Instrumental Analysis Final ACS Exam Questions and Answers

Instrumental Analysis Final ACS Exam
Questions and Answers
Know the different types of cuvettes (plastic and quartz) and when they are used -
ANSWER--cuvettes are usually made of plastic, glass and quartz
-plastic and glass are cheaper than quartz
-for light sources >280 nm = plastic
-for light sources >320 nm = glass
-for light sources <320 nm = quartz

Know all the differences and the advantages of Chemical ionization and Electron Impact
- ANSWER-Electron Ionization:
-ionization is direct result of impact of high-energy electrons with analyte molecule
-can be used for organic and inorganic compounds
-causes significant fragmentation in analyte
-it is possible for fragments to collide which may produce new fragments that do not
represent the bond structure of the original precursor molecule (decrease pressure of
the system to avoid this; less molecules available for collision, less collisions of
fragments)
-hard ionization
Chemical Ionization:
-soft ionization
-ionization results from collision of analyte molecules with ions of a reagent gas that is
introduced to the ionization chamber
-reagent gas is ionized with Electron ionization
-reagent gas = methane, ammonia, isobutane
-electrons in EI of reagent gas are much higher in energy than in typical EI (70 eV vs.
200 V)
-negative ion ionization is common (unlike EI)- this is bc reagent gas slows electrons
down enough so they can be captured
-NCI (negative chem. ionization) is common for halogenated cmpds

Know the differences between all the mass analyzers including the m/z that each one
measures at - ANSWER-

Know FT-MS - ANSWER-

Know the advantages of flame and graphite furnace - ANSWER-

Keep an eye out for which instruments are used for trace analysis - ANSWER-

Know how to calculate the resolution of two peaks - ANSWER-

, Potential instruments vs current instruments - ANSWER-

Grating monochromator, spectrometer focal length - ANSWER-

Know Raman detectors - ANSWER-

Calculations for Raman Stokes and anti-stokes lines, Raleigh scattering and Raman
scattering - ANSWER--Rayleigh scattering -same frequency
E = hν
- Raman scattering -changes in frequency
- Stokes lines: E = hν - ΔE
- Anti-Stokes lines: E = hν +ΔE

Appropriate sources/materials used in various instrumentation - ANSWER-

Signal to noise calculations - ANSWER-

Beer's law theory and calculations - ANSWER-A = a·b·c
A =ε·b·c
Transmittance T = P/Po
• Percent Transmittance %T =(P/Po)x100%
• Absorbance A = -logT = -log(P/Po)

Mass spec hard vs. soft ionization sources (examples of each, how are they different?) -
ANSWER-Hard:
-EI
-
Soft:
-electrospray
-MALDI
-chemical

Mass spec instruments, advantages for quadrupole, TOF, etc. - ANSWER-

Theory behind MALDI - ANSWER--used for high-boiling materials
-usually produces monovalent ions
-dissolve target analyte in solution containing crystal forming cmpd; droplets of solution
are deposited on a metal plate and solvent is allowed to evaporate, leaving analyte
trapped in crystalline matrix

Atomic emission/ ICP theory, deviations to Beers law - ANSWER-

Precision, sensitivity trade-offs with GFAA, flame, ICP? - ANSWER-

Stokes shift theory for fluorescence - ANSWER-