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Analytical Chemistry > Spectrophotometry > Flashcards

Spectrophotometry Flashcards

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1
Q

-Study that observe how radiated matter and energy interact with each other

A

Spectroscopy

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2
Q
  • It involves measurement of the light transmitted by a solution to determine the concentration of the light–absorbing substance in the solution
A

Spectrophotometry

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3
Q

7 Classifications of Spectroscopic Methods

-Classified according to the region of the electromagnetic spectrum

A

1.Gamma Rays
2.X- rays
3.Ultraviolet (UV
4.Visible
5.Infrared
6.Microwave
7.Radio – frequency (RF)

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4
Q

provide the most widely used tools for the elucidation of molecular structure as well as the quantitative and qualitative determination of both inorganic and organic compounds.

A

Spectrochemical Methods

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5
Q

-is a form of energy that is transmitted through space at enormous velocities

-described as a wave with properties of wavelength, frequency, velocity, and amplitude

-treated as discrete packets of energy or particles called photons or quanta.

A

Electromagnetic Radiation

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6
Q

-It is a vector quantity of an electromagnetic wave that provides a measure of the electric of magnetic field strength at a maximum in the wave

A

Amplitude

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7
Q

-It is the time in seconds of electromagnetic wave for successive maxima or minima to pass a point in space

A

Period (p)

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8
Q

-It is the number of oscillation that occur in one second -oscillations of the electric field vector per unit time and is equal to 1/p.

A

Frequency (v)

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9
Q

is determined by the source that emits it and remains constant regardless of the medium traversed

A

frequency of a light wave or any wave of electromagnetic radiation

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10
Q
  • Is the linear distance between successive maxima or minima of a wave
A

Wavelength (λ)

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11
Q

5 Wave Characteristics

A

amplitude
period, p
frequency, v
wavelength
velocity

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12
Q

Radiation velocity and wavelength both _______ as the radiation passes from a vacuum or from air to a denser medium. Frequency remains ________.

A

decrease, constant

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13
Q

The amplitude of the wave is the ______ of the electric field vector at the wave maximum, while the wavelength is the _______________ successive maxima.

A

length, distance between

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14
Q

Wavelength Units for Various Spectral Regions

Region: X-ray
Unit:
Definition:

A

Angstrom unit, Å
10^-10 m

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15
Q

Wavelength Units for Various Spectral Regions

Region: Ultraviolet/visible
Unit:
Definition:

A

Nanometer, nm
10^-9 m

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16
Q

Wavelength Units for Various Spectral Regions

Region: Infrared
Unit:
Definition:

A

Micrometer, µm
10^-6 m

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17
Q

-Is the energy of a beam the reaches a given area per unit time
-Unit is in Watts (W)

A

Radiant Power (P)

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18
Q

-Is the radiant power-per-unit solid angle

A

Intensity

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19
Q

Both quantities are proportional to the square of the amplitude of the electric field

A

Intensity, Radiant Power (P)

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20
Q

States that the relationship between wavelength and energy are INVERSELY PROPORTIONAL.

A

Planck’s Law

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21
Q

Planck’s Law

E = hv

Where:
h =
V =

A

6.63 x 10^-34 J.s (constant)
frequency

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22
Q

Interaction of Radiation and Matter

•interesting and useful interactions in spectroscopy are those in which __________ occur between different energy levels of chemical species

A

transitions

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23
Q

Interaction of Radiation and Matter

•interactions, such as reflection, refraction, elastic scattering, interference, and diffraction, are often related to the ________________________ rather than to the unique energy levels of specific molecules or atoms

A

bulk properties of materials

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24
Q

Interaction of Radiation and Matter

•the specific types of interactions observed depend strongly on the _______ of the radiation used and the

A

energy, mode of detection

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25
Q

Electromagnetic Spectrum

Region
UV (ultraviolet) region

Wavelengths?

A

Wavelength
< 400 nm
400 – 700 nm
>700 nm

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26
Q

Spectroscopic Measurement

Samples are stimulated by applying energy (5)

A

1.Heat
2.Electrical energy
3.Light
4.Particles
5.Chemical reaction

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27
Q

Ground State -

Excited State -

A

Lowest Energy

Higher energy

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28
Q

Emission or chemilumi-nescence processes.

the sample is excited by applying _______________________________________ No radiant energy is used to produce excited states, and so, these are called non-radiative processes.

A

thermal, electrical, or chemical energy.

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29
Q

-Refers to the methods in which the stimulus is heat or electrical energy

A

Emission Spectroscopy

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30
Q

-Refers to excitation of the analyte by a chemical reaction

A

Chemiluminescence Spectroscopy

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31
Q

both measures the radiant power emitted that can give the analytes’ identity and concentration

A

Emission Spectroscopy
Chemiluminescence Spectroscopy

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32
Q

Chemiluminescence is found in the _________________________.

An enzyme luciferase catalyzes the oxidative phosphorylation reaction of luciferin with adenosine triphosphate (ATP) to produce oxyluciferin, carbon dioxide, adenosine monophosphate (AMP), and light.

A

light emitted by a firefly

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33
Q

Chemiluminescence involving a biological or enzyme reaction is often termed _______________.

A

bioluminescence

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34
Q

is another familiar example of chemiluminescence.

A

The popular light stick

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35
Q

-Amount of light absorbed is measured as a function of wavelength

-Absorption measurement can give both qualitative and quantitative information about the sample

A

Absorption Spectroscopy

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36
Q

-The emission of photons is measured following absorption

A

Photoluminescence Spectroscopy

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37
Q

Forms of Photoluminescence

A

1.Fluorescence
2.Phosphorescence

38
Q

-States that the concentration of the unknown substance is directly proportional to the absorbed light (absorbance or optical density) and inversely proportional to the amount of transmitted light (% Transmittance).

-Mathematically establishes the relationship between concentration and absorbance.

A

Beer’s Law

39
Q

-It is the amount of light absorbed -It is proportional to the inverse log of transmittance

-Mathematically derived from %T (% transmittance)

A

Absorbance (A)

40
Q

Absorbance (A)

A = abc = 2 – log%T

Where:

A

A = Absorbance
a = molar absorptivity; absorptivity of the compound under standard conditions
b = length of light through the solution
c = concentration of absorbing molecules/solution

41
Q

-It is the ratio of radiant energy transmitted (T) divided by the radiant energy incident (I) on the sample.

A

Percent Transmittance

42
Q

%T = It/Io x 100

Where:

A

It= Transmitted light thru the sample Io= Intensity of light striking the sample

43
Q

•The % T measured by commercial spectrophotometers is the ratio of the sample transmitted beam divided by the blank transmitted beam.

A

% T = sample beam signal / blank beam signal x 100

44
Q

In actual practice, the light transmitted by blank is substituted for

A

Io

45
Q

-Is an apparatus for measuring the intensity of light in a part of the spectrum, especially as transmitted or emitted by a particular substances.

A

Spectrophotometer

46
Q

FREQUENCY: The lower the wave frequency, the longer the __________

The wavelength is inversely related to frequency and energy: the shorter the wavelength, the ______ the frequency and energy and vice versa.

A

wavelength
higher

47
Q

Analytical Technique

A

PHOTOMETRIC MEASUREMENT
SPECTROPHOTOMETRIC MEASUREMENT

48
Q

Analytical Technique

measurement of light intensity without consideration of wavelength.

A

PHOTOMETRIC MEASUREMENT

49
Q

Analytical Technique

: measures light intensity in a narrower wavelength. (spectrum of light).

A

SPECTROPHOTOMETRIC MEASUREMENT

50
Q

Parts of Spectrophotometer

A

1.Light Source
2.Entrance Slit
3.Monochromator
4.Cuvette/ Sample Cell/ Analytical Cell 5.Exit Slit
6.Photodetector
7.Readout device

51
Q

Part of Spectrophotometer

-Provides energy that the sample will modify or attenuate by absorption -The light is polychromatic ( all visible wavelength is present)

A

Light Source

52
Q

Part of Spectrophotometer

  • emits radiation that changes in intensity
  • most common

ex:
_________ Light Bulb – most commonly used light source in the visible and near infrared region

A

Continuum Source
Tungsten

53
Q

Part of Spectrophotometer

  • emits limited radiation and wavelength
  • limited number of discrete line or bands of radiation
A

Line Source

54
Q
  • Mercury Arc
  • Deuterium Lamp
  • Hydrogen Lamp
A

UV Spectrum <400 nm

55
Q
  • Mercury Arc
  • Nernst Glower
  • Globar
A

IR Spectrum >700 nm

56
Q

Part of Spectrophotometer

-Minimizes stray light
-Prevent entrance of scattered light -“GATE” only permits the needed light

A

Entrance Slit

57
Q

-Wavelength outside the band
-Can cause absorbance error
-Stray light limits the maximum absorbance that spectrophotometer can achieve
-Most common cause of loss of linearity at high analyte concentration

A

STRAY LIGHT

58
Q

Part of Spectrophotometer

-Isolates specific/individual wavelength of the light l

-DEGREE OF ISOLATION is affected the monochomator and the width of entance and exit slit

A

Monochromator

59
Q

Different Monochromators

A

•FILTERS
•PRISM
•DIFFRACTION GRATINGS

60
Q

Type of Monochromator

-Simple least expensive , not precise but useful
-Made by placing semi – transparent silver films on both sides of dielectric such as magnesium fluoride produce monochromatic light based on the principle of constructive interference of light waves.
-Usually pass a wide band of radiant energy and have an ion transmittance of the selected wavelength

A

Colored Filters

61
Q

Type of Monochromator

-Wedge– shaped pieces of glass, quarts, or sodium chloride
-A narrow light focused on a prism is refracted as it enters more dense glass
-Can be rotated allowing only the desired wavelength to pass through exit slit

A

Prisms

62
Q

-“Most Commonly Used”, better resolution than prism
-Made by cutting grooves ( parallel groves) or slit into an aluminized surface of a flat pieceof crown glass
- wavelengths are bent as they pass a sharp corner

A

Diffraction Gratings

63
Q

the breaking up of a ray of light into component wavelengths based on the principle that WAVELENGTHS BENDS AS THEY PASS A SHARP CORNER

A

DIFFFRACTION

64
Q
  1. A broad spectrum light (halogen, incandescent) is shone through a sample.
  2. Some colors are absorbed more than others depending on its composition
  3. Diffraction gratings splits light into colors so they can be measured separately.
  4. A webcam measures each color and graphs their intensities. This is compared to known samples.
A

Diffraction Gratings

65
Q

Part of Spectrophotometer

-It holds the solution whose concentration is to be measured -It should be scratched free which can cause erroneous result -Most common is rectangular shape, it is easier to maintain the length of light

A

Cuvette/ Sample Cell/Analytical Cell

66
Q

Part of Spectrophotometer

Types of Cuvette/ Sample Cell/Analytical Cell

A

•Glass Cuvettes – for visible range •Quartz of Fused Silica – for UV range •Borosilicate – 350 – 2000 nm

67
Q

Part of Spectrophotometer

-It controls the with of light beam (band pass). It only allows a fraction of the spectrum to reach the sample cuvette.
-Spectral purity of the spectrophotometer is reflected by the band pass – the narrower the band pass, the greater the resolution.
-Accurate absorbance measurement requires a band pass < 1/5 the natural band pass of the spectrophotometer.
-The degree of wavelength isolation is a function of the type of device used and the with of entrance and exit slit

A

Exit Slit

68
Q

– the range of wavelength between point at which transmittance is one half peak transmittance

A

BAND PASS

69
Q

Part of Spectrophotometer

-Converts transmitted radiant an equivalent amount of electrical energy

A

Photodetector

70
Q

Part of Spectrophotometer

Types of Photodetector

A

PHOTOCELL
PHOTOTUBE
PHOTOTRANSISTOR/PHOTODIODE PHOTOMULTIPLIER TUBE

71
Q

Part of Spectrophotometer

Type of Photodetector

– simplest and least expensive, low sensitivity and fatigue are the downfall of this, needs frequent replacement

A

PHOTOCELL

72
Q

Part of Spectrophotometer

Type of Photodetector

– contains anode and cathode in a tube, it gives off electron when energy strikes it •

A

PHOTOTUBE

73
Q

Part of Spectrophotometer

Type of Photodetector

– more sensitive than vacuum phototube but less sensitive than Photomultiplier

A

PHOTOTRANSISTOR/PHOTODIODE

74
Q

Part of Spectrophotometer

Type of Photodetector

– most common, detect wide range (Visible and UV)
- 200 x more sensitive, it amplifies radiant energy
- detect very low light energy and quick bust of light

A

PHOTOMULTIPLIER TUBE

75
Q

Part of Spectrophotometer

Type of Photodetector

-It displays the output of the detection system

A

Read Out Device

76
Q

Part of Spectrophotometer

Type of Photodetector

Kinds of Read Out Device

A

•Galvanometer: the more electrical energy the more the hand will move •Ammeter
•Led Display

77
Q

-it is an important instrument that splits the monochromatic light into two components

-One beam passes through the sample and the other through a reference solution of blank

-The additional beam corrects for variation in light source intensity

-The absorbance of the sample can be recorded directly as the electrical output of the sample beam

A

Double – Beam Spectrophotometer

78
Q

Two Types of Double – Beam Spectrophotometer

A

•Double – Beam in Space
•Double – Beam in Time

79
Q

Type of Double – Beam Spectrophotometer

  • uses 2 photodetectors (for the sample beam and reference beam)
A

•Double – Beam in Space

80
Q

Type of Double – Beam Spectrophotometer

  • uses one photodetector and alternatively passes the monochromatic light through the sample cuvette and then reference cuvette using a chopper
A

•Double – Beam in Time

81
Q

If a solution absorbs light of a certain color (2ndcolumn) the observed color of the solution is the

A

complementary color

82
Q

-Measures the light (wavelength) emitted by a single atom burned in flame
-Principle: Excitation of electrons from lower to higher energy state -Light Source: Flame
-Method: Indirect Internal Standard Method
-Internal Standard: Lithium/ Cesium
– to correct for variations in flame and atomizer characteristics -It is used for the measurement of excited ions (sodium and potassium) -Flickering light indicates charges in the fuel reading of the instrument

A

Flame Emission Photometry FEP

83
Q

-Measures the light absorbed by atoms dissociated by heat
-Light Source: Hallow – Cathode Lamp
-Principle: Element is not excited by merely dissociated from its chemical bond and place in an unionized, unexcited, ground state -It is used for the measurement of unexcited trace metals (calcium and magnesium)
-More sensitive than FEP; it is accurate, precise and very specific -Internal Standard is not need
– changes in aspiration have little effect on the number of ground state atoms
-An atomizer (nebulizer/graphite furnace) is used to convert ions to atoms; a chopper is used to modulate the light source
-Lanthanum or Strontium Chloride is added to samples to form stable complexes with phosphate to avoid calcium interference

A

Atomic Absorption Spectrophotometry

84
Q

Turbidity readings on spectrophotometer are ______ in the blue region than in the red region of the spectrum
•A slight error in wavelength adjustment can introduce a ____________ error in absorbance reading.

A

greater
significant

85
Q
  • the wavelength indicated on thee control dial is the actual wavelength of light passed by the monochromator.
A

Wavelength Accuracy

86
Q

– Used to check wavelength accuracy

A

Didymium or Holmium Oxide Filter

87
Q

– Verify absorbance accuracy on linearity

A

Neutral Density filters and Dichromate Solution

88
Q

– contain all the components of the solution to be analyzed except to the one compound being tested

A

Blank Solution

89
Q

corrects absorbance caused by the color of the reagents

A

Reagent blank

90
Q

measures absorbance of the sample and reagent in the absence of the end product and corrects the measurement for the optical interference

A

Sample blank

Analytical Chemistry (2 decks)

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