Instrumental final exam misconceptions

• What are the four types of gratings mentioned in the content? Describe each.

• Echelle: short side of blazes is where reflection occurs

• Echellette: long side of blazes is where reflection occurs

• Concave: gratings are present on a concave surface

• Holographic: produced by optical fabrication process

What is the typical wavelength range for plastic cuvettes?

• 350-900nm range

• What are the typical wavelength ranges produced by a D2 lamp?

• 190-350nm

How does a tungsten/halogen lamp differ from a regular tungsten lamp?

• Burns at 3500K

• Longer lifetime

• Higher intensities

• Extends output into UV region

• What are the advantages and disadvantages of using a filter compared to a monochromator?

• Simpler

• More sensitive

• Faster

• Limited wavelength selection

• What is the wavelength range of a xenon arc lamp?

• 200-1000nm

• What common functional groups or compounds are associated with chemiluminescence?

• Oxalate esters

• Luminol

• Dioxetanes

• Functional group: the one with C=O and a NH-NHR attached to the carbonyl)

• Do aliphatic compounds fluoresce or phosphoresce?

• No, aliphatic compounds won’t fluoresce or phosphoresce

• This is due to the lack of pi→pi* and n→pi* transitions (alkanes and alkenes are examples of aliphatics)

• What is internal conversion in the context of a Jablonski diagram?

• This is where a molecule de-excites by transferring energy to the vibrational modes of the same or lower electronic state without emitting a photon

• Occurs during S₂ to S₁ transition and sometimes results in relaxation from S₁ to S_o

• What is quenching in fluorescence? What are the two types?

• Static, where a complex forms between the ground-state fluorophore and the quencher (a dark complex forms)

• Dynamic (or collisional), where collisions between excited species and quenching agent occur that disrupt fluorescence

What is the primary absorption in inner-filter effects?

• Primary absorption is when the radiant power is not uniform and excess absorption occurs by only part of the sample

• What is the secondary absorption in inner-filter effects?

• Mainly refers to deviations in linearity due to exceedingly high concentration of analyte

• What are the main components of a fluorometer?

• Radiation source (high pressure Hg vapor lamp w/fused silica window)

• Wavelength selectors (filters)

• Sample in sample holder

• Beam split (reference and sample)

• Transducers (2PMTs, one for sample and one for reference)

• Readout

• Differs from spectrofluorometer because it uses filters instead of two monochromators

• What are the limitations of using Mass Spectrometry (MS) for analysis?

• Cannot be used for:

• Large biomolecules

• Non-volatile compounds

• Mixtures (or if it is, must be separated into individual components first)

• Highly reactive compounds

• What are some examples of continuous sources in UV-vis spectrometry?

• Xenon lamp, D₂ lamp, tungsten lamp, LEDs

• What are some examples of line sources in UV-vis spectrometry?

• Hallow cathode lamp, lasers

What are the cuvette materials most commonly used for UV-vis spectrometry and/or IR and what are the wavelength ranges for each?

• Plastic: 350-900nm

• Borosilicate glass: 350-2000nm

• Quartz (200-3000nm)

• For IR: salt plates (200-15000nm)

• What are the two types of detectors used in optical spec and what type of noise limits each? What are each used for?

• Photon detectors: limited by shot noise, used for UV, vis, and near IR

• Thermal detectors: used for IR, limited by thermal (Johnson) noise

• Give the wavelength range of emissions from a tungsten lamp

• 350-1100nm