1、Designation: E 386 90 (Reapproved 2004)Standard Practice forData Presentation Relating to High-Resolution NuclearMagnetic Resonance (NMR) Spectroscopy1This standard is issued under the fixed designation E 386; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard contains definitions of basic terms, con-ventions, and recommend
3、ed practices for data presentation inthe area of high-resolution NMR spectroscopy. Some of thebasic definitions apply to wide-line NMR or to NMR of metals,but in general it is not intended to cover these latter areas ofNMR in this standard. This version does not include definitionspertaining to doub
4、le resonance nor to rotating frame experi-ments.2. Terminology Nomenclature and Basic Definitions2.1 nuclear magnetic resonance (NMR) spectroscopythatform of spectroscopy concerned with radio-frequency-inducedtransitions between magnetic energy levels of atomic nuclei.2.2 NMR apparatus; NMR equipmen
5、tan instrument com-prising a magnet, radio-frequency oscillator, sample holder,and a detector that is capable of producing an electrical signalsuitable for display on a recorder or an oscilloscope, or whichis suitable for input to a computer.2.3 high-resolution NMR spectrometer an NMR appara-tus tha
6、t is capable of producing, for a given isotope, line widthsthat are less than the majority of the chemical shifts andcoupling constants for that isotope.NOTE 1By this definition, a given spectrometer may be classed as ahigh-resolution instrument for isotopes with large chemical shifts, but maynot be
7、 classed as a high-resolution instrument for isotopes with smallerchemical shifts.2.4 basic NMR frequency, nothe frequency, measured inhertz (Hz), of the oscillating magnetic field applied to inducetransitions between nuclear magnetic energy levels. The staticmagnetic field at which the system opera
8、tes is called Ho(Note1) and its recommended unit of measurement is the tesla (T) (1T=104gauss).2.4.1 The foregoing quantities are approximately connectedby the following relation:no5g2pHo(1)where g = the magnetogyric ratio, a constant for a givennuclide (Note 2). The amplitude of the magnetic compon
9、ent ofthe radio-frequency field is called H1. Recommended units aremillitesla and microtesla.NOTE 2This quantity is normally referred to as B by physicists. Theusage of H to refer to magnetic field strength in chemical applications isso widely accepted that there appears to be no point in attempting
10、 to reacha totally consistent nomenclature now.NOTE 3This expression is correct only for bare nuclei and will beonly approximately true for nuclei in chemical compounds, since the fieldat the nucleus is in general different from the static magnetic field. Thediscrepancy amounts to a few parts in 106
11、for protons, but may be ofmagnitude 1 3 103for the heaviest nuclei.2.5 NMR absorption linea single transition or a set ofdegenerate transitions is referred to as a line.2.6 NMR absorption band; NMR band a region of thespectrum in which a detectable signal exists and passes throughone or more maxima.
12、2.7 reference compound (NMR)a selected material towhose signal the spectrum of a sample may be referred for themeasurement of chemical shift (see 2.9).2.7.1 internal reference (NMR)a reference compound thatis dissolved in the same phase as the sample.2.7.2 external reference (NMR)a reference compoun
13、d thatis not dissolved in the same phase as the sample.2.8 lock signalthe NMR signal used to control the field-frequency ratio of the spectrometer. It may or may not be thesame as the reference signal.2.8.1 internal locka lock signal which is obtained from amaterial that is physically within the con
14、fines of the sampletube, whether or not the material is in the same phase as thesample (an annulus for the purpose of this definition isconsidered to be within the sample tube).2.8.2 external locka lock signal which is obtained from amaterial that is physically outside the sample tube. Thematerial s
15、upplying the lock signal is usually built into theprobe.NOTE 4An external lock, if also used as a reference, is necessarily anexternal reference. An internal lock, if used as a reference, may be eitheran internal or an external reference, depending upon the experimentalconfiguration.2.8.3 homonuclea
16、r locka lock signal which is obtainedfrom the same nuclide that is being observed.1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Chromatography and is the direct responsibility of SubcommitteeE13.15 on Analytical Data.Current edition approved Nov. 1, 2004
17、. Published January 2005. Originallyapproved in 1969. Last previous edition approved in 1999 as E 386 90 (1999).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.8.4 heteronuclear locka lock signal which is obtainedfrom a different n
18、uclide than the one being observed.2.9 chemical shift, dthe defining equation for d is thefollowing:d5DnnR3 106(2)where nRis the frequency with which the reference sub-stance is in resonance at the magnetic field used in theexperiment and Dn is the frequency of the subject line minusthe frequency of
19、 the reference line at constant field. The sign ofDn is to be chosen such that shifts to the high frequency sideof the reference shall be positive.2.9.1 If the experiment is done at constant frequency (fieldsweep) the defining equation becomesd5DnnR3S1 2DnnRD3 10 (3)2.9.2 In case the experiment is d
20、one by observation of amodulation sideband, the audio upper or lower sidebandfrequency must be added to or subtracted from the radiofrequency.2.10 spinning sidebandsbands, paired symmetricallyabout a principal band, arising from spinning of the sample ina field (dc or rf) that is inhomogeneous at th
21、e sample position.Spinning sidebands occur at frequencies separated from theprincipal band by integral multiples of the spinning rate. Theintensities of bands which are equally spaced above and belowthe principal band are not necessarily equal.2.11 satellitesadditional bands spaced nearly symmetri-c
22、ally about a principal band, arising from the presence of anisotope of non-zero spin which is coupled to the nucleus beingobserved. An isotope shift is normally observed which causesthe center of the satellites to be chemically shifted from theprincipal band. The intensity of the satellite signal in
23、creaseswith the abundance of the isotope responsible.2.12 NMR line widththe full width, expressed in hertz(Hz), of an observed NMR line at one-half maximum height(FWHM).2.13 spin-spin coupling constant (NMR), Ja measure,expressed in hertz (Hz), of the indirect spin-spin interaction ofdifferent magne
24、tic nuclei in a given molecule.NOTE 5The notationnJABis used to represent a coupling over nbonds between nuclei A and B. When it is necessary to specify a particularisotope, a modified notation may be used, such as,3J (15NH).3. Types of High-Resolution NMR Spectroscopy3.1 sequential excitation NMR;
25、continuous wave (CW)NMRa form of high-resolution NMR in which nuclei ofdifferent field/frequency ratio at resonance are successivelyexcited by sweeping the magnetic field or the radio frequency.3.1.1 rapid scan Fourier transform NMR; correlation spec-troscopy a form of sequential excitation NMR in w
26、hich theresponse of a spin system to a rapid passage excitation isobtained and is converted to a slow-passage spectrum bymathematical correlation with a reference line, or by suitablemathematical procedures including Fourier transformations.3.2 broad-band excitation NMRa form of high-resolutionNMR i
27、n which nuclei of the same isotope but possibly differentchemical shifts are excited simultaneously rather than sequen-tially.3.2.1 pulse Fourier transform NMRa form of broad-bandexcitation NMR in which the sample is irradiated with one ormore pulse sequences of radio-frequency power spaced atunifor
28、m time intervals, and the averaged free induction decayfollowing the pulse sequences is converted to a frequencydomain spectrum by a Fourier transformation.3.2.1.1 pulse Fourier difference NMRa form of pulseFourier transform NMR in which the difference frequenciesbetween the sample signals and a str
29、ong reference signal areextracted from the sample response prior to Fourier transfor-mation.3.2.1.2 synthesized excitation Fourier NMR a form ofpulse Fourier NMR in which a desired frequency spectrum forthe exciting signal is Fourier synthesized and used to modulatethe exciting radio frequency.3.2.2
30、 stochastic excitation NMRa form of broad bandexcitation NMR in which the nuclei are excited by a range offrequencies produced by random or pseudorandom noisemodulation of the carrier, and the frequency spectrum isobtained by Fourier transforming the correlation functionbetween the input and output
31、signals.3.2.3 Hadamard transform NMRa form of broad bandexcitation NMR in which the phase of the excitation signal isswitched according to a binary pseudorandom sequence, andthe correlation of the input and output signals by a Hadamardmatrix yields an interference pattern which is then Fourier-trans
32、formed.4. Operational Definitions4.1 Definitions Applying to Sequential Excitation (CW)NMR:4.1.1 field sweeping (NMR)systematically varying themagnetic field strength, at constant applied radio-frequencyfield, to bring NMR transitions of different energies succes-sively into resonance, thereby makin
33、g available an NMRspectrum consisting of signal intensity versus magnetic fieldstrength.4.1.2 frequency sweeping (NMR)systematically varyingthe frequency of the applied radio frequency field (or of amodulation sideband, see 4.1.4), at constant magnetic fieldstrength, to bring NMR transitions of diff
34、erent energies suc-cessively into resonance, thereby making available an NMRspectrum consisting of signal intensity versus applied radiofrequency.4.1.3 sweep ratethe rate, in hertz (Hz) per second atwhich the applied radio frequency is varied to produce anNMR spectrum. In the case of field sweep, th
35、e actual sweeprate in microtesla per second is customarily converted to theequivalent in hertz per second, using the following equation:DnDt5g2pDHDt(4)4.1.4 modulation sidebandsbands introduced into theNMR spectrum by, for example, modulation of the resonancesignals. This may be accomplished by modu
36、lation of the staticE 386 90 (2004)2magnetic field, or by either amplitude modulation or frequencymodulation of the basic radio frequency.4.1.5 NMR spectral resolutionthe width of a single line inthe spectrum which is known to be sharp, such as, TMS orbenzene (1H). This definition includes sample fa
37、ctors as well asinstrumental factors.4.1.6 NMR integral (analog)a quantitative measure of therelative intensities of NMR signals, defined by the areas of thespectral lines and usually displayed as a step function in whichthe heights of the steps are proportional to the areas (intensi-ties) of the re
38、sonances.4.2 Definitions Applying to Multifrequency Excitation(Pulse) NMR:4.2.1 pulse (v)to apply for a specified period of time aperturbation (for example, a radio frequency field) whoseamplitude envelope is nominally rectangular.4.2.2 pulse (n)a perturbation applied as described above.4.2.3 pulse
39、widththe duration of a pulse.4.2.4 pulse flip anglethe angle (in degrees or radians)through which the magnetization is rotated by a pulse (such asa 90-deg pulse or p/2 pulse).4.2.5 pulse amplitudethe radio frequency field, H1,intesla.NOTE 6This may be specified indirectly, as described in 8.3.2.4.2.
40、6 pulse phasethe phase of the radio frequency field asmeasured relative to chosen axes in the rotating coordinatesystem.2NOTE 7The phase may be designated by a subscript, such as, 90xor(p/2)x.4.2.7 free induction decay (FID)the time response signalfollowing application of an r-f pulse.4.2.8 homogene
41、ity spoiling pulse; homo-spoil pulse; inho-mogenizing pulsea deliberately introduced temporary dete-rioration of the homogeneity of the magnetic field H.4.2.9 filter bandwidth; filter passband the frequencyrange, in hertz, transmitted with less than 3 dB (50 %)attenuation in power by a low-pass filt
42、er.NOTE 8On some commercial instruments, filter bandwidth is definedin a slightly different manner.NOTE 9Other parameters, such as rate of roll-off, width of passband,or width and rejection of center frequency in case of a notch filter, may berequired to define filter characteristics adequately.4.2.
43、10 data acquisition rate; sampling rate; digitizingratethe number of data points recorded per second.4.2.11 dwell timethe time between the beginning of sam-pling of one data point and the beginning of sampling of thenext successive point in the FID.4.2.11.1 aperture timethe time interval during whic
44、h thesample-and-hold device is receptive to signal information. Inmost applications of pulse NMR, the aperture time is a smallfraction of the dwell time.NOTE 10Sampling Time has been used with both of the abovemeanings. Since the use of this term may be ambiguous, it is to bediscouraged.4.2.12 detec
45、tion methoda specification of the method ofdetection.4.2.12.1 single-phase detectiona method of operation inwhich a single phase-sensitive detector is used to extract signalinformation from a FID.4.2.12.2 quadrature detectiona method of operation inwhich dual phase-sensitive detection is used to ext
46、ract a pair ofFIDs which differ in phase by 90.4.2.13 spectral widththe frequency range representedwithout foldover. (Spectral width is equal to one half the dataacquisition rate in the case of single-phase detection; but isequal to the full data acquisition rate if quadrature detection isused.)4.2.
47、14 foldover; foldbackthe appearance of spurious linesin the spectrum arising from either (a) limitations in dataacquisition rate or (b) the inability of the spectrometer detectorto distinguish frequencies above the carrier frequency fromthose below it.NOTE 11These two meanings of foldover are in com
48、mon use. Type(a) is often termed “aliasing.” Type (b) foldover is obviated by the use ofquadrature detection.4.2.15 data acquisition timethe period of time duringwhich data are acquired and digitized; equal numerically to theproduct of the dwell time and the number of data pointsacquired.4.2.16 comp
49、uter-limited spectral resolutionthe spectralwidth divided by the number of data points.NoteThis will be a measure of the observed line widthonly when it is much greater than the spectral resolutiondefined in 4.1.5.4.2.17 pulse sequencea set of defined pulses and timespacings between these pulses.NOTE 12There may be more than one way of expressing a sequence,for example, a series (90, t)nmay be one sequence of n pulses or nsequences each of the form (90,t ).4.2.18 pulse intervalthe time between two pulses of asequ
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