ASTM D2008-91(2006)
(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
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 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 determination of the absorbance of white mineral oil, 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.
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 and health 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.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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AnAmerican National Standard
Designation:D2008–91 (Reapproved 2006)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E275 Practice for Describing and Measuring Performance
of Ultraviolet, Visible, and Near-Infrared Spectrophotom-
1.1 This test method covers the measurement of the ultra-
eters
violet absorption of a variety of petroleum products. It covers
the absorbance of liquids or the absorptivity of liquids and
3. Terminology
solids, or both, at wavelengths in the region from 220 to
3.1 Definitions—Definitions of terms and symbols relating
400nm of the spectrum.
toabsorptionspectroscopyinthistestmethodshallconformto
1.2 Theuseofthistestmethodimpliesthattheconditionsof
Terminology E131. Terms of particular significance are the
measurement—wavelength, solvent (if any), sample path
following:
length, and sample concentration—are specified by reference
3.1.1 radiant energy, n—energy transmitted as electromag-
to one of the examples of the application of this test method in
netic waves.
the annexes or by a statement of other conditions of measure-
3.1.2 radiant power, P, n—the rate at which energy is
ment.
transported in a beam of radiant energy.
1.3 Examples of the application of this test method are the
3.1.3 transmittance, T, n—the molecular property of a
determination of the absorbance of white mineral oil, the
substance that determines its transportability of radiant power,
absorptivity of refined petroleum wax, and the absorptivity of
expressed by:
USP petrolatum.
P
1.4 The values stated in SI units are to be regarded as the
T 5 (1)
P
standard. The values stated in fahrenheit, feet, and inches,
o
indicated in parentheses, are for information only.
where:
1.5 This standard does not purport to address all of the
P = the radiant power passing through the sample and
safety concerns, if any, associated with its use. It is the
P = the radiant power incident upon the sample.
o
responsibility of the user of this standard to establish appro-
3.1.4 absorbance, A, n—the molecular property of a sub-
priate safety and health practices and determine the applica-
stance that determines its ability to take up radiant power,
bility of regulatory limitations prior to use. For specific
expressed by:
warning statements, see 7.3.1, 7.3.3, and 13.4.
A 5log ~1/T!52log T (2)
10 10
2. Referenced Documents
where T is the transmittance as defined in 3.1.3.
2.1 ASTM Standards:
3.1.4.1 Discussion—Absorbance expresses the excess ab-
D1193 Specification for Reagent Water
sorption over that of a specified reference or standard. It is
E131 Terminology Relating to Molecular Spectroscopy
implied that compensation has been affected for reflectance
E169 Practices for General Techniques of Ultraviolet-
losses, solvent absorption losses, and refractive effects, if
Visible Quantitative Analysis
present, and that attenuation by scattering is small compared
with attenuation by absorption.
3.1.5 dilution factor, f, n—theproportionofsolventincrease
This test method is under the jurisdiction of ASTM Committee D02 on
made to reduce the concentration and thus the absorbance of a
PetroleumProductsandLubricantsandisthedirectresponsibilityofSubcommittee
solute, expressed by the ratio of the volume of the diluted
D02.04 on Hydrocarbon Analysis.
solutiontothevolumeoforiginalsolutioncontainingthesame
Current edition approved May 1, 2006. Published June 2006. Originally
approved in 1962. Last previous edition approved in 2001 as D2008–91 (2001).
quantity of solute as the diluted solution.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.6 absorptivity, a, n—thespecificpropertyofasubstance
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
toabsorbradiantpowerperunitsampleconcentrationandpath
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. length, expressed by:
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
D2008–91 (2006)
a 5 Af/bc (3)
Sample path lengths must be known to within 60.5% of
nominal sample path length or better. Unless otherwise speci-
where:
fied, 1-cm sample path length cells are recommended. Suitable
A = the absorbance defined in 3.1.4,
procedures for testing and cleaning cells are described in
f = the dilution factor defined in 3.1.5,
Practice E275.
b = sample cell path length, and
c = the quantity of absorbing substance contained in a
7. Reagents and Materials
volume of solvent.
7.1 Purity of Reagents—Reagent grade chemicals shall be
3.2 Definitions of Terms Specific to This Standard:
used in all tests. Unless otherwise indicated, it is intended that
3.2.1 sample cell pathlength, b, n—the distance in centime-
all reagents shall conform to the specifications of the Commit-
tres, measured in the direction of propagation of the beam of
tee onAnalytical Reagents of theAmerican Chemical Society,
radiant energy, between the surface of the specimen on which
where such specifications are available. Other grades may be
the radiant energy is incident and the surface of the specimen
used, provided it is first ascertained that the reagent is of
from which it is emergent.
sufficiently high purity to permit its use without lessening the
3.2.1.1 Discussion—This distance does not include the
accuracy of the determination.
thickness of the cell in which the specimen is contained.
7.2 Purity of Water—Unlessotherwiseindicated,references
3.2.2 concentration, c, n—the quantity of absorbing sub-
towatershallbeunderstoodtomeanreagentwaterconforming
stance in grams per litre.
to Specification D1193, Type III.
4. Summary of Test Method
7.3 Solvents:
7.3.1 Isooctane—(Warning—Extremely flammable, harm-
4.1 The ultraviolet absorbance of a liquid is determined by
ful if inhaled.), for use as the preferred spectroscopic solvent.
measuring the absorption spectrum of the undiluted liquid in a
7.3.2 Technical isooctane is a satisfactory base stock for the
cell of known path length under specified conditions.
preparation of spectroscopic solvent. Allow about 4 or 5 L of
4.2 The ultraviolet absorptivity of a solid or a liquid is
this material to percolate through a column of activated silica
determined by measuring the absorbance, at specified wave-
gel 50 to 75 mm (2 to 3 in.) in diameter and 0.6 to 0.9 m (2 to
lengths, of a solution of the liquid or solid at known concen-
3 ft) in depth. Collect only the portion of the solvent that has
tration in a cell of known path length.
anabsorbancelessthan0.05overtheentirespectralrangefrom
5. Significance and Use
240 to 300 nm in a 1-cm cell when compared to water in a
1-cm cell.
5.1 The absorbance of liquids and the absorptivity of liquid
and solids at specified wavelengths in the ultraviolet are useful 7.3.3 Decahydronaphthalene (Decalin)—(Warning—
Combustible, vapors harmful.), for use as the first alternative
in characterizing petroleum products.
spectroscopic solvent.
6. Apparatus
7.3.4 The silica gel percolation described in 7.3.2 is also
6.1 Spectrophotometer, equipped to handle liquid samples
recommended for the preparation of decahydronaphthalene as
incellshavingsamplepathlengthsupto10cmandcapableof
a spectroscopic solvent.
measuring absorbance in the spectral region from 220 to
7.3.5 Some common, commercially available solvents of
400nm with a spectral slit width of 2 nm or less. Wavelength
“spectroscopic purity” are listed in Practices E169. One of
measurement shall be repeatable and known to be accurate
them can be selected for use in absorptivity measurements but
within 60.2 nm or less as measured by the mercury emission
only when indicated in Section 13.
line at 313.16 nm. At the 0.4 absorbance level in the spectral
8. Sampling
region between 220 and 400 nm, absorbance measurements
shall be repeatable within 61.0%.
8.1 Precautionsmustbetakentoensurethatarepresentative
6.2 For recommended methods of testing spectrophotom-
sampleisobtainedsinceultravioletabsorptionisverysensitive
eters to be used in this test method, refer to Practice E275.
to small amounts of extraneous material contaminating the
6.3 An instrument is considered suitable when it can be
sample through careless handling. If possible, samples should
operated in a manner to give test results equivalent to those
be obtained from packaged products that have been protected
described in 6.1.
from accidental contamination.
6.4 Measurements requiring the use of cells having sample
8.2 If the petroleum product to be tested is available as a
path lengths less than 10 cm can be made on instruments
bulk sample weighing more than 1 kg, a representative sample
equipped to handle only these cells. It is desirable, but not
of approximately 1 kg shall be taken and made homogeneous.
essential, that the instrument be automatic recording when an
8.3 If the petroleum product to be tested is available as a
extended range of the spectrum must be examined. Manually
bulk sample weighing less than 1 kg but more than 100 g, the
operated spectrometers are suitable for obtaining absorbance
entire sample shall be taken and made homogeneous.
readings at specified analytical wavelengths. If measurements
are to be made at temperatures higher than room temperature,
“ReagentChemicals,AmericanChemicalSocietySpecifications,”Am.Chemi-
the spectrophotometer must be provided with a means for
cal Soc., Washington, D.C. For suggestions on the testing of reagents not listed by
maintaining cells at the selected test temperature.
theAmericanChemicalSociety,see“ReagentChemicalsandStandards,”byJoseph
6.5 One or more pairs of fused silica cells having sample
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States
pathlengthsintherangefrom0.1000to10.00cmarerequired. Pharmacopeia.”
D2008–91 (2006)
8.4 In no case shall a sample of a petroleum product be 11.2 Ifthenumericalvalueoftheabsorbancepercentimetre
considered representative if it weighs less than 100 g. How- of an undiluted liquid sample is reported, it must accompany it
ever, measurements may be made on samples weighing less with a statement of the wavelength of measurement.
than 100 g if the origin, sampling procedure, and basis of
ABSORPTIVITY OF SOLIDS AND LIQUIDS
selectionofthesamplearerecordedandreportedaspartofthe
results of this test method.
12. Summary of Test Methods
12.1 The range of absorptivities for petroleum products can
ABSORBANCE OF UNDILUTED LIQUIDS
be very wide. Probably most absorptivities of interest would
−4
9. Procedure
fall in the range from 10 to 10 L/g·cm.
12.2 Indeterminingabsorptivitiesitisnecessarytomeasure
9.1 Fill a 1.0-cm reference cell with water. Make sure the
absorbances in the range from 0.1 to 1.0 for optimum results.
cell windows are clean. Position the cells in the cell compart-
This is done by preparing solutions and selecting cells of
ment of the spectrophotometer and obtain absorbance at the
sample path length to give absorbances in the 0.1 to 1.0 range.
wavelengths of interest within the range from 220 to 400 nm.
For an individual petroleum product the absorptivity may
This data gives a cell correction for the 1.0-cm cell. It can be
change so rapidly with wavelength that it is necessary to
ignored at all wavelengths where the absorbance is between
prepare several solutions in order to cover the required
−0.01 and +0.01. After the cell correction data has been
wavelength interval. Consideration must be given to the
determined, the cells shall be designated reference and sample
selection of solvent, the selection of concentration levels, and
cells and shall be maintained as such.
theselectionofsamplepathslengthstoobtainoptimumresults.
9.2 Fill a 1.0-cm sample cell with undiluted liquid sample
(aftercompleteremovalofwater)andobtaintheabsorbanceas
13. Selection of Solvent
described in 9.1.
13.1 Refer to the applicable section of Practices E169 for a
9.3 The absorbance-wavelength curve can be conveniently
brief discussion of solvents for ultraviolet use. The choice of
obtained starting at the long wavelength end of the spectrum.
solvent is dictated by the solubility of the petroleum product
Take readings at successively shorter wavelengths until an
and the transparency of the solvent in the region of interest.
absorbance greater than 1.0 is obtained.When using automatic
13.2 Use isooctane unless restricted by solubility require-
recordinginstruments(recommended)makethecellcorrection
ments.
scan and the sample scan on the same chart. In the longer
13.3 Use decahydronaphthalene as the first alternative sol-
wavelength region of the spectrum, it may be desirable to use
vent to be used if the sample is not sufficiently soluble in
longer path length cells than those recommended to obtain
isooctane.
readable absorbances. See the applicable paragraph of Prac-
13.4 If neither isooctane nor decahydronaphthalene will
tices E169. In the shorter wavelength region of the spectrum,
dissolve a sufficient quantity of sample to prepare the required
absorbances can become too high for accurate measurement in
solution,thenoneofthesolventslistedinthetableinPractices
the0.1-cmcell.Recordthesevaluesonlyasgreaterthan1.0.If
E169. As indicated in the table in Practices E169, not all of
numerical values are required it is recommended that absorp-
thesesolventsareusableovertheentirespectralrangecovered
tivity be measured rather than absorbance.
by this test method. For the purposes of this test method a
9.4 Repeat 9.1 and 9.2 using a 0.1-cm cell in place of the
solvent shall be considered to have sufficient “spectroscopic
1.0-cm cell (9.3). Record all measurements.
purity”whenitsabsorbanceina1-cmcell,usingreagentwater
10. Calculation
ina1-cmcellasareference,islessthan0.05atallwavelengths
where a sample absorbance is to be measured in a 1-cm cell.
10.1 Calculatetheabsorbanceofanundilutedliquidsample
Cyclohexane (Warning—Extremely flammable. Harmful if
at each analytical wavelength as follows:
inhaled.), carbon tetrachloride, chloroform (Warning—
A 5 A 2 A (4)
L C
Carbontetrachlorideandchloroformcanbefatalifswallowed.
Harmful if inhaled. Can produce toxic vapors if burned.), and
where:
A = absorbance of undiluted liquid sample, the alcohols listed in the table in Practices E169 are useful
A = chart or absorbance reading of sample-filled sample alternative spectroscopic solvents.
L
cell, and
14. Selection of
...
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