1、Designation: E60 11Standard 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, the year of last r
2、evision. 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 Department of Defense.1. Scope1.1 This practice covers general recommendation
3、s 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 attempt has been made,howev
4、er, 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 spectrophotometric meth
5、ods 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 and spectrophotom-eters, while “spectrophotometry” is reserved for spectropho-tome
6、ters 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 limitations prior to use.2. R
7、eferenced 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 Techniques of Ultraviol
8、et-Visible Quantitative AnalysisE275 Practice for Describing and Measuring Performanceof Ultraviolet and Visible Spectrophotometers3. Terminology Definitions and Symbols3.1 For definitions of terms relating to this practice, refer toTerminology E135.3.2 For definitions of terms relating to absorptio
9、n spectros-copy, 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 con
10、centration 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 transmi
11、ttance 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 abs
12、orption 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) (see
13、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,which is due only to the reagents used. It reflects both theamount of the element sought present as an impuri
14、ty in thereagents, and the effect of interfering species.1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices.Current edition approved May 1, 2011.
15、 Published July 2011. Originally approvedin 1946. Last previous edition approved in 2004 as E60 98 (Reapproved 2004).DOI: 10.1520/E0060-11.2For additional information on the theory and photoelectric photometry, see thelist of references at the end of this practice.3For referenced ASTM standards, vis
16、it 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.4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.1C
17、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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
18、solvent. 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 (pr
19、eferably 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, s
20、pectrophotometers, 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 combi
21、ned in thefollowing 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 = intern
22、al cell length (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
23、 of the Bouguer-Beer equa-tion, A = abc, it is evident that at constant b, a plot of A versusc gives a straight line if Beers law is followed. This line willpass through the origin if the usual practice of cancelling outsolvent reflections and absorption and other blanks is em-ployed.5.4 In photomet
24、ry it is customary 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
25、law, c = A/ab, it 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
26、an absorbingsystem, a single measurement at a given wavelength on asolution of known concentration will suffice. Actually, how-ever, it is safer to use the average value obtained with three ormore concentrations, covering the range over which the deter-minations are likely to be made and making seve
27、ral readings ateach concentration. 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 thefoll
28、owing:NOTE 1The choice of an 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
29、 be compact, rugged enough to 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. I
30、t is advantageous to have an 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 filte
31、r),6.1.3 One or more absorption cells to hold the sample,standards, reagent blank, or reference solution, 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 measur
32、ing current or potential.6.2 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 spectrop
33、hotometers, andusually isolate relatively broad bands of radiant energy. In mostcases the absorption peak of the compound being measured isrelatively broad, and sufficient accuracy can be obtained usinga fairly broad band (10 nm to 75 nm) of radiant energy for themeasurement (Note 2). In other cases
34、 the absorption peaks arenarrow, and radiant energy of high purity (1 nm to 10 nm) isrequired. This applies particularly if accurate values are to beobtained in those systems of measurement based on theadditive nature of absorbance values.NOTE 2One nanometre (nm) equals one millimicron (m).7. Types
35、of Photometers and Spectrophotometers7.1 Single-Photocell InstrumentsIn most single-photocellinstruments, the radiant energy passes from the monochroma-tor or filter through the reference solution to a photocell. Thephotocurrent is measured by a galvanometer or a microamme-ter and its magnitude is a
36、 measure of the incident radiantpower, Po. An identical absorption cell containing the solutionof the absorbing component is now substituted for the cellE60112containing the reference solution and the power of the trans-mitted radiant energy, P, is measured. The ratio of the currentcorresponding to
37、P to that of Pogives the 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 scal
38、e or zero on the logarithmic 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 b
39、y means of a resistance 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 is to control the quantity ofradiant energy striking the photocell with the aid of a dia-phragm somewhere in
40、 the path of radiant energy.NOTE 3Kortm (3) has pointed out on theoretical grounds thismethod of controls is faulty, since the change in voltage applied to thelamp not only changes the radiant energy emitted but also alters itschromaticity. Actually, however, instruments employing this principle are
41、giving good service in industry, so the errors involved evidently are nottoo great.7.2 Two-Photocell InstrumentsIn order to eliminate theeffect of fluctuation of the source, a great many types oftwo-photocell instruments have been proposed. Most of theseare good, but some have poorly designed circui
42、ts and do notaccomplish the purpose for which they are designed. Followingis a brief description of two types of two-photocell photometersand spectrophotometers that have been found satisfactory:7.2.1 In the first type of two-photocell instrument, beams ofradiant energy from the same source are pass
43、ed through thereference solution and the sample solution and are focused ontheir respective photocells. Prior to insertion of the sample, thereference solution is placed in both absorption cells, and thephotocells are balanced with the aid of a potentiometric bridgecircuit (Note 4). The reference so
44、lution and sample are theninserted and the balance reestablished by manipulation of thepotentiometer until the galvanometer again reads zero. Bychoosing suitable resistances and by using a graduated slidewire, the scale of the latter can be made to read directly intransmittance. It is important that
45、 both photocells show linearresponse, and that they have identical radiation sensitivity ifthe light is not monochromatic.NOTE 4Since b is defined as the internal cell length, the cancellationof radiant energy lost at the glass-liquid interfaces and within the glassmust be accomplished by inserting
46、the reference solution in the absorptioncells.7.2.2 The second type of two-photocell instrument is similarto the first, except that part of the radiant energy from thesource is passed through an absorption cell to the firstphotocell; the remainder is impinged on the second photocellwithout, however,
47、 passing through an absorption cell. Adjust-ment of the calibrated slide wire to read 100 on the percentagescale, with the reference solution in the cell, is accomplishedby rotating the second photocell. The reference solution is thenreplaced by the sample and the slide wire is turned until thegalva
48、nometer 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 example,when an analysis calls for the use of radiant energy ofwavelengths below 400
49、 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 operating 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 o
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1