ASTM E386-90(2004)
(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
ABSTRACT
This practice elaborates on the different types, definition of basic operational terms, conventions, referencing procedures and substances, and terms and recommended means for signal-to-noise ratio determination and data presentation in the area of high-resolution nuclear magnetic resonance (NMR) spectroscopy. Some of the basic definitions apply to wide-line NMR or to NMR of metals, but this practice is generally not intended to cover these latter areas of NMR. Also, this version does not include definitions pertaining to double resonance, nor to rotating frame experiments.
SCOPE
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(Reapproved2004)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.4.1 The foregoing quantities are approximately connected
by the following relation:
1.1 This standard contains definitions of basic terms, con-
ventions, and recommended practices for data presentation in g
n 5 H (1)
o o
the area of high-resolution NMR spectroscopy. Some of the 2p
basicdefinitionsapplytowide-lineNMRortoNMRofmetals,
where g=the magnetogyric ratio, a constant for a given
but in general it is not intended to cover these latter areas of
nuclide (Note 2).The amplitude of the magnetic component of
NMRinthisstandard.Thisversiondoesnotincludedefinitions
the radio-frequency field is called H . Recommended units are
pertaining to double resonance nor to rotating frame experi-
millitesla and microtesla.
ments.
NOTE 2—This quantity is normally referred to as B by physicists. The
usage of H to refer to magnetic field strength in chemical applications is
2. Terminology Nomenclature and Basic Definitions
sowidelyacceptedthatthereappearstobenopointinattemptingtoreach
2.1 nuclear magnetic resonance (NMR) spectroscopy—that
a totally consistent nomenclature now.
form of spectroscopy concerned with radio-frequency-induced
NOTE 3—This expression is correct only for bare nuclei and will be
transitions between magnetic energy levels of atomic nuclei. only approximately true for nuclei in chemical compounds, since the field
at the nucleus is in general different from the static magnetic field. The
2.2 NMR apparatus; NMR equipment—an instrument com-
discrepancy amounts to a few parts in 10 for protons, but may be of
prising a magnet, radio-frequency oscillator, sample holder,
−3
magnitude 1 310 for the heaviest nuclei.
and a detector that is capable of producing an electrical signal
2.5 NMR absorption line—a single transition or a set of
suitable for display on a recorder or an oscilloscope, or which
is suitable for input to a computer. degenerate transitions is referred to as a line.
2.3 high-resolution NMR spectrometer— an NMR appara- 2.6 NMR absorption band; NMR band— a region of the
tusthatiscapableofproducing,foragivenisotope,linewidths spectruminwhichadetectablesignalexistsandpassesthrough
that are less than the majority of the chemical shifts and one or more maxima.
coupling constants for that isotope. 2.7 reference compound (NMR)—a selected material to
whose signal the spectrum of a sample may be referred for the
NOTE 1—By this definition, a given spectrometer may be classed as a
measurement of chemical shift (see 2.9).
high-resolutioninstrumentforisotopeswithlargechemicalshifts,butmay
2.7.1 internalreference(NMR)—areferencecompoundthat
not be classed as a high-resolution instrument for isotopes with smaller
chemical shifts. is dissolved in the same phase as the sample.
2.7.2 externalreference(NMR)—areferencecompoundthat
2.4 basic NMR frequency, n —the frequency, measured in
o
is not dissolved in the same phase as the sample.
hertz (Hz), of the oscillating magnetic field applied to induce
2.8 lock signal—the NMR signal used to control the field-
transitions between nuclear magnetic energy levels. The static
frequency ratio of the spectrometer. It may or may not be the
magnetic field at which the system operates is called H (Note
o
same as the reference signal.
1)anditsrecommendedunitofmeasurementisthetesla(T)(1
4 2.8.1 internal lock—a lock signal which is obtained from a
T=10 gauss).
material that is physically within the confines of the sample
tube, whether or not the material is in the same phase as the
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
sample (an annulus for the purpose of this definition is
Spectroscopy and Chromatography and is the direct responsibility of Subcommittee
considered to be within the sample tube).
E13.15 on Analytical Data.
Current edition approved Nov. 1, 2004. Published January 2005. Originally
approved in 1969. Last previous edition approved in 1999 as E386–90(1999).
DOI: 10.1520/E0386-90R04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E386–90 (2004)
2.8.2 external lock—a lock signal which is obtained from a different field/frequency ratio at resonance are successively
material that is physically outside the sample tube. The excited by sweeping the magnetic field or the radio frequency.
material supplying the lock signal is usually built into the 3.1.1 rapid scan Fourier transform NMR; correlation spec-
probe. troscopy —a form of sequential excitation NMR in which the
response of a spin system to a rapid passage excitation is
NOTE 4—An external lock, if also used as a reference, is necessarily an
obtained and is converted to a slow-passage spectrum by
external reference.An internal lock, if used as a reference, may be either
mathematical correlation with a reference line, or by suitable
an internal or an external reference, depending upon the experimental
configuration. mathematical procedures including Fourier transformations.
3.2 broad-band excitation NMR—a form of high-resolution
2.8.3 homonuclear lock—a lock signal which is obtained
NMRinwhichnucleiofthesameisotopebutpossiblydifferent
from the same nuclide that is being observed.
chemical shifts are excited simultaneously rather than sequen-
2.8.4 heteronuclear lock—a lock signal which is obtained
tially.
from a different nuclide than the one being observed.
3.2.1 pulse Fourier transform NMR—a form of broad-band
2.9 chemical shift, d—the defining equation for d is the
excitation NMR in which the sample is irradiated with one or
following:
more pulse sequences of radio-frequency power spaced at
Dn
uniform time intervals, and the averaged free induction decay
d5 310 (2)
n
R
following the pulse sequences is converted to a frequency
domain spectrum by a Fourier transformation.
where n is the frequency with which the reference sub-
R
stance is in resonance at the magnetic field used in the 3.2.1.1 pulse Fourier difference NMR—a form of pulse
Fourier transform NMR in which the difference frequencies
experiment and Dn is the frequency of the subject line minus
thefrequencyofthereferencelineatconstantfield.Thesignof between the sample signals and a strong reference signal are
extracted from the sample response prior to Fourier transfor-
Dn is to be chosen such that shifts to the high frequency side
of the reference shall be positive. mation.
3.2.1.2 synthesized excitation Fourier NMR— a form of
2.9.1 If the experiment is done at constant frequency (field
sweep) the defining equation becomes pulse Fourier NMR in which a desired frequency spectrum for
the exciting signal is Fourier synthesized and used to modulate
Dn Dn
d5 3 1 2 310 (3)
S D
the exciting radio frequency.
n n
R R
3.2.2 stochastic excitation NMR—a form of broad band
2.9.2 In case the experiment is done by observation of a
excitation NMR in which the nuclei are excited by a range of
modulation sideband, the audio upper or lower sideband
frequencies produced by random or pseudorandom noise
frequency must be added to or subtracted from the radio
modulation of the carrier, and the frequency spectrum is
frequency.
obtained by Fourier transforming the correlation function
2.10 spinning sidebands—bands, paired symmetrically
between the input and output signals.
about a principal band, arising from spinning of the sample in
3.2.3 Hadamard transform NMR—a form of broad band
a field (dc or rf) that is inhomogeneous at the sample position.
excitation NMR in which the phase of the excitation signal is
Spinning sidebands occur at frequencies separated from the
switched according to a binary pseudorandom sequence, and
principal band by integral multiples of the spinning rate. The
the correlation of the input and output signals by a Hadamard
intensities of bands which are equally spaced above and below
matrix yields an interference pattern which is then Fourier-
the principal band are not necessarily equal.
transformed.
2.11 satellites—additional bands spaced nearly symmetri-
cally about a principal band, arising from the presence of an
4. Operational Definitions
isotope of non-zero spin which is coupled to the nucleus being
4.1 Definitions Applying to Sequential Excitation (CW)
observed. An isotope shift is normally observed which causes
NMR:
the center of the satellites to be chemically shifted from the
4.1.1 field sweeping (NMR)—systematically varying the
principal band. The intensity of the satellite signal increases
magnetic field strength, at constant applied radio-frequency
with the abundance of the isotope responsible.
field, to bring NMR transitions of different energies succes-
2.12 NMR line width—the full width, expressed in hertz
sively into resonance, thereby making available an NMR
(Hz), of an observed NMR line at one-half maximum height
spectrum consisting of signal intensity versus magnetic field
(FWHM).
strength.
2.13 spin-spin coupling constant (NMR), J—a measure,
4.1.2 frequency sweeping (NMR)—systematically varying
expressed in hertz (Hz), of the indirect spin-spin interaction of
the frequency of the applied radio frequency field (or of a
different magnetic nuclei in a given molecule.
modulation sideband, see 4.1.4), at constant magnetic field
n
strength, to bring NMR transitions of different energies suc-
NOTE 5—The notation J is used to represent a coupling over n
AB
bondsbetweennucleiAandB.Whenitisnecessarytospecifyaparticular cessively into resonance, thereby making available an NMR
3 15
isotope, a modified notation may be used, such as, J ( NH).
spectrum consisting of signal intensity versus applied radio
frequency.
3. Types of High-Resolution NMR Spectroscopy
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
E386–90 (2004)
rate in microtesla per second is customarily converted to the 4.2.11.1 aperture time—the time interval during which the
equivalent in hertz per second, using the following equation: sample-and-hold device is receptive to signal information. In
most applications of pulse NMR, the aperture time is a small
Dn g DH
5 · (4)
fraction of the dwell time.
Dt 2p Dt
4.1.4 modulation sidebands—bands introduced into the NOTE 10—Sampling Time has been used with both of the above
meanings. Since the use of this term may be ambiguous, it is to be
NMR spectrum by, for example, modulation of the resonance
discouraged.
signals. This may be accomplished by modulation of the static
magneticfield,orbyeitheramplitudemodulationorfrequency
4.2.12 detection method—a specification of the method of
modulation of the basic radio frequency.
detection.
4.1.5 NMRspectralresolution—thewidthofasinglelinein
4.2.12.1 single-phase detection—a method of operation in
the spectrum which is known to be sharp, such as, TMS or
whichasinglephase-sensitivedetectorisusedtoextractsignal
benzene( H).Thisdefinitionincludessamplefactorsaswellas
information from a FID.
instrumental factors.
4.2.12.2 quadrature detection—a method of operation in
4.1.6 NMRintegral(analog)—aquantitativemeasureofthe
whichdualphase-sensitivedetectionisusedtoextractapairof
relative intensities of NMR signals, defined by the areas of the
FID’s which differ in phase by 90°.
spectral lines and usually displayed as a step function in which
4.2.13 spectral width—the frequency range represented
the heights of the steps are proportional to the areas (intensi-
without foldover. (Spectral width is equal to one half the data
ties) of the resonances.
acquisition rate in the case of single-phase detection; but is
4.2 Definitions Applying to Multifrequency Excitation
equal to the full data acquisition rate if quadrature detection is
(Pulse) NMR:
used.)
4.2.1 pulse (v)—to apply for a specified period of time a
4.2.14 foldover; foldback—the appearance of spurious lines
perturbation (for example, a radio frequency field) whose
in the spectrum arising from either (a) limitations in data
amplitude envelope is nominally rectangular.
acquisition rate or (b) the inability of the spectrometer detector
4.2.2 pulse (n)—a perturbation applied as described above.
to distinguish frequencies above the carrier frequency from
4.2.3 pulse width—the duration of a pulse.
those below it.
4.2.4 pulse flip angle—the angle (in degrees or radians)
through which the magnetization is rotated by a pulse (such as
NOTE 11—These two meanings of foldover are in common use. Type
a 90-deg pulse or p/2 pulse). (a) is often termed “aliasing.” Type (b) foldover is obviated by the use of
quadrature detection.
4.2.5 pulse amplitude—the radio frequency field, H,in
tesla.
4.2.15 data acquisition time—the period of time during
NOTE 6—This may be specified indirectly, as described in 8.3.2. whichdataareacquiredanddigitized;equalnumericallytothe
product of the dwell time and the number of data points
4.2.6 pulse phase—the phase of the radio frequency field as
acquired.
measured relative to chosen axes in the rotating coordinate
4.2.16 computer-limited spectral resolution—the spectral
system.
width divided by the number of data points.
NOTE 7—The phase may be designated by a subscript, such as, 90° or
x
Note—This will be a measure of the observed line width
(p/2) .
x
only when it is much greater than the spectral resolution
4.2.7 free induction decay (FID)—the time response signal
defined in 4.1.5.
following application of an r-f pulse.
4.2.17 pulse sequence—a set of defined pulses and time
4.2.8 homogeneity spoiling pulse; homo-spoil pulse; inho-
spacings between these pulses.
mogenizing pulse—a deliberately introduced temporary dete-
rioration of the homogeneity of the magnetic field H. NOTE 12—There may be more than one way of expressing a sequence,
for example, a series (90°, t) may be one sequence of n pulses or n
4.2.9 filter bandwidth; filter passband— the frequency n
sequences each of the form (90°,t ).
range, in hertz, transmitted with less than 3 dB (50%)
attenuation in power by a low-pass filter.
4.2.18 pulse interval—the time between two pulses of a
sequence.
NOTE 8—On some commercial instruments, filter bandwidth is defined
in a slightly different manner. 4.2.19 waiting time—the time be
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