1、Designation: E 387 04Standard Test Method forEstimating Stray Radiant Power Ratio of DispersiveSpectrophotometers by the Opaque Filter Method1This standard is issued under the fixed designation E 387; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、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 Stray radiant power (SRP) can be a significant source oferror in spectrophotometric mea
3、surements, 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 transmitted through t
4、he 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 the mid-infrared
5、 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 particular care
6、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 E 275.1.2 These procedures are neither all-inclusive nor infallible.Because of th
7、e 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 visible and the ne
8、arinfrared, 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 cases and for typ
9、icalapplications. 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 reduceSRP.1.3 The
10、 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 maybe difficu
11、lt 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 underestimatesthe true SRP
12、R. 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 double monochrom
13、ator, 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 thanwould normally
14、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 filter. What mu
15、st 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 biasedby SRP in the
16、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 necessary to incr
17、ease sensitivity in some1This method is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and is the direct responsibility of Subcommittee E13.01 on Ultravioletand Visible Spectroscopy.Current edition approved Feb. 1, 2004. Published March 2004. Originallyapproved in 1969. Last p
18、revious edition approved in 1995 as E 387 84 (1995)e1.2The 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 Conshohocken, PA 19428-2959, United States.way during the test in order to eva
19、luate 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, some instruments automaticallyincrease sensitivity by increasing dynode vo
20、ltages 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 instruments have only absorbancescales, which obviously do not extend to zero tra
21、nsmittance.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 % transmittance, because of poor attenuator linearity. The spectropho-tomete
22、r 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 % may besufficient. However, regulatory requirements, or the needs of aparti
23、cular analysis, may require much higher accuracy. Pains-taking measurements are always desirable.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 establish appro-priate safety and health
24、practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 131 Terminology Relating to Molecular SpectroscopyE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near Infrared Spectrophotom-eters3. Ter
25、minology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology E 131.3.2 Definitions 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 (tha
26、t is, less than 0.01 %).3.2.1.1 DiscussionThe bandpass transmittance filters usedin some spectrophotometers to reduce SRP 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
27、 as fast as for sharpcutoff filters.3.2.2 blocked-beam spectruma spectrum recorded with anopaque (that is, transmittance 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 transmit
28、tance (absorbance)spectrum of a SRP filter after the measured spectrum has beenadjusted for the offset of the open-beam spectrum 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
29、 0.01 %.3.2.5 filter, longpassan optical filter having high transmit-tance at wavelengths longer than its absorption edge.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
30、range of a spectrophotometer.3.2.7 filter, narrow blocking-bandan optical filter havinghigh transmittance at shorter and 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 l
31、ow transmittance at shorter and longer wave-lengths than those of a narrow band within which sometransmittances exceed 10 %.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 wavele
32、ngthregion.3.2.10 filter, opaquean optical filter that has transmit-tances less than 0.01 % over a specified band of wavelengths.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 transmit
33、tance (that is,less than 0.001 %) and that continues in that low transmittancestate to at least the end of the spectral region 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
34、for determining SRPR.3.2.14 limiting transmittance (absorbance)the minimumtransmittance (maximum absorbance) of the SRP filter 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 pow
35、er of wavelengths(wavenumbers) within several spectral bandwidths from thespectral position of the spectrophotometer (3).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 positio
36、n of the monochromator thatare preferentially transmitted; of a sharp cutoff filter: thewavelength region of high transmittance 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).
37、3.2.19 specified wavelength (wavenumber)the wave-length (wavenumber) specified by the manufacturer of a3For 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
38、 Document Summary page onthe ASTM website.E387042spectrophotometer (or by the spectroscopist) as that at whichthe 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
39、 either SRP or SRPR.4. Summary of Test Method4.1 The following test procedures are written for spectro-photometers 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
40、either the transmittance or the absorbance mode.The data sets to be collected are: (1) open-beam spectrum:100 % transmittance 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 disc
41、ussion.NOTE 4For instruments that lack digital recording capability, tradi-tional methods of correcting open-beam 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 SRP
42、filters are used, the specified wavelengths should be near, but alittle toward the lower transmittance side, of the 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
43、Table 1 orsharp cutoff filters that are now available from various manu-facturers and distributors.4Cutoff wavelengths 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
44、filters themselvesdefine the specified wavelength.NOTE 5In some cases, manufacturers state SRPR at a wavelengthwell 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 care
45、fully the specific informationprovided about the test used to determine the stated SRPR.4.2.2 The SRP filter materials 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 s
46、ealed cuvettes, interference filters, glass filters,neutral density filters, and materials for mid-infrared filters can be found in AnnualBuyers Guides of several scientific organizations, in advertisements in trade journalsthat serve optical and spectroscopic disciplines, in catalogs of suppliers o
47、f opticaland spectroscopic materials, and by searching the Internet, using concatenations ofselected terms: filter, optical, stray light, color, absorbing, solution (or liquid)cuvette, spectrophotometer cell, interference, cutoff, sharp cut, longpass, shortpass,bandpass, neutral density; for mid inf
48、rared materials: infrared cells, infraredcrystals, infrared accessories, fused silica.TABLE 1 Filters for Tests for Stray Radiant Power RatioCutoff Wavelength,WavenumberATransmittance,B80 %Wavelength or WavenumberFilterCSourceDDetectorEA. Sharp Cutoff Types173.5 nm 183 nm 0.01 cm H2OFUV UV183.5 nm 1
49、95 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 cm-11240 cm-16mmCaF2IR IR400 cm-11030 cm-16 mm NaF IR IR250 cm-1650 cm-16 mm NaCl IR IR200 cm-1420 cm-16 mm KBr IR IRB. Passband FiltersApproximate Stop Band600 to 660 nm. 1.00 cm 0.005 % (m
