슬라이드 1

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1 Chapter 25. Voltammetry Potentiometry : no net current flow 전위차측정 Voltammetry (polarography): App. potential resulting current flow measurement. Polarography differential pulse polarography stripping analysis Introduction Principally, in voltammetry : 전류 vs 전압곡선해석 (voltammograms) Cell에전압을변화시키면서 생성전류 check Cell content : a Solution of interest b Stable reference electrode c Indicator electrode

2 25A Excitation signals in voltammetry Indicator electrode DMC 일경우 polarography (1922, Heyrovsky 가발명 ) DME 및 polarography cell 의구조 Hg drop rate : constant rate(5-30 방울 / 분 ) Hg drop 의 life : 2-12sec Voltage scanning rate : mV/min(DC polarography) 특징 : 1 Reproducibility 大 2 Every mercury drop 항상 surface 가새롭다 3 Electrolytic solution 의양 적게必要 4 Hg 대부분수용액에서화학적으로비활성 5 H 2 의 overvoltage 가크다 6 많은종의화학종에관해연구가능 단점 V vs SCE 이상의 + 전위에서 Hg 의 anodic dissolution 으 로인해측정불가

3 Fig Voltage versus time excitation signals used in voltammetry.

4 Polarography Ilkovic Equation: - Cell 을흐르는전류 1 전극반응의속도 Fast 2 전극표면으로물질의이동속도 Slow 그러므로 limiting current 는물질이동 ( 확산 ) 속도에비례 A : 전극의면적 D : 확산계수 DME : 실제로구형 volume : 수은의유속으로결정 (mg/sec) A = 0.851(mt) 2/3

5 id : 확산계수 C : 농도 D : 확산계수 m : 수은의유속 t : 수은방울의수명

7 Currents controlled by factor other than Diffusion Diffusion외에 Charge transfer Chemical reaction 산화환원종의전극표면흡착에의한전류 Kinetic current : 전류의크기가화학반응속도에의해통제되는전류 ex) Catalytic Currents 1) 전극부근에서화학반응에의해다시가수분해되 는반응에의한전류 ( 촉매과정에지배 ) 2) 물질의환원이촉매가없을때보다더 + 에서일어날경우 ex) 1) 2) H+ ion 의촉매환원

8 Adsorption Current 산화또는환원종이 전극에흡착 ( 이때전류크기 : available 전극표면에의해제한 ) Adsorption prewave 의 height 어떤특정농도까지소극제농도小大 환원종이더이상흡착되지않는곳의전위에서제 2 파발생 확산지배파 1 파 + 2 파 height 농도에비례

9 * Effect of complex formation on pornographic waves Ec, Ea 가영향 complex 생성에의해보다 negative (table 21-1 참조 ) Complex reagent 의농도의함수로 E 1/2 K 값결정에이용 The combining ratio of liquid to metal ion 결정可

10 * Pornographic maxima

11 발생원인 : 1 전극부근에서연속적인 stirring 2 흡착 억제방법 : 1 Hg flow 속도를느리게 2 지지전해질의노도증가및 chemical nature 변화 3 전극활성종의농도를낮춘다 4 계활성제를사용 (gelatin, 아교, tritonx-100) 계면활성제에서의농도 : trial & error 式으로결정

12 * Capillary characteristics : capillary constant 에서 maximum

13 * Temperature D : temperature sensitive 2.5%/1 Tests for Current-Limiting process Diffusion, kinetic, adsorption, and catalytic currents 구분하는기준 (1)-(5) 에관계된파고의변화 (1) 전극활동종의농도 (2) Hg 압력 ( 수은주의높이를변화 ) (3) ph (4) Buffer 농도 (5) 온도 ( 촉매, kinetic 포함 )

14 (1) 농도에대한한계전류의관계 Fig 3.6 참조 (A) (B), (C) -> 흡착, 촉매전류와의관계 (2) 수은주높이를변화 Fig 3.7 참조 전류가농도에무관한농도에서측정해야한다

15 (3) Simple Hg drop 의수명에대한전류의변화 Most valuable criterion for determining the current-limiting process ㄱ ) 시간에따른확산층의두께시간에따른수은방울면적의크기 ㄴ ) Kinetic & catalytic currents에대한반응속도는용액의체적에의존즉, 면적에비례ㄷ ) Adsorption-limited currents frest Hg 표면이나타나는속도

16 * Residual or charging current limit by 새로운전극표면이형성되는속 도즉, 즉, id는시간에따라증가 ic는시간에따라감소 Drop 수명의late -> ( 초기와평균보다 ) -> sens 大 (4) i d, i a 는 ph에무관 i k, i c 는 ph에의존 i c : buffer농도에의존 i k,d : 온도에의해영향

17 25B Voltammetric instrumentation 25B-1 Working Electrodes 25-1 식참조 Fig An operational amplifier potentiostat.

18 Working Electrodes

19 Fig 25-4.Potential ranges for three types of electrodes in various supporting electrolytes

20 25B-2 Modified Electrodes: Fig Functional groups formed on (a) a metal or (b) a carbon surface by oxidation.

22 25B-3 Voltammograms Fig Linear-sweep voltammogram for the reduction of a hypothetical species A to give a product P.

23 25B-4 Circuit Model of a Working Electrode Fig shows a schematic of three of a number of possible circuit models for the electrochemical cell.

24 25C Hydrodynamic Voltammetry 25C-1 Concentration Profiles at Electrode Surfaces. Fig A three-electrode cell for hydrodynamic voltammetry

25 Supporting electrolytes : (0.1M-1.0M정도) 사용이유 : ᄀ Soln. 의저항감소ᄂ Electrical field에의한전기적이동이아니고 Diffusion에의해서만전기활성종이이동해야한다. 선택 : Strong acid : HCl, H 2 SO 4 Strong based : (NaOH, LiOH) Neutral salt : (chlorides, perchlorates sulfates of alkali metal, tetraalkyloammonium ion) Complexing agents: (tartrate, citrates, cyanides, fluorides, amine)

26 *Limiting current : 전류급상승후전압을계속가하여도전류가거의변화하지않는부분 물질의전극에도달하는속도의제한을받기때문 실험조건조절하여확산속도만으로규정되면 ( 한계전류 확산전류 ) Half wave potential : 확산전류의 1/2 에해당하는전위 물질확인에使用 잔류전류의발생원인 : 1 바탕용액의존재하는미량의불순물의환원에기인 2 충전 or 축전전류에기인 용액에대한수은방울에전하를띄게하는전자의흐름때문

27 제거법 : 1 Blank의 polarogram을얻고시료용액의 polarogram으로부터얻어이두확산전극의차이無 2 보정법 : 분해전위까지의 polarogram을직선으로부터외연장하는법 E 1/2 : half wave potential 확산전류의반이되는점에서전위 i j (i d ) : limiting current residual 과 plateau current 사이의차 ( 용액의속의활성중의농도와비례 ) Residual current (charging, condenser current) 어떤종의산화-환원성질의특징 (25-3)

28 Profiles for Planar Electrodes in Unstirred Solution. Figure 25-9 E-t and I-t curves

29 Fig Concentration distance profiles (diffusion controlled reduction).

30 Fig Flow patterns at the electrode surface

31 Fig

32 Fig Concentration profiles at an electrode/solution interface.

33 25C-2 Voltammetric currents (Eqs. 25-5,6,7) C o A 0, the current becomes the limiting current, Eq into 25-6 eq. 25-8

34 Similarly, for the products. c = i 0 k P / P E E E appl appl 1/ 2 = = E E E 1/ 2 1/ 2 0 A = E E ref 0 A log n log n i 1 i i k k A P E ref

35 Fig Voltammograms for Mixtures of Reactions

36 Fig Mixed Anodic/Cathodic Voltammograms

37 25C-3 Oxygen Waves Fig

38 Removal of Oxygen Dissolved oxygen 정량방해물 분석전에제거 O 2 + 2H + + 2e - = H 2 O 2 H 2 O 2 + 2H + + 2e - = 2H 2 O 제 1 파 제 2 파 ph7 에서 E 1/2 = 0--1V vs SCE Air-saturated aqueous solution : 4mM O 2 level 5 μa id 유발 제거방법 : 순수한 He, N 2 로 5-20 분간용액을 bubble 시 N 2 tank 에미량 혼입된 O 2 는 acidic V 2+ or Cr 2+ 또는 hot copper 의위를질소를 통기하므로써제거

39 25C-4 Applications of Hydrodynamic Voltammetry Fig Voltammetric detect in Chromatography

40 Fig The Flow Cell

41 Fig The Clark Oxygen Sensor Cathodic : O 2 + 4H + + 4e - = 2H 2 O Anodic : Ag + Cl - = AgCl(s) + e - glucose + O2 H 2 O 2 + OH - glucose oxidase O 2 + H 2 H 2 O 2 O + 2e + gluconic acid -

43 Fig Amperometric titration curves

44 Rotating Electrodes Voltammetry at rotating Pt Elctrode, 600ppm이상으로 rotating 물질이동 : diffusion & mechanical mixing i 1 이 diffusion only보다 20배이상大 1/2I 2...Na 2 S 2 O 3 표준액으로적정

45 Fig

46 25D Cyclic Voltammetry Fig

47 E i P P = E Pa E = Pc 5 n = 3/ / n AcD 1/ 2 v 1/ 2

48 25D-1 Fundamental Studies Fig Parathion in acetate buffer R-C 6 H 4 NO 2 + 4e - + 4H + R-C 6 H 4 NHOH + H 2 O R-C 6 H 4 NHOH R-C 6 H 4 NO + 2H + + 2e - R-C 6 H 4 NO + 2e - + 2H + R-C 6 H 4 NHOH

50 Potential sweep triangle form 1-2 sec 內에 sweep완료 (Fig 참조 ) 1) 물질을환원이환원종을다시산화 A, D 사이의차 =( /n)V reversible Rate of OX-Red process, mechanism of OX-Red preelec의연구에주로이용

51 25D-2 Determination of Analytes Using CV Fig shows how the sandwich arrangement is assembled on the surface of the gold electrode.

52 25D-3 Digital Simulation of Cyclic Voltammograms Fig shows an experimental cyclic voltammogram of the Fe(CN) 6 3- Fe(CN) 6 4- couple at a borondoped diamond thin-film electrode compared to a cyclic voltammogram simulated by DigiSim.

53 1.1. Instrumentation and Apparatus 구성 : 1) Cell 2) Electrode 3) Potentiostat or polarograph, 4) O 2 제거 system 1) Cell (ⅰ) DME 삽입구 ( 팬극전극 ) (ⅱ) Inert gas 통기구 (inlet, outlet) (ⅲ) 반대극연결단자 Reference Hg pool cell SCE 用 cell (H-cell) 크기 : 5-10ml 用

54 항온조에담구어측정 H-cell 구조설명 fig 3.9, 3.10 Reference 연결 KCl 포화용액 Potentiostats : (3전극법) 용액의저항을보상하기위해 reference, concenter, indicator전극을使用 Ref. feed back 전압보상된전위 counter electrode에가해진다.

55 Applications 작도법 : 대각선법, 교정법 Determination of Concentration 절대정량법 : i d, D, m, t, 실험적으로결정 ->C정량 1 검량선법 : 시료와동일조건 표준용액 검정선작성시료의파고측정 검정선으로부터농도결정 Error 1% 2 표준첨가법 : 1 시료용액일정량 (Yml) (i d ) s 측정 2 시료용액 + Cs의 Vml 을넣고 (i d ) s 측정 Error 5%

56 3 내부표준법 (Internal standard or pilot ion method) 시료용액 (C 1 ) + 기시량의내부표준물질 (C 2 ) 검량선착성 K는확산전류정수비 ( 적화전극특성과무관, 용액의점도, 온도에무관 ) Scope of Application 1 Electroactive species : 무기양이온, 음이온, 분자 2 Nature of sample 3 Detection limit 4 Interference

57 Varication of the conventional polarographic method 1940 년초반기에활발히연구 (Breyer, Gutmann, Grahame ) AC polarography DC 전압 + 수 mv 정도의교류전압중첩 적하전극에공급 전체전류중교류성분만을증폭, 정류한다음 직류가전압 vs 교류전류를 detector Cell impedance에기여하는 physical processes a) Ionic migration which, among other things, determines the ohmic resistances b) Charging of the electrical double layer at the electrode - solution interface c) The fafrdic process primary subject

58 O x +ne Red( 가역적, fast) 위반응에서 faradic ac currents가흐른다분해전위에서반좌전위바로앞까지 이때 ac전류는에의해결정반좌전위이후에는 ac전류 [O x ] 에의해결정반좌전위파라데이터관류최대 최대함께전류범위에도달전류 0

59 정현파교류 polaro 에서가역파의평균 peek 전류크기 q : 2.4F(3m/4πd) 2/3 t 2/3 용도 : 1 정량 정량에使用 10-6 M 까지정량 2 전극반응의반응속도를연구

60 2. Pulse polarography (25E. Pulse voltammetry) Charging currunt(non-faraday current) 을최소로하기위한기술 S.w. 충전전류제거해도 DME 사용하면 전극표면적이변화하므로 유발전류 (charging current) 제거방법 : 연속적인전압증가가아닌단속적방출수명의끝부분에 rectangular voltage pulse 加 [ 약40msec] 교류전류 17msec 사이에 draw out 1 Pulse : voltage pulse 의 amplitude 를증가. Fig3.16 (A) (B) (C) 2 Differential pulse : constant amplitude를증가시키는 voltage에중첩시킴. Fig 3.16 (D) (E) (F)

61 1) Pulse : drop life의끝부분에서 40msec동안 s.w. pulse 전압加 Pulse의 1/2 뒷부분에서 20msec 동안전류측정 (charging current min) 2) 가전압 pulse의 amplitude 시간에따라증가 DC wave와유사 3) Differential pulse (25E-1 Differential-Pulse Voltammetry) 1) pulse 와同一 2) Constant amplitude(5-100mv) 의 pulse voltage를중첩시켜加 3) 전류측정 pulse을加하기전의전류와 pulse 끝에서각각측정하여차를낸다. Detection limit : M

62 Fig

63 Fig

64 3. Square wave polarography (25E-2. Square-wave voltammetry) Sine wave CH선 sw 加장점 : 비파라데이전류 시간이증가 지수함수적으로감소 매반주기의끝에서단속적으로측정 바탕선전류가거의없다. 고감도정량범위 : 10-8 M 실제구형파 고주파 (100kHz-4MHz) 로변주 고주파전압加 저주파전류out( 감도증가 )

65 Fig Fig

66 4. Rapid-scan osillographic voltammetry ( 책 25F ) Principles : drop time 동안 or 일부동안 voltage scan을 accomplish. I vs E curve 측정 At positive more than peak DC polarography와동일한 mode로전류가흐른다. At potential of more negative than E p 물질이동의이동이느리기때문에전류감소 Theory : E p =E 1/2-1.1RT/nF i P =kn 3/2 AD 1/2 Cν 1/2 A : 전극표면적 ν : scan (V/sec) D : 확산계수 n : 전자수 ( 전극반응에참여하는 ) C : 농도 k : Randles-sevik 상수 Dection range : M

68 25G Application of Voltammetry 25G-1 Inorganic Applications Voltammetry is applicable to the analysis of many inorganic substances. 25G-2 Organic Voltammetric Analysis Effect of ph on Voltammograms Solvents for Organic Voltammetry

69 Reactive Functional Groups

70 Stripping Voltammetry( 책 25H ) Principle : Hg와 analgam을이루는 cation 및 Hg와 slightly soluble compounds을만드는 anion정량에利用 1 전해농축 : limiting current에대한전위에고정하여전압加 (Preconcentration step) 2 정치 배농축 3 Stripping : 1 cation + 에서 - 전위로 sweep 2 anion - 에서 + 전위로 sweep

71 Fig

72 Electrodes : 1 HMDE (hanging mercurry drop elec) 2 Hg-coated pt 3 Glassy carbon (Pre step) HMDE :1Hg 2-3 drop teflon spoon으로 pt wire 끝에붙인다. 2 Graphite rod, carbon rod, pt wire에 Hg film(10-100μm ) 로 plating. (1step) Coating된전극혹은 HMDE 의 Hg에산화종이환원되어농축 (cathodic deposition) Cu, Pb, Cd, Bi, Zn ions... (2step) 정치 (3step) Stripping (cathodic or anodic)

73 Sensitivity : 1) (Pre-elctrolysis) 때생성되는양에의존 a 용액속의물질의농도 b 전극의모양 c 전해농축시의전류밀도 d 물질의전극쪽으로이동 e 전해시간 2) Stripping step에서사용된방법 ex) Linear-sweep voltammetry Differential- pulse voltammetry Sens. limit : 바탕전해질이나희석시의시약에의한흔적량의불순물오염 0.1 M KCl (0.0002%) -> 10-7 M Pb에해당 Detection range : M

74 Voltammetry at Solid Electrodes DME 의 limitation vs SCE 에서측정不 ( 수용액 ) 2 Low sensitivity 1) Voltammetry at Stationary Electrodes 1 Organic compound anodic oxidation 측정에주로이용 (Pt, Au, C, etc) 2 Adsorption, deposition or oxide film formation Process : time dependent 3 Initial current -> 수분후 constant current 측정要 4 Instantaneous current 를 recorder linear sweep voltammetry, sweep rate 74mV/min 5 Current maximum height concentration Peak height r : voltage sweep rate App : DO 측정

77 25I Voltammetry with Microelectrodes ) 1 1 ( ) 1 1 ( ) 1 1 ( 0 A 0 A 0 A A r nfadc i r c r Dt c x c + = + = + = δ δ π 25I-1 Voltammetric Currents at Microelectrodes The advantage of microelectrodes 8 가지책참조 As shown in Fig 25-37, microelectrodes take several forms.

78 Fig

80 25I-2 Applications of Microelectrodes In section 25F-2, we described the use of a carbon fiber electrode to monitor concentration of the neurotransmitter dopamine in rat brains in response to be havioral change. 25I-3 The scanning Electrochemical Microscope Another application of microelectrodes is the scanning electrochemical microscope(secm), introduced by Bard in 1989.

81 The Cell Biology of Extracelluar acidification Fig. IA4-1

82 Fig. IA4-2

10 (10.1) (10.2),,

10 (10.1) (10.2),, Chapter 16 Precipitation Equilibria Copyright 2001 by Harcourt, Inc. All rights reserved. Requests for permission to make copies of any part of the work should be mailed to the following address: Permissions