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Analytical Chemistry > UV-Vis Spectroscopy > Flashcards

UV-Vis Spectroscopy Flashcards

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1
Q

UV-Vis Transitions

A

bonding to antibonding
sigma to sigma*
pie to pie*

nonbonding to antibonding
n to sigma*
n to pie*

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2
Q

Forbidden UV-Vis Transitions

A

sigma to pie*
pie to sigma*

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3
Q

Lowest to highest energy
pie, sigma, sigma, pie, n

A

sigma, pie, n, pie, sigma

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4
Q

Functional groups that absorb in the UV and Vis regions

A

Chromophores

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5
Q

functional groups that do not absorb in the UV and Vis region but have effect of shifting chromophore peaks to different wavelengths

A

Auxochromes

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6
Q

absorbing species that shared pi and sigma electrons, unshared outer electrons

A

organic compounds

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7
Q

absorbing species which have unfilled d and f orbitals

A

inorganic species

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8
Q

Type of Shifts

A

Bathochromic
Hypsochromic
Hyperchromic
Hypochromic

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9
Q

shift in lamba max to longer wavelength

A

bathochromic shift

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10
Q

shift in lamba max to shorter wavelength

A

hypsochromic shift

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11
Q

increase in the intensity of UV maxima

A

hyperchromic shift

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12
Q

decrease in intensity of UV maxima

A

hypochromic shift

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13
Q

Basic Instrumentation (UV-Vis)

A

Radiation Source
Wavelength Selector
Sample Holder
Detector
*Computer for signal processing and output

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14
Q

Common Radiation Source for UV-Vis

A

Deuterium arc lamp
Tungsten halogen lamp

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15
Q

radiation source that emits in one direction only and had a half-life; common for UV

A

deuterium arc lamp

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16
Q

Radiation source common for Vis; polychromatic light is required; low noise

A

Tungsten Halogen Lamp

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17
Q

Device that uses filter as wavelength selector; for visible region; single wavelength

A

Photometer

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18
Q

Uses monochromator as wavelength selector; multiple wavelength; for UV-Vis region (occ for IR)

A

Spectrometer/ Spectrophotometer

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19
Q

small tube-like container with straight sides and a square cross-section

A

cuvette

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20
Q

distance of light that goes through the interior walls of a cuvette; inner distance from front to back window

A

Cuvette Path Length

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21
Q

Standard Cuvette Path Length

A

10mm

22
Q

Lowest in cost cuvette; not resistant to all solvents; for Vis region only

A

acrylic plastic cells

23
Q

Type of cell that is slightly more expensive than acrylic cells ; used in visible region only

A

Silicate glass cells

24
Q

type of cuvette characterized for being very expensive; used for both UV and Vis region

A

Fused quartz cells

25
Q

type of cell that can be used when sample volume is extremely limited (5microL)

A

microcells

26
Q

The loss of sensitivity of microcells depends on the ____ and __

A

degree of aperturing and optical geometry

27
Q

Do not touch the ____ with fingers, as oil can cause ___

A

optical surface; significant absorbance

28
Q

If optical surfaces get mild contamination, the cell can be wiped with ___

A

photographic tissue

29
Q

Remedy for serious contamination of optical surface

A

Using mild sulfonic detergent

30
Q

Remedy for severe contamination of optical surfaces

A

Treatment with hydrochloric acid or nitric acid

31
Q

Spectrophotometers usually contain either ___ or ___ detector

A

photomultiplier tube or photodiode detector

32
Q

contain several photodiode detectors instead of a single one

A

photodiode array

33
Q

Types of instruments (UV-Vis)

A

Single-beam
Double-beam in space
Double-beam in time
multichannel

34
Q

type of instrument where there is only one light beam or optical path from source to detector

A

Single-beam

35
Q

two beams are formed in space by a V-shape mirror called beamsplitter

simultaneously

A

double-beam in space

36
Q

beams are separated in time by a rotating sector mirror that directs the entire beam from monochromator first through the reference cell and then the sample cell

alternately

A

double-beam in time

37
Q

type of instrument that able to scan an entire spectrum in 0.1 seconds

A

multichannel

38
Q

Problems in Measurement (UV-Vis)

A

Strong Absorbance
Weak Absorbance
Interference
Sample Decomposition

39
Q

Remedy for strong Absorbance

A

dilute sample to an absorbance level within the linear dynamic range

40
Q

Reducing the noise level will?

A

directly improves the precision of results

41
Q

Increasing slit width will?

A

Allow more light, reduce the noise level, and improves the precision of results

42
Q

Types of interference

A

Scattering
Fluorescence

43
Q

Scattering effect can be reduced by?

A

placing the sample as close as possible to detector

44
Q

Types of scattering

A

Rayleigh
Tyndall

45
Q

occurs when the particles are small relative to the wavelength of light and is inversely proportional to the fourth power of wavelength

A

Rayleigh scattering

46
Q

occurs when the particles are large relative to wavelength of light and is inversely proportional to the square of wavelength

A

Tyndall scattering

47
Q

____ in the light can eliminate the error due to fluorescence

A

Placing a filter

48
Q

How to prevent sample decomposition?

A

Placing a filter to eliminate low-wavelength UV light

49
Q

Qualitative Analysis (UV-Vis) (4)

A

Detection of Impurities
Detection of Isomers
Detection of Functional Groups
Determination of MW

50
Q

Quantitative Analysis

A

Determination of Concentration
Multicomponent Analysis
Spectrophotometric Titration

51
Q

UV wavelength range

A

200-380 nm

52
Q

Visible Light wavelength range

A

380 - 800 nm

Analytical Chemistry (13 decks)

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