ASTM E131-10(2023)
(Terminology)Standard Terminology Relating to Molecular Spectroscopy
Standard Terminology Relating to Molecular Spectroscopy
SCOPE
1.1 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E131 − 10 (Reapproved 2023)
Standard Terminology Relating to
1, 2
Molecular Spectroscopy
This standard is issued under the fixed designation E131; 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 3. Terminology
1.1 The values stated in SI units are to be regarded as absorbance, A—the logarithm to the base 10 of the reciprocal
standard. No other units of measurement are included in this
of the transmittance, (T).
standard.
A 5 log ~1/T!52log T (1)
10 10
DISCUSSION—In practice the observed transmittance must be substi-
1.2 This international standard was developed in accor-
tuted for T.Absorbance expresses the excess absorption over that of a
dance with internationally recognized principles on standard-
specified reference or standard. It is implied that compensation has
ization established in the Decision on Principles for the
been effected for reflectance losses, solvent absorption losses, and
Development of International Standards, Guides and Recom-
refractive effects, if present, and that attenuation by scattering is small
mendations issued by the World Trade Organization Technical
comparedwithattenuationbyabsorption.Apparentdeviationsfromthe
Barriers to Trade (TBT) Committee. absorption laws (see absorptivity) are due to inability to measure
exactly the true transmittance or to know the exact concentration of an
absorbing substance.
2. Referenced Documents
absorption band—a region of the absorption spectrum in
2.1 ASTM Standards:
which the absorbance passes through a maximum.
E135Terminology Relating to Analytical Chemistry for
Metals, Ores, and Related Materials
absorption coefficient, α—a measure of absorption of radiant
E168Practices for General Techniques of Infrared Quanti-
energy from an incident beam as it traverses an absorbing
−αb
tative Analysis
medium according to Bouguer’s law, P/P = e .
o
E204Practices for Identification of Material by Infrared
DISCUSSION—In IRS, α is a measure of the rate of absorption of
Absorption Spectroscopy, Using the ASTM Coded Band
energy from the evanescent wave.
and Chemical Classification Index (Withdrawn 2014)
absorption parameter, a—the relative reflection loss per
E284Terminology of Appearance
reflection that results from the absorption of radiant energy
E386Practice for Data Presentation Relating to High-
at a reflecting surface: a=1− R, and R=the reflected
Resolution Nuclear Magnetic Resonance (NMR) Spec-
fraction of incident radiant power.
troscopy (Withdrawn 2015)
E456Terminology Relating to Quality and Statistics
absorption spectrum—a plot, or other representation, of
absorbance, or any function of absorbance, against
2.2 Other Document:
wavelength, or any function of wavelength.
ISOGuide30–1981(E)Terms and definitions used in con-
nections with reference materials
absorptivity, a—the absorbance divided by the product of the
concentration of the substance and the sample pathlength,
a = A ⁄bc. The units of b and c shall be specified.
This terminology is under the jurisdiction of ASTM Committee E13 on DISCUSSION—1—The recommended unit for b is the centimetre. The
Molecular Spectroscopy and Separation Science and is the direct responsibility of
recommended unit for c is kilogram per cubic metre. Equivalent units
3 3
Subcommittee E13.94 on Terminology.
are g/dm , g/L, or mg/cm .
Current edition approved Jan. 1, 2023. Published January 2023. Originally
approved in 1957. Last previous edition approved in 2015 as E131– 10 (2015).
DISCUSSION—2—The equivalent IUPAC term is “specific absorption
DOI: 10.1520/E0131-10R23.
coefficient.”
Forotherdefinitionsrelatingtonuclearmagneticresonance,seePracticeE386.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
absorptivity, molar, ε—the product of the absorptivity, a, and
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
the molecular weight of the substance.
Standards volume information, refer to the standard’s Document Summary page on
DISCUSSION—The equivalent IUPAC term is “molar absorption coef-
the ASTM website.
4 ficient.”
The last approved version of this historical standard is referenced on
www.astm.org.
acceptance angle, n—for an optical fiber,themaximumangle,
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. measuredfromthelongitudinalaxisorcenterlineofthefiber
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E131 − 10 (2023)
to an incident ray, within which the ray will be accepted for aperture of an IRE, A'—that portion of the IRE surface that
transmission along the fiber by total internal reflection. can be utilized to conduct light into the IRE at the desired
DISCUSSION—If the incidence angle exceeds the acceptance angle,
angle of incidence.
optical power in the incident ray will be coupled into leaky modes or
rays, or lost by scattering, diffusion, or absorption in the cladding. For apodization—modification of the ILS function by multiplying
a cladded step-index fiber in the air, the sine of the acceptance angle is
the interferogram by a weighting function the magnitude of
givenbythesquarerootofthedifferenceofthesquaresoftherefractive
which varies with retardation.
indexes of the fiber core and the cladding, that is, by the relation as
DISCUSSION—This term should strictly be used with reference to a
follows:
weighting function whose magnitude is greatest at the centerburst and
decreases with retardation.
2 2
sin A 5 = n 2 n (2)
1 2
where A is the acceptance angle and n and n are the refractive in-
1 2
attenuated total reflection (ATR)—reflection that occurs
dexes of the core and cladding, respectively. If the refractive index is a
when an absorbing coupling mechanism acts in the process
function of distance from the center of the core, as in the case of
of total internal reflection to make the reflectance less than
graded index fibers, then the acceptance angle depends on the distance
unity.
from the core center. The acceptance angle is maximum at the center,
and zero at the core-cladding boundary. At any radius, r, the sine of the DISCUSSION—In this process, if an absorbing sample is placed in
acceptance angle of a graded index fiber is defined in compliance with contact with the reflecting surface, the reflectance for total internal
that of a step-index fiber as follows: reflection will be attenuated to some value between zero and unity (O
2 2
sin A 5 =n 2 n (3)
r 1 2 power can take place.
where A is the acceptance angle at a point on the entrance face at a
r
distance, r, from the center, n is the refractive index of the core at a attenuation index, κ—a measure of the absorption of radiant
r
radius, r, and n is the refractive index of the cladding. In air, sin A
energy by an absorbing material. κ is related to the absorp-
and sin A are the numerical apertures. Unless otherwise stated, accep-
r
tion coefficient by: nκ= αc /4πν, where c =the speed of
o o
tance angles and numerical apertures for fiber optics are those for the
light in vacuo, ν=the frequency of radiant energy, and
center of the endface of the fiber, that is, where the refractive index,
n=the refractive index of the absorbing medium.
and hence the numerical aperture, is the highest.
background—apparent absorption caused by anything other
accuracy—the closeness of agreement between an observed
than the substance for which the analysis is being made.
value and an accepted reference value (see Terminology
E456).
baseline—any line drawn on an absorption spectrum to estab-
DISCUSSION—The term accuracy, when applied to a set of observed
lish a reference point representing a function of the radiant
values, will be a combination of a random component and a common
power incident on a sample at a given wavelength.
systematic error or bias component. Since in routine use, random
components and bias components cannot be completely separated, the
basic NMR frequency, ν —the frequency, measured in hertz
reported “accuracy” must be interpreted as a combination of these two
(Hz), of the oscillating magnetic field applied to induce
components.
transitions between nuclear magnetic energy levels.
active fiber optic chemical sensor, n—a fiber optic chemical
sensor in which a transduction mechanism other than the
bathochromic shift, n—change of a spectral band to longer
intrinsic spectroscopic properties of the analyte is used to wavelength (lower frequency) because of structural modifi-
modulate the optical signal.
cations or environmental influence; also known as “red
DISCUSSION—Examples include a pH sensor composed of a chemical
shift.”
indicator substance whose color changes with pH, and an oxygen
sensor coupled to an optical fiber bearing a chemical indicator whose beamsplitter—a semireflecting device used to create, and
fluorescence intensity depends on oxygen concentration.
often to recombine, spatially separate beams.
DISCUSSION—Beamsplitters are often made by depositing a film of a
aliasing—the appearance of features at wavenumbers other
high refractive index material onto a flat transmitting substrate with an
than their true value caused by using a sampling frequency
identical compensator plate being held on the other side of the film.
less than twice the highest modulation frequency in the
interferogram; also known as “folding.”
beamsplitter efficiency—the product 4RT, where R is the
reflectance and T is the transmittance of the beamsplitter.
analytical curve—the graphical representation of a relation
between some function of radiant power and the concentra-
Beer’s law—the absorbance of a homogeneous sample con-
tion or mass of the substance emitting or absorbing it.
taininganabsorbingsubstanceisdirectlyproportionaltothe
concentration of the absorbing substance (see also absorp-
analytical wavelength—any wavelength at which an absor-
tivity)
bance measurement is made for the purpose of the determi-
nation of a constituent of a sample.
bias—a systematic error that contributes to the difference
angle of incidence, θ—the angle between an incident radiant
between a population mean of the measurements or test
beam and a perpendicular to the interface between two
results and an accepted or reference value (see Terminology
media.
E456).
DISCUSSION—Bias is determined by the following equation:
anti-Stokes line (band)—a Raman line (band) that has a
frequency higher than that of the incident monochromatic
n
bias 5 e¯ 5 e (4)
i
(i51
beam. n
E131 − 10 (2023)
where: with a core of higher refractive index material used to
achieve total internal reflection.
n = the number of observations for which the accuracy is
DISCUSSION—The cladding confines electromagnetic waves to the
determined,
core, provides some protection to the core, and also transmits evanes-
e = the difference between a measured value of a property
i
cent waves that usually are bound to waves in the core.
and its accepted reference value, and
e¯ = the mean value of all the e.
concentration, c—the quantity of the substance contained in a
I
unit quantity of sample.
Bouguer’s law—the absorbance of a homogeneous sample is
DISCUSSION—For solution work, the recommended unit of concen-
directly proportional to the thickness of the sample in the
tration is grams of solute per litre of solution.
optical path.
core, n—of an optical fiber, the center region of an optical
DISCUSSION—Bouguer’s law is sometimes also known as Lambert’s
waveguide through which radiant energy is transmitted.
law.
DISCUSSION—In a dielectric waveguide such as an optical fiber, the
boxcar truncation—identical effective weighting of all points
refractive index of the core must be higher than that of the cladding.
inthemeasuredinterferogrampriortotheFouriertransform; Most of the radiant energy is confined to the core.
allpointsoutsideoftherangeofthemeasuredinterferogram
correlation coefficient (r)—a measure of the strength of the
take a value of zero.
linear relationship between X and Y, calculated by the
equation:
buffer—in fiber optics, see fiber optic buffer.
n
X Y
~ !
(i51 i i
bulk reflection—reflection in which radiant energy is returned
r 5 (7)
xy n 1/2 n 1/2
2 2
exclusively from within the specimen. X Y
~ ! ~ !
(i51 i (i51 i
DISCUSSION—Bulk reflection may be diffuse or specular.
where:
centerburst—the region of greatest amplitude in an interfero-
n = the number of observations in X and Y.
gram.
DISCUSSION—X and Y areanytwomeancorrectedvariables.Forthe
i i
DISCUSSION—For unchirped or only slightly chirped interferograms,
simple linear regression only,
this region includes the “zero path difference point” and the “zero
2 1/2
retardation point.”
r 5 R 5 signof b R (8)
~ !~ !
xy 1
certified reference material, n—a reference material, the
where:
composition or properties of which are certified by a
R = the coefficient of multiple determination.
recognized standardizing agency or group.
critical angle, θ —theanglewhosesineisequaltotherelative
DISCUSSION—Acertified reference material produced by the National c
refractive index for light striking an interface from the
Institute of Standards and Technology (NIST) is designated a Standard
−1
Reference Material (SRM).
greater to the lesser refractive medium: θ =sin n , where
c 21
n =the ratio of the refractive indices of the two media.
chemical shift (NMR), δ—the defining equation for δ is the
DISCUSSION—Total reflection occurs when light is reflected in the
following:
more refractive of two media from the interface between them at any
angle of incidence exceeding the critical angle.
∆ν
δ 5 310 (5)
ν
R
depth of penetration, d —in internal reflection spectroscopy,
p
the distance into the less refractive medium at which the
where ν is the frequency with which the reference sub-
R
−1
amplitude of the evanescent wave is e (that is, 36.8%) of
stance is in resonance at the magnetic field used in the ex-
its value at the surface:
periment and ∆ν is the frequency difference between the ref-
erence substance and the substance whose chemical shift is
λ
d 5 (9)
p 2 2 1/2
being determined, at constant field. The sign of ∆ν is to be 2π sin θ 2 η
~ !
chosen such that shifts to the high frequency side of the ref-
where: n =n /n = refractive index of sample divided by
21 2 1
erence shall be positi
...
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