ISO 6923:2023

INTERNATIONAL ISO
STANDARD 6923
First edition
2023-09
Paints and varnishes — Determination
of monomeric diisocyanate content in
coating materials and similar products
using high performance liquid
chromatography with ultraviolet
detection (HPLC-UV)
Reference number
ISO 6923:2023(E)
© ISO 2023

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ISO 6923:2023(E)
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© ISO 2023
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Published in Switzerland
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ISO 6923:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus . 1
6 Reagents . 3
7 Reference standards . 4
8 Sampling . 4
9 Procedure .4
9.1 Sample preparation . 4
9.2 Calibration . 5
9.2.1 Preparation of the standard . 5
9.2.2 Quantification . 5
10 Calculation . 7
11 Expression of results . 8
12 Test report . 8
Annex A (informative) Details of validation. 9
Bibliography .10
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ISO 6923:2023(E)
Foreword
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This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 16, Chemical analysis.
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ISO 6923:2023(E)
Introduction
The analytical method described in this document was developed in 2011. The validity of this method
has been continuously tested until it was finalized in 2015 for the low content monomer diisocyanate
under 0,20 % mass fraction. Several internal interlaboratory tests have clearly demonstrated its
reproducibility. Moreover, under the framework of interlaboratory tests organized by the Association
of the European Adhesive and Sealant Industry (FEICA), it has been shown that the described method is
accurate in determining monomer diisocyanate content in various polyurethane (PU) matrices.
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INTERNATIONAL STANDARD ISO 6923:2023(E)
Paints and varnishes — Determination of monomeric
diisocyanate content in coating materials and similar
products using high performance liquid chromatography
with ultraviolet detection (HPLC-UV)
1 Scope
This document specifies a method for the quantitative determination of monomeric diisocyanate
content in coating materials, adhesives and other liquid or pasty materials.
This method is suitable for the quantification of the following monomeric diisocyanates: methylene
diphenyl diisocyanate (MDI, 2,4’-MDI and 4,4’-MDI), toluene diisocyanate (TDI, 2,6-TDI, 2,4-TDI), (cis/
trans) isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI,1,6-HDI) in various
matrices for concentrations ranging from 0,01 % to 2,0 % mass fraction. For higher concentrations, a
suitable dilution before the derivatization with p-nitrobenzyl-N-propylamine (PNBPA) is performed.
The measurements are carried out using ultra high performance liquid chromatography (UHPLC) with
a multiple wavelength detector.
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 4618, Paints and varnishes — Vocabulary
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
The sample is directly weighed into a 10 ml measuring flask (the mass depends on the isocyanate
content). The flask is filled with dry acetonitrile to the mark. Subsequently, in a vial, an aliquot of the
solution is derivatised with PNBPA in dry acetonitrile (1+1 by volume). After filtration, the clear solution
is injected directly into the HPLC.
5 Apparatus
Use ordinary laboratory apparatus and glassware together with the following.
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ISO 6923:2023(E)
5.1 HPLC/UV with the parameters given in Table 1.
Table 1 — Parameters
b
System HPLC system with a pressure up to 600 bar and a quaternary gradient pump, including a
thermostat oven
Detector Multiple wavelength detector
Column HPLC column superficial porous particles, C18 100 Å, particle size 2,6 µm, column dimension
TMa
100 x 3 mm, e.g. Kinetex
Column oven (30 ± 1) °C
Mobile phase A 40 mM sodium acetate (pH 4,5)
Mobile phase B fresh deionised water
Mobile phase C acetonitrile
Gradient
Time A % B % C %
(min)
 −4,00 55 0 45
 0,00 55 0 45
 3,25 45 0 55
 5,70 35 0 65
 5,80 0 35 65
 6,00 0 35 65
 7,00 0 5 95
 10,00 0 5 95

Flow rate 1,40 ml/min
Detection UV 275 nm 2,6-TDI, 2,4-TDI, c/t-IPDI, 1,6-HDI
UV 250 nm 2,4’-MDI; 4,4’-MDI
Injection volume 2,5 µl
a
Kinetex is the trade name of a product supplied by Phenomenex. This information is given for the convenience of users
of this document and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if
they can be shown to lead to the same results.
b 5 2
1 bar = 0,1 MPa = 10 Pa; 1 MPa = 1 N/mm .
5.2 Balance
In the 60 g range, expect readability of 0,01 mg, repeatability of 0,015 mg, and linearity of ±0,08 mg.
5.3
...