On-Line Elemental-Reaction Analyzer as an Organic Analysis System S. A. Liebman, D. H. Ahlstrom, and C. D. Nauman Armstrong Cork Company, Research and Development Center, Lancaster, Pa. 7 7604
I?. Averitt, J . L. Walker, and E. J . Levy Chemical Data Systems, Inc., Oxford, Pa. 79363
A realistic combination of gas chromatography ( G C ) and reaction microchemistry has been accomplished for the on-line determination of empirical formula, functional group, and/or heteroatoms (S, Halogens, 0 , N ) at trace levels mol/l.). A stop-flow arrangement in the separating GC unit allows such detailed information to be obtained on individual GC species in multicomponent mixtures which may be transferred as desired to the Pyrochrom elemental-reaction analyzer for any or all of the denoted analyses. The previously described engineering design and development effort has resulted in this unique modular organic analysis system. Significant advances have been made in design and applications which are discussed in the present report.
Providing a general route for accessible, informative aids in identification of gas chromatographic (GC) effluents has been a difficult analytical problem. The use of reaction microchemistry and GC in recent years has provided accurate elemental analysis for weighed organic species by several types of commercially available instrumentation (1-4). Workers in 1955 (5) discussed the determination of elemental C, H content for vapor-phase species by reaction GC; and since that time, a significant array of equipment and methods for several elements has followed (3, 6-14). Most recently, Russian, Hungarian, and Italian workers reported from their respective laboratories that GC effluents were analyzed by reaction GC to provide elemental (C, H, N, or 0) content (7, 8). Our current work has led to a general organic analysis scheme to achieve economical, rapid-on-line determination of elemental content (simultaneous CHNO), heteroatom (S, Halogens, 0, N), and/or functional group analysis (FGA). Additionally, illustration is given of the Pyro(1) E . J. Levy. e f ai.. Eastern Analytical Symposium, New York, N . Y . , 1971 ( 2 ) S. A .
Liebman, D. H . Ahlstrom. et a i . . Pittsburgh Conference on A n alytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1972; to be pubiished in Thermochim. Acta. (3) S. A. Liebman. D. ti. Ahlstrom. T. C. Creighton. G . D. Pruder. R. Averitt. and E. J. Levy, Ana/. Chem., 44, 1411 (19721, and references within. (4) S. A. Liebman, D. H. Ahlstrom. C. D. Nauman, G . D. Pruder. R . Averitt, and E . J . Levy, Res. Develop. 24 ( 1 9 7 2 ) . (5) A . E . Martin and J . Smart, Nature (London), 175, 422 (1955) (6) C. F. Nightingale and S. M .Walker, Anal. Chem., 34, 1435 (1962). ( 7 ) V . G. Berezkin and V . S. Tatarinskii. Zh. Anal. Kh,m.. 25. 398 (1971). (8) V. Real. B. Kaplanoua. and J. Janak, J. Chromafogr.. 65, 4 7 (1972). (9) S. S. Krivoiapov. E. S. Rusaeu. and A . A . Antonov, Zavod. Lab.. 37, 142 (1972). (10) M . N . Chumachenko. N . A. Khabarova, M . V . Egorushkina. and R . A. Ivanchilkova. i z v . Akad. NaukSSSR. Ser. Khim., 1150 (1971). (11) I . Klesment,J. Chromatogr.. 69, 37 ( 1 9 7 2 ) . (12) L. D. Wallace, eta/.. Ana/. Chem., 42, 387 ( 1 9 7 0 ) . ( 1 3 ) A . N. Korol. Russ Chem. Rev., 40, ( 2 ) . 184 ( 1 9 7 1 ) . ( 1 4 ) E . Peliaand B. Colombo, Anal. Chem.. 44, 1563 (197'2).
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chrom elemental-reaction analyzer providing specialty analyses, Le., the number of methyl groups as substituents on an aromatic ring or the total organic carbon in ppm detection levels using "chemical amplication" in the catalytic reactor module.
EXPERIMENTAL T h e detailed diagram and applications of the chromatographic stop-flow valving in GC No. 1 has been described previously, as has the main portion of the elemental-reaction analyzer (3, 4). The present reactor module is shown schematically in Figure 1. The advanced organic analysis system now includes the use of a n 8-port microvalve and reactors as arranged in Figure 2. With the microvalve in position A for FGA, carrier gas is directed from t h e inlet through line A containing a n empty quartz reactor tube positioned within a high temperature oven (900 "C) a n d a second stage empty quartz reactor in the low temperature oven (450 "C). The heteroatom mode for resistant halogen- or sulfur-containing aromatic compounds was performed with P t / R h foil (CDS, Inc., Oxford, Pa.) placed in the 900-950 "C quartz reactor portion. With the microvalve in position B, the carrier flow is directed from the inlet along line B, containing in the 900 "C portion a reactor tube with ca. 2 in. of CuO wire packing (Hewlett-Packard, Avondale, Pa.) and in the lower temperature reactor (450 "C), ca. 2 in. of reduced Cu wires (Hewlett-Packard), both catalysts contained in place by quartz wool plugs (Perkin-Elmer Corporation, Norwalk, Conn.). A specially designed splitter-valve controls the carrier flow in line B into a parallel reactor line which contains the center 2-in. portion filled with 5% Pt on charcoal (ROC/RIC, 11686 Sheldon, S u n Valley, Calif.). Thereby, C H N analysis is performed in one side of line B, while 0 content is determined in the parallel side for simultaneous C H K O studies. In a separate study. using Hz carrier gas and only the A line, conversion of CO/COz-producing species t o CHI was possible by allowing pyrolysis in the empty quartz reactor a t 900 "C a n d having the second-stage (400 "C) reactor contain a Xi catalyst (Girdler T 1647RS, 53.6% Xi, Chemetron Corporation, Catalyst Division, Louisville, Ky. 40201). The "chemical amplifier" experiment utilized a cobalt oxide catalyst, Coboxide, obtainable from Coleman Instruments, Maywood, Ill., located in the 900 "C reactor. The Pyrochrom internal analytical chromatographic columns utilized were either Porapak Q + T , 11-ft X l/s in. ss, run isothermally a t 95 "C with ca. 20 cm3/min He carrier flow for C H N or FGA studies, or Porapak Q + R , 8-ft + 8-ft each in l/g-in. Teflon-lined Al, programmed from -10 to 50 "C a t lO"/min. Backflushing after separation of Kz and CO allowed for the H 2 0 , COz separation within ea. 15 min from injection for simultaneous CHNO.
RESULTS AND DISCUSSION Heteroatom Content (S, Halogens, 0, N). The detailed arrangement for analysis of the above elemental components is given in the Experimental section. Normal functional group analysis (FGA) allows detection of alkyl halides and sulfur species, but the latter hetero elements in some aromatic systems require a modified FGA procedure, i . e . , reductive pyrolysis. Fragmentation of thiophene has been used in this work as a guide to reductive pyrolytic conditions necessary and sufficient to handle the more thermally resistant compounds in the heteroatom mode. Below 825-850 "C, the
THIOPHENE H2 Pt
Figure 1. Two-stage reactor module located within Pyrochrorn elemental-reaction analyzer
C A T A L Y S T 850C
Figure 4. Heteroatom analysis for 0.1 pI thiophene with H2 carrier gas, Pt foil catalyst, and reactor at 850 "C
INLET
T I C CELL
REACTOR " B"
I
POSITION A-----
r--y---
POSITION -B
I
I
7 RED Cu
REACTOR .I. FGA
IU
I
I
I
I
I
HELIUM PURGE FLOW C O N T R O L L E R
Figure 2. Flow diagram of microvalve-reactor assembly
Figure 3. FGA for 0.1 pI thiophene with He carrier gas and reactor at 850 "C
Figure 5. Heteroatom analysis for 0.1 pl tetrahydrothiophene with same conditions as in Figure 4 ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
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PEAK AREA
CO2 11411
CARBON
HYDROGEN CHLORINE
Hi0 1501.5
51150
I O T A 1 AREA 365100.
0'
6' -0 0 2 '6 -0 6 0
14.19/1 1 4 5911
Heteroatom and C,H analysis for 0.1
pl of
chloroben-
zene thiophene ring system was not fragmented under the normal helium atmosphere in FGA, or using a hydrogen carrier flow system. However, in the 850-950 "C range, with the latter carrier and Pt foil in the reactor, detection and identification were possible for the fragment hydrocarbons and H2S from 0.005 pl of thiophene. Efficient ring fragmentation was not successful in a helium atmosphere, with or without Pt, a t these elevated temperatures. Clearly, reductive pyrolysis is necessary to crack the thiophene system under these experimental conditions. Aliphatic sulfur-containing compounds, such as sulfides, mercaptans, etc., were readily detected in the normal FGA procedure, providing the respective hydrocarbon fragments, as well as H2S. These aliphatic species were pyrolyzed even below 850 "C in a helium or hydrogen atmosphere, with or without a Pt foil. Hence, such response to experimental conditions additionally provides a means of differentiation on a group basis of aromatic from nonaromatic sulfur-containing species. Figures 3-5 record these observations using thiophene and tetrahydrothiophene comparisons. Likewise, differentiation of aromatic from nonaromatic halogen-containing species was possible because of the resistance of the aromatic ring to fragmentation under these experimental conditons. Nonaromatic chlorohydrocarbons were fragmented to provide a hydrocarbon pattern in addition to the respective H-X species, whether helium or hydrogen carrier was used, with or without the Pt a t 900 "C (4) The polychlorinated aromatics (tri-, tetrachlorinated, etc.) were more thermally resistant and require increased temperatures (950 "C or higher) or more efficient Pt catalyst with hydrogenolytic conditions for HC1 detection. Use of heteroatom determination is illustrated with chlorobenzene (Figure 6) showing the HC1 and total normalized peak area calculations to be utilized in conjunction with the CH determination from a separate elemental analysis run. These input data, experimental 70 C1 and 70 CH, allow empirical formula calculations to be performed manually or in the molecular formula computer program (15) Computer input specifications of the determined (or estimated) accuracy limits (1.0% in illustration) and a search limit to Cl2 resulted in an output of the probable structures having the given % C, H , C1 content (Figure 7). Information from simple retention time or FGA mode would provide the final chlorobenzene identification. The same data treatment would be used for other halogen- or sulfur-containing hydrocarbons to provide likely empirical formulas up to a limit of C50. Lower accuracy levels, permitting 2-370 error in any or all of the elemental determi(15) D. A. Usher, J . G. Gougoutas. and R . 8 . Woodward, A n a / . Chem., 37, 330 ( 1 9 6 5 ) .
1362
C
64 62 IO0
RtSPONSE THEORtTlCll CALCULATED FACTORS PERCENT PERCENT 64 62 1 25 64 03 4 43 0 65 4 48 3 20 31 5 0 30 9 5
T H E O R E T l C l L C / H RATIO U N K N O W N C/H RATIO Figure 6.
CHlOROBfNZtNt
HCI
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
Oc H 4 43 100
OOCI
30 9 5 100
'4
CI
M W
-0 8 2
0 83
112
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ell
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0 55
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225 226
SEARCH COMPltIE THROUGH C12
Figure 7.
Molecular formula computer program output for deter-
mined per cent of C, H , CI values
nations, may still be useful for initial structure possibilities using this computer program. The nitrogen and oxygen detection and determination are generally performed in conjunction with the standard elemental procedure (CHO, CHN, or CHNO), but could also be studied as heteroatoms. That is, 0 or N detection in a heteroatom scan is achieved if the line A reactor tube is packed with a nickel catalyst and placed in the low temperature portion at ca. 400 "C (see Figure 1 and Experimental). With Hz carrier gas, conversion of nitrogencontaining species to NH3 would be indicative of the N corltent. Oxygen-containing species producing CO/CO2 fragments would result in their conversion to CHI with this catalyst. Additionally, previous workers showed (16) that conditions of 950 "C and Pt gauze catalyst in a Hz stream permitted detection of N as NH3 and P-containing compounds as PH3. In our reductive pyrolysis scheme, therefore, the heteroatoms halogens, sulfur, nitrogen, oxygen, and potentially phosphorus may be determined within the above organic analysis system. Functional Group Analysis (FGA). Once heteroatom content has been determined for the GC effluent or for a directly injected sample, operation of the Pt-containing stainless steel or quartz reactor at 900 "C may be used for FGA. This involves changeover of the Hz carrier gas to He (if the reductive pyrolysis scan was needed initially) and, with proper valve adjustments, direction of sample flow from the inlet(s) through the FGA (line A) reactor. These noncatalytic thermal fragmentation patterns appear similar, although not identical to those patterns obtained without Pt catalyst in the quartz reactor ( 4 ) . Previous workers have discussed in detail the functional group correlations and controlled thermolytic fragmentation patterns possible in this analytical mode (17-20). The illustration of an ester. ethyl acetate, FGA pattern is included in Figure 8 using the above heteroatom conditions. Chemically significant information can thus be rapidly obtained from the presence or absence of CO, Con, CH4, CzH6, as (16) H . P. Burchfield. D. E. Johnson, J, W. Rhodes, and R . J. Wheeler, J . Gas Chromatogr.. 5 , 28 ( 1 9 6 5 ) . (17) E. J . Levy and D. G . Paul, J . Gas Chromatogr.. 5 , 136 (1965). (18) S. F. Sarner. J . Chromatogr. Sci. 10, 65 ( 1 9 7 2 ) . (19) C. Merritt. Jr.. and C. DiPietro. Ana/. Chem., 44. 57 (1972) 120) W. R . Feairheller. Jr.. and F. F. Bentley, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1972, paper No 21
Bf
Figure 9. Simultaneous CHNO determination for 0.3 pI nitro-
methane
Figure 8. FGA for 0.1 pl ethyl acetate with Ha carrier gas, Pt foil catalyst, and reactor at 850 “ C
well as HX, H2S, or NH3 fragments from the simple halogens, mercaptans, and amines, respectively. Simultaneous CHNO, CHN, CHO, or CH Elemental Analysis. On any or all of the GC effluents emerging from GC No. 1 from complex mixture separations, one may obtain simultaneous CHNO content or any other indicated combination (CHN, CHO, CH). Larger sample size, ca. 0.1 to 0.5 p1, appears necessary in the CHNO or CHO analyses than the amount used in other elemental modes (CHN, CH), since the sample is split into two parallel reactors within line B (see Figure 2) for the respective conversions to C02, HzO, N2, and CO. Figure 9 shows the results from CHNO analysis for 0.3 p1 of nitromethane. Currently, standardization of catalysts packings and optimizing internal chromatographic separation parameters are in progress for the CHNO mode. The above input data, in conjunction with the heteroatom mode, should other denoted elements be determined, are used in the molecular formula program (as illustrated above with chlorobenzene or by manual calculations) to provide likely empirical formulas. Specialty Analyses. Using the reductive pyrolysis mode (Hz carrier) the determination of methyl substituents on an aromatic ring was performed for the series toluene, p-xylene, 1,2,3,-trimethylbenzene,and 1,2,3,4-tetramethylbenzene (durene). Figure 10 records the resultant CH4 peak area us. the number of methyl substituents per aromatic ring. A least-squares treatment shows excellent results with the heteroatom or FGA mode application for determination of aromatic methyl group substituents. Other discrete group analysis ( i e . , ethyl, methoxy) may be conducted similarly using direct calibration series which require ca. 10 min/run and ca. 0.1 pl sample size. To extend the detection limits for total organic carbon determination, the “chemical amplification principle” (21, 22) was attempted. A quartz reactor tube containing 5 alternating 114 in. segments of Co203 oxidizer and 5% Pt/C reducing catalyst was placed in the high temperature reactor portion (900 “C) of line A. The resultant reactor products of COz and CO showed on the internal chromatographic analysis that the successive (21) A . J.
P. Martin, R. P. W . Scott, and T. W . Wilkins, Chromatogra-
phia. 2, 85 (1969) (221 V . M . Sakharov, G. S. Beskova. and A . I . Butusova. J . Chromatogr.. 69, 71 ( 1 9 7 2 ) .
/
i
/
/
/
Ll 2
3
1
5
1
1
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Figure 10. Determination of methyl group substituents on an ar.
omatic ring GC # I C H R O M A T O G A A M PtlK 1
A.
h
I
SIlRI
A
V I O P FLOW
TRlNSFtR.
PYROCHROMTMEIEMENTAl.REACTOR ANALYZER FUNCTIONAL GROUP ANALYSIS [FCAI/HETEROATOM
LIL ELEMENTAL ANALYSIS
~
Pt,:
2
~
IC, H , N . 01
M A N U A L O R COMPUTER D A T A T R E A T M E N T
t
P E A K IOtNII~IGATION G C ? I R t l t N l l O N TIME fllNCllONAl GROUP H t I t R O A I O M tltMtNTA1 ANAlYSlS
Figure 11. General scheme for trace organic analysis
co,
C
2C0,2CO
20
+
2c0,.
etc., sequence was not totally complete. Nevertheless, there resulted an approximate 20-fold enhancement in sensitivity detection for CO,; i. e . , the thermal conductiviANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
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ty detector normally gave full-scale response to 0.1 p1 of benzene sample on a single-stage conversion reactor, while the “chemical multiplier reactor” gave full-scale response to 0.005 pl a t the same attenuation. Thus, total organic carbon content may be detected in ppm levels by rapid on-line reaction GC analysis within this instrumentation scheme. In summary, a truly modular organic analysis system has been designed and proved effective in certain organic structure and reaction problems (2-4). The general scheme is shown in Figure 11. Accuracy and detection limits have been tentatively indicated for routine use as 0.5% for the CHN, CH analysis, on samples as small as 0.01 1,. .For heteroatom or simultaneous CHO, CHNO, sample size and accuracy limits are presently higher (ca. 0.10 111) and the analyses are nonroutine in operation. Further effort is directed to optimizing and extending groupreaction GC analyses, examining more complex combina-
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ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
tions of heteroatoms within a given molecule ( i e . , 0, C1, N or F, C1, N, etc.), and maximizing operational flexibility. This unique elemental-reaction analyzer represents an organic analysis system that provides a means to obtain efficient and chemically significant information for a wide variety of problems encountered in academic, industrial, and consulting laboratories. Current development and applications will be continued in this context for further problem-solving capability.
ACKNOWLEDGMENT We appreciate the technical assistance of T. C. Creighton and D. Messersmith, Armstrong Cork Company, and Frank McLafferty, CDS, Inc. Received for review November 13, 1972. -4ccepted February 2, 1973.
