1、Designation: E 958 93 (Reapproved 2005)Standard Practice forMeasuring Practical Spectral Bandwidth of Ultraviolet-Visible Spectrophotometers1This standard is issued under the fixed designation E 958; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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 practice describes a procedure for measuring thepractical spectral bandwidth of a s
3、pectrophotometer in thewavelength region of 185 to 820 nm. Practical spectralbandwidth is the spectral bandwidth of an instrument operatedat a given integration period and a given signal-to-noise ratio.1.2 This practice is applicable to instruments that utilizeservo-operated slits and maintain a con
4、stant period and aconstant signal-to-noise ratio as the wavelength is automati-cally scanned. It is also applicable to instruments that utilizefixed slits and maintain a constant servo loop gain by auto-matically varying gain or dynode voltage. In this latter case, thesignal-to-noise ratio varies wi
5、th wavelength. It can also be usedon instruments that utilize some combination of the twodesigns, as well as on those that vary the period during thescan. For digitized instruments, refer to the manufacturersmanual.1.3 This practice does not cover the measurement of limit-ing spectral bandwidth, def
6、ined as the minimum spectralbandwidth achievable under optimum experimental conditions.1.4 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
7、and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 131 Terminology Relating to Molecular SpectroscopyE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near-Infrared Spectrophotom-eters3. Terminology3.
8、1 Definitions:3.1.1 integration period, nthe time, in seconds, requiredfor the pen or other indicator to move 98.6 % of its maximumtravel in response to a step function.3.1.2 practical spectral bandwidth, designated by the sym-bol:Dl!pS/N(1)where:Dl = spectral bandwidth,p = integration period, andS/
9、N = signal-to-noise ratio measured at or near 100 % T.3.1.3 signal-to-noise ratio, nthe ratio of the signal, S,tothe noise, N, as indicated by the readout indicator. Therecommended measure of noise is the maximum peak-to-peakexcursion of the indicator averaged over a series of fivesuccessive interva
10、ls, each of duration ten times the integrationperiod. (This measure of noise is about five times the root-mean-square noise.)3.1.4 spectral bandwidth, nthe wavelength interval ofradiation leaving the exit slit of a monochromator measured athalf the peak detected radiant power. It is not synonymous w
11、ithspectral slit width, which is the product of the mechanical slitwidth and the reciprocal linear dispersion of the spectropho-tometer.4. Summary of Practice4.1 The pen period and signal-to-noise ratio are set at thedesired values when the instrument is operated with its normallight source and adju
12、sted to read close to 100 % T. Themechanical slit width, or the indicated spectral bandwidth,required to give the desired signal-to-noise ratio is recorded.The continuum source is replaced with a line emission source,such as a mercury lamp, and the apparent half-intensitybandwidth of an emission lin
13、e occurring in the wavelengthregion of interest is measured using the same slit width, or1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Chromatography and is the direct responsibility of SubcommitteeE13.01 on Ultra-Violet and Visible Spectroscopy.Current
14、edition approved April 1, 2005. Published April 2005. Originallyapproved in 1983. Last previous edition approved in 1999 as E 958 93 (1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volum
15、e information, refer to 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.indicated spectral bandwidth, as was used to establish thesignal-to-noise ratio with the continuum source.
16、5. Significance and Use5.1 This practice should be used by a person who developsan analytical method to ensure that the spectral bandwidthscited in the practice are actually the ones used.NOTE 1The method developer should establish the spectral band-widths that can be used to obtain satisfactory res
17、ults.5.2 This practice should be used to determine whether aspectral bandwidth specified in a method can be realized witha given spectrophotometer and thus whether the instrument issuitable for use in this application.5.3 This practice allows the user of a spectrophotometer todetermine the actual sp
18、ectral bandwidth of the instrumentunder a given set of conditions and to compare the result to thespectral bandwidth calculated from data given in the manufac-turers literature or indicated by the instrument.5.4 Instrument manufacturers can use this practice to mea-sure and describe the practical sp
19、ectral bandwidth of aninstrument over its entire wavelength operating range. Thispractice is highly prefered to the general practice of stating thelimiting or the theoretical spectral bandwidth at a singlewavelength.6. Test Materials and Apparatus6.1 Table 1 lists reference emission lines that may b
20、e usedfor measuring the spectral bandwidth of ultraviolet/visibleinstruments at the levels of resolution encountered in mostcommercial instruments.All of the lines listed have widths lessthan 0.02 nm, suitable for measuring spectral bandwidths ofgreater than 0.2 nm. The wavelengths of these lines in
21、nanometres are listed in the first column. Values refer tomeasurements in standard air (760 nm, 15C) except for thetwo lines below 200 nm. The wavelength for these lines referto a nitrogen atmosphere at 760 nm and 15C.6.1.1 The second column in Table 1 lists the emitter gas ofsix sources. Only sourc
22、es operating at low pressure should beused, as line broadening can introduce errors. The hydrogen,deuterium, and mercury lamps used to obtain these data wereBeckman lamps operated on Beckman spectrophotometerpower supplies. The other lamps are all of the “pencil-lamp”type.3A mercury vapor Pen-Ray la
23、mp4was used to obtain the3Suitable lamps are available from laboratory supply houses as well asmanufacturers, which include UVP, Inc., 5100 Walnut Grove Ave., P.O. Box 1501,San Gabriel, CA 91778-1501; Spectronics Corp., 956 Brush Hollow Rd., P.O. Box483, Westbury, NY 11590-0483; Jelight Co., Inc., 2
24、3052 Alcalde, Unit E, P.O. Box2632, Laguna Hills, CA 92653-2632; and BHK, Inc., 2885 Metropolitan Place,Pomona, CA 91767.TABLE 1 Emission Lines Useful for Measuring Spectral BandwidthReference Line,nmEmitter Intensity Nearest Neighbor, nm Separation, nm INeighbor/IReferenceWeak Neighbor, nm184.91 Hg
25、 8 194.17 9.26 0.13194.17 Hg 8 184.91 9.26 0.13 197.33205.29 Hg 4 202.70 2.59 0.08226.22 Hg 5 237.83 11.61 0.06 226.03253.65 Hg 10 . . . 253.48275.28 Hg 5 280.35 5.07 0.08289.36 Hg 6 296.73 7.37 0.42296.73 Hg 8 302.15 5.42 0.04318.77 He 5 294.51 24.26 0.06334.15 Hg 7 313.18 20.97 0.70341.79 Ne 5 344
26、.77 2.98 0.20359.35 Ne 5 352.05 7.30 0.14 360.02388.87 He 7 447.15 58.28 0.04404.66 Hg 8 407.78 3.12 0.04427.40 Kr 5 431.96 4.56 0.28 428.30435.95 Hg 9 407.78 28.17 0.02 435.75447.15 He 5 471.31 24.16 0.04471.31 He 4 492.19 20.88 0.25486.0 D2. . . .486.13 H26 492.87 6.74 0.03 485.66501.57 He 5 492.1
27、9 9.38 0.06546.07 Hg 8 577.12 31.05 0.04557.03 Kr 3 587.09 30.06 0.30 556.22587.56 He 7 706.52 118.96 0.03 667.82603.00 Ne 5 607.43 4.43 0.54614.31 Ne 7 616.36 2.05 0.04626.65 Ne 6 630.48 3.83 0.07640.23 Ne 7 638.30 1.93 0.11656.1 D2. . . .656.28 H27 . . . 656.99667.82 He 5 706.52 38.70 0.50692.95 N
28、e 6 703.24 10.29 0.45703.24 Ne 7 692.95 10.29 0.06 702.41724.52 Ne 5 703.24 21.28 0.02 717.39743.89 Ne 4 724.52 19.37 1.4 748.89785.48 Kr 3 769.45 16.03 0.7819.01 Kr 2 811.29 7.72 3.1E 958 93 (2005)2data shown in Fig. 1. In many applications the mercury andhydrogen (or deuterium) lines suffice.6.1.2
29、 Relative intensity data for the reference lines are givenin the third column of Table 1. The data refer to measurementsmade with a double prism-grating spectrophotometer equippedwith a silica window S-20 photomultiplier (RCA-C70109E).These intensities will be different when using detectors ofdiffer
30、ent spectral sensitivity. They may also vary somewhatamong sources.All of the lines are intense ones, but all may notalways be sufficiently intense to allow the spectrophotometer tobe operated with very narrow slit widths.6.1.3 Information on nearest neighbors of appreciable inten-sity is needed in
31、order to set an upper limit on the measurablespectral bandwidth. If the resolution of the instrument inquestion is so poor that two lines or bands of the test source orsample overlap, the measured half bandwidth will not indicatethe spectral bandwidth of the instrument. Very few of the lineslisted i
32、n Table 1 are so well isolated from other lines ofappreciable intensity that they could always be used withoutinterference or overlap. The atomic hydrogen (deuterium) lineat 656 nm and the very intense mercury resonance line at 253nm fall in a category of “isolation,” but in all other casesinterferi
33、ng lines are nearby. The nearest neighboring lineshaving an intensity more than 15 % of the reference lines aregiven in the fourth column of Table 1. The separation innanometers between the reference and nearest neighbor lines islisted in the fifth column. In general, lines cannot be used fora spect
34、ral bandwidth test when the spectral bandwidth exceedsone half the separation between reference and nearest neighborlines.6.1.4 To some extent this rule can be modified by therelative intensities of neighbor to reference lines. This ratio,Ineighbor/Ireference, is listed in column 6. Neighboring line
35、shaving an intensity less than 15 % of the reference lines willnot seriously distort bandwidth measurements. However, toaccommodate the possible situation of sources with intensityrelationships different from that encountered in this study,neighboring lines weaker than 15 % are tabulated in theseven
36、th column under the heading “weak neighbor.”7. Procedure7.1 Instruments with Servo-Operated SlitsThese instru-ments maintain a constant period and signal-to-noise ratio aswavelength is automatically scanned. The determination ofpractical spectral bandwidth requires a preliminary determina-tion of th
37、e mechanical slit width necessary to yield a givensignal-to-noise at a given integration period. This is bestaccomplished by first establishing the desired period. Nextdetermine the slit widths required to yield a given signal-to-noise ratio throughout the region of interest using the standardcontin
38、uum source of the instrument. Then use appropriate linesources to illuminate the monochromator, and record thespectral bandwidths obtained at the appropriate mechanical slitwidths for the wavelengths in question.7.1.1 Although the integration period may be indicated onthe instrument or in the manufa
39、cturers literature, check thevalue as follows:7.1.1.1 For recording instruments, set the wavelength at anyconvenient position and adjust the 0 and 100 % T controls fornormal recorder presentation. Using 100 % T as the base line,block the sample beam and measure the time required for thepen to reach
40、the 2 % T level (Note 2).NOTE 2The time may be measured with a stopwatch or from thedistance the chart moves, if a fast chart speed recorder is being used.Integration periods of1sorless can only be estimated by either technique,but generally this estimate is adequate to determine if the indicated pe
41、riodis approximately correct.7.1.1.2 For instruments that can be operated only in theabsorbance mode, follow the same procedure, with the excep-tion that 0 A replaces 100 % T and 1.7 A replaces 2 % T.7.1.2 The signal-to-noise ratio is measured as follows:7.1.2.1 Set the instrument at a convenient wa
42、velength andadjust the pen to read either 100 % T or 0 A. For low-noiselevels use an expanded scale, if available.7.1.2.2 Adjust the slit width either to its normal value or toa value that gives the desired signal-to-noise ratio.7.1.2.3 Disengage the wavelength drive, start the chartdrive, and allow
43、 the pen to record for at least 2 min or 50integration periods, whichever is longer.7.1.2.4 Divide the recording into five approximately equalsegments and determine the maximum peak-to-peak excursionin each segment (Note 3).NOTE 3Care should be taken that the noise level is not partiallyobscured by
44、a detectable recorder dead zone.7.1.2.5 Average the five readings to obtain the noise, N.7.1.2.6 If a % T recording is being used, divide 100 by N toobtain the signal-to-noise ratio, S/N. If an absorbance record-ing is being used, divide 0.43 by N to determine S/N.7.1.2.7 The signal-to-noise ratio s
45、hould be independent ofwavelength for a given source and detector combination, but itis advisable to check this point experimentally. For example,many instruments are operated with different slit programs inthe ultraviolet and visible regions and thus exhibit differentsignal-to-noise ratios in the t
46、wo regions.7.1.3 Set the period and signal-to-noise ratio to the valuesused in 7.1.1 and 7.1.2, scan to the wavelength of interest (seeTable 1), and record the resulting mechanical slit widths orspectral bandwidth (Note 4).NOTE 4It may be desirable to scan the entire wavelength range of theinstrumen
47、t and record the slit width at suitable intervals so that a curve ofslit width versus wavelength may be constructed (usually 25- and 50-nm4Available from UVP, Inc.FIG. 1 Comparison of Measured and Calculated SpectralBandwidthsE 958 93 (2005)3intervals are satisfactory for the ultraviolet and visible
48、 regions, respec-tively).7.1.4 Measure the spectral bandwidth of the instrument asfollows:7.1.4.1 Position the appropriate line source so that it illumi-nates the entrance slit of the monochromator (Note 5). Thepositioning is not critical if sufficient light enters the mono-chromator.NOTE 5The conti
49、nuum source is turned off unless one of its lines isused to measure the spectral bandwidth.7.1.4.2 Select the “single-beam” or “energy” mode of op-eration, and set the slit width to the value recorded in 7.1.3.7.1.4.3 Slowly scan through the region of the line to locatethe wavelength of maximum emission, adjusting the gain ordynode voltage as necessary to keep the signal on scale but stillas large as possible.7.1.4.4 Scan to longer wavelengths until the signal returnsto a level close to 0 % T and remains relatively constant overa few nanometer range. Reverse the scan
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