Gas Chromatographic-Mass Spectrometric Identification of Volatiles Released from a Rubber Stock during Simulated Vulcanization S. M. Rappaport"
' and D. A. Fraser
Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hi//, Chapel Hill, N.C., 275 74
Methods were developed for simulating a rubber vulcanization process in the laboratory and for analyzing the volatile organic compounds released. Vapors generated from a typical stock and from individual compounding ingredients were collected on activated charcoal and were then eluted with diethyl ether. Specific peaks in the subsequent gas chromatogram were correlated with retention limes of volatiles released from various additives. Combined gas chromatography-mass spectrometry was employed to identify individual substances in the CS to C25 boiling range.
The evolution of volatile organic compounds from rubber stocks during vulcanization is little understood. Individual substances released into the surrounding air may include specific additives and associated impurities or may be the products of chemical reactions within the matrix. Given the diversity of ingredients incorporated in a rubber product, this mixture undoubtedly contains numerous compounds of varying chemical and toxicological properties. Identification of these emissions is of considerable interest to those concerned with potential contamination of the air environment and the health of the workers in industry. Unfortunately, little data concerning the identities of vulcanization discharges have been published. Information t h a t is available has been gleaned from studies involving either the heating of elastomers and stocks to vulcanization temperatures or from investigations into the reaction kinetics of various cross-linking systems. Fernando and Wijeskera heated stocks to 120 "C in air and resolved via GLC some of the compounds released but made no identifications (1). Cleverley and Herrmann studied the distillate collected from elastomers a t 200 "C and described the composition as a blend of specific additives in the forms of crystals, resins, waxes, and liquids ( 2 ) . Popov and Garshunova compared the evolution of volatiles from various rubber samples maintained a t 70 "C in argon (3). Preliminary analysis pointed primarily to hydrocarbons in the C7 to boiling range. Bourne et al. heated portions of two commercial stocks to temperatures between 135 and 153 "C and reported the release of unspecified nitriles ( 4 ) . Other workers have correlated the rates of volatilization of specific compounding ingredients with relevant process variables (5-7). These studies have shown that the liberation of volatiles is a function of several factors, including the curing temperature, vapor pressures, stock thickness, and the flow rate of gas over the rubber surface. Unfortunately, the additives used in rubber processing are of technical grade, and limited qualitative data are available concerning their compositions. T h e active agents of some ingredients are not even specified but are described, instead, as products of two chemical species, e.g., the aldehydePresent address, University of California, Los Alamos Scientific Laboratory, Los Alamos, N.M. 87545. 476
ANALYTICAL CHEMISTRY, VOL. 48,
NO. 3,
MARCH 1976
amine reaction products used as accelerators (8).Other additives such as oils are crude mixtures and may contribute numerous compounds to the total vulcanization effluent (9-1 3 ) . Another difficulty in predicting vulcanization emissions is the barrage of chemical reactions which may produce volatile compounds. Specific mechanisms are quite complex and follow predominantly ionic or free radical pathways depending upon the particular polymer and crosslinking systems involved (14-26). The chemistry of vulcanization can be visualized as a reducing phase during which the actual cross-linking reactions take place followed by an oxidative stage which is initiated when the mold opens, thereby exposing the hot rubber surface to air. Likely products which could be released during the reducing phase are amines and organic sulfides associated with accelerator fragments and cross-linking reactions. Sulfenamide accelerators, for instance, decompose a t a critical temperature to yield mercaptobenzothiazole and characteristic amines (20, 22, 27, 28). T h e oxidative step which follows could also produce many products, including amines, peroxysubstituted amines, and acids from reactions between aromatic amine antidegradants and air (29). The present study was undertaken to provide insight into the composition of curing effluents by identifying volatile compounds released from a rubber stock during simulated vulcanization and by correlating them with chemicals used in the formulation.
EXPERIMENTAL The stock selected for study was the tread portion of a bias-ply passenger tire produced by a larger rubber manufacturer. The formulation is given in Table I. I t was prepared with bench scale processing equipment; slabs were milled to a thickness of 0.64 cm and stored in 30.5 cm X 30.5 cm sections a t 0 O C until ready for use. Portions of all compounding ingredients were also stored for use in correlation experiments. Figure 1 depicts the apparatus used for generating and collecting the curing volatiles. A 50-g piece of uncured stock was placed in a 200 cm3 capacity stainless steel vessel (Model 4280, pressure filtration funnel, Gelman Instrument Co., Ann Arbor, Mich.), which was purged with nitrogen and sealed with shut-off valves (Figure 1, Top). Free of air, the chamber was heated in an oven (Model 800 Gas Chromatograph Oven, Perkin-Elmer Corp., Norwalk, Conn.) to simulate the true press closing and vulcanization stages. As the stock cured over a 20-min period, volatiles were released from it and retained in the closed system. The vessel contained 47 mm absolute glass fiber filters a t both its inlet and outlet to prevent particulate matter from contaminating the system. Following the curing stage, the microvolume valve was switched to the alternate position and the oven was turned off (Figure 1, Bottom). T h e vessel was slowly cooled and concurrently purged with 70 ml of air per min to wash the effluent into an adsorbent downstream. Activated charcoal was selected for this purpose because of its high collection efficiency for organic compounds, the ease of solvent desorption, and the insensitivity to water (30-38). This portion of the cycle was analogous to the actual press opening and cooling stages, and lasted 30 min during which the organic fraction consisting of CS and above was retained. The adsorbent
Table I. F o r m u l a t i o n of S t o c k Used in T h i s Investigation Ingredient
7% b y weight, Appro xi mate
Polymer Styrene-Butadiene R u b b e r (1) Styrene-Butadiene R u b b e r ( 2 ) cis-Polybutadiene R u b b e r Antidegradanta
N-Phenyl-N'-sec-butyl-p-phenylenediamine
18.5 18.5 10 0.5
Acceleratorb
N-tert-butyl-2-benzothiazole sulfenamide
0.5
Diphenylguanidine 0.1 Oil Aromatic (Totalc) 20 C a r b o n Black F u r n a c e Black 30 Miscellaneous Sulfur 0.5 Activated Zinc O x i d e 0.5 Stearic Acid 0.5 S u n p r o o f Wax 0.5 a T r a d e n a m e , F l e x z o n e 5L. b T r a d e n a m e , S a n t o c u r e NS. C Since s o m e oil is used to e x t e n d t h e SBR's, t h e figure s h o w n h e r e is t h e t o t a l weight % f o r all oils. trap was stainless steel tubing 80 mm X 6.5 mm 0.d. X 4 mm i d . , containing 200 mg of 80/lOO mesh activated coconut charcoal (Fisher Scientific Co., Pittsburgh, Pa.) held by silane-treated glass wool plugs. I t was positioned inside the oven t o prevent condensation of the higher boiling components. A preliminary investigation determined the relationship between percent weight loss of the stock and temperature. Fourteen randomized trials were conducted between 160 and 200 "C a t 10 OC increments with a constant duration of 20 min. Figure 2 displays the first-order regression of percent weight loss on temperature, which was significant ( P < 0.001) with no significant lack of fit (0.10 < P < 0.25). These results showed the generation procedure to be reproducible with gross volatilization varying between 0.19 and 0.27% of the stock by weight. Remaining experiments utilized the temperature of 180 OC for the same 20-min period to approximate the actual curing cycle for this particular stock. T o correlate discharges from the stock with those from specific additives, each of the compounding ingredients was carried through the same generation and collection procedures but using twice the estimated amount contained in a 50-g stock sample. The adsorbed volatiles from these ingredients were treated exactly as were those from the stock in subsequent desorption and separation stages. However, a small amount of styrene was added to the extracts (except those from the two styrene-butadiene rubbers, SBR's) to serve as an internal reference for determination of relative retention times. (Styrene was found to be a component of both the stock and SBR extracts in a preliminary GC-MS run.) The charcoal adsorption tube was oriented with its inlet side down and connected to an 18-gauge stainless steel syringe needle using a Swagelok stainless steel reducing union. Four hundred pl of nanograde diethyl ether were added to the top of the charcoal and allowed t o descend into the bed for 20 s, whereupon a 1-ml gastight syringe with a LuerLok tip was positioned within the needle hub (this halted the descent of solvent a t the base of the adsorbent). T h e tube was capped with Teflon tape and allowed to stand for 30 min. An additional 1000 pl of solvent were then added to the tube with simultaneous collection in the receiving syringe. The eluate was transferred to a l - m l microreaction vessel and reduced in volume to approximately 75 pl under dry nitrogen, whereupon the vessel was capped with a Teflon-lined rubber septum. Individual compounds were separated by GLC utilizing a gas chromatograph equipped with flame ionization detectors (Model 990, Perkin-Elmer Corp., Norwalk, Conn.). The column consisted of two stainless steel sections, each 7.6 m in length by 2.16-mm i.d., which were packed by the suction plus vibration technique and joined together with a Swagelok stainless steel union. T h e liquid phase was a methyl silicone oil (SP-2100) coated a t 3.1% w/w on SO/lOO mesh Gas Chrom-Q. Silane-treated glass wool plugs retained the packing in the column. The desired separation was achieved by temperature programming the column from 50 to 160 O C at 2 OC/min and from 160 to 330 "C a t 6 "C/min, while inlet and detector temperatures were maintained a t 200 "C. Gas flow
Figure 1. Apparatus for generation and collection of volatiles. Top, generation stage: Bottom, collection stage
0'4-01 0
-
I
160
I
170
1
I
180 190 Temp ( O C )
I
200
I
210
Figure 2. First-order regression of percent weight loss from the stock on temperature. Y = -0.15328 4-0.00212X, ? = 0.818
rates were 30, 35, and 400 ml/min for the carrier gas (He), hydrogen, and air, respectively. Identifications were obtained from combined gas chromatography-mass spectrometry utilizing a Model 5700A gas chromatograph with a Model 5930-A dodecapole mass spectrometer and a Model 5932-A data system, all obtained from Hewlett-Packard Co., Palo Alto, Calif. The same column was used as previously, though the temperature program was terminated at 180 "C to prevent excessive contamination of the MS detector. The separator, a single stage silicone membrane, and the GC inlet were maintained a t 200 O C . The scan rate was 100 amu/s between 33 and 360 amu. A programmed 6-s delay between scans brought the total cycle time to 10.5 s. The ion source was operated at an emission current of 250 pA and a target current of 220 pA utilizing a magnetically constrained tungsten-rhenium filament a t 70 eV. The detector was a continuous dynode electron multiplier (Bendix Corp., Davenport, Iowa). Identifications were based upon interpretation and/or comparison of mass spectra with standard spectra (39-44), upon comparison of gas chromatographic retention times with those of analytical standards, and upon an estimation of the compound's boiling point (derived from the gas chromatogram) and comparison with the known value.
RESULTS AND DISCUSSION F i g u r e 3 d e p i c t s t h e s e p a r a t i o n of c o m p o u n d s f r o m the s t o c k eluate as recorded t h r o u g h the f l a m e ionization detector. The c h r o m a t o g r a m reveals m a n y p e a k s t h r o u g h o u t the temperature p r o g r a m w i t h the m a j o r ones i n the lower boiling region. Analysis of a series of n-alkanes d e f i n e d the a p p r o x i m a t e boiling r a n g e for these p e a k s t o b e b e t w e e n 80 and 250 O C ( p e a k s 3-32). It w a s observed that s o m e of the m o r e volatile c o m p o u n d s i n the e f f l u e n t b r o k e t h r o u g h the a c t i v a t e d charcoal trap. To d e f i n e t h i s loss, eluates f r o m identical adsorbent t u b e s c o n n e c t e d i n series were analyzed. The results i n d i c a t e d that a residual q u a n t i -
(c6-c~~)
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH
1976 * 477
9C
5%
Temp ("C) I30 15C I90
I0
250
310 330
I
90
50
r
1
I
13i
10
Temp (OC) I50 93
25C
1
3l033C I '
~
E
26
1I
2P
I
0
i
20
40
30
50 60 Time (rnin)
70
80
90
100
90
110
190
190
15C
230
310330
~
(minl
Figure 6. Gas chromatogram of volatiles released from cis-polybutadiene rubber (Peak numbers refer to Figure 3)
( T I
Temp 73
0 Time
Figure 3. Gas chromatogram of volatiles released from the stock
51
I
~
5[
70
~
90
Ili3
Temp ("C) 170 I90
' : O
250
,
3,C 330
I
Styrene
(I S I
27 I
0
IO
20
30
L
t
40
50 60 Time (rnin]
70
80
90
100
Figure 4. Gas chromatogram of volatiles released from styrene-butadiene rubber (1) (Peak numbers refer to Figure 3)
50
r
'0 7
9C
110
Temp ("C) I30 I50 I93
I
0
20
40
50
3lC33C
7C
I
I
60
40
50 60 Time (minl
70
80
90
100
Time ( m i n l
70
80
90
I 0
(Peak numbers refer to Figure 3) 3
90
I30
("C)
I53
)90 250
310 33C
1
,,
I
30
30
Figure 7. Gas chromatogram of volatiles released from aromatic oil
~
IO
20
Temp 250
I
9
0
IO
0
Slyrene I1 S I
2,3
",1 1; ~
10
20
30
40
!
50 60 Time lrninl
.70
,
80
90
!
, 100 ~
Figure 5. Gas chromatogram of volatiles released from styrene-butadiene rubber (2)(Peak numbers refer to Figure 3)
Figure 8. Gas chromatogram of volatiles released from Kphenyl-
ty of each volatile substance was retained by the first trap even a t the highest expermental temperature of 200 "C. Thus, qualitative data concerning the entire mixture of compounds were obtained by analyzing a single adsorbent eluate.
The GC comparison of volatiles released from specific ingredients with those emitted from the stock provided several interesting correlations. Figures 4 through 10 show a number of peaks matching those from the stock quite closely by several criteria, including retention time, relative
478
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
N'-sec-butyl-pphenylenediamine (Peak number refers to Figure 3)
90
,
I10
30 I
Temp ("CI 150 190
,
Time
I
250
310330
5C
I
,
70
90
110
Temp ("Cl 150 I90
130
r
I
250
,
310330 I
1
Time (min)
bin)
Figure 9. Gas chromatogram of volatiles released from Kterf-butyl-
Figure 10. Gas chromatogram of volatiles released from diphenyl-
2-benzothiazole sulfenamide (Peak numbers refer to Figure 3)
guanidine (Peak numbers refer to Figure
response, and shape. T h e correspondence between relative retention times of these peaks is given in Table 11. Chromatograms related to five ingredients (sulfur, zinc oxide, stearic acid, sunproof wax, and the furnace black) are not shown since no significant peaks were resolved. T h e GC-MS analysis often confirmed t h e correlation of compounds released from the stock with those from specific additives. Table I11 lists the assortment of substances identified in the stock effluent. T h e oligomers of butadiene were abundant, especially the dimer, 4-vinylcyclohexene, which was primarily responsible for the characteristic odor of the stock. Other oligomers present included the dimer, 1,5-cyclooctadiene, and the 1,5,9-cyclododecatriene trimers. Peaks 27, 28, and 29 are listed as 1,3-butadiene trimers although structures could not be assigned. T h e general appearances of their mass spectra (especially the molecular ions a t mle 162) and the cis-Polybutadiene Rubber which was suspected to be the source seemed to confirm this. T h e presence of methylbenzene, which represented the largest resolved peak (peak No. 5 ) was also confirmed. Although the particular spectrum is characteristic of other
C7Hs hydrocarbons, e.g., cycloheptatriene, the peak's chromatographic retention time matched that of methylbenzene perfectly. Other confirmed compounds included styrene (residual monomer from the styrene-butadiene rubbers), benzothiazole (from the accelerator), and several alkylbenzenes and -naphthalenes (probably from the aromatic oil). T h e identities of compounds mentioned thus far were partially inferred by comparison with standard mass spectra which are available in the open literature ( 4 1 - 4 4 ) . Comparison spectra were not obtained for some of the other compounds, however. Table IV lists the spectrum of peak No. 23. T h e molecular ion a t m/e 149 shows losses of methyl and ethyl radicals to yield the prominent ions a t mle 134 and 120, respectively. T h e odd mass of the molecular ion indicates a probable formula of C10H15N with four rings double bonds (39, 40). Likely structures are N-substituted pyridines and anilines. However, since the only alkyl losses are methyl and ethyl, N-sec-butylaniline is the most logical choice. This structure is consistent with that of the antiozonant which generates a peak (a probable impurity) with the
3)
+
Table 11. Comparison of Retention Times of Volatiles Released from Rubber Additives with Those from the Compounded Stock Peak No.
4 5 6 9 11 12 14 16 17 18 19 20 21 22 23 24 26 27 28 29 a Retention
RRTa
Stock
0.56 0.62 0.82 1.00 1.16 1.29 1.48 1.69 1.90 2.00 2.03 2.10 2.26 2.32 2.40 2.55 2.66 2.75 2.79 2.81 time relative to styrene.
Additive
Additive
0.60 0.62 0.82 1.00 1.16 1.29 1.49 1.66 1.90 1.98 2.03 2.09 2.26 2.34 2.40 2.55
Styrene-Butadiene Rubbers (1 & 2 ) cis-Polybutadiene Rubber cis-Polybutadiene Rubber Styrene-Butadiene Rubbers (1 & 2 ) cis-Polybutadiene Rubber Diphenylguanidine Aromatic oil Diphenylguanidine Aromatic oil Styrene-Butadiene Rubber ( 2 ) Styrene-Butadiene Rubber ( 2 ) Styrene-Butadiene Rubber ( 2 ) N-tert-Butyl-2-benzothiazole sulfenamide N-tert-Butyl-2-benzothiazole sulfenamide l\r-Phenyl-N'-sec-butyl-p-phenylenadiamine cis-Polybutadiene Rubber cis-Polybutadiene Rubber cis-Polybutadiene Rubber cis-Polybutadiene Rubber cis-Polybutadiene Rubber
2.66
2.74 2.78 2.80
ANALYTICAL CHEMISTRY, VOL. 48, NO.
3, MARCH 1976
479
Table 111. Compounds Identified in the Stock Effluent Peak No.
5 6 7 8
M e t h o d of identificationa
Compound
Methylbenzene 4-Vinylcyclohexene Ethylbenzene Dimethylbenzene (1,3- and 1 , 4 - ) Styrene tert-Butylisothiocyanate
MS MS MS MS
22
1,5-Cyclooctadiene Benzothiazole
MS + GC MS + GC
23
N-sec-Butylaniline
MS + GC
9 10 11
+
+ GC + GC
1,5,9-Cyclododecatriene MS + GC 24 Methylnapthalene MS + GC 25 1,5,9-Cyclododecatriene MS + GC 26 1,3-Butadiene trimer MS + BPe,, 27 1,3-Butadiene trimer MS + BPest 28 1,3-Butadiene trimer MS + BPest 29 Ethylnaphthalene MS + GC 30 MS + BPest Dimethylnaphthalene 31 Dimethylnaphthalene MS + BPest 32 a MS = Mass Spectrometry, GC = Gas Chromatographic retention time, BPest = matogram.
Mass/ charge
Re1 abundance
32 39 42 44 51 65 66 77 78 91 92 93 94 103
2.73 2.88 2.18 1.22 4.41 4.50 2.12 9.00 3.17 3.25 2.90 5.55 1.22 2.47
Mass/ charge
Re I
abundance
104 105 106 118 119 120 121 130 132 133 134 148 149 150
3.34 1.16 1.42 9.18 4.91 100.00 8.63 1.19 3.14 1.34 11.07 1.54 17.46 1.95
Table V. Mass Spectrum of Peak No. 10, tert-Butyliso thiocyanate Mass/ charge
Re1 abundance
charge
Re1 abundance
32 37 39 40 41 42 43 44 46 50 56 57
3.34 1.49 1.95 1.03 10.69 13.68 13.98 1.54 3.65 1.75 7.1 5 7.35
58 59 60 67 70 85 86 87 100 101 115 116
100.00 2.93 13.78 1.34 1.03 1.54 8.53 1.39 15.73 5.60 17.58 1.95
Mass/
same GC retention time. T h e GC retention time of standard N-sec-butylaniline matches t h a t of peak No. 23 exactly. Table V lists the spectrum of peak No. 10, tentatively identified as tert-butylisothiocyanate. T h e spectrum is characterized by a probable molecular ion at mle 115 with losses of methyl and butyl radicals to yield ions at mle 100 480
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
cis-Polybutadiene Rubber cis-Polybutadiene Rubber Aromatic oil Aromatic oil
GC
+ GC
MS + GC MS + BPes,
Table IV. Mass Spectrum of Peak No. 23,.hr-sec.Butylaniline
Probable source
Styrene-Butadiene Rubber N-tert-Butyl-2-benzothiazole sulfenamide cis-Polybutadiene Rubber N-tert-Bu tyl-2-benzothiazole sulfenamide N-Phe nyl-N '-sec-butyl-pphenylenediamine cis-Polybutadiene Rubber Aromatic oil cis-Polybutadiene Rubber cis-Polybutadiene Rubber cis-Polybutadiene Rubber cis-Polybutadiene Rubber Aromatic oil Aromatic oil Aromatic oil Estimation of boiling point from gas chro-
Table VI. Mass Spectrum of Peak No. 12, Unidentified Mass/ charge
Re1 abundance
Mass/ charge
Re1 abundance
32 39 40 41 42 43 44 50 51 52 53 54 55 56 57 58 62
2.38 9.29 2.35 18.58 3.20 7.01 1.24 1.08
63 67 77 82 83 84 96 97 99 103 105 106 120 139 140 154 155
1.84 6.21 2.54 3.68 100.00 7.23 1.36 3.84 4.22 1.81 16.52 1.33 5.68 32.56 3.01 7.70 1.05
1.11 1.01
2.28 1.74 7.80 19.18 73.08 4.85 1.05
and 58, respectively. Though mass spectra of tert-butylisothiocyanate were not available, this spectrum is consistent with the treatment of the class by Budzikiewicz e t al. (41). Presence of the tert-butyl group eliminates the possibility of cleavage to yield CHzNCS (m/e 72); thus, this characteristic ion is not present. Since this peak elutes immediately after styrene, an estimated boiling point of 140 t o 150 "C is consistent with the reported boiling point of 140 "C ( 4 5 ) . T h e similarity in structure between this compound and the sulfenamide accelerator infers its source t o be a reaction involving this additive in the rubber matrix. If it were released strictly as an impurity or thermal fragment, a corresponding peak should have been volatilized from t h e isolated accelerator (Figure 10). Another potential reaction product is peak No. 12, whose spectrum is given in Table VI. Though several structures were postulated for this compound whose probable molecular weight is 154, none were consistent with the entire fragmentation pattern. A peak volatilized from t h e diphenylguanidine activator (Figure 10) elutes a t the same time as No. 12 but is probably aniline, reportedly a decomposition
+
product of this additive having the same retention time (19).
ACKNOWLEDGMENT T h e authors thank G. W. Sovocool, M. T. Shafik, and L. Feige of the U.S. E.P.A. National Environmental Research Center (Research Triangle Park, N.C.) for their assistance in providing the GC-MS instrumentation used in this investigation.
LITERATURE CITED M. R. Fernando and R. 0. Wijeskera, J. Chromatogr., 65, 560 (1972). B. Cleverley and R. Herrmann, J . Appl. Chem., 10, 192 (1960). A. M. Popov and A . I. Garshunova, Soviet Rubber Techno/. (Engl. Transl.), 28, 26 (1969). H. G. Bourne, H. T. Yee, and S. Sefarian, Arch. Environ. Health, 16, 700 (1968). I. G. Angert, A. S. Kuzminskii, and A. I. Zenchenko, Rubber Chem. Techno/., 34, 807 (1961). H. L. Bullard, Rubber Chem. Techno/., 37, 210 (1964). H. L. Bullard, Rubber Chem. Techno/., 38, 134 (1965). E . I. DuPont de Nemours and Co., Wiimington, Dei., Elastomer Chemical Dept., "Accelerators, Vulcanizing Agents and Retarders", 1967. H. Storey, Rubber Chem. Technol., 34, 1402 (1961). M. L. Deviney and J. E. Lewis, Rubber Chem. Techno/., 40, 1570 (1967). J. Duke, lnd. Eng. Chem., 47, 1077 (1955). R. W. King, S. S. Kurtz, and J. S. Sweely, Ind. Eng. Chem., 48, 2232 (1956). F. J. Linnig and J. E. Stewart, J. Res. Nat. Bur. Stand., Sect. A, 59, 27 (1957). L. E. Oneacre in "Introduction to Rubber Technology", M. Morton, Ed., Van Nostrand-Reinhold, New York, N.Y. 1959, pp 109-129. J. E. Jacques in "Rubber Technology and Manufacture", C. M. Blow, Ed., C.R.C. Press, Cleveland, Ohio, 1971, pp 308-129. G. G. Morton and G. 8. Quinton in "Rubber Technology and Manufacture", C. M. Blow, Ed., C.R.C. Press, Cleveland. Ohio, 1971, pp 345371. W. Hoffman, "Vulcanization and Vulcanizing Agents", New York Palmerton, New York, N.Y.. 1967. D. A. Chapman, Rubber Chem. TechnoL, 43,572 (1970). B. A. Dogadkin and V. A. Shershenev, Rubber Chem. Technol., 35, 1 (1962). S. Banerjee and S. P. Manik, Rubber Chem. Technol., 43, 1311 (1970).
(21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) . , (40) (41) (42) (43) (44) (45)
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RECEIVEDfor review June 18, 1975. Accepted November 24, 1975. This research is contained in a Dissertation submitted to the University of North Carolina a t Chapel Hill by S. M. Rappaport in partial fulfillment of the requirements for the degree of Doctor of Philosophy (August 1974) and was supported in part by Training Grant No. 5-T01OH-00099-04 awarded by the National Institute of Occupational Safety and Health.
Device for Thermally-Induced Vapor Phase Transfer of Adsorbed Organics Directly from an Adsorbent to a Gas Chromatograph-Mass Spectrometer Woodfin V. Ligon, Jr." and Robert L. Johnson, Jr. General Electric Corporate Research and Development Center, Schenecfady, N. Y. 1230 1
A device is described which provides a simple means for transferring volatiles adsorbed on a substrate from the substrate to a gas chromatograph-mass spectrometer. A discussion of the design and an evaluation of the performance in terms of efficiency and reproducibility are provided. A test of the upper molecular weight limit for effective transfer is described for a particular combination of temperature, adsorbent, and sample.
A need exists for a free standing device which can efficiently accomplish the thermally-induced vapor phase transfer of organics from an adsorbent substrate such as charcoal to the front of a gas chromatographic (GC) column. I t is the intent of the present communication to describe such a device, to discuss the philosophy of its design and to provide an evaluation of the performance observed.
A thermal desorption apparatus should include a means for providing fast heat-up of the substrate for quick efficient transfer to a gas chromatographic column. If a reasonably large number of samples will be run, it is important t h a t samples can be changed quickly and that the time constant of the heating device either be very short or sample changing should not require cool down. Further, the device should not include any type of septa or ferrules which might be unstable a t the desorption temperature since the decomposition of such materials could cause serious artifacts in the analysis. In addition for GC-MS applications the apparatus should provide means whereby air can be prevented from reaching the mass spectrometer. Zlatkis and co-workers (1, 2 ) have described a system for trapping volatiles on an adsorbent with subsequent thermal desorption. Their system utilizes a "modified injector port" which replaces the standard port. Sample tubes are ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
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