ASTM E928-01

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 928 – 01
Standard Test Method for
Determination of Purity by Differential Scanning
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Calorimetry
This standard is issued under the fixed designation E 928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method covers the determination of purity by 3.1 Definitions—The definitions relating to thermal analysis
use of differential scanning calorimetry and the evaluation of appearing in Terminology E 473 shall be considered applicable
the results using the van’t Hoff equation. to this test method.
1.2 This test method is generally applicable to thermally
4. Summary of Test Method
stable compounds with well-defined melting temperatures.
4.1 This test method consists of melting the test specimen
1.3 Determination of purity by this test method is only
applicable when the impurity dissolves in the melt and is that is subjected to a temperature-controlled program while
recording the heat flow (power) into the specimen as a function
insoluble in the crystal.
1.4 Computer- or electronic-based instruments, techniques, of time. The resulting endotherm area is often measured to
yield the enthalpy of fusion. The melting endotherm area is
or data treatments equivalent to this test method may also be
used. then partitioned into a series of fractional areas (about ten,
comprising the first 10 to 50 % of the total area). Each
NOTE 1—Since all data treatments are not equivalent, it is the respon-
fractional area is assigned a temperature. A plot of the
sibility of the user to verify equivalency prior to use.
reciprocal fractional areas and their corresponding tempera-
1.5 SI values are the standard.
tures is then produced. The resulting plot is seldom a straight
1.6 This standard does not purport to address all of the
line. To linearize the plot, an incremental amount is added to
safety concerns, if any, associated with its use. It is the
the enthalpy of fusion and the fractional areas recalculated and
responsibility of the user of this standard to establish appro-
plotted. The purity level is then calculated from the slope of
priate safety and health practices and determine the applica-
this straight line.
bility of regulatory limitations prior to use.
1.7 There is no ISO method equivalent to this method.
5. Significance and Use
5.1 The melting temperature range of a compound broadens
2. Referenced Documents
as the impurity level rises. This phenomenon is described
2.1 ASTM Standards:
approximately by the van’t Hoff equation for melting point
2
E 473 Terminology Relating to Thermal Analysis
depressions. Measuring and recording the instantaneous heat
E 793 Test Method for Enthalpies of Fusion and Crystalli-
flow (power) into the specimen as a function of time or
2
zation by Differential Scanning Calorimetry
temperature during such a melting process is a practical way
E 967 Practice for Temperature Calibration of Differential
for the generation of data suitable for analysis by the van’t Hoff
Scanning Calorimeters and Differential Thermal Analyz-
equation.
2
ers
5.2 The results obtained include: sample purity (expressed
E 968 Practice for Heat Flow Calibration of Differential
as mol percent); enthalpy of fusion (expressed as joules per
2
Scanning Calorimeters
mol); and the melting temperature (expressed in Kelvin) of the
pure form of the major component.
5.3 Generally, the repeatability of this test method decreases
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as the purity level decreases. This test method is ordinarily
This test method is under the jurisdiction of ASTM Committee E37 on Thermal
Measurements and is the direct responsibility of Subcommittee E37.01 on Test
considered unreliable when the purity level of the major
Methods and Recommended Practices.
component of the mixture is less than 98.5 mol % or when the
Current edition approved Feb. 10, 2001. Published March 2001. Originally
incremental enthalpy correction (x) exceeds 20 % of the
published as E 928 – 83. Last previous edition E 928 – 96.
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Annual Book of ASTM Standards, Vol 14.02. original detected enthalpy of fusion.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 928
5.4 This test method is used for quality control, specifica- 7.2 Planimeter, computer- or electronic-based data treat-
tion acceptance, and research. ment or other instrumentation to de
...