414
Anal. Chem. 1983, 55, 414-416
by again applying the impregnation procedure described in this paper. Registry No. Silver nitrate, 7761-88-8;hinesol, 23811-08-7; 0-eudesmol, 473-15-4.
(2) Heftmann, E.; Saunders, G. A,; Haddon, W. J . Chromatogr. 1978, 156, 71. (3) Hara. S.J. Chromatoor. 1977. 137. 41. (4) Nishikawa, Y.; Watanibe, Y.; Seto, T. Syoyakugaku Zasshi 1975, 29, 139. (5) Heath, R. R.; Sonnet, P. E. J . Liq. Chromatogr. 1980, 3 , 1129.
LITERATURE CITED (1) Hara, S.;Ohsawa, A,; Endo, J.; Sashida, y.; Itokawa, H. Ana/, them. 1980, 52, 428.
RECEIVED for review June 7, 1982. Accepted November
10,
1982.
Positive and Negative Chemical Ionization Pyrolysis Mass Spectrometry of Polymers Robert E. Adams American Enka Company, A Part of Akzona, Inc., Research Department, Enka, North Carolina 28728
Electron ionization (EI) mass spectrometry has been most frequently used for characterizing polymers (I). Chemical ionization (CI) has had limited application in the study of polymer pyrolysis products. Conway and Marak (2) examined several polymers with a time of flight mass spectrometer and pyrolysis temperatures generally above 400 "C. Shimizu and Munson (3) used a magnetic sector instrument and lower temperatures. An earlier study from this laboratory used negative chemical ionizaion and a quadrupole mass spectrometer to study two aromatic polyesters (4). The introduction of instrumentation capable of scanning both negative and positive CI (5) has facilitated the use of CI in the identification of polymer degradation products. This report illustrates the use of positive and negative CI to identify various polymers.
POSITIVE
c,
EXPERIMENTAL SECTION A Finnigan 4021 (Sunnyvale, CA) quadrupole mass spectrometer equipped with the pulsed positive ion negative ion chemical ionization (PPINICI) accessory and an Incos data system was used to obtain the mass spectra. The instrument was alternatively scanned in positive and negative modes from m / z 50 to 1000 in 3.0 s. The ion source was maintained at 200 OC with approximately 1.0 torr (130 Pa) of methane as a reagent-mediator gas. The polymers were pyrolyzed in the ion source using a standard Finnigan direct probe, heated ballistically from 30 "C to 400 "C at approximately 100 OC/min. The sample size was less than 0.1 mg. When larger samples were used, frequent cleaning of the ion source was necessary. Samples were obtained from various sources. Some samples came from Aldrich Chemical Co. (Milwaukee,WI). Other samples were manufactured in the American Enka Co. pilot plant.
TiME [MIN:
Figure 1. Total ion current tracing as poly(methy1 methacrylate) is heated from 30 O C to 400 OC. Top is postive ion current and bottom is negative ion current.
loo
1
I
RESULTS AND DISCUSSION The use of PPINICI to obtain the mass spectra of polymer thermal degradation products can lead to the identification of the type of polymer present in only 10-15 min. Infrared analysis normally requires approximately 1 h when sample preparation time is included. By use of both positive and negative chemical ionization, spectra characteristic of the material can usually be obtained. Figure 1shows the total ion current tracing for poly(methy1 methacrylate) (PMMA). This polymer gives signficant positive (top) and negative ion (bottom) tracings. Figure 2A is the positive chemical ionization spectrum and Figure 2B the
M/Z
Figure 2. (A) Positive chemical ionization spectrum of poly(methyi methacrylate). (B) Negative chemical ionization spectrum of poiy(methyl methacrylate).
0003-2700/83/0355-0414$01.50/00 1983 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
415
Table I. Chemical Ionization of Some Commercially Important Polymers characteristic ionsa polymer
repeat unit structure
negative
positive
poly( methyl methacrylate)
69 (211, 85 (3), 101 (loo), 201 (l), 301 (1)
Nylon 6 [poly(E-caprolactam)]
114 (loo), 227 (4), 340 (5), 453 (2) 85 (loo), 143 (16), 183 ( 1 5 ) , 227 (15), 343 (47), 369 (31), 409 (25)
Nylon 66 [poly(hexamethylene adipate)]
poly(ethy1ene terephthalate)
165 (2), 192 (25), 340 (28), 532 (76), 576 (loo), 724 (14), 768 (69), 960 (26)
poly(buty1ene terephthalate)
368 (38), 385 (95), 440 (79), 457 (61), 562 (23), 588 ( l o o ) , 605 (56), 660 (73), 714 (48), 934 (25)
poly(styrene)
91 (35), 105 (loo), 1 1 7 (49)
6-cH2+n
poly(viny1 chloride)
79 (100)
poly(carbonate)
95 (loo), 135 (44), 215 (12), 255 (16), 509 (lo), 763 ( 6 )
poly( butadiene)
-fc H*-
CHC IH
55 ( l o o ) , 81 (47), 95 (37), 109 (46), 164 (13)
- c H&,
poly(pheny1ene sulfide)
111 (loo), 141 (35),
217 (35), 433 ( Z O ) , 541 (55), 649 (95) a
85 (60), 99 (40), 101 (30), 127 (loo), 131 (45), 185 (52), 198 (31)
140 (25), 433 (18), 464 (lo), 541 (23), 648 (83), 756 (100)
Percent relative intemitv is in oarentheses.
i l 5 1
i
; =
I
’
501
I
I
Figure 4. Negative chemical ionization spectrum of poly(ethy1ene terephthalate)(polyester).
negative ionization spectrum. Both give ions characteristic of the thermal degradation pmducts of PMMA. The monomer
is identified by peaks at m / z 101 (M m / z 99 (M - 1) in Figure 2B.
+ 1) in Figure 2A and
416
ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
However, most polymers do not give a significant spectrum in both the positive and negative mode. Nylon 6 poly([caprolactam) gives primarily a positive chemical ionization spectrum (Figure 3). The major peaks correspond to the pseudomolecular (M + 1)ions for the monomer ( m / z = 114), dimer ( m / z = 227), trimer ( m / z = 340), and tetramer ( m / z = 453). Negative ions are the predominant species in the pyrolysis mass spectra of aromatic polyesters. Figure 4 shows the negative ion spectrum of poly(ethy1ene terephthalate). Peaks characteristic of the oligomers ranging from monomer ( m / z = 192) up to pentamer ( m / z = 960) can be seen. Fragments resulting from thermal degradation processes have been discussed previously ( 4 ) . The structure of the various polymer fragments determines whether positive CI or negative CI is best suited for ionization. Table I lists a few of the polymers from which spectra have been obtained, along with the basic repeat unit and ions characteristic of the material. Chemical ionization mass spectra yield another tool for the analyst in the identification of polymers. The large number of these materials in use commercially makes the development of a spectral library advantageous and a comparison with known polymers may allow unknowns to be identified. The pyrolysis spectrum also
yields information relating to the thermal degradation processes and thus may provide insight into the mechanisms involved in polymer degradation.
Registry No. Poly(methy1methacrylate), 9011-14-7; Nylon 6,25038-54-4; Nylon 66,32131-17-2;poly(ethy1eneterephthalate), 25038-59-9; poly(buty1ene terephthalate), 24968-12-5; 1,4-butanediol terephthalic acid copolymer, 26062-94-2; poly(styrene), 9003-53-6; poly(viny1 chloride), 9002-86-2; bisphenol A poly(carbonate), 24936-68-3; bisphenol A carbonic acid copolymer, 25037-45-0;poly(butadiene), 9003-17-2;poly(pheny1ene sulfide), 25212-74-2. LITERATURE CITED (1) Luderwald, I. Pure Appl. Chem. 1982, 54, 255-265. (2) Conway, D. C.; Marak, R. J . Polym. Sci., Polym. Chem. Ed. 1982, 20, 1765-1774. (3) Shlmlzu, Y.; Munson, 6. J . Polym. Sei., Polym. Chem. Ed. 1979, 17, 1991-2001. (4) Adams, R. E. J . Polym. Scl., Polym. Chem. Ed. 1982, 20, 119-129. (5) Hunt, D. F.; Stafford, 0. C., Jr.; Crow, F. W.; Russell, J. W. Anal. Chem. 1976, 4 8 , 2098-2105.
RECEIVED for review July 19,1982. Accepted October 19,1982. Presented a t the 33rd Southeastern Regional Meeting of the American Chemical Society, Lexington, KY, Nov 4-6, 1981.
CORRECTION Potentiometric Stripping Analysis in Flow Cells Leif Anderson, Daniel Jagner, and Mats Josefson (Anal.
Chem. 1982,54, 1371). An error was introduced into this paper in the final stages of the production cycle, after author review of the galley proof. On p 1372, under Theory, the first sentence should read as follows: By application of the equations derived by Levich (21) and Hanekamp and Nieuwerk (22) ... .
