Characterization of Synthetic Polymers by Electrospray-Assisted

Anal. Chem. 2005, 77, 7744-7749

Characterization of Synthetic Polymers by Electrospray-Assisted Pyrolysis Ionization-Mass Spectrometry Hsiu-Jung Hsu,† Tseng-Long Kuo,‡ Shu-Huey Wu,‡ Jung-Nan Oung,§ and Jentaie Shiea*,†

Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan, Exploration and Development Research Institute, Chinese Petroleum Co., Miaoli, Taiwan, and Exploration and Production Business Division, Chinese Petroleum Co., Taiwan

Rapid characterization of synthetic polymers based on the differences in the appearance of the polar pyrolysate ions was achieved by electrospray-assisted pyrolysis ionizationmass spectrometry. The pyrolytical products produced by a commercial Curie point pyroprobe were conducted to the tip of a capillary, where charged methanol droplets were generated continuously by electrospray. Polar components in the pyrolysates may react directly with the protonated methanol ions or fuse with the charged methanol droplets; electrospray ionization proceeds from the fused droplets to generate protonated analyte ions. The mass spectra obtained through this approach were used to rapidly distinguish the polymer standards that differ in the nature of building units, degrees of polymerization, and copolymerization coefficients. The characterization of macromolecules is a formidable challenge for analytical chemists. Generally, polar and nonvolatile highmolecular-weight compounds, such as synthetic polymers, are not amenable to conventional gas chromatographic and spectroscopic techniques, but upon their controlled thermal degradation, such as that occurs through pyrolysis, these compounds often yield volatile and gas chromatographable products.1-3 In general, the volatile ingredients of the sample are produced in a pyrolytic probe (e.g., based on Curie point, hot ribbon, or furnace-heated pyrolysis) and are then transferred into a preheated GC injection port or the ion source of a mass spectrometer. The volatile ingredients detected by pyrolysis-mass spectrometry (Py-MS) or Py-GC/MS are then served as fingerprints of the formulation.4-10 Such * To whom the correspondence should be addressed. E-mail: jetea@ mail.nsysu.edu.tw. † National Sun Yat-Sen University. ‡ Exploration and Development Research Institute, Chinese Petroleum Co. § Exploration and Production Business Division, Chinese Petroleum Co. (1) Anhalt, J. P.; Fenselau, C. Anal. Chem. 1975, 47, 219. (2) Gutteridge, C. S. Methods Microbiol. 1987, 19, 227. (3) Yang, R.; Liu, Y.; Wang, K.; Yu, J. J. Anal. Appl. Pyrolysis 2003, 70, 413. (4) Snyder, A. P.; McClennen, W. H.; Dworzanski, J. P.; Meuzelaar, H. L. C. Anal. Chem. 1990, 62, 2565. (5) Goodacre, R.; Berkeley, R. C. W.; Beringer, J. E. J. Anal. Appl. Pyrolysis 1991, 22, 19. (6) DeLuca, S. J.; Voorhees, K. J. J. Anal. Appl. Pyrolysis 1993, 24, 211. (7) Smith, P. B.; Snyder, A. P. J. Anal. Appl. Pyrolysis 1993, 24, 199. (8) Shute, L. A.; Gutteridge, C. S.; Norris, J. R.; Berkeley, R. C. W. J. Gen. Microbiol. 1984, 130, 343.

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techniques are used commonly to characterize soil samples (e.g., bound residues of pesticides or humic substances), synthetic polymers, crude oils, coals, paints, and biomasses (e.g., microorganisms and lignin).6-15 Pyrolysis of macromolecules produces a wide range of chemical compounds that range in polarity from nonpolar (e.g., alkanes and alkenes), midpolar (e.g., alcohols and carboxylic acids), to highly polar (e.g., polyols). The polar compounds provide particularly useful diagnostic information concerning the structure of certain materials. Examples of this approach include the pyrolyses of polyesters giving polybasic acids and alkenes, epoxies giving phenolic compounds, and polyamides giving amines and carboxylic acids.16-19 Unfortunately, in the pyrolytical process, many macromolecules break down to the compounds that do not gas chromatograph well because they are retained in the pyrolytical zone, injection system, or capillary column as a consequence of their high polarity or molecular weight.20,2120-21 Even when the polar pyrolysates do enter the separation column, they often display peak-tailing characteristics, poor reproducibility, long elution times, and, in many cases, no chromatographic peaks.22,23 Introduction of the pyrolysates directly into the electron impact (EI) ionization source of a mass spectrometer (through the use of a modified direct insertion probe) does not help in the detection of the polar component in the pyrolysates because the majority of the pyrolysates are usually nonpolar and their signals over(9) Stack, M. V.; Donoghue, H. D.; Tyler, J. E. Appl. Environ. Microbiol. 1978, 35, 45. (10) Stack, M. V.; Donoghue, H. D.; Tyler, J. E. J. Anal. Appl. Pyrolysis 1981/ 1982, 3, 221. (11) Voorhees, K. J.; DeLuca, S. J.; Noguerola, A. J. J. Anal. Appl. Pyrolysis 1992, 24, 1. (12) Smith, C. S.; Morgan, S. L.; Parks, C. D.; Fox, A.; Pritchard, D. G Anal. Chem. 1987, 59, 1410. (13) Evans, N.; Williamson, J. E. Adv. Mass Spectrom. 1980, 8A, 103. (14) Smith, P. B.; Snyder, A. P. J. Anal. Appl. Pyrolysis 1992, 24, 23. (15) Li, D.; Li, W.; Chen, H.; Li, B. Fuel Process. Technol. 2004, 85, 815. (16) Williamson, J. E.; Cocksedge, M. J.; Evans, N. J. Anal. Appl. Pyrolysis 1980, 2, 195. (17) Marshall, G. L. Eur. Polym. J. 1983, 19, 439. (18) Shiea, J.; Wang, W. S.; Chen, C. H.; Chou, C. H. Anal. Chem. 1996, 68, 1062. (19) Galipo, R. C.; Egan, W. J.; Aust, J. F.; Myrick, M. L.; Morgan, S. L. J. Anal. Appl. Pyrolysis 1998, 45, 23. (20) Moss, C. W.; Dees, S. B.; Guerrant, G. O. J. Clin. Microbiol. 1980, 12, 127. (21) Holzer, G.; Bourne, T. F.; Bertsch, W. J. Chromatogr. 1989, 468, 181. (22) Derbyshire, F.; Davis, A.; Lin, R. Energy Fuels 1989, 3, 431. (23) Manion, J. A.; McMillen, D. F.; Malhorta, R. Energy Fuels 1996, 10, 776. 10.1021/ac051116m CCC: $30.25

© 2005 American Chemical Society Published on Web 10/27/2005

whelm those from the polar pyrolysates (the so-called “ion suppression effect”).24,25 The solution to this problem in conventional way is to collect the pyrolysates from a pyrolyzer in a cold receiver. The pyrolysis products are then derivatized externally, separated, and analyzed using GC/MS.21,22 This process is, however, usually labor, cost, and time consuming. Previously, we reported an interface for successfully combining ESI-MS with GC to detect semivolatile polar compounds (i.e., alkyl fatty acids).26 The GC/ESI interface comprised multiple electrosprayers surrounding the GC column. In this system, electrospraying was performed continuously from the capillary electrosprayers using an acidic methanol solution. As the neutral analytessa series of fatty acids having different alkyl chainss exited from the GC column individually, they subsequently entered a zone full of charged species: protons, protonated methanol, methanol cluster ions, and charged methanol droplets. The formation of the protonated fatty acids may then arise from (1) ion-molecule reactions (IMRs) between the gaseous fatty acid molecules (M) and protons (H+) or protonated methanol ions (MeOH2+ or (MeOH)2H+) or (2) fatty acid molecules dissolving (or fusing) into the charged methanol droplets and electrospray ionization proceeding from the droplets to generate protonated analyte ions (MH+). Only those compounds with polar functional groups are able to obtain a proton (i.e., be ionized) in these ways. The use of multiple electrosprayers ensures that there are enough charged species available to react with the polar compounds. The same design has also been used to detect reactive ketene monomers generated by flash vacuum pyrolysis.27,28 In this study, we adapted the concept of GC/ESI-MS to develop an electrospray-assisted pyrolysis ionization-mass spectrometry (ESA-Py-MS) technique that is capable of rapidly detecting the polar components in the pyrolysates of synthetic polymers. Qualitative analyses of these samples were also performed using pyrolysis GC/MS and thermal gravimetric analysis (TGA) to compare their results with those obtained when the ESA-Py-MS approach was used. EXPERIMENTAL SECTION The chemicals were purchased from Sigma and Aldrich and were used without further purification. The synthetic polymer standards used in this study include polycarbonate (PC), poly(butyl acrylate) (PBA), and poly(methyl methacrylate) (PMMA) and methyl methacrylate-butyl acrylate (MMA-BA) and methyl methacrylate-butyl methacrylate (MMA-BMA) copolymers. Polycarbonate (MW 2200) and poly(butyl acrylate) (MW 9900) and a series of poly(methyl methacrylate)s were purchased from Aldrich and Polymer Lab. Co., respectively. The MMA-BA and MMA-BMA copolymers (MW ∼200 000) were prepared in-house through radical polymerization. Please be cautious because all of the synthetic polymers used in this study are toxic and are severe irritants. The breakdown temperature of the polymer standard was obtained by TGA (Perkin-Elmer model TGA7). Approximately 5 (24) Tang, L.; Kebarle, P. Anal. Chem. 1991, 63, 2709. (25) Ikonomou, M. G.; Blades, A. T.; Kebarle, P. Anal. Chem. 1991, 63, 1989. (26) Lee, C. Y.; Shiea, J. Anal. Chem. 1998, 70, 2757. (27) Wang, W. S.; Shiea, J.; Huang, M. W.; Huang, J. P. J. Am. Soc. Mass Spectrom. 1998, 9, 1168. (28) Hong, C. M.; Tsai, F. C.; Shiea, J. Anal. Chem. 2000, 72, 1175.

Figure 1. Schematic diagram of an ESA-Py-MS apparatus for analyzing large and polar pyrolysates from synthetic polymer standards.

mg of the sample powder was used for TGA analysis. The TGA furnace was purged with nitrogen (40 mL/min) during the analysis, and the temperature of the sample in the furnace was increased from 50 to 900 °C at a rate of 20 °C/min. Conventional Py-GC/MS (Agilent 6890/7123N) was used to detect the volatile components in the polymer standard. The sample powder (∼0.2 mg) wrapped in a Curie point foil (Ni-Fe alloy) was inserted into the tip of a pyrolytic probe (model JHP-3S, Jai Co.) and was heated rapidly to the Curie point of the foil metal through the induction of radio frequency. The temperature of the GC column (UA-5; 5% phenyl silicone; 30 m × 0.25 mm × 0.5 µm; Frontier Laboratories Ltd.) was programmed: 40 (initial temperature, 2 min), 40-60 (4 °C/min), 60-300 (10 °C/min), and 300 °C (10 min). A quadrupole mass analyzer equipped with an EI ionization source was used to detect the GC eluents. The polar components in the pyrolysates were analyzed either by (1) collecting the pyrolysates in the methanol solution followed by ESI-MS analysis or (2) direct analysis by electrospray-assisted pyrolysis-mass spectrometry. The first approach utilized 4 mg of the polymer powder. The pyrolysates were purged and collected in a vial containing pure methanol (∼10 mL); the methanol solution was then concentrated by blowing the solution down to ∼50 µL using pure N2; a portion of this solution (20 µL) was then injected into a commercial ESI-MS source equipped with a Q-TOF mass analyzer (Bruker BioTOF q). Three Curie point foils (F256, F445, and F590; Jai Co.) were chosen to perform the pyrolyses at 256, 445, and 590 °C, respectively. For the second approach (ESA-Py-MS), the pyrolytic probe was interfaced with a home-built ESI source through one arm of a glass reaction cell (Figure 1). An acidic methanol solution (1% trifluoroacetic acid) was electrosprayed continuously from a fused-silica capillary column located at the center of the reaction cell. The capillary was connected to a three-way tee, and a syringe pump delivered the acidic methanol solution through the capillary (1.6 µL/min). This approach used 2 mg of the polymer powder. The gaseous pyrolysates were conducted (using N2) into the reaction cell to react with protons or to fuse with the charged methanol droplets generated by electrospraying the acidic methanol solution. The exit of the glass reaction cell was positioned at the sampling skimmer of a Q-TOF mass analyzer to detect the ions generated in the cell. Details of the dimensions of the glass reaction cell are Analytical Chemistry, Vol. 77, No. 23, December 1, 2005

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Figure 2. TGA traces of the three polymer standards: PMMA (120 kDa), PBA (100 kDa), and PC (22.6 kDa).

available elsewhere.29,30 The mass analyzer was scanned from m/z 10 to 1500 at a rate of ∼1 s/scan. RESULTS AND DISCUSSION Three synthetic polymers possessing different building unitss PMMA (120 kDa), PBA (99 kDa), and PC (22.6 kDa) were both analyzed by (1) conventional Py-GC/MS and (2) ESA-Py-MS using the interface developed in this study. The thermal decomposition temperatures of the polymer standards were obtained by TGA. The results of TGA indicate that the breakdown temperatures of the polymer standards are ∼300-450 °C for PMMA (120 kDa) and PBA (100 kDa) and 500-600 °C for PC (22.6 kDa) (Figure 2). No obvious pyrolytic products were detected in conventional Py-GC/MS at temperatures below 256 °C for all of the three samples. Although the ion signals of pyrolytic products from PMMA and PBA at 445 °C were detected, no obvious ion signals arising from PC pyrolysates was detected at this temperature. As the pyrolytic temperature increased to 590 °C, the ion signals derived from the pyrolysates were obtained for all of the samples. In the following experiments, for consistency, the temperature of all pyrolytic assays was then performed at 590 °C. Figure 3 displays the total ion chromatograms (TICs), obtained from conventional Py-GC/MS, of these three polymer standards. The TICs of PMMA and PBA are extremely simple: only the signals of the respective monomer unit ions were detected (i.e., methyl methacrylate for PMMA (m/z 100) and butyl acrylate for BA (m/z 128)]. Signals of other large or polar pyrolysates are not present. The insets in Figure 3a and b display the EI mass spectra of the major compounds shown on the TICs. The molecular ion of butyl acrylate (m/z 128) was far too weak to be seen on the EI mass spectra (see inset in Figure 3b). A more complicated TIC for PC was obtained (Figure 3c); not only do we detect bisphenol A (retention time (RT) 26.6 min) but also phenol (RT 9.7 min) and other alkyl phenols (RT 12.0, 13.8, and 15.1 min). To characterize larger and polar pyrolysates generated from the synthetic polymer standards, collecting the pyrolysates in the methanol solution followed by ESI-MS analysis was performed on a PMMA (2200 Da) standard. The polymer powder (4 mg) was pyrolyzed at 590 °C, and the pyrolysates were purged and collected in a methanol solution in a plastic vial. After concentra(29) Shiea, J.; Chang, D. Y.; Lin, C. H.; Jiang, S. J. Anal. Chem. 2001, 73, 4983. (30) Chang, D. Y.; Lee, C. C.; Shiea, J. Anal. Chem. 2002, 74, 2465.

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Figure 3. (TICs of the three polymer standardss(a) PMMA (120 kDa), (b) PBA (100 kDa), and PC (22.6 kDa)sobtained through conventional Py-GC/MS. The insets in (a) and (b) display the EI mass spectra of the major ions detected on the TIC.

tion (by blowing the methanol solution with pure N2 to reduce the solution’s volume to ∼100-fold), the sample solution was analyzed by injecting 20 µL into a Q-TOF mass analyzer equipped with an ESI source. Figure 4a displays the ESI mass spectrum of the collected PMMA pyrolysates. Since the ionization was performed by ESI, only the pyrolysates with polar functional group will be ionized. A similar technique has been used to characterize trace polar components in the crude oils.31-33 The m/z values of the ions detected by this approach range from 50 to 500; the major ion peaks include those at m/z 74, 99, 127, 209, 269, and 323 (Figure 4a). Compared to the base peak (m/z 269; protonated MMA trimer without OCH3 group; ((MMA)3 - OCH3)H+), the intensity of protonated monomer ion (i.e., protonated methyl methacrylate, (MMA)H+; m/z 101) is quite weak (∼30% of the base peak). This result is quite different from that observed through conventional Py-GC/MS (Figure 3a). The presence of MMA cluster ions on the mass spectrum (dimer, (MMA)2H+, m/z 201; trimer, (MMA)3H+, m/z 301) indicates that the IMRs responsible for the formation of these ions may occur during pyrolysis. The IMRs between (MMA)n (n g 1) molecules and various PMMA fragment ions may also be responsible for the formation of the unknown ions, such as those at m/z 127, 209, and 323. These ions, however, may also arise from direct thermal decomposition of larger PMMA fragments during pyrolysis. Figure 4b displays the mass spectrum of PMMA (2200 Da) obtained through ESA-Py-MS analysis. In this analysis, the (31) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G. Anal. Chem. 2002, 74, 4145. (32) Wu, Z.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2004, 18, 1424. (33) Marshall, A. G.; Rodgers, R. P. Acc. Chem. Res. 2004, 37, 53.

Figure 4. (a) Positive ESI mass spectrum of the pyrolysates from PMMA 2200. The polymer standard was pyrolyzed at 590 °C, and the pyrolysates were purged and collected in the methanol solution. After concentration, the solution was analyzed by conventional ESIMS. (b) Positive ion mass spectrum of PMMA 2200 Da obtained by ESA-Py-MS.

polymer standard powder (2 mg) was pyrolyzed at 590 °C and the gaseous pyrolysates were nitrogen purged into the glass reaction cell to react with proton or protonated methanol ion or to fuse with the charged methanol droplets. The charged solvent ion species and the methanol droplets were generated by electrospraying acidic methanol solution from a capillary electrosprayer located at the center of the cell. Only the pyrolysates with a polar functional group are able to grab a proton from the charged solvent species. The ions generated in the reaction cell were detected by a Q-TOF mass analyzer located at the exit of the cell. Generally speaking, the major ion peaks observed on the mass spectrum in Figure 4b are similar to those in Figure 4a, except that the intensities of the smaller pyrolytical ions (i.e., those in the range m/z 100-200) are lower. This phenomenon can be rationalized by considering the kinetic barriers during fusion and ionization for the pyrolysates with different chemical properties. Due to their low polarity, some of the pyrolysates may be difficult to fuse with the charged methanol droplets, thus, showing lower ion intensity. Moreover, in ESA-Py-MS analysis, the short time for the IMRs between the gaseous pyrolysates and the charged methanol species may cause low ionization efficiency of some small pyrolysates and result in low ion intensity. However, since no sample collection and concentration procedures are required, the fact that we obtained similar mass spectra of the PMMA (2200 Da) standard when using both approaches suggests that ESAPy-MS is a useful technique to rapidly characterize a range of synthetic polymers. Relative to analyses performed using conventional Py-GC/MS, the information regarding to larger and morepolar pyrolysates are obtained by ESA-Py-MS. Figure 5 presents the results of the ESA-Py-MS analysis of three polymer standards prepared from different monomer units (i.e., PMMA (120 kDa), PBA (99 kDa), and PC (22.6 kDa)). Since the building units of the three polymer standards are different (i.e., methyl methacrylate for PMMA, butyl acrylate for PBA, and

Figure 5. Positive ion mass spectra of (a) PMMA (120 kDa), (b) PBA (99 kDa), and (c) PC (22.6 kDa) obtained by ESA-Py-MS.

carbonate for PC), it is not surprising to see that different ESAPy-MS spectra are obtained and none of the major ion peaks among the mass spectra are overlapped (Figure 5). The mass spectrum of PBA (Figure 5b) is dominated by BA cluster ions (e.g., m/z 255 for [M2 - H]+, m/z 385 for M3H+, and m/z 407 for M3Na+) and unidentified ions (such as those at m/z 213, 311, and 343). The signal intensity for protonated BA ion (m/z 129) is weak. Because the structure of PC (see Figure 3c) is much more fragile and reactive than that of either PMMA or PBA, we expected that a greater number of pyrolytic ions and IMR product ions would be produced during the electrospray-assisted pyrolysis ionization processes, such that the mass spectrum of PC would be different from that of PMMA and PBA. As can be seen, although no signals from the PC building block (m/z 254 for bisphenol A) and related cluster ions were observed, when compared to the mass spectra of PMMA and PBA (Figure 5a and b), the mass spectrum of PC (Figure 5c) is much more complicated and the mass range of the detected ions is higher (extended to m/z > 1000). Since the signal of the building block of PC was not detected on ESA-Py mass spectra, further studies are still required to construct the relationship between the pyrolysate ion types and polymer structure for providing identification information of the reactive polymers (e.g., PC). However, based on present results, rapid differentiation of polymer standards with three different building blocks by ESA-Py-MS is promising. To study the effect that the degree of polymerization has on the pyrolysate signals in ESA-Py-MS, the mass spectra of five PMMA standards with different molecular masses (i.e., 2.2, 120, 174, 518, and 1520 kDa) were compared (Figures 4b, 5a, and 6aAnalytical Chemistry, Vol. 77, No. 23, December 1, 2005

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Figure 7. ESA-Py-MS mass spectra of the copolymers (a) MMABA and (b) MMA-BMA. The symbol b refers to ions derived from PMMA; f refers to ions derived from PBA.

Figure 6. Positive ESA-Py-MS spectra of PMMA standards having different molecular masses: (a) 174, (b) 518, and (c) 1520 kDa.

c). Two types of the mass spectra are obtained from the PMMA standards. In general, all of the ion species detected from the five PMMA standards are similar, except that the relative intensities of small pyrolysate ions (m/z < 200) of PMMA (2.2 kDa), PMMA (120 kDa), and PMMA (174 kDa) are weaker than those of the larger pyrolysate ions (m/z > 200) (Figures 4b, 5a, and 6a). The intensities of the ion patterns are reversed for PMMA (518 kDa) and PMMA (1520 kDa): the signals of the larger ions are weaker than those of the smaller ions (Figure 6b and c). Differences in the m/z values of the base peaks (m/z 269 for PMMA (2.2 kDa), PMMA (120 kDa), and PMMA (174 kDa); m/z 155 for PMMA (518 kDa) and PMMA (1520 kDa)) in these mass spectra provide a clear indication of these phenomena. The reasons why we obtain stronger ion signals for small pyrolysates from large PMMA polymers remains unclear. Nevertheless, our results suggest that ESA-Py-MS analysis may be a useful technique for rapidly distinguishing between polymers having different degrees of polymerization, though further studies (such as examining different polymer standards and studying the effect of pyrolytic temperature, etc.) are required before the technique can be used to determine the degree of polymerization. We also used ESA-Py-MS to discern two copolymers: MMABA and MMA-BMA. Again, because of the differences in the building units, the two copolymers are rapidly distinguished by the appearances of their ESA-Py-MS mass spectra (Figure 7). The ions detected on the mass spectrum of the MMA-BA copolymer arise mainly from its PMMA (labeled as b in Figure 7a; cf. Figure 7748 Analytical Chemistry, Vol. 77, No. 23, December 1, 2005

5a) and PBA (labeled as f in Figure 7a; cf. Figure 5b) units and very few other ions are observed. Obviously, this phenomenon is due to the high copolymerization coefficient (ra ) 2.46) of MMABA, which indicates that homopolymerization occurs to a great degree during the bicopolymerization processes.34,35 The major degradation products should then arise mainly from the MMAand BA-rich areas in the copolymer and the few areas where the MMA and BA molecules adjoin each other. Regarding the results of the MMA-BMA copolymer, although the mass spectrum is complicated (Figure 7b), we detect no ions that originate from PMMA or BMA units. Since the ra of the MMA-BMA copolymer is only 0.91, the low ra value implies that the copolymer contains a more-mixed MMA and BMA structure. The composition of the pyrolysates of the copolymer would then be a combination of MMA and BMA units. Again, since only two copolymer samples were studied, more examinations of different types of samples are required before ESA-Py-MS can be used to study detailed pictures of copolymers, such as the degree of polymerization of each polymer in a copolymer. CONCLUSIONS The polar pyrolysates obtained from synthetic polymer standards are rapidly ionized and detected by ESA-Py-MS. The major ions detected on the mass spectrum include the cluster ions of the building unit (mainly formed through IMRs in the pyrolytic probe or in the ESA-Py interface) together with various thermally degraded and IMR products of unidentified structures. The advantages of using this technique to distinguish between synthetic polymers include the following: (1) relative to analyses performed using conventional Py-GC/MS, larger and more-polar pyrolysate ions are detected; (2) the assembly of the ESA-Py interface is simple and can be interfaced to common mass spectrometers in most chemistry laboratories; (3) the time (34) Elias, H. G. An Introduction to Polymer Science; VCH: Weinheim, 1997; pp 107-117. (35) Odian, G. Principles of Polymerization, 4th ed.; John Wiley & Sons: Hoboken, NJ, 2004; pp 466-478.

required for analysis is short and the procedures for sample pretreatment are minimized. We were able to rapidly distinguish three polymer standards formed from different building units (PMMA, PBA, PC) and two copolymers [MMA-BA (ra 2.46), MMA-BMA (ra 0.91)] through the analysis by ESA-Py-MS. Two types of mass spectrum from PMMA standards having different degrees of polymerization were obtained. These results suggest that the ESA-Py-MS technique may be applicable for rapidly distinguishing the polymer standards that differ in the nature of building blocks, degrees of polymerization, and copolymerization

coefficients, but further work is still required to attain this objective. ACKNOWLEDGMENT We appreciate the financial support of the National Science Council and the Petroleum Foundation, Ministry of Economic Affairs, Taiwan. Received for review June 23, 2005. Accepted September 30, 2005. AC051116M

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