/
Principles of Spectrophotometry and Clinical Automation
Save to my account
Sign up
Principles of Spectrophotometry and Clinical Automation
Principles of Spectrophotometry and Clinical Automation
Study
1
Question
What are the five significant components of a typical spectrophotometer?
Page 87
Answer
Stable source of radiant energy, wavelength selector or monochromator, sample holder, photodetector, and readout device.
2
Question
How is the velocity of electromagnetic radiation propagation mathematically defined?
Page 82
Answer
Velocity of propagation equals frequency multiplied by wavelength, expressed as \(v_i = \nu l_i\).
3
Question
What is the energy of a photon in terms of its frequency and wavelength?
Page 83
Answer
Photon energy equals Planck's constant times frequency or \(hc / \lambda\), where \(h\) is Planck's constant and \(c\) is the speed of light.
4
Question
What defines Rayleigh scatter in the context of light interaction with particles?
Page 84
Answer
Light scatter by molecules or particles much smaller than the radiation wavelength, with intensity proportional to the inverse fourth power of wavelength.
5
Question
According to Lambert's law, how does radiant power change through an absorber of constant concentration?
Page 85
Answer
Radian power decreases logarithmically as the light path increases arithmetically.
6
Question
What is the mathematical expression for absorbance in terms of incident and transmitted power?
Page 85
Answer
\(A = -\log P / P_0\) or \(A = \log 1/T\).
7
Question
How does the Beer-Lambert law relate absorbance to analyte properties?
Page 85
Answer
\(A = abc\), where \(a\) is absorptivity, \(b\) is light path length, and \(c\) is concentration.
8
Question
Why does plotting percent transmittance versus concentration yield a nonlinear curve?
Page 86
Answer
Percent transmittance decreases exponentially with concentration, following \(T = 10^{-abc}\).
9
Question
What causes deviation from linearity in Beer-Lambert plots at high absorbance values?
Page 86
Answer
Absorbance values greater than 2.0 due to interactions of light with increased particles or instrument/chemical issues.
10
Question
What continuum light sources are commonly used in spectrophotometry?
Page 88
Answer
Tungsten-halogen lamps for visible region, deuterium lamps for UV, and xenon lamps for UV-visible.
11
Question
What is the nominal wavelength of a monochromator?
Page 88
Answer
The wavelength in nanometers at peak light transmittance.
12
Question
How does spectral bandwidth relate to monochromator quality?
Page 88
Answer
Spectral bandwidth is the range at half peak height; narrower bandwidth indicates higher quality.
13
Question
What distinguishes interference filters from absorption filters?
Page 89
Answer
Interference filters use optical interference for narrow bands (∼1.5% wavelength); absorption filters absorb portions using colored glass (30-50 nm bandwidth).
14
Question
What material is used for cuvettes in the UV region below 350 nm?
Page 90
Answer
Fused silica or quartz.
15
Question
How does a photovoltaic cell generate a photocurrent?
Page 90
Answer
Photons break covalent bonds in semiconductor, creating electrons and holes that flow as current proportional to radiant power.
16
Question
What amplifies the signal in a photomultiplier tube?
Page 91
Answer
Dynodes, where each photoelectron releases multiple secondary electrons across 9 stages.
17
Question
What is assessed by wavelength accuracy checks in spectrophotometers?
Page 92
Answer
Whether the instrument measures at the selected wavelength using didymium or holmium oxide filters.
18
Question
How is stray light evaluated in spectrophotometers?
Page 92
Answer
Using cutoff filters; excess stray light indicates leaks or room light issues.
19
Question
What differentiates a single-beam from a double-beam spectrophotometer?
Page 93
Answer
Single-beam measures sample sequentially after reference; double-beam splits beam for simultaneous or alternating sample/reference comparison.
20
Question
In reflectometry, what is diffuse reflectance?
Page 95
Answer
Reflection from nonpolished surfaces where light scatters in many directions based on layer properties.
21
Question
What is the principle of atomic absorption spectrometry for metal analysis?
Page 95
Answer
Absorption of element-specific monochromatic light by ground-state atoms in a flame aspirated sample.
22
Question
What distinguishes fluorescence from phosphorescence in luminescence?
Page 97
Answer
Fluorescence from singlet excited state (lifetime 10^{-9} to 10^{-6} s); phosphorescence from triplet state (10^{-4} to 10 s).
23
Question
Why is the detector placed at 90 degrees in fluorometers?
Page 98
Answer
To minimize scattered excitation light and cuvette reflection reaching the emission monochromator.
24
Question
What advantage does fluorescent polarization immunoassay offer over other methods?
Page 98
Answer
Homogeneous assay measuring bound fraction in presence of free without physical separation.
25
Question
What defines the test menu of an automated analyzer?
Page 103
Answer
The specific analytes or tests the instrument can perform.
26
Question
What is throughput in the context of automated analyzers?
Page 81
Answer
The number of tests performed per unit time, often exceeding 3000 tests per hour in large systems.
27
Question
How does a chopper function in double-beam-in-time spectrophotometers?
Page 94
Answer
Rotating mirrors alternately direct beam through sample and reference cuvettes to one detector.
28
Question
What is carryover in automated analysis?
Page 103
Answer
Contamination from previous sample affecting subsequent results.
29
Question
What distinguishes discrete testing from batch analysis?
Page 103
Answer
Discrete allows individual sample tests independently; batch processes samples sequentially as a group.
30
Question
What is random-access testing in analyzers?
Page 103
Answer
Ability to perform any test on any sample in any order without fixed sequence.