INSTRUMENTAL ANALYSIS UPDATED EXAMS SCRIPT
QUESTIONS AND SOLUTIONS GUARANTEE A+
✔✔How to handle solid samples (IR) - ✔✔neat or KBr pellets
✔✔How to handle liquid samples (IR) - ✔✔neat or solution
✔✔What to consider with IR solutions - ✔✔solvent choice and liquid cells
✔✔Why are KBr pellets used - ✔✔Do not absorb in the IR region
✔✔Optical materials used in IR - ✔✔KBr, AgBr, AgCl, CaF2, NaCl, Diamond
✔✔Transmission v ATR - ✔✔Absorptions occur at the same frequency for both
techniques, however the intensity of the absorptions will be different. Or, reflecting (off
sample) rather than transmitting.
✔✔What are the advantages of ATR - ✔✔More time efficient and results are
reproducible
✔✔Limitation of ATR - ✔✔Less libraries of spectra available
✔✔Where is the fingerprint region in IR - ✔✔Less than 1500 cm-1
✔✔NMR samples - ✔✔A few milligrams of material is dissolved in a deuterated solvent
and placed in a 5 mm tube. The NMR sample tube is inserted into the spinner and
positioned using the depth gauge (ours is clear).
✔✔What is in an NMR's magnet can? - ✔✔The superconducting magnet is immersed in
liquid helium (4 K). The outer insulated chamber is filled with liquid nitrogen (77 K).
✔✔What is under the magnet can of an NMR? - ✔✔The probe and the shim stack are
inserted into the magnet from below. Spectrometer connections to the Shim Stack and
the Probe are made here
✔✔Within the magnet - ✔✔The sample sits inside the Shim Stack, which adjusts the
magnetic field for maximum homogeneity
✔✔Within the shim stack - ✔✔The sample sits in the probe
✔✔Within the probe - ✔✔The NMR sample is located within two RF coils. The inner and
outer coils transmit RF to the sample and measure the RF received from the sample.
, ✔✔What is the purpose of RF coils - ✔✔tune coils to elements. (Like tuning a
radio/turning to a different channel
✔✔What is the purpose of the shim coil - ✔✔Shim coils fix magnetic field (create
homogenous magnetic field)
✔✔Easiest way to improve signal to noise ration - ✔✔increase sample concentration or
take more scans
✔✔Why do we have two coils - ✔✔allows the probe to respond to multiple frequencies,
and to allow the excitation/irradiation of multiple nuclei
✔✔Inner Coil - ✔✔Highest Sensitivity and closest to sample
Broadband observe coil, normally tuned to observe carbon (13C) and phosphorous
(31P)
Helmholtz-style coil
✔✔Outer Coil - ✔✔Proton (1H) and fluorine (19F) observe/decouple coil
✔✔We say that the probe does most of the work. Why? - ✔✔The probe contains the
radiofrequency (Rf) coils, tuned at specific frequencies for specific nuclei in a given
magnetic field
Saddle coil
These coils are less efficient than Helmholtz-style coils
✔✔What makes a good solvent for NMR - ✔✔Should not contain hydrogen atoms
Should be inert
Low boiling
Inexpensive
✔✔Protons show up on NMR. How do we get around this when using solvents? -
✔✔Deuterated Solvents
✔✔Common Solvents for NMR - ✔✔CDCl3 (d-chloroform)
D2O (d2-water)
C6D6 (d6-benzene)
CD3OD (d4-methanol)
CD3COCD3 (d6-acetone)
✔✔How to "lock" a magnetic field (NMR) - ✔✔A reference nucleus is continuously
irradiated and monitored
Corrections are made for a drift in the field
The reference signal is the deuterium in the solvent
QUESTIONS AND SOLUTIONS GUARANTEE A+
✔✔How to handle solid samples (IR) - ✔✔neat or KBr pellets
✔✔How to handle liquid samples (IR) - ✔✔neat or solution
✔✔What to consider with IR solutions - ✔✔solvent choice and liquid cells
✔✔Why are KBr pellets used - ✔✔Do not absorb in the IR region
✔✔Optical materials used in IR - ✔✔KBr, AgBr, AgCl, CaF2, NaCl, Diamond
✔✔Transmission v ATR - ✔✔Absorptions occur at the same frequency for both
techniques, however the intensity of the absorptions will be different. Or, reflecting (off
sample) rather than transmitting.
✔✔What are the advantages of ATR - ✔✔More time efficient and results are
reproducible
✔✔Limitation of ATR - ✔✔Less libraries of spectra available
✔✔Where is the fingerprint region in IR - ✔✔Less than 1500 cm-1
✔✔NMR samples - ✔✔A few milligrams of material is dissolved in a deuterated solvent
and placed in a 5 mm tube. The NMR sample tube is inserted into the spinner and
positioned using the depth gauge (ours is clear).
✔✔What is in an NMR's magnet can? - ✔✔The superconducting magnet is immersed in
liquid helium (4 K). The outer insulated chamber is filled with liquid nitrogen (77 K).
✔✔What is under the magnet can of an NMR? - ✔✔The probe and the shim stack are
inserted into the magnet from below. Spectrometer connections to the Shim Stack and
the Probe are made here
✔✔Within the magnet - ✔✔The sample sits inside the Shim Stack, which adjusts the
magnetic field for maximum homogeneity
✔✔Within the shim stack - ✔✔The sample sits in the probe
✔✔Within the probe - ✔✔The NMR sample is located within two RF coils. The inner and
outer coils transmit RF to the sample and measure the RF received from the sample.
, ✔✔What is the purpose of RF coils - ✔✔tune coils to elements. (Like tuning a
radio/turning to a different channel
✔✔What is the purpose of the shim coil - ✔✔Shim coils fix magnetic field (create
homogenous magnetic field)
✔✔Easiest way to improve signal to noise ration - ✔✔increase sample concentration or
take more scans
✔✔Why do we have two coils - ✔✔allows the probe to respond to multiple frequencies,
and to allow the excitation/irradiation of multiple nuclei
✔✔Inner Coil - ✔✔Highest Sensitivity and closest to sample
Broadband observe coil, normally tuned to observe carbon (13C) and phosphorous
(31P)
Helmholtz-style coil
✔✔Outer Coil - ✔✔Proton (1H) and fluorine (19F) observe/decouple coil
✔✔We say that the probe does most of the work. Why? - ✔✔The probe contains the
radiofrequency (Rf) coils, tuned at specific frequencies for specific nuclei in a given
magnetic field
Saddle coil
These coils are less efficient than Helmholtz-style coils
✔✔What makes a good solvent for NMR - ✔✔Should not contain hydrogen atoms
Should be inert
Low boiling
Inexpensive
✔✔Protons show up on NMR. How do we get around this when using solvents? -
✔✔Deuterated Solvents
✔✔Common Solvents for NMR - ✔✔CDCl3 (d-chloroform)
D2O (d2-water)
C6D6 (d6-benzene)
CD3OD (d4-methanol)
CD3COCD3 (d6-acetone)
✔✔How to "lock" a magnetic field (NMR) - ✔✔A reference nucleus is continuously
irradiated and monitored
Corrections are made for a drift in the field
The reference signal is the deuterium in the solvent
