UV-Vis spektrometrie. Brno 2016, Dominik Heger, Ústav chemie a RECETOX, MU

Transcription

1 UV-Vis spektrometrie Brno 2016, Dominik Heger, Ústav chemie a RECETOX, MU

2 Sluneční světlo

3 What is UV-VIS spectroscopy measuring? Electronic transitions. l / nm Vacuum-UV Near-UV (quartz) Visible E int = E el + E vib + E rot D E = h n 3

4 Spectrum Abscissa (x) ~ D E ~ ~ 1/l Ordinat (y) ~ intensity ~ probability of transition the oscillator strength f 4.3e-9 e d ~ n ~ 4.3e-9 e max D ~ n 1/2 D E =hn =hc/l=hc n ~ n ~ 4

5 Překryvový integrál Dipólový moment Hueckel molecular orbital method (HMO) 5

6 Elektronová spektroskopie 6

7 Beer Lambert Bouguer law -log (F t /F 0 ) = -log t i = ecb = A(l) t i = F t /F 0 = F r /F 0 internal transmittance (transmission factor) reflectance (reflection factor) a = F a /F 0 = 1 t absorptance (absorption faktor) Term Symbol Unit Monochromatic radiant power F W F 0 F a F t (decadic) internal absorbance A 1 F r Molar (decadic) absorption coefficient e L mol -1 cm -1 Absorption pathlength b cm -1 Cell pathlength l cm -1 Extinction sum of absoption, scattering and luminescence.

8 Beer Lambert Bouguer law Calibration Curve of Fe A 510nm Equation y = a + b*x No Weighting Weight E-4 Residual Sum of Squares Adj. R-Square Value Standard Error A 510nm Intercept E A 510nm Slope Fe2+ (mm) 8

9 Beer Lambert Bouguer law limitations Chemical reasons chemical equilibria (acid-base reaction, self-association, complexation, thermal reaction, photochemical reaction, inhomogenous samples) Physical reasons thermochromism, saturation effects depletion of the ground state, incident radiation must be parallel 9

10 Jak funguje spektrometr?

11 Single beam UV VIS spectrophotometer with diod array detector 11

12 Single beam UV VIS spectrophotometer 12

13 Double beam UV VIS spectrophotometer 13

14 Double beam, double monochromators UV VIS spectrophotometer 14

15 UV VIS spectrophotometer Light source Continuum spectral-line source W-halogen lamp <330; 1200) nm D 2 lamp <UV; 330> nm Xe arc lamp <190; 1000> nm Detectors Spectrometer Single beam double beam Sequential simultaneous Cuvettes shape volume material photo-emisive detectors (evacuated phototubes, photomultiplier...) semiconuctive detectors (photodiods; detectors with a spacial resolution CCD charge-coupled device) use of matched cells 15

16 Lamps 16

17 Methyl-Naftalen A t log (F t /F 0 ) = -log t i = ecb = A(l) 17

18 Franck-Condon Principle; Vertical excitation 18

19 Franck-Condon Principle Benzene in hexane ~n / ( m 1 ) A 0.0 l / nm band Hot band 19

20 Shifts Effects hyperchromic Absorption bands of organic molecules hypsochromic hypochromic bathochromic Type of transition e max n p * (R) < 100 p p * (K) > (B benzenoid) (E - ethylenic) ~

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23 UV-VIS-NIR spekrum vody C8785_Photophysical_spectroscopic_methods 23

24 Measuring techniques Kvantitativní analýza Multicomponent analysis Derivative spectroscopy-finding of maxima Antonov Step by step filter (SBSF) Resolution of overlapping bands (x deconvolution) Curve fitting Gaussian or others Nonparametric methods Singular Value Decomposition, Target Factoral Analysis Difference absorption spectroscopy Absorbance matching 24

25 Derivative spectroscopie 25 Antony J. Owen: Uses of Derivative Spectroscopy, Agilent Technologies, 1995

26 Application of derivative spectroscopy to benzene 26

27 Derivative spectroscopy 1 st derivative e / (M -1 cm -1 ) ~n / ( m 1 ) l / nm nd derivative 3 th derivative 4 th derivative e / (M -1 cm -1 ) ~n / ( m 1 ) e / (M -1 cm -1 ) ~n / ( m 1 ) e / (M -1 cm -1 ) ~n / ( m 1 ) 4.00E E l / nm l / nm l / nm E-008

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29 ph titration o-nitrophenol Photochromism 29

30 solvatochromism change in the position, intensity, and shape of absorption bands due to the surrounding medium = perichromism (peri - around) surrounding medium - liquids, solids, glasses, and surfaces negative solvatochromism a blue (hypsochromic) shift positive solvatochromism a red (bathochromic) shift N E T E T O N +O O solvent polarity increases solvent polarity increases 30

31 Reichardt s dye betaine-30 2,6-diphenyl-4-(2,4,6-triphenyl-pyridium)phenolate dipol moment - dipol/dipol, dipol/induced dipol interaction S 0 S 1 p electron system - dispersion interaction phenolate oxygen - highly basic EPD ceter N hn N O O dipol moment in 1,4-dioxane g = D e = D 31

32 E T (30) and E T N scale of solvent polarity E T - molar electronic transition energy Látka E T N [E T ] = kcal/mol n-hexan [E TN ] = 1 Dichlor methan n ~ E T (30) = hc max N A = ( E -3)( max / cm -1 ) =28591/(l max / nm) n ~ EtOH Voda 1 E TN = (E T (solvent)-e T (TMS))/(E T (water)-e T (TMS)) = (E T (solvent) )/32.4 E T N (TMS) = E TN (H 2 O) = TMS = Tetramethylsilane 32

33 Literature Silverstein R. M. et all: Spectrometric indentification of organic compounds, John Wiley & Sons, inc. Reichardt, C. (1994). "Solvatochromic Dyes as Solvent Polarity Indicators." Chemical Reviews 94(8): UV-vis spectra Heinz-Helmut Perkampus: UV-VIS Atlas of Organic Compounds science-softcon "UV/Vis+ Spectra Data Base" (UV/Vis+ Photochemistry Database) 7th Edition (2010); ISBN UV-vis diffuse reflectance Francis M. Mirabella: Modern Techniques in Applied Molecular Spectroscopy 33

34 Diffuse Reflectance Spectroscopy Diffuse (volume) reflection phenomenon resulting from the reflection, refraction, diffraction and absorption MgO BaSO 4 PTFE polytetrafluoret hylene = halon = Spectralon 34

35 Diffuse Reflectance Spectroscopy 35

36 Diffuse Reflectance Spectroscopy 36

37 Diffuse Reflectance Spectroscopy Harrick - Praying Mantis 37