ASTM D7252-06

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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An American National Standard
Designation:D7252–06
Standard Test Method for
Polyurethane Raw Materials: Determination of Monomer and
Isomers in Isocyanates
This standard is issued under the fixed designation D7252; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 5. Significance and Use
1.1 This test method determines the percent by weight of 5.1 This test method can be used for research or for quality
monomeric isomers and total monomer in crude or modified control to characterize isocyanates used in polyurethane prod-
isocyanates. The test method is applicable to methylene-bis- ucts.
(4-phenylisocyanate) (MDI) and polymethylene polyphenyli-
6. Apparatus
socyanates (PMDI). (See Note 1.)
6.1 High Performance Liquid Chromatograph, consisting
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the of:
6.1.1 Binary (or greater) solvent pump, capable of main-
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- taining a pulse-free flow rate of 1-3 millilitres per minute
6.1.2 Sample injector, automatic or manual, capable of
bility of regulatory limitations prior to use.
reproducibly injecting a 2 microlitre volume
NOTE 1—There is no known ISO equivalent to this standard.
6.1.3 Column heater, capable of maintaining a temperature
of 30 6 0.2°C
2. Referenced Documents
6.1.4 UV detector, capable of measurements at 235 nm.
2.1 ASTM Standards:
6.1.5 Chart recorder or Data system, capable of peak area
D883 Terminology Relating to Plastics
integration.
E682 Practice for Liquid Chromatography Terms and Rela-
6.2 HPLC analytical column, 250 mm by 4.6 mm by 5 µm
tionships
cyano stationary phase
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method NOTE 2—Other chromatographic columns can be used provided it is
ascertained that similar chromatographic performance is obtained.
3. Terminology
6.3 Magnetic Stirring Hotplate.
3.1 For definitions of terms used in these test methods see
Terminology D883. 7. Reagents and Materials
7.1 Purity of Reagents—Reagent-grade chemicals are to be
4. Summary of Test Method
used in all tests. Unless otherwise indicated, it is intended that
4.1 The sample is reacted (derivatized) with methanol to
all reagents conform to the specifications of the Committee on
form a mixture of methyl urethanes. The urethanes mixture is
Analytical Reagents of theAmerican Chemical Society, where
then separated by normal phase high performance liquid
such specifications are available. Other grades can be used,
chromatography (HPLC). The separated, derivatized isomers
provided it is first ascertained that the reagent is of sufficiently
are quantified through the use of an internal standard.
high purity to permit its use without lessening the accuracy of
the determination.
7.1.1 Acetanilide, 99.9 % purity, to be used as an internal
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
standard.
and is the direct responsibility of Subcommittee D20.22 on Cellular Materials -
7.1.2 Acetonitrile, dry. Dry this and reagents below over
Plastics and Elastomers.
molecular sieve for twenty-four hours.
Current edition approved April 1, 2006. Published April 2006. DOI: 10.1520/
D7252-06.
7.1.3 Ethanol, dry. Use of ethanol denatured with methanol
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
(such as SDA-30) can be used if more readily available.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
7.1.4 Hexane, dry.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 7.1.5 Methanol, dry.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7252–06
7.1.6 Eluent solution, Mix 1:1 by volume of dry methanol test, agreement on the standard material to be used in testing
and ethanol. must be obtained between the testing laboratory and the
7.1.7 Derivatization solution, Dissolve 0.20 g of acetanilide recipient of the final test results. Several strategies in obtaining
in 1 L of dry methanol. suitable standard material have been used.
10.1.1 Several isomers of suitable purity are commercially
8. Sampling available, such as those from Sigma/Aldrich (2,4’-MDI
#51881-6; 4,4’-MDI #25643-9). These individual isomers are
8.1 Since organic isocyanates react with atmospheric mois-
combined to produce a primary standard with isomers in the
ture to form ureas, take special precautions in sampling. Usual
same range as the samples.
sampling methods (for example, sampling an open drum with
10.1.2 Alternatively, monomer of suitable purity consisting
athief),evenwhenconductedrapidly,cancausecontamination
of unknown quantities of the isomers of interest can be
of the sample with insoluble urea. Therefore, blanket the
analyzed by gas chromatography with a flame ionization
sample with dry air or nitrogen at all times. (Warning—
detector. An area percent technique is employed to determine
Organic isocyanates are toxic when absorbed through the skin,
the isomer content. Again, agreement between the testing
or when the vapors are breathed. Provide adequate ventilation
laboratory and the recipient of the final test results must be
and wear protective gloves and eyeglasses.)
obtained for the specific conditions of the gas chromatographic
determination.
9. Instrument Preparation
10.2 Regardless of which of the strategies above is used, the
9.1 Theinstrumentsettingsherearetobeusedasaguidefor
primary standard is prepared and analyzed as described in the
laboratoryspecificinstrument-columncombinations,whichare
following sections.
to be adjusted to provide adequate separation and sensitivity as
described in Practice E682.
11. Procedure
9.1.1 Pump
11.1 Sample Preparation
Flow = 1.5 mL/min
11.1.1 Weigh the sample to be analyzed in a 250 mLbeaker.
Eluent A (hexane) = 90 %
Use the formula below to determine the correct weight. Record
Eluent B (1:1 by volume ethanol:methanol) = 10 %
actual weight to the nearest 0.1 milligram.
9.1.2 Detector
Wavelength = 235 nm
Weight of sample ~milligrams! 5
Expected wt % monomer in sample
Output Range = 2.000 au full scale
(1)
9.1.3 Additional Settings
11.1.2 Dissolve the sample in 20 mL of dry acetonitrile and
Injection volume=2µL
add exactly 100 mL of the derivatization solution. Add a
Column Temperature = 30°C
stirring bar, cover with watch glass and heat on hotplate/stirrer
Stop Time = 25 minutes
for fifteen minutes. The hotplate temperature must be set such
Post Run Time = 10 minutes
that the sample solution begins to boil in 7-10 minutes.
9.1.4 Solvent Program
11.1.3 Remove the sample solution from heat and allow to
9.1.4.1 After the components of interest have eluted, it is
cool to room temperature.
desirable to flush the remainder of the material from the
11.2 Analysis
column to avoid interference with subsequent analyses. A
11.2.1 Prior to injecting any sample, allow the chromato-
solvent program such as the one below can be used for analysis
graphic system to equilibrate by pumping the initial eluent
and cleanup:
through the column for at least 20-30 minutes. When a stable
(1) Initial
baseline is observed, analyze an aliquot of the derivatized
Eluent A = 90 %
sample solution.After all isomers of interest have eluted, flush
Eluent B = 10 %
the column as specified by the solvent program above.
Hold for 15 minutes.
(2) Column Flush
12. Calculation
EluentA=0%
12.1 Calculate the weight percent of isomer “i” as follows:
Eluent B = 100 %
Hold for 10 minutes. sample
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