current issues in measurement of airborne isocyanates ... · current issues in measurement of...

Current Issues in Measurement of Airborne Isocyanates

Gunnar Skarping, Marianne Dalene, Daniel Karlsson, Daniel Gylestam

socyanates & Health, past present and future 2013 04 04

Isocyanate exposure

• Physical state, particle/gas phase• Reacting aerosol• Thermal degradation products

+

Polyurethane is formed in an exoterm reaction between isocyanates and diols. Necessary properties are achieved with additives.

The diols are typically esters or ethers. Aromatic amines such as MOCA and MDA are used in elastomers

Additives: Catalysts, Fire retardants, Water, Solvents, Pigments Formic acid, Waxes Antistatic, Foaming and Crosslinking agents,

dioldiol

dioldiol

dioldiol

dioldioldiol

diol

dioldiol

diisocyanate

diisocyanate

diisocyanate

diisocyanatediisocyanatediisocyanate

diisocyanate

diisocyanatediisocyanate

diisocyanate

diisocyanate

diisocyanate

diisocyanate


diisocyanate


diisocyanate

dioldiol

dioldiol

dioldiol

diol

dioldiol

diol

dioldiol

By-product

By-productBy-product

diisocyanate diol diisocyanatediol diisocyanate

diol diisocyanate dioldiisocyanate diol

diisocyanate

diol

4

diisocyanate diol diisocyanatediol diisocyanate

diol diisocyanate dioldiisocyanate diol

diisocyanate

diol

diisocyanate diol diisocyanate

Heat/Energy decompose PUR-polymers

Mono-isocyanates:, PIC, BIC PhI, ICA, MIC, EIC

Carbonyl compounds

Aromatic/ aliphatic amines e.g. TDA, MDA

Aminoisocyanate

Biocides, Fire-retardants, Pigments, etc.

Gas and particles are formed

diisocyanate diol

diisocyanate diol

5

Spraying applicationsIn car repair shops

Spraying applications

MDI based PUR

Spraying applications

• Identification of molecular ions [M+H]+, [MNa]+

• Identification of typical fragments [DBA+H]+, [MH-DBA]+

• Comparison with spectra from d9-DBA derivative

MS characterisation

Thermal degradation

In car repair shops

CO

OR

OC

N

O

HN

CH3

C

H

O

OR

OC

N

O

H CH3

NC

H

O

OR

OCO

CH3

NCOOCN

CH3

NCOH2N

CH3

NH2H2N

CH3

NH2OCN

CH3

NCOOCN NH2

CH3

H2N

NCOCH3

H2N

Thermal degradation

Emission of amines and aminoisocyanates

Isocyanate emission during fire- Small-scale combustion experiments in a Cone Calorimeter

0

1

10

100

1000

10000

Glass w

ool

Nitrile

rubbe

r

Melamine

PUR (rigid

)PIR

Particle

board

Wool te

xtile

Mineral

woo

l

Room te

st-Sofa

PUR (flex

ible)

FR4-lam

inate

Optica

l cab

le

Bitumen PVC

Fluoroc

arbon

-cable

PVC-cable

Plywoo

d

PVC+fluo

rocarb

on-ca

bleWoo

d

Polyeth

ylene

-cable

Polyeth

ylene

-pelle

ts

Tota

l iso

cyan

ates

in e

xhau

st d

ucts

(ppb

)

Full-scale experiment

Average concentrations of total isocyanate measured in the exhaust duct in a small-scale tests and in a single full-scale Room test (logarithmic scale on y-axis).

Material Isocyanates Inorganic gases

Glass wool 1.42 HCN = 0.04; NH3 = 0.04; CO = 0.01

Nitrile rubber 0.72 HCl = 1.19; HCN = 0.12; SO2 = 0.11; NH3 = 0.06; CO = 0.05

Melamine 0.62 HCN = 0.12; SO2 = 0.11; CO = 0.08; NO = 0.08; NH3 = 0.01

PUR (rigid) 0.60 HCN = 0.44; HCl = 0.23; CO = 0.15; NO = 0.14

PIR 0.56 HCN = 0.12; HCl = 0.07; CO = 0.05Particle board 0.45 NO = 0.16; CO = 0.02; NH3 = 0.02

Wool textile 0.19 SO2 = 0.21; NO = 0.10; (HCN < 0.04; CO < 0.01; NH3 < 0.01)

Mineral wool 0.18 (HCN < 0.04; NH3 < 0.01; CO < 0.01)

Polyethylene-pellets 0.0010 CO = 0.02

Sofa; full-scale experiment

0.17 CO = 0.30*

Isocyanate emission during fire- Small-scale combustion experiments in a Cone Calorimeter

Toxic hazard factors’ (quotient of measured average concentration and NIOSH IDLH-value) for total isocyanates compared to inorganic gas species for materials that produced isocyanates in the tests.

Monitoring of isocyanates in air• Many isocyanates with different physical properties

Collection of both gas and particle phase isocyanates

• Reactive compounds Derivatisation upon collection into stable derivatives

• Low occupational exposure limits High demands on the analysis

Impinger flasksGas and particles

Dry samplersGas and particles

Diffusive samplingGas phase - not common

Direct reading instrumentsGas phase

Alternatives for air sampling

• Isocyanate-containing particles < 2 µm are poorly collected by impingers; however, they are efficiently collected by the filter.

• In situations where the physical/chemical nature of the atmosphere is unknown the impinger/filter combination is the most appropriate

Alternatives for air samplingImpinger + filter backup

Alternatives for air sampling

• Incomplete derivatization with the reagent may occur due to the presence of other reactive species in the particle

• If the physical/chemical composition of the air being sampled is unknown, samples should be collected using an impinger containing a derivatisingagent with filter backup

Impregnated filters

Derivatisation reagents

9-(N-methylaminomethyl)-antracene (MAMA)

CH2N

CH3

H

1-(2-methoxyphenyl)-piperazine (MP)

N

OCH3

N

H

1-(9-antracenylmethyl)-piperazine (MAP)

CH2N

NH

Di-n-butylamine (DBA)

HNC4H9

C4H9

1-(2-pyridyl)piperazine [PP}

The Double-Filter method

The sampler is a two stage filter sampler where the first stage is a polytetrafluoroethylene(PTFE) filter which physically traps airborne particles and is subsequently immersed in MP solution to derivatise (stabilize) any trapped isocyanate species immediately after sampling. The second stage consists of a glass fibre filter (GFF) impregnated with 9-(methylaminomethyl) anthracene (MAMA) positioned after the PTFE filter, where any isocyanate vapours present in the air sample are instantaneously derivatised. Similar to other filter methods, both gas and particle-borne isocyanates can be efficiently collected; however, because the first stage filter (PTFE) is devoid of any derivatising reagent (to stabilise the isocyanate) the sampler should not be used where there are possibilities of trapped isocyanate species reacting with other compounds, e.g., sampling reacting aerosols or sampling for prolonged periods.

N

OCH3

N

H

CH2N

CH3

H

The MAP-method

Depending on the environment to be sampled, the sampler can consist of a MAP-impregnated filter, an impinger containing a solution of MAP in butyl benzoate, or a MAP impinger followed by a MAP-impregnated filter

2013-05-07 / Namn Namn, Institution eller liknande

CH2N

NH

The MP-method

The sampler consists of an impinger containing a toluene solution of 1-(2-methoxyphenyl)piperazine (MP) with a MP coated filter placed in series after the impinger. Solvent free sampling is performed with a glass fibre filter coated with MP.


N

OCH3

N

H

PP

• The following method is under preparation: ISO DIS 14382: Workplace Atmospheres - Determination of toluene diisocyanate vapours using 1-(2-pyridyl)piperazine-coated glass fibre filters and analysis by high performance liquid chromatography with ultraviolet and fluorescence detectors.

• The sampler is a glass fibre filter impregnated with 1-(2-pyridyl)piperazine (PP).


The DBA-method

The sampler consists of an impinger containing a toluene solution of DBA with a glass fibre filter placed in series after the impinger. Solvent free sampling is performed using a sampler consisting of a tube with an inner wall coated with a filter, coupled in series with a filter. The filters are impregnated with equimolar amounts of DBA and acetic acid, which reduces evaporation of the volatile DBA.

HNC4H9

C4H9

Denuder End filter

Sampler description

• In the denuder, gaseous substances are collected by diffusion and collection on the sampler walls. The diffusion of particles is too slow for collection on the denuder walls. The particles pass through the denuder and are collected on a reagent impregnated glass fibre filter connected in series with the denuder

ASSET-NCO sampler (Supelco, Bellefonte, PA, US)

Samplers - Transportation / StorageStorage

• Shelf life• Storage of exposed samplers

Transportation• Unexposed samplers• Exposed samplers

Direct reading instruments

Summary of isocyanate sampling /analytical methods (ISO/TR17737, Workplace air — Guidelines for selecting analytical methods for sampling and analysing isocyanates in air)

MethodDBA Double-filter MAP MP PP

Sampling:Phase separation (vapour/particle) +/- +a − − −

Efficient collection (small particle) + +b +b +b +b

Non-impinger version available c + + + + +

Maximum sampling time (hours) 0,25 - 8d 0,25 10 0,25 - 8d 0,25 - 4

Accurate analysis of:Unknown species (identification) e + + / − + / − + / −e −

Low-molecular mass species(e.g. methyl NCO) f

+ + / − + / − + / − −

Unstable species + +g + + +Volatile species + +a + + +Large particles + +h + + +l

Amino isocyanates + − − − −Pre-polymers − − − − −

NCO group(direct measure) +i −e +j +k −

TRIG• The sampling of the Total Reactive Isocyanate Group (TRIG)

has been performed using 2-MP, MAMA and MAP as isocyanate derivativatising agents.

• TRIG analysis demands equal signal strengths from a detector for all isocyanate compounds. The isocyanate group can be quantified without using isocyanate standards.

• TRIG can work as an indicator of the presence of isocyanate groups but does not give any molecule structural information.

Losses due to interfering reactions

Brorson T., Sangö C., Skarping G., RenmanL., Evaluation of chromatographic methods for the determination of isocyanates in air., Intern. J. Environ. Anal. Chem., 1990, 38, 399-413

Method I: Sampling in 0.4 M HCl.

Method II: Sampling in toluenwith 2x10-4M MP reagent.

Method III: Sampling in toluenwith 1x10-4M MAMA reagent.

2,4-TDI 2,6-TDI 2,4-TDI 2,6-TDI 2,4-TDI 2,6-TDIDiethylamine 1 - - 30 34 90 90

10 - - 98 99 99 99100 - - 99 99 100 100

Dimethylethylamine 1 - - - - - -10 - - - - - -

100 - - - - 27 26N-methylmorpholine 1 - - - - 10 5

10 - - 6 6 26 26100 - - 16 18 93 93

1 - - - - - -10 - - 31 28 12 9

100 - - 40 32 53 521 - - 12 12 - -

10 - - 14 17 11 11100 - - 48 44 45 47

Aniline 1 - - - - - -10 - - - - - -

100 - - - - - -Phenol 1 - - - - - -

10 - - - - - -100 - - - - - -

Ethanol 1 - - - - - -10 - - 10 9 - -

100 - - 22 19 - -

Method IIILosses due to interfering substances (%)

1,4-Diazabicyklot(2,2,2)-octane (DABCO)

1,4-Diazabicyklot(2,2,2)-octane (DABCO) from a solution of 33% in polyol

Concentration (ppm)

Interfering compoundMethod I Method II

Moisture

Derivatisation reagentsChromatograms from different air sampling methods

LC-MS/MS (MRM) chromatograms of different dibutylamine (DBA) and D9-DBA (Internal standards) derivatives

Dry sampler- Results – sampling times in the range of 0.5 h – 32 h

The amount of isocyanates was plotted against the duration of the sampling in the chamber. Correlation of sampling time with amount of sampled isocyanate. HDI( ):y = 0.0467x - 1.1041, R² = 0.999; IPDI1 ( ):y = 0.0263x - 0.6393, R² = 0.999; IPDI2 ( ):y = 0.0112x - 0.2692, R² = 0.999; 2,4-TDI ( ):y = 0.0334x - 1.3532, R² = 0.998; 2,6-TDI ( ):y = 0.0076x - 0.2762, R² = 0.998.

Isocyanate standards

• Toxic compounds - paper work to ship• Many different isocyanates• Many not commercially available• Dilute standards solutions are not stable


Isocyanate derivative standards• Many not commercially available• With the exception for the DBA derivatives several

of the different derivatives are not stable• Standards may be necessary to freshly be prepared


Internal standards• There are different approaches for external

internal standards. Sometime the standards are not isocyanate related compounds.

• Deuterium labelled internal standards are available for many of the isocyanate derivatives

• Unstable internal standards is a problem.

Interpretation of results

• Representative sampling, number of samples• The uncertainty associated with the method• Method bias

Uncertainty estimates

Combined uncertainty: 12%Expanded uncertainty: 24%

Climate chamber studies

• Controlled studies with regards to:• Temperature• Humidity• Interferences• Wind speed conditions / ventilation

• Necessary for method comparisons and method validation

Future

• The use of isocyanates is increasing• Millions are exposed• Satisfactory PPE is necessary• Biggest need is to reduce exposure• Monitoring with this purpose is urgent

– Degradation products of TDI, TDA, etc– Differentiation between gas and particles.– Speciation of different isocyanates.– More reliable results. (Increased general use of LC-MS). – Methods for total isocyanates

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