ASTM D2008-91(2001)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 2001)
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 3. Terminology
1.1 This test method covers the measurement of the ultra- 3.1 Definitions—Definitions of terms and symbols relating
violet absorption of a variety of petroleum products. It covers toabsorptionspectroscopyinthistestmethodshallconformto
the absorbance of liquids or the absorptivity of liquids and Terminology E131. Terms of particular significance are the
solids, or both, at wavelengths in the region from 220 to 400 following:
nm of the spectrum. 3.1.1 radiant energy, n—energy transmitted as electromag-
1.2 Theuseofthistestmethodimpliesthattheconditionsof netic waves.
measurement—wavelength, solvent (if any), sample path 3.1.2 radiant power, P, n—the rate at which energy is
length, and sample concentration—are specified by reference transported in a beam of radiant energy.
to one of the examples of the application of this test method in 3.1.3 transmittance, T, n—the molecular property of a
the annexes or by a statement of other conditions of measure- substance that determines its transportability of radiant power,
ment. expressed by:
1.3 Examples of the application of this test method are the
P
T 5 (1)
determination of the absorbance of white mineral oil, the
P
o
absorptivity of refined petroleum wax, and the absorptivity of
where:
USP petrolatum.
P = the radiant power passing through the sample and
1.4 The values stated in SI units are to be regarded as the
P = the radiant power incident upon the sample.
o
standard. The values stated in fahrenheit, feet, and inches,
3.1.4 absorbance, A, n—the molecular property of a sub-
indicated in parentheses, are for information only.
stance that determines its ability to take up radiant power,
1.5 This standard does not purport to address all of the
expressed by:
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- A 5log ~1/T!52log T (2)
10 10
priate safety and health practices and determine the applica-
where T is the transmittance as defined in 3.1.3.
bility of regulatory limitations prior to use. For specific
3.1.4.1 Discussion—Absorbance expresses the excess ab-
warning statements, see 7.3.1, 7.3.3, and 13.4.
sorption over that of a specified reference or standard. It is
implied that compensation has been affected for reflectance
2. Referenced Documents
losses, solvent absorption losses, and refractive effects, if
2.1 ASTM Standards:
present, and that attenuation by scattering is small compared
D1193 Specification for Reagent Water
with attenuation by absorption.
E131 Terminology Relating to Molecular Spectroscopy
3.1.5 dilution factor, f, n—theproportionofsolventincrease
E169 Practices for General Techniques of Ultraviolet-
made to reduce the concentration and thus the absorbance of a
Visible Quantitative Analysis
solute, expressed by the ratio of the volume of the diluted
E275 Practice for Describing and Measuring Performance
solutiontothevolumeoforiginalsolutioncontainingthesame
of Ultraviolet, Visible, and Near-Infrared Spectrophotom-
quantity of solute as the diluted solution.
eters
3.1.6 absorptivity, a, n—thespecificpropertyofasubstance
toabsorbradiantpowerperunitsampleconcentrationandpath
length, expressed by:
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee
a 5 Af/bc (3)
D02.04on Hydrocarbon Analysis.
Current edition approved Oct. 15, 1991. Published December 1991. Originally
where:
published as D2008–62T. Last previous edition D2008–90.
A = the absorbance defined in 3.1.4,
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 03.06.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
D2008
fied, 1-cm sample path length cells are recommended. Suitable
f = the dilution factor defined in 3.1.5,
procedures for testing and cleaning cells are described in
b = sample cell path length, and
Practice E275.
c = the quantity of absorbing substance contained in a
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. 4
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 D1193, 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
240 to 300 nm in a 1-cm cell when compared to water in a
5.1 The absorbance of liquids and the absorptivity of liquid
1-cm cell.
and solids at specified wavelengths in the ultraviolet are useful
7.3.3 Decahydronaphthalene —(Decalin)—(Warning—
in characterizing petroleum products.
Combustible, vapors harmful.), for use as the first alternative
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 400
7.3.5 Some common, commercially available solvents of“
nm with a spectral slit width of 2 nm or less. Wavelength
spectroscopicpurity”arelistedinPracticesE169.Oneofthem
measurement shall be repeatable and known to be accurate
can be selected for use in absorptivity measurements but only
within 60.2 nm or less as measured by the mercury emission
when indicated in Section 13.
line at 313.16 nm. At the 0.4 absorbance level in the spectral
region between 220 and 400 nm, absorbance measurements
8. Sampling
shall be repeatable within 61.0%.
6.2 For recommended methods of testing spectrophotom- 8.1 Precautionsmustbetakentoensurethatarepresentative
eters to be used in this test method, refer to Practice E275.
sampleisobtainedsinceultravioletabsorptionisverysensitive
6.3 An instrument is considered suitable when it can be
to small amounts of extraneous material contaminating the
operated in a manner to give test results equivalent to those
sample through careless handling. If possible, samples should
described in 6.1.
be obtained from packaged products that have been protected
6.4 Measurements requiring the use of cells having sample
from accidental contamination.
path lengths less than 10 cm can be made on instruments
8.2 If the petroleum product to be tested is available as a
equipped to handle only these cells. It is desirable, but not
bulk sample weighing more than 1 kg, a representative sample
essential, that the instrument be automatic recording when an
of approximately 1 kg shall be taken and made homogeneous.
extended range of the spectrum must be examined. Manually
8.3 If the petroleum product to be tested is available as a
operated spectrometers are suitable for obtaining absorbance
bulk sample weighing less than 1 kg but more than 100 g, the
readings at specified analytical wavelengths. If measurements
entire sample shall be taken and made homogeneous.
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.
“ReagentChemicals,AmericanChemicalSocietySpecifications,”Am.Chemi-
6.5 One or more pairs of fused silica cells having sample
cal Soc., Washington, D.C. For suggestions on the testing of reagents not listed by
pathlengthsintherangefrom0.1000to10.00cmarerequired.
theAmericanChemicalSociety,see“ReagentChemicalsandStandards,”byJoseph
Sample path lengths must be known to within 60.5% of
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States
nominal sample path length or better. Unless otherwise speci- Pharmacopeia.”
D2008
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 be-
prepare several solutions in order to cover the required
tween−0.01and+0.01.Afterthecellcorrectiondatahasbeen
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 Solution Concentration
A = chart or absorbance reading of water-filled sample
C
cell.
14.1 Select an initial concentration of the sample high
10.2 Calculate the absorbance per centimetre path length
enough to provide measurab
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