ISO 15033:2018

© ISO 2018 – All rights reserved
ISO/TC 61/SC 5
Deleted: 04
Date:  2018‐06
ISO/PRF 15033:2018(E)
ISO/TC 61/SC 5/WG 11
Secretariat:  DIN
Plastics — Determination of caprolactam and its cyclic and linear oligomers
by HPLC
Plastiques — Détermination du caprolactame et de ses oligomères cycliques et linéaires
par CLHP
Document type: International Standard
Document subtype:
Document stage: (40) Enquiry
Document language: E
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Contents Page
Foreword . 3
Introduction . 4
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 3
7 Test sample . 4
8 Procedure. 4
8.1 Calibration . 4
8.1.1 Method A. 4
8.1.2 Method B. 5
8.2 Determination . 5
8.2.1 Method A. 5
8.2.2 Method B. 7
9 Calculations . 7
9.1 Calculation of calibration factors . 7
9.1.1 Calibration factors for cyclic oligomers . 7
9.1.2 Calibration factors for linear oligomers . 8
9.2 Test sample . 8
9.2.1 Calculation of cyclic oligomer concentrations . 8
9.2.2 Calculation of linear oligomer concentrations . 9
10 Precision . 9
11 Test report . 10
Annex A (normative) HPLC parameters and injector programme — Using eluent A . 11
Annex B (normative) HPLC parameters and injector programme — Using eluent B . 12
Annex C (informative) Schematic diagram of HPLC apparatus . 13
Bibliography . 14

© ISO 2018 – All rights reserved
ii
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
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matters of electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
This third edition cancels and replaces the second edition (ISO 15033:2007), which has been technically
revised to add method B.
© ISO 2018 – All rights reserved
iii
Introduction
The method A specified in this document can be used for HPLC determination of the cyclic oligomers of
caprolactam (n = 1) up to and including the hexamer (n = 6), using UV detection. If desired, after post‐
column reaction of the primary amine with 1,2‐phthalic dicarboxaldehyde, online determination of the
linear oligomers up to and including the hexamer can also be carried out.
The determination is not quantitative for oligomers higher than the hexamer (n > 6). In the
determination of cyclic oligomers the sensitivity for the tetramer and higher oligomers is constant,
which means that calibration should take place up to and including the tetramer (n = 4).
The linear oligomers are determined by the fluorescence of the iso‐indole group, which is a product of
the reaction between the primary amino group, 1,2‐phthalic dicarboxaldehyde and
3 mercaptopropionic acid. The calibration with the linear oligomers should be carried out up to and
including the hexamer (n = 6).
The method B included in this document is intended for the determination of caprolactam and its cyclic
dimer only, following the same principle and using the same equipment as method A, but significantly
faster.
© ISO 2018 – All rights reserved
iv
Deleted: INTERNATIONAL
INTERNATIONAL STANDARD ISO 15033:2018(E)
STANDARD
Plastics — Determination of caprolactam and its cyclic and
linear oligomers by HPLC
SAFETY STATEMENT — Persons using this document should be familiar with normal laboratory
practice, if applicable. This document does not purport to address all of the safety concerns, if any,
associated with its use. It is the responsibility of the user to establish appropriate safety and health
practices and to determine the applicability of any other restrictions.
1 Scope
This document describes a high‐performance liquid chromatography (HPLC) method for determining
the concentrations of cyclic oligomers of caprolactam, from 0,01 % by mass upwards, and linear
oligomers of caprolactam, from 5 mg/kg upwards, both up to and including the hexamer of caprolactam
(n = 6), in samples of polyamide 6, caprolactam and mixtures of rearrangement products in water.
A second, significantly faster, HPLC method is included for determination of caprolactam and its cyclic
dimer, based on the same principle and using the same equipment as the first method.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 Principle
A test sample is dissolved in, or diluted with, formic acid and the oligomers separated in the presence of
a low‐pH mobile phase using a column filled with reversed‐phase packing material. The cyclic oligomers
are detected by UV absorption at 200 nm. If desired, the linear oligomers can be detected by
fluorescence after post‐column reaction of the primary amino group with 1,2‐phthalic
dicarboxaldehyde and 3‐mercaptopropionic acid. The concentrations are calculated by comparison of
the measured values with those of calibration solutions.
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade.
5.1 Water, ultrapure or double‐distilled.
5.2 Phosphoric acid, 85 % by mass.
© ISO 2018 – All rights reserved
5.3 Phosphoric acid, 1 mol/l. Introduce 68 ml of phosphoric acid (5.2) into a 1 l volumetric flask,
make up to the mark with water (5.1) and mix well.
5.4 Acetonitrile.
5.5 Formic acid, concentrated.
5.6 Caprolactam.
5.7 Cyclic dimer of caprolactam, isolated by HPLC (see Note).
5.8 Cyclic trimer of caprolactam, isolated by HPLC (see Note).
5.9 Mixture of cyclic oligomers of caprolactam, isolated by HPLC (see Note).
5.10 ε-Aminocaproic acid.
5.11 Linear dimer of ε-aminocaproic acid.
5.12 Linear trimer of ε-aminocaproic acid.
5.13 Linear tetramer of ε-aminocaproic acid.
5.14 Linear pentamer of ε-aminocaproic acid.
5.15 Linear hexamer of ε-aminocaproic acid.
5.16 Helium.
5.17 Eluent.
— Eluent A
Add 10 ml of acetonitrile (5.4) and 10 ml of phosphoric acid (5.3) to 900 ml of water (5.1). Raise the
pH of the solution to 2,6 using sodium hydroxide flakes (5.19). Make up to 1 l and saturate with
helium (5.16).
— Eluent B
Add 10 ml of phosphoric acid (5.3) to 900 ml of water (5.1). Raise the pH of the solution to 2,6 using
sodium hydroxide flakes (5.19). Make up to 1 land saturate with helium (5.16).
NOTE The analysis time for determination of caprolactam and its dimer using eluent B is significantly shorter
than using eluent A.
5.18 Sodium tetraborate decahydrate.
5.19 Sodium hydroxide flakes.
5.20 1,2-Phthalic dicarboxaldehyde.
5.21 Methanol, 96 % by volume.
5.22 3-Mercaptopropionic acid.
5.23 Post-column derivatization reagent.
© ISO 2018 – All rights reserved
Dissolve 76 g of sodium tetraborate decahydrate (5.18) and 6 g of sodium hydroxide (5.19) in 2 l of
water (5.1). Dissolve 1,6 g of 1,2‐phthalic dicarboxaldehyde (5.20) in 40 ml of methanol (5.21) and add
this solution to the sodium tetraborate decahydrate reagent. Add 1,5 ml of 3‐mercaptopropionic acid
(5.22) and mix well.
The stability of the post‐column derivatization reagent is limited. Do not keep for longer than 3 days.
NOTE The cyclic dimer, the cyclic trimer and the mixture of cyclic oligomers of caprolactam can be isolated
from a methanol extract of polyamide 6 (PA6) by preparative HPLC, using the HPLC methods described here. The
purity of the dimer and the possible presence of other oligomers can be checked using the methods described in
this document.
6 Apparatus
6.1 HPLC equipment, having the following specifications:
— Eluent pump, including mixer, damper and manometric module, giving an eluent flow rate of
0,51 ml/min and a pressure drop of approximately 10 MPa.
— Injector, e.g. an auto‐sampler capable of 1 µl to 250 µl injections, equipped to carry out a variable
injector programme (see Annex A). The injector shall be capable of accommodating at least three
components in the sample loop, i.e. the injector programme shall be capable of controlling the
“sandwich” injection of up to three components into the sample loop plus a solvent injection in one
HPLC run.
— Column:
— stainless steel;
— inside diameter: 3 mm;
— length: 250 mm;
— temperature: 40 °C;
— packing: reversed‐phase C18 silica or equivalent;
— particle size: 0,005 mm.
The resolution of the column shall be such that baseline separation of the
...