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MEDL-210 MB > Module 7: Spectrophotometers > Flashcards

Module 7: Spectrophotometers Flashcards

1
Q

6 parts of a spec

A 
light source
wavelength selector (monochromator)
sample holder
photodetector
signal processor
display
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2
Q

types of light source

A

Tungsten bulb
Tungsten-halogen (for visible light range)
Hydrogen lamp (for UV range)
Mercury and xenon Arc (very high intensity of UV light)
LED (for very specific wavelengths)
Laser (high intensity, nearly monochromatic)

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3
Q

wavelength selector used to

A

isolate a characteristic wavelength that the analyte to be measured absorbs or emits

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4
Q

desired wavelength

A

nominal wavelenth

represent peak intensity of the light leaving the wavelength selector

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5
Q

Band pass or spectral bandwidth

A

the range of wavelengths on either side of the nominal wavelength that exit the monochromator
ex. nominal wl = 450
bandwidth of 10
actual wavelength would be 445-455

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6
Q

the better the ability of device to select narrow wl

A

the better the spectral resolution

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7
Q

wavelength selector in a photometer

A

called a filter

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8
Q

wavelength selector in a spec

A

called a monochromator

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9
Q

2 filters used in photometry

A 
glass absorption (green filter allows green through but no other wavelengths)
Interference
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10
Q

Monochromator used in spectrophotometers

A 
prisms (refraction of white light, nonlinear spectrum)
Diffraction grating (diffraction of white light, linear spectrum)
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11
Q

3 parts of a monochromator

A

entrance slit
dispersing device
exit slit

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12
Q

2 types of gratings used

A

transmission (spectrum made as light passes through grating)

Reflection (spectrum made when light reflects off mirror surface with etched lines; more efficient; most common type)

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13
Q

Sample holder (Cuvet)

A

usually a set width

affects beers law

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14
Q

types of cuvets

A 
borosilicate glass (visible range)
Quartz or silica (UV range)
Plastic (for visible and uv, but not good for repeated use)
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15
Q

photoelectric effect

A

some metals when the surface atoms are hit by radiant energy become excited and cause a current to flow

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16
Q

spectral response of a photodetector

A

the range of wavelengths over which it operates

17
Q

Dark current

A

current that flows from a photodetector even though no light is hitting it
compensated for setting 0%T

18
Q

Types of photodetectors

A

vacuum and gas photodiodes
photomultiplier tubes (PMTs)
Solid state photodiodes
Linear diode arrays

19
Q

advantages to diode array spectrophotometers

A

speed
measurements for multiple wl at once
fewer mechanical parts

20
Q

signal processor

A

amplifies and cleans electrical signal from photodetector and converts it into usable data relating to measurement

21
Q

3 error signals in photometry measurements

A

drift
noise
artifact

22
Q

Display

A

displays measurement data to operator

23
Q

types of output displays

A 
panel peter (analog)
LED (digital)
Video display terminals (VDT)
Chart recorders
Printers
24
Q

Single beam photometer

A

single light path from light source

prone to variations of light intensity, drift in dark current

25
Q

Double beam photometer

A

beam of light from source is split using beam splitters

26
Q

2 types of beam splitters

A

dichroic mirror

photochopper

27
Q

wavelength accuracy

A

check that the wl of light striking the sample is the one selected on the wl dial of the instrument

28
Q

photometric linearity

A

check ensures that for a given change in concentration, there will be a proportional change in absorbance

29
Q

linearity is affected by (5)

A 
the detector
samples response to beers law
wide band pass
stray light
molecular fluorescence of the sample
30
Q

Stray light

A

all radiant energy that does not pass through the sample but still reaches the photodetector

31
Q

sources of stray light

A

light scatter by dust
smudges/scratches on optica surfaces
scattering and diffraction within monochromator
fluorescence of the solution
reflected light from the light source
room light leaking into the sample compartment

32
Q

Stray light produces

A

a decrease in sensitivity and an apparent deviation from beers law by falsely decreasing the A

33
Q

Photometric accuracy

A

check to verify that the A displayed by instrument is the true A of the sample

34
Q

sensitivity vs slope

A

steeper slope = greater sensitivity

35
Q

Instrument calibration

A

setting 0%T and 100%t on photometer

Calibrate and slope on pH meter

MEDL-210 MB (13 decks)

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