Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

1105 Analytical Principles > Spectrophotometer > Flashcards

Spectrophotometer Flashcards

(38 cards)

Start Studying
1
Q

Photometers are?

A

Coloured filters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Spectrophotometer use

A

Devices that create a spectrum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Light sources

A

Provide high intensity, stable radiation at the wavelength of interest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Monochromatic light

A

One specific wavelength (most methods are based off this)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Ideal light source

A

Provides a constant intensity over an infinite range of wavelengths (does not exist)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Visible light sources

A

Tungsten filament lamp, quartz halide lamp, LED, LASER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

UV light sources

A

Deuterium lamp, xenon lamp, high pressure mercury lamp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Tungsten Filament Lamp

A

• produces visible light
• output is a function of filament temperature
- higher temperatures; the output shifts towards blue end of the spectrum
- lower temperatures; look yellow
• emits a continuous nonlinear spectrum
• most output is in the IR region (heat)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Quartz Halide Lamp AKA Tungsten-halogen Lamp

A

•Quartz bulb filled with an inert gas + halogen gas
• The presence of the halogen gas causes the tungsten that evaporated from the filament to deposit back into the filament

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Light Emitting Diode AKA LED

A

• A semiconductor light source
• Commonly used as indicator lights
• Semiconductor material is created by a process called “doping”
• p-n junction; p-type (+) material contains excess “holes” and n-type(-) material contains excess electrons
• Has two legs; long leg(anode) and short leg(cathode)
• Higher band gap the higher energy of light emitted
• Band gap is determined by materials forming p-n junction
• Monochromatic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

LASER

A

• Monochromatic
• Various types and wavelengths available
• Important for flow cytometry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Deuterium Lamp

A

• Low pressure deuterium gas inside a fused silica (quartz) bulb
• Tungsten filament excited the deuterium gas molecules to an elevated state
-when the electrons relax to their ground state, light is emitted
• 160-375nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Xenon Arc Lamp

A

• Ionized xenon gas produces high intensity white light
• 250-1000nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Mercury Vapour Lamp

A

• Uses mercury in an excited state to produce light
• Emits a non-continuous spectrum; 184nm, 254nm, 365nm, 405nm, 436nm, 546nm, 578nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Sources of Error

A

• Dirty light source
• Power fluctuations
• Forgetting to blank after changing wavelength setting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Wavelength Selector System

Study These Flashcards
A

Used for isolating the desired wavelength from the light source

1) filters
2) monochromators

There is always a range of wavelengths transmitted

17
Q

Bandpass (or Bandwidth)

Study These Flashcards
A

The width (in nm) of the spectral transmittance curve of a filter at a point equal to one half the peak transmittance

• As bandwidth increases, more wavelengths are transmitted
• It is desirable to have a lower bandpass
Example: a bandpass of 5nm is 507.5-512.5nm

18
Q

Filters

Study These Flashcards
A

Two types:
1) Absorption filters
- useful for visible wavelengths
2) Interference filters
- useful for UV and visible wavelengths

19
Q

Absorption Filters

Study These Flashcards
A

• Made of coloured glass or plastic
• Designed to selectively transmit certain wavelengths
• Other wavelengths are absorbed
• Low transmission intensity and require high intensity light source
• Wide bandpass filters (25-50nm)

20
Q

Interference Filters

Study These Flashcards
A

• Made if multiple thin layers
- thickness of layers determines which wavelengths are transmitted
• Other wavelengths are removed by destructive interference or by reflection
• transmit up to 90% of incident light energy
• narrow bandpass (1-15nm)

21
Q

Bandpass Fliters

Study These Flashcards
A

Transmit a specific range of wavelength for analysis

on automated analyzers these filters are typically on a filter wheel

22
Q

Shortpass/Longpass Filters

Study These Flashcards
A

Shortpass
• transmit shorter wavelengths (cut-off wavelength)

Longpass
• transmit longer wavelengths (cut-on wavelength)

23
Q

Dichroic Filters

Study These Flashcards
A
  • Some wavelengths are transmitted
  • Some wavelengths are reflected
24
Q

Neutral Density Filters

Study These Flashcards
A

• Used to reduce light intensity across a wide range of wavelengths
• Not used to isolate specific wavelengths

25
Monochromators
Devices that are able to select a desired wavelength from a range of wavelengths (can choose any in the visible spectrum) Two types : 1) Prisms 2) Diffraction gratings
26
Prisms
• Disperse white light into a continuous spectrum by refraction (bending of light) • Short wavelengths are bent the most • Long wavelengths are bent the least
27
Diffraction Gratings
• Produce a spectrum by diffraction • Made by etching a series of parallel lines or grooves onto a surface Transmission gratings - produce a spectrum by passage of light through the grating Reflection gratings - have lines etched onto a reflective surface so that the spectrum is produced by reflection of the incident light • Each line on a grating produces its own spectrum • because the lines are so close together, these spectra interfere with each other and a series of spectra(orders) are produced
28
Diffraction Gratings vs Prisms
• diffraction gratings are capable of better resolution (can better separate two wavelengths) • Diffraction Gratings can be used for all wavelengths (visible and UV) • Very low bandwidth
29
Monochromator Optics
Another component assisting in wavelength selection • Lenses are used to collimate the light rays so that they are parallel when they strike the prism/grating surface • Mirrors are used to divert or focus light (focusing the light onto the cuvette) • Filters absorb unwanted wavelengths (Shortpass/Longpass completely absorb one side of the spectrum) • Entrance slit provides a narrow source of radiation • Exit slit selects a narrow band of the spectrum
30
Wavelength Calibration
• Absorbance peaks of chemical solutions • chemical solutions have characteristic spectra with specific peaks • the solution should be scanned across a range of wavelengths (look for expected peaks and that there are no extra peaks) • mercury lamps are the most accurate method of wavelength calibration
31
Cuvettes
• Holds the sample • Sets the path length, b Quartz or Fused Silica - visible/UV Borosilicate Glass - visible only Plastic - visible and near-UV
32
Photon Detectors
• converts the light energy transmitted by sample into an electrical signal that can be recorded • All photon detectors are a form of transducer (a device that converts one form of energy into a different form) • Uses photoelectric effect 1) Photoemmissive effect 2) Photoconductive effect
33
Photoconductive Effect
• conductivity of detector changes due to absorption of light energy • electrons are not released from the photosensitive material • similar to photoemissive effect
34
Properties of Photon Detectors
• respond to light energy over a broad wavelength range • be sensitive to low levels of radiant energy • exhibit a fast response time • produce an electrical signal that is directly proportional to the amount of light detected • produce minimal output signal in absence of illumination
35
Types of Photon Detectors
1) Vacuum/Gas Phototube 2) Photomultiplier Tube (PMT) 3) Solid State Photodiode 4) Diode Arrays
36
Vacuum Phototube
• Photoemissive Two main parts: - emitter(cathode) ; photosensitive material, generates electrons when light hits surface -collector(anode) ; positively charged wire, collects electrons ejected from cathode • flow of electrons generates current • number of electrons generates is proportional to the intensity of the light
37
Photomultiplier Tube (PMT)
• highly sensitive photon detector • consists of: - photosensitive cathode emitter - secondary emitters: DYNODES - anode • cascade effect; - each dynode emits several electrons (3-6) for each electron that strikes its surface - one photon striking the cathode can end up producing 10^8-10^17 electrons - number of electrons is directly proportional to the intensity of light hitting cathode
38
Photodiode vs LED
• LEDs convert electrical energy into light • photodiodes convert light into electricity • LEDs principle: electroluminescence • Photodiode principle: photoconduction • LEDs intensity of light proportional to applied voltage • Photodiode current generated is proportional to intensity of light striking p-n junction

1105 Analytical Principles (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions