[PDF] Ultraviolet and visible spectrometry





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How to Read and Interpret UV-VIS Spectrophotometric Results in

13-Jun-2021 The absorption of radiation causes the promotion of electrons from the ground state to the excited state in functional groups called chromophore ...



Spectroscopic studies of neocarzinostatin and its chromophore: UV

+ uv. + BME. 9. 8. 7. 6. 5. 4. 3. 2. Chemical Shift (pprn). Figure 6. 360-MHz spectra of native and UV-irradiated chromophore and chromophore from BME-treated 



CHEMISTRY PAPER No. 12: ORGANIC SPECTROSCOPY

Learning Outcomes. 2. Introduction. 3. Important terminologies in UV-Vis spectroscopy. 3.1 Chromophore. 3.2 Auxochrome. 3.3 Bathochromic shift or red shift.



Excited-state properties of the indole chromophore: electronic

From measurements of UV and IR linear dichroism on molecules partially oriented instretched polyethylene host the transition moment directions for the first 



Detection of UV-transparent Compounds by Addition of a Mass

While. UV detection is used for qualitative analysis and quantitative analytical measurements the compound of interest must have a UV chromophore. For 



Synthesis of Chromophore-Labeled Polymers and Their Molecular

In this experiment the need for a GPC system is eliminated by introducing a chromophore group and UV–vis spectroscopy is used to determine the Mn values of the 



UV Spectroscopy

UV Spectroscopy. III. Chromophores. C. Substituent Effects. General – Substituents may have any of four effects on a chromophore i. Bathochromic shift (red 



Chromophore- An Utility in UV Spectrophotometer

Chemical structure of beta-carotene [1-2]. The eleven conjugated double bonds that form the chromophore of the molecule are highlighted in red [3]. When white 



Impact of the redox state of flavin chromophores on the UV–vis

12-Sept-2019 Impact of the redox state of flavin chromophores on the UV–visible spectra redox and acidity constants and electron affinities. Padmabati ...



3. Spectroscopie UV-Visible

d'onde se situent dans le domaine de l'ultraviolet (200 nm – chromophore : partie de la molécule responsable de l'absorption d'un photon.



Chapitre III: Les spectres UV-visible et infrarouge

Chapitre III: Les spectres UV-visible et infrarouge Rappel: un « chromophore » est un groupe d'atomes responsable d'une absorption caractéristique.



Ultraviolet and visible spectrometry

chromophore a group of atoms responsible for UV/VIS absorption of the molecule. e.g. double bonds C=C



Chapitre XI Transitions électroniques Spectroscopie UV-visible 1

On appelle chromophore (de ????? couleur et ??????



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La Spectroscopie UV est une bonne méthode pour l'étude des équilibres en solution très diluée dans la mesure où ils impliquent un changement du chromophore.



INTRODUCTION A LA SPECTROSCOPIE

La spectroscopie UV-Visible est une spectroscopie moléculaire d'absorption Le spectre UV-Visible permet l'identification du groupement chromophore qu'il.



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Schématiquement le chromophore est donc le groupement Spectre d'absorption UV du chlorhydrate de terbinafine dans le méthanol. CRAPC-EXPERTISE.



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Ultraviolet (UV) and Visible Spectroscopy - hmmcollegeacin

Chromophore A covalently unsaturated group responsible for absorption in the UV or visible region is known as a chromophore For example C = C C C C = O C N N = N NO 2 etc If a compound absorbs light in the visible region (400-800 nm) only then it appears coloured Thus



Searches related to chromophore uv PDF

occurs is called chromophore (Table 1) A chromophore is defined as an isolated covalently bonded group that shows a characteristic absorption in UV/Visible region For example C=C C=C C=O C=N N=N R-NO 2 etc Table 1 Typical absorption of simple isolated chromophores Chromophore Transition ? max (nm) ? max ? –bonded electrons C-C C-H

What is a chromophore in UV analysis?

A chromophore is a region in a molecule where the energy difference between 2 different molecular orbitals falls within the range of the visible spectrum. The present review is an attempt to provide detail knowledge and informations about cuurent status of chromophore utilization in the field of UV analysis. Content may be subject to copyright. ...

What is a chromophore?

Molecules or parts of molecules that absorb light strongly in the UV-vis region are called chromophores. Let’s revisit the MO picture for 1,3-butadiene, the simplest conjugated system. Recall that we can draw a diagram showing the four pi MO’s that result from combining the four 2p z atomic orbitals.

What happens when light passes through a chromophore?

When light passes through the compound, energy from the light is used to promote an electron from a bonding or non-bonding orbital into one of the empty anti-bonding orbitals. A chromophore is a region in a molecule where the energy difference between 2 different molecular orbitals falls within the range of the visible spectrum.

How can chromophores improve EO properties of polymeric NLO materials?

Moreover, the unique nanoscale environment created by the shape and size, dielectric properties, and distribution of chromophores in crosslinkable polymers with dendrons and dendrimers can all play critical roles in maximizing the macroscopic EO properties of polymeric NLO materials.

Advanced strategies in food analysis UV/VIS spectrometry

Richard

Ultraviolet and visible spectrometry

Theoretical overview

Molecular absorption of electromagnetic radiation

changes of energy state of the molecule include electronic state Ee =150-600 kJ/mol (electron transitions between orbitals) vibrational state Ev =2-60 kJ/mol rotational state Er relation to the absorbed radiation wavelength

E Ee Ev Er = h . Ȟ = h . c / Ȝ

h = 6.626 . 10-34 J s (Planck constant)

Spectral regions

Region Ȝ Absorbing compounds

Far ultraviolet (vacuum UV region) 190 nm saturated and mono-unsaturated (Near) ultraviolet 190-380 nm poly-unsaturated and aromatic

Visible light region 380-780 nm coloured

Visible light absorption

Table of complementary colours:

Ȝ (nm) Colour of light Colour of absorbing body

400435 violet yellow-green

435480 blue yellow

480490 green-blue orange

490500 blue-green red-orange

500560 green red

560580 green-yellow violet

580595 yellow-orange blue

595620 red-orange green-blue

620760 red blue-green

Advanced strategies in food analysis UV/VIS spectrometry

Richard

Labert-Beer law

transmittance T = I/I0 in a diluted solution the value of absorbance A measured at the specific wavelength is proportional to the concentration of absorbing compound

AȜ = - log T = log (I0/I) = İȜ . b . c

Energy changes of electronic transitions

Probability of transition influences the value of absorption coefficient relation to spin state of excited electron

1) transition S0 (ground singletĺS1 (upper singlet) is allowed

İmax 3105 l.mol-1.cm-1

2) ĺ

İmax 0 l.mol-1.cm-1

E ı*

n nĺı* Advanced strategies in food analysis UV/VIS spectrometry

Richard

Terms used in UV/VIS spectrometry

chromophore a group of atoms responsible for UV/VIS absorption of the molecule, e.g. double bonds C=C, C=C-C=C, C=O, N=N, aromatic rings etc. auxochrome a substituent that increases absorption of a molecule, typically methyl, hydroxyl, alkoxyl or amino group or an atom of halogen;

ʌ-electron system,

the Ȝmax value is shifted to a longer wavelength (bathochromic efect) bathochromic effect (red shift) Ȝmax to longer wavelength caused by molecule modification or a change of solvent hypsochromic effect (blue shift) a shift to shorter wavelength hyperchromic effect an increase of absorption hypochromic effect a decrease of absorption Some chromophores and the corresponding transitions

Chromophore

an example of compound

Transition Ȝmax (nm)

H2O ıĺı 183

C-C a C-H, CH4 ıĺı cca 170, 173

C-X, CH3OH, CH3NH2, CH3I ĺı 180-260, 187, 215, 258

C=C, H2C=CH2 ʌĺʌ 160-190, 162

H22 ʌĺʌ 217

C=O, ĺʌʌĺʌ 270, 170-200, 270, 185

H2 ĺʌʌĺʌ 328, 208

C=N ĺıĺʌ 190, 300

N=N ĺʌ 340

C=S ĺʌ 500

NO2 ĺʌ 420-450

N=O ĺʌ 630-700

Advanced strategies in food analysis UV/VIS spectrometry

Richard

The effect of conjugation

Conjugated polyenes:

n n CH3n3

Ȝmax (nm) log İ Ȝmax (nm) log İ

2 217 4.3 223 4.4

3 268 4.7 275 4.5

4 304 ? 310 4.9

5 334 5.1 341 5.1

Į-Ȝmax= 447 nm

ȕ-Ȝmax= 451 nm

Ȗ-Ȝmax= 462 nm

Ȝmax= 476 nm

Advanced strategies in food analysis UV/VIS spectrometry

Richard

Benzene and its derivatives

Compound Ȝmax (nm) log İ Ȝmax (nm) log İ Ȝmax (nm) log İ benzene 204 3.9 254 2.0 - - toluene 207 3.8 261 2.4 - - brombenzene 210 3.9 261 2.3 - - phenol 211 3.8 270 3.2 - - benzaldehyde 250 4.1 280 3.0 320 1.7 acetophenone 246 4.0 280 3.0 320 1.7 benzoic acid 230 4.1 273 3.0 - - aniline 230 3.9 280 3.5 - - styrene 247 4.0 281 2.0 - - cinnamaldehyde 285 4.4 - - - - cinnamic acid 273 4.3 - - - - biphenyl 248 4.2 - - - -

Heterocyclic compounds

5-membered

Compound Ȝmax (nm) log İ Ȝmax (nm) log İ furan 200 4.0 - -

2-furaldehyde 227 3.3 272 4.1

2-acetylfuran 225 3.4 269 4.1

pyrrole 210 4.2 240 2.5

2-acetylpyrrole 250 3.6 287 4.2

thiophene - - 235 3.7

2-acetylthiophene 260 3.9 285 3.7

thiazole - - 240 3.6 Advanced strategies in food analysis UV/VIS spectrometry

Richard

6-membered

Compound Ȝmax (nm) log İ Ȝmax (nm) log İ Ȝmax (nm) log İ

Pyridine 195 - 250 3.3 - -

2-Picoline - - 262 3.4 - -

Pyrazine - - 260 3.7 - -

Quinoline 227 4.6 275 3.7 313 3.4

Isoquinoline 218 4.9 262 3.6 317 3.5

Pyrimidine - - - - 343 3.3

Polycyclic aromatic hydrocarbons

Advanced strategies in food analysis UV/VIS spectrometry

Richard

Practical rules for spectrophotometric measurement choice of a measuring cell quartz: for UV glass: for VIS plastic: for some routine measurement in VIS length of a cell: most commonly 0.15 cm optimum absorbance 0.12 choice of a solvent the kind of solvent may influence the position of spectral band and the maximum absorbance spectrum recording scan rate very fast scan higher noise of the spectrum spectral band-width narrow SBW (0.20.5 nm) better resolution and higher noise of the spectrum wide SBW (24 nm) low resolution, low noise; suitable for the recording of wide bands (VIS region) and the highly precise measurement of a single absorbance value sample dilution allowed only for stable species

Solvents for UV spectrometry

Table the lowest wavelengths of measurement with the solvent

Solvent Ȝ (nm) Solvent Ȝ (nm)

acetonitrile, water 190 chloroform 240 isooctane, cyclohexane 195 ethylacetate 260 hexane 201 dimethylformamide 270 methanol, ethanol 205 acetic acid. 270

1,4-dioxane 215 benzene 280

diethylether 220 toluene 285 glycerol 230 pyridine 300 dichloromethane 233 acetone 330 Advanced strategies in food analysis UV/VIS spectrometry

Richard

Effect of solvent on the absorption spectrum

The kind of solvent slightly affects

Ȝmaxİ

shape of the spectrum

Spectra of biologically important compounds

Compound Ȝmax (nm) İ (l.mol-1.cm-1)

NAD, NADP 260 15 000

NADH, NADPH

260 15 000

340 6 200

FMN, FAD

260 15 000

375 10 000 (FMN)

9 000 (FAD)

445 12 500 (FMN)

450 11 000 (FAD)

pyridoxal

250 3 000

320 6 000

spectra of phenol measured in isooctane and ethanol Advanced strategies in food analysis UV/VIS spectrometry

Richard

Compound Ȝmax (nm) İ (l.mol-1.cm-1)

cholesterol 235 20 000 calciferols 265 18 300

ȕ-carotene 450 120 000

retinol 330 45 000 trans, trans-9,12- octadecenoic acid.

231 35 000

adenosine 267 12 300 guanosine 248 11 000 cytidine 271 9 100 thymidine 267 9 650 uridine 262 8 500 Advanced strategies in food analysis UV/VIS spectrometry

Richard

Two-component analysis

Rule of absorbance additivity:

Advanced strategies in food analysis UV/VIS spectrometry

Richard

Derivative spectrometry

T = /0

A = - log10T = - 2,303 . ln T = . b . c

dA/d = -2.303 . (1/T) . dT/d = b . c . d /d the first (and also the second) derivative of absorbance is proportional to the concentration of the absorbing compound original spectrum

A vsȜ

1st derivative

dA/dȜ vs. Ȝ

2nd derivative

d2A/dȜ2 vs. Ȝ Advanced strategies in food analysis UV/VIS spectrometry

Richard

Flow injection analysis FIA

an optional arrangement of a (spectrophotometric) measurement instead of the batch-preparation of the measured solution the sample is injected into the flow of the carrier solution or the reagent solution and then measured (usually using a spectrophotometer) FIA is much faster than traditional batch analysis and can be easily automated An example of FIA arrangement: determination of chlorides

Chemical principle:

2 Cl- + Hg(SCN)2 ĺ HgCl2 + 2 SCN-

SCN- + Fe3+ ĺ [FeSCN]2+

absorbance of a red-coloured solution of ferric-thiocyanate complex is measured

FIA arrangement:

Equipment for FIA

peristaltic pump (tubes of a diameter of 0.25 to 2 mm, flow rate 0.0005 to 10 ml/min)

PTFE capillaries, join pieces

low pressure injection valve (sample loop 5O additional parts: filters, micro-columns, valves, thermostat detector (most often a spectrophotometer with a flow-through cell) a peristaltic pump delivers the reagent (a solution of mercury thiocyanate and ferric sulphate) at a constant flow rate a sample ȝis injected into the flow the reactions takes place in the capillary the product is measured in a flow-through cell of a spectrophotometric detector operated at 480 nm and an absorbance peak is recorded the next injection follows after 40 s approx. 100 samples per hour can be analysedquotesdbs_dbs16.pdfusesText_22
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