Spectrometry Flashcards

1
Q
  • Meas. light intensity in a much narrower WL using a device (prism/grating) to
    disperse the light source into a cont. spectrum
A

Spectrophotometry

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2
Q

Quantitation of subs of spectrophotometry

A

meas. amt of light absorbed after appropriate treatment

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3
Q

spectrophotometry advantage

A
  • Therefore, it gives a relatively high sensitivity, greater ease of rapid meas.
    compared to visual colorimetry

-High degree of specificity reacts the subs of interest w/ proper rgts = diff colors
(analytical separation prior to color formation rxns)

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4
Q

Filter Photometry

A
  • meas light intensity of multiple WL
  • uses filter to isolate part of spectrum
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5
Q

Parts of Spectrophotometer:

A

Source→(EnS)→monochromator→(ExS)→cuvet→detector→meter/read out device(Galvanometer)

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6
Q

provides radiant energy to monochromator—separates into discrete WL

A

Light Source

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7
Q

is a form of electromagnetic energy Transmitted via electromagnetic waves Characterized by frequency and wavelength

A

Light

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8
Q

is the distance of 2 successive waves (nanometers). Waves are measured by nanometers (wavelength).

A

Wavelength

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9
Q

is number of vibrations of wave motions per second;

A

Frequency

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10
Q

Wavelength is _______ proportional to the frequency and energy.

A

inversely

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11
Q

Shorterwavelength,

A

↑Freq,↑Energy

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12
Q

LongerWavelength

A

↓Freq,↓Energy

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13
Q

Visible spectrum – wavelength

A

400-700 nm

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14
Q

Invisible spectrum ranges below 400 nm

A

UV Region

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15
Q

Invisible spectrum ranges below 700 nm

A

Infrared Region

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16
Q

below 400 nm

A
  • Gamma Rays
  • X-Rays
  • UV
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17
Q

greater 700 nm

A

Infrared and Radio Waves

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18
Q

Spectrum of energy from a short wavelength
of Gamma Rays and X-rays to a longer wavelength of Infrared and Radio waves

Between the invisible Region, the Visible light falls in those regions

A

Spectrum of energy from a short wavelength
of Gamma Rays and X-rays to a longer wavelength of Infrared and Radio waves

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19
Q

Spectrophotometric measurement is related to the principle of beer’s law

A

Beer’s Law

20
Q

The concentration of a substance is Beer’s Law

A

o Directly proportional to amount of light
absorbed
o Inversely proportional to amount of transmitted
light

21
Q

The amount of light absorbed, which is proportional to concentration

Not directly measured by spectrophotometer; derived from percent transmittance

A

Absorbance

22
Q

measures amount of
transmitted light or percent transmittance

A

Spectrophotometer

23
Q

Directly proportional to the inverse logarithm of
percent transmittance

A

Absorbance

24
Q

-Ratio of transmitted light through the sample
(aka the light that is not absorbed by the sample) and the intensity of light striking the sample (from the light source) multiplied by 100

-As light passes through the sample, some of them are absorbed while the remainder passes through

  • Light strikes the light detector and is converted to an electrical signal (% transmittance)
A

% T r a n s m i t t a n c e

25
Measures light transmitted by a solution to determine the concentration of substance in the solution
Spectrophotometry
26
Components of a Spectrophotometer
Light Source Entrance Slit Monochromator Exit slip Sample Cell Photodetector Read-out Device
27
Provide incident light for the system
Light Source
28
For visible and near infrared spectrum (wavelengths ranging from 320-700 nm)
Incandescent Tungsten or Tungsten iodide lamp
29
For UV Spectrum To provide UV radiation in analytic spectrometers (wavelengths ranging from 165-350 nm)
Deuterium-discharge lamp and Mercury arc lamp
30
For infrared spectrum
Silicone carbide
31
Exclude unwanted or “stray light” Before the monochromator
Entrance Slit o Wavelength outside the band transmitted by the monochromator o Does not originate from the light source o Causes absorbance error
32
Isolates specific/individual wavelength of light that is desired for measurement In short, it selects and isolates desired wavelength that will strike the sample
Monochromator
33
- Based on constructive interference of waves - Simple, useful, least expensive but not precise - Passes a wide band of radiant energy (even the unwanted wavelengths can pass through)
Interference Filter
34
Separates white light into a continuous spectrum It can be rotated allowing only the desired wavelength to pass through/exit
Prism Wed-shaped pieces of glass, quartz or sodium chloride (NaCl)
35
When light strikes, it separates light into component wavelengths
Diffraction gratings
36
Better resolution than Prism
Diffraction gratings
37
Most commonly used monochromator Made of cutting or parallel groups or slits and produce a widely dispersed spectrum
Diffraction gratings
38
Controls width of light beam or band pass Allows only a fraction of light to reach the sample
Exit slip
39
Band pass is total range of wavelength transmitted The narrower the band pass, the greater the resolution
Exit slip
40
After the monochromator
Exit slip
41
Aka Cuvette absorption cell or analytical cell Holds the solution of which the absorption is to be measured
Sample Cell
42
For visible range
Glass Cuvette
43
For UV range
Quarts or Fused Silica
44
Converts transmitted radiant energy into an equivalent amount of electrical energy Detects amount of light that passes through the sample
Photodetector
45
-Simplest and least expensive -Generates electromotive force (no -external voltage) -Relies on internal electron transfer -Output is not amplified
Photocell (Barrier layer cell, selenide cell)