ASTM D6953-03
(Test Method)Standard Test Method for Determination of Antioxidants and Erucamide Slip Additives in Polyethylene Using Liquid Chromatography (LC)
Standard Test Method for Determination of Antioxidants and Erucamide Slip Additives in Polyethylene Using Liquid Chromatography (LC)
SIGNIFICANCE AND USE
Separation and identification of stabilizers used in the manufacture of polyethylene resins are necessary in order to correlate performance properties with polymer composition. This test method provides a means to determine BHT, BHEB, Isonox 129, erucamide slip, Irgafos 168, Irganox 1010, Irganox 1076 and TNPP levels in polyethylene samples. This test method should be applicable for the determination of other antioxidants such as Ultranox 626, Ethanox 330, Santanox R, and Topanol CA, but the stability of these during extraction has not been investigated.
The additive extraction procedure is made effective by the relatively low solubility of the polymer sample in solvents generally used for liquid chromatographic analysis. In this method, isopropanol and cyclohexane were chosen because of their excellent extraction efficiencies as well as for safety reasons. Other solvents including ethylacetate, isobutanol, chloroform and methylene chloride can also be used.
Methods other than refluxing that have been used to remove additives from the polymer matrix include microwave, ultrasonic, and supercritical fluid extractions. For the separation of the extracted additives, SFC and GC have been used successfully for several of the additives.
Under optimum conditions, the lowest level of detection for an antioxidant is approximately 2 ppm.
SCOPE
1.1 This test method covers a liquid-chromatographic procedure for the separation of some additives currently used in polyethylene. These additives are extracted with either isopropanol (resin densities 3) or cyclohexane (resin densities > 0.94 g/cm3) prior to liquid-chromatographic separation. The ultraviolet absorbance of the eluting compound(s) is measured and quantitation is performed using external calibration.
1.2 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. Specific precautionary statements are given in Section 9.
Note 1—There is no equivalent ISO standard.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D6953–03
Standard Test Method for
Determination of Antioxidants and Erucamide Slip Additives
in Polyethylene Using Liquid Chromatography (LC)
This standard is issued under the fixed designation D6953; 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 E1657 Practice for Testing Variable-Wavelength Photomet-
ric Detectors Used in Liquid Chromatography
1.1 This test method covers a liquid-chromatographic pro-
IEEE/ASTM SI 10 Standard for Use of the International
cedure for the separation of some additives currently used in
System of Units (SI): The Modern Metric System
polyethylene. These additives are extracted with either isopro-
panol (resin densities < 0.94 g/cm ) or cyclohexane (resin
3. Terminology
densities > 0.94 g/cm ) prior to liquid-chromatographic sepa-
3.1 Definitions:
ration. The ultraviolet absorbance of the eluting compound(s)
3.1.1 For definitions of plastic terms and detector terminol-
is measured and quantitation is performed using external
ogy used in this test method, see Terminologies D883, D1600,
calibration.
and E1657.
1.2 This standard does not purport to address all of the
3.1.2 Forunitsandsymbolsusedinthistestmethod,referto
safety concerns, if any, associated with its use. It is the
Terminology E131 or IEEE/ASTM SI 10.
responsibility of the user of this standard to establish appro-
3.2 Additives:
priate safety and health practices and determine the applica-
3.2.1 BHEB, Prodox 500—2,6-di-t-butyl-4-ethylphenol or
bility of regulatory limitations prior to use. Specific precau-
butylated hydroxyethyl benzene, CAS No. 4130-42-1.
tionary statements are given in Section 9.
3.2.2 BHT, CAO-3, Noclizer M-17—2,6-di-t-butylcresol or
NOTE 1—There is no equivalent ISO standard.
butylated hydroxy toluene, CAS No. 128-37-0.
3.2.3 Irgafos 168—Tris(2,4-di-t-butylphenyl)-phosphite,
2. Referenced Documents
CAS No. 31570-04-4.
2.1 ASTM Standards:
3.2.3.1 Oxidized Irgafos 168—Tris(2,4-di-t-butylphenyl)-
D883 Terminology Relating to Plastics
phosphate.
D1600 Terminology for Abbreviated Terms Relating to
3.2.4 Irganox 1010—Tetrakis[methylene(3,5-di-t-butyl-4-
Plastics
hydroxyhydrocinnamate)] methane CAS No. 6683-19-8.
D4697 Guide for Maintaining Test Methods in the User’s
3.2.5 Irganox 1076—Octadecyl-3-(3,5-di-t-butyl-4-
Laboratory
hydroxyphenyl)-propionate, CAS No. 2082-79-3.
E131 Terminology Relating to Molecular Spectroscopy
3.2.6 Isonox 129—2,2’-ethylidene bis(4,6-di-t-
E169 Practices for General Techniques of Ultraviolet-
butylphenol), CAS No. 112-84-5.
Visible Quantitative Analysis
3.2.7 Kemamide-E, Erucamide—Cis-13-docosenamide,
E275 Practice for Describing and Measuring Performance
CAS No. 112-84-5.
of Ultraviolet and Visible Spectrophotometers
3.2.8 TNPP, Weston 399—Tris(nonylphenyl)phosphite,
E691 Practice for Conducting an Interlaboratory Study to
CAS No. 26523-78-4.
Determine the Precision of a Test Method
3.2.8.1 Hydrolyzed TNPP—Nonylphenol, CAS No. 104-
40-5.
3.2.8.2 Oxidized TNPP—Tris(nonylphenyl)phosphate, CAS
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
No. 26569-53-9 (available in small quantities from GE Spe-
Current edition approved July 10, 2003. Published August 2003. DOI: 10.1520/
cialty Chemicals as XR2616).
D6953-03.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4. Summary of Test Method
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
4.1 The polyethylene sample is ground to a 1-mm (~20
the ASTM website.
mesh) or 0.5-mm (~40 mesh) particle size and extracted by
Withdrawn. The last approved version of this historical standard is referenced
refluxing with either isopropanol or cyclohexane.
on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6953–03
4.2 The solvent extract is analyzed by liquid chromatogra- 7.3 DataAcquisition/Handling System, providing the means
phy. for determining chromatographic peak areas and for handling
4.3 Additive concentrations are determined from external and reporting data.This is best accomplished using a computer
calibration curves using reverse phase chromatography (C-8 or with appropriate software.
C-18 column) with ultraviolet (UV) detection at wavelengths 7.4 Mill—Cutting Mill (Wiley) or Centrifugal Grinding Mill
corresponding to the wavelengths of an absorption apex of (Brinkmann), equipped with 1-mm (~20 mesh) and 0.5-mm
each additive (except erucamide which does not have an (~40 mesh) screens.
absorption maximum in the accessible UV region). 7.5 Reflux Extraction Apparatus, consisting of a condenser,
(24/40 ground-glass joint), a round-bottom 125-mL flask
5. Significance and Use having a 24/40 ground-glass joint, and a heating mantle.
7.6 Boiling Chips.
5.1 Separation and identification of stabilizers used in the
7.7 Filter System, (PTFE ), for non-aqueous solutions (pore
manufacture of polyethylene resins are necessary in order to
size of 0.22 µm).
correlate performance properties with polymer composition.
7.8 Analytical Balance, capable of weighing to 60.0001 g.
This test method provides a means to determine BHT, BHEB,
7.9 Top Loading Balance, capable of weighing to 60.01 g.
Isonox129,erucamideslip,Irgafos168,Irganox1010,Irganox
1076 and TNPP levels in polyethylene samples. This test
8. Reagents and Materials
method should be applicable for the determination of other
8.1 Solvents:
antioxidants such as Ultranox 626, Ethanox 330, Santanox R,
8.1.1 Isopropanol—HPLC grade, spectro-quality or chro-
andTopanolCA,butthestabilityoftheseduringextractionhas
matography quality reagent.
not been investigated.
8.1.2 Cyclohexane—HPLC grade, spectro-quality or chro-
5.2 The additive extraction procedure is made effective by
matography quality reagent.
the relatively low solubility of the polymer sample in solvents
8.1.3 Water—HPLC, or UV quality reagent, degassed by
generally used for liquid chromatographic analysis. In this
sparging with high-purity helium or by filtration under
method, isopropanol and cyclohexane were chosen because of
vacuum.
their excellent extraction efficiencies as well as for safety
8.1.4 Acetonitrile—HPLC, spectro-quality or chromatogra-
reasons. Other solvents including ethylacetate, isobutanol,
phy quality reagent (a reagent whose UV cutoff is about 190
chloroform and methylene chloride can also be used.
nm).
5.3 Methods other than refluxing that have been used to
8.2 Additives:
remove additives from the polymer matrix include microwave,
8.2.1 High purity additives and degradation products (see
ultrasonic, and supercritical fluid extractions. For the separa-
3.2).
tion of the extracted additives, SFC and GC have been used
successfully for several of the additives.
9. Precautions
5.4 Under optimum conditions, the lowest level of detection
9.1 Isopropanol and cyclohexane are flammable. This ex-
for an antioxidant is approximately 2 ppm.
traction procedure should be carried out in a fume hood.
6. Interferences
10. Preparation of Solutions
6.1 Any material eluting at or near the same retention time
10.1 Polymer Samples:
as the additive can cause erroneous results. This includes
10.1.1 Grind the sample to a particle size of 1 mm, that is,
degradation products of the additives.
~20 mesh (density < 0.94 g/cm ) or 0.5 mm, that is, ~40 mesh
6.2 A major source of interferences can be from solvent
(density > 0.94 g/cm ).
impurities. For this reason, the solvents should be examined by
HPLC using the same analysis conditions as for the samples
NOTE 2—Unless sample amount is limited, grind a minimum of 10 g. It
(see Section 12). is important to minimize the time of grinding to prevent any thermal
degradation of the additives in the polymer. Some erucamide is known to
6.3 The grinding process may cause a low bias. For ex-
be lost during grinding.
ample, some erucamide slip is known to be lost to the grinder
NOTE 3—Acutting-type mill is needed for film samples. Because of its
surface and excessive grinding may cause degradation of the
higher efficiency, a centrifugal-type mill is recommended for pellet
antioxidants.
samples.
10.1.2 Weigh,tothenearest0.01g,approximately5gofthe
7. Apparatus
sample, that is, W , into a pre-weighed (to the nearest 0.01
sample
7.1 Liquid Chromatograph, equipped with a multiple wave-
g) 125-mL flat-bottom flask containing boiling chips, that is,
length (see Practices E169 and E275) or photodiode array
W . Add approximately 50.0 mL of isopropanol or cyclo-
flask
ultraviolet detector, heated column compartment, and gradient
hexane and boil for a minimum of 2 h.
elution capabilities. The liquid chromatograph should be
NOTE 4—Isopropanol is used as the extraction solvent for densities of
equipped with a means for a 10-µL injection such as a sample
3 3
lessthan0.94g/cm andcyclohexanefordensitieshigherthan0.94g/cm .
loop.
7.2 Chromatographic Column, C-8 or C-18 reverse phase, 10.1.3 Cool the solution to room temperature by raising the
5-µm particle size, 15 cm by 4.6 mm or equivalent, capable of flask from the heating mantle while still attached to the
separating the additives and their degradation products. condenser.
D6953–03
10.1.4 Weigh the cooled flask to the nearest 0.01 g, that is, 2~t 2 t !
R,2 R,1
R 5 (4)
~W 1 W !
W .
1 2
(flask + sol)
10.1.5 Attach a filter disk assembly to a 5-mL Luer-Lok tip
where:
hypodermic syringe.
t ,t = peak elution time in minutes of Additives 1
R,1 R,2
10.1.6 Decant approximately 4 mL of the solvent extract
and 2, and
into the above syringe.
W,W = peak width in minutes of Additives 1 and 2
1 2
10.1.7 Insert the plunger and carefully apply pressure to
determined by measuring the distance between
force the solvent extract through the filter into a sample vial.
the baseline intercepts of lines drawn tangent
10.1.8 Calculate the amount (mg) of sample per kg of
to the peak inflection points.
solution, [Sample] :
sol
11.1.1 For an extracted additives mixtures containing any
10 W combination (including degradation products) of those listed in
sample
@Sample# 5 (1)
sol
~W 2 W !
3.2, the resolution of any two peaks measured at a single
~flask 1 sol! flask
wavelength must be greater than one, that is, R > 1. For peaks
10.2 Concentrated Additive Standards:
with R# 1, two wavelengths are needed to measure the two
10.2.1 Prepare two to three mixtures in 125-mL septum
components (see 15.2).
bottles by weighing the bottles, including septum and cap, to
the nearest 0.1 mg.
NOTE 5—A resolution of R = 1 represents a peak overlap of approxi-
mately 3 %.
10.2.2 Weigh into a bottle, to the nearest 0.1 mg, approxi-
mately 0.2 g of each additive.
11.2 Plate Count Number—A 10-cm column packed with
10.2.3 Fill the bottle with either isopropanol or cyclohex-
5-µm particles is expected to have a plate count in excess of
ane, cap and weigh the bottle on a top loading balance to the
60 000 plates calculated in accordance with the following
nearest 10 mg.
expression:
10.2.4 Agitate the bottle to speed up dissolution.
t
R
10.2.5 Calculate the concentration, [Additive] , of each N 5 16 (5)
S D
conc
W
additive in the concentrated standard in mg/kg (that is, ppm) as
follows: where:
t = peak elution time in minutes, and
R
10 W
add
W = peak width in minutes as determined as outlined in
@Additive# 5 (2)
conc
~W 1 W !
Tadd sol
Section 11.
11.2.1 No minimum number is required as long as the
where:
resolution requirement of 11.1 is met.
W = weight (g) of individual additive,
add
W = total weight (g) of all additives, and
Tadd
12. Preparation of Liquid Chromatograph
W = weight (g) of solvent.
sol
12.1 Flow Rate—2.0 mL/min.
10.3 Dilute Additive Standards:
12.2 Mobile Phase Gradient:
10.3.1 Prepare four dilute standards of each concentrated
12.2.1 Initial Mobile Phase—60 % acetonitrile and 40 %
standard by weighing 30-mLseptum bottles, including septum
water.
and cap, to the nearest 0.1 mg.
12.2.2 Final Mobile Phase Condition—100 % acetonitrile
10.3.2 Add with a 5-mL syringe, 0.5 mL, 1.0 mL, 2.0 mL,
and 0 % water.
and 5.0 mL of a concentrated solution to each of four of the
12.2.3 Gradient Length—6 min.
30-mL bottles and weigh to the nearest 0.1 mg.
12.2.4 Gradient Curve—Linear.
10.3.3 Fill the bottles with isopropanol or cyclohexane, cap,
12.2.5 Hold at 100 % acetonitrile and 0 % water for 3 min.
mix and weigh to the nearest 1 mg.
12.2.6 Return to 60 % acetonitrile and 40 % water at 9 min
10.3.4 Calculate the concentration, [Additive] , of each
dil
at a flow rate of 2 mL/min for 4 min.
additive in the dilute standards in mg/kg (that is, ppm) as
follows:
NOTE 6—The flow rate and gradient conditions listed in 12.1 and 12.2
havebeenusedsuccessfullywitha15-cmby4.6-mmcolumnpackedwith
W @Additive#
conc conc
@Additive# 5 (3)
dil 5-µm C-8 reverse phase particles (see Fig. 1).The optimum flow rate (that
~W 1 W !
conc sol
is, 1.0 to 2.0 mL/min) and the exact gradient will depend on the column
used and the additive formulations typically analyzed (see Section 11 for
where:
performance requirements).
W = weight (g) of concentrated standard solu-
conc
tion,
12.3 Detector—Ultraviolet detector with a range setting of
[Additive] = concentration (mg/kg) of additive in con-
conc about 0.1 AUFS at the following wavelengths:
centrated standard (see 10.2.5), and
200 nm for erucamide slip
W = weight (g) of solvent used for dilution.
210 nm for oxidized Irgafos 168
sol
217 nm for TNPP and its degradation products
270 nm for Irgafos 168
11. Performance Requirements
280 nm for BHEB, BHT, Irganox 1010, Irganox 1076 and Isonox 129
11.1 Resolution—The resolution (R) provides an indication
NOTE 7—Erucamide does not have an absorption peak in the accessible
of the component separation and band broadening of a column.
UV region. The absorption at 200 nm represents the tailing end of an
For Gaussian-shaped peaks, the resolution is defined as: absorption peak at a wavelength of less than 190 nm. Because of the steep
D6953–03
FIG. 1 Chromatogram of Multicomponent Antioxidant Standard Recorded at 200 nm
slopeoftheshoulder,awavelengthprecisionofbetterthan1nmisneeded
14. Procedure
to avoid unacceptable fluctuations in detector response (that is, extinction
14.1 Useliquidchromatographicconditionsasprescribedin
coefficient). Frequent injections of an eruc
...
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