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Principles of Clinical Spectrophotometry and Analytical Chemistry
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Principles of Clinical Spectrophotometry and Analytical Chemistry
Principles of Clinical Spectrophotometry and Analytical Chemistry
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1
Question
What dual nature characterizes electromagnetic radiation according to the classical wave model and particle model?
Page 104
Answer
EMR exists as sinusoidal waves with parameters like wavelength, frequency, velocity, and amplitude, and also as discrete packets of energy called photons.
2
Question
How does the photon energy of electromagnetic radiation relate to its frequency and wavelength?
Page 105
Answer
\(E = h\nu = \frac{hc}{\lambda}\) where \(h\) is Planck’s constant, \(\nu\) is frequency, \(c\) is speed of light, and \(\lambda\) is wavelength.
3
Question
Why does the wavelength of electromagnetic radiation decrease when passing from air into a denser medium like water?
Page 105
Answer
Frequency remains fixed by the source, but velocity decreases due to interaction with electrons in the medium, so wavelength shortens per \(v_i = \nu \lambda_i\).
4
Question
What distinguishes Rayleigh scatter from other scattering phenomena in terms of particle size relative to wavelength?
Page 106
Answer
Rayleigh scatter occurs when particle dimensions are much smaller than the radiation wavelength, with intensity proportional to \(1/\lambda^4\) and same wavelengths for absorption and emission.
5
Question
How does the Tyndall effect differ from Rayleigh scatter in terms of observable scatter and particle characteristics?
Page 107
Answer
Tyndall effect involves visible scatter from colloidal-sized particles, used to determine size and shape of polymers and colloids.
6
Question
In what way does Raman scatter produce emission at longer wavelengths than the excitation energy?
Page 107
Answer
Raman scatter involves photon absorption causing vibrational excitation, followed by emission at longer wavelengths differing by a constant energy amount.
7
Question
According to Bouguer and Lambert, how does transmittance vary with absorber thickness for monochromatic radiation?
Page 107
Answer
\(T = e^{-a x}\) where \(a\) is absorption coefficient and \(x\) is thickness, showing logarithmic decrease.
8
Question
What relationship holds between absorbance and percent transmittance in Lambert's law derivation?
Page 108
Answer
\(A = \log_{10}(100/\%T) = 2 - \log_{10}(\%T)\), making absorbance and transmittance inversely related.
9
Question
How does Beer's law extend Lambert's law to include concentration dependence for monochromatic radiation?
Page 108
Answer
\(A = abc\) or \(A = \epsilon b c\) where \(a\) or \(\epsilon\) is absorptivity or molar absorptivity, \(b\) path length, \(c\) concentration.
10
Question
What causes chemical deviations from Beer's law in absorbance versus concentration plots?
Page 110
Answer
Deviations arise from chemical reactions altering absorptivity or interactions among absorbing species at high concentrations.
11
Question
Why do spectrophotometric techniques prefer absorbance values below 2.0 for best adherence to Beer's law?
Page 110
Answer
Absorbance >2.0 leads to deviations from linearity due to increased particle interactions bending the plot upward.
12
Question
What are the five essential components common to all absorption spectrophotometers?
Page 110
Answer
Stable radiant energy source, wavelength selector (monochromator), sample holder (cuvette), photodetector, and readout device.
13
Question
How does a deuterium lamp differ from a tungsten-halogen lamp in spectral output for spectrophotometry?
Page 111
Answer
Deuterium provides continuous UV radiation; tungsten-halogen provides visible region radiation.
14
Question
What advantage do line sources like mercury vapor lamps offer over continuum sources in specific spectroscopy applications?
Page 111
Answer
Line sources emit discrete wavelengths ideal for atomic absorption and fluorescence without broad continuum interference.
15
Question
Why do interference filters provide narrower spectral bandwidths than absorption filters in spectrophotometers?
Page 111
Answer
Interference filters use optical interference for ~1.5% wavelength bandwidth; absorption filters absorb broadly over 30-50 nm.
16
Question
How does effective bandwidth relate to monochromator quality in wavelength selectors?
Page 111
Answer
Effective bandwidth is ~1.5% of nominal wavelength; narrower bandwidth indicates higher quality monochromator.
17
Question
What distinguishes echellette gratings from holographic gratings in terms of groove production and stray light?
Page 112
Answer
Echellette mechanically ruled for efficient diffraction; holographic laser-etched with fewer ghosts and stray radiation.
18
Question
Why are fused silica cuvettes required for UV spectrophotometry below 350 nm?
Page 113
Answer
Fused silica or quartz transmits UV; silicate glass absorbs below 350 nm.
19
Question
How does a photomultiplier tube amplify signals compared to a vacuum phototube for low radiant power?
Page 113
Answer
PMT uses dynodes with ~90V each to multiply electrons up to one million times via secondary emission.
20
Question
What key difference allows charge-injection devices to nondestructively measure pixel charge unlike CCDs?
Page 114
Answer
CIDs use sensing electrodes to monitor accumulated charge independently per pixel without readout destruction.
21
Question
Which holmium oxide filter peak is used to verify wavelength accuracy at 360 nm in spectrophotometers?
Page 115
Answer
Holmium oxide shows sharp absorption peak at 360 nm; deviation beyond ±1 nm tolerance indicates monochromator failure.
22
Question
How does stray light impact absorbance measurements and what test reveals excessive stray light?
Page 115
Answer
Stray light reduces measured absorbance by adding non-sample light to detector; cutoff filters test by checking transmission outside passband.
23
Question
What distinguishes a double-beam-in-space spectrophotometer from a double-beam-in-time design?
Page 116
Answer
Double-beam-in-space uses two separate detectors for sample/reference; double-beam-in-time uses one detector with chopper alternating beams.
24
Question
In reflectometry for dry chemistry slides, why is reflectance nonlinear with analyte concentration?
Page 117
Answer
Diffuse reflectance depends on layered interactions absorbing specific wavelengths and reflecting others multidirectionally.
25
Question
What makes atomic absorption spectrometry specific for metals using hollow cathode lamps?
Page 118
Answer
Hollow cathode lamp emits element-specific EMR absorbed only by ground-state atoms of that metal in flame-aspirated sample.
26
Question
Why is the detector positioned at 90 degrees to the excitation source in fluorometers?
Page 119
Answer
90-degree angle minimizes direct excitation beam, scattered light, and cuvette reflections reaching emission monochromator.
27
Question
How does fluorescent polarization immunoassay avoid physical separation of bound and free fractions?
Page 119
Answer
Measures polarization of emitted light from labeled antigen; bound complexes rotate slower, polarizing more than free label.
28
Question
What enables time-resolved fluorescence immunoassays using Eu3+ chelates to outperform conventional fluorophores?
Page 119
Answer
Eu3+ has long fluorescence lifetime (10-1000 μs) versus nanoseconds for fluorescein, allowing time-gating to reduce background.
29
Question
Unlike fluorescence, what energy source triggers light emission in chemiluminescence assays?
Page 120
Answer
Chemical or electrochemical oxidation reactions excite products that emit light returning to ground state.
30
Question
How does nephelometry differ from turbidimetry in detecting particle concentrations?
Page 121
Answer
Nephelometry measures scattered light intensity at angles (e.g., 90°); turbidimetry measures forward transmitted light reduction.