ASTM E928-08
(Test Method)Standard Test Method for Determination of Purity by Differential Scanning Calorimetry
Standard Test Method for Determination of Purity by Differential Scanning Calorimetry
SIGNIFICANCE AND USE
The melting temperature range of a compound broadens as the impurity level rises. This phenomenon is described approximately by the van't Hoff equation for melting point depressions. Measuring and recording the instantaneous heat flow into the specimen as a function of temperature during such a melting process is a practical way for the generation of data suitable for analysis by the van't Hoff equation.
The results obtained include: sample purity (expressed as mole percent); enthalpy of fusion (expressed as joules per mole); and the melting temperature (expressed in Kelvin) of the pure form of the major component.
Generally, the repeatability of this test method decreases as the purity level decreases. This test method is ordinarily considered unreliable when the purity level of the major component of the mixture is less than 98.5 mol % or when the incremental enthalpy correction (c) exceeds 20 % of the original detected enthalpy of fusion.
This method is used for quality control, specification acceptance, and research.
SCOPE
1.1 This method describes the determination of purity of materials greater than 98.5 mole percent purity using differential scanning calorimetry and the van't Hoff equation.
1.2 This test method is applicable to thermally stable compounds with well-defined melting temperatures.
1.3 Determination of purity by this test method is only applicable when the impurity dissolves in the melt and is insoluble in the crystal.
1.4 SI values are the standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.6 There is no ISO method equivalent to this method.
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Designation: E928 − 08
StandardTest Method for
1
Purity by Differential Scanning Calorimetry
This standard is issued under the fixed designation E928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E1970PracticeforStatisticalTreatmentofThermoanalytical
Data
1.1 Thistestmethoddescribesthedeterminationofpurityof
materials greater than 98.5 mole percent purity using differen-
3. Terminology
tial scanning calorimetry and the van’t Hoff equation.
3.1 Definitions—The definitions relating to thermal analysis
1.2 This test method is applicable to thermally stable
appearing in Terminology E473 shall be considered applicable
compounds with well-defined melting temperatures.
to this test method.
1.3 Determination of purity by this test method is only
4. Summary of Test Method
applicable when the impurity dissolves in the melt and is
3
insoluble in the crystal.
4.1 Thistestmethodisbaseduponthevan’tHoffequation :
1.4 The values stated in SI units are to be regarded as 2
T 5 T 2 ~RT χ!/~HF! (1)
s o o
standard. No other units of measurement are included in this
where:
standard.
T = specimen temperature, K
s
1.5 This standard does not purport to address all of the
T = melting temperature of 100% pure material, K
o
safety concerns, if any, associated with its use. It is the
−1 −1
R = gas constant (= 8.314 J mol K ),
responsibility of the user of this standard to establish appro-
χ = mole fraction of impurity,
priate safety and health practices and determine the applica- −1
H = heat of fusion, J mol , and
bility of regulatory limitations prior to use.
F = fraction melted.
1.6 There is no ISO method equivalent to this test method.
4.2 This test method consists of melting the test specimen
that is subjected to a temperature-controlled program while
2. Referenced Documents
recording the heat flow into the specimen as a function of
2
2.1 ASTM Standards:
temperature.Theresultingmeltingendothermareaismeasured
E473Terminology Relating to Thermal Analysis and Rhe-
to yield the enthalpy of fusion, H.The melting endotherm area
ology
is then partitioned into a series of fractional areas (about ten,
E793Test Method for Enthalpies of Fusion and Crystalliza-
comprisingthefirst10to50%ofthetotalarea).Thefractional
tion by Differential Scanning Calorimetry
area, divided by the total area, yields the fraction melted, F.
E794TestMethodforMeltingAndCrystallizationTempera-
Each fractional area is assigned a temperature, T .
s
tures By Thermal Analysis
4.3 Eq1hastheformofY=mX+bwhereY= T,X=1/F,
s
E967Test Method for Temperature Calibration of Differen-
2
m=−(RT χ)/ H, and b = T . A plot of Y versus X should
o o
tial Scanning Calorimeters and Differential ThermalAna-
produce a straight line with slope m and intercept b.
lyzers
E968Practice for Heat Flow Calibration of Differential 4.4 In practice, however, the resultant plot of T versus 1 /F
s
Scanning Calorimeters is seldom a straight line. To linearize the plot, an incremental
amount of area is added to the total area and to each fractional
area to produce a revised value for F. The process of
incremental addition of area is continued until a straight line is
1
ThistestmethodisunderthejurisdictionofASTMCommitteeE37onThermal
Measurements and is the direct responsibility of Subcommittee E37.01 on Calo- obtained.
rimetry and Mass Loss.
F 5 ~A 1c!/~A 1c! (2)
part total
Current edition approved Sept. 1, 2008. Published November 2008. Originally
approved in 1983. Last previous edition approved in 2003 as E928–03. DOI:
10.1520/E0928-08.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Brennan, W. P., DiVito, M. P., Fynas, R. L., Gray,A. P., “An Overview of the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Calorimetric Purity Measurement”, in Purity Determinations by Thermal Methods,
Standards volume information, refer to the standard’s Document Summary page on R. L. Blaine and C. K. Schoff (Eds.), Special Technical Publication 838,American
the ASTM website. Society for Testing and Materials, West Conshohocken, PA 1984, pp. 5 - 15.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E928 − 08
where: 6.2.2 Thesolubilityoftheimpurityinthesolidofthemajor
constituent is negligible; and
A = area of fraction melted, mJ
part
6.2.3 The major constituent displays a single well-defined
A = total area, mJ and
total
c = incremental area, mJ. meltingendotherminthetemperaturerangeofinterest.Micro-
NOTE 1—The best fit straight line m
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:E928–03 Designation: E 928 – 08
Standard Test Method for
1
Purity by Differential Scanning Calorimetry
This standard is issued under the fixed designation E928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This method describes the determination of purity of materials greater than 98.5 mole percent purity using differential
scanning calorimetry and the van’t Hoff equation.
1.2 This test method is applicable to thermally stable compounds with well-defined melting temperatures.
1.3 Determination of purity by this test method is only applicable when the impurity dissolves in the melt and is insoluble in
the crystal.
1.4Computer- or electronic-based instruments, techniques, or data treatments equivalent to this test method may also be used.
NOTE1—Since all data treatments are not equivalent, it is the responsibility of the user to verify equivalency prior to use.
1.5SI values are the standard.
1.6
1.4 SI values are the standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
1.7There1.6 There is no ISO method equivalent to this method.
2. Referenced Documents
2
2.1 ASTM Standards:
E473 Terminology Relating to Thermal Analysis and Rheology
2
E793Test Method for Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry Test Method for
Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry
E794 Test Method for Melting And Crystallization Temperatures By Thermal Analysis
E967Practice Test Method for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal
Analyzers
E968 Practice for Heat Flow Calibration of Differential Scanning Calorimeters
E1970 Practice for Statistical Treatment of Thermoanalytical Data
3. Terminology
3.1 Definitions—The definitions relating to thermal analysis appearing in Terminology E473 shall be considered applicable to
this method.
4. Summary of Method
3
4.1 This method is based upon the van’t Hoff equation :
2
T 5 T 2 ~RT x!/ ~HF! (1)
s o o
where:
1
This test method is under the jurisdiction ofASTM Committee E37 onThermal Measurements and is the direct responsibility of Subcommittee E37.01 onThermalTest
Methods and Recommended Practices.
Current edition approved March 10, 2003.Sept. 1, 2008. Published July 2003.November 2008. Originally published as E928–83.approved in 1983. Last previous edition
E928–96.approved in 2003 as E928–03.
2
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For AnnualBookofASTM Standards
, Vol 14.02.volume information, refer to the standard’s Document Summary page on the ASTM website.
3
Brennan,W.P.,DiVito,M.P.,Fynas,R.L.,Gray,A.P.,“AnOverviewoftheCalorimetricPurityMeasurement”,inPurityDeterminationsbyThermalMethods,Methods,
R. L. Blaine and C. K. Schoff (Eds.), Special Technical Publication 838, American SocieitySociety for Testing and Materials, West Conshohocken, PA 1984, pp.5-15.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
E928–08
T = specimen temperature, K
s
T = melting temperature of 100% pure material, K
o
−1 −1
R = gas constant (= 8.314 J mol K ),
x = mole fraction of impurity,
−1
H = heat of fusion, J mol , and
F = fraction melted.
4.2 Thismethodconsistsofmeltingthetestspecimenthatissubjectedtoatemperature-controlledprogramwhilerecordingthe
heat flow into the specimen as a function of temperature. The resulting melting endotherm area is measured to yield the enthalpy
of fusion, H. The melting endotherm area is then partitioned into a series of fractional areas (about ten, comprising the first 10 to
50%ofthetotalarea).Thefractionalarea,dividedbythetotalarea,yieldsthefractionmelted, F.Eachfractionalareaisassigned
a temperature, T .
s
2
4.3 Eq 1 has the form of Y = mX + b where Y = T,X=1/F,m=−(RT x)/ H, and b = T . A plot of Y versus X should
s o o
produce a straight line with slope m and intercept b.
4.4 Inpractice,however,theresultantplotofT versus1/Fisseldomast
...
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