Analytical Flashcards
define:
a) precision
b) accuracy
a) agreement between set of results (question of error)
b) how close is result to ‘true’ answer
What are 2 ways to improve the precision of data and why?
- run analysis multiple times
- use SOPs (standard operating procedures
both reduce the potential for human error
What does accuracy rely on the generation of?
standards - repeated on the day of analysis or at beginning and end of each batch of samples to ensure performance of method is maintained
What must machines be to maintain accuracy? (c….)
calibrated
What is the robustness?
the method’s reliability in changing conditions e.g. can it be done in colder temperatures, etc.
What is spectroscopy?
study of interaction of electromagnetic radiation with matter
What part of the EM spectrum concerns NMR?
radiowaves
What 4 observations can be made from ¹H NMR?
1) number of signals
2) chemical shift (position of signal)
3) integration
4) peak splitting (coupling)
What information can we get from observing the number of signals?
the number of ¹H environments
What information can we get from observing the chemical shift (position of signal)?
the type of ¹H environment
What information can we get from observing the integration?
the number of ¹H of each type
What information can we get from observing the peak splitting (coupling)?
the number of adjacent ¹H
Why do spectra contain more than 1 peak for all hydrogens?
- magnitude of ΔE = dependent on size of the magnetic field experienced by the nucleus
- the multiple peaks tell us not all protons experience the same magnetic field
- due to the e- surrounding the ¹H nuclei; generate an electric current that shields the nucleus lowering the magnetic field strength experienced, changing ΔE
How does electronegativity affect the nature of a ¹H NMR peak?
- Hs attached to electron-withdrawing groups/atoms have a lower share of electrons
= nuclei experience higher magnetic field due to less shielding from less e- density
- this increases the ppm value, moving the peak downfield
How does electronegativity affect the nature of a ¹H NMR peak?
study of interaction of electromagnetic radiation with matter
What property of fundamental particles/intrinsic form of angular momentum does NMR utilise?
spin
property of spin is fundamentally linked to…?
magnetism
some nuclei also possess imbalanced spin states -> magnetic properties essential for NMR!
What property of fundamental particles utilised by NMR is seen in electrons?
spin - electrons occupy orbitals in pairs with opposing spin states
What are 6 examples of atoms with an overall spin, and why do they have it?
¹H (proton NMR), ¹³C (13C NMR), ¹⁹F, ¹⁴N, ¹⁰B, ²H (deuterium)
all possess an odd number of protons and neutrons resulting in imbalanced spin
Why don’t ⁴He, ¹²C, and ¹⁶O possess an overall spin?
they don’t have an odd number of protons and neutrons
need odd number for spin!
NMR relies on the relationship between s_ and m_
spin and magnetism
How are the spin angles of nuclei in atoms normally oriented?
What happens when we apply a magnetic field?
Are the molecules free to move?
- randomly orientated
- become aligned with/ against magnetic field
- molecules can still move freely but w nuclei in defined orientation
What is the energy state of nuclei that align AGAINST the magnetic field?
the higher energy state known as beta (β)
What is the energy state of nuclei that align WITH the magnetic field?
the lower energy state known as alpha (α)