Chemistry
660 Supplemental Materials--Fall 2003
Professor James Ingle
not revised for Fall 2002 or 2002- but a good study guide
CONCEPTS (OUTCOMES))
Be able to define the differences between
critical
1. wavelength & frequency & energy & wavenumber
2. reflection & emission & chemiluminescence & transmission & scattering & refraction & absorption & photoluminescence
3. atomic & molecular spectroscopy
4. signal-to-background ratio (S/B) & relative standard deviation (RSD) & signal-to-noise ratio (S/N)
5. ground and excited states or energy levels
6. sensitivity & detection limit
7. concomitant and interferent
important
8. selectivity & accuracy & precision & dynamic range
9. initial & analytical sample
10. quantitative & qualitative analysis
Be able to state the definitions of
critical
spectrum
analyte
matrix and matrix effects
interference
blank and ideal blank
blank or reference signal
analytical signal
calibration function
propagation of uncertainty mathematics
important
emission spectroscopy
calibration, analytical, or working curve standards
standard deviation
simplex optimization
multiple species capability
Be able to
specify the wavelength regions of the near UV, visible, and near IR regions of the electromagnetic radiation
discuss what types of transitions are associated with the visible region and the IR region of the electromagnetic spectrum
Be able to
critical
1. define and use of radiometric quantities such as radiant power, radiance, irradiance, and energy density.
2. discuss the expressions relating the radiant power of emission or luminescence or the transmission or absorbance to analyte concentration and other variables.
3. use the readout equations (e.g., the total and blank signals) and to draw the instrumental configurations for absorption, emission, and photoluminescence spectroscopy.
4. explain the differences between a monochromator & spectrograph & polychromator (e.g., how many slits, detectors, etc.).
5. calculate the radiant power incident on a receptor of known area from the source radiant intensity or radiance and source area viewed and the source-receptor distance including
to decide when to use the radiant intensity or the radiance for the source
to indicate what intensity terms can be used to describe a point source and which ones cannot.6. calculate the population of excited levels with the Boltzmann distribution and decide when the the partition function can be approximated as the statistical weight of the ground state.
7. interconvert between frequency, wavelength, energy, and wavenumber and between intervals of these quantities. For example, discuss why the formula for converting wavelength to frequency is different from the formula for converting wavelength interval to frequency interval (why Dn does not equal c/Dl?).
important
8. discuss the steps and instrumental components involved in a complete spectrochemical measurement.
9. interconvert between spectral radiant power per nm and spectral radiant power per Hz.
10. convert between energy density and irradiance.
revised to this point for F 2001
Be able to
critical
1. calculate the reflection from the Fresnel equation, the angle of refraction from Snell's law, and the absorbance from Beer's law
2. state the conditions necessary for constructive and destructive interference and use the appropriate equations to calculate the spacing and widths of the diffraction pattern with one or more slits.
3. apply the equations that describe imaging with optical components (lenses and mirrors) to calculate the image distance, magnification, image irradiance, and solid angle of collection from the focal length and object distance.
4. inter-convert among measures of absorption strength such as absorptivity, absorption cross section, and absorption coefficient.
5. state the assumptions used to derive Beer's law and the basis to evaluate if these assumptions are valid in a given situation.
6. describe the difference between non-polarized and linear polarized radiation and how polarized radiation is produced and to define phenomena or quantities that depend on polarization including Brewster's angle, linear dichroism, or birefringence
7. state and use the equations governing the acceptance angle of fiber optics and the central wavelength of the transmission band of interference filters.
8. calculate the transmission through one or more layers of material based on absorption and reflection losses.
9. describe in words and with equations how gratings (and prisms) provide angular wavelength dispersion.
10. provide word definitions and state and use the mathematical equations for monochromator performance characteristics including angular, linear, or reciprocal linear dispersion, F/n, solid angle, spectral bandpass, resolution, resolving power, optical efficiency, and throughput
11. State which monochromator performance characteristics depend on entrance and exit slit widths, the focal lengths of the collimating and focusing elements, and the dispersion element size.
12. Describe how wavelength resolution depends on the order.
13. Describe how an echelle monochromator achieves high resolution with a coarse grating and the pattern of slit images in the focal plane.
14. Define stray light and how can it be minimized.
15. Describe the construction of a Fabry-Perot interferometer or etalon and what determines its free spectral range (just material in lectures, no details or equations).
16. Describe how the source light beam is divided and recombined in a Michelson interferometer and how the interferogram is converted into a spectrum.
important
17. Define a beam splitter and modulator.
18. List common types of optical aberrations (just material covered in lecture notes).
19. Describe linear polarization in terms of the electric vector and the sum of two orthogonal waves of varying phase difference.
20. Define optical pathlength (OPL) (e.g., used to describe operation of interference filters and lasers).
Note yet revised below this point for F01 (basically quite usable)
Be able to
critical
1. The use of the blackbody equations to characterize real sources.
2. Use of Einstein coefficients to calculate rates of emission and absorption. How these quantities are related to other quantities that measure transition strength such as the absorption coefficient or absorptivity (see Appendix F)
3. The difference between line and continuum sources including incandescent lamps and arc lamps.
4. How lasers work, the types of lasers, and in what situations they are useful. Conditions necessary for continuous and pulsed operation. Three- vs four-level systems. When a 4-level system is pulsed because it is self-terminating and when it is pulsed because the pump is pulsed.
5. The differences between thermal and photon detectors. The differences between photoemissive and semiconductor detectors.
6. For photoemissive detectors and photodiodes, how to inter-convert among photocathodic current (i), photoanodic current (i), and pulse rates (r)and to calculate these quantities from the incident radiant power, photocathodic quantum efficiency, and photomultiplier gain (m). For diode arrays and charge transfer detectors, how the signal in terms of number of electron-hole pairs (n) and charge (q) is related to incident radiant power, quantum efficiency, and integration time.
7. The basic differences between the multichannel semiconductor detectors in terms of the arrangement of pixels (linear array or 2-D) the type of charge readout system used.
8. The basic differences between processing of DC signals and processing of fast changing signals or modulated signals with lock-in amplifiers, boxcar integrators, & digitizers.
9. The differences and areas of application for single channel, double beam, fixed-wavelength, scanning, rapid or slew scanning, and multichannel spectrometers.
10. The use of quantitative readout expressions (calculating voltage signals from characteristics of the monochromator, photodetector, etc.).
important
11. The difference between analog, digital, and photon counting signal processing.
12. The types of functions performed by signal processing circuitry (not details about electronic circuits).
Be able to
critical
1. Characterization of noise by the following means:
a. by the signal source [(analytical) signal, background, blank, or dark)
b. as fundamental or non-fundamental
c. as white or non-white (1/f or interference)
d. by dependence on the signal (shot vs flicker)
2. How the total noise (a sum from individual noise sources) and S/N change with increasing
a. "averaging time" [electronic bandwidth (time constant (t) or integration time(t)) or number of measurements (n)]
b. the signal magnitude (e.g., counts or photocathodic current )
- when observe a square root relationship?
- when the S/N levels off?
3. How to determine the effect of an experimental variable (e.g., W, wavelength) on the rms noise or S/N (i.e., one must figure out how the variable in question affects nS (ES) or nB (EB)
4. How to convert between radiant power in photons per s on Watts and from noise in terms of counts (e.g., electron-hole pairs) and current or voltage).
5. How the S/N can vary for different kinds of detectors when the light levels are relatively low (problems sets 7 - 9)
6. The frequency content of noise: 1) how the noise amplitude varies with frequency for 1/f noise, 2) how filters reduce the observed noise by restricting the frequency range observed
7. How choosing the time constant or integration time is a compromise and dependent on the temporal behavior of the type of signal observed
8. How to enhance the S/N
a. Learning about what noises are limiting (dominant) for a given instrument and how they can be determined from repetitive measurements of the dark current, blank, and total signal.
b. When signal shot noise and any kind of shot noise are limiting
c. When blank noise or specific types of blank noise (background or dark or readout noise) are limiting.
d. When adjusting the S/B will help, when a better detector will help
e. When source flicker noise is dominant
f. How modulation techniques can improve the S/N when 1/f amplifier-readout noise or 1/f background emission noise in absorption measurements are limiting
9. For absorption measurements, understand the basic dependence of precision (sA/A) on analyte concentration, sample signal (Es), transmittance, or absorbance. Know which types of noise are often dominant at low, moderate, and high absorbances.
important
10. When double-beam configurations or photon counting improve the S/N.
Be able to
critical
1. The standard analysis procedure with external standards and where errors can arise.
2. define te difference between random and systematic errors.
3. define and contrast an additive interference and a multiplicative interference and how the quality of the blank affects each one.
4. discuss the difference between systematic error, random error, and drift.
5. How to calculate standard deviations and apply them 1) to compare an experimental mean to a expected value and 2) to establish a confidence interval around the experimental mean.
6. The difference between sensitivity and detection limit.
7. Detection limit: how to calculate, the different ways of expressing, and what it means.
8. Techniques for compensation of interferences and measurement errors (e.g., dilution, saturation, standard additions, internal standard method, matrix modifier (buffer) method, internal blank method, matrix match method, separation, instrumental correction ): what problems they address, their limitations, their basis. ck if others
9. The situations in which automated analyzers are useful.
10. Compare batch vs. continuous unsegmented flow analyzers including FIA vs. SIA
important
11. What factors affect the precision of an analytical determination such as sampling, sample presentation, sample preparation, etc.
12. When the "t" statistic is used instead of the "z" statistic.
material below revised 11/30/00
Be able to
1. describe the methods for introducing samples into atomizers including nebulizers, hydride generators, electrothermal vaporizers, and probes (also see chap. 10).
2. discuss the design, advantages, and limitations of different types of nebulizers (pneumatic vs. ultrasonic vs. high-solids) and how nebulizers differ between flames and plasmas.
3. describe the processes that occur during atomization (e.g., desolvation, volatilization, dissociation, and ionization) and how the efficiency of these processes can depend on the analyte, sample matrix, type of atomizer, and temperature.
4. explain how temperature influences numerous parameters in atomic spectroscopy including the fraction of excited atoms or ions, the overall atomization efficiency, and line widths (e.g., if T increases, what goes up and what goes down?).
5. calculate the number density of atoms or ions in a flame or plasma from parameters including the analyte concentration, gas and sample flow rates, and overall atomization efficiencies.
6. explain why the number density described in concept 5 varies with the element and the type of atomizer.
7. describe the types of multiplicative interferences that are common to AAS, AES and ICP/MS and the specific types of spectral interferences that are unique for each of the above techniques.
8. discuss the processes that broaden atomic lines, calculate half-widths (natural, collisional, or Doppler), list typical values for half-widths, and provide the definition of the "a parameter" in the Voigt profile.
9. use the equations that indicates how the analyte emission intensity (BE) or the analyte absorbance depends on instrumental and analyte parameters including number density, Einstein coefficient, pathlength, wavelength, and temperature.
Be able to
1. explain why the ICP has become the dominant excitation source for atomic emission spectrometry (relative to the flame) and how its characteristics compare to those of an ideal emission source?
2. use the Boltzmann distribution to predict the fraction of excited atoms or ions (and hence the relative emission signal observed) and to explain why the atomizer temperature and analyte wavelength are so important for emission.
3. discuss the differences between excitation, ionization, and translational temperature.
4. describe the causes of plasma background emission.
5. diagram an ICP torch and label the RF coil and various gas flows
6. discuss and contrast the different designs of ICP emission spectrometers including sequential versus simultaneous and for simultaneous spectrometers (direct reader vs multichannel detector (CTD) ).
7. compare the advantages and disadvantages of simultaneous and sequential emission measurements
8. apply the equation describing the dependence of the analyte emission signal on instrumental and analyte variables (e.g., temperature, slit width, flow rates, atomization efficiency, etc.) to explain why emission signals vary with the element, with the wavelength chosen for a given element, and for a given element and wavelength with different spectrometers.
9. write down the general S/N expression for emission measurements and identify the noise sources, to describe how the S/N depends on concentration, to identify the limiting noise sources at low and high analyte concentrations, and to describe how the how the S/N varies with slit width at low concentrations.
10. describe why and how background correction is implemented in ICP emission spectrometry.
11. contrast the advantages and limitations of the radial and axial torch configurations (i.e., calibration sensitivity, detection limit, linearity, interferences).
12. diagram how an ICP is used as an ion source in ICP/MS.
13. describe what determines the position and height of the peaks observed for each element in an ICP/MS spectrum.
14. list the possible causes of spectral overlap problems in ICP/MS.
15. list the factors that determine the magnitude of the signal (counts) for a given element (i.e, the calibration sensitivity ) and why the detection limits with ICP/MS are usually extremely good (around a pptr).
16. discuss when internal standard and standard addition methods are useful in ICP/AES or ICP/MS spectrometry.
Be able to
1. draw a block diagram of an AA spectrometer and discuss the advantages of double-beam systems.
2. describe how to select between an air/C2H2 or an N2O/C2H2 flame for flame AAS based on the atomization efficiency and background emission characteristics (table on p. 10-1 of lecture notes or material in section 8-2, pp. 228-230).
3. contrast the use of flame and electrothermal atomizers for AAS and explain why detection limits are often better with electrothermal atomization compared to flame atomization.
4. describe how the ash step and matrix modifiers are used to minimize interferences with electrothermal atomization.
5. explain how you would choose the atomization/sample introduction technique (i.e., flame vs. electrothermal vs. hydride vs. cold vapor) for a given situation based on factors such as the analyte concentration and particular element (e.g., As, Se, and Hg)
6. apply the equation describing the dependence of the analyte absorbance on atomizer, spectrometer, and analyte variables (e.g., atomizer temperature, flow rates, atomization efficiency, etc.) to explain why the absorbance varies with the element, with the wavelength chosen for a given element, and with the type of atomizer/sample introduction technique for a given element and wavelength.
7. identify the limiting noise sources in different absorbance regions.
8. describe under what circumstances, background correction is required and the basic principles and advantages and limitations of the different common approaches (continuum vs. Zeeman vs. pulsed HCL).
9. discuss how instrumental conditions (e.g., W, HCL current, etc) affect linearity.
10. Compare ICP/AES, ICP/MS, and flame and electrothermal AAS in terms of instrumentation, detection limit, S/N, interferences, accuracy, precision, linearity, multielement capability, and applicability.
Be able to
1. discuss what determines the shape, spectral position, and intensity of electronic absorption bands?
2. describe the various processes (e.g., internal conversion, external conversion, fluorescence, intersystem crossing) by which a molecule dissipates excess energy after absorption of a photon and how the rates of these processes affect the fluorescence and phosphorescence quantum efficiencies and lifetimes.
3. define the difference between quantum efficiency and power yield.
4. discuss the mechanism of dynamic quenching and desctibe how dynamic quenching affects fluorescence signals, lifetimes, and quantum efficiencies.
5. apply the Stern-Volmer equation to determine the attenuation of the luminescence signal.
6. discuss how structural features and substituent groups in a molecule can affect the nature of the first excited state and quantum efficiencies for fluorescence and phosphorescence.
7. define the difference between the internal and external heavy atom effect.
8. discuss how the solvent, temperature, and pH might affect the luminescence characteristics of a given molecule.
Be able to
1. specify the necessary instrumental conditions to ensure that Beer's law can be applied with a specified level of accuracy (e.g., the effects of stray radiation, polychromatic radiation, and spectral bandpass). Review table 3-1.
2. list the factors which cause a non-zero intercept or a nonlinearity in A vs. c plots and comment about the relative importance of these factors.
3. define chemical and instrumental causes of nonlinearity and discuss how to experimentally determine which cause is limiting.
4. draw a block diagram of a spectrophotometer and discuss the types and characteristics of the instrumental components.
5. discuss how precision and the detection limit are affected by instrumental variables (e.g., slit width, lamp radiance, wavelength) and how to improve these performance characteristics.
6. discuss the difference (concepts and equations) between the absorbance by two different compounds at one wavelength and the absorbance of one compound at two different wavelengths. The concept and equations for absorption at two or more wavelengths by one compound are discussed in more detail in the lecture notes and in the Beer's law handout (part B).
7. contrast the advantages and disadvantages of single-beam vs. double beam and single detector (PMT) vs. multichannel detector (diode array) spectrophotometers.
8. describe how the radiant power seen by the detector depends on instrumental and sample cell or solution variables and the factors which affect the transmission of radiation through a sample cell filled with a reference or an analyte solution.
9. identify the limiting noise sources at low and high absorbances.
10. discuss the basis of multicomponent analysis.
11 identify the factors that control the detection limit.
these concepts from section 13-4 and 13-5 are not covered on the test
12. The different qualitative, fundamental, and quantitative applications of molecular absorption spectrophotometry.
13. The factors affecting the choice of instrument, instrumental conditions, and solutions conditions for a particular analysis.
14. How to compare spectrophotometers according to their specifications.
15. Automated spectrophotometric measurements.
16. The advantages of computerized spectrophotometers.
17. The advantages and limitations of spectrophotometric titrations and reaction rate methods.
18. The use of spectrophotometry in chromatographic applications.
19. The different ways in which concomitants affect the accuracy of determinations.
20. Why spectrophotometric determinations are often based on a selective analytical reaction?
21. Contrast the advantages and disadvantages of instrumental configurations or options such as derivative mode, dual-wavelength mode, and difference spectra.
material below not covered F00
Be able to
only the material covered in lecture
1. discuss the types and characteristics of the instrumental components that make up a fluorometer or spectrofluorometer.
2. discuss the choices of cell geometry and how the cell geometry can affect results.
3. define the difference between emission and excitation spectra.
4. define the meaning of total luminescence, synchronous, and derivative spectra and discuss their use.
5. define what "corrected" means for excitation and emission spectra?
6. define a quantum counter and describe how it is used?
Extra - not important
chap 13
9. The difference between chromophores and auxophores.
10. How transition probabilities, absorptivities, absorption coefficients, and absorption cross sections are interrelated (see also appendix F).
11. The definitions of bathochromic shift, hyposchromic shift, hyperchromic effect, and hypochromic effect.
chapter 7.
g10. discuss and use critical equations in SA (in terms of what they indicated about real measurements) include 7-6, 7-9, 7-17, 7-23, 7-28, 7-31, 7-32, 7-38, 7-45, 7-48.
http://www.chem.orst.edu/ch560-1/ch560/ch560sm.htm
Last updated on September 26, 2003
