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Liz's Clinical Chemistry Module 1 > Optical Techniques > Flashcards

Optical Techniques Flashcards

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1
Q

The distance traveled by one complete wave cycle

A

Wavelength

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2
Q

Wavelength is measured in terms of ____

A

Nanometers (nm)

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3
Q

The number of cycles per second, inversely proportional to wavelength

A

Frequency

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4
Q

The peak height of a wave

A

Amplitude

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5
Q

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

A

Short wavelength

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6
Q

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

A

Long wavelength

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7
Q

Wavelength (in nm) of visible light

A

380-800 nm

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8
Q

Wavelength (in nm) of UV light

A

?

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9
Q

The visible colors correspond to the wavelengths that are ____ to our eyes

A

Transmitted

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10
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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11
Q

These experiments were w/ the interaction of monochromatic (one wavelength) electromagnetic radiation w/ varying thickness of absorbing material

A

Lambert’s Experiments

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12
Q

____ is inversely and logarithmically related to %T

A

Absorbance

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13
Q

Experiments w/ transmittance of a solution under differing concentrations

A

Beer’s Experiments

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14
Q

As concentration increases, absorbance increases linearly and transmittance decreases exponentially

A

Beer’s Experiments

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15
Q

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

A

Beer’s Law

A = absorbance, a = molar absorptivity constant (g/L), b = path length of cuvette, C = concentration

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16
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 aren’t parallel
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17
Q

Function is to be a source of radiant energy

A

Light source

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18
Q

Four types of light sources

A
  1. Tungsten filament w/ halogen vapor
  2. UV
  3. Hollow cathode lamp
  4. Laser
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19
Q

Function is to focus light into a narrow beam

A

Entrance slit

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20
Q

Function is to isolate the desired wavelength and exclude others

A

Monochromator

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21
Q

3 types of monochromators

A
  1. Glass filters
  2. Prisms
  3. Diffraction gratings (used in lab)
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22
Q

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

A

Colored agent of a glass filter

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23
Q

Augment wavelengths in phase, destroy those out of phase

A

Interference filters (glass)

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24
Q

Eliminate transmission of wavelengths above or below a set wavelength

A

Glass cut-off filters

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25
Q

Made of glass or quartz, these do not give a linear dispersion of light, but creates a bend in light

A

Prisms

26
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

27
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 the max absorbance

A

Exit slit

28
Q

Function is to act as a receptacle for the sample

A

Cuvette

29
Q

____ cuvettes are used for visible measurements

A

Glass

30
Q

____ cuvettes are used for UV measurements

A

Quartz

31
Q

Function is to convert transmitted light energy to electrical energy

A

Detector

32
Q

Thin layer of semiconductor (selenium) deposted on metal base (iron). Selenium is coated w/ thin silver lacquer and covered by protective glass, encased in plastic

A

Barrier layer cell (detector)

33
Q

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

A

Photodiode

34
Q

Photomultiplier tube components

A

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

35
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 10^6x more than initial energy

A

Photomultiplier tube (PM)

36
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.

37
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

38
Q

3 types of spectorphotometers

A

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

39
Q

The most common spectrophotometer

A

Single beam

40
Q

Advantage of double beam spectrophotometers

A

Useful when you need 100% accuracy

41
Q

These spectophotometers run w/ a reference and are twice as big as a single

A

Double beam and split (dual) beam

42
Q

Quality control

  • Purpose
  • Method for wavelength accuracy
A
  • To ensure wavelength is really going through the sample

- Replacement of source lamp, holmium oxide (rare earth) glass filter, didymium filter

43
Q

Quality control

  • Purpose
  • Method for bandwidth
A
  • Monitor range of wavelengths

- Use mercury vapor lamp to verify

44
Q

Quality control

  • Purpose
  • Method for stray light
A
  • No ambient room light

- Use glass cut-off filters to verify

45
Q

Quality control

  • Purpose
  • Method for linearity
A
  • Make sure absorbance vs. concentration

- Didymium filter

46
Q

Quality control

  • Purpose
  • Method for photometric accuracy
A
  • Checking performance of instrument/spectorphotometer

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

47
Q

Failure to get reading in spectrophotometer?

A

Usually electrical

48
Q

Erratic readings in spectorphotometer?

A

Improper warm-up

49
Q

Incorrect wavelength in spectrophotometer

A

We want 450 nm but can be a misaligned monochromator

50
Q

Scattered light in spectrophotometer?

A

Scratched or improper cuvette

51
Q

Unsteady baseline in spectorphotometer?

A

Grounding problem; when you zero instrument, get crazy results

52
Q

Dark current in spectrophotometer?

A

Residual current when instrument is turned off

53
Q

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

A

Fluorescence

54
Q

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

A

Longer, less

55
Q

____ detects emitted light and follows Beer’s Law

A

Fluorometry

56
Q

Why do fluorometers have a right angle design?

A

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

57
Q

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

A

Chemiluminescence

58
Q

Measures the decrease in %T through a solution; increased concentration of particles = less light transmitted through solution; follows Beer’s Law and assays may be performed on a spectorphotometer

A

Turbidimetry

59
Q

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

A

Nephelometer

60
Q

Two common chemiluminescent materials used

A

Luminol and acridinium ester (AE)

Liz's Clinical Chemistry Module 1 (5 decks)

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