1、Designation: E387 04 (Reapproved 2009)Standard Test Method forEstimating Stray Radiant Power Ratio of DispersiveSpectrophotometers by the Opaque Filter Method1This standard is issued under the fixed designation E387; the number immediately following the designation indicates the year oforiginal adop
2、tion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 Stray radiant power (SRP) can be a significant source oferror in spectro
3、photometric measurements, and the danger thatsuch error exists is enhanced because its presence often is notsuspected (1-4).2This test method affords an estimate of therelative radiant power, that is, the Stray Radiant Power Ratio(SRPR), at wavelengths remote from those of the nominalbandpass transm
4、itted through the monochromator of an absorp-tion spectrophotometer. Test-filter materials are described thatdiscriminate between the desired wavelengths and those thatcontribute most to SRP for conventional commercial spectro-photometers used in the ultraviolet, the visible, the nearinfrared, and t
5、he mid-infrared ranges. These procedures applyto instruments of conventional design, with usual sources,detectors, including array detectors, and optical arrangements.The vacuum ultraviolet and the far infrared present specialproblems that are not discussed herein.NOTE 1Research (3) has shown that p
6、articular care must be exercisedin testing grating spectrophotometers that use moderately narrow band-pass SRP-blocking filters. Accurate calibration of the wavelength scale iscritical when testing such instruments. Refer to Practice E275.1.2 These procedures are neither all-inclusive nor infallible
7、.Because of the nature of readily available filter materials, witha few exceptions, the procedures are insensitive to SRP of veryshort wavelengths in the ultraviolet, or of lower frequencies inthe infrared. Sharp cutoff longpass filters are available fortesting for shorter wavelength SRP in the visi
8、ble and the nearinfrared, and sharp cutoff shortpass filters are available fortesting at longer visible wavelengths. The procedures are notnecessarily valid for “spike” SRP nor for “nearby SRP.” (SeeAnnexes for general discussion and definitions of these terms.)However, they are adequate in most cas
9、es and for typicalapplications. They do cover instruments using prisms orgratings in either single or double monochromators, and withsingle and double beam instruments.NOTE 2Instruments with array detectors are inherently prone tohaving higher levels of SRP. See Annexes for the use of filters to red
10、uceSRP.1.3 The proportion of SRP(that is, SRPR) encountered witha well-designed monochromator, used in a favorable spectralregion, typically is 0.1 % transmittance or better, and with adouble monochromator it can be less than 1310-6, even with abroadband continuum source. Under these conditions, it
11、maybe difficult to do more than determine that it falls below acertain level. Because SRP test filters always absorb some ofthe SRP, and may absorb an appreciable amount if the specifiedmeasurement wavelength is not very close to the cutoffwavelength of the SRP filter, this test method underestimate
12、sthe true SRPR. However, actual measurement sometimesrequires special techniques and instrument operating condi-tions that are not typical of those occurring during use. Whenabsorption measurements with continuum sources are beingmade, it can be that, owing to the effect of slit width on SRPin a dou
13、ble monochromator, these test procedures may offset insome degree the effect of absorption by the SRP filter; that is,because larger slit widths than normal might be used to admitenough energy to the monochromator to permit evaluation ofthe SRP, the stray proportion indicated could be greater thanwo
14、uld normally be encountered in use (but the net effect is stillmore likely to be an underestimation of the true SRPR).Whether the indicated SRPR equals or differs from thenormal-use value depends on how much the SRP is increasedwith the wider slits and on how much of the SRP is absorbedby the SRP fi
15、lter. What must be accepted is that the numericalvalue obtained for the SRPR is a characteristic of the particulartest conditions as well as of the performance of the instrumentin normal use. It is an indication of whether high absorbancemeasurements of a sample are more or less likely to be biasedb
16、y SRP in the neighborhood of the analytical wavelengthwhere the sample test determination is made.1.4 The principal reason for a test procedure that is notexactly representative of normal operation is that the effects ofSRP are “magnified” in sample measurements at high absor-bance. It might be nece
17、ssary to increase sensitivity in some1This test method is under the jurisdiction of ASTM Committee E13 onMolecular Spectroscopy and Separation Science and is the direct responsibility ofSubcommittee E13.01 on Ultra-Violet, Visible, and Luminescence Spectroscopy.Current edition approved Oct. 1, 2009.
18、 Published December 2009. Originallyapproved in 1969. Last previous edition approved in 2004 as E387 04. DOI:10.1520/E0387-04R09.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con
19、shohocken, PA 19428-2959, United States.way during the test in order to evaluate the SRP adequately.This can be accomplished by increasing slit width and soobtaining sufficient energy to allow meaningful measurementof the SRP after the monochromatic energy has been removedby the SRP filter. However,
20、 some instruments automaticallyincrease sensitivity by increasing dynode voltages of thephotomultiplier detector. This is particularly true of high-enddouble monochromator instruments in their ultraviolet andvisible ranges. A further reason for increasing energy orsensitivity can be that many instru
21、ments have only absorbancescales, which obviously do not extend to zero transmittance.Even a SRP-proportion as large as 1 % may fall outside themeasurement range.NOTE 3Instruments that have built-in optical attenuators to balancesample absorption may make relatively inaccurate measurements below10 %
22、 transmittance, because of poor attenuator linearity. The spectropho-tometer manufacturer should be consulted on how to calibrate transmit-tance of the attenuator at such lower level of transmittance.1.5 High accuracy in SRP measurement is not alwaysrequired; a measurement reliable within 10 or 20 %
23、 may besufficient. However, regulatory requirements, or the needs of aparticular analysis, may require much higher accuracy. Pains-taking measurements are always desirable.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7
24、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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Docum
25、ents2.1 ASTM Standards:3E131 Terminology Relating to Molecular SpectroscopyE275 Practice for Describing and Measuring Performanceof Ultraviolet and Visible Spectrophotometers3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology E131.3.2 Definition
26、s of Terms Specific to This Standard:3.2.1 absorption edgeof a sharp cutoff filter: the wave-length interval over which the transmittance changes rapidlyfrom high to very low (that is, less than 0.01 %).3.2.1.1 DiscussionThe bandpass transmittance filters usedin some spectrophotometers to reduce SRP
27、 within their band-pass are considered to have both a short wavelength and a longwavelength absorption edge. The rate of change of transmit-tance in the absorption edge may not be as fast as for sharpcutoff filters.3.2.2 blocked-beam spectruma spectrum recorded with anopaque (that is, transmittance
28、less than 0.001 %) object in thesample beam; the level of opacity must exist over the range ofwavelengths where the photodetector is sensitive.3.2.3 corrected spectrumthe transmittance (absorbance)spectrum of a SRP filter after the measured spectrum has beenadjusted for the offset of the open-beam s
29、pectrum and (trans-mittance mode) of the blocked-beam spectrum.3.2.4 cutoff wavelength (wavenumber)the wavelength(wavenumber) at which the transmittance of a sharp cutofffilter is 0.01 %.3.2.5 filter, longpassan optical filter having high transmit-tance at wavelengths longer than its absorption edge
30、.3.2.6 filter, moderately narrow bandpass SRP-blockingafilter used to reduce remote SRP by transmitting efficientlyover a limited band of wavelengths within a nominal wave-length range of a spectrophotometer.3.2.7 filter, narrow blocking-bandan optical filter havinghigh transmittance at shorter and
31、at longer wavelengths than anarrow band within which the transmittance is very low (thatis, less than 0.001 %).3.2.8 filter, narrow transmission bandan optical filterhaving very low transmittance at shorter and longer wave-lengths than those of a narrow band within which sometransmittances exceed 10
32、 %.3.2.9 filter, neutral (also, neutral density: ND)a filter thatattenuates the radiant power reaching the detector by the samefactor at all wavelengths within a prescribed wavelengthregion.3.2.10 filter, opaquean optical filter that has transmit-tances less than 0.01 % over a specified band of wave
33、lengths.3.2.11 filter, sharp cutoffan optical filter that has a veryrapid transition in wavelengths (wavenumbers) from a state ofhigh transmittance to a state of very low transmittance (that is,less than 0.001 %) and that continues in that low transmittancestate to at least the end of the spectral r
34、egion that is beingtested.3.2.12 filter, shortpassa sharp cutoff filter having a hightransmittance at wavelengths shorter than its absorption edge.3.2.13 filter, SRPa test filter for determining SRPR.3.2.14 limiting transmittance (absorbance)the minimumtransmittance (maximum absorbance) of the SRP f
35、ilter that isobserved in the SRPR test; the transmittance (absorbance)indicated when the spectral curve levels off or starts to increase(decrease).3.2.15 near SRPstray radiant power of wavelengths(wavenumbers) within several spectral bandwidths from thespectral position of the spectrophotometer (3).
36、3.2.16 open-beam spectrumthe spectrum recorded withno attenuating medium in the sample beam.3.2.17 passbandof a monochromator, the band of wave-lengths around the spectral position of the monochromator thatare preferentially transmitted; of a sharp cutoff filter: thewavelength region of high transmi
37、ttance of the filter.3.2.18 remote SRPstray radiant power of wavelengths(wavenumbers) more than several spectral bandwidths fromthe spectral position of the spectrophotometer (3).3.2.19 specified wavelength (wavenumber)the wave-length (wavenumber) specified by the manufacturer of a3For referenced AS
38、TM 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.E387 04 (2009)2spectrophotometer (or by the spectroscopist) as that at whichthe
39、 SRPR is stated (or measured).3.2.20 SRPstray radiant power.3.2.21 SRPRstray radiant power ratio.3.2.22 stray lightthe term used in much technical andmanufacturers literature to represent either SRP or SRPR.4. Summary of Test Method4.1 The following test procedures are written for spectro-photometer
40、s that have provision for recording (that is, forcollecting and storing) spectral data digitally. Processing maybe by built-in programs or in a separate computer. Data may becollected in either the transmittance or the absorbance mode.The data sets to be collected are: (1) open-beam spectrum:100 % t
41、ransmittance or zero absorbance; (2) blocked-beamspectrum: 0 %T, transmittance mode only; and (3) SRP filterspectra. Filter spectra are assumed to have been corrected inthe following discussion.NOTE 4For instruments that lack digital recording capability, tradi-tional methods of correcting open-beam
42、 and blocked-beam spectra mustbe applied.4.2 Specified Wavelength Method:4.2.1 Manufacturers typically specify stray light, meaningSRPR, at one or more wavelengths. Where sharp cutoff SRPfilters are used, the specified wavelengths should be near, but alittle toward the lower transmittance side, of t
43、he cutoff wave-length of the chosen SRP filter. Other wavelengths can bespecified by the spectroscopist, according to the need ofparticular analyses, using sharp cutoff filters listed in Table 1 orsharp cutoff filters that are now available from various manu-facturers and distributors.4Cutoff wavele
44、ngths of some solu-tion filters for the ultraviolet and cutoff wavenumbers of somesolid filters for the mid-infrared are given in Table 1. Wherenarrow blocking-band filters are used, the filters themselvesdefine the specified wavelength.NOTE 5In some cases, manufacturers state SRPR at a wavelengthwe
45、ll removed from the cutoff wavelength of the cited SRP filter. This canresult in an appreciable underestimate of the true SRPR at the specifiedwavelength. Users are cautioned to note carefully the specific informationprovided about the test used to determine the stated SRPR.4.2.2 The SRP filter mate
46、rials are selected for sharp cutoff,freedom from fluorescence, and sufficiently high absorptionthat their transmittance in the stop band can be neglected.4Sources of solution filters in sealed cuvettes, interference filters, glass filters,neutral density filters, and materials for mid-infrared filte
47、rs can be found in AnnualBuyers Guides of several scientific organizations, in advertisements in trade journalsthat serve optical and spectroscopic disciplines, in catalogs of suppliers of opticaland spectroscopic materials, and by searching the Internet, using concatenations ofselected terms: filte
48、r, optical, stray light, color, absorbing, solution (or liquid)cuvette, spectrophotometer cell, interference, cutoff, sharp cut, longpass, shortpass,bandpass, neutral density; for mid infrared materials: infrared cells, infraredcrystals, infrared accessories, fused silica.TABLE 1 Filters for Tests f
49、or Stray Radiant Power RatioCutoff Wavelength,WavenumberATransmittance,B80 %Wavelength or WavenumberFilterCSourceDDetectorEA. Sharp Cutoff Types173.5 nm 183 nm 0.01 cm H2OFUV UV183.5 nm 195 nm 1.00 cm H2OFUV UV200 nm 214 nm 1.00 cm 12 g/L KCl aqueousFUV UV223 nm 232 nm 1.00 cm 10 g/L NaBr aqueousFUV UV259 nm 271 nm 1.00 cm 10 g/L NaI aqueous UV UV259 nm 271 nm 1.00 cm 10 g/L KI aqueous UV UV325 nm 339 nm 1.00 cm acetone UV UV385 nm 420 nm 1.00 cm 50 g/L NaNO2aqueous VIS UV1200 cm-12800 cm-12.0-mm fused silicaG(2) IR IR800 cm-11760 cm-16 mm LiF IR IR600 c
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