Analytical Chemistry (2005, 4, 11)
I. Briefly Differentiate the following terms (8% each, 48% total)
1. Aptamers and molecular beacon
2. Angular dispersion and linear dispersion
3. Internal conversion and intersystem crossing
4. Iosbestic point and isoelectric point
5. Flurescence and phosphorescence
6. White noise and drift noise
II. Answer the following questions (8% each, 48% total):
1. Plot the titration curve when 25 mL of aqueous solution consisting of 0.1M
A2+ and B+ is titrated with a solution of 0.1M Y4- if the formation constant
values for the complexes of AY2- and BY3- are 1000 and 100, respectively,
and the molar absorptivity values of AY2- and BY3- are 5000 and 10 at 700nm.
2. Estimate the LOD of compound A if the analyses of compound A and B are
carried out under the same conditions. Assume that the fluorescence
intensity of compound B at the concentration of 3 nM is 450 counts and the
noise is 5 counts, and the molar absorptivity values(and quantum yield) of
compounds A and B are 1000(0.6)and 10000(0.4), respectively.
3. Why is it most accurate to measure the absorbance in the range of A=0.4-0.9?
4. Why time-resolved fluorescence is popular in immunoassays?
5. Why does pyrene fluoresce stronger in SDS micelles? Can you determine the
critical micelle concentration of SDS using an optical method?
6. Why can attenuated total reflectance be used to improve sensitivity? Can it
be determine the thickness of a coating material on a substrate?If yes, how?
III. Using the following data to determine the stoichiometry of the
metal-ligand complex if the concentration of the metal was held constant at
0.365 mM(10%).
[ligand](mM) 0.1 0.3 0.5 0.6 0.7 0.9 1.0
Absorbance 0.122 0.376 0.625 0.752 0.873 0.962 1.001
IV. Optical methods(10% each, 30% total)
1. Determine TNT at the concentration less than 100 nM.
2. Determine the dissociation constant of an organic acid that is a common
acid-base indicator.
3. Determine the binding constant for an enzyme and its substrate.
V. Instrumentation (40% total)
1. Block diagrams for molecular fluorescence spectrometers using (A) continuous
light source, and (B) a photodiode array. (20%)
2. Block diagrams for molecular UV-Vis absorption spectrometer using (A) a
double beam configuration, and (B) a photodiode array. (20%)
VI. Immunoassays (10% each, 30% total)
1. What is ELISA? Why enzyme is usually used in the assay?
2. Can chemiluminescence be used in ELISA? Why?
3. How can you simultaneously determine the concentrations of a pesticide at
the concentration less than 10 nM in 20 samples?
VII. Monochromator (30%)
1. What are the differences between grating, filter, and prism? (10%)
2. (A) What resolution is required for a diffraction grating to resolve
wavelength of 510.02 and 510.12? (B) Calculate the third-order resolution of
a grating that is 1.0 cm long and is ruled at 2000 line/mm. (C) What is the
third-order wavelength at the reflection angle 20' when the incidence angle
is 30'? (D) What is the angular dispersion of grating? (5% each, 20% total)
VIII Beer's law(40%)
1. What is the Beer's law? You must give an equation and clearly define all the
parameters. (5%)
2. What will cause the deviation of the linearity? (15%)
3. How can you improve the precision and sensitivity of UV-Vis absorption
measurements? (10%)
4. Describe a method in detail to determine the concentrations of iron in blood
samples. (10%)
IX Quenching (30% total)
1. Derive the Stern-Volmer equation. (15%)
2. How can you determine the Stern-Volmer constant? (5%)
3. Suggest a method to determine the concentration of O2. (10%)
X Fourier transform infrared spectroscopy (25%)
1. Schematic diagram of Michelson interferometer (10%)
2. What are the maximum retardation and resolution if the interferometer mirror
travel ±2 cm? (10%)
3. At what retardation interval must the interferogram be sampled to cover a
spectral range of 0 to 2000 cm^-1? (5%)
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