Fourier Transformation Flashcards
what is FID
free induction decay
how is the FID generated
the FID is the signal that decreases as the vector relaxes to the z axis
what must be done to the FID to allow manipulation
it must be digitised
describe the process of Fourier transformation
FID is measured at range of frequencies
FID is multiplied by a cosine wave of same frequency
the integral of the product wave is measured and plotted
how can the decaying of the FID be mitigated
use time constant T^2
how can the signal magnitude in the x axis be calculated at a given time
Sx(t) = S(0) cos(offset t) e^-t/T^2
how does the value of T^2 relate to the rate of decay
smaller T^2 = faster rate of decay
how does the rate constant relate to the time constant
R^2 = 1/T^2
what is the formula for absorbtion (W)
SoR2 / R2 + (W-offset)^2
why does phase need to be corrected to form an NMR spectrum
nature of absorption depends on the position of the vector in the xy plane
how can phase correction be acheived
my multiplying by e^(iphi(corr))
how does FT reduce the amount of noise seen in a spectrum
collects multiple FIDs signals compound noise cancels
what is the ratio of signal / noise upon addition of spectra
root(number of spectra) x S(NMR)/S(noise)
what are the 4 main methods of improving an NMR spectrum
zero filling
truncation
sensitivity enhancement
resolution enhancement
how does zero filling work
as the digitised data is acquired a line of zeros is added to the end of the data to reduce the noise % in the spectrum
