2228
Anal. Chem.
1982,5 4 , 2228-2233
the fragments do not rearrange during the CID interaction time* The to examine the MS/MS/MS behavior Of ion-molecule reaction products could be useful in chemical ionization studies.
ACKNOWLEDGMENT The authors wish to thank the members of the Nicolet Instrument Co. Mass Spec. Group, and in particular R. B. Spencer, for their technical assistance.
LITERATURE CITED (1) Comlsarow, M. 6.; Marshall, A. G. Chem. Phys. Lett. 1974, 25,282. (2) Parisod, G.; Comisarow, M. B. Adv. Mass Spectrom. 1980, 8 , 218. (3) Ledford, E. B., Jr.; Ghaderi, S.;White, R. L.; Spencer, R. B.; Kulkarni, P. S.;Wilkins, C. L.; Gross, M. L. Anal. Chem. 1980, 52, 463-468. (4) Hunter, R. L.; McIver, R. T. Anal. Chem. 1979, 5 1 , 699-704. (5) Ghaderi, S.; Kulkarni, P. S.; Ledford, E. B., Jr.; Wllkins, C. L.; Gross, M. L. Anal. Chem. 1981, 53,428-437. (6) Burnier, R. C.; Byrd, G. D.; Freiser, B. S. Anal. Chem. 1980, 52, 1841-1650. (7) Cody, R. 6.; Burnier, R. C.; Reents, W. D., Jr.; Carlin, T. J. McCrery, D. A.; Lengel, R. K.; Freiser, 8 . S. Int. J . Mass Spectrom. Ion Phys. 1980, 33,37-43. (8) McCrery, D. A.; Ledford, E. B., Jr.; Gross, M. L. Anal. Chem. 1982, 54. 1435-1437. (9) Coby, R. 6.; Freiser, B. S.Int. J . Mass Spectrom. Ion Phys. 1982, 4 7, 199-204.
(10) Cody, R. B.; Burnier, R. C.; Freiser, B. S. Anal. Chem. 1982, 54, 96-101. (11) Burnier, R. C.; Cody, R. B.; Freiser, B. S. J . Am. Chem. SOC.,in press. (12) Cody, R. 6.; Burnier, R. C.; Sallans, L.; McLuckey, S.; Verma, S.; Freiser, 8. S.;Cooks, R. G. Int. J . Mass Spectrom. Ion Phys., in press. (13) Cody, R. B.;Freiser, B. S. Anal. Chem. 1982, 5 4 , 1431-1433. (14) McIver, R. T. Workshop on Newer Aspects of Ion Cyclotron Resonance (Fourier Transform Mass Spectrometry), 29th Annual Conference of Mass Spectrometry and Allied Topics, Minneapolis, MN, 1981; D 798. (15) Proctor, C. J.; Brenton, A. G.; Beynon, J. H.; Kralj, B.; Marsel, J. Int. J . Mass Spectrom. Ion Phys. 1980, 35,393-403. (16) Proctor, C. J.; Kralj, B.; Brenton, A. G.; Beynon, J. H. Org. Mass Spectrom. 1980, 75, 619-631. (17) Boyd, R. K.; Shushan, B. Int. J . Mass Spectrom. Ion Phys. 1981, 3 7 , 355-368. (18) Burinsky, D. J.; Cooks, R. G.; Chess, E. K.; Gross, M. L. Anal. Chem. 1982, 5 4 , 295-299. (19) Maquestiau, A.; Meyran, P.; Flammang, R. Org. Mass Spectrom. 1982, 77, 96-101.
RECEIVEDfor review March 23,1982. Accepted July 30, 1982. Acknowledgment is made to the Department of Energy (DE-AC02-80ER10689) for supporting this research and the National Science Foundation (CHE-8002685) for providing funds to purchase the FTMS.
Linear Programmed Thermal Degradation Mass Spectrometry of Polystyrene and Poly(viny1 chloride) T. H. Risby" and J. A. Yergey Division of Environmental Chemistry, Department of Environmental Health Sciences, School of Hygiene and Public Health, The Johns Hopkins University, 6 15 North Wolfe Street, Baltimore, Maryland 2 1205
J. J. Scocca Department of Biochemistry, School of Hygiene and Public Health, The Johns Hopkins University, 6 15 North Wolfe Street, Baltimore, Maryland 2 1205
The use of a computer-controlled temperature-programmable platinum filament as a probe for linear programmed thermal degradation mass spectrometry Is reported. A study of time-resolved pyrolysis of various polystyrene samples and 01 poly(vlny1 Chloride) was made: results show a stepwlse thermal degradation process. Energies of activation and preexponentlal factors for these thermal degradations were determined.
Linear programmed thermal degradation mass spectrometry (LPTD-MS) (1,2) as a monitor of thermal decomposition of high molecular weight samples has been used to distinguish between bacterial species and serotypes (3) and between various normal and abnormal human lymphocytes ( 4 ) . However, the fragments that were used to distinguish between specimens could not be chemically characterized; differentiation of samples was based on empirical data. Thermal decomposition as a means of characterizing high molecular weight compounds has been used in pyrolysis gas chromatography (PyGC) and pyrolysis mass spectrometry (PyMS) for a wide range of samples. Whereas PyMS and PyGC involve a single mass spectrum or gas chromatogram obtained after rapid heating of the samples to a fixed tem0003-2700/82/0354-2228$0 1.25/0
perature, LPTD-MS is based on a collection of sequential mass spectra during the programmed heating of the sample. The LPTD-MS data, with temporal dependence, allow detection of subtle differences in structure which would not be apparent with data from PyGC or PyMS. In addition, activation energies and preexponential factors for the decomposition processes can be obtained from LPTD-MS by changing the rate of sample heating; such results cannot be obtained by PyGC or PyMS. The major advance made in this study is the redesign of the temperature programmable probe and controller to allow accurate measurements of decomposition temperature. A similar probe is available commercially (Pyroprobe, Chemical Data Systems) but lacks the capability for computer-controlled variations in heating rates. Our improved design has been evaluated by studying the temperature-resolved pyrolysis of two well-characterized polymers, polystyrene and poly(viny1 chloride). The design of the probe and controller, data on the mechanisms of thermal decomposition, activation energies, and preexponential factors of these polymers are reported in this paper.
EXPERIMENTAL SECTION Apparatus. These studies were performed with a chemical ionization mass spectrometer (Scientific Research Instruments 0 1982 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 13, NOVEMBER 1982
Table I. Polymer Samples polymer structure polystyrene un-cross-linked polystyrene un-cross-linked polystyrene 1%cross-linked divinylbenzene polystyrene 4% cross-linked divinylbenzene polystyrene 12% cross-linked diviny 1benzene poly(viny1 un-cross-linked chloride)
M, source and name 390 000 Polysciences Inc. 100 000 Polysciences Inc. Polysciences Inc., 1%DVB copolymer Polysciences Inc., Poly Sep 4% Polysciences Inc., Poly Sep 12% B.F. Goodrich, Geon-103EPF 76
Corp., BI0SPECT)-data system (Modular Computer Systems, Inc., MODCOMP 11/25) as described previously (51, except that the data system is now dedicated to the mass spectrometer. The mass to charge ratios of the various fragment ions were determined with the mass marker which had been calibrated to the computer by using methyl stearate as the standard. Samples. Aliquots (0.5 pL) of a solution of polystyrene (1 mg/mL) in chloroform or of poly(viny1 chloride) (1 mg/mL) in tetrahydrofuran were placed on the platinum filament by using a microsyringe. Most of the solvent was allowed to evaporate under ambient conditions and any residual solvent was removed by the rough vacuum prior to insertion into the source of the chemical ionization mass spectrometer. A reproducible coating of about 500 ng of the sannple on the filament was obtained; the small sample size ensures that there is intimate contact between the sample and the platinum filament. Table I lists the polymers used in this study. Temperature Programmable Probe and Controller. The temperature programmable probe and controller were constructed to allow the temperature of a platinum wire to be increased linearly and stepwise, over a temperature range (ambient to 600 "C), under on-line computer control. At each temperature step a mass spectrum is collected to give one X-Y section of the three-dimensional (3-D) graph (e.g., as seen in Figure 2). The temperature is then jumped to the next temperature, and the subsequent X-K section of the graph is obtained. This process is repeated until the complete thermal degradation has been produced and the results can be represented by a 3-D graph. The mass spectral and temperature data are collected a t each step. The rate of temperature increase can be in the range of 300 "C s-l to 0.05 "C s-l. The maximum rate of heating is dictated by the electronics in the detection system of the mass spectrometer. The probe tip consists of U-shaped platinum wire (0.2548mm o.d., -2 cm long) spot welded to heavy gauge nickel wires (1.5 mm 0.d.) at the end of a modified solids probe (BIOSPECT, Scientific Research Instruments Corp.) (6.0 mm 0.d.). This configuration allows the platinum wire to act both ,asthe sample heater and as a platinum resistance thermometer; the average temperature over the platinum wire can be calculated from its resistance. The use of double nickel wires connected to each side of the platinum wire enables just the voltage drop across the filament to be measured, without contribution from the nickel leads. Figure 1 is a block diagram of the electronics used to operate the probe under on-line computer control. The digital input voltage is scaled in an analog-to-digital (A/I>) converter. These pulses are generated by an interval timer, which also generates a hardware interrupt hence initiating an interrupt routine by which the various voltages are updated. A complete discussion of the computer-mass spectrometer interface and the associated software has been published previously (5). The overlays calibrate temperature probe (CTPROB), manipulate temperature file (MTFILE), and view temperature data (VTDATA) have been added to the program CAD so that the probe can be calibrated and the temperature data stored and displayed (6). This arrangement allows direct and accurate measurements of the voltage and current at the platinum filament. Resistance (R, Q) can be calculated a t each datum sampling point by the application of Ohm's law. The cross-sectional area ( A , cm2) of the platinum filament is known. In the temperature range of 0 to 500 "C the resistivity of platinum ( p , Q crn) and temperature
2229
Probe c u r r e n t
?lultipii:atio, Resistor 0 , 1568
Precisicn Scaling Potentiometer
P t Filament
t
Controller
1 I n o u t o u t p u t Interface
1
Hardware
Interrupt
A
Figure 1. Block diagram of temperature programmable platinum wire probe and controller.
(T,"C) have a linear relationship and the temperature coefficient [ ( p T - p T o ) / p T r ] is 0.003618 (7). Therefore, if the length (1, cm) of the wire is Known, the resistivity ( p T ) and temperature ( T ,"C) of the platinum filament in the range of 0 "C to 500 "C can be calculated by using the following equations: R =pl/A T=
( p -~(9.81 X
10*))(2.82
(1) X
lo7 "C Q-l cm-').
(2)
The length of the platinum filament, which is determined by the exact points of electrical contact with the nickel leads, is difficult to determine mechanically and hence was measured electrically. A scan of the input voltage (0.000-0.125 V) was made while the filament was immersed in an ice bath. The thermal capacity of the ice bath was sufficient to maintain a constant temperature (constant resistance) for the platinum filament and thereby enable the length to be calculated by using eq 1 and 2. This calibration was checked daily for a month and the calculated length was found to remain constant. The accuracy of the temperature measurements was checked by using either a boiling water bath or a furnace, and the measurements were found to be accurate within 3-5 % . Procedure. In order to simplify the pyrolysis data, we held many of the variables constant for all the experiments: reactant gas, methane (at 1 torr); source temperature, 120 "C; 20 mass spectral scans/min (polystyrene, 80-480 m u ; poly(viny1 chloride) (+ve ion detection) 60-460 amu and (-ve ion detection) 10-410 amu). The experiment was initiated on insertion of the probe, and the fiist 10 mass spectra were collected without the application of a voltage to the platinum filament. This 30-9delay was found to increase the reproducibility of the data; during this time the temperature of the probe reached approximately 70 "C as a result of heat conduction from the source. After this initial hold the voltage to the platinum filament was increased stepwise to give a final temperature of approximately 540 "C. The platinum filament was maintained at this temperature for a further 10 mass spectra (30 s) in order to ensure total removal of the sample. Various rates of temperature increase (ramps) were used (1-16 "C s-') in order to study the temperature-resolved pyrolysis of the polymers.
2230
ANALYTICAL CHEMISTRY, VOL. 54,NO. 13,NOVEMBER 1982
r,
E
8
II*
1
IP
Flgure 2. Threedimensional plot for thermal degradation at 16 "CIS of uncross-linked polystyrene (M,100000)shown as m l z vs. intensity vs. scan number (10 = 73 "C, 30 = 563 "C). r
I SCAh
SCIU
Figure 4. Specific ion profiles for thermal degradation at 16.0 "Cls of un-cross-linked polystyrene (M,lOOOOO),shown as intensity vs. scan number: (A) mass 105 mlz, temperature of evolution maximum 423 OC; (B) mass 117 m l z , temperature of evolution maximum 423 "C; (C) mass 209 m / z , temperature of evolution maximum 423 "C; (D) mass 221 m l z , temperature of evolution maximum 423 "C.
I=
Figure 3. Three-dimensionalplot for thermal degradation at 15.5 "C/s
of polystyrene-12% divinylbenzene, shown as m l z vs. intensity vs. scan number (10 = 97 "C, 30 = 564 "C)
RESULTS AND DISCUSSION
SUN
5th
When a series of temperature ramps are used, plots of In
[ M /Tmkj2] vs. [ 1/ Tmkj] give values for Ekjand Kokj according to the following equation (2):
where M is the temperature ramp (dT/dt), Tmkjis the temperature that corresponds to the maximum evolution of the kth fragment by the j t h process, Ekj is the activation energy of the production of the kth fragment by the j t h process, and Kokjis the preexponential factor. 1. Polystyrene. Polystyrene samples (Table I) were selected for investigation of the effects of polymer chain length and degree of cross-linking on the thermal degradation evolution profiles. These polymers were pyrolyzed in triplicate. Figures 2 and 3 show the mass spectra as a function of temperature for the thermal degradations of un-cross-linked polystyrene, M , 1OOOO0, and 12% divinyl benzene cross-linked polystyrene. The difference between the samples is clearly shown, as the heavily cross-linked polystyrene starts to degrade a t a lower temperature, and the degradation occurs over a wider temperature range. These differences appear even more dramatic in Figures 4 and 5 which are the profiles for specific ions (105,117,209, and 221 m / z )as a function of scan number (sample temperatures). In Figure 4 more than one kinetic process for the evolution of the monomer fragment (105 m / z ) is indicated since the profile is clearly broader than the profiles for the specific ions at 117, 209, and 221 m / z . These differences in evolution profiles may perhaps be explained by different types of microstructures within the un-cross-linked polystyrene which can lose a styrene fragment; the activation energies for the removal of the monomer from these microstructures would be expected to differ. This hypothesis of different microstructures within the polystyrene is supported
ir
I
G-
' "I I '", '+ LClH
I' 20
Is
8CIN
Flgure 5. Specific ion profiles for thermal degradation at 15.5 "CIS of polystyrene-1 2 % divinylbenzene, shown as intensity vs. scan number: (A) mass 105 m l r , temperatures of evolution maxima 177, 394, 500, 559 "C; (B) mass 177 m l z , temperatures of evolution maxima 117,394 "C; (C) mass 209 m l r , temperature of evolution maximum 394 "C; (D) mass 221 m l z , temperatures of evolution maxima 177,500 "C.
by further evidence. The evolution profiles for larger fragments are sharper, suggesting less variety in kinetic processes of evolution, i.e., less variance in microstructure. In Figure 5 (cross-linked polystyrene) profiles for all the fragments are broad suggesting that each ion may be produced by a variety of kinetic processes. Cross-linking would be expected to produce different types of microstructures. (However, differences could be explained by the fragments having arisen from either styrene or divinylbenzene.) Polystyrene with a lower degree of cross-linking (Figure 6) has a more random structure and would be expected to have many different microstructures. This is indeed supported by the complex profiles shown in Figure 6. The temperatures ("C)which correspond to the maxima of the evolution profiles are also shown in Figures 4-6. There are temperature maxima variations for the evolution of different fragments from the same sample and for the same fragment from different samples. Also, the cross-linked
ANALYTICAL CHEMISTRY, VOL. 54, NO. 13, NOVEMBER 1982 I
1
iA I t
h T V SCAN
SFUi
SCAN
BEAH
;Ij I
Flgure 6. Specific lion profiles for thermal degradation at 15.6 "Cls of polystyrene-1 % divinylbenzene, shown as Intensity vs. scan number: (A) mass 105 m l z , temperatures of evolution maxima 129, 448, 551 "C; (B) mass 117 m l r , temperatures of evolutlon maxima 129, 395, 503 "C; (C) mass 209 mlz, temperature of evolution maximum 393 "C; (D) mass i!21 m l z , temperatures of evolution maxima 175,
393 "C. Table 11. Temperature Data, Activation Energies, and Preexponential Factors €or Un-Cross-Linked Polystyrenes M , 390 000 M , 100 000 -ramp rate, temp of ramp rate, temp of "Cis maxima, "C "Cis maxima, "C 15.9 7.79 3.92 1.97 0.99
activation energy preexponential factor
390 385 363 352 345
16.0 7.77 3.87 1.99 0.99
4 2 kcal 3.6
x 10"
388 386 365 349 343 40 kcal
s-'
6.1 X 101's-'
polymers begin pyrolyzing at temperatures 200 "C lower than the maximum evolution temperature. This is not observed with the un-cross-linked polymers. Since it was impossible to separate and identify the kinetic processes corresponding 1x1the loss of specific fragments from the samples of cross-linked polystyrene, and difficult to ensure that the same chemical species were involved, no attempt wm made to obtain values for the activation energies by varying rate of sample heating. In addition, evolution profiles for specific fragmentri from un-cross-linked polystyrene samples were complex, and values for the activation energies given in Table I1 are basedl on the 235 m/z. There is good agreement between the values for the activation energies and the preexponential factors for the two un-cross-linked polystyrenes as would be expected since they differ only in molecular weight. Also, there is reasonable agreement of the value for activation energy with a literature value of 48.04 kcal (8) obtained with a much larger sample size. The major fragment ions observed for the polystyrene samples are listed in Table 111. These fragments have been observed by other workerri using pyrolysis gas chromatography and/or mass spectrometry (9-23) and using chemical ionization mass spectrometry (14). 2. Poly(viny1 chloride). Poly(viny1 chloride) was selected for study because of its bnmodal pyrolysis (14,24-29). Initial evolution of hydrogen chloride leads to a conjugated polyene which subsequently pyrolyzes to hydrocarbon fragments. The
2231
Table 111. Polystyrene Pyrolysis Products mass of ion with max intens in the % total region of ion current at basic structure of fragment mol wt max evolutiona CH=CH, 104 4.0 Ph CH,=CHCH 117 4.7 Ph 1.8 130 CH,=CHCHCH Ph CH,=CHCH,CH=CH 144 2.1 Ph CHCH,CH 194 1.9 Ph *Ph 208 9.7 CH,CHCH,CH Ph Ph CH,CHCH,CHCH, 222 2.4 Ph Ph CH=CHCH,CH=CHCH, 234 6.0 Ph Ph a Un-cross-linked, M, 390 000. ability to observe this bimodal evolution is dependent upon the sample heating rate. Since these evolution profiles involve fragments with different polarities, namely, hydrogen chloride and hydrocarbons, both negative and positive ion methane chemical ionization mass spectrometry were used to follow the progress of the pyrolysis. Negative ion detection was used in order to selectively detect halogenated species since there is some controversy as to whether halogenated hydrocarbons are also evolved with hydrogen chloride. Positive ion detection was used to detect the evolution of the hydrocarbon fragments. a. Negative Ions. Poly(viny1 chloride) showed a bimodal evolution profile in the negative ion detection mode, but the first evolution was due to the release of the residual solvent, tetrahydrofuran. The second evolution was due to the following major species: [Cll- (35, 37 m / z ) , [HC12]- (71, 73, 75 m / z ) ,and [PhCHClI- (125, 126,127,128 m / z ) . Presence of the ions [Cll- and [HClJ indicates the loss of hydrogen chloride from the polymer; the latter ion has been observed previously in the low pressure negative methane chemical ionization mass spectra of pesticides (30). The loss of the fragment [PhCHClI- has not been observed previously, although other workers have reported the detection of minor amounts of benzene (29),chlorobenzene (31),and oxygenated hydrocarbons (31) with the evolution of hydrogen chloride. Benzyl chloride has been observed by PyGCMS analysis of a poly(viny1 chloride) resin containing the mixed ester plasticizer butyl benzyl o-phthalate (25). It was suggested (25) that benzyl chloride was the pyrolysis product of the plasticizer and was produced by the reaction of benzyl alcohol with hydrogen chloride. However, the poly(viny1 chloride) used in this study did not contain any plasticizer and [PhCHClImay be a pyrolysis product of poly(viny1chloride) itself. The specific ion profiles for the loss of the chlorine-containing fragments in the second evolution were broader than the evolution profiles for the fragments lost from polystyrene, These differences in the widths of the evolution profiles can be rationalized: dehydrochlorination produces allylic groups that will cyclize and the subsequent losses of hydrogen chloride will have different kinetics. Examples of these profiles are shown in Figure 7. Examination of specific ion profiles shows that the onset of the evolution of hydrogen chloride (loss of C1-) occurs prior to the onset of the evolution of [HClJ or [PhCHClI- suggesting that the latter ions may be the products of secondary gas phase reactions. Although the evolution profiles were broad, the average activation energy could be
2232
ANALYTICAL CHEMISTRY, VOL. 54, NO. 13, NOVEMBER 1982
A
n
iB
SCLH
Flgure 7. Specific negative ion profiles for thermal degradation at 7.8 'Cis of poly(vlny1chloride), shown as intensity vs. scan number: (A) mass 35 mlz, temperature of evolution maximum 331 OC; (B)mass 71 m l z , temperature of evolution maximum 305 OC; (C) mass 125 mlz, temperature of evolution maximum 305 OC.
Table IV. Temperature Data, Activation Energies, and Preexponential Factors for Poly(viny1 chloride) thermal degradation dehydrochlorination of polyene ramp rate, temp of max, ramp rate, temp of max, "C
CIS 15.5 7.80 3.96 1.98
1.00
activation energy preexponential factor
326 306 29 8 286 27 6
"C
"CIS 15.65 7.99 4.00 2.01 1.02
319 294, 283, 275, 254,
Table V. Hydrocarbon Pyrolysis Products from Poly(viny1 chloride) (7.80 "C/s) mass of ion with % total max intens ion current in region at max evolution of mol wt
hydrocarbon fragment benzene toluene styrene ethylbenzene propylenebenzene Propylbenzene naphthalene methylnaphthalene ethylnaphthalene propylenenaphthalene Propylnaphthalene anthracene methylanthracene ethylanthracene propyleneanthracene Propylanthracene
temp of evolution max, "C
79 93 105 107 119
5.8 1.0 2.0 3.0 3.4
266-294 321-348 294 266-294 294
121
1.4
294
129 142
4.2 0.9
294 321-348
156
1.4
294
169
0.9
294
171
0.8
294
179 192
0.7 0.6
294, 3 2 1 294,321
206
0.5
294
219
0.2
294, 3 2 1
221
0.2
294
354 349 340 334
33 kcal
25, 72 kcal
6.3 X 101's-'
6.3 X 9.1
lo8, x 10% S-I
obtained by the measurement of the temperature maxima as a function of sample heating rates. The results of these studies are given in Table IV. Various values for the activation energy for the dehydrochlorination of the poly(viny1 chloride) have been reported in the literature and they range from 20.00 to 33.03 kcal (32-34). The value obtained by this study falls within this range. b. Positive Ions. Since the background ion current of the positive ion methane chemical ionization mass spectrum in the region of 10-60 m / z was intense, no attempt was made to monitor the evolution of hydrogen chloride (+H2C1m / t 36, 38). Protonated molecular ions were observed for the major fragments with the exception of methylnaphthalene, ethylnaphthalene, methylanthracene, and ethylanthracene. The nominal structures for the fragments that result from the thermal degradation of the polyene are shown in Table V. The specific ion current decreased with increasing molecular weight as would be expected. There was some evidence of the evolution of aliphatic hydrocarbons, but they were not characterized. The evolution profiles for some of the aromatic hydrocarbon fragments, shown in Figure 8, were bimodal and the first evolution maximum occurred concomitantly with the dehydrochlorination step. These results confirm that the ion [PhCHClI- was formed in secondary gas phase reactions since it was not observed in the positive ion spectra. It is interesting to note that not all the ions had this bimodal evolution profile. Although some of the evolution profiles for the loss of these aromatic hydrocarbon fragments were bimodal and were
scu
SCAN
I H
I\
I\ I\
ocw
E N
s I ? V
SUN
Figure 8. Specific ion profiles for thermal degradation at 8.0 ' C I S of poly(viny1 chloride), shown as intenslty vs. scan number: (A) mass 79 mlz, temperature range of evolutlon maxima 266-394 OC; (B) mass 107 m / z , temperature range of evolution maxima 266-394 OC; (C) mass 119 m l z , temperature of evolution maximum 294 OC; (D) mass 142 m l z , temperature range of second evolution maxima 321-348 OC.
clearly due to multiple kinetic processes, attempts were made to measure average activation energies. The activation energies for dehydrochlorination and polyene degradation are presented in Table IV. The activation energy of the first evolution maxima was lower than the average activation energy for the dehydrochlorination. This is difficult to rationalize since dehydrochlorination must precede or occur concomitantly with the formation of the polyene. However, this difference may not be significant and may reflect errors in the measurement of the activation energies by this method. If this difference is significant, it may be because this technique measures the average activation energy for the loss of
Anal. Chem.
1902, 5 4 , 2233-2238
the particular fragment; the loss of hydrogen chloride has a much greater variation in activation energy than does the loss of the hydrocarbons. This may explain the wide variation in published activation energies for the same processes. The second evolution profile has a much higher activation energy similar to the value found for the thermolysis of isoprene (351, 56-63.05 kcal, which has a similar degree of unsaturation. These results clearly show the usefulness of this technique to study the temperature-resolved pyrolysis of synthetic polymers and currently well-defined biopolymers are being studied.
ACKNOWLEDGMENT We thank Joel Balogh for the construction of the control electronics for the probe and Tatyana Frenkel for helping to obtain the data. The helpful discussions of M. S. B. Munson and R. Lattimer are gratefully acknowledged.
LITERATURE CITED Risby, T. H.; Yorgey, A. L. US. Patent No. 4075475, Feb 21, 1978. Rlsby, T. H.; Yergey, A. L. Anal. Chem. 19781, 50, 326A. Risby, T. H.; Yergey, A. L. J . Phys. Chem. 1876, 8 0 , 2839. Yeraev, A. L.:Risbv, T. H.: Golomb. H. M. Blomed. Mass Spectrom. 197&.5, 47. (5) Campana, J. E.; Rlsby, T. H.; Jurs, P. C. Anal. Chim. Acta 1979, 712,
(1) (2) (3) (4) .,
--
371..
(6) Yergey, J. A. Pt1.D. Thesis, The Pennsylvania State University, Universitv Park. PA. 1981. (7) Wise,€.'M., Ed.-'The Platinum Metals and Thulr Alloys"; The International Nickel Co.. Inc.: New York. 1941. (8) Wegner, J.; Patat, F. J . Po/ym. SC;.1970, 37, 121. (9) Madorsky, S.L.; Strauss, S. J . Res. Natl. Bur. Stand. (U.S.) 1948, 4 0 , 417. (IO) Bradt, P.; Dibeier, V.; Mohler, F. L. J . Res. Natl. Bur. Stand. (U.S.) 1953, 5 0 , 201. (11) Wiiey, R. H.; Smlthson, L. H., Jr. J . Macromol. Sci. Chem. 1968, 2 , 589
(12) %man, A. I n "Thermal Analysis"; Wiedeman, H. G., Ed.; Birkhauser Verlag: Basel, 1972. (13) Stenhagen, E.; Abrahamson, S.; Mclafferty, F. W. "Atlas of Mass Spectral Data"; Wiiey-Interscience: New York, 1969; Voi. 4, p 645.
2233
(14) Shimizu, Y.; Munson, M. S. B. J . Polym. Sci., Polym. Chem. Ed. 1979, 17, 1991. (15) Cascaval, C. N. Mater. Plast. (Bucharest) 1979, 76,120. (16) Blazso, M.; Varhegyi, G.; Jakab, E. J . Anal. Appl. Pyrolysis 1980, 2 , 177. (17) Oehme, G.;Baudisch, H.; Mix, H. Makromol. Chem. 1976, 177, 2657. (18) Kiran, E.; Glliham, J. K. J . Appl. Polym. Sci. 1977, 2 1 , 1159. (19) Cameron, G. C.; MacCaiium, J. R. J . Macromol. Sci., Rev. Macromol. Chem. 1967, 61. 327. (20) Rudin, A.; Samanta, M. C.; Relliy, P. M. J . Appl. Polym. Sci. 1979, 2 4 , 171. (21) Cameron, G. G.; Meyer, J. M.; McWaiter, I.T. Macromolecules 1978, 7 7 , 696. (22) Cascaval, C. N.;Straus, S.; Brown, D. W.; Florin, R. E. J . Polym. Sci. 1976, 5 7 , 81. (23) Rudin, A.; Samanta, M. C.; Van der Hoff, B. M. E. J . Polym. Scl., Polym. Chem. Ed. 1979, 1 7 , 493. (24) Buriiie, P.; Bert, M.; Michei, A.; Guyot, A. J . Polym. Sci., Polym. Lett. Ed. 1978, 76,181. (25) O'Mara, M. M. J . Polym. Sci., Polym. Chem. Ed. 1970, 8 , 1887. (26) Chang, E. P.; Saiovey, R. J . Polym. Sci., Polym. Cbem. Ed. 1976, 12, 2927. (27) Ahlstrom, D. H.; Liebman, S. A.; Abbas, K. B. J . Polym. Sci., Polym. Chem. Ed. 1976, 14, 2479. (28) Aiajberg, A.; Arpino, P.; DeurSiftar, D.; Ginochow, G. J . Anal. Appl. Pyrol. 1980, 7 , 203. (29) Ballistreri, A.; Foti, S.; Montaudo, G.; Scamporrtno, E. J . Polym. Sci., Polym. Chem. Ed. 1960, 78, 1147. (30) Dougherty, R. Org. Mass Spectrom. 1972, 16, 1171. (31) Thinius, K.; Schroeder, E.; Guste, A. Plaste Kautsch. 1984, 1 7 , 67. (32) Guyot, A.; Benevise, J. P.; Trambouze, Y. J . Appl. Polym. Sci. 1962, 6, 103. (33) Taiamini, G.; Pezzin, G. Makromol. Chem 1960, 39, 26. (34) Stromberg, R. R.; Straus, S.;Achhammer, B.G. J , Polym. Sci. 1959,
.
35,355. (35) Straus,
S.;Madorsky, S.L. Ind. Eng. Chem. 1956, 4 8 , 1212.
RECEIVED for review March 15, 1982. Accepted August 12, 1982. This work was supported by a grant from the National Institute of Allergy and Infectious Diseases (AI 16384). The MODCOMP 11/25 computer system was purchased with funds from the U.S. Environmental Protection Agency (R-806558), the National Institute of Allergy and Infectious Diseases (AI 16384),and the Division of Research Resources at the National Institutes of Health (RR-05445).
Selectivity in Liquid Chromatography with Micellar Mobile Phases Paul Yarmchuk, Robert Weinberger, FI. F. Hirsch, and L. J. Cline Love* Seton Hall University, Department of Chemistry, South Orange, New Jersey 07079
Mlcellar mobile phases are shown to offer control over selectlvity In liquld chromatography. While retentlon of all solutes decreases with increasing surfactant concentration, the rate of decrease varies considerably, producing lnverslons In retentlon orders. The retsntlon order reversals are the result of two competlng csqulllbrla, namely, solute-mlcelle assoclation characterized by K,, and solute-stetlonary phase interactlon Characterized by Kws. Increased micelle concentration can drlve the solute into the movlng mlcellar phase whlle havlng little or no effect on the stationary phase equillbrla. A second Important micellar effect on retention Is electrostatlc interactions between lonlc surfactant and ionlzable solutes In a manner analogous to Ion-lnteractlon chromatography. The nature of thls effect, whether repulsion or attractlon, depends on the lonlc character (anionlc or catIonic) of the surfactant and the correspondlng solute. Examples are given to show hew selectlvity can be enhanced by proper choke of surfactant type and moblWe phase concentratlon.
Ionic surfactants have been employed extensively in liquid chromatographic (LC) mobile phases as ion interaction reagents, typically in conjunction with conventional mobile phase modifiers (1-3). The benefit obtained via these secondary equilibria or side reactions is enhanced selectivity for separations of interactive solutes. More recently, aqueous solutions of similar ionic surfactants, but at concentrations above the critical micelle concentration (CMC), have been shown to have properties analogous to those of conventional mobile phases for reversed-phase LC (4). The fundamental properties of these micellar solutions which enhance the organization of reactants on a molecular level have been used to advantage in catalysis ( 5 ) ,room-temperature phosphorescence (6), and drug absorption (7), as well as in chromatographic separations. Recently, it has been shown that micellar solutions can be utilized in a total analytical scheme involving micellar LC with micelle-stabilized roomtemperature phosphorescence detection (8). A theoretical basis for the chromatographic resolving power
0003-2700/82/0354-2233$01.25/00 1982 American Chemical Society
