BS ISO 15033:2018 pdf download – Plastics — Determination of caprolactam and its cyclic and linear oligomers by HPLC
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
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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.
5.23 Post-column derivatization reagent. 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 components of interest is obtained.
The lifetime of the reversed-phase C18 column is very strongly influenced by the C18-silica bonding of the packing material. Therefore, columns equipped with a packing material containing monofunctional silanes with diisobutyl side-chain groups are preferred. These side groups sterically protect the key silanes from hydrolytic attack at low pH, making the stationary phase stable at such pH (pH 1).BS ISO 15033 pdf download.