ASTM D2008-12(2018)
(Test Method)Standard Test Method for Ultraviolet Absorbance and Absorptivity of Petroleum Products
Standard Test Method for Ultraviolet Absorbance and Absorptivity of Petroleum Products
SIGNIFICANCE AND USE
5.1 The absorbance of liquids and the absorptivity of liquid and solids at specified wavelengths in the ultraviolet are useful in characterizing petroleum products.
SCOPE
1.1 This test method covers the measurement of the ultraviolet absorption of a variety of petroleum products. It covers the absorbance of liquids or the absorptivity of liquids and solids, or both, at wavelengths in the region from 220 nm to 400 nm of the spectrum.
1.2 The use of this test method implies that the conditions of measurement—wavelength, solvent (if any), sample path length, and sample concentration—are specified by reference to one of the examples of the application of this test method in the annexes or by a statement of other conditions of measurement.
1.3 Examples of the application of this test method are the absorptivity of refined petroleum wax, and the absorptivity of USP petrolatum.
1.4 The values stated in SI units are to be regarded as the standard. The values stated in Fahrenheit, feet, and inches, indicated in parentheses, are for information only.
1.5 Warning—Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use Caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see 7.3.1, 7.3.3, and 13.4.
1.7 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
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Designation: D2008 − 12 (Reapproved 2018)
Standard Test Method for
Ultraviolet Absorbance and Absorptivity of Petroleum
Products
This standard is issued under the fixed designation D2008; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This test method covers the measurement of the ultra-
ization established in the Decision on Principles for the
violet absorption of a variety of petroleum products. It covers
Development of International Standards, Guides and Recom-
the absorbance of liquids or the absorptivity of liquids and
mendations issued by the World Trade Organization Technical
solids, or both, at wavelengths in the region from 220 nm to
Barriers to Trade (TBT) Committee.
400 nm of the spectrum.
1.2 The use of this test method implies that the conditions of 2. Referenced Documents
measurement—wavelength, solvent (if any), sample path 2
2.1 ASTM Standards:
length, and sample concentration—are specified by reference
D1193 Specification for Reagent Water
to one of the examples of the application of this test method in
E131 Terminology Relating to Molecular Spectroscopy
the annexes or by a statement of other conditions of measure-
E169 Practices for General Techniques of Ultraviolet-Visible
ment.
Quantitative Analysis
1.3 Examples of the application of this test method are the E275 Practice for Describing and Measuring Performance of
absorptivity of refined petroleum wax, and the absorptivity of Ultraviolet and Visible Spectrophotometers
USP petrolatum.
3. Terminology
1.4 The values stated in SI units are to be regarded as the
3.1 Definitions of terms and symbols relating to absorption
standard. The values stated in Fahrenheit, feet, and inches,
spectroscopy in this test method shall conform to Terminology
indicated in parentheses, are for information only.
E131. Terms of particular significance are the following:
1.5 Warning—Mercury has been designated by many regu-
3.2 Definitions:
latory agencies as a hazardous substance that can cause serious
3.2.1 radiant energy, n—energy transmitted as electromag-
medical issues. Mercury, or its vapor, has been demonstrated to
netic waves.
be hazardous to health and corrosive to materials. Use Caution
when handling mercury and mercury-containing products. See 3.2.2 radiant power, P, n—the rate at which energy is
the applicable product Safety Data Sheet (SDS) for additional transported in a beam of radiant energy.
information. The potential exists that selling mercury or
3.2.3 transmittance, T, n—the molecular property of a sub-
mercury-containing products, or both, is prohibited by local or
stance that determines its transportability of radiant power,
national law. Users must determine legality of sales in their
expressed by:
location.
P
T 5 (1)
1.6 This standard does not purport to address all of the
P
o
safety concerns, if any, associated with its use. It is the
where:
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- P = the radiant power passing through the sample and
P = the radiant power incident upon the sample.
mine the applicability of regulatory limitations prior to use.
o
For specific warning statements, see 7.3.1, 7.3.3, and 13.4.
3.2.4 absorbance, A, n—the molecular property of a sub-
stance that determines its ability to take up radiant power,
expressed by:
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.04.0F on Absorption Spectroscopic Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2018. Published November 2018. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1962. Last previous edition approved in 2012 as D2008 – 12. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D2008-12R18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2008 − 12 (2018)
A 5 log ~1/T! 5 2log T (2) line at 313.16 nm or the absorption spectrum of either holmium
10 10
oxide glass at 287.5 nm or holmium oxide solution at
where T is the transmittance as defined in 3.2.3.
287.1 nm. At the 0.4 absorbance level in the spectral region
3.2.4.1 Discussion—Absorbance expresses the excess ab-
between 220 nm and 400 nm, absorbance measurements shall
sorption over that of a specified reference or standard. It is
be repeatable within 61.0 %.
implied that compensation has been affected for reflectance
6.2 For recommended methods of testing spectrophotom-
losses, solvent absorption losses, and refractive effects, if
eters to be used in this test method, refer to Practice E275.
present, and that attenuation by scattering is small compared
with attenuation by absorption.
6.3 An instrument is considered suitable when it can be
3.2.5 dilution factor, f, n—the proportion of solvent increase operated in a manner to give test results equivalent to those
made to reduce the concentration and thus the absorbance of a described in 6.1.
solute, expressed by the ratio of the volume of the diluted
6.4 Measurements requiring the use of cells having sample
solution to the volume of original solution containing the same
path lengths less than 10 cm can be made on instruments
quantity of solute as the diluted solution.
equipped to handle only these cells. It is desirable, but not
3.2.6 absorptivity, a, n—the specific property of a substance
essential, that the instrument be automatic recording when an
to absorb radiant power per unit sample concentration and path
extended range of the spectrum must be examined. Manually
length, expressed by:
operated spectrometers are suitable for obtaining absorbance
readings at specified analytical wavelengths. If measurements
a 5 Af/bc (3)
are to be made at temperatures higher than room temperature,
where:
the spectrophotometer must be provided with a means for
A = the absorbance defined in 3.2.4,
maintaining cells at the selected test temperature.
f = the dilution factor defined in 3.2.5,
6.5 One or more pairs of fused silica cells having sample
b = sample cell path length, and
path lengths in the range from 0.1000 cm to 10.00 cm are
c = the quantity of absorbing substance contained in a
required. Sample path lengths must be known to within
volume of solvent.
60.5 % of nominal sample path length or better. Unless
3.3 Definitions of Terms Specific to This Standard:
otherwise specified, 1 cm sample path length cells are recom-
3.3.1 sample cell pathlength, b, n—the distance in
mended. Suitable procedures for testing and cleaning cells are
centimetres, measured in the direction of propagation of the
described in Practice E275.
beam of radiant energy, between the surface of the specimen on
which the radiant energy is incident and the surface of the
7. Reagents and Materials
specimen from which it is emergent.
7.1 Purity of Reagents—Reagent grade chemicals shall be
3.3.1.1 Discussion—This distance does not include the
used in all tests. Unless otherwise indicated, it is intended that
thickness of the cell in which the specimen is contained.
all reagents shall conform to the specifications of the Commit-
3.3.2 concentration, c, n—the quantity of absorbing sub-
tee on Analytical Reagents of the American Chemical Society,
stance in grams per litre. 3
where such specifications are available. Other grades may be
used, provided it is first ascertained that the reagent is of
4. Summary of Test Method
sufficiently high purity to permit its use without lessening the
4.1 The ultraviolet absorbance of a liquid is determined by
accuracy of the determination.
measuring the absorption spectrum of the undiluted liquid in a
7.2 Purity of Water—Unless otherwise indicated, references
cell of known path length under specified conditions.
to water shall be understood to mean reagent water conforming
4.2 The ultraviolet absorptivity of a solid or a liquid is to Specification D1193, Type III.
determined by measuring the absorbance, at specified
7.3 Solvents:
wavelengths, of a solution of the liquid or solid at known
7.3.1 Isooctane—(Warning—Extremely flammable, harm-
concentration in a cell of known path length.
ful if inhaled.), for use as the preferred spectroscopic solvent.
7.3.2 Technical isooctane is a satisfactory base stock for the
5. Significance and Use
preparation of spectroscopic solvent. Allow about 4 L or 5 L of
5.1 The absorbance of liquids and the absorptivity of liquid this material to percolate through a column of activated silica
and solids at specified wavelengths in the ultraviolet are useful
gel 50 mm to 75 mm (2 in. to 3 in.) in diameter and 0.6 m to
in characterizing petroleum products.
0.9 m (2 ft to 3 ft) in depth. Collect only the portion of the
solvent that has an absorbance less than 0.05 over the entire
6. Apparatus
6.1 Spectrophotometer, equipped to handle liquid samples in
cells having sample path lengths up to 10 cm and capable of
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
measuring absorbance in the spectral region from 220 nm to
listed by the American Chemical Society, see Annual Standards for Laboratory
400 nm with a spectral slit width of 2 nm or less. Wavelength
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
measurement shall be repeatable and known to be accurate
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
within 60.2 nm or less as measured by the mercury emission MD.
D2008 − 12 (2018)
spectral range from 240 nm to 300 nm in a 1 cm cell when wavelength region of the spectrum, it may be desirable to use
compared to water in a 1 cm cell. longer path length cells than those recommended to obtain
7.3.3 Decahydronaphthalene (Decalin)—(Warning— readable absorbances. See the applicable paragraph of Prac-
Combustible, vapors harmful.), for use as the first alternative tices E169. In the shorter wavelength region of the spectrum,
spectroscopic solvent. absorbances can become too high for accurate measurement in
7.3.4 The silica gel percolation described in 7.3.2 is also the 0.1 cm cell. Record these values only as greater than 1.0. If
recommended for the preparation of decahydronaphthalene as numerical values are required it is recommended that absorp-
a spectroscopic solvent. tivity be measured rather than absorbance.
7.3.5 Some common, commercially available solvents of
9.4 Repeat 9.1 and 9.2 using a 0.1 cm cell, or a 0.5 cm cell
“spectroscopic purity” are listed in Practices E169. One of
when appropriate, in place of the 1.0 cm cell (9.3). Record all
them can be selected for use in absorptivity measurements but
measurements.
only when indicated in Section 13.
10. Calculation
7.4 Holmium Oxide Glass or Holmium Oxide Solution—
Used to verify the wavelength accuracy of the spectrophotom- 10.1 Calculate the absorbance of an undiluted liquid sample
eter. at each analytical wavelength as follows:
A 5 A 2 A (4)
L C
8. Sampling
where:
8.1 Precautions must be taken to ensure that a representative
A = absorbance of undiluted liquid sample,
sample is obtained since ultraviolet absorption is very sensitive
A = chart or absorbance reading of sample-filled sample
to small amounts of extraneous material contaminating the
L
cell, and
sample through careless handling. If possible, samples should
A = chart or absorbance reading of water-filled sample cell.
be obtained from packaged products that have been protected C
from accidental contamination.
10.2 Calculate the absorbance per centimetre path length
8.2 If the petroleum product to be tested is available as a
that is equal to A/b, where b is the sample cell path length in
bulk sample weighing more than 1 kg, a representative sample
centimetres.
of approximately 1 kg shall be taken and made homogeneous.
8.3 If the petroleum product to be tested is available as a
11. Report
bulk sample weighing less than 1 kg but more than 100 g, the
11.1 If the numerical value of the absorbance of an undi-
entire sample shall be taken and made homogeneous.
luted liquid sample is reported, accompany it with a statement
8.4 In no case shall a sample of a petroleum product be
of the wavelength of measurement and the sample path length
considered representative if it weighs less than 100 g.
expressed in centimetres.
However, measurements may be made on samples weighing
11.2 If the numerical value of the absorbance per centimetre
less than 100 g if the origin, sampling procedure, and basis of
of an undiluted liquid sample is reported, it must accompany it
selection of the sample are recorded and reported as part of the
with a statement of the wavelength of measurement.
results of this test method.
ABSORPTIVITY OF SOLIDS AND LIQUIDS
ABSORBANCE OF UNDILUTED LIQUIDS
12. Summary of Test Methods
9. Procedure
12.1 The range of absorptivities for petroleum products can
9.1 Fill a 1.0 cm reference cell with water. Make sure the
be very wide. Probably most absorptivities of interest would
cell windows are clean. Position the cells in the cell compart- −4
fall in the range from 10 L ⁄g·cm to 10 L/g·cm.
ment of the spectrophotometer and obtain absorbance at the
12.2 In determining absorptivities it is necessary to measure
wavelengths of interest within the range from 220 nm to
absorbances in the range from 0.1 to 1.0 for optimum results.
400 nm. This data gives a cell correction for the 1.0 cm cell. It
This is done by preparing solutions and selecting cells of
can be ignored at all wavelengths where the absorbance is
sample path length to give absorbances in the 0.1 to 1.0 range.
between −0.01 and +0.01. After the cell correction data has
For an individual petroleum product the absorptivity may
been determined, the cells shall be designated reference and
change so rapidly with wavelength that it is necessary to
sample cells and shall be maintained as such.
prepare several solutions in order to cover the required
9.2 Fill a 1.0 cm sample cell with undiluted liquid sample
wavelength interval. Consideration must be given to the
(after complete removal of water) and obtain the absorbance as
selection of solv
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D2008 − 12 D2008 − 12 (Reapproved 2018)
Standard Test Method for
Ultraviolet Absorbance and Absorptivity of Petroleum
Products
This standard is issued under the fixed designation D2008; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*Scope
1.1 This test method covers the measurement of the ultraviolet absorption of a variety of petroleum products. It covers the
absorbance of liquids or the absorptivity of liquids and solids, or both, at wavelengths in the region from 220220 nm to 400 nm
of the spectrum.
1.2 The use of this test method implies that the conditions of measurement—wavelength, solvent (if any), sample path length,
and sample concentration—are specified by reference to one of the examples of the application of this test method in the annexes
or by a statement of other conditions of measurement.
1.3 Examples of the application of this test method are the absorptivity of refined petroleum wax, and the absorptivity of USP
petrolatum.
1.4 The values stated in SI units are to be regarded as the standard. The values stated in Fahrenheit, feet, and inches, indicated
in parentheses, are for information only.
1.5 Warning—Mercury has been designated by EPA and many stateregulatory agencies as a hazardous materialsubstance that
can cause central nervous system, kidney, and liver damage. serious medical issues. Mercury, or its vapor, may has been
demonstrated to be hazardous to health and corrosive to materials. Caution should be taken Use Caution when handling mercury
and mercury-containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA’s website
(http://www.epa.gov/mercury/faq.htm) for additional information. Users should be aware (SDS) for additional information. The
potential exists that selling mercury or mercury-containing products, or both, in your state may be prohibited by state law.is
prohibited by local or national law. Users must determine legality of sales in their location.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific warning statements, see 7.3.1, 7.3.3, and 13.4.
1.7 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.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
E131 Terminology Relating to Molecular Spectroscopy
E169 Practices for General Techniques of Ultraviolet-Visible Quantitative Analysis
E275 Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
3. Terminology
3.1 Definitions of terms and symbols relating to absorption spectroscopy in this test method shall conform to Terminology E131.
Terms of particular significance are the following:
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.04.0F on Absorption Spectroscopic Methods.
Current edition approved June 1, 2012Oct. 1, 2018. Published October 2012November 2018. Originally approved in 1962. Last previous edition approved in 20092012
as D2008D2008 – 12.–09. DOI: 10.1520/D2008-12.10.1520/D2008-12R18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2008 − 12 (2018)
3.2 Definitions:
3.2.1 radiant energy, n—energy transmitted as electromagnetic waves.
3.2.2 radiant power, P, n—the rate at which energy is transported in a beam of radiant energy.
3.2.3 transmittance, T, n—the molecular property of a substance that determines its transportability of radiant power, expressed
by:
P
T 5 (1)
P
o
where:where:
P = the radiant power passing through the sample and
P = the radiant power incident upon the sample.
o
3.2.4 absorbance, A, n—the molecular property of a substance that determines its ability to take up radiant power, expressed
by:
A 5 log ~1/T! 52log T (2)
10 10
where T is the transmittance as defined in 3.2.3.
3.2.4.1 Discussion—
Absorbance expresses the excess absorption over that of a specified reference or standard. It is implied that compensation has been
affected for reflectance losses, solvent absorption losses, and refractive effects, if present, and that attenuation by scattering is small
compared with attenuation by absorption.
3.2.5 dilution factor, f, n—the proportion of solvent increase made to reduce the concentration and thus the absorbance of a
solute, expressed by the ratio of the volume of the diluted solution to the volume of original solution containing the same quantity
of solute as the diluted solution.
3.2.6 absorptivity, a, n—the specific property of a substance to absorb radiant power per unit sample concentration and path
length, expressed by:
a 5 Af/bc (3)
where:
where:
A = the absorbance defined in 3.2.4,
f = the dilution factor defined in 3.2.5,
b = sample cell path length, and
c = the quantity of absorbing substance contained in a volume of solvent.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 sample cell pathlength, b, n—the distance in centimetres, measured in the direction of propagation of the beam of radiant
energy, between the surface of the specimen on which the radiant energy is incident and the surface of the specimen from which
it is emergent.
3.3.1.1 Discussion—
This distance does not include the thickness of the cell in which the specimen is contained.
3.3.2 concentration, c, n—the quantity of absorbing substance in grams per litre.
4. Summary of Test Method
4.1 The ultraviolet absorbance of a liquid is determined by measuring the absorption spectrum of the undiluted liquid in a cell
of known path length under specified conditions.
4.2 The ultraviolet absorptivity of a solid or a liquid is determined by measuring the absorbance, at specified wavelengths, of
a solution of the liquid or solid at known concentration in a cell of known path length.
5. Significance and Use
5.1 The absorbance of liquids and the absorptivity of liquid and solids at specified wavelengths in the ultraviolet are useful in
characterizing petroleum products.
D2008 − 12 (2018)
6. Apparatus
6.1 Spectrophotometer, equipped to handle liquid samples in cells having sample path lengths up to 10 cm 10 cm and capable
of measuring absorbance in the spectral region from 220220 nm to 400 nm with a spectral slit width of 2 nm 2 nm or less.
Wavelength measurement shall be repeatable and known to be accurate within 60.2 nm 60.2 nm or less as measured by the
mercury emission line at 313.16 nm 313.16 nm or the absorption spectrum of either holmium oxide glass at 287.5 nm 287.5 nm
or holmium oxide solution at 287.1 nm. 287.1 nm. At the 0.4 absorbance level in the spectral region between 220220 nm and 400
nm, 400 nm, absorbance measurements shall be repeatable within 61.0 %.
6.2 For recommended methods of testing spectrophotometers to be used in this test method, refer to Practice E275.
6.3 An instrument is considered suitable when it can be operated in a manner to give test results equivalent to those described
in 6.1.
6.4 Measurements requiring the use of cells having sample path lengths less than 10 cm can be made on instruments equipped
to handle only these cells. It is desirable, but not essential, that the instrument be automatic recording when an extended range of
the spectrum must be examined. Manually operated spectrometers are suitable for obtaining absorbance readings at specified
analytical wavelengths. If measurements are to be made at temperatures higher than room temperature, the spectrophotometer must
be provided with a means for maintaining cells at the selected test temperature.
6.5 One or more pairs of fused silica cells having sample path lengths in the range from 0.10000.1000 cm to 10.00 cm 10.00 cm
are required. Sample path lengths must be known to within 60.5 % of nominal sample path length or better. Unless otherwise
specified, 1-cm1 cm sample path length cells are recommended. Suitable procedures for testing and cleaning cells are described
in Practice E275.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
7.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to
Specification D1193, Type III.
7.3 Solvents:
7.3.1 Isooctane—(Warning—Extremely flammable, harmful if inhaled.), for use as the preferred spectroscopic solvent.
7.3.2 Technical isooctane is a satisfactory base stock for the preparation of spectroscopic solvent. Allow about 44 L or 5 L 5 L
of this material to percolate through a column of activated silica gel 50 to 75 mm (2 to 3 in.) 50 mm to 75 mm (2 in. to 3 in.) in
diameter and 0.6 to 0.9 m (2 to 3 ft) 0.6 m to 0.9 m (2 ft to 3 ft) in depth. Collect only the portion of the solvent that has an
absorbance less than 0.05 over the entire spectral range from 240240 nm to 300 nm 300 nm in a 1-cm1 cm cell when compared
to water in a 1-cm1 cm cell.
7.3.3 Decahydronaphthalene (Decalin)—(Warning—Combustible, vapors harmful.), for use as the first alternative spectro-
scopic solvent.
7.3.4 The silica gel percolation described in 7.3.2 is also recommended for the preparation of decahydronaphthalene as a
spectroscopic solvent.
7.3.5 Some common, commercially available solvents of “spectroscopic purity” are listed in Practices E169. One of them can
be selected for use in absorptivity measurements but only when indicated in Section 13.
7.4 Holmium Oxide Glass or Holmium Oxide Solution—Used to verify the wavelength accuracy of the spectrophotometer.
8. Sampling
8.1 Precautions must be taken to ensure that a representative sample is obtained since ultraviolet absorption is very sensitive
to small amounts of extraneous material contaminating the sample through careless handling. If possible, samples should be
obtained from packaged products that have been protected from accidental contamination.
8.2 If the petroleum product to be tested is available as a bulk sample weighing more than 1 kg, 1 kg, a representative sample
of approximately 1 kg 1 kg shall be taken and made homogeneous.
8.3 If the petroleum product to be tested is available as a bulk sample weighing less than 1 kg 1 kg but more than 100 g, 100 g,
the entire sample shall be taken and made homogeneous.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by
the American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D2008 − 12 (2018)
8.4 In no case shall a sample of a petroleum product be considered representative if it weighs less than 100 g. 100 g. However,
measurements may be made on samples weighing less than 100 g 100 g if the origin, sampling procedure, and basis of selection
of the sample are recorded and reported as part of the results of this test method.
ABSORBANCE OF UNDILUTED LIQUIDS
9. Procedure
9.1 Fill a 1.0-cm1.0 cm reference cell with water. Make sure the cell windows are clean. Position the cells in the cell
compartment of the spectrophotometer and obtain absorbance at the wavelengths of interest within the range from 220220 nm to
400 nm. 400 nm. This data gives a cell correction for the 1.0-cm1.0 cm cell. It can be ignored at all wavelengths where the
absorbance is between −0.01 and +0.01. After the cell correction data has been determined, the cells shall be designated reference
and sample cells and shall be maintained as such.
9.2 Fill a 1.0-cm1.0 cm sample cell with undiluted liquid sample (after complete removal of water) and obtain the absorbance
as described in 9.1.
9.3 The absorbance-wavelength curve can be conveniently obtained starting at the long wavelength end of the spectrum. Take
readings at successively shorter wavelengths until an absorbance greater than 1.0 is obtained. When using automatic recording
instruments (recommended) make the cell correction scan and the sample scan on the same chart. In the longer wavelength region
of the spectrum, it may be desirable to use longer path length cells than those recommended to obtain readable absorbances. See
the applicable paragraph of Practices E169. In the shorter wavelength region of the spectrum, absorbances can become too high
for accurate measurement in the 0.1-cm0.1 cm cell. Record these values only as greater than 1.0. If numerical values are required
it is recommended that absorptivity be measured rather than absorbance.
9.4 Repeat 9.1 and 9.2 using a 0.1-cm0.1 cm cell, or a 0.5-cm0.5 cm cell when appropriate, in place of the 1.0-cm1.0 cm cell
(9.3). Record all measurements.
10. Calculation
10.1 Calculate the absorbance of an undiluted liquid sample at each analytical wavelength as follows:
A 5 A 2 A (4)
L C
where:
where:
A = absorbance of undiluted liquid sample,
A = chart or absorban
...
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