ASTM D2008-23

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 (Reapproved 2018) D2008 − 23
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 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.
1.5 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.
1.6 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:
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.
Current edition approved Oct. 1, 2018May 1, 2023. Published November 2018June 2023. Originally approved in 1962. Last previous edition approved in 20122018 as
D2008 – 12.D2008 – 12 (2018). DOI: 10.1520/D2008-12R18.10.1520/D2008-23.
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 − 23
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:
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:
P = the radiant power passing through the sample and
P = the radiant power incident upon the sample.
o
3.2.1 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 (1)
10 10
where T is the transmittance as defined in 3.2.33.2.6.
3.2.1.1 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.
3.2.2 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 (2)
where:
A = the absorbance defined in 3.2.1,
f = the dilution factor defined in 3.2.3,
b = sample cell path length, and
c = the quantity of absorbing substance contained in a volume of solvent.
3.2.3 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.
3.2.4 radiant energy, n—energy transmitted as electromagnetic waves.
3.2.5 radiant power, P, n—the rate at which energy is transported in a beam of radiant energy.
3.2.6 absorptivity, a,transmittance, T, n—the specificmolecular property of a substance to absorb radiant power per unit sample
concentration and path length, that determines its transportability of radiant power, expressed by:
a 5 Af/bc (3)
D2008 − 23
P
T 5 (3)
P
o
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.
P = the radiant power passing through the sample and
P = the radiant power incident upon the sample.
o
3.3 Definitions of Terms Specific to This Standard:
3.3.1 concentration, c, n—the quantity of absorbing substance in grams per litre.
3.3.2 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.
3.3.2.1 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.
6. Apparatus
6.1 Spectrophotometer, equipped to handle liquid samples in cells having sample path lengths up to 10 cm and capable of
measuring absorbance in the spectral region from 220 nm to 400 nm with a spectral slit width of 2 nm or less. Wavelength
measurement shall be repeatable and known to be accurate within 60.2 nm or less as measured by the mercury emission line at
313.16 nm or the absorption spectrum of either holmium oxide glass at 287.5 nm or holmium oxide solution at 287.1 nm. At the
0.4 absorbance level in the spectral region between 220 nm and 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.
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6.5 One or more pairs of fused silica cells having sample path lengths in the range from 0.1000 cm to 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 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 4 L or 5 L of this
material to percolate through a column of activated silica gel 50 mm to 75 mm (2 in. to 3 in.) in diameter and 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
240 nm to 300 nm in a 1 cm cell when compared to water in a 1 cm cell.
7.3.3 Decahydronaphthalene (Decalin)—(Warning—Combustible, vapors harmful.), for use as the first alternative spectroscopic
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, a representative sample of
approximately 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 but more than 100 g, the entire
sample shall be taken and made homogeneous.
8.4 In no case shall a sample of a petroleum product be considered representative if it weighs less than 100 g. However,
measurements may be made on samples weighing less than 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.
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, American Chemical Society, Washington, DC. For Suggestionssuggestions on the testing of reagents not listed by the American Chemical Society, see
AnnualAnalar 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 − 23
ABSORBANCE OF UNDILUTED LIQUIDS
9. Procedure
9.1 Fill a 1.0 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 220 nm to 400 nm. This data
gives a cell correction for the 1.0 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 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 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 cm cell, or a 0.5 cm cell when appropriate, in place of the 1.0 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:
A = absorbance of undiluted liquid sample,
A = chart or absorbance reading of sample-filled sample cell, and
L
A = chart or absorbance reading of water-filled sample cell.
C
10.2 Calculate the absorbance per centimetre path length that is equal to A/b, where b is the sample cell path length in centimetres.
11. Report
11.1 If the numerical value of the absorbance of an undiluted liquid sample is reported, accompany it with a statement of the
wavelength of measurement and the sample path length expressed in centimetres.
11.2 If the numerical value of the absorbance per centimetre of an undiluted liquid sample is reported, it must accompany it with
a statement of the wavelength of measurement.
ABSORPTIVITY OF SOLIDS AND LIQUIDS
12. Summary of Test Methods
12.1 The range of absorptivities for petroleum products can be very wide. Probably most absorptivities of interest would fall in
−4
the range from 10 L ⁄g·cm to 10 L/g·cm.
12.2 In determining absorptivities it is necessary to measure absorbances in the range from 0.1 to 1.0 for optimum results. This
is done by preparing solutions and selecting cells of sample path length to give absorbances in the 0.1 to 1.0 range. For an
individual petroleum product the absorptivity may change so rapidly with wavelength that it is necessary to prepare several
D2008 − 23
solutions in order to cover the required wavelength interval. Consideration must be given to the selection of solvent, the selection
of concentration levels, and the selection of sample paths lengths to obtain optimum results.
13. Selection of Solvent
13.1 Refer to the applicable section of Practices E169 for a brief discussion of solvents for ultraviolet use. The choice of solvent
is dictated by the solubility of the petroleum product and the transparency of the solvent in the region of interest.
13.2 Use isooctane unless restricted by solubility requirements.
13.3 Use decahydronaphthalene as the first alternative solvent to be used if the sample is not sufficiently soluble in isooctane.
13.4 If neither isooctane nor decahydronaphthalene will dissolve a sufficient quantity of sample to prepare the required solution,
then one of the solvents listed in the table in Practices E169. may be used. As indicated in the table in Practices E169, not all of
these solvents are usable over the entire spectral range covered by this test method. For the purposes of this test method a solvent
shall be considered to have sufficient “spectroscopic purity” when its absorbance in a 1 cm cell, using reagent water in a 1 cm cell
as a reference, is less than 0.05 at all wavelen
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