ASTM D2008-91(1996)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
AnAmerican National Standard
ϵ1
Designation:D2008–91(Reapproved 1996)
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 (ϵ) indicates an editorial change since the last revision or reapproval.
ϵ NOTE—Paragraph 3.1.3 was editorially corrected in January 1996.
1. Scope E169 Practices for General Techniques of Ultraviolet-
Visible Quantitative Analysis
1.1 This test method covers the measurement of the ultra-
E275 Practice for Describing and Measuring Performance
violet absorption of a variety of petroleum products. It covers
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
the absorbance of liquids or the absorptivity of liquids and
eters
solids, or both, at wavelengths in the region from 220 to 400
nm of the spectrum.
3. Terminology
1.2 Theuseofthistestmethodimpliesthattheconditionsof
3.1 Definitions—Definitions of terms and symbols relating
measurement—wavelength, solvent (if any), sample path
toabsorptionspectroscopyinthistestmethodshallconformto
length, and sample concentration—are specified by reference
Terminology E131E131. Terms of particular significance are
to one of the examples of the application of this test method in
the following:
the annexes or by a statement of other conditions of measure-
3.1.1 radiant energy, n—energy transmitted as electromag-
ment.
netic waves.
1.3 Examples of the application of this test method are the
3.1.2 radiant power, P, n—the rate at which energy is
determination of the absorbance of white mineral oil, the
transported in a beam of radiant energy.
absorptivity of refined petroleum wax, and the absorptivity of
3.1.3 transmittance, T, n—the molecular property of a
USP petrolatum.
substance that determines its transportability of radiant power,
1.4 The values stated in SI units are to be regarded as the
expressed by:
standard. The values stated in fahrenheit, feet, and inches,
indicated in parentheses, are for information only. P
T 5 (1)
P
1.5 This standard does not purport to address all of the
o
safety concerns, if any, associated with its use. It is the
where:
responsibility of the user of this standard to establish appro-
P = the radiant power passing through the sample and
priate safety and health practices and determine the applica-
P = the radiant power incident upon the sample.
o
bility of regulatory limitations prior to use. For specific
3.1.4 absorbance, A, n—the molecular property of a sub-
warning statements, see 7.3.1, 7.3.2, and 14.4.
stance that determines its ability to take up radiant power,
expressed by:
2. Referenced Documents
A 5log ~1/T!52log T (2)
2.1 ASTM Standards: 10 10
D1193 Specification for Reagent Water
where T is the transmittance as defined in 3.1.3.
E131 Terminology Relating to Molecular Spectroscopy
3.1.4.1 Discussion—Absorbance expresses the excess ab-
sorption over that of a specified reference or standard. It is
implied that compensation has been affected for reflectance
1 losses, solvent absorption losses, and refractive effects, if
This test method is under the jurisdiction of ASTM Committee D-2 on
present, and that attenuation by scattering is small compared
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.04 on Hydrocarbon Analysis.
with attenuation by absorption.
Current edition approved Oct. 15, 1991. Published December 1991. Originally
3.1.5 dilution factor, f, n—theproportionofsolventincrease
published as D2008–62T. Last previous edition D2008–90.
2 made to reduce the concentration and thus the absorbance of a
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 03.06. solute, expressed by the ratio of the volume of the diluted
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
ϵ1
D2008–91 (1996)
solutiontothevolumeoforiginalsolutioncontainingthesame operated spectrometers are suitable for obtaining absorbance
quantity of solute as the diluted solution. readings at specified analytical wavelengths. If measurements
3.1.6 absorptivity, a, n—thespecificpropertyofasubstance are to be made at temperatures higher than room temperature,
toabsorbradiantpowerperunitsampleconcentrationandpath the spectrophotometer must be provided with a means for
length, expressed by: maintaining cells at the selected test temperature.
6.5 One or more pairs of fused silica cells having sample
a 5 Af/bc (3)
pathlengthsintherangefrom0.1000to10.00cmarerequired.
where:
Sample path lengths must be known to within 60.5% of
A = the absorbance defined in 3.1.4,
nominal sample path length or better. Unless otherwise speci-
f = the dilution factor defined in 3.1.5,
fied, 1-cm sample path length cells are recommended. Suitable
b = sample cell path length, and
procedures for testing and cleaning cells are described in
c = the quantity of absorbing substance contained in a
Practice E275E275.
volume of solvent.
3.2 Definitions of Terms Specific to This Standard:
7. Reagents and Materials
3.2.1 sample cell pathlength, b, n—the distance in cm,
7.1 Purity of Reagents—Reagent grade chemicals shall be
measuredinthedirectionofpropagationofthebeamofradiant
used in all tests. Unless otherwise indicated, it is intended that
energy, between the surface of the specimen on which the
all reagents shall conform to the specifications of the Commit-
radiantenergyisincidentandthesurfaceofthespecimenfrom
tee onAnalytical Reagents of theAmerican Chemical Society,
which it is emergent.
where such specifications are available. Other grades may be
3.2.1.1 Discussion—This distance does not include the
used, provided it is first ascertained that the reagent is of
thickness of the cell in which the specimen is contained.
sufficiently high purity to permit its use without lessening the
3.2.2 concentration, c, n—the quantity of absorbing sub-
accuracy of the determination.
stance in grams per litre.
7.2 Purity of Water—Unlessotherwiseindicated,references
towatershallbeunderstoodtomeanreagentwaterconforming
4. Summary of Test Method
to Specification D1193D1193, Type III.
4.1 The ultraviolet absorbance of a liquid is determined by
7.3 Solvents:
measuring the absorption spectrum of the undiluted liquid in a
7.3.1 Isooctane—(Warning—Extremely flammable, harm-
cell of known path length under specified conditions.
ful if inhaled.), for use as the preferred spectroscopic solvent.
4.2 The ultraviolet absorptivity of a solid or a liquid is
7.3.2 Technical isooctane is a satisfactory base stock for the
determined by measuring the absorbance, at specified wave-
preparation of spectroscopic solvent. Allow about 4 or 5 L of
lengths, of a solution of the liquid or solid at known concen-
this material to percolate through a column of activated silica
tration in a cell of known path length.
gel 50 to 75 mm (2 to 3 in.) in diameter and 0.6 to 0.9 m (2 to
3 ft) in depth. Collect only the portion of the solvent that has
5. Significance and Use
anabsorbancelessthan0.05overtheentirespectralrangefrom
5.1 The absorbance of liquids and the absorptivity of liquid
240 to 300 nm in a 1-cm cell when compared to water in a
and solids at specified wavelengths in the ultraviolet are useful
1-cm cell.
in characterizing petroleum products.
7.3.3 Decahydronaphthalene —(Decalin)—(Warning—
Combustible, vapors harmful.), for use as the first alternative
6. Apparatus
spectroscopic solvent.
6.1 Spectrophotometer, equipped to handle liquid samples
7.3.4 The silica gel percolation described in 7.3.2 is also
incellshavingsamplepathlengthsupto10cmandcapableof
recommended for the preparation of decahydronaphthalene as
measuring absorbance in the spectral region from 220 to 400
a spectroscopic solvent.
nm with a spectral slit width of 2 nm or less. Wavelength
7.3.5 Some common, commercially available solvents of“
measurement shall be repeatable and known to be accurate
spectroscopic purity” are listed in Practices E169E169. One
within 60.2 nm or less as measured by the mercury emission
of them can be selected for use in absorptivity measurements
line at 313.16 nm. At the 0.4 absorbance level in the spectral
but only when indicated in Section 14.
region between 220 and 400 nm, absorbance measurements
shall be repeatable within 61.0%.
8. Sampling
6.2 For recommended methods of testing spectrophotom-
8.1 Precautionsmustbetakentoensurethatarepresentative
eters to be used in this test method, refer to Practice
sampleisobtainedsinceultravioletabsorptionisverysensitive
E275E275.
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
described in 6.1.
6.4 Measurements requiring the use of cells having sample
“ReagentChemicals,AmericanChemicalSocietySpecifications,”Am.Chemi-
path lengths less than 10 cm can be made on instruments
cal Soc., Washington, D.C. For suggestions on the testing of reagents not listed by
equipped to handle only these cells. It is desirable, but not
theAmericanChemicalSociety,see“ReagentChemicalsandStandards,”byJoseph
essential, that the instrument be automatic recording when an
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States
extended range of the spectrum must be examined. Manually Pharmacopeia.”
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
ϵ1
D2008–91 (1996)
be obtained from packaged products that have been protected
A = chart or absorbance reading of water-filled sample
C
from accidental contamination.
cell.
8.2 If the petroleum product to be tested is available as a
11.2 Calculate the absorbance per centimetre path length
bulk sample weighing more than 1 kg, a representative sample
that is equal to A/b, where b is the sample cell path length in
of approximately 1 kg shall be taken and made homogeneous.
centimetres.
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
12. Report
entire sample shall be taken and made homogeneous.
12.1 If the numerical value of the absorbance of an undi-
8.4 In no case shall a sample of a petroleum product be
luted liquid sample is reported, accompany it with a statement
considered representative if it weighs less than 100 g. How-
of the wavelength of measurement and the sample path length
ever, measurements may be made on samples weighing less
expressed in centimetres.
than 100 g if the origin, sampling procedure, and basis of
12.2 Ifthenumericalvalueoftheabsorbancepercentimetre
selectionofthesamplearerecordedandreportedaspartofthe
of an undiluted liquid sample is reported, it must accompany it
results of this test method.
with a statement of the wavelength of measurement.
ABSORBANCE OF UNDILUTED LIQUIDS
ABSORPTIVITY OF SOLIDS AND LIQUIDS
9. Procedure
13. Summary of Test Methods
9.1 Fill a 1.0-cm reference cell with water. Make sure the
13.1 The range of absorptivities for petroleum products can
cell windows are clean. Position the cells in the cell compart-
be very wide. Probably most absorptivities of interest would
ment of the spectrophotometer and obtain absorbance at the −4
fall in the range from 10 to 10 L/g·cm.
wavelengths of interest within the range from 220 to 400 nm.
13.2 Indeterminingabsorptivitiesitisnecessarytomeasure
This data gives a cell correction for the 1.0-cm cell. It can be
absorbances in the range from 0.1 to 1.0 for optimum results.
ignored at all wavelengths where the absorbance is be-
This is done by preparing solutions and selecting cells of
tween−0.01and+0.01.Afterthecellcorrectiondatahasbeen
sample path length to give absorbances in the 0.1 to 1.0 range.
determined, the cells shall be designated reference and sample
For an individual petroleum product the absorptivity may
cells and shall be maintained as such.
change so rapidly with wavelength that it is necessary to
9.2 Fill a 1.0-cm sample cell with undiluted liquid sample
prepare several solutions in order to cover the required
(aftercompleteremovalofwater)andobtaintheabsorbanceas
wavelength interval. Consideration must be given to the
described in 9.1.
selection of solvent, the selection of concentration levels, and
9.3 The absorbance-wavelength curve can be conveniently
theselectionofsamplepathslengthstoobtainoptimumresults.
obtained starting at the long wavelength end of the spectrum.
Take readings at successively shorter wavelengths until an
14. Selection of Solvent
absorbance greater than 1.0 is obtained.When using automatic
14.1 RefertotheapplicablesectionofPracticesE169E169
recordinginstruments(recommended)makethecellcorrection
forabriefdiscussionofsolventsforultravioletuse.Thechoice
scan and the sample scan on the same chart. In the longer
ofsolventisdictatedbythesolubilityofthepetroleumproduct
wavelength region of the spectrum, it may be desirable to use
and the transparency of the solvent in the region of interest.
longer path length cells than those recommended to obtain
14.2 Use isooctane unless restricted by solubility require-
readable absorbances. See the applicable paragraph of Prac-
ments.
tices E169E169. In the shorter wavelength region of the
14.3 Use decahydronaphthalene as the first alternative sol-
spectrum, absorbances can become too high for accurate
vent to be used if the sample is not sufficiently soluble in
measurement in the 0.1-cm cell. Record these values only as
isooctane.
greater than 1.0. If numerical values are required it is recom-
14.4 If neither isooctane nor decahydronaphthalene will
mended that absorptivity be measured rather than absorbance.
dissolve a sufficient quantity of sample to prepare the required
9.4 Repeat 9.1 and 9.2 using a 0.1-cm cell in place of the
solution,thenoneofthesolventslistedinthetableinPractices
1.0-cm cell (9.3). Record all measurements.
E169E169.As indicated in the table in Practices E169E169,
not all of these solvents are usable over the entire spectral
10.
range covered by this test method. For the purposes of this test
method a solvent shall be considered to have sufficient “spec-
11. Calculation
troscopic purity” when its absorbance in a 1-cm cell, using
11.1 C
...