ASTM E386-90(1999)
(Practice)Standard Practice for Data Presentation Relating to High-Resolution Nuclear Magnetic Resonance (NMR) Spectroscopy
Standard Practice for Data Presentation Relating to High-Resolution Nuclear Magnetic Resonance (NMR) Spectroscopy
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1.1 This standard contains definitions of basic terms, conventions, and recommended practices for data presentation in the area of high-resolution NMR spectroscopy. Some of the basic definitions apply to wide-line NMR or to NMR of metals, but in general it is not intended to cover these latter areas of NMR in this standard. This version does not include definitions pertaining to double resonance nor to rotating frame experiments.
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Designation:E386–90(Reapproved 1999)
Standard Practice for
Data Presentation Relating to High-Resolution Nuclear
Magnetic Resonance (NMR) Spectroscopy
This standard is issued under the fixed designation E386; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope where g5the magnetogyric ratio, a constant for a given
nuclide (Note 2).The amplitude of the magnetic component of
1.1 This standard contains definitions of basic terms, con-
the radio-frequency field is called H . Recommended units are
ventions, and recommended practices for data presentation in
millitesla and microtesla.
the area of high-resolution NMR spectroscopy. Some of the
basicdefinitionsapplytowide-lineNMRortoNMRofmetals,
NOTE 2—This quantity is normally referred to as B by physicists. The
but in general it is not intended to cover these latter areas of usage of H to refer to magnetic field strength in chemical applications is
sowidelyacceptedthatthereappearstobenopointinattemptingtoreach
NMRinthisstandard.Thisversiondoesnotincludedefinitions
a totally consistent nomenclature now.
pertaining to double resonance nor to rotating frame experi-
NOTE 3—This expression is correct only for bare nuclei and will be
ments.
only approximately true for nuclei in chemical compounds, since the field
at the nucleus is in general different from the static magnetic field. The
2. Terminology Nomenclature and Basic Definitions
discrepancy amounts to a few parts in 10 for protons, but may be of
−3
2.1 nuclear magnetic resonance (NMR) spectroscopy—that
magnitude 1 310 for the heaviest nuclei.
form of spectroscopy concerned with radio-frequency-induced
2.5 NMR absorption line—a single transition or a set of
transitions between magnetic energy levels of atomic nuclei.
degenerate transitions is referred to as a line.
2.2 NMR apparatus; NMR equipment—an instrument com-
2.6 NMR absorption band; NMR band— a region of the
prising a magnet, radio-frequency oscillator, sample holder,
spectruminwhichadetectablesignalexistsandpassesthrough
and a detector that is capable of producing an electrical signal
one or more maxima.
suitable for display on a recorder or an oscilloscope, or which
2.7 reference compound (NMR)—a selected material to
is suitable for input to a computer.
whose signal the spectrum of a sample may be referred for the
2.3 high-resolution NMR spectrometer— an NMR appara-
measurement of chemical shift (see 2.9).
tusthatiscapableofproducing,foragivenisotope,linewidths
2.7.1 internalreference(NMR)—areferencecompoundthat
that are less than the majority of the chemical shifts and
is dissolved in the same phase as the sample.
coupling constants for that isotope.
2.7.2 externalreference(NMR)—areferencecompoundthat
NOTE 1—By this definition, a given spectrometer may be classed as a
is not dissolved in the same phase as the sample.
high-resolutioninstrumentforisotopeswithlargechemicalshifts,butmay
2.8 lock signal—the NMR signal used to control the field-
not be classed as a high-resolution instrument for isotopes with smaller
frequency ratio of the spectrometer. It may or may not be the
chemical shifts.
same as the reference signal.
2.4 basic NMR frequency, n —the frequency, measured in
2.8.1 internal lock—a lock signal which is obtained from a
o
hertz (Hz), of the oscillating magnetic field applied to induce
material that is physically within the confines of the sample
transitions between nuclear magnetic energy levels. The static
tube, whether or not the material is in the same phase as the
magnetic field at which the system operates is called H (Note
sample (an annulus for the purpose of this definition is
o
1)anditsrecommendedunitofmeasurementisthetesla(T)(1
considered to be within the sample tube).
T 510 gauss).
2.8.2 external lock—a lock signal which is obtained from a
2.4.1 The foregoing quantities are approximately connected
material that is physically outside the sample tube. The
by the following relation:
material supplying the lock signal is usually built into the
probe.
g
n 5 H (1)
o o
2p
NOTE 4—An external lock, if also used as a reference, is necessarily an
external reference.An internal lock, if used as a reference, may be either
1 an internal or an external reference, depending upon the experimental
These practices are under the jurisdiction of ASTM Committee E-13 on
configuration.
Molecular Spectroscopy and are the direct responsibility of Subcommittee E13.07
on Nuclear Magnetic Resonance Spectroscopy.
2.8.3 homonuclear lock—a lock signal which is obtained
Current edition approved June 29, 1990. Published August 1990. Originally
from the same nuclide that is being observed.
published as E386–69T. Last previous edition E386–78.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E386
2.8.4 heteronuclear lock—a lock signal which is obtained 3.2 broad-band excitation NMR—a form of high-resolution
from a different nuclide than the one being observed. NMRinwhichnucleiofthesameisotopebutpossiblydifferent
chemical shifts are excited simultaneously rather than sequen-
2.9 chemical shift, d—the defining equation for d is the
tially.
following:
3.2.1 pulse Fourier transform NMR—a form of broad-band
Dn
d5 310 (2) excitation NMR in which the sample is irradiated with one or
n
R
more pulse sequences of radio-frequency power spaced at
where n is the frequency with which the reference sub-
uniform time intervals, and the averaged free induction decay
R
stance is in resonance at the magnetic field used in the following the pulse sequences is converted to a frequency
experiment and Dn is the frequency of the subject line minus
domain spectrum by a Fourier transformation.
thefrequencyofthereferencelineatconstantfield.Thesignof 3.2.1.1 pulse Fourier difference NMR—a form of pulse
Dn is to be chosen such that shifts to the high frequency side Fourier transform NMR in which the difference frequencies
of the reference shall be positive. between the sample signals and a strong reference signal are
extracted from the sample response prior to Fourier transfor-
2.9.1 If the experiment is done at constant frequency (field
mation.
sweep) the defining equation becomes
3.2.1.2 synthesized excitation Fourier NMR— a form of
Dn Dn
pulse Fourier NMR in which a desired frequency spectrum for
d5 3 1 2 310 (3)
S D
n n
R R
the exciting signal is Fourier synthesized and used to modulate
2.9.2 In case the experiment is done by observation of a
the exciting radio frequency.
modulation sideband, the audio upper or lower sideband 3.2.2 stochastic excitation NMR—a form of broad band
frequency must be added to or subtracted from the radio excitation NMR in which the nuclei are excited by a range of
frequency. frequencies produced by random or pseudorandom noise
modulation of the carrier, and the frequency spectrum is
2.10 spinning sidebands—bands, paired symmetrically
obtained by Fourier transforming the correlation function
about a principal band, arising from spinning of the sample in
between the input and output signals.
a field (dc or rf) that is inhomogeneous at the sample position.
3.2.3 Hadamard transform NMR—a form of broad band
Spinning sidebands occur at frequencies separated from the
excitation NMR in which the phase of the excitation signal is
principal band by integral multiples of the spinning rate. The
switched according to a binary pseudorandom sequence, and
intensities of bands which are equally spaced above and below
the correlation of the input and output signals by a Hadamard
the principal band are not necessarily equal.
matrix yields an interference pattern which is then Fourier-
2.11 satellites—additional bands spaced nearly symmetri-
transformed.
cally about a principal band, arising from the presence of an
isotope of non-zero spin which is coupled to the nucleus being
4. Operational Definitions
observed. An isotope shift is normally observed which causes
4.1 Definitions Applying to Sequential Excitation (CW)
the center of the satellites to be chemically shifted from the
NMR:
principal band. The intensity of the satellite signal increases
4.1.1 field sweeping (NMR)—systematically varying the
with the abundance of the isotope responsible.
magnetic field strength, at constant applied radio-frequency
2.12 NMR line width—the full width, expressed in hertz
field, to bring NMR transitions of different energies succes-
(Hz), of an observed NMR line at one-half maximum height
sively into resonance, thereby making available an NMR
(FWHM).
spectrum consisting of signal intensity versus magnetic field
2.13 spin-spin coupling constant (NMR), J—a measure,
strength.
expressed in hertz (Hz), of the indirect spin-spin interaction of
4.1.2 frequency sweeping (NMR)—systematically varying
different magnetic nuclei in a given molecule.
the frequency of the applied radio frequency field (or of a
n modulation sideband, see 4.1.4), at constant magnetic field
NOTE 5—The notation J is used to represent a coupling over n
AB
strength, to bring NMR transitions of different energies suc-
bondsbetweennucleiAandB.Whenitisnecessarytospecifyaparticular
3 15
isotope, a modified notation may be used, such as, J ( NH). cessively into resonance, thereby making available an NMR
spectrum consisting of signal intensity versus applied radio
3. Types of High-Resolution NMR Spectroscopy
frequency.
4.1.3 sweep rate—the rate, in hertz (Hz) per second at
3.1 sequential excitation NMR; continuous wave (CW)
which the applied radio frequency is varied to produce an
NMR—a form of high-resolution NMR in which nuclei of
NMR spectrum. In the case of field sweep, the actual sweep
different field/frequency ratio at resonance are successively
rate in microtesla per second is customarily converted to the
excited by sweeping the magnetic field or the radio frequency.
equivalent in hertz per second, using the following equation:
3.1.1 rapid scan Fourier transform NMR; correlation spec-
Dn g DH
troscopy —a form of sequential excitation NMR in which the
5 · (4)
Dt 2p Dt
response of a spin system to a rapid passage excitation is
obtained and is converted to a slow-passage spectrum by 4.1.4 modulation sidebands—bands introduced into the
mathematical correlation with a reference line, or by suitable NMR spectrum by, for example, modulation of the resonance
mathematical procedures including Fourier transformations. signals. This may be accomplished by modulation of the static
E386
meanings. Since the use of this term may be ambiguous, it is to be
magneticfield,orbyeitheramplitudemodulationorfrequency
discouraged.
modulation of the basic radio frequency.
4.1.5 NMRspectralresolution—thewidthofasinglelinein
4.2.12 detection method—a specification of the method of
the spectrum which is known to be sharp, such as, TMS or
detection.
benzene( H).Thisdefinitionincludessamplefactorsaswellas
4.2.12.1 single-phase detection—a method of operation in
instrumental factors.
whichasinglephase-sensitivedetectorisusedtoextractsignal
4.1.6 NMRintegral(analog)—aquantitativemeasureofthe
information from a FID.
relative intensities of NMR signals, defined by the areas of the
4.2.12.2 quadrature detection—a method of operation in
spectral lines and usually displayed as a step function in which
whichdualphase-sensitivedetectionisusedtoextractapairof
the heights of the steps are proportional to the areas (intensi-
FID’s which differ in phase by 90°.
ties) of the resonances.
4.2.13 spectral width—the frequency range represented
4.2 Definitions Applying to Multifrequency Excitation
without foldover. (Spectral width is equal to one half the data
(Pulse) NMR:
acquisition rate in the case of single-phase detection; but is
4.2.1 pulse (v)—to apply for a specified period of time a
equal to the full data acquisition rate if quadrature detection is
perturbation (for example, a radio frequency field) whose
used.)
amplitude envelope is nominally rectangular.
4.2.14 foldover; foldback—the appearance of spurious lines
4.2.2 pulse (n)—a perturbation applied as described above.
in the spectrum arising from either (a) limitations in data
4.2.3 pulse width—the duration of a pulse.
acquisition rate or (b) the inability of the spectrometer detector
4.2.4 pulse flip angle—the angle (in degrees or radians)
to distinguish frequencies above the carrier frequency from
through which the magnetization is rotated by a pulse (such as
those below it.
a 90-deg pulse or p/2 pulse).
NOTE 11—These two meanings of foldover are in common use. Type
4.2.5 pulse amplitude—the radio frequency field, H,in
(a) is often termed “aliasing.” Type (b) foldover is obviated by the use of
tesla.
quadrature detection.
NOTE 6—This may be specified indirectly, as described in 8.3.2.
4.2.15 data acquisition time—the period of time during
4.2.6 pulse phase—the phase of the radio frequency field as
whichdataareacquiredanddigitized;equalnumericallytothe
measured relative to chosen axes in the rotating coordinate
product of the dwell time and the number of data points
system.
acquired.
4.2.16 computer-limited spectral resolution—the spectral
NOTE 7—The phase may be designated by a subscript, such as, 90° or
x
(p/2) .
width divided by the number of data points.
x
Note—This will be a measure of the observed line width
4.2.7 free induction decay (FID)—the time response signal
only when it is much greater than the spectral resolution
following application of an r-f pulse.
defined in 4.1.5.
4.2.8 homogeneity spoiling pulse; homo-spoil pulse; inho-
4.2.17 pulse sequence—a set of defined pulses and time
mogenizing pulse—a deliberately introduced temporary dete-
spacings between these pulses.
rioration of the homogeneity of the magnetic field H.
4.2.9 filter bandwidth; filter passband— the frequency
NOTE 12—There may be more than one way of expressing a sequence,
range, in hertz, transmitted with less than 3 dB (50%)
for example, a series (90°, t) may be one sequence of n pulses or n
n
attenuation in power by a low-pass filter. sequences each of the form (90°,t ).
NOTE 8—On some commercial instruments, filter bandwidth is defined
4.2.18 pulse interval—the time between two pulses of a
in a slightly different manner.
sequence.
NOTE 9—Other parameters, such as rate of roll-off, width of passband,
4.2.19 waiting time—the time between the end of data
orwidthandrejectionofcenterfrequencyincaseofanotchfilter,maybe
acquisition after the last pulse of a sequence and the initiation
required to define filter characteristics adequately.
of a new sequence.
4.2.10 data acquisition rate; s
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