1、Designation: D2008 12Standard Test Method forUltraviolet Absorbance and Absorptivity of PetroleumProducts1This standard is issued under the fixed designation D2008; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the measurement of the ultra-violet absorption of a variety of petroleum products. It coversthe abs
3、orbance 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 pathlength, and sample concentrationare specified by refe
4、renceto 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 theabsorptivity of refined petroleum wax, and the absorptivity ofUSP petrolatum.1.4 The values stated in SI u
5、nits are to be regarded as thestandard. The values stated in Fahrenheit, feet, and inches,indicated in parentheses, are for information only.1.5 WarningMercury has been designated by EPA andmany state agencies as a hazardous material that can causecentral nervous system, kidney, and liver damage. Me
6、rcury, orits vapor, may be hazardous to health and corrosive tomaterials. Caution should be taken when handling mercury andmercury-containing products. See the applicable product Ma-terial Safety Data Sheet (MSDS) for details and EPAs website(http:/www.epa.gov/mercury/faq.htm) for additional informa
7、-tion. Users should be aware that selling mercury or mercury-containing products, or both, in your state may be prohibited bystate law.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to est
8、ablish 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. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE131 Terminology Relating to Molecular S
9、pectroscopyE169 Practices for GeneralTechniques of Ultraviolet-VisibleQuantitative AnalysisE275 Practice for Describing and Measuring Performance ofUltraviolet and Visible Spectrophotometers3. Terminology3.1 Definitions of terms and symbols relating to absorptionspectroscopy in this test method shal
10、l conform to TerminologyE131. Terms of particular significance are the following:3.2 Definitions:3.2.1 radiant energy, nenergy transmitted as electromag-netic waves.3.2.2 radiant power, P, nthe rate at which energy istransported in a beam of radiant energy.3.2.3 transmittance, T, nthe molecular prop
11、erty of a sub-stance that determines its transportability of radiant power,expressed by:T 5PPo(1)where:P = the radiant power passing through the sample andPo= the radiant power incident upon the sample.3.2.4 absorbance, A, nthe molecular property of a sub-stance that determines its ability to take u
12、p radiant power,expressed by:A 5 log101/T! 52log10T (2)where T is the transmittance as defined in 3.2.3.3.2.4.1 DiscussionAbsorbance expresses the excess ab-sorption over that of a specified reference or standard. It isimplied that compensation has been affected for reflectance1This test method is u
13、nder the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.04.0F on Absorption Spectroscopic Methods.Current edition approved June 1, 2012. Published October 2012. Originallyapproved in 1962. Last previous edition approved in 2
14、009 as D200809. DOI:10.1520/D2008-12.2For 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 the standards Document Summary page onthe ASTM website.*A Summary of Changes se
15、ction appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1losses, solvent absorption losses, and refractive effects, ifpresent, and that attenuation by scattering is small comparedwith attenuation by abs
16、orption.3.2.5 dilution factor, f, nthe proportion 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.3.2.6
17、 absorptivity, a, nthe specific property of a substanceto absorb radiant power per unit sample concentration and pathlength, expressed by:a 5 Af/bc (3)where:A = the absorbance defined in 3.2.4,f = the dilution factor defined in 3.2.5,b = sample cell path length, andc = the quantity of absorbing subs
18、tance contained in avolume of solvent.3.3 Definitions of Terms Specific to This Standard:3.3.1 sample cell pathlength, b, nthe distance incentimetres, measured in the direction of propagation of thebeam of radiant energy, between the surface of the specimen onwhich the radiant energy is incident and
19、 the surface of thespecimen from which it is emergent.3.3.1.1 DiscussionThis distance does not include thethickness of the cell in which the specimen is contained.3.3.2 concentration, c, nthe quantity of absorbing sub-stance in grams per litre.4. Summary of Test Method4.1 The ultraviolet absorbance
20、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 specifiedwavelengths, of a solution of the liquid or sol
21、id at knownconcentration 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 Spectrophotometer, equipped to handle liqui
22、d samples incells 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 less as measured by the mercury emissio
23、nline at 313.16 nm or the absorption spectrum of either holmiumoxide glass at 287.5 nm or holmium oxide solution at 287.1nm. At the 0.4 absorbance level in the spectral region between220 and 400 nm, absorbance measurements shall be repeatablewithin 61.0 %.6.2 For recommended methods of testing spect
24、rophotom-eters to be used in this test method, refer to Practice E275.6.3 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
25、 on instrumentsequipped to handle only these cells. It is desirable, 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.
26、If measurementsare to be made at temperatures higher than room temperature,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
27、.Sample path lengths must be known to within 60.5 % ofnominal sample path length or better. Unless otherwisespecified, 1-cm sample path length cells are recommended.Suitable procedures for testing and cleaning cells are describedin Practice E275.7. Reagents and Materials7.1 Purity of ReagentsReagent
28、 grade chemicals shall beused in all tests. Unless otherwise indicated, 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
29、 ascertained that the reagent is ofsufficiently high purity to 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 D1193, Type III.7.3 Solvents:7.3.1 I
30、sooctane(WarningExtremely flammable, harm-ful if inhaled.), for 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
31、to 75 mm (2 to 3 in.) in diameter and 0.6 to 0.9 m (2 to3 ft) 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)(WarningCombus
32、tible, vapors harmful.), for use as the first alternativespectroscopic solvent.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for Labor
33、atoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D2008 1227.3.4 The silica gel percolation described in 7.3.2 is alsorecommended for the preparation of decahydronaphthalene asa spectrosco
34、pic solvent.7.3.5 Some common, commercially available solvents of“spectroscopic purity” are listed in Practices E169. One ofthem can be selected for use in absorptivity measurements butonly when indicated in Section 13.7.4 Holmium Oxide Glass or Holmium Oxide SolutionUsed to verify the wavelength ac
35、curacy of the spectrophotom-eter.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 possible, samples shouldbe obtained
36、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 petroleum product to be tested is a
37、vailable as abulk sample weighing less than 1 kg but more than 100 g, theentire sample shall be taken and made homogeneous.8.4 In no case shall a sample of a petroleum product beconsidered representative if it weighs less than 100 g.However, measurements may be made on samples weighingless than 100
38、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. Make sure thecell windows are clean. Position the cells in the cell com
39、part-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 absorbance is between0.01 and +0.01. After the cell correction data has been
40、determined, 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 in 9.1.9.3 The absorbance-wavelength curve can be convenientlyobtained
41、 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 correctionscan and the sample scan on the same chart. In the longerwavelength
42、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 E169. In the shorter wavelength region of the spectrum,absorbances can become too high for accurate measurement inthe 0.1-cm cel
43、l. 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, or a 0.5-cm cellwhen appropriate, in place of the 1.0-cm cell (9.3). Record allmeasurements.10. Calcula
44、tion10.1 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 water-filled sample cell.10.2 Calcul
45、ate 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 of measurement and the sample pat
46、h 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 Methods12.1 The range of absorptivities
47、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 preparing solutions and selecting cell
48、s 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. Consideration must be given to theselection
49、 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 E169 for abrief discussion of solvents for ultraviolet use. The choice ofsolvent 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.D2008 12313.3 Use decahydronaphthalene as the first alternative sol-vent to be used if the sample is not su
