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Chemistry Module 1 > Optical Techniques > Flashcards

Optical Techniques Flashcards

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0
Q

wavelength is measured in terms of _______

A

nanometers (nm)

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1
Q

the distance traveled by one complete wave cycle

A

wavelength

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2
Q

the number of cycles per second, inversely proportional to wavelength

A

frequency

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3
Q

the peak height of a wave

A

amplitude

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4
Q

wavelength that has a high frequency and high energy (400 nm)

A

short wavelength

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5
Q

wavelength that has a low frequency and low energy (700 nm)

A

Long wavelength

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6
Q

wavelength (in nm) of visible light

A

380-800 nm

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7
Q

wavelength (in nm) of ultraviolet light

A

<380 nm

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8
Q

The visible colors correspond to the wavelenghts that are _______ to our eyes

A

transmitted

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9
Q

Only colors we can see are transmitted to the eyes, others are ______ but not seen. This color is the complementary color of the transmitted color.

A

absorbed

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10
Q

these experiements were with the interaction of monochromatic (one wavelength) electromagnetic radiation with varying thickness of absorbing material

A

Lambert’s Experiments

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11
Q

______ is inversely and logarithmically related to %T

A

absorbance

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12
Q

experiments with transmittance of a solution under differing concentrations

A

Beer’s Experiments

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13
Q

As concentration increases, absorbance increases linearly and transmittance decreases exponentially

A

Beer’s Experiments

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14
Q

A=abC , state the law and what each letter represents

A

Beer’s Law; A=absorbance, a= molar absorptivity constant in g/L, b=path length of cuvette, C=concentration

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15
Q

Beer’s Law is not valid if…(5 limitations)

A

1 very elevated concentrations are measured
2 incident light is not monochromatic
3 solvent absorption is significant compared to solute absorption (HIL)
4 radiant energy is transmitted by other mechanisms (stray light)
5 sides of the cuvette are not parallel

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16
Q

function is to be a source of radiant energy

A

light source

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17
Q

Four types of light sources

A

tungsten filament with halogen vapor, ultraviolet, hollow cathode lamp, and laser

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18
Q

function is to focus light into a narrow beam

A

entrance slit

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19
Q

function is to isolate the desired wavelength and exclude others

A

monochromator

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20
Q

3 types of monochromators

A

glass filters, prisms, and diffraction gratings (used in lab)

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21
Q

used for readings in the visible and near visible range of spectrum

A

colored agent of a glass filter

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22
Q

augment wavelengths in phase, destroy those out of phase

A

interference filters (glass)

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23
Q

eliminate transmission of wavelengths above or below a set wavelength

A

glass cut-off filters

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24
Q

made of glass or quartz, these do not give a linear dispersion of light, creates bends in light

A

prisms

25
Q

a diamond point used to cut tiny furrows into aluminized face of perfect, flat piece of glass; precise angle and distance; will bounce off at different angles to determine which light will go through

A

diffraction grating

26
Q

function is to determine the bandpass (bandwidth) or range of wavelengths that will reach the sample, last line of defense before light hits the sample, defined as the bandwidth of the absorbance curve at a point equal to one-half of the max absorbance.

A

exit slit

27
Q

function is to act as a receptacle for the sample

A

cuvette

28
Q

______ cuvettes are used for visible measurements

A

glass

29
Q

_______ cuvettes are used for UV measurements

A

quartz

30
Q

function is to convert transmitted light energy to electrical energy

A

detector

31
Q

thin layer of semiconductor (selenium) deposited on metal base (iron), selenium coated with thin silver lacquer and covered by protective glass, encased in plastic

A

barrier layer cell (detector)

32
Q

semiconductors which change their charged voltage upon being struck by light; voltage change is converted to current (electron flow) and measured

A

Photodiode

33
Q

photomultiplier tube components

A

cathode, anode, photosensitive electrodes, encased in evacuated glass envelope

34
Q

Light energy strikes cathode, electrons are emitted and focus on first dynode; dynode emits an increased number of electrons, and each successive dynode does the same; final amplification may be 10^6 times more than initial energy

A

Photomultiplier Tube (PM)

35
Q

why are PM tubes preferred detectors for clinical laboratory spectrophotometers?

A

use a small amount of transmitted light to multiply the signal and expand the range of absorption vs concentration. This lessens the need to dilute a sample.

36
Q

function is to display the electrical signal from the detector in an understandable form; may be an LED, meter, recorder, printer, digital display, etc.

A

readout device

37
Q

3 types of spectrophotometers

A

single beam, double beam (in time/in space/dual), and recording

38
Q

Most common spectrophotometer

A

single beam

39
Q

advantage of double beam spectrophotometers

A

Useful when you need 100% accuracy

40
Q

These spectrophotometers run with a reference and are twice as big as a single

A

double beam and split (dual) beam (see picutres page 14 in notes)

41
Q

Quality control 1 purpose and 2 method for wavelength accuracy

A

1 to ensure wavelength is really going through the sample

2 replacement of source lamp, holmium oxide (rare earth) glass filter, didymium filter

42
Q

Quality control 1 purpose and 2 method for band width

A

1 monitor range of wavelengths

2 use mercury vapor lamp to verify

43
Q

Quality control 1 purpose and 2 method for stray light

A

1 no ambient room light

2 use glass cut-off filters to verify

44
Q

Quality control 1 purpose and 2 method for linearity

A

1 make sure absorbance vs concentration

2 didymium filter

45
Q

Quality control 1 purpose and 2 method for photometric accuracy

A

1 checking performance of instrument/spectrophotometer

2 National Bureau of Standards (NBS) glass filters or potassium dichromate solutions

46
Q

failure to get reading in spect

A

usually electrical

47
Q

erratic readings in spec

A

improper warm-up

48
Q

incorrect wavelength in spec

A

we want 450 nm but can be a misaligned monochromator

49
Q

scattered light in spec

A

scratched or improper cuvette

50
Q

unsteady baseline in spec

A

grounding problem; when you zero instrument get crazy results

51
Q

dark current in spec

A

residual current when instrument is turned off

52
Q

emission of light by an atom or molecule after absorption of an excitation photon

A

fluorescence

53
Q

Emitted light has a _______ wavelength and _______ energy than the excitation light

A

longer, less

54
Q

______ detects emitted light and follows Beer’s law

A

fluorometry

55
Q

Why do fluorometers have a right angle design?

A

To minimize the amount of excitation light that may reach the detector, improving sensitivity and specificity of fluorometers

56
Q

Technique where a chemical reaction (oxidation) of an organic compound causes immediate light flash

A

Chemiluminescence

57
Q

Measures the decrease in percent transmittance through a solution; increased conc of particles=less light transmitted through solution; follows Beer’s Law and assays may be performed on a spectrophotometer

A

Turbidimetry

58
Q

Measures the amount of light that is scattered toward a detector at a variety of angles (not 0 or 180)

A

Nephelometer

59
Q

Two common chemiluminescent materials used

A

Luminol and acridinium ester (AE)

Chemistry Module 1 (18 decks)

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