 100% 10% 1% 0.1% A P o a beam of light with an (initial) radiant intensity P intensity of the light after passage through the solution (where absorption occurs) P 0 P transmittance (T) = P/P 0 (units = %) absorbance (A) (units = none) hv A = abc (or εbc) a = absorptivity (L/g cm) 흡광계수 b b = path length (cm) 통과길이 c = concentration (g/l) 농도 ε = 몰흡광계수 (L/mol cm) used when concentration is in molar units

6 P 0 = 10,000 P = 5,000 T P P b- 0.5 A = -log T = -log (0.5) = P 0 = 10,000 P = 2,500 T P P b A =-log T = -log (0.25) =

7 Transmittance Absorbance absorption vs. transmission Thickness, b Transmittance, T A = -log T A A log T abc log P P Thickness, multiples of b T = 10 -abc A = abc Thickness, multiples of b

8 2.1. Beer s Law 적용한계 A 와 b; A 와농도 (b 일정 ) at high concentrations charge distribution effects occur causing electrostatic interactions between absorbing species ( 묽은용액흡광에만성립 ) Chemical analyte dissociates/associates or reacts with solvent( 화학편차 / 화학종사이의상호작용 ( 전하분포에서로영향 ) 시료농도에따른오차 Instrumental ( 기기편차 ) ε = f(λ); most light sources are polychromatic not monochromatic (small effect) 단색광과다색광 ε 차이 stray light comes from reflected radiation in the monochromator reaching the exit slit.

9 Instrumental limitations ε = f(λ) How/Why does ε vary with λ? Consider a wavelength scan for a molecular compound at two different wavelength bands In reality, a monochromator can not isolate a single wavelength, but rather a small wavelength band

10 Instrumental limitations stray light How does stray light effect absorbance and beer s Law? A = -log P/P o = log P o /P When stray light (P s ) is present, the absorbance observed (A apparent ) is the sum of the real (A real ) and stray absorbance (A stray ) A app = A real + A stray = Po log P P P As the analyte concentration increases ([analyte] ), the intensity of light exiting the absorbance cell decreases (P ) eventually, P < P s s s

11 Instrumental limitations stray light non-linear absorption (analyte vs. conc.) as a function of analyte concentration Similar to polychromatic light limitations p. 24: 일반적으로 최소한의상대오차 T= (36.8%), A=0.434

12 2.2. 자외선및가시선의흡광화합종 ( 흡광원리 ) 물질통과 특정주파수감소 ( 흡수 ) : 복사선 E 일부가물질의원자또는분자로이동 (= 흡수 ) 결과 : 들뜬상태됨 ( 높은에너지준위로이동 ) 분자전이 (molecular transition) M + hν M * ( 들뜬입자, 수명 10-8 ~10-9 s) 이완과정 M -e ( 에너지소실 ) 일반적열로변환 ( 흡광분광법 ) 혹은형광 / 인광복사선발광 (3 장 ) 새로운화학종생성 ( 광화학반응 )

14 전자전이는항상진동, 회전전이를수반 진동에너지전이 ( 적외선영역 1~15 μm) 회전에너지전이 ( 마이크로파 10~10,000 μm) 전자전이종류 : 자 / 가시선흡수 결합전자들뜸 흡수봉우리 ( 화합종의결합형태 ) 분자내작용기, 흡광원자단정량적분석

15 분자내전자 4 가지다른형태 (1) 결합에관여하지않는닫힌껍질 (closed-shell) 전자들매우높은에너지 ( 자 - 가시선영역해당치않음 ) (2) 공유단일결합 (covalent single bond) 전자들 (σ 전자들 ) 역시자 - 가시선에너지흡수에기여치않음 (3) 비결합바깥껍질 (paired nonbonding outer-cell) (η 전자들 ) N, O, S 및할로겐에서와같이짝지어진 (4) π 궤도함수에있는전자들 ( 이중, 삼중결합전자들 ) 가장쉽게들뜸. 자 - 가시선대부분스펙트럼 H H C x x O σ, π, η

16 분자의전자전이는분자의전자구조와밀접한관계 UV 영역의전자전이 = 주로분자의최외각전자 원자가결합하여분자이루면분자궤도함수결합분자오비탈 (bonding molecular orbital)- 낮은에너지반결합분자오비탈 (antibonding) - 높은에너지 ( 바닥상태에있는분자중의전자들이결합궤도함수를점유 ) 결합 반결합이동 σ,η,π- 전자전이, d, f- 전자전이, 전하이동전이선택규칙 σ σ*, η σ*, η π*, π π* 전이가장쉽게들뜸. 자 - 가시선대부분스펙트럼

17 * n * n * * 높은에너지흡수, vacuum UV 높은에너지흡수, 150~250 nm 가장낮은에너지흡수, 200~700 nm 중간에너지흡수, 200~700 nm

18 발색단 chromophore 일반적불포화결합을포함하는흡광원자단. 유기물경우작용기 무기물의경우에 2 원자이상으로된음이온대부분자외선부에서흡수가일어난다 η π *, π π * 전자전이 조색단 auxochrome 자신은자외선부의빛을흡수하지않으면서, 분자내에존재하게되면최대흡수파장을이동시킴

19 유기물에의한흡광 many common organic compounds absorb in the UV region

20 무기물에의한흡광 many free metals and inorganic metal complexes absorb in the visible region of the spectrum

Absorption by charge transfer complexes Many inorganic and organic complexes form charge transfer complexes A charge transfer complex consists of an electron donor group bonded to

21 Absorption by charge transfer complexes Many inorganic and organic complexes form charge transfer complexes A charge transfer complex consists of an electron donor group bonded to an electron acceptor group Charge transfer complexes exhibit broad band absorption in the visible region of the EMR spectrum Useful analytically because of the large molar absorption

22 (example) Charge-Transfer Complex

23 (example) Charge-Transfer Complex λ max Nitrite can be determined analytically by adding reagents to form a colored charge transfer complex. The complex exhibits broad band absorption in the visible region of the EMR spectrum The wavelength of maximum absorption (λ max ) can be determined with a wavelength scan Measurements are then made at λ max

24 Choice of solvents Most absorption measurements are conducted by dissolving the analyte in a solvent The solvent (and sample holder) should be transparent in the region of the spectrum where the analyte absorbs

25 2.3. 분광광도계와부분장치 분광분석법상당히비슷한기기부품으로구성 ( 광원 / 시료용기 / 파장선택기 / 검출기 / 신호처리기록 ) 광원 : 안정한복사에너지지원 시료용기 : 시료를담는투명한용기 파장선택기 : 측정이용한정된파장영역분리하는장치 검출기 : 복사선검출또는유용한신호 ( 일반적전기 ) 변환 신호처리기록 : 독해장치

29 광원 충분한세기의복사선, 안정하게유지 - 연속광원 ( 넓은파장영역. 주로분자흡수분광법 ) - 선광원 ( 소수의불연속적복사선, 원자흡수, 라만등 ) 종류 : 중수소와수소등 - 자외선영역. 중수소나수소를전기적 160~375 nm 영역에서유용 텅스텐, 필라멘트등 - 가장일반적, 가시광및 근적외선. 온도 2870K 방출하는 350~2500nm 영역 크세논, 아아크등 - 크세논기체에전류, 250~600nm

Tungsten lamp (provides visible spectrum; 400-1200 nm)

30 Two types: 1. Continuous source Produces spectra over broad range Tungsten lamp (provides visible spectrum; nm) Deuterium lamps (provides ultra-violet spectrum; nm) Light sources Tungsten Lamp Deuterium Lamp

31 2. Discontinuous or Discrete sources produce only specific (discrete) wavelengths e.g. hollow cathode lamp (HCL) or an electrodeless discharge lamp (EDL) A hollow cathode lamp

32 파장선택기 필요한파장을선택 어떤파장필요? 제한된좁고연속적인파장의다발띠 (band) 좁은띠나비? 측정감도증가, 선택도높임, 신호 / 농도직선 가장이상상태 ( 단일파장, 단일진동수복사선, but it's dream?) 두가지형태파장선택기 : 필터, 단색화장치 a. Filter - 흡수필터와간섭필터 (interference filter) 흡수필터 ( 가시선영역. 일정부분의스펙트럼흡수. 색유리등 ) 간섭필터 ( 두개의투명한금속필름사이에투명한유전체 - CaF 2 MgF 2 채움. 두께조절 복사선의파장결정.

33 b. Chromator ( 단색화장치 ): 넓은범위에걸쳐연속적으로복사선파장을변화시킬필요 grating과 prism 부분장치 - 입구슬릿, 평행한복사선 ( 평행화렌즈또는거울프리즘 / 회절발 ( 복사선을성분파장으로분산 ), 초점면 / 출구슬릿최근단색화장치는대부분반사회절발 (reflection grating) echellette-type 넓은사용면, 좁은비사용면 concave-grating holographic-grating 레이저이용하여회절발제작 echelle-grating 에셀레트와비슷. 낮은홈선밀도

34 Wavelength selector Prisim (monochrometer) Grating monochromator

35 Grating monochromator Isolates individual wavelengths of light from the spectrum produced by the light source(s) Individual wavelengths are selected by rotating the grating or moving a mirror or slit. Czerney-Turner Monochromator

36 Monochromator slit settings Effect on spectral resolution Decreasing slit width results in greater spectral resolution

37 측정기기일반적형태 : 홑빛살형, 겹빛살형, 다이오드배열 single beam

A double beam instrument is one in which the light source can be passed (simultaneously) through both a reference and a sample cell Purpose and approach 1.

38 A double beam instrument is one in which the light source can be passed (simultaneously) through both a reference and a sample cell Purpose and approach 1. adjust light output of the instrument to 100% transmission (0 % absorbance) 2. allows correction of the sample absorbance signal for nonanalyte absorbance Light beam is split using a chopper

39 시료용기 ( 용기 cell 또는 cuvette) 사용스펙트럼영역의복사선이통과하는물질 반사손실최소화 빛의방향에대해완전히수직. 실린더형 ( 통로길이, 반사손실 ) 주의 : 용기벽지문. 다른부착물. 사용전후세척. 물리적손상주의 ( 메탄올세척후휘발 ) 석영. 용융실리카 (200 ~ 350nm), 규산유리 (350 ~ 2000nm), plastic ( 가시선영역 )

40 Sample holder Sample is placed in a cell or cuvette 1, 5, & 10 cm path lengths are commonly available Glass or plastic Visible region Quartz or fused silica Ultra-violet and visible region

41 Detectors Two types Heat sensitive detectors Photon detectors Types of photon detectors Photovoltaic cells Phototubes Photomultiplier Tubes (PMT s) Photoconductivity Silicon photodiodes

42 Signal processors/readout Signal Processing Amplify the signal coming from the detector Converts signal coming from detector into a form that is easily displayed. e.g. current to (DC) voltage Many forms of readout Computer display Digital or analog readout Strip chart recorder Integrator

43 2.4. 정성및정량분석 정성분석 : 다소제한. 넓은흡수띠 정량분석 ( 가장유용하게이용 ) 비흡광화학종 검정선작성 표준물첨가법 혼합물동시분석 : 흡광화학종이두종류이상일경우

44 검량선작성 (standard curve) signal: 시료에대한기기분석의결과 blank signal: analyte 를함유하고있지않은시료에대한 signal 대부분의경우신호는 analyte 농도에비례 S = mc + S b m= sensitivity; S b =blank signal 44

45 표준물질첨가법 : A = εbv x C x /V t + εbv s C s /V t = unknown + known = mv s + I m= εbc s /V t I/m=V x C x /C s 따라서 C x = IC s /mv x 혼합물동시분석 : 전체흡광도 = 각성분흡광도의합 (sum) A 1 = A x1 + A y1 = ε x1 bc x + ε y1 bc y A 2 = A x2 + A y2 = ε x2 bc x + ε y2 bc y

46 혼합물동시분석 : 1M-H 2 SO 4 에 K 2 Cr 2 O 7 과 KMnO 4 혼합용액겹치는흡수 스펙트럼 A max440 =0.405, A max545 = 혼합물흡광도. 각이온의농도는? (Crλ max 440nm), (Mnλ max 545nm) 순수용액흡광도 1M-H 2 SO 4 에 K 2 Cr 2 O 7 (10-3 M) 과 KMnO 4 (2x10-4 M) A 440Cr =0.374, A 545Cr = A 440Mn =0.019, A 545Mn = A 1 = A x1 + A y1 = ε x1 bc x + ε y1 bc y A 2 = A x2 + A y2 = ε x2 bc x + ε y2 bc y

기기분석 _ 전자기복사선 Radiation source ( 광원 ) 1

기기분석 _ 전자기복사선 Radiation source ( 광원 ) 1 2-2. 2. Radiation source ( 광원 ) 1 a) Continuous wave(cw) sources ( 지속광원 : 띠파장 ) UV : D2 lamp, High pressure - Arc lamps (Ar, Xe, Hg) Vis : tungsten lamp (Halogen lamp) IR : Inert solid 1500~2000K eg.)