EPA/600/A-94/042
Field Test and Validation of a Source Test Method for Methylene Diphenyl Diisocyanate
Frank W. Wilshire
U.S. Environmental Protection Agency
Methods Research and Development Division
Research Triangle Park, NC 27711
Joseph E. Knoll
U.S. Environmental Protection Agency
Methods Research and Development Division
Research Triangle Park, NC 27711
and
James F. McGaughey
Radian Corporation
Research Triangle Park, NC 27709
Samuel C. Foster, Jr.
Radian Corporation
Research Triangle Park, NC 27711
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A72
Field Test and Validation of a Source Test Method for
Methylene Diphenyl Diisocyanate
F.W. Wilshire and J.E. Knoll
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
and
J.F. McGaughey and S.C. Foster, Jr.
Radian Corporation
Research Triangle Park, NC 27709
ABSTRACT
Four isocyanates are listed for regulation in the Clean Air Act Amendments of 1990:
hexamethylene-1,6 diisocyanate, methylene diphenyl diisocyanate, and2,4-toluene diisocyanate, each
of which is used in the production of polymers, and methyl isocyanate which is an intermediate in
the manufacture of insecticides, such as Sevin® dust.
To support projected regulations, a study is under way to develop a source sampling and analysis
method for the four pollutants cited above. In the procedure under development, the isocyanates
are collected in a modified Method 5 sampling train and stabilized with a derivatizing reagent, l-(2-
pyridyl)piperazine in toluene. Derivatized samples are then returned to the laboratory and
analyzed by High Performance Liquid Chromatography with UV detection (HPLC-UV). An
isocyanate generator was developed in the laboratory to provide isocyanate atmospheres for
optimization of sampling parameters and chromatographic conditions. The accuracy and precision
of the method is determined in the field using train spiking and multiprobe sampling techniques,
following the procedures outlined in EPA Method 301.
A field test of the isocyanate method, following EPA Method 301 procedures, was performed at
a pressed board manufacturing facility. Results were excellent, with an overall analyte spike
recovery of 92.2 ± 6.5 %. The method's limit of quantitation (LOQ) was determined to be 366
ng of MDI/m3.
INTRODUCTION
A class of compounds identified as isocyanates are contained in the list of 189 pollutants to be
regulated by the Environmental Protection Agency under Title in of the Clean Air Act
Amendments1 (CAAA) of 1990. There are four isocyanates of interest in the CAAA; methyl
isocyanate (MI), hexamethylene 1,6- diisocyanate (HDI), methylene diphenyl diisocyanate (MDI),
and 2,4-toluene diisocyanate (TDI).
Isocyanates are used extensively throughout industry. A few examples of their use are in the
production of flexible foam products, synthetic rubber products, insecticides, enamel wire coatings,
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A72
and in the pressed board industry. Methylene diphenyl diisocyanate is used in industry as an
intermediate in the production of polyurethane elastomers, polyurethane lacquer coatings,
thermoplastic polyurethane resins, and in the pressed board industry as a constituent in a
phenol/formaldehyde binder. Because of their widespread use, isocyanates possess the potential
to affect many who are sensitive to this class of chemical compounds. Some of the adverse
physiological effects associated with exposure to isocyanates are severe skin and eye irritations,
eczema, nausea, and bronchial asthma.2 The 1991 OSHA Permissible Exposure Limit (PEL) for
MDI is listed at 0.02 ppm and the IDLH Level (Immediately Dangerous to Life and Health) is 10
ppm.3
Several critical problems exist when sampling for isocyanates. They polymerize in the presence of
concentrated alkaline compounds, react with water and alcohols, discolor upon exposure to sunlight,
and form toxic gases, such as carbon monoxide and hydrogen cyanide, upon decomposition.
Consequently, isocyanates must be collected rapidly and stabilized immediately with a derivatizing
reagent to insure sample integrity.
The EPA's Source Methods Research Branch, in the Atmospheric Research and Exposure
Assessment Laboratory, Research Triangle Park, North Carolina through a contract with Radian
Corporation, Research Triangle Park, NC, has developed a method for the collection, identification,
and measurement of two of the isocyanates of interest; 2,4-toluene diisocyanate and methylene
diphenyl diisocyanate. TDI collection and analysis was the subject of a previous EPA/AWMA
presentation4.
In both the TDI and MDI methods, samples are collected at the source using a modification of the
EPA Method 5 sampling train (without the in-line filter). Stack gas is withdrawn at a flow rate of
0.5 ft3/min. for approximately sixty minutes through a heated, glass-lined probe and into two
impingers containing a solution of the derivatizing reagent, l-(2-pyridyl)piperazine in toluene
[1,2PP]. The first impinger is fitted with a water-cooled condenser on the outlet of the impinger
to minimize carryover of the organic solvent into the second impinger. MDI reacts with the
derivatizing reagent [1,2PP] to form a stable MDI/urea derivative. When sampling is completed,
the probe and connecting glassware are rinsed with toluene and acetonitrile and the rinses are
saved for laboratory analysis. Each impinger solution (MDI/urea derivative) is recovered
separately and saved for laboratory analysis. All samples are stored in a cooler at 0 to 4° C until
returned to the laboratory for analysis by HPLC-UV detection. Quantitation is by a
standards/retention time comparison procedure.
EXPERIMENTAL
Laboratoiy Evaluation
The laboratory study was initially set up to meet seven objectives for the four isocyanates of
interest. However, budget constraints required the focus of the study to be limited to two of the
isocyanates of interest (TDI and MDI). As mentioned earlier, TDI was the subject of the initial
laboratory and field test work. This presentation describes the next phase of the study, the
laboratory evaluation and field test of MDI. Seven objectives were planned for the isocyanates of
interest and are listed in Table 1. All seven objectives were met for TDI and MDI. Although the
focus was limited to TDI and MDI, some of the objectives were met for MI and HDI and are also
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listed in Table 1.
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Derivative Formation
Efforts to form a stable isocyanate/urea derivative for all four isocyanates, using ethanol as the
derivatizing reagent were only marginally successful. Solid derivatives for MDI, HDI, and TDI
were obtained, but formation of a derivative for MI was unsuccessful. Chromatograms for
derivatized and underivatized isocyanates were compared. Since no chromophore existed for MI
or HDI no chromatographic peaks were observed for MI or HDI, either derivatized or
underivatized. However, peaks were easily detected for TDI and MDI. Based upon the results and
a desire to find a method applicable to all four of the isocyanates of interest, ethanol was
eliminated from consideration as a derivatizing agent.
In previous work, Goldberg5 and associates used a secondary amine, l-(2-pyridyl)piperazine as the
derivatizing agent while collecting ambient air samples in midget impingers. Since no current
source method for isocyanates exists, l-(2-pyridyl)piperazine was investigated as a possible
alternative for ethanol as a derivatizing reagent. Using 1,2PP as the derivatizing reagent resulted
in the formation of derivatives for all of the isocyanates of interest. Approximately 0.2 grams of
TDI, HDI, MDI was added to separate solutions of 0.3 mL of 1,2PP in 10 mL of acetonitrile
(ACN). The solutions were allowed to stand for 24 hours to insure enough time for the reaction
to take place. Each solid derivative was then recovered by filtration, rinsed with 150 mL of
distilled water and allowed to air dry before being redissolved with acetonitrile and brought to a
standardized volume prior to analysis by HPLC. A derivative for the MI was prepared by
transferring 100 fiL of MI to 1 mL of ACN and adding 300 /lL of 1,2PP. The solution was shaken
for five minutes and then diluted 1:1000 for analysis by HPLC. A 1,2PP solution was prepared as
previously mentioned for blank analysis on the HPLC. Also, a solution of the 1,2PP with HDI,
MDI, and TDI was prepared to determine the retention time of each derivative. Calibration of the
standards was shown to be linear over the operating range of 1 jig/mL to 48 jig/mL of the
isocyanate derivatives. The results were excellent, demonstrating that a mixture of the three
isocyanates could be analyzed with good chromatographic separation and quantitation (see Figure
1).
Isocyanate Generator
An isocyanate atmosphere generator was constructed to provide a source of isocyanates for testing
within the laboratory. It was expected that this generator would be applicable to all four of the
isocyanates listed in the CAAA, but for the reasons explained earlier the generator was tested only
for TDI. The generator test for TDI and the TDI field test confirmed the method's applicability
to isocyanate testing and a field test for MDI collection was scheduled.
METHOD VALIDATION
A field test of the method was performed in September, 1993, at a pressed board manufacturing
facility, which used MDI as a constituent in the binder for the pressed board process. A modified
Method 5 sampling train (with a water-cooled condenser on the outlet of the first impinger) was
used to collect source gas from the plant's process stack (see Figure 2). The sample gas stream
was passed through a heated glass-lined/stainless steel probe and through two impingers containing
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All
the 1,2PP absorbing solution, one empty impinger (carryover trap), one silica gel impinger, and one
impinger containing charcoal (to trap any organic vapors). Note: any use of stopcock grease while
sampling will cause problems during sampling (i.e., foaming of the absorbing solution). Sampling
was performed both isokinetically (0.75 ft3/min) and non-isokinetically (0.5 ft3/min) for 60 minutes.
Non-isokinetic sampling was performed in addition to isokinetic sampling to determine the
method's collection efficiency in sampling an aerosol source under both conditions. The data in
Tables 2 and 3 indicate that for this source, there was no significant difference in the data
collected. Two of the sampling trains for each quadruplicate run (as per EPA Method 301
requirements) were spiked with an MDI derivatized standard (MDI/urea derivative in ACN,
which was equivalent to 651 ng of underivatized MDI). This was twice the amount of MDI, as
indicated by the presurvey, that we could expect to collect in sixty minutes of sampling. Impingers
and other glassware used in the sampling train were rinsed first with toluene and then with ACN.
Probe rinse and associated glassware rinses were combined with the contents of the first impinger
for subsequent analysis by HPLC-UV. Toluene/acetonitrile rinses from the condenser and second
and third impingers were also combined for HPLC analysis. Samples were kept on ice at 0 to 4°
C until returned to the laboratory.
Operating parameters for the HPLC were as follows:
Instrument:	Rainin HPXL delivery system with Waters 710B WISP
autosampler.
Data System:	Nelson 2600 (1 volt)
Column:	Zorbax ODS (4.6 mm ID x 25 cm)
Mobile Phase: ACN/0.1M ammonium acetate buffer
Gradient:	25:75 ACN/0.1M ammonium acetate buffer, pH 6.2, hold 2 min,
then to 60:40 ACN/0.1M ammonium acetate buffer for 19.5 min.
Detector Wavelength: 254 nm
Flow Rate:	2 mL/min.
Results from the field test were excellent (see Tables 2 & 3). The mean recovery of spikes was
91 ± 14 (with an outlier) and 91 ± 6% for isokinetic and non-isokinetic sampling, respectively.
When the outlier for the isokinetic samples was statistically eliminated (using a "rejection
quotient"6 technique), the recovery for the isokinetic samples improved to 95 ± 6 %, as shown in
Table 2. The method's overall analyte spike recovery, with the outlier removed, was 92.2 ± 6.5
percent. Breakthrough, as measured by the recoveries in the second impingers, were 10 percent
or less, indicating near complete recoveries in the first impinger. Background or emissions
concentrations for one hour samples (as determined by analysis of the unspiked trains) ranged from
63 ng/m3 to 254 ng/m3. The method's Limit of Quantitation (LOQ) for MDI, calculated as
outlined in EPA Method 3017, was determined to be 366 ng/m3. The LOQ of the method is
defined as ten times the standard deviation of the mean of the data set whereas the method Limit
of Detection (LOD) would be calculated as 3.3 times the standard deviation of the mean of the
data set.
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CONCLUSIONS
A72
A method has been developed for the collection and analysis of TDI and MDI (as stated earlier,
the TDI method was reported on at a previous EPA/AWMA symposium4). Method validation
procedures are completed for TDI and MDI, and results from the field tests indicate that the
TDI/MDI method can now be used to determine stationary source emissions from the
manufacturing of flexible foam products and from the pressed board industry. It is anticipated that
this method can be successfully applied to the measurement of HDI and MI emissions as well.
Current plans are for another field test in the near future, at an industry which emits HDI from
its manufacturing process. Conditions not experienced in the sampling of source emissions during
the first two field tests (i.e., higher humidity, particulate loadings, and/or warmer stack gas
temperatures) are tentatively planned for future field tests.
Finally, based upon the breakthrough data collected during the MDI study, we recommend that
when sampling for MDI, a third impinger containing 200 mL of the derivatizing reagent (1,2PP)
be used to assure that no sample is lost through the system.
REFERENCES
1.	Clean Air Act Amendments of 1990, Public Law 101-549, U.S. Congress, November 15,
1990, 104 STAT., pp. 2533-2535.
2.	Material Safety Data Sheet, No. 331, Genium Publishing Corporation, Schenectady, NY,
Nov. 1978.
3.	Material Safety Data Sheet, No. 835, Genium Publishing Corporation, Schenectady, NY,
June 1992.
4.	Wilshire, F.W., et al., "Validation of a Source Test Method for Isocyanates", U.S.
EPA/AWMA International Symposium on the Measurement of Toxic and Related Air
Pollutants, Durham, NC, May 1993, EPA/600/A93/024.
5.	Goldberg, P.A, R.F. Walker, P.A Ellwood, and H.L. Hardy, 11 Determination of Trace
Atmospheric Isocyanate Concentrations by Reversed-Phase High-Perfonnance Liquid
Chromatography Using l-(2-pyridyl)piperazine Reagent", Journal of Chromatography.
212, 1981, pp 93-104.
6.	Dean, R.B., and W.J. Dixon, "Rejection Quotient", Analytical Chemistry, Vol. 23, 636,
(1951).
7.	"Field Validation of Emission Concentrations from Stationary Sources," Method 301 Federal
Register, U.S. Government Printing Office, Washington, D.C., December 1992.
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A72
DISCLAIMER
This paper has been reviewed in accordance with the U.S. Environmental Protection Agency's peer
and administrative review policies and approved for presentation and publication. Mention of trade
names or commercial products does not constitute endorsement or recommendation for use.
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Table 1. Isocyanate project objectives.
A72
No.
Objective Description
MI
MDI
HDI
TDI
1
Find one derivatizing
reagent to react rapidly
with all four isocyanates
yes1
yes
yes
yes
2
Set up analytical HPLC
method (for a single
chromatographic run)
yes
yes
yes
yes
3
Develop instrument and
method detection limits
no
yes
yes
yes
4
Determine spike recovery
from derivatizing reagent
no
yes
no
yes
5
construct an isocyanate
generator
no
yes2
no
yes
6
Determine recoveries from
spiked Method 5 train
no
yes
no
yes
7
Field test of method and
validation
no
yes
no
yes
Yes indicates that objectives have been met. No indicates that an attempt has not been made to meet the
objectives.
No laboratory testing for MDI using the isocyanate generator was necessary since TDI recoveries using the
generator verified established the method's operating parameters. Spike recoveries listed in Tables 2 and 3
confirmed the method's applicability to MDI sampling.
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Table 2. MDI spike recoveries while sampling isokinetically.
Run No.
Sampling Rate
(ft3/min)
Amt. of Spike
(fig MDI)
Spike
Recovery
(fig MDI)
Percent
Recovery
1A
0.75
651
660
101
IB
II
It
631
97
2C
II
II
677
104
2D
II
II
573
88
3A
II
II
544
84
3B
II
II
615
94
4C
II
II
607
93
4D
II
II
645
99
5A1
II
11
359
55
5B
II
II
612
94



'






Mean/w



91
S/w



14
Mean/wo



95
S/wo J



6
Outlier, as determined by the Dixon "rejection quotient" test.
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Table 3. Spike recoveries with non-isolcinetic sampling.
Run No.
Sampling
Rate
(ft3/min)
Amount of
Spike
(fig MDI)
Ami of
Spike Recovered
Otg MDI)
Percent
Recovery
6C
0,5
651
525
81
6D
11
II
537
82
7A
II
II
622
96
7B
II
II
583
90
8C
H
II
552
85
8D
II
tl
540
83
9A
II
It
602
92
9B
II
II
555
85
10C
fl
II
629
97
10D
II
If
659
101
11A
If
If
619
95
11B
if
ff
592
91
12C
II
1*
623
96
12D
II
11
607
93










Mean



91
S



6
10

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2,6-TDI
2,4-TDl
1/
L
1,6-HDI
X
1
10
—r~
12
~~r-
14
16
—r~
18
—I
20
Figure 1. Chromatographic separation of HDI, TDI, and MDI.
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8tadc
Wall

T
	*—'—
Ab«orttng Solution
ToluwiwPlparun*
Vacuum
Una
Oy3a
Matar
Pump
Figure 2. Isocyanate sampling train configuration.
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TECHNICAL REPORT DATA
(Plant reed Instructions on the reverse before completing)
1. REPORT NO.
EPA/600/A-94/042
3. REI
4. TITLE AND SUBTITLE
Field Test and Validation of a Source Test Method for Methylene
Diphenyl Diisocyanate
6. REPORT DATE
6. PERFORMING ORGANIZATION CODE
AUTHOR(S) F Wilshire and J. Knoll, AREAL/MRDD/SMRB, U.S.
Environmental Protection Agency, RTP, NC 27711 and J. McGaughey
and S. FosterRadian Corp., RTP, NC 27709	
I. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation,
Research Triangle Park, NC 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-D1-0010
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
AREAL/MRDD/SMRB (MD-77A)
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Symposium paper
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Symposium presentation for June 1994 AWMA Meeting
16. ABSTRACT				
Four isocyanates are listed for regulation in the Clean Air Act Amendments of 1990: hexamethyiene-1,6
diisocyanate, methylene diphenyl diisocyanate, and 2,4-toluene diisocyanate, each of which is used in the
production of polymers, and methyl isocyanate which is an intermediate in the manufacture of insecticides.
To support projected regulations, a study is under way to produce a source sampling and analysis method
for the four pollutants cited above. In the procedure under development, the isocyanates are collected in a
modified Method 5 sampling train and stabilized with a derivatizing reagent, 1-(2-pyridyl)piperazine in toluene.
Derivatized samples are then returned to the laboratory and analyzed by High Performance Liquid
Chromatography with UV detection (HPLC-UV). An isocyanate generator was developed in the laboratory to
provide isocyanate atmospheres for optimization of sampling parameters and chromatographic conditions. The
accuracy and precision of the method is determined in the field using train spiking and multiprobe sampling
techniques, following the procedures outlined in EPA Method 301.
A field test of the isocyanate method, following EPA Method 301 procedures was performed at a pressed
board manufacturing facility. Results were excellent, with an overall analyte spike recovery of 92.2 + 6.5 %.
The method's limit of quantitation (LOQ) was determined to be 366 ng of MDI/M3.
17.
3.
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