1、Designation: E60 11 (Reapproved 2016)Standard Practice forAnalysis of Metals, Ores, and Related Materials bySpectrophotometry1This standard is issued under the fixed designation E60; the number immediately following the designation indicates the year of originaladoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This practice covers
3、 general recommendations for pho-toelectric photometers and spectrophotometers and for photo-metric practice prescribed in ASTM methods for chemicalanalysis of metals, sufficient to supplement adequately theASTM methods. A summary of the fundamental theory andpractice of photometry is given. No atte
4、mpt has been made,however, to include in this practice a description of everyapparatus or to present recommendations on every detail ofpractice in ASTM photometric or spectrophotometric methodsof chemical analysis of metals.21.2 These recommendations are intended to apply to theASTM photometric and
5、spectrophotometric methods forchemical analysis of metals when such standards make definitereference to this practice, as covered in Section 4.1.3 In this practice, the terms “photometric” and “photom-etry” encompass both filter photometers andspectrophotometers, while “spectrophotometry” is reserve
6、d forspectrophotometers alone.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 and determine the applica-bility of regulatory limitation
7、s prior to use.2. Referenced Documents2.1 ASTM Standards:3E131 Terminology Relating to Molecular SpectroscopyE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE169 Practices for General Tech
8、niques of Ultraviolet-VisibleQuantitative AnalysisE275 Practice for Describing and Measuring Performance ofUltraviolet and Visible Spectrophotometers3. Definitions and Symbols3.1 For definitions of terms relating to this practice, refer toTerminology E135.3.2 For definitions of terms relating to abs
9、orptionspectroscopy, refer to Terminology E131.3.3 Definitions of Terms Specific to this Practice:3.3.1 background absorptionany absorption in the solu-tion due to the presence of absorbing ions, molecules, orcomplexes of elements other than that being determined iscalled background absorption.3.3.2
10、 concentration rangethe recommended concentra-tion range shall be designated on the basis of the optical pathof the cell, in centimetres, and the final volume of solution asrecommended in a procedure. In general, the concentrationrange and path length shall be specified as that which willproduce tra
11、nsmittance readings in the optimum range of theinstrument being used as covered in Section 14.3.3.3 initial settingthe initial setting is the photometricreading (usually 100 on the percentage scale or zero on thelogarithmic scale) to which the instrument is adjusted with thereference solution in the
12、 absorption cell. The scale will thenread directly in percentage transmittance or in absorbance.3.3.4 photometric readingthe term “photometric reading”refers to the scale reading of the instrument being used.Available instruments have scales calibrated in transmittance,T, (1)4or absorbance, A, (2) (
13、see 5.2), or even arbitrary unitsproportional to transmittance or absorbance.3.3.5 reagent blankthe reagent blank determination yieldsa value for the apparent concentration of the element sought,1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, a
14、nd Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices.Current edition approved Aug. 1, 2016. Published August 2016. Originallyapproved in 1946. Last previous edition approved in 2011 as E60 11. DOI:10.1520/E0060-11R16.2For additional information on the
15、theory and photoelectric photometry, see thelist of references at the end of this practice.3For 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 Su
16、mmary page onthe ASTM website.4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1which is due only to the reagents used. It reflects both theam
17、ount of the element sought present as an impurity in thereagents, and the effect of interfering species.3.3.6 reference solutionphotometric readings consist of acomparison of the intensities of the radiant energy transmittedby the absorbing solution and the radiant energy transmitted bythe solvent.
18、Any solution to which the transmittance of theabsorbing solution of the substance being measured is com-pared shall be known as the reference solution.4. Reference to This Practice in Standards4.1 The inclusion of the following paragraph, or a suitableequivalent, in any ASTM test method (preferably
19、after thesection on scope) shall constitute due notification that thephotometers, spectrophotometers, and photometric practiceprescribed in that test method are subject to the recommenda-tions set forth in this practice.“Photometers, Spectrophotometers, and PhotometricPracticePhotometers, spectropho
20、tometers, and photometricpractice prescribed in this test method shall conform to ASTMPractice E60, Practice for Analysis of Metals, Ores, andRelated Materials by Spectrophotometry.5. Theory5.1 Photoelectric photometry is based on Bouguers andBeers (or the Lambert-Beer) laws which are combined in th
21、efollowing expression:P 5 Po102abcwhere:P = transmitted radiant power,Po= incident radiant power, or a quantity proportional to it,as measured with pure solvent in the beam,a = absorptivity, a constant characteristic of the solutionand the frequency of the incident radiant energy,b = internal cell l
22、ength (usually in centimetres) of thecolumn of absorbing material, andc = concentration of the absorbing substance, g/L.5.2 Transmittance, T, and absorbance, A, have the followingvalues:T 5 P/PoA 5 log101/T! 5 log10Po/P!where P and Pohave the values given in 5.1.5.3 From the transposed form of the B
23、ouguer-Beerequation, A = abc, it is evident that at constant b, a plot of Aversus c gives a straight line if Beers law is followed. This linewill pass through the origin if the practice of cancelling outsolvent reflections and absorption and other blanks is em-ployed.5.4 In photometry it is customar
24、y to make indirect compari-son with solutions of known concentration by means ofcalibration curves or charts. When Beers law is obeyed andwhen a satisfactory instrument is employed, it is possible todispense with the curve or chart. Thus, from the transposedform of the Bouguer-Beer law, c = A/ab, it
25、 is evident that oncea has been determined for any system, c can be obtained, sinceb is known and A can be measured.5.5 The value for a can be obtained from the equationa = A/cb by substituting the measured value of A for a given band c. Theoretically, in the determination of a for an absorbingsyste
26、m, a single measurement at a given wavelength on asolution of known concentration will suffice. However, it issafer to use the average value obtained with three or moreconcentrations, covering the range over which the determina-tions are likely to be made and making several readings at eachconcentra
27、tion. The validity of the Bouguer-Beer law for aparticular system can be tested by showing that a remainsconstant when b and c are changed.APPARATUS6. General Requirements for Photometers andSpectrophotometers6.1 A photoelectric photometer consists essentially of thefollowing:NOTE 1The choice of an
28、instrument may naturally be based on priceconsiderations, since there is no point in using a more elaborate (and,incidentally, more expensive) instrument than is necessary. In addition tosatisfactory performance from the purely physical standpoint, the instru-ment should be compact, rugged enough to
29、 stand routine use, and notrequire too much manipulation. The scales should be easily read, and theabsorption cells should be easily removed and replaced, as the clearing,refilling, and placing of the cells in the instrument consume a majorportion of the time required. It is advantageous to have an
30、instrument thatpermits the use of cells of different depth (see Practice E275).6.1.1 An illuminant (radiant energy source),6.1.2 A device for selecting relatively monochromatic radi-ant energy (consisting of a diffraction grating or a prism withselection slit, or a filter),6.1.3 One or more absorpti
31、on cells to hold the sample,calibration, reagent blank, or reference solutions, and6.1.4 An arrangement for photometric measurement of theintensity of the transmitted radiant energy, consisting of one ormore photocells or photosensitive tubes, and suitable devicesfor measuring current or potential.6
32、.2 Precision instruments that employ monochromators ca-pable of supplying radiant energy of high purity at any chosenwavelength within their range are usually referred to asspectrophotometers. Instruments employing filters are knownas filter photometers or abridged spectrophotometers, andusually iso
33、late relatively broad bands of radiant energy. Fre-quently the absorption peak of the compound being measuredis relatively broad, and sufficient accuracy can be obtainedusing a fairly broad band (10 nm to 75 nm) of radiant energyfor the measurement (Note 2). Other times the absorptionpeaks are narro
34、w, and radiant energy of high purity (1 nm to 10nm) is required. This applies particularly if accurate values areto be obtained in those systems of measurement based on theadditive nature of absorbance values.NOTE 2One nanometre (nm) equals one millimicron (m).7. Types of Photometers and Spectrophot
35、ometers7.1 Single-Photocell InstrumentsIn most single-photocellinstruments, the radiant energy passes from the monochroma-tor or filter through the reference solution to a photocell. TheE60 11 (2016)2photocurrent is measured by a galvanometer or a microamme-ter and its magnitude is a measure of the
36、incident radiantpower, Po. An identical absorption cell containing the solutionof the absorbing component is now substituted for the cellcontaining the reference solution and the power of the trans-mitted radiant energy, P, is measured. The ratio of the currentcorresponding to P to that of Pogives t
37、he transmittance, T,ofthe absorbing solution, provided the illuminant and photocellare constant during the interval in which the two photocurrentsare measured. It is customary to adjust the photocell output sothat the galvanometer or microammeter reads 100 on thepercentage scale or zero on the logar
38、ithmic scale when theincident radiant power is Po, in order that the scale will readdirectly in percentage transmittance or absorbance. This ad-justment is usually made in one of three ways. In the firstmethod, the position of the cross-hair or pointer is adjustedelectrically by means of a resistanc
39、e in the photocell-galvanometer circuit. In the second method, adjustment ismade with the aid of a rheostat in the source circuit (Note 3).The third method of adjustment controls the quantity of radiantenergy striking the photocell with the aid of a diaphragmsomewhere in the path of radiant energy.N
40、OTE 3Kortm (3) has noted on theoretical grounds this method ofcontrols is faulty, since the change in voltage applied to the lamp not onlychanges the radiant energy emitted but also alters its chromaticity.Actually, however, instruments employing this principle are giving goodservice in industry, so
41、 the errors involved evidently are not excessive.7.2 Two-Photocell InstrumentsTo eliminate the effect offluctuation of the source, many types of two-photocell instru-ments have been proposed. Most of these are good, but somehave poorly designed circuits and do not accomplish thepurpose for which the
42、y are designed. Following is a briefdescription of two types of two-photocell photometers andspectrophotometers that have been found satisfactory:7.2.1 lution and are focused on their respective photocells.Prior to insertion of the sample, the reference solution is placedin both absorption cells, an
43、d the photocells are balanced withthe aid of a potentiometric bridge circuit. Since b is defined asthe internal cell length, the cancellation of radiant energy lostat the glass-liquid interfaces and within the glass must beaccomplished by inserting the reference solution in the absorp-tion cells. Th
44、e reference solution and sample are then insertedand the balance reestablished by manipulation of the potenti-ometer until the galvanometer again reads zero. By choosingsuitable resistances and by using a graduated slide wire, thescale of the latter can be made to read directly in transmittance.It i
45、s important that both photocells show linear response, andthat they have identical radiation sensitivity if the light is notmonochromatic.7.2.2 The second type of two-photocell instrument is similarto the first, but part of the radiant energy from the source ispassed through an absorption cell to th
46、e first photocell; theremainder is impinged on the second photocell without,however, passing through an absorption cell.Adjustment of thecalibrated slide wire to read 100 on the percentage scale, withthe reference solution in the cell, is accomplished by rotatingthe second photocell. The reference s
47、olution is then replacedby the sample and the slide wire is turned until the galvanom-eter again reads zero.8. Radiation Source8.1 In most of the commercially available instruments theilluminant is an incandescent lamp with a tungsten filament.This type of illuminant is not ideal for all work. For e
48、xample,when an analysis calls for the use of radiant energy ofwavelengths below 400 nm, it is necessary to maintain thefilament at as high a temperature as possible in order to obtainsufficient radiant energy to ensure the necessary sensitivity forthe measurements. This is especially true when opera
49、ting witha photovoltaic cell, for the response of the latter falls offquickly in the near ultraviolet. The use of high-temperaturefilament sources may lead to serious errors in photometricwork if adequate ventilation is not provided in the instrumentin order to dissipate the heat.Another important source of errorresults from the change of the shape of the energy distributioncurve with age. As a lamp is used, tungsten will be vaporizedand deposited on the walls. As this condensation proceeds,there is a decrease in the radiation power emitted and, in someinstances,
