ISO 15373:2024

International
Standard
ISO 15373
Second edition
Plastics — Polymer dispersions —
2024-12
Determination of free formaldehyde
Plastiques — Dispersions de polymères — Dosage du
formaldéhyde libre
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Interference. 2
5.1 Method A .2
5.2 Method B .2
6 Reagents (method A and B) . 2
7 Apparatus . 4
8 Procedure . 7
8.1 Preparation of test solution .7
8.1.1 Dilution of test sample.7
8.1.2 Filtration .7
8.1.3 Centrifugation . .7
8.1.4 Coagulation .7
8.2 Blank solution .8
8.3 Check test (method B) .8
8.4 Calibration .8
8.4.1 Method A . . .8
8.4.2 Method B . .8
8.5 Determination of formaldehyde .10
8.5.1 Method A . . .10
8.5.2 Method B .10
9 Calculation .10
10 Precision for method B .11
10.1 Precision estimates .11
10.2 Repeatability .11
10.3 Reproducibility . . 12
10.4 Bias . 12
11 Test report .12
Bibliography .13

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Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 9, Thermoplastic
materials.
This second edition cancels and replaces the first edition (ISO 15373:2001), which has been technically
revised.
The main changes are as follows:
— text is revised according to the latest ISO Directive, Part 2.
— added Figure 1, as illustration of the principle of this method.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 15373:2024(en)
Plastics — Polymer dispersions — Determination of free
formaldehyde
1 Scope
This document specifies two methods for the determination of free formaldehyde (HCHO) in polymer
dispersions.
This document is applicable to acrylic, acrylonitrile butadiene, carboxylated styrene-butadiene and vinyl
acetate polymer dispersions. It is also applicable to polymer dispersions of other compositions.
Method A (UV/Vis spectrometer method) is applicable to polymer dispersions with a free-formaldehyde
content higher than 10 mg/kg.
Method B (HPLC method) is applicable for determining lower formaldehyde contents or carrying out
arbitration analyses.
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 2227, Formaldehyde solutions for industrial use — Determination of formaldehyde content
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
No terms and definitions are listed in this document.
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 polymers dispersed in a polymer dispersion are separated from the aqueous phase by filtration,
centrifuge or coagulation. The resulting aqueous sample solution containing formaldehyde reacts with
2,4-pentanedione to yield a lutidine derivative (see Figure 1), which can be analysed by UV detector at 410 nm.
Figure 1 — Reaction of formaldehyde with 2,4-pentanedione

In method A, 2,4-pentanedione is added directly to the resulting aqueous solution. Absorption at 410 nm is
measured with a UV/Vis spectrometer. The concentration of formaldehyde is determined using a calibration
plot obtained by plotting the absorption at 410 nm of formaldehyde standards against the corresponding
formaldehyde concentrations.
In method B, formaldehyde in the resulting aqueous solution is separated from other species by liquid
chromatography on an octadecyldimethylsilyl (C18) reversed-phase column using an aqueous mobile phase.
The detection system includes a post-column reactor which produces a lutidine derivative by reaction of
formaldehyde with 2,4-pentanedione and a UV/Vis detector operating at 410 nm. The concentration of free
formaldehyde in the resulting aqueous solution is determined using peak areas from the standard and
sample chromatograms (calibration by external standard).
5 Interference
5.1 Method A
The following species have been identified as possible interferants in the method:
— acetaldehyde;
— glyoxylic acid.
However, interference by acetaldehyde and glyoxylic acid is to be expected only when the species concerned
is present in excess amounts (100-fold and more) compared with the formaldehyde concentration.
5.2 Method B
This method is specific for formaldehyde because potential interferants such as acetaldehyde, acetone,
benzaldehyde, formamide, formic acid, glyoxylic acid and propionaldehyde are either chromatographically
separated from formaldehyde or do not react with the post-column reagent.
However, to adapt for various composition in different polymer dispersions, extended chromatography run
time is recommended to allow for late-eluting compounds in Method B. Compounds which remain on the
column after an analysis have potential interference with the formaldehyde peak in subsequent runs.
6 Reagents (method A and B)
Unless otherwise stated, use only reagents of recognized analytical grade and only grade 1 water as defined
in ISO 3696.
6.1 Acetic acid (CH CO H), glacial.
3 2
6.2 Ammonium acetate (CH CO NH ).
3 2 4
6.3 Formaldehyde (HCHO), mass fraction 37 % solution in water.
6.4 2,4-Pentanedione (acetyl acetone) (CH COCH COCH ).
3 2 3
6.5 Phosphoric acid solution, 33 mmol/l.
Dissolve 2,3 ml of mass fraction 85 % phosphoric acid (H PO ) in water and dilute to 1 l with water.
3 4
6.6 Potassium ferrocyanide trihydrate solution, 36 g/l (Carrez solution I).
Dissolve 36 g of potassium ferrocyanide trihydrate (K Fe(CN) ·3H O) in water and dilute to 1 l with water.
4 6 2
6.7 Zinc sulfate heptahydrate solution (ZnSO ·7H O), 72 g/l (Carrez solution II).
4 2
Dissolve 72 g of zinc sulfate heptahydrate (ZnSO ·7H O) in water and dilute to 1 l with water.
4 2
6.8 Sodium hydroxide (NaOH), 0,1 mol/l.
Dissolve 4 g of sodium hydroxide (NaOH) in water and dilute to 1 l with water.
6.9 Sodium phosphate, dibasic (Na HPO ).
2 4
6.10 Nash reagent, post-column reagent, prepared as follows.
6.10.1 Transfer 62,5 g of ammonium acetate (6.2) to a 1 l amber bottle (7.1) that contains a stir bar. Add
600 ml of water to the bottle and mix on a stir plate until the ammonium acetate has completely dissolved.
6.10.2 Pipette 7,5 ml glacial acetic acid (6.1) into the bottle. Pipette 5 ml of 2,4-pentanedione (6.4) into the
bottle. Add 387,5 ml of water to the bottle and mix thoroughly (45 min of mixing is suggested).
If nece
...