1、Designation: E958 93 (Reapproved 2005)E958 13Standard Practice forMeasuring Practical Estimation of the Spectral Bandwidth ofUltraviolet-Visible Spectrophotometers1This standard is issued under the fixed designation E958; the number immediately following the designation indicates the year oforiginal
2、 adoption 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 This practice describes a procedure procedures for measuringestimat
3、ing the practical spectral bandwidth of a spectropho-tometer in the wavelength region of 185 to 820 nm. Practical spectral bandwidth is the spectral bandwidth of an instrumentoperated at a given integration period and a given signal-to-noise ratio.1.2 This practice is applicable to instruments These
4、 practices are applicable to all modern spectrophotometer designs utilizingcomputer control and data handling. This includes conventional optical designs, where the sample is irradiated by monochromaticlight, and reverse optic designs coupled to photodiode arrays, where the light is separated by a p
5、olychromator after passingthrough the sample. For spectrophotometers that utilize servo-operated slits and maintain a constant period and a constantsignal-to-noise ratio as the wavelength is automatically scanned. It is also applicable to instruments that scanned, and/or utilizefixed slits and maint
6、ain a constant servo loop gain by automatically varying gain or dynode voltage. In this latter case, thesignal-to-noisevoltage, refer to the procedure described in Annex A1ratio varies with wavelength. It can also be used oninstruments that utilize some combination of the two designs, as well as on
7、those that vary the period during the scan. For digitizedinstruments, refer to the manufacturers manual This procedure is identical to that described in earlier versions of this practice.1.3 This practice does not cover the measurement of limiting spectral bandwidth, defined as the minimum spectral
8、bandwidthachievable under optimum experimental conditions.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the
9、 responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E131 Terminology Relating to Molecular SpectroscopyE275 Practice for Describing and Measur
10、ing Performance of Ultraviolet and Visible Spectrophotometers2. Terminology2.1 Definitions:3.1.1 integration period, nthe time, in seconds, required for the pen or other indicator to move 98.6 % of its maximum travelin response to a step function.3.1.2 practical spectral bandwidth, designated by the
11、 symbol:!pi S/N (1)where: = spectral bandwidth,pi = integration period, andS/N = signal-to-noise ratio measured at or near 100 % T.1 This practice is under the jurisdiction of ASTM Committee E13 on Molecular Spectroscopy and Separation Science and is the direct responsibility of SubcommitteeE13.01 o
12、n Ultra-Violet, Visible, and Luminescence Spectroscopy.Current edition approved April 1, 2005Jan. 1, 2013. Published April 2005February 2013. Originally approved in 1983. Last previous edition approved in 19992005 asE958 93 (1999).(2005). DOI: 10.1520/E0958-93R05.10.1520/E0958-13.This document is no
13、t an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriat
14、e. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.3 signal-to-noise ratio, nthe ratio of the signal, S, to the no
15、ise, N, as indicated by the readout indicator. The recommendedmeasure of noise is the maximum peak-to-peak excursion of the indicator averaged over a series of five successive intervals, eachof duration ten times the integration period. (This measure of noise is about five times the root-mean-square
16、 noise.)2.1.1 spectral bandwidth, nthe wavelength interval of radiation leaving the exit slit of a monochromator measured at half thepeak detected radiant power. It is not synonymous with spectral slit width, which is the product of the mechanical slit width andthe reciprocal linear dispersion of th
17、e spectrophotometer.3. Summary of Practice3.1 The following test procedures are written for all spectrophotometer designs that have provision for recording (that is,collecting and storing) spectral data digitally. Processing may be by built-in programs or in a separate computer. Data may becollected
18、 in either the transmittance or the absorbance mode, although for the Liquid Ratio procedure, the peak and trough valuesmust be measured in absorbance.3.2 Line Emission Source ProcedureThe pen period and signal-to-noise ratio are set at the desired values when the instrumentis operated with its norm
19、al light source and adjusted to read close to 100 % T. The mechanical slit width, or the indicated spectralbandwidth, required to give the desired signal-to-noise ratio is recorded. The continuum source is replaced with a line emissionsource, such as a mercury lamp, and the apparent half-intensity b
20、andwidth of an emission line occurring in the wavelength regionof interest is measured using the same slit width, or indicated spectral bandwidth, as was used to establish the signal-to-noise ratiowith the continuum source. bandwidth required to be estimated. This procedure can be used for instrumen
21、tation having spectralbandwidths in the range 0.1 to 10 nm.NOTE 1In photodiode array instrumentation, the array spacing between the diode elements may invalidate this procedure.3.3 Liquid Ratio ProcedureThe calculated spectral peak to trough ratio of a defined small percentage of toluene in hexane w
22、illvary with the spectral bandwidth of the spectrophotometer when scanned in the UV region. This procedure can be used for allinstrumentation having spectral bandwidths in the range 0.5 to 3.0 nm.3.4 Benzene Vapor ProcedureThe characteristics of a spectrum of benzene vapor in the UV region will vary
23、 significantly withthe spectral bandwidth of the spectrophotometer. This procedure can be used for instrumentation having spectral bandwidths in therange 0.1 to 0.5 nm.4. Significance and Use4.1 This practiceThese practices should be used by a person who develops an analytical method to ensure that
24、the spectralbandwidths cited in the practice are actually the ones used.NOTE 2The method developer should establish the spectral bandwidths that can be used to obtain satisfactory results.4.2 This practiceThese practices should be used to determine whether a spectral bandwidth specified in a method
25、can be realizedwith a given spectrophotometer and thus whether the instrument is suitable for use in this application. If accurate absorbancemeasurements are to be made on compounds with sharp absorption bands (natural half band widths of less than 15 nm) the spectralbandwidth of the spectrometer us
26、ed should be better than 18th of the natural half band width of the compounds absorption.4.3 This practice allowsThese practices allow the user of a spectrophotometer to determineestimate the actual spectralbandwidth of the instrument under a given set of conditions and to compare the result to the
27、spectral bandwidth calculated fromdata given in the manufacturers literature or indicated by the instrument.5.4 Instrument manufacturers can use this practice to measure and describe the practical spectral bandwidth of an instrumentover its entire wavelength operating range. This practice is highly
28、prefered to the general practice of stating the limiting or thetheoretical spectral bandwidth at a single wavelength.5. Test Materials and Apparatus5.1 Table 1 lists reference emission lines that may be used for measuring the spectral bandwidth of ultraviolet/visibleinstruments at the levels of reso
29、lution encountered in most commercial instruments. All of the lines listed have widths less than0.02 nm, suitable for measuring spectral bandwidths of greater than 0.2 nm. The wavelengths of these lines in nanometres are listedin the first column. Values refer to measurements in standard air (760 nm
30、, 15C) except for the two lines below 200 nm. Thewavelength for these lines refer to a nitrogen atmosphere at 760 nm and 15C.Line Emission Source Procedure:5.1.1 Table 1 lists reference emission lines that may be used for measuring the spectral bandwidth of ultraviolet/visibleinstruments at the leve
31、ls of resolution encountered in most commercial instruments. All of the lines listed have widths less than0.02 nm, suitable for measuring spectral bandwidths of greater than 0.2 nm.5.1.2 The second column in Table 1 lists the emitter gas of sixvarious sources. Only sources operating at low pressure
32、shouldbe used, as line broadening can introduce errors. The hydrogen, deuterium, and mercury lamps used to obtain these data wereBeckman lamps operated on Beckman spectrophotometer power supplies. The other lamps are all of the “pencil-lamp” type.areE958 132either the instrument source lamps or “pen
33、cil-lamp” types.2 A mercury vapor Pen-Ray lamp was used to obtain the data shown inFig. 1. In many applications the mercury and hydrogen (or deuterium) lines suffice.6.1.2 Relative intensity data for the reference lines are given in the third column of Table 1. The data refer to measurementsmade wit
34、h a double prism-grating spectrophotometer equipped with a silica window S-20 photomultiplier (RCA-C70109E). Theseintensities will be different when using detectors of different spectral sensitivity. They may also vary somewhat among sources.All of the lines are intense ones, but all may not always
35、be sufficiently intense to allow the spectrophotometer to be operated withvery narrow slit widths.6.1.3 Information on nearest neighbors of appreciable intensity is needed in order to set an upper limit on the measurablespectral bandwidth. If the resolution of the instrument in question is so poor t
36、hat two lines or bands of the test source or sampleoverlap, the measured half bandwidth will not indicate the spectral bandwidth of the instrument. Very few of the lines listed inTable 1 are so well isolated from other lines of appreciable intensity that they could always be used without interferenc
37、e or overlap.The atomic hydrogen (deuterium) line at 656 nm and the very intense mercury resonance line at 253 nm fall in a category of“isolation,” but in all other cases interfering lines are nearby. The nearest neighboring lines having an intensity more than 15 %of the reference lines are given in
38、 the fourth column of Table 1. The separation in nanometers between the reference and nearestneighbor lines is listed in the fifth column. In general, lines cannot be used for a spectral bandwidth test when the spectralbandwidth exceeds one half the separation between reference and nearest neighbor
39、lines.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. ForThese alternative source lampsare often available as an accessory for a given spectrophotometer from the instrument Annual Book of ASTM Standardsvendor, or commerciall
40、y available. volumeinformation, refer to the standards Document Summary page on the ASTM website.TABLE 1 Emission Lines Useful for Measuring SpectralBandwidthReference Line,nm Emitter194.16 Hg205.29 Hg237.83 Hg226.22 Hg253.65 Hg275.28 Hg289.36 Hg296.73 Hg312.57 Hg318.77 He334.15 Hg314.79 Ne359.35 Ne
41、365.02 Hg388.87 He404.66 Hg427.40 Kr435.83 Hg447.15 He471.31 He486.00 D2486.13 H2501.57 He541.92 Xe546.08 Hg557.03 Kr576.96 Hg579.07 Hg587.56 He603.00 Ne614.31 Ne626.65 Ne640.23 Ne656.10 D2656.28 H2667.82 He692.95 Ne703.24 Ne724.52 Ne743.89 Ne750.39 Hg785.48 Kr811.53 Ar819.01 KrE958 1336.1.4 To some
42、 extent this rule can be modified by the relative intensities of neighbor to reference lines. This ratio, Ineighbor/Ireference, is listed in column 6. Neighboring lines having an intensity less than 15 % of the reference lines will not seriously distortbandwidth measurements. However, to accommodate
43、 the possible situation of sources with intensity relationships different fromthat encountered in this study, neighboring lines weaker than 15 % are tabulated in the seventh column under the heading “weakneighbor.”5.2 Liquid Ratio ProcedureThis procedure uses a 0.02 % v/v solution of toluene in hexa
44、ne3 in a 10-mm far UV quartz cuvettemeasured against a similar hexane filled cuvette.5.3 Benzene Vapor ProcedureThis procedure uses a sealed far UV 10-mm path length cuvette containing benzene vapor.3NOTE 3A suitable vapor filled cell can be produced by placing a 10 l drop of liquid benzene in the c
45、uvette and sealing.6. Procedure6.1 Instruments with Servo-Operated SlitsLine Emission Source Procedure: These instruments maintain a constant period andsignal-to-noise ratio as wavelength is automatically scanned. The determination of practical spectral bandwidth requires apreliminary determination
46、of the mechanical slit width necessary to yield a given signal-to-noise at a given integration period. Thisis best accomplished by first establishing the desired period. Next determine the slit widths required to yield a given signal-to-noiseratio throughout the region of interest using the standard
47、 continuum source of the instrument. Then use appropriate line sourcesto illuminate the monochromator, and record the spectral bandwidths obtained at the appropriate mechanical slit widths for thewavelengths in question.7.1.1 Although the integration period may be indicated on the instrument or in t
48、he manufacturers literature, check the valueas follows:7.1.1.1 For recording instruments, set the wavelength at any convenient 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 the p
49、ento reach the 2 % T level (Note 2).NOTE 2The time may be measured with a stopwatch or from the distance the chart moves, if a fast chart speed recorder is being used. Integrationperiods of 1 s or less can only be estimated by either technique, but generally this estimate is adequate to determine if the indicated period is approximatelycorrect.7.1.1.2 For instruments that can be operated only in the absorbance mode, follow the same procedure, with the exception that0 A replaces 100 % T and 1.7 A replaces 2 % T.7.1.2 The signal-to-noise ratio is measur
