ISO 16014-1:2003

INTERNATIONAL ISO
STANDARD 16014-1
First edition
2003-03-15


Plastics — Determination of average
molecular mass and molecular mass
distribution of polymers using size-
exclusion chromatography —
Part 1:
General principles
Plastiques — Détermination de la masse moléculaire moyenne et de la
répartition des masses moléculaires des polymères par
chromatographie d'exclusion stérique —
Partie 1: Principes généraux




Reference number
ISO 16014-1:2003(E)
©
ISO 2003

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ISO 16014-1:2003(E)
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ISO 16014-1:2003(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle . 2
5 Reagents . 3
6 Apparatus. 4
7 Procedure. 8
8 Data acquisition and processing. 8
9 Expression of results. 10
10 Precision . 13
11 Test report. 13
Annex A (informative) Supplementary information. 15
Annex B (informative) Narrow molecular mass distribution standards. 16

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ISO 16014-1:2003(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16014-1 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
ISO 16014 consists of the following parts, under the general title Plastics — Determination of average
molecular mass and molecular mass distribution of polymers using size-exclusion chromatography:
 Part 1: General principles
 Part 2: Universal calibration method
 Part 3: Low-temperature method
 Part 4: High-temperature method


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INTERNATIONAL STANDARD ISO 16014-1:2003(E)

Plastics — Determination of average molecular mass and
molecular mass distribution of polymers using size-exclusion
chromatography —
Part 1:
General principles
1 Scope
This part of ISO 16014 specifies a general method for determining the average molecular mass and the
molecular mass distribution of polymers using size-exclusion chromatography (SEC). The average molecular
mass and the molecular mass distribution are calculated from a calibration curve constructed using polymer
standards. Therefore this method is classified as a relative method (see Clause A.1 in Annex A).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 472, Plastics — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 472 and the following apply.
3.1
size-exclusion chromatography
SEC
a liquid chromatographic technique in which the separation is based on the hydrodynamic volume of
molecules eluting in a column packed with porous non-adsorbing material having pore dimensions that are
similar in size to the molecules being separated
NOTE The term gel permeation chromatography (GPC) should only be used where the porous non-adsorbing
packing material is a gel; however, the term size-exclusion chromatography (SEC) is preferred.
3.2
molecular mass
M
sum of the masses of the atoms making up a molecule
NOTE Molecular weight is also used for molecular mass.
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ISO 16014-1:2003(E)
3.3 Average molecular mass
Four types of average molecular mass are defined by the following equations, where N is the number of
i
molecules of species i of molecular mass M and a is the exponent of the Mark-Houwink-Sakurada equation.
i
3.3.1
number-average molecular mass
M
n
∞
()NM×
ii
∑
i=1
M = (1)
n
∞
N
∑ i
i=1
3.3.2
mass-average molecular mass
M
w
∞
2
()NM×
ii
∑
i=1
M = (2)
w
∞
()NM×
∑ ii
i=1
3.3.3
z-average molecular mass
M
z
∞
3
()NM×
ii
∑
i=1
M = (3)
z
∞
2
()NM×
∑ ii
i=1
3.3.4
viscosity-average molecular mass
M
v
1/ a
∞

a+1
()NM×
ii
∑

i=1
M = (4)
v
∞

()NM×
∑ ii


i=1
4 Principle
A polymer sample is dissolved in a suitable solvent to make a dilute solution. This solution is injected into the
mobile phase and onto the SEC column, which is packed with non-adsorbing material made up of small
particles having pores of similar or varying size. As the polymer sample passes through the column, the
polymer molecules are separated from each other according to the difference in their molecular masses, or
more precisely, the difference in their molecular sizes (i.e. their hydrodynamic volume). In SEC, the larger-size
molecules cannot permeate into the pores, and thus elute faster, while smaller molecules can permeate into
the pores and elute more slowly. The polymer concentration in the eluate is continuously monitored by a
concentration-sensitive detector to give an SEC chromatogram.
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ISO 16014-1:2003(E)
The molecular mass at any elution time on the SEC chromatogram is determined from a calibration curve
which is constructed using reference polymer standards with a narrow molecular mass distribution. The
average molecular mass and the molecular mass distribution is calculated by using the molecular mass and
concentration data corresponding to each elution time.
5 Reagents
5.1 Eluent
The required purity of the eluent used for SEC varies with the application, but in general the solvent should be
free of particulate matter and substances that react with the polymer or interfere with detection of the polymer.
Additives such as antioxidants and salts can be used to prevent the degradation of the eluent, the aggregation
of polymer molecules, the adsorption of the polymer on the packing material and for other purposes. A mixed
eluent may also be used for SEC measurements to modify the solubility and the refractive index, or to reduce
the cost of the mobile phase.
5.2 Reagent for column evaluation
A low molecular mass compound is used for the determination of the theoretical plate number, asymmetry
factor and resolution factor of the column.
5.3 Molecular mass standards
This test method is not an absolute method but a relative one and requires a calibration curve for the
calculation of the average molecular mass and the molecular mass distribution from the SEC chromatogram.
The calibration curve is constructed by the use of standards of known molecular mass and narrow molecular
mass distribution, the value of M and/or M of the standard being determined by an absolute method, such
w n
as light scattering, membrane osmometry, vapour pressure osmometry, ultracentrifugation, end-group
analysis. The polydispersity M /M is calculated by dividing the absolute value of M by the absolute value of
w n w
M . The polydispersity of the polymer standards shall lie within the following ranges:
n
3
M < 2 × 10 M /M < 1,20
p w n
3 6
2 × 10 u M < 10 M /M < 1,10
p w n
6
10 u M M /M < 1,20
p w n
where
M is the mass-average molecular mass;
w
M is the number-average molecular mass;
n
M is the molecular mass at peak maximum, calculated using Equation (5) if the molecular mass
p
distribution of the polymer sample shows a logarithmic normal distribution (in the case of very
efficient separation giving many peaks, use the highest peak):
1/ 2
MM=×()M (5)
pn w
Some examples of commercially available molecular mass standards are given in Annex B.
5.4 Reagent for flow rate marker (internal standard)
A low molecular mass compound is used to monitor the accuracy of the elution time, i.e. to evaluate whether
or not the data are within the specification.
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ISO 16014-1:2003(E)
5.5 Additives
Additives to the eluents may be used to improve SEC performance and prevent sample degradation and the
like.
6 Apparatus
6.1 General
A schematic diagram of an SEC system is shown in Figure 1. The essential components are an eluent
reservoir, a pumping system, an injector, column(s), a detector, tubing, a recorder, a temperature-control
system, and a data-processing system. Any component that meets the performance requirements specified
for this method may be used.
Both commercially available SEC systems and SEC systems assembled in the laboratory may be used for this
method, provided they meet the required levels of performance.

Key
1 eluent reservoir 6 computer
2 pump 7 recorder
3 injector 8 display
4 columns 9 plotter
5 detector 10 to waste
Figure 1 — Schematic diagram of SEC system

6.2 Eluent reservoir
The eluent reservoir shall have sufficient capacity to hold the amount of eluent required for column calibration
and successive measurements. Dissolved air in the eluent shall be removed before use by placing the solvent
in a suitable container designed to reduce the pressure and placing this container in an ultrasonic bath, or by
using a vacuum degasser between the reservoir and the pumping system. Particles in the eluent may be
removed by membrane filtration. It is desirable in addition to bubble an inert gas through the eluent in the
reservoir and blanket the surface of the eluent with the gas, and to shield the reservoir from light.
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ISO 16014-1:2003(E)
6.3 Pumping system
A constant, pulseless flow of eluent through the column is desirable. It is recommended that the flow rate be
3
adjusted to about 1 cm /min for a column of around 8 mm inner diameter. The SEC system shall have an
overall flow-rate precision of within ± 0,3 %. Lower flow rates are recommended for high molecular mass
and/or shear-sensitive polymers and viscous eluents. To keep the flow rate constant, temperature control
providing stability to at least ± 1 °C is needed for the pumping system.
The flow rate shall be monitored frequently by the use of an internal standard, or by a direct method such as
volume or mass measurements, and corrected in the event of significant deviations. In this test method,
knowledge of the value of the flow rate is not required because the method is a relative one in which the result
is calculated from a calibration curve constructed from measurements on molecular mass standards.
6.4 Injector
In addition to having an eluent bypass capability, the injector shall be able to hold the sample solution and
inject the sample solution into the columns with minimum band broadening and minimum pressure change.
To maintain the required precise flow rate, temperature control equipment, or a precise air conditioner, is
needed for the injection system.
6.5 Columns
6.5.1 General
The function of the columns is to separate the sample molecules according to differences in their molecular
size (mass). Columns usually consist of a stainless-steel tube with end fittings, filters and a porous packing
material. There is no limitation on the column length or diameter or on the packing-material particle size. The
performance of the columns shall be such that they are suitable for use with an SEC system as specified in
this part of ISO 16014.
6.5.2 Determination of theoretical plate number
Use a low molecular mass compound, such as ethylbenzene, to obtain a peak (see Figure 2) and calculate
the theoretical plate number N of the set of columns from equation (6) or (7):
2
Nt=×5,55 ( /W ) (6)
e1/2
2
Nt=×16 ( /W ) (7)
e
where
t is the elution time to the peak maximum;
e
W is the peak width at half height;
1/2
W is the difference between the intersection of the two tangents of the peak and the baseline.
6.5.3 Determination of resolution factor
The resolution factor R of the set of columns can be calculated from Equation (8) by the use of the calibration
curve (see 9.1 and Figure 5) and a molecular mass standard (see 5.3 and Figure 3) with a narrow molecular
mass distribution that elutes at a point close to the apex of the sample peak:
RD=×1/( W ) (8)
STD
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