1、Designation: D 2008 91 (Reapproved 2006)An American National StandardStandard Test Method forUltraviolet Absorbance and Absorptivity of PetroleumProducts1This standard is issued under the fixed designation D 2008; the number immediately following the designation indicates the year oforiginal adoptio
2、n or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement of the ultra-violet absorption of
3、a variety of petroleum products. It coversthe absorbance of liquids or the absorptivity of liquids andsolids, or both, at wavelengths in the region from 220 to400 nm of the spectrum.1.2 The use of this test method implies that the conditions ofmeasurementwavelength, solvent (if any), sample pathleng
4、th, and sample concentrationare specified by referenceto one of the examples of the application of this test method inthe annexes or by a statement of other conditions of measure-ment.1.3 Examples of the application of this test method are thedetermination of the absorbance of white mineral oil, the
5、absorptivity of refined petroleum wax, and the absorptivity ofUSP petrolatum.1.4 The values stated in SI units are to be regarded as thestandard. The values stated in fahrenheit, feet, and inches,indicated in parentheses, are for information only.1.5 This standard does not purport to address all of
6、thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specificwarning statements, see 7.3.1, 7.3.3, and 13.4.2. Refer
7、enced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE 131 Terminology Relating to Molecular SpectroscopyE 169 Practices for General Techniques of Ultraviolet-Visible Quantitative AnalysisE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near-Inf
8、rared Spectrophotom-eters3. Terminology3.1 DefinitionsDefinitions of terms and symbols relatingto absorption spectroscopy in this test method shall conform toTerminology E 131. Terms of particular significance are thefollowing:3.1.1 radiant energy, nenergy transmitted as electromag-netic waves.3.1.2
9、 radiant power, P, nthe rate at which energy istransported in a beam of radiant energy.3.1.3 transmittance, T, nthe molecular property of asubstance that determines its transportability of radiant power,expressed by:T 5PPo(1)where:P = the radiant power passing through the sample andPo= the radiant p
10、ower incident upon the sample.3.1.4 absorbance, A, nthe molecular property of a sub-stance that determines its ability to take up radiant power,expressed by:A 5 log101/T! 52log10T (2)where T is the transmittance as defined in 3.1.3.3.1.4.1 DiscussionAbsorbance expresses the excess ab-sorption over t
11、hat of a specified reference or standard. It isimplied that compensation has been affected for reflectancelosses, solvent absorption losses, and refractive effects, ifpresent, and that attenuation by scattering is small comparedwith attenuation by absorption.3.1.5 dilution factor, f, nthe proportion
12、 of solvent increasemade to reduce the concentration and thus the absorbance of asolute, expressed by the ratio of the volume of the dilutedsolution to the volume of original solution containing the samequantity of solute as the diluted solution.3.1.6 absorptivity, a, nthe specific property of a sub
13、stanceto absorb radiant power per unit sample concentration and pathlength, expressed by:1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.04 on Hydrocarbon Analysis.Current edition approved May 1
14、, 2006. Published June 2006. Originallyapproved in 1962. Last previous edition approved in 2001 as D 2008 91 (2001).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to
15、the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a 5 Af/bc (3)where:A = the absorbance defined in 3.1.4,f = the dilution factor defined in 3.1.5,b = sample cell path length, andc
16、= the quantity of absorbing substance contained in avolume of solvent.3.2 Definitions of Terms Specific to This Standard:3.2.1 sample cell pathlength, b, nthe distance in centime-tres, measured in the direction of propagation of the beam ofradiant energy, between the surface of the specimen on which
17、the radiant energy is incident and the surface of the specimenfrom which it is emergent.3.2.1.1 DiscussionThis distance does not include thethickness of the cell in which the specimen is contained.3.2.2 concentration, c, nthe quantity of absorbing sub-stance in grams per litre.4. Summary of Test Met
18、hod4.1 The ultraviolet absorbance of a liquid is determined bymeasuring the absorption spectrum of the undiluted liquid in acell of known path length under specified conditions.4.2 The ultraviolet absorptivity of a solid or a liquid isdetermined by measuring the absorbance, at specified wave-lengths
19、, of a solution of the liquid or solid at known concen-tration in a cell of known path length.5. Significance and Use5.1 The absorbance of liquids and the absorptivity of liquidand solids at specified wavelengths in the ultraviolet are usefulin characterizing petroleum products.6. Apparatus6.1 Spect
20、rophotometer, equipped to handle liquid samplesin cells having sample path lengths up to 10 cm and capable ofmeasuring absorbance in the spectral region from 220 to400 nm with a spectral slit width of 2 nm or less. Wavelengthmeasurement shall be repeatable and known to be accuratewithin 60.2 nm or l
21、ess as measured by the mercury emissionline at 313.16 nm. At the 0.4 absorbance level in the spectralregion between 220 and 400 nm, absorbance measurementsshall be repeatable within 61.0 %.6.2 For recommended methods of testing spectrophotom-eters to be used in this test method, refer to Practice E
22、275.6.3 An instrument is considered suitable when it can beoperated in a manner to give test results equivalent to thosedescribed in 6.1.6.4 Measurements requiring the use of cells having samplepath lengths less than 10 cm can be made on instrumentsequipped to handle only these cells. It is desirabl
23、e, but notessential, that the instrument be automatic recording when anextended range of the spectrum must be examined. Manuallyoperated spectrometers are suitable for obtaining absorbancereadings at specified analytical wavelengths. If measurementsare to be made at temperatures higher than room tem
24、perature,the spectrophotometer must be provided with a means formaintaining cells at the selected test temperature.6.5 One or more pairs of fused silica cells having samplepath lengths in the range from 0.1000 to 10.00 cm are required.Sample path lengths must be known to within 60.5 % ofnominal samp
25、le path length or better. Unless otherwise speci-fied, 1-cm sample path length cells are recommended. Suitableprocedures for testing and cleaning cells are described inPractice E 275.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise in
26、dicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.3Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to
27、permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type III.7.3 Solvents:7.3.1 Isooctane(WarningExtremely flammable, harm-ful if inhaled.), fo
28、r use as the preferred spectroscopic solvent.7.3.2 Technical isooctane is a satisfactory base stock for thepreparation of spectroscopic solvent. Allow about 4 or 5 L ofthis material to percolate through a column of activated silicagel 50 to 75 mm (2 to 3 in.) in diameter and 0.6 to 0.9 m (2 to3 ft)
29、in depth. Collect only the portion of the solvent that hasan absorbance less than 0.05 over the entire spectral range from240 to 300 nm in a 1-cm cell when compared to water in a1-cm cell.7.3.3 Decahydronaphthalene (Decalin)(WarningCombustible, vapors harmful.), for use as the first alternativespect
30、roscopic solvent.7.3.4 The silica gel percolation described in 7.3.2 is alsorecommended for the preparation of decahydronaphthalene asa spectroscopic solvent.7.3.5 Some common, commercially available solvents of“spectroscopic purity” are listed in Practices E 169. One ofthem can be selected for use
31、in absorptivity measurements butonly when indicated in Section 13.8. Sampling8.1 Precautions must be taken to ensure that a representativesample is obtained since ultraviolet absorption is very sensitiveto small amounts of extraneous material contaminating thesample through careless handling. If pos
32、sible, samples shouldbe obtained from packaged products that have been protectedfrom accidental contamination.8.2 If the petroleum product to be tested is available as abulk sample weighing more than 1 kg, a representative sampleof approximately 1 kg shall be taken and made homogeneous.8.3 If the pe
33、troleum product to be tested is available as abulk sample weighing less than 1 kg but more than 100 g, theentire sample shall be taken and made homogeneous.3“Reagent Chemicals,American Chemical Society Specifications,”Am. Chemi-cal Soc., Washington, D.C. For suggestions on the testing of reagents no
34、t listed bytheAmerican Chemical Society, see “Reagent Chemicals and Standards,” by JosephRosin, D. Van Nostrand Co., Inc., New York, NY, and the “United StatesPharmacopeia.”D 2008 91 (2006)28.4 In no case shall a sample of a petroleum product beconsidered representative if it weighs less than 100 g.
35、 How-ever, measurements may be made on samples weighing lessthan 100 g if the origin, sampling procedure, and basis ofselection of the sample are recorded and reported as part of theresults of this test method.ABSORBANCE OF UNDILUTED LIQUIDS9. Procedure9.1 Fill a 1.0-cm reference cell with water. Ma
36、ke sure thecell windows are clean. Position the cells in the cell compart-ment of the spectrophotometer and obtain absorbance at thewavelengths of interest within the range from 220 to 400 nm.This data gives a cell correction for the 1.0-cm cell. It can beignored at all wavelengths where the absorba
37、nce is between0.01 and +0.01. After the cell correction data has beendetermined, the cells shall be designated reference and samplecells 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 asdescribed i
38、n 9.1.9.3 The absorbance-wavelength curve can be convenientlyobtained starting at the long wavelength end of the spectrum.Take readings at successively shorter wavelengths until anabsorbance greater than 1.0 is obtained. When using automaticrecording instruments (recommended) make the cell correctio
39、nscan and the sample scan on the same chart. In the longerwavelength region of the spectrum, it may be desirable to uselonger path length cells than those recommended to obtainreadable absorbances. See the applicable paragraph of Prac-tices E 169. In the shorter wavelength region of the spectrum,abs
40、orbances can become too high for accurate measurement inthe 0.1-cm cell. Record these values only as greater than 1.0. Ifnumerical values are required it is recommended that absorp-tivity be measured rather than absorbance.9.4 Repeat 9.1 and 9.2 using a 0.1-cm cell in place of the1.0-cm cell (9.3).
41、Record all measurements.10. Calculation10.1 Calculate the absorbance of an undiluted liquid sampleat each analytical wavelength as follows:A 5 AL2 AC(4)where:A = absorbance of undiluted liquid sample,AL= chart or absorbance reading of sample-filled samplecell, andAC= chart or absorbance reading of w
42、ater-filled samplecell.10.2 Calculate the absorbance per centimetre path lengththat is equal to A/b, where b is the sample cell path length incentimetres.11. Report11.1 If the numerical value of the absorbance of an undi-luted liquid sample is reported, accompany it with a statementof the wavelength
43、 of measurement and the sample path lengthexpressed in centimetres.11.2 If the numerical value of the absorbance per centimetreof an undiluted liquid sample is reported, it must accompany itwith a statement of the wavelength of measurement.ABSORPTIVITY OF SOLIDS AND LIQUIDS12. Summary of Test Method
44、s12.1 The range of absorptivities for petroleum products canbe very wide. Probably most absorptivities of interest wouldfall in the range from 104to 10 L/gcm.12.2 In determining absorptivities it is necessary to measureabsorbances in the range from 0.1 to 1.0 for optimum results.This is done by prep
45、aring solutions and selecting cells ofsample path length to give absorbances in the 0.1 to 1.0 range.For an individual petroleum product the absorptivity maychange so rapidly with wavelength that it is necessary toprepare several solutions in order to cover the requiredwavelength interval. Considera
46、tion must be given to theselection of solvent, the selection of concentration levels, andthe selection of sample paths lengths to obtain optimum results.13. Selection of Solvent13.1 Refer to the applicable section of Practices E 169 for abrief discussion of solvents for ultraviolet use. The choice o
47、fsolvent is dictated by the solubility of the petroleum productand the transparency of the solvent in the region of interest.13.2 Use isooctane unless restricted by solubility require-ments.13.3 Use decahydronaphthalene as the first alternative sol-vent to be used if the sample is not sufficiently s
48、oluble inisooctane.13.4 If neither isooctane nor decahydronaphthalene willdissolve a sufficient quantity of sample to prepare the requiredsolution, then one of the solvents listed in the table in PracticesE 169. As indicated in the table in Practices E 169, not all ofthese solvents are usable over t
49、he entire spectral range coveredby this test method. For the purposes of this test method asolvent shall be considered to have sufficient “spectroscopicpurity” when its absorbance in a 1-cm cell, using reagent waterin a 1-cm cell as a reference, is less than 0.05 at all wavelengthswhere a sample absorbance is to be measured in a 1-cm cell.Cyclohexane (WarningExtremely flammable. Harmful ifinhaled.), carbon tetrachloride, chloroform (WarningCarbon tetrachloride and chloroform can be fatal if swallowed.Harmful if inhaled. Can produce toxic vapors if burned.), a
