ISO 17735:2009
(Main)Workplace atmospheres — Determination of total isocyanate groups in air using 1-(9-anthracenylmethyl)piperazine (MAP) reagent and liquid chromatography
Workplace atmospheres — Determination of total isocyanate groups in air using 1-(9-anthracenylmethyl)piperazine (MAP) reagent and liquid chromatography
ISO 17735:2009 gives general guidance for the sampling and analysis of airborne organic isocyanates in workplace air. ISO 17735:2009 is appropriate for a wide range of organic compounds containing isocyanate groups, including monofunctional isocyanates (e.g. phenyl isocyanate), diisocyanate monomers (e.g. 1,6-hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and isophorone diisocyanate (IPDI), prepolymers (e.g. the biuret and isocyanurate of HDI), as well as intermediate products formed during production or thermal breakdown of polyurethane. In mixed systems of HDI and IPDI products, it is impossible to identify and quantify low levels of IPDI monomer using ISO 17735:2009, due to coelution of IPDI monomer with HDI-uretidinedione. The useful range of the method, expressed in moles of isocyanate group per species per sample, is approximately 1 x 10-10 to 2 x 10-7.
Air des lieux de travail — Dosage des groupements isocyanates totaux dans l'air par réaction avec la 1-(9-anthracénylméthyl)pipérazine (MAP) et par chromatographie en phase liquide
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 17735
First edition
2009-03-15
Workplace atmospheres — Determination
of total isocyanate groups in air using
1-(9-anthracenylmethyl)piperazine (MAP)
reagent and liquid chromatography
Air des lieux de travail — Dosage des groupements isocyanates totaux
dans l'air par réaction avec la 1-(9-anthracénylméthyl)pipérazine (MAP)
et par chromatographie en phase liquide
Reference number
ISO 17735:2009(E)
©
ISO 2009
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ISO 17735:2009(E)
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ii © ISO 2009 – All rights reserved
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ISO 17735:2009(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Principle. 1
4 Reagents and materials . 3
5 Apparatus . 7
6 Air sampling . 9
6.1 Pre-sampling laboratory preparation. 9
6.2 Pre-sampling field preparation. 10
6.3 Collection of air samples . 10
6.4 Blanks and negative controls. 11
6.5 Bulk products. 11
6.6 Shipment of samples. 11
6.7 Filter test samples . 11
6.8 Impinger test samples. 12
7 HPLC analysis . 12
7.1 Instrumental settings. 12
7.2 HPLC programme . 12
8 Data handling . 14
8.1 Monomer measurement . 14
8.2 Oligomer measurement (total detectable isocyanate). 14
9 Calibration and quality control. 14
9.1 Standard matching solutions . 14
9.2 Calibration curves. 15
9.3 Blank tests. 15
9.4 Bulk products. 15
9.5 Quality control spikes . 15
10 Calculations. 15
10.1 Monomer. 15
10.2 Oligomers (total detectable isocyanate). 16
11 Interferences . 16
12 Determination of performance characteristics. 17
12.1 Introduction . 17
12.2 Assessment of performance characteristics. 18
Annex A (informative) Performance characteristics. 25
Bibliography . 27
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ISO 17735:2009(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 17735 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 2, Workplace
atmospheres.
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ISO 17735:2009(E)
Introduction
This International Standard specifies the use of 1-(9-anthracenylmethyl)piperazine (MAP) to measure
monomeric and oligomeric isocyanate species in workplace atmospheres. MAP was designed to improve the
reliability of identification of isocyanate species in sample chromatograms and to improve the accuracy of
quantification of these species relative to established reagents. The high performance liquid chromatography
(HPLC) analysis uses a pH gradient to selectively accelerate the elution of MAP derivatives of oligomeric
isocyanates that might be unobservable in an isocratic analysis. The performance of MAP has been compared
to other reagents used for total isocyanate analysis (Reference [7]). MAP has been found to react with phenyl
isocyanate (used as a model isocyanate) as fast or faster than other reagents commonly used for isocyanate
analysis. The UV response of MAP derivatives is comparable to that of 9-(methylaminomethyl)anthracene
(MAMA) derivatives and considerably greater than other commonly used reagents [approximately three times
greater than 1-(2-methoxyphenyl)piperazine (1-2MP) derivatives of aromatic isocyanates and 14 times greater
than 1-2MP derivatives of aliphatic isocyanates]. The compound-to-compound variability of UV response per
isocyanate group for MAP derivatives is smaller than the variability of any other commonly used
reagent/detector combination (the coefficient of variation is 3,5 % for five model isocyanates). This results in
accurate quantification of detectable non-monomeric isocyante species based on a calibration curve
generated from analysing standards of monomeric species. The monomeric species used for calibration is
generally the one associated with the product being analysed, but others could be used due to the very small
compound-to-compound response variability of the MAP derivatives. The intensity of fluorescence response of
MAP derivatives is comparable to that of MAMA derivatives and considerably greater than other reagents (e.g.
approximately 30 times more intense than that of tryptamine derivatives). The compound-to-compound
variability in fluorescence response has been found to be smaller than that of MAMA derivatives but larger
than that of tryptamine derivatives (MAMA = 59 % coefficient of variation, MAP = 33 % coefficient of variation,
and tryptamine = 16 % coefficient of variation for 5 model isocyanates). The compound-to-compound
fluorescence variability of MAP derivatives is considered too great for accurate quantification of non-
monomeric isocyanate species based on calibration with monomer standards. However, the sensitivity of the
fluorescence detection makes it especially suitable for quantification of low levels of monomer, and the
selectivity is very useful to designate an unidentified HPLC peak as a MAP derivative. MAP derivatives also
give a strong response by electrochemical detection. The pH gradient used in the HPLC analysis selectively
accelerates the elution of amines (MAP derivatives are amines), and is very strong (it accelerates MDI more
than 100-fold). Re-equilibration to initial conditions is almost immediate. Many oligomeric species can be
measured in the 30 min MAP analysis that may be unobservable in a much longer isocratic analysis.
MAP has been used in several studies comparing it side-by-side with other methods. Reference [8] found
MAP impingers and NIOSH 5521 impingers (comparable to MDHS 25) to give comparable results in spray
painting environments. Reference [8] used MAP reagent, but the pH gradient was not employed.
Reference [9] compared MAP impingers with several other impinger methods (NIOSH 5521 and NIOSH 5522)
and the double filter method. The average MAP oligomer value was substantially higher than the other
impinger methods and slightly higher than the double filter method. The pH gradient was used in these MAP
analyses.
The MAP method is currently available as NIOSH Method 5525 (Reference [11]). The performance
characteristics of the method have been evaluated in Reference [12].
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INTERNATIONAL STANDARD ISO 17735:2009(E)
Workplace atmospheres — Determination of total isocyanate
groups in air using 1-(9-anthracenylmethyl)piperazine (MAP)
reagent and liquid chromatography
1 Scope
This International Standard gives general guidance for the sampling and analysis of airborne organic
isocyanates in workplace air.
This International Standard is appropriate for a wide range of organic compounds containing isocyanate
groups, including monofunctional isocyanates (e.g. phenyl isocyanate), diisocyanate monomers (e.g.
1,6-hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), 4,4’-diphenylmethane diisocyanate (MDI),
and isophorone diisocyanate (IPDI), prepolymers (e.g. the biuret and isocyanurate of HDI), as well as
intermediate products formed during production or thermal breakdown of polyurethane.
In mixed systems of HDI and IPDI products, it is impossible to identify and quantify low levels of IPDI
monomer using this International Standard, due to coelution of IPDI monomer with HDI-uretidinedione.
The useful range of the method, expressed in moles of isocyanate group per species per sample, is
−10 −7
approximately 1 × 10 to 2 × 10 .
2 Normative references
The following referenced documents are indispensable for the application 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 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 16200-1, Workplace air quality — Sampling and analysis of volatile organic compounds by solvent
desorption/gas chromatography — Part 1: Pumped sampling method
3 Principle
A measured volume of air is drawn through either an impinger containing a solution of
1-(9-anthracenylmethyl)piperazine (MAP), a filter impregnated with MAP, or a sampling train consisting of an
impinger followed by an impregnated filter. The choice of sampler depends on the chemical and physical
characteristics of the airborne isocyanate (Reference [13]). If an impinger is used, the solution is subjected to
solid-phase extraction (SPE) and the eluate is concentrated and analysed by reverse phase high performance
liquid chromatography (HPLC) with ultraviolet (UV) absorbance and fluorescence (FL) detection in series. If an
impregnated filter is used for sampling, it is extracted with solvent either in the field after completion of
sampling or in the laboratory. Waiting to extract the filter until after the sample has been received by the
analytical laboratory is acceptable only for analysis of isocyanates collected as vapour. This solution is filtered
and analysed by HPLC/UV/FL. Isocyanate-derived peaks are identified based on their UV and FL responses
and by comparison with the chromatogram of a derivatised bulk isocyanate product if available. Quantification
of compounds for which analytical standards are available (generally monomers) is achieved by comparison
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ISO 17735:2009(E)
of the FL peak height of the sample peak with the FL peak height of standard matching solutions.
Quantification of compounds for which analytical standards are not available is achieved by comparison of the
UV area of the sample peak with the UV area of the appropriate monomer standard (i.e. the monomer from
which the isocyanate product is derived).
Structures of some common diisocyanate monomers are shown in Figure 1.
Key
1 methyl isocyanate
2 butyl isocyanate
3 phenyl isocyanate
4 4,4’-MDI
5 2,6-TDI
6 HDI
7 2,4-TDI
8 IPDI
9 HMDI
Figure 1 — Structures of some common isocyanates
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ISO 17735:2009(E)
4 Reagents and materials
CAUTION — Observe appropriate safety precautions when preparing reagents. Carry out preparations
under a fume hood to avoid exposure to solvents, isocyanates or other volatile reagents. Wear nitrile
gloves when manipulating reagents and solvents.
During the analysis, unless otherwise stated, use only reagents of HPLC grade or better, and water of HPLC
grade.
4.1 MAP reagent
MAP is prepared by the reaction of 9-(chloromethyl)anthracene with piperazine as shown in Figure 2.
The procedure using HPLC grade solvents is as follows.
Dissolve 10,8 mmol (2,47 g) of 9-(chloromethyl)anthracene (98 % mass fraction) in 25 ml methylene chloride.
Place this solution in a dropping funnel.
Dissolve 54,4 mmol (4,69 g) of piperazine (99 % mass fraction) and 21,8 mmol (3,04 ml) of triethylamine
(99,5 % mass fraction) in 37 ml methylene chloride. Place this solution in a 250 ml 2-necked round-bottomed
flask with a magnetic stirring bar.
While stirring this solution, add the 9-(chloromethyl)anthracene solution dropwise over a 30 min period. Rinse
down the dropping funnel with an additional 10 ml of methylene chloride. Allow the reaction to continue while
stirring for at least 2 h.
Using a separating funnel, wash the reaction mixture three times with 130 ml water by shaking vigorously for
1 min. Discard the emulsion that forms after the first wash, which contains primarily an impurity and not MAP.
Discard the aqueous washings.
Place the washed MAP solution in a weighed round-bottomed flask. Allow the methylene chloride to evaporate
under a steady stream of nitrogen. Weigh the flask with the residue to obtain an approximate yield. This crude
MAP can be safely stored in a freezer until further purification.
MAP is purified by column chromatography followed by sublimation. Using a glass chromatography column of
internal diameter approximately 50 mm, add a slurry of silica gel in toluene until the silica gel bed is
approximately 80 mm deep. Wash the sides of the column down with toluene and allow the toluene to run
through the column until the toluene is even with the silica gel surface.
Dissolve the crude MAP in 80 ml of toluene. Sonicate the mixture for 5 min and filter through filter paper. Save
the filtrate. Resuspend the residue in 20 ml toluene, sonicate for 5 min, and filter through filter paper. Discard
the residue. Combine the filtrates and carefully load them onto the top of the silica gel bed. Pass an additional
bed volume of toluene through the column. Discard the toluene eluate.
Begin to elute with ethyl acetate. Begin collecting 20 ml fractions in disposable vials with caps lined with
polytetrafluoroethylene (PTFE). Monitor the fractions by spotting 1 µl of each on a thin layer chromatography
(TLC) sheet (see below) and viewing the intensity of the spot under UV light after the solvent has evaporated.
This procedure indicates the presence of compounds in the fraction, which may or may not be MAP. Elute
with ethyl acetate until the yellow colour has been eluted, which requires about 400 ml ethyl acetate. The MAP
should be completely retained on the column at this point. After elution of the yellow colour, begin eluting with
methanol, which requires 1,0 l to 1,5 l methanol.
The elution of the MAP can be readily followed by TLC. A portion of the fractions that had given a significant
spot on the TLC sheet are analysed by TLC to determine which fractions contain MAP.
The TLC procedure is carried out as follows. Use commercially available TLC sheets coated with silica gel
and containing a fluorescent indicator. A portion of a sheet measuring 100 mm × 30 mm is adequate. Spot
aliquots of volume 1 µl of several fractions adjacent to each other approximately 15 mm from the bottom of the
sheet and place the sheet in a small jar containing methanol 10 mm deep. Cover the jar and allow the
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ISO 17735:2009(E)
methanol to climb up the sheet to 5 mm from the top. Remove the sheet and allow the methanol saturating the
sheet to evaporate. MAP produces a dark spot when viewed under short wavelength UV light which glows
under irradiation with long wavelength UV. Identify the MAP spot by comparing the retention factor, R , of the
f
aliquot spots with the R of a MAP standard.
f
Based on TLC analyses, combine the fractions containing pure MAP. Weigh a round-bottomed flask to be
used for rotary evaporation. Add the combined fractions to the flask, but do not exceed half the volume of the
flask at any given time. Heat the evaporator bath to 35 °C to 40 °C and use water aspirator vacuum. After
evaporation and trace solvent removal from all of the combined MAP fractions under high vacuum, weigh the
flask and its contents to assess the yield.
Purify the MAP powder further by sublimation. Dissolve the MAP in a small volume of methylene chloride
(< 20 ml) and transfer the solution to a sublimation apparatus. Allow the methylene chloride to evaporate
under a gentle stream of nitrogen, keeping the MAP below the level of the bottom of the coldfinger. When the
methylene chloride has evaporated, seal the vessel and reduce the pressure with a vacuum pump to
1)
6,67 mPa or less. Begin a slow flow of cold water through the coldfinger and place the sublimation vessel in
a wax bath maintained at 125 °C to 130 °C. Sublimation takes many hours and may need to continue
overnight. Sublimation is complete when there is no further growth of MAP crystals on the coldfinger and the
small amount of material remaining at the bottom of the apparatus appears constant. When complete, remove
the crystals from the coldfinger with a spatula. A typical yield is 2,236 g (74 % mass fraction). The melting
point of the MAP is 146 °C to 147 °C. The purity of MAP as assessed by HPLC is typically 99 % mass fraction.
Key
1 9-(chloromethyl)anthracene
2 piperazine
3 MAP
Figure 2 — Preparation of MAP
4.2 Reagent solutions
4.2.1 Impinger solution
Butyl benzoate, 99 % mass fraction, is used as the impinger solvent. The butyl benzoate is further purified by
passing it through a bed of chromatography-grade silica gel. Dissolve MAP in the butyl benzoate to make a
−4
1 × 10 mol/l solution (27,6 mg/l). Store the solution in a refrigerator until use.
1) 1 Pa = 7,5 torr.
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ISO 17735:2009(E)
4.2.2 Solution for filter impregnation
MAP is dissolved in acetonitrile to make a solution of 2 mg/ml. Store in a freezer until use.
4.2.3 Filter extraction solution
−4
MAP is dissolved in acetonitrile to make a 1 × 10 mol/l solution (27,6 mg/l). Store in a freezer until use.
4.2.4 Stability of reagent solutions
It is best to make filter-spiking solution immediately before use, but this solution can be stored for up to
2 weeks in a freezer. The impinger and filter extraction solutions are stable for at least 1 month in a
refrigerator.
4.3 Standard matching solutions
The UV detector response is nearly identical for all MAP-derivatised isocyanate groups. This allows the use of
the MAP-derivatised monomer of the isocyanate product of interest as a standard for quantification of the
other unknown oligomeric MAP-derivatised species in the chromatogram. A calibration curve, plotting UV
response as a function of number or concentration of isocyanate groups, can then be used to quantify the
oligomeric species for which there is no standard available. For this reason, it is conceptually simpler to use
standard matching solutions quantified in terms of their concentration of isocyanate groups rather than in
terms of mass concentration of isocyanate compound.
An equivalent is the amount of substance of isocyanate compound containing a mole of isocyanate group or
the amount of substance of MAP-derivatised isocyanate compound containing a mole of bound MAP groups.
The equivalent mass of an isocyanate compound is the relative molecular mass divided by the number of
isocyanate groups per molecule, n. The equivalent mass of a MAP-derivatised isocyanate compound is the
relative molecular mass divided by the number of MAP groups per molecule. The number of isocyanate
groups, irrespective of their attachment, can be measured in moles per litre. Table 1 lists relative molecular
masses and equivalent masses for common isocyanates and their MAP derivatives.
4.3.1 Preparation of monomer derivatives
Accurately weigh approximately 0,5 mmol (1 milliequivalent) of diisocyanate or 1 mmol (1 milliequivalent) of a
monoisocyanate and record the amount of substance to four decimal places. Dissolve in 10 ml of toluene.
Weigh approximately 1,2 mmol of MAP (20 % mass fraction excess) and record the amount of substance to
four decimal places. Dissolve in 20 ml of toluene. While stirring the MAP solution, add the isocyanate solution
dropwise over a period of 10 min to 15 min. Continue to stir for at least 1 h. Tightly cover the solution and
store overnight in a freezer to maximise precipitation of product. Collect the precipitate using a Büchner funnel.
Wash the precipitate several times with cold toluene to remove residual MAP, then wash it several times with
cold hexane to displace the toluene. Transfer the solid derivative to a preweighed 20 ml disposable vial.
Subject the vial to high vacuum until constant mass is obtained and seal with a PTFE-lined cap. Yields are
typically > 95 % mass fraction and purity is sufficient to use this material for standard matching solutions.
Experience shows that when stored in the dark in a freezer, these derivatives are stable for several years.
4.3.2 Preparation of standard solutions of monomer derivatives for HPLC analysis
−5 −5
Of a MAP derivative, weigh approximately 5,0 × 10 mol (monoisocyanate) or 2,5 × 10 mol (diisocyanate)
−5 [1]
(5,0 × 10 equivalents) into a 10 ml one-mark volumetric flask, ISO 1042 , class A. Dissolve in several
millilitres dimethyl formamide (DMF) and fill to the mark with DMF. Methylene chloride can be used instead, if
desired, for MAP derivatives that are very soluble in methylene chloride (aliphatic diisocyanates and 2,4-TDI).
−3 −3
The stock solutions are of approximate concentration 5,0 × 10 mol/l (monoisocyanate) or 2,5 × 10 mol
(diisocyanate). Store the stock solutions in a freezer. Working standards are made by dilution into acetonitrile,
−4
with the highest concentration standard being approximately 2,0 × 10 mol/l (monoisocyanate) or
−4
1,0 × 10 mol/l (diisocyanate). Other concentrations can be made by serial dilution, typically the lowest
−7 −7
concentration being approximately 1 × 10 mol/l (monoisocyanate) or 0,5 × 10 mol/l (diisocyanate). These
stock solutions and dilutions are stable for up to 3 months when stored in a refrigerator.
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ISO 17735:2009(E)
Table 1 — Relative molecular masses and equivalent masses of some common isocyanates
and their MAP derivatives
Equivalent
Relative MAP derivative
Short MAP derivative
mass
Compound molecular relative molecular
form equivalent mass
mass mass
m[eq]
1-(9-Anthracenylmethyl)piperazine MAP 276,38 276,38 — —
Methyl isocyanate 57,05 57,05 333,43 333,43
Butyl isocyanate 99,13 99,13 375,51 375,51
Phenyl isocyanate 119,12 119,12 395,50 395,50
1,6-Hexamethylene diisocyanate
HDI 168,20 84,10 720,96 360,48
1,6-diisocyanatohexane
Toluene diisocyanate (both 2,4-
TDI 174,16 87,08 726,92 363,46
and 2,6-diisocyanatotoluene)
Isophorone diisocyanate
1-isocyanato-3-isocyanatomethyl- IPDI 222,29 111,14 775,05 387,52
3,5,5-trimethylcyclohexane
4,4’-Diphenylmethane diisocyanate 4,4’-
250,26 125,13 803,02 401,51
Di-(4-isocyanatophenyl)methane MDI
Hydrogenated MDI
Methylenebis(cyclohexyl-4-isocyanate)HMDI 262,35 131,18 815,11 407,56
4,4’-Dicyclohexylmethane diisocyanate
Isocyanate group NCO 42 42 — —
4.3.3 Preparation of standard solutions of monomer derivatives for solid-phase extraction (SPE)
Evaluate recovery of MAP-derivatised monomers through solid-phase extraction (SPE) cartridges periodically.
Stock solutions in DMF cannot be used to make SPE standards because even low concentrations of DMF
appear to cause premature elution of MAP derivatives. Standards to be passed through an SPE cartridge
...
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