408
Anal. Chem. 1983, 55, 408-409
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BM
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Spectra from 1000 to 600 cm'' in a ZnSe transmission cell of a gasoline sample (A) with MTBE and (B) without MPBE. Spectrum (C) is the difference spectrum (A) minus (B) with the 965-cm-' band used for normalization. Figure 1.
of 0.997. Ten samples of 7.0 vol % MTBE in gasoline were prepared and analyzed by using the aforementioned calibration plot. The mean was 6.9 vol % with a standard deviation of A0.07.
A series of 26 standards, in the 2 to 36 vol % range, of MTBE in gasoline was prepared for use in the ATR cell. Absorbance values for the 851-cm-l band were calculated for each standard by using peak heights. The resultant linear calibration plot yielded a correlation coefficient of 0.999. Ten samples of 7.2 vol % MTBE were prepared and analyzed by using this calibration curve. The mean of these determinations was 7.2 vol % with a standard deviation of f0.12. Both techniques appear to be readily adaptable to onstream processes. The ZnSe used in the windows and crystal is impervious to attack by water and is fairly durable as long as uneven stress is not applied to the crystal. The use of either technique provides reliable analyses in a short analysis time. Registry No. MTBE, 1634-04-4.
LITERATURE CITED (1) Taniguchi, B.; Johnson, R. CHEMTECH 1979, 9 , 502-510. (2) Pecci, G.; Floris, T. Hydrocarbon Process. 1977, 56 (12), 89-102. (3) Battiste, D. R.; Fry, S. E.; White, F. T.; Scoggins, M. W.; McWiiliams, T. 6 . Anal. Chem. 1981, 53, 1096-1099.
RECEIVED for review November 9, 1981. Resubmitted and accepted November 5, 1982.
Determination of Extractable Methylenebis(ani1ine) in Polyurethane Films by Liquid Chromatography David A. Ernes" and David T. Hanshumaker BF Goodrich Chemical Group, Avon Lake Technical Center, P.O. Box 122, Avon Lake, Ohio 440 12
Polyurethanes, reaction products of a polyester or polyether-based poly01 and a diisocyanate, have been the subject of discussion regarding the toxicological properties of the diisocyanates themselves. A recent article related this toxicity to the hydrolysis product of the diisocyanate, the corresponding diamine (2). One paper described the detection of 4,4'-methylenebis(aniline) (MBA), the hydrolysis product of 4,4'-diphenylmethane diisocyanate (MDI), from polyurethane fiis following autoclave extraction (2). This article, however, did not describe fully the methodology used to detect and confirm the presence of MDA in the aqueous extracts. As a result of the impact of these data, its validity must be confirmed. An extraction program was then initiated t o fully evaluate the results described in that report. As a part of this study, an analytical method was developed to detect and quantify MDA in aqueous ext,racts a t the parts-per-billion level. Many methods are available to determine the parent diisocyanate, primarily in the area of workplace environmental monitoring (3-5). Diisocyanates have also been determined in polyurethane prepolymers (6,7). For air monitoring studies, some form of derivatization was used to enhance the sensitivity of the analyte. This work details the formation of the N,N'-dibenzamide of MBA to increase the sensitivity of the amine by a factor of 2 to 3.
EXPERIMENTAL SECTION Apparatus. Separations were achieved with a Model 6000A pump, WBondapak C18 column (3.9 mm X 30 cm) and a Model 440 absorbance detector with dual accessory allowing 254- and 280-nm detection (Waters Associates, Milford, MA). The output
was monitored with a Model 730 Data Module (Waters) with integration of the 280 nm output of the detector. A Valco loop injector was used to introduce the samples. Reagents. The mobile phase was prepared from HPLC Grade tetrahydrofuran containing no inhibitor (Fisher Scientific, Pittsburgh, PA) and triple-distilledwater prepared with a Gilmont Ultrapure Water Still Model 111. Samples of 4,4'-methylenebis(ani1ine) dihydrochloride and 2,4-toluenediamine (TDA) monohydrochloride were obtained from Eastman (Eastman Organic Chemicals-Eastman Kodak Co., Rochester, NY). N,N'-Benzamide Derivatives. A sample of the diamine hydrochloride salt (4-5 g) was dissolved in water and neutralized with 10% sodium hydroxide. The free amine was extracted with chloroform and the organic phase was dried with anhydrous sodium sulfate. Triethylamine was added to the organic phase in a 2:l molar ratio with the diamine, followed by a stoichiometric amount of benzoyl chloride. After 15 min the solvent was evaporated and the residue was redissolved in a 50/50 water/ether mixture. The organic phase was isolated and dried with anhydrous magnesium sulfate. After evaporation of the ether the crude products were recrystallized from ethanol. Melting points for 4,4'-methylenebis(ani1ine) dibenzamide and 2,4-toluenediamine dibenzamide were 249-250 OC and 222-224 OC, respectively. Both products were identified by mass spectrometry. Procedure. ( A )Extraction. Extractions of the polyurethane films were performed at 47-48 OC in an incubator for 2 weeks with a 20-mL aliquot taken after 1day, 1week, and 2 weeks. One set of samples was autoclaved at 125 OC for 90 min prior to extraction. The samples were prepared by placing 2.54 X 10 cm polyurethane strips, cut from 0.250 to 0.50 mm thick sheets into 1-L Wheaton 400 bottles (Fisher Scientific) containing 850 mL of the solution tested. Solution blanks were also prepared. 'The surface areato-volume ratio was adjusted to either 3.25 or 6.5 cm2/mL with
0003-2700/83/0355-0408$01.50/00 1983 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 5 5 , NO. 2 , FEBRUARY 1983
409
Table 11. Concentration of MBA in Aqueous Extracts of Polyurethane Films after Autoclave Treatment (90 min at 125 "C) Poly urethane polyester A polyester B polyether C blank polyester A polyester B polyester B polyester B polyether C blank a
Figure 1. Chromatogram of 0.190 kg/mL solution of MBA: 25-pL injection; elution conditions, 5 0 / 5 0 THF/water at 2.0 mL/min; detection, UV 280 nm at 0.02 aufs (inset at 0.005 aufs); peak identification, (peak 1) internal standard, (peak 2 ) MBA derivative.
Table I. Verification of the Analytical Method-Analysis of Standard MBA Solutions
a
std concn, pg/mL
no. of samples
0.790 0.238 0.0196 0.010 0.0050
is
4
4 2 !2
resultsa 0.776 c 0.009 0.241 * 0.012 0.0198 * 0.00005 0.0089 k 0.002 0.0055 c 0.002
At 95% confidence level.
the appropriate number of strips. (B)Analysis. The 20-mldaliquots of each sample were analyzed by first extracting with anhydrous ether (3 X 15 mL). The combined ether extracts were treated with 0.15 mL of triethyl. amine solution (1:20 (v/v) in heptane) followed by 0.10 mL of benzoyl chloride solution (1:20 (v/v) in heptane) and allowed to react for 1h at ambient temperatures. Excess benzoyl chloride was consumed by addition of 0.05 mL of neat morpholine, after which the ether was evaporated at 50 "C in vacuo to dryness. The residue was then redissolved in 2.0 mL of THF containing 3.4 pg/mL of the 2,4-toluenediamine dibenzamide, used as the internal standard, and analyzed by HPLC (see Figure 1).
RESULTS AND DISCUSSION I. Analytical Method. The accuracy and precision of the method were determined by replicate analysis of the MBA-2HC1 solutions of known concentration equivalent to 0.79 pg/mL to 0.005 wg/mL MBA. Twenty-milliliter aliquots of each solution were analyzed as outlined in the Experimental Section with the results Bhown in Table I. The minimum detectable concentration was established at 0.05 pg/mL MBA with a signal-to-noise ratio of 4 1 when detected at 0.005 ads. With the 10-fold concentration increase obtained by redissolving the residue from a 20-mL aliquot in 2.0 mL, the minimum detectable limit is 0.005 pg/mL MBA. The response of the 4,4'-methylenebis(ani1ine) dibenzamide was found to be linear from 0.1 to 10 pg/mL (or 0.05 to 5 pg/mL when expressed as MBA). Dual detection was employed for two reasons. First, because of the proximity of the peak due to
concn of MBA, pg/mL solution
day 1
0.0148 0.0166 0.0231 N/Da deionized water 0.0074 deionized water 0.0104 deionized water 0.0146 deionized water 0.0135 deionized water 0.0241 deionized water N/D
week 1 week 2
0.9% NaCl (aq)
0.0112 0.0186 N/D
0.0082 0.0159 N/D
0.0097 0.0195 0.0131 0.0217 N/D
0.0105 0.0187 0.0093 0.0163 N/D
N/D = less than 0.005 pg/mL.
benzoyl chloride and the 4,4'-methylenebis(ani1ine) dibenzamide peak, 254-nm detection was used to confirm the absence of the former (benzoyl chloride has a greater response at 254 nm) as a possible interference. Secondly, absorbance ratios were determined for the 4,4'-methylenebis(aniline) dibenzamide derivative to confirm its identity (A280m/A254,,,,,= 1.5). 2. Extraction Study. No detectable MBA (50.005 pg/ mL) was found in solution after extraction of both polyester and polyether-based polyurethanes a t 47-48 "C for 2 weeks. The surface area to volume ratio remained essentially the same (3.25) after the removal of the 20-mL aliquots from a total volume of 850 mL. Additional aliquots analyzed after the samples had remained a t 47-48 "C for over 6 months also failed to show MBA. Results were the same for both solvents used (water and a 3% acetic acid solution). A second set of samples extracted at 6.5 cm2/mL was autoclaved a t 125 "C for 90 min prior to being placed in the 47-48 "C environment. Analysis of aliquots from these samples indicated 10 to 25 ng/mL MBA. The decrease with time for some samples was not explained but did indicate that the MBA was generated during the autoclave pretreatment. This was confirmed by the detection of MBA from a sample extracted in boiling water for 17 h. The MBA was probably generated from the breakdown of the polyurethane as evidenced by a change in appearance following the autoclave treatment. Registry No. MBA, 101-77-9.
LITERATURE CITED ( 1 ) Anderson, M.; Binderup, J. L.; Kid, P.; Larson, M.; Maxild, J. Scand. J . Work, Environ. Health 1980, 6 , 221-226. (2) Darby, T. D.; Johnson, H. J.; Northup, S. J. Toxicol. Appl. Pharmacol. 1978, 4 6 , 449-453. (3) Sango, C. J . Liq. Chromatogr. 1979, 2 , 763-774. (4) Hardy, Horace L.; Walker, Ronald F. Ana/yst (London) 1979, 104, 690-892. (5) Levlne, S.P.;Hoggatt, J. H.; Chladek, E.: Jungclaus, G.; Gerlock, J. L. Anal. Chem. 1979, 51, 1006-1109. (6) Furukawa, Mutsuhisa; Yokoyama, Tetsuo J . Chromatogr. 1980, 198, 2 12-2 16. ( 7 ) Edwards, D. J. H. HRC CC,J . Hlgh Resolut. Chromatogr. Chromatogr. Commun. 1980, 3 , 190-192.
RECEIVED for review September 28,1982. Accepted November 18, 1982.
