Spectrometry

Question 1

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

Answer 1

Spectrophotometry

Question 2

Quantitation of subs of spectrophotometry

Answer 2

meas. amt of light absorbed after appropriate treatment

Question 3

spectrophotometry advantage

Answer 3

• 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)

Question 4

Filter Photometry

Answer 4

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

Question 5

Parts of Spectrophotometer:

Answer 5

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

Question 6

provides radiant energy to monochromator—separates into discrete WL

Answer 6

Light Source

Question 7

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

Answer 7

Light

Question 8

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

Answer 8

Wavelength

Question 9

is number of vibrations of wave motions per second;

Answer 9

Frequency

Question 10

Wavelength is _______ proportional to the frequency and energy.

Answer 10

inversely

Question 11

Shorterwavelength,

Answer 11

↑Freq,↑Energy

Question 12

LongerWavelength

Answer 12

↓Freq,↓Energy

Question 13

Visible spectrum – wavelength

Answer 13

400-700 nm

Question 14

Invisible spectrum ranges below 400 nm

Answer 14

UV Region

Question 15

Invisible spectrum ranges below 700 nm

Answer 15

Infrared Region

Question 16

below 400 nm

Answer 16

• Gamma Rays
• X-Rays
• UV

Question 17

greater 700 nm

Answer 17

Infrared and Radio Waves

Question 18

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

Answer 18

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

Question 19

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

Answer 19

Beer’s Law

Question 20

The concentration of a substance is Beer’s Law

Answer 20

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

Question 21

The amount of light absorbed, which is proportional to concentration

Not directly measured by spectrophotometer; derived from percent transmittance

Answer 21

Absorbance

Question 22

measures amount of
transmitted light or percent transmittance

Answer 22

Spectrophotometer

Question 23

Directly proportional to the inverse logarithm of
percent transmittance

Answer 23

Absorbance

Question 24

-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)

Answer 24

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

Question 25

Measures light transmitted by a solution to determine the concentration of substance in the solution

Answer 25

Spectrophotometry

Question 26

Components of a Spectrophotometer

Answer 26

Light Source

Entrance Slit

Monochromator

Exit slip

Sample Cell

Photodetector

Read-out Device

Question 27

Provide incident light for the system

Answer 27

Light Source

Question 28

For visible and near infrared spectrum
(wavelengths ranging from 320-700 nm)

Answer 28

Incandescent Tungsten or Tungsten iodide
lamp

Question 29

For UV Spectrum

To provide UV radiation in analytic
spectrometers (wavelengths ranging from
165-350 nm)

Answer 29

Deuterium-discharge lamp and Mercury arc
lamp

Question 30

For infrared spectrum

Answer 30

Silicone carbide

Question 31

Exclude unwanted or “stray light”

Before the monochromator

Answer 31

Entrance Slit

o Wavelength outside the band transmitted by the monochromator
o Does not originate from the light source
o Causes absorbance error

Question 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

Answer 32

Monochromator

Question 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)

Answer 33

Interference Filter

Question 34

Separates white light into a continuous
spectrum

It can be rotated allowing only the
desired wavelength to pass through/exit

Answer 34

Prism

Wed-shaped pieces of glass, quartz or
sodium chloride (NaCl)

Question 35

When light strikes, it separates light into component wavelengths

Answer 35

Diffraction gratings

Question 36

Better resolution than Prism

Answer 36

Diffraction gratings

Question 37

Most commonly used monochromator Made of cutting or parallel groups or slits and produce a widely dispersed
spectrum

Answer 37

Diffraction gratings

Question 38

Controls width of light beam or band pass

Allows only a fraction of light to reach the
sample

Answer 38

Exit slip

Question 39

Band pass is total range of wavelength transmitted

The narrower the band pass, the greater the resolution

Answer 39

Exit slip

Question 40

After the monochromator

Answer 40

Exit slip

Question 41

Aka Cuvette absorption cell or analytical cell
Holds the solution of which the absorption is to be measured

Answer 41

Sample Cell

Question 42

For visible range

Answer 42

Glass Cuvette

Question 43

For UV range

Answer 43

Quarts or Fused Silica

Question 44

Converts transmitted radiant energy into an equivalent amount of electrical energy
Detects amount of light that passes through the sample

Answer 44

Photodetector

Question 45

-Simplest and least expensive
-Generates electromotive force (no
-external voltage)
-Relies on internal electron transfer
-Output is not amplified

Answer 45

Photocell (Barrier layer cell, selenide cell)