ISO 17734-1:2026

Workplace air — Determination of organonitrogen compounds in air using liquid chromatography and mass spectrometry — Part 1: Isocyanates using dibutylamine derivatives

This document specifies a method for the determination of organic isocyanates in workplace air using derivatization with di-n-butylamine (DBA) and chromatographic analysis. This document is applicable to the determination of a wide range of organic isocyanates present in both the gas phase and the particle phase in workplace atmospheres, including monofunctional isocyanates such as isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), butyl isocyanate (BIC) and phenyl isocyanate (PhI); monomeric diisocyanates, including 1,6-hexamethylene diisocyanate (HDI), 2,4- and 2,6-toluene diisocyanate (TDI), 4,4′-methylenediphenyl diisocyanate (MDI), 1,5-naphthyl diisocyanate (NDI), isophorone diisocyanate (IPDI) and 4,4′-dicyclohexylmethane diisocyanate (H12MDI); and multifunctional isocyanates, including oligomeric, prepolymeric and polymeric forms such as biuret-, isocyanurate- and allophanate-adducts. The method covers air sampling using impingers, filters or combinations thereof, and analysis by liquid chromatography with mass spectrometric detection. The useful analytical range is approximately 2,5 ng to 500 ng of isocyanate per sample. For a nominal air sample volume of 15 l, this corresponds to approximately 0,2 µg/m3 to 33 µg/m3. These values can vary depending on the isocyanate analysed. This document does not apply to the determination of amines or aminoisocyanates. For the determination of amines and aminoisocyanates, the method specified in ISO 17734-2[11].

Titre manque — Partie 1: Titre manque

Zrak na delovnem mestu - Določanje organskih dušikovih spojin v zraku s tekočinsko kromatografijo in masno spektrometrijo - 1. del: Določanje izocianatov preko derivatov dibutilamina

ISO 17734-1:2013 podaja splošna navodila za vzorčenje in analizo izocianatov v zraku na delovnem mestu. Kadar se sumi, da se sproščajo amini in aminoizocianati (npr. zaradi toplotne razgradnje PUR), je priporočljivo, da se poleg izocianatov v zraku določijo tudi amini in aminoizocianati, pri čemer se kot reagenta uporabita DBA in etil kloroformat (glej ISO 17734-2).
Metoda je primerna za določanje širokega spektra različnih izocianatov tako v plinski kot delčni fazi. Tipični monofunkcionalni izocianati, ki jih je mogoče določiti, so izocianova kislina (ICA), metil izocianat (MIC), etil izocianat (EIC), propil izocianat (PIC), butil izocianat (BIC) in fenil izocianat (PhI). Tipični monomerni diizocianati vključujejo 1,6-heksametilen diizocianat (HDI), 2,4- in 2,6-toluenski diizocianat (TDI), 4,4'-metilendifenil diizocianat (MDI), 1,5-naftil diizocianat (NDI), izoforon diizocianat (IPDI) in 4,4'-dicikloheksilmetan diizocianat (HMDI). Večfunkcionalni izocianati, ki jih je mogoče določiti, so običajno oligomeri v polimernem MDI, biuret-, izocianurat- in alofanat-adukti ter predpolimerni obliki izocianatov.
Instrumentalna meja zaznavnosti za alifatske izocianate je približno 5 nmol/vzorec, za aromatske izocianate pa približno 0,2 nmol/vzorec. Za vzorec zraka 15 l to ustreza 0,6 ng∙m?3 za HDI in 0,02 ng∙m?3 za TDI.
Uporabno območje metode za vzorec zraka 5 l je približno od 0,001 µg∙m?3 do 200 mg∙m?3 za TDI.

General Information

• Status: Published
• Publication Date: 19-May-2026
• ICS: 13.040.30 - Workplace atmospheres
• Technical Committee: ISO/TC 146/SC 2 - Workplace atmospheres
• Drafting Committee: ISO/TC 146/SC 2 - Workplace atmospheres
• Current Stage: 6060 - International Standard published
• Start Date: 20-May-2026
• Due Date: 22-May-2026
• Completion Date: 20-May-2026
• Ref Project: oSIST ISO 17734-1:2026 - Workplace air - Determination of organonitrogen compounds in air using liquid chromatography and mass spectrometry - Part 1: Isocyanates using dibutylamine derivatives

Relations

• Revises: ISO 17734-1:2013 - Determination of organonitrogen compounds in air using liquid chromatography and mass spectrometry — Part 1: Isocyanates using dibutylamine derivatives
• Effective Date: 27-May-2023

Overview

ISO 17734-1:2026 outlines a standardized method for the determination of organic isocyanates in workplace air. Developed by the International Organization for Standardization (ISO), this standard is essential for ensuring accurate monitoring of isocyanate exposure in occupational environments. It specifies the use of derivatization with di-n-butylamine (DBA) followed by liquid chromatography and mass spectrometry (LC-MS) for the analysis of airborne isocyanates. The method is applicable to both the gas and particle phases, covering a wide range of isocyanate compounds, including monofunctional, monomeric diisocyanates, and multifunctional forms such as oligomeric, prepolymeric, and polymeric isocyanates.

Accurate assessment of isocyanates is critical since these compounds are widely used in the production of polyurethane and present significant health risks such as asthma and dermatitis. Due to their high reactivity and sensitisation potential, isocyanates require sensitive and selective analytical approaches for reliable monitoring well below occupational exposure limits.

Key Topics

• Derivatization with DBA: The core of the method involves capturing isocyanates by reacting them immediately during sampling with di-n-butylamine, forming stable derivatives suitable for chromatographic analysis.
• Air Sampling Techniques: The standard covers the use of impingers and glass fibre filters, either singly or in combination, to collect both gaseous and particulate isocyanates from workplace air. It also addresses solvent-free sampling using DBA-impregnated tubes.
• Chromatographic Analysis: After sampling, isocyanate-DBA derivatives are analyzed by high-performance liquid chromatography (HPLC) with mass spectrometric detection (LC-MS). Alternative detection techniques such as chemiluminescent nitrogen detection (LC-CLND) or ultraviolet detection (LC-UV) may also be employed for some compounds.
• Wide Compound Coverage: The method is suitable for a broad range of isocyanates, such as ICA, MIC, EIC, PIC, BIC, PhI, HDI, TDI, MDI, NDI, IPDI, H12MDI, and various multifunctional derivatives.
• Analytical Range: The method is capable of detecting isocyanate levels from approximately 0.2 µg/m³ up to 33 µg/m³, facilitating workplace exposure assessments below regulatory thresholds.

Applications

• Occupational Exposure Monitoring: The primary application is the routine surveillance and assessment of worker exposure to airborne isocyanates in environments such as polyurethane manufacturing, painting, and plastics production.
• Regulatory Compliance: Organizations can use this standard method to demonstrate compliance with national and international workplace air quality regulations concerning isocyanate exposure.
• Industrial Hygiene: The method supports industrial hygienists in identifying sources of isocyanate emissions and designing effective engineering controls or personal protective equipment programs.
• Research and Product Stewardship: Chemical manufacturers and researchers can use the standardized method for product development, studying isocyanate emissions from new materials, or investigating degradation products during thermal breakdown.

Related Standards

• ISO 17734-2: This part of the series details the determination of amines and aminoisocyanates in workplace air, providing complementary methodologies for comprehensive organonitrogen compound monitoring.
• ISO 3696: Specifies the quality of water required for analytical laboratory use, relevant for sample preparation and reagent solutions in the ISO 17734-1 method.
• ISO 5725-2: Addresses repeatability and reproducibility of measurement methods, essential for validating and verifying laboratory analyses.
• ISO 13137: Sets requirements for pumps used for personal sampling of chemical and biological agents, including their suitability for use with the sampling devices described in this standard.

ISO 17734-1:2026 is an indispensable reference for occupational health and safety professionals, laboratory analysts, and regulatory authorities concerned with the safe handling and monitoring of isocyanates in workplace air. By ensuring reliable, sensitive, and reproducible results, compliance with this standard helps to protect worker health and maintain regulatory adherence.

Standards Content (Sample)

International
Standard
ISO 17734-1
Third edition
Workplace air — Determination of
2026-05
organonitrogen compounds in air
using liquid chromatography and
mass spectrometry —
Part 1:
Isocyanates using dibutylamine
derivatives
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents and materials . 3
6 Preparation of standard solutions . 4
6.1 Reference compounds .4
6.2 DBA derivatives of isocyanates .5
6.2.1 Preparation of isocyanate-DBA derivatives of commercially available isocyanates .5
6.2.2 Preparation of ICA and MIC-DBA .5
6.2.3 Preparation of deuterium-labelled isocyanate-DBA derivatives .5
6.2.4 Characterization .6
6.3 DBA derivatives of bulk isocyanates .6
6.3.1 Preparation .6
6.3.2 Characterization .6
6.4 DBA derivatives of isocyanates in thermal decomposition products of polyurethane
(PUR) or urea-based resins .7
6.4.1 Preparation .7
6.4.2 Characterization .7
6.5 Stability .7
7 Apparatus . 7
8 Air sampling . 10
8.1 Pre-sampling laboratory preparation .10
8.1.1 Cleaning of the sampling equipment .10
8.1.2 Preparation of the reagent solution and extraction solution tubes .10
8.2 Pre-sampling field preparations .10
8.3 Collection of air samples .11
8.3.1 Measurement task .11
8.3.2 Impinger-filter sampling .11
8.3.3 Solvent-free sampling . 12
8.3.4 Post-sampling field preparations . 12
8.4 Blanks . 13
8.5 Raw material . 13
8.6 Shipment of samples . 13
9 Laboratory sample preparation .13
9.1 Sample sequence . 13
9.2 Work-up procedure . 13
9.2.1 General . 13
9.2.2 Solvent-free sampling . 13
10 Instrumental settings . 14
10.1 HPLC program (LC-MS) .14
10.2 HPLC program (LC-CLND) .14
10.3 Mass spectrometer .14
11 Data handling .15
11.1 Identification . 15
11.2 Calibration curves . 15
11.3 Quantification . . . 15
12 Interferences .15

iii
13 Test report .15
14 Determination of performance characteristics .16
14.1 General .16
14.2 Relevant uncertainty contributions and criteria .16
14.3 Assessment of performance characteristics (following the detailed approach in
Reference [20]) .16
14.3.1 Collection efficiency — Relative to particle size distribution .16
14.3.2 Air sampling .16
14.3.3 Analysis .18
14.3.4 Mass of compound in sample blank . 22
14.3.5 Between-laboratory uncertainty contributions . 22
14.3.6 Combined uncertainty . 23
14.3.7 Expanded uncertainty . 23
14.3.8 Uncertainty from performance criteria . 23
Annex A (informative) Performance characteristics .24
Annex B (informative) Examples .26
Annex C (informative) Commercially available products .30
Bibliography .31

iv
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.
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 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
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 146, Air quality, Subcommittee SC 2, Workplace
atmospheres.
This third edition cancels and replaces the second edition (ISO 17734-1:2013), which has been technically
revised.
The main changes are as follows:
— this document has been extensively revised to bring it into line with the current ISO/IEC Directives, Part
2, including updates to structure, terminology, and drafting style;
— the references have been reviewed and updated, and obsolete references have been removed or replaced
where appropriate;
— the Scope has been revised to comply with current ISO requirements and to improve clarity on the
applicability of the method;
— an error regarding the presentation of the analytical performance of the method has been corrected.
A list of all parts in the ISO 17734 series can be found on the ISO website.
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.

v
Introduction
Isocyanates are organic compounds containing the isocyanate functional group (–N=C=O) and have been
used in industry for about 50 years. They are commercially important chemicals mainly used for the
production of polyurethane (PUR). In spite of controls to limit exposures, there are adverse health effects
such as asthma, contact dermatitis and hypersensitivity pneumonitis as consequences of exposure to
isocyanates in some industrial sectors.
The analytical method for the determination of isocyanates in workplace air must be sensitive due to the
high irritation and sensitization properties of isocyanates. Extremely low occupational exposure limits
(OELs) exist in many countries, and concentrations well below the OEL, often less than one hundredth of the
limit, are often to be determined. Isocyanates are very reactive and therefore cannot be analysed directly.
Derivatization during sampling is required in order to prevent interfering reactions. Hundreds of different
isocyanates are used in industry, and many more are formed during thermal degradation of PUR. Therefore,
high selectivity of the analytical method is required for accurate results.
The determination of isocyanates in the work environment using di-n-butylamine (DBA) as a reagent
and liquid chromatography-mass spectrometric detection (LC-MS) has been demonstrated to be a robust
method. The development of the method was initiated when difficulties using the “older” methods during
[1][2]
sampling of isocyanates in complex atmospheres were encountered (e.g. thermal decomposition of PUR).
[3]
The reaction rate between DBA and isocyanates was found to be fast, and high concentrations can be used
[4][5]
to secure instantaneous reactions and eliminate problems with interfering compounds. Using impinger
flasks containing a reagent solution and a filter in series efficiently collects and derivatizes isocyanates in
[6]
both the gas and the particle phase. LC-MS/MS of the isocyanate-DBA derivatives enables highly selective
−6 [7]
and precise determinations down to levels below 10 of the OEL .
Solvent-free sampling can also be performed by using a tube coated with a DBA-impregnated glass fibre
filter followed by an impregnated filter. An impregnation solution containing DBA together with an acid is
[8]
used, and the formed ion pair reduces volatility. DBA remains on the filter even after 8 h of sampling .
Monomeric isocyanates that are formed during thermal decomposition of polymers [typically PUR and
phenol-formaldehyde urea (PFU) resins], such as isocyanic acid and methyl isocyanate, can also be
[6][7][8][9][10]
determined. Volatile isocyanate-DBA derivatives can be determined using gas chromatography-
[9]
mass spectrometric detection (GC-MS). Using the DBA method and derivatization with ethyl chloroformate
makes simultaneous determinations of amine, aminoisocyanates and isocyanates possible, as described in
[11]
the companion method in ISO 17734-2 .
For quantification, reference compounds are necessary but are only available for a few monomeric
isocyanates. Most of the isocyanates that are used in industry for the production of PUR can only be obtained
in technical grade mixtures. Many isocyanates that are formed during thermal degradation are not available
and are not easily synthesized. In this method, a nitrogen-sensitive detector has been used for quantifying
isocyanates in reference solutions. This technique has been demonstrated to be a useful tool, together with
[10][12][13]
MS characterization, in greatly facilitating the production of reference solutions .
For quantifying isocyanates in complex mixtures, MS detection appears to be the current best available
detection technique and provides a unique possibility of identifying unknown compounds. This method
has enabled assessment of new areas for which exposure to isocyanates was not known previously and has
[6][7][8][9][10][12][13]
identified new kinds of isocyanates in the work environment .

vi
International Standard ISO 17734-1:2026(en)
Workplace air — Determination of organonitrogen
compounds in air using liquid chromatography and mass
spectrometry —
Part 1:
Isocyanates using dibutylamine derivatives
1 Scope
This document specifies a method for the determination of organic isocyanates in workplace air using
derivatization with di-n-butylamine (DBA) and chromatographic analysis.
This document is applicable to the determination of a wide range of organic isocyanates present in both
the gas phase and the particle phase in workplace atmospheres, including monofunctional isocyanates
such as isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), butyl
isocyanate (BIC) and phenyl isocyanate (PhI); monomeric diisocyanates, including 1,6-hexamethylene
diisocyanate (HDI), 2,4- and 2,6-toluene diisocyanate (TDI), 4,4′-methylenediphenyl diisocyanate (MDI),
1,5-naphthyl diisocyanate (NDI), isophorone diisocyanate (IPDI) and 4,4′-dicyclohexylmethane diisocyanate
(H12MDI); and multifunctional isocyanates, including oligomeric, prepolymeric and polymeric forms such
as biuret-, isocyanurate- and allophanate-adducts.
The method covers air sampling using impingers, filters or combinations thereof, and analysis by liquid
chromatography with mass spectrometric detection.
The useful analytical range is approximately 2,5 ng to 500 ng of isocyanate per sample. For a nominal air
3 3
sample volume of 15 l, this corresponds to approximately 0,2 µg/m to 33 µg/m . These values can vary
depending on the isocyanate analysed.
This document does not apply to the determination of amines or aminoisocyanates. For the determination of
[11]
amines and aminoisocyanates, the method specified in ISO 17734-2 .
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 3696, Water for analytical laboratory use — Specification and test methods
ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method for
the determination of repeatability and reproducibility of a standard measurement method
ISO 13137, Workplace atmospheres — Pumps for personal sampling of chemical and biological agents —
Requirements and test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
isocyanate
chemical compound containing one or more –N=C=O functional groups
3.2
monomer
chemical compound that joins with other identical compounds to form dimers, trimers, oligomers or
polymers
Note 1 to entry: Classes of isocyanate monomers (include: monoisocyanates, containing one isocyanate functional
group (e.g. methyl isocyanate), diisocyanates [e.g. di(4-isocyanatophenyl)methane (MDI)] and triisocyanates [e.g.
tri(4-isocyanatophenyl)methane].
3.3
diisocyanate
chemical compound with two isocyanate functional groups
3.4
oligomer
compound of low relative molecular mass with multiple isocyanate functional groups, formed by the
combination of isocyanate monomers
3.5
prepolymer
isocyanato-terminated reaction product of a di- or poly-isocyanate that has a stochiometric deficiency, with
a hydroxyl-terminated polyol
Note 1 to entry: These compounds are further reacted to form polyurethanes or similar compounds.
3.6
technical isocyanate
isocyanates produced by isocyanate manufacturers and used as is or with other components according to
its use in the industry
4 Principle
Samples are collected by drawing a known volume of air through a midget impinger flask followed by a
–1
filter. The impinger contains 10 ml of 0,01 mol·l of DBA in toluene and the filter is a glass fibre filter with
no binder.
Solvent-free sampling can also be performed by drawing air through a tube coated with a DBA-impregnated
glass fibre filter followed by an impregnated filter. An impregnation solution containing DBA together with
acetic acid is used, the ion pair so formed reduces the volatility and enables long-time sampling.
After sampling, deuterium-labelled isocyanate-DBA derivatives (used as internal standard) are added
to the sample solutions. The excess reagent and solvent are evaporated, and the samples are dissolved in
acetonitrile. The samples are analysed using reversed-phase LC and electrospray (ESP)-MS detection,
monitoring positive ions. Quantification is made by monitoring selected ions. See Figure 1.
Quantification and qualitative determinations can be performed using different LC-MS or LC-MS/
MS techniques. Liquid chromatography-chemiluminescent nitrogen detection (LC-CLND) or liquid
chromatography-ultraviolet detection (LC-UV) for aromatic isocyanates, can be used for the determination
of higher concentrations of isocyanates.
Reference materials can be characterized using LC-MS/CLND. For characterization of volatile compounds,
gas chromatography-thermionic specific detector (GC-TSD) can also be used.

Figure 1 — Example of a flow diagram of the whole procedure for sampling, sample preparation,
analysis and reporting
5 Reagents and materials
5.1 DBA reagent.
Analytical grade di-n-butylamine is commercially available.
5.2 Solvents.
The reagent solvent, typically toluene and other solvents, such as acetonitrile, isooctane and methanol,
should be of liquid chromatographic quality.
5.3 Formic acid, concentrated formic acid, analytical grade.
5.4 Acetic acid, concentrated acetic acid, analytical grade.
5.5 Pyridine, analytical grade.

5.6 Sodium hydroxide, reagent grade.
5.7 Ethyl chloroformate, analytical grade.
5.8 Urea, analytical grade.
5.9 1,3 dimethyl urea, analytical grade.
5.10 Water, in accordance with ISO 3696, grade 2 water (electrical conductivity less than 0,1 mS/m and
resistivity greater than 0,01 MΩ·m at 25 °C).
5.11 Sulfuric acid 5 mM, 0,27 ml of concentrated sulfuric acid (98 %) analytical grade is added to 1 000 ml
of water.
5.12 Reagent solution.
In a 1 l volumetric flask, dilute 1,69 ml of DBA in toluene and make up to the mark. The solution is stable and
no special care during storage is necessary.
5.13 Reagent solution, for solvent-free sampler.
–1
5.13.1 Solution 1: 0,74 mol·l DBA.
Mix 80 ml methanol and 12,5 ml DBA in a 100 ml volumetric flask. Then while stirring, slowly add 4,16 ml of
acetic acid to the flask. Finally, add methanol to the flask, and make up to the mark.
–1
5.13.2 Solution 2: 1,5 mol·l DBA.
Mix 60 ml methanol and 25 ml DBA in a 100 ml volumetric flask. Then while stirring, slowly add 8,32 ml of
acetic acid to the flask. Finally, add methanol to the flask, and make up to the mark.
5.14 HPLC mobile phases.
5.14.1 LC-MS.
The weak mobile phase (mobile phase A) consists of water and acetonitrile at a volume fraction of 95 %
water and 5 % acetonitrile, with 0,05 % formic acid. The strong mobile phase (mobile phase B) consists of
water and acetonitrile at a volume fraction of 5 % water and 95 % acetonitrile, with 0,05 % formic acid. The
mobile phases are degassed prior to use. The mobile phases are degassed prior to use.
5.14.2 LC-CLND.
The weak mobile phase (mobile phase C) consists of water and methanol at a volume fraction of 95 % water
and 5 % methanol, with 0,05 % formic acid. The strong mobile phase (mobile phase D) consists of water and
methanol at a volume fraction of 5 % water and 95 % methanol, with 0,05 % formic acid. The mobile phases
are degassed prior to use.
6 Preparation of standard solutions
6.1 Reference compounds
Reference compounds are necessary for LC-MS determination of isocyanate derivatives. For the
commercially available isocyanates, the DBA derivatives are easily prepared by direct derivatization with
DBA. DBA derivatives for the isocyanates not commercially available can be made from the bulk material or

from the thermal decomposition of PUR or urea-based resins used at the work place. Alternatively, standard
solutions can be purchased (see Annex C).
6.2 DBA derivatives of isocyanates
6.2.1 Preparation of isocyanate-DBA derivatives of commercially available isocyanates
Many frequently used isocyanates are commercially available from companies supplying laboratory
chemicals such as HDI, 2,4-TDI, 2,6-TDI, 4,4’-MDI, 4,4’-HMDI, 1,5-NDI, IPDI, PhI, MIC, EIC, PIC and BIC. The
purity of the isocyanates varies and some contain isomers.
Calibration standards are made by spiking accurately weighed amounts or volumes (approximately
0,1 mmol) of isocyanates in 100 ml of isooctane. A 1 ml volume is added to 100 ml of toluene containing
–1 –1
0,01 mol∙l of DBA (approximately 0,01 µmol∙ml of the DBA derivative).
The procedure for the synthesis of derivatives is as follows:
a) Dilute 6 mmol of isocyanate in 2 ml of isooctane.
b) Dissolve 60 mmol of DBA in 20 ml of isooctane.
c) Add the isocyanate solution to the DBA solution dropwise under continuous stirring.
d) Evaporate the reaction mixture to dryness in a rotating evaporator.
e) Dry the residue under vacuum to remove excess DBA.
It is also possible to prepare the isocyanate-DBA derivatives by collecting the thermal degradation products
of the corresponding carbamate esters in an impinger flask containing a DBA solution (as specified in
6.2.3.3).
6.2.2 Preparation of ICA and MIC-DBA
When urea is thermally degraded, ICA is formed.
Heat an amount of urea (20 mg) to about 300 °C in a glass tube. Collect the degradation products in an
–1
impinger flask containing DBA in toluene (0,5 mol∙l ). Wash the toluene solution containing the ICA-DBA
derivatives with water, whereupon the organic phase is evaporated in a vacuum centrifuge and the residue
is dissolved in methanol. Characterize the solution, as described in 6.2.4.
The same procedure can be applied for preparation of MIC-DBA derivatives, by collecting thermal
degradation products of 1,3-dimethyl urea.
6.2.3 Preparation of deuterium-labelled isocyanate-DBA derivatives
6.2.3.1 Internal standards
For accurate LC-MS quantifications, internal standards shall be used, not only to compensate for variations
during the work-up procedure, but also to compensate for fluctuation in the MS instrument response.
Ideally, each analyte should have its own deuterium-labelled analogue. For isocyanate-DBA determinations,
it is possible to use DBA derivatives of deuterium-labelled isocyanates or d - and d -DBA derivatives of the
9 18
isocyanates as internal standards.
The quality of the quantification is influenced by the number of deuterium substitutions in the internal
standard (less deuterium in the molecule result in higher precision). Having the deuterium on the isocyanate,
and not on the DBA, has advantages when performing structural identification using MS and MS/MS. It is
then possible to distinguish between labelled and non-labelled fragments that originate from the isocyanate
itself. Therefore, the ideal internal standards are the DBA derivatives of the deuterium-labelled isocyanates.
However, they are labour intensive to prepare and they are only available for a few isocyanates.

The deuterium-labelled d - and d -DBA derivatives are easy to prepare, and any technical isocyanate or
9 18
thermal degradation product can be derivatized and used as internal standard.
6.2.3.2 DBA derivatives of deuterium-labelled isocyanates
Dissolve a 10 mmol aliquot of the deuterium-labelled corresponding amine in 20 ml of toluene. Thereafter,
–1
add 150 µl pyridine and 40 ml of 5 mol∙l sodium hydroxide. Then add 1,5 ml of ethyl chloroformate dropwise
under continuous stirring. After 10 min, the toluene phase is separated, and the solvent is evaporated.
Place the residue containing the formed amine carbamate ester (10 µl) in a glass tube. Heat the tube to
–1
about 300 °C. By connecting the tube to an impinger flask, containing 0,5 mol∙l DBA in toluene, the formed
deuterium-labelled isocyanate is collected as a DBA derivative. Evaporate the solvent and dissolve the
residue in methanol to an appropriate concentration. Characterize the solution, as described in 6.2.4.
6.2.3.3 d -DBA and d -DBA derivatives of the isocyanates
9 18
Prepare the deuterium-labelled d - and d -DBA derivatives by dissolving accurately weighed amounts of
9 18
–1
the isocyanates in 10 ml of 0,1 mol∙l d -DBA or d -DBA in toluene.
9 18
Prepare the deuterium-labelled derivatives of ICA and MIC by placing 20 mg of urea for ICA and 1,3-dimethyl
urea for MIC in a glass tube. Heat the tube to about 300 °C and collect the formed ICA and MIC in impinger
–1
flasks containing 0,1 mol∙l d -DBA or d -DBA in toluene. Evaporate the solutions containing the isocyanate
9 18
d -DBA or d -DBA derivatives to dryness and dissolve the residues in methanol. Characterize the solution,
9 18
as described in 6.2.4.
6.2.4 Characterization
The solutions are diluted in methanol to appropriate concentrations and characterized on the LC-MS and
quantified on the LC-CLND. This technique is nitrogen specific and any nitrogen-containing compound
[14][15][16]
can be used as an external standard, e.g. caffeine. The technique is used in several applications.
Quantification of volatile isocyanate-DBA derivatives can also be made by using GC-TSD.
6.3 DBA derivatives of bulk isocyanates
6.3.1 Preparation
Technical isocyanates are produced by isocyanate manufacturers and are used as is or with other
components according to its use in the industry. These isocyanates are typically multifunctional.
If product data sheets are available and correct, standard solutions for the technical isocyanates can be
prepared in the same way as described in 6.2.1, by adding a known amount of bulk isocyanate to a toluene
solution of DBA. If data regarding the composition and concentrations of different isocyanates are of poor
quality or missing, the bulk material shall be characterized.
The procedure for the technical-grade isocyanate is as follows:
–1
a) Add an aliquot of 10 mg of the isocyanate product to a 10 ml vial containing 0,5 mol∙l DBA.
b) Sonicate the solution and evaporate it to dryness and then dissolve it in methanol.
c) Further dilute the solution with methanol to appropriate concentrations.
d) Characterize the solution, as described in 6.3.2.
6.3.2 Characterization
If the isocyanates that are present in the bulk are known or reference compounds are available, calibration
standards can be prepared as described in 6.2.1.

If the isocyanates that are present in the bulk are unknown, qualitative data are obtained with full-scan
chromatograms for DBA-derivatized bulk material. The obtained structural data together with the LC-
CLND data make it possible to calculate the concentrations of the different components in the solution. The
characterized bulk sample solution is used as a calibration standard for LC-MS.
When prepolymeric forms or complex isocyanates are to be determined, it can be difficult to quantify each
individual isocyanate using LC-MS. However, one or more components can be used as index compounds. The
total isocyanate group (NCO) concentration of the bulk is obtained by titration with DBA (see Reference [17])
and standard solutions can be prepared (dilution). The concentration of isocyanates in the air sample is
estimated by comparison of peak areas. This can be performed with the assumption that the composition
of the bulk material reflects the composition of the airborne isocyanates. The obtained result gives the
concentration of the total isocyanate content in the air. However, detection limits are increased by the factor
of the ratio of the total isocyanate concentration and the assumed concentration of the index isocyanate.
Still, in most cases, levels below one tenth of the threshold limit value (TLV) are possible to determine.
6.4 DBA derivatives of isocyanates in thermal decomposition products of polyurethane
(PUR) or urea-based resins
6.4.1 Preparation
During the thermal decomposition of PUR or urea-based resins, isocyanates that are not commercially
available are formed. PUR or urea-based materials can be thermally decomposed at appropriate
temperatures. The emitted degradation products are collected in impinger flasks (filters in series) containing
–1
0,5 mol∙l DBA. The solutions are evaporated to dryness and the residues are dissolved in methanol.
6.4.2 Characterization
Qualitative data are obtained with LC-MS. The obtained structural data together with the LC-CLND data
make it possible to calculate the concentrations of different components in the solution. The characterized
and diluted sample solution is used as a calibration standard for LC-MS.
6.5 Stability
Solutions of isocyanate-DBA derivatives (MDI, 2,4- and 2,6-TDI, HDI, IPDI, PhI, BIC, PIC, EIC, MIC, and ICA)
have been found stable in toluene, acetonitrile, and methanol for 6 months when stored at 8 °C. NDI-DBA has
limited stability and shall be freshly prepared and quantified before use as a calibration standard.
7 Apparatus
7.1 Sampler, can be either an impinger (7.1.3) followed by a filter (7.1.1) connected in series to the
sampling pump (7.1.5) through a vapour trap (7.1.7) or a solvent-free sampler (7.1.4) connected to the
sampling pump (7.1.5).
7.1.1 Filter.
Use a 13 mm glass fibre filter (binder free) with a pore size of 0,3 µm.
7.1.2 Filter holder.
Use a 13 mm polypropylene filter holder with luer-lock connections.
7.1.3 Midget impingers.
A midget impinger consists of a tapered inlet tube. Match the two parts so that the distance between the
inlet and the receiver bottom is 1 mm to 2 mm. The filter holder is attached to the outlet of the impinger,
by using an impinger with a luer-lock fitting on the outlet. Alternatively, the filter holder is attached to the
outlet of the impinger by flexible tubing.

7.1.4 Solvent-free sampler.
Cut three kinds of glass fibre filters from a glass fibre filter sheet (binder free) with a pore size of 0,3 µm:
a) rectangular filter, 2,5 cm × 5,7 cm;
b) rectangular filter, 1,4 cm × 5,7 cm;
c) round filter, 13 mm diameter.
To prepare the sampler, the different filters are mounted in the tube and the filter holder unimpregnated.
The inside of the tube is lined with filter 1 (2,5 cm × 5,7 cm), so that it covers the inner walls of the tube. Filter
2 (1,4 cm × 5,7 cm) is folded as a “V” and also placed inside the tube to increase the collection efficiency, by
increasing the number of channels in the tube.
The dry sampler is then impregnated by dropwise adding 1,5 ml 1,4 M DBA-acetic acid in methanol to the
filters at the top of the tube. After impregnation, the tube is dried by blowing nitrogen through the tube for
evaporation of methanol.
The round-end filters (diameter of 13 mm) are impregnated by adding 100 µl 0,7 M DBA-acetic acid solution
and dried under nitrogen in open cassettes. When solvent evaporation is complete, the end filters are
mounted on the denuder. Then the complete sampler is sealed at both ends. Impregnation and drying of the
filters are performed in a container filled with nitrogen to avoid contamination. The solvent-free sampler is
shown in Figure 2.
Alternatively, the sampler can be purchased (see Annex C).
Dimensions in millimetres
Figure 2 — Solvent-free sampler

7.1.5 Sampling pump.
–1 –1
Sampling pump capable of maintaining the flow rate at 1 l∙min for impinger-filter sampling and 0,2 l∙min
–1
to 0,8 l∙min for solvent-free sampling during the sampling time.
7.1.6 Tubing.
Use rubber tubing of suitable length and of appropriate diameter to ensure a leak-proof fit to both the pump
and the sampler outlet.
7.1.7 Vapour trap.
Use a vapour trap (with an internal diameter of 17 mm and a length of 140 mm) filled with charcoal (with a
median particle size <3 mm) between the impinger filter and the sampling pump. This is for the protection
of the pump from toluene vapour. The charcoal in the vapour trap needs to be frequently replaced and
recycled, depending on sampling time.
7.2 Flow meter.
Use a portable flow meter capable of measuring the appropriate flow rate with an acceptable accuracy.
7.3 Liquid chromatographic system.
In this method, a micro-LC system is used in order to improve the sensitivity, to minimize the maintenance
on the MS, and to minimize the consumption of the mobile phase. The micro-LC system is described in the
following paragraphs. If desired, this system can be replaced by a conventional LC system.
7.3.1 Autosampler.
7.3.1.1 LC-MS.
On-column focusing is performed by partially filled loops with a total volume of 10 µl. The injection consists
of 2 µl of sample bracketed by two aliquots of 4 µl of a water, methanol and acetonitrile mixture (50 %, 20 %
and 30 %, volume fractions). Any commercially available autosampler capable of making partially filled loop
injections and making sample injections of acceptable accuracy and precision can be used.
7.3.1.2 LC-CLND.
On-column focusing is performed by partially filled loops with a total volume of 10 µl. The injection consists
of 2 µl of sample bracketed by two aliquots of 4 µl of a water and methanol mixture (50 % and 50 %, volume
fractions). Any commercially available autosampler capable of making partially filled loop injections and
making sample injections of acceptable accuracy and precision can be used.
7.3.2 Pumping system (LC-MS and LC-CLND).
–1
An HPLC pump capable of gradient elution with a flow rate of 100 µl∙min is required.
7.3.3 Analytical column (LC-MS and LC-CLND).
An HPLC column capable of separating the different isocyanate derivatives is required.
® 1)
EXAMPLE P
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