Graphitized carbon in gas-liquid-solid ... - ACS Publications

400

ANALYTICAL CHEMISTRY, VOL. 51, NO. 3, MARCH 1979

Graphitized Carbon in Gas-Liquid-Solid Chromatography and Gas Chromatography/Mass Spectrometric Analysis of High Boiling Hydrocarbon Mixtures Paolo Ciccioli' and John M. Hayes Departments of Chemistry and Geology, Indian University, Bloomington, Indiana

Gianfranco Rinaldi2 and Kenneth B. Denson Department of Geology, Indiana University, Bloomington, Indiana

Warren G. Meinschein" Department of Geology and School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana

method of analyzing organic mixtures containing compounds which boil over a wide range of temperatures. For example, data are reported on the GLSC separations of alkanes isolated from the New Albany Shale by: (1) solvent extraction and (2) pyrolysis at 500 "C. Although GLSC analyses are presented which show that alkanes ranging in size from C4 to Cl0 can be readily handled in a single temperature-programmed run, major emphasis in this paper will be paid the GLSC and tandem gas chromatographic-mass spectrometric (GC-MS) analyses of the C15and larger alkanes which include isoprenoid alkanes a n d steranes t h a t structurally resemble constituents of biological lipids ( 2 3 ) . Special attention will be given t h e steranes in the carbon tetrachloride (CC1,) extract of the shale. Some of these steranes have different gas chromatographic retention times and mass spectrometric fragmentation patterns than d o either 50- or 5p-steranes. Alternative structures to those recently proposed for apparently equivalent steranes in geological samples (14) are suggested.

Gas-liquid-solid chromatography (GLSC) employing a poly(phenyl ether) (PPE 20) liquid phase on graphitized carbon black (GCB) is applicable to the analyses of crude oils and distillates of sedimentary rocks. The elution of C, to C,, hydrocarbons which consist of n-alkanes, isoprenoid-type alkanes, steranes, olefins, and aromatic hydrocarbons can be handled in a single GC run. A GLSC column in tandem with a mass spectrometer provides an excellent means for the identification of geochemically significant organic compounds in complex natural mixtures.

T h e surface properties generally and the gas chromatographic behavior specifically of graphitized carbon black (GCB) have been studied (1-4). These studies have recently been extended t o investigations of changes in the adsorption characteristics of GCB caused by various amounts of different liquid coatings (5-7). Such investigations have indicated that t h e resolution of a GCB column can be tailored for a specific separation by coating G C B with a n appropriate quantity of liquid phase which has t h e proper polarity and thermal properties. Because t h e liquid phase influences t h e separations occurring on the GCB surface, the process of resolving mixtures of volatile compounds on columns packed with liquid coated GCB is called gas-liquid-solid chromatography (GLSC). Many applications of GLSC are cited ( & ] I ) , GLSC analyses of particular interest include separations of complex mixtures of organic compounds of different isomeric structures and isotopic compositions (81, and of trace pollutants in air ( 9 ) . Most applications of GLSC have been restricted to low-boiling compounds, b u t a few GLSC analyses have been performed on high-boiling compounds (10-12). Some of the reasons that have limited the use of GLSC for separations of high-boiling compounds may be summarized as follows: (1)T h e elution temperatures of high boiling compounds frequently exceed the maximum temperatures to which most widely used liquid phases may be heated; (2) T h e knowledge of the gas chromatographic properties of GCB is limited t o coating of only a few molecular layers in thickness; and (3) Data are lacking about t h e maximum operating temperatures of most liquid phases on GCB. T h i s paper presents evidence that GLSC using GCB a n d certain liquid coatings can provide a selective and versatile

EXPERIMENTAL Column Materials and Preparation. Packed columns were constructed from 3.2 mm o.d. x 2 mm i.d. stainless steel tubing. Stainless steel micropacked columns were constructed from 1.6 mm 0.d. X 1.0 mm i.d. tubing, while glass micropacked columns used 6 mm o.d. X 1 mm i.d. Pyrex tubing. All columns were 2 m in length, and each column was cleaned with 3:l benzene/ methanol and dried over-night at 110 "C prior to being packed. Carbopack A with a surface area of 15 m'/g and Carbopack C with a surface area of 1 2 m2/g were purchased from Supelco (Bellefonte, Pa). These graphitized carbon blacks (GCB) were used as GC supports. The packed columns were filled with 80/100 mesh supports, and 100/120 mesh supports were used for the micropacked columns. Coating of the solid support was carried out by dissolving the liquid phase in a suitable solvent. such as chloroform, and adding it t o the support in a Teflon container. After gentle mixing, the solvent was allowed t o evaporate at room temperature under a stream of nitrogen, and the dried and coated GCB was sieved prior to use. Apparatus. Varian 1400 Series Gas Chromatographs equipped with linear temperature programmer and injectors modified to reduce dead volume and to decrease septum temperature were used for all gas chromatographic analyses. The two chromatographs used for GC analyses were each equipped with a flame ionization detector (FIDI. FID and an electron capture detector (ECD) could be interchanged on the chromatograph used in tandem with the mass spectrometer. When the ECD was used, the air flame gas inlet was capped off, and a supplementary flow of about 100 mL/min of 95% argon-5% methane (Matheson, East Rutherford, N.J.) was added to the detector via the inlet used for hydrogen when the FID was operative. Helium was used as the carrier gas.

Present address: Laboratorio Sull'Inguinamento, Atmosferico del C.N.R., Via Montorio Romano 36, Roma, Italy EXXON Research Center, Houston. Texas 0003-2700/79/0351-0400$01 O O / O

C

1979 American Chemical Society


Varian 620

401

I

i Data O u t p u t

Figure 1. Schematic of tandem GC-MS system. (1) Injector, (2) rnicropacked column, (3)connection tube, (4)GC detector, (5) splitter, (6) heater, (7) capillary, (8) make-up gas line, (9) jet separator, (10) valves

Table I. Temperature Limits and McReynold's Indices of t h e Liquid Phases Commonly Used in the Analyses of High Boiling Compounds name

chemical composition

" C minimax

X'

Y'

2'

U'

S'

Dexsil 400

poly( carborane siloxane) poly(pheny1 ether) 50% phenyl-50% methyl silicone

50/500 1251375 0/375

07 2

108 355 158

118

166 433 243

---

PPE 20 OV 1 7

A modified Consolidated Electrodynamics 21-llOB mass spectrometer was coupled with the GC for GC-MS analyses. The ion source housing was modified to accommodate an Edwards EO-4 600 L / s oil diffusion pump, VT-4 cold trap, and QY-4 butterfly valve (Edwards High Vacuum, Inc., Grand Island, N.Y). A diagram of the GC-MS coupling is shown irl Figure 1. The line running from the splitter to the GC detector is a 30 cm in length X 0.25 mm i.d. stainless steel tube (see 3 in Figure l),while the 60-cm coiled length of the same tubing (see 7 in Figure 1) serves as a flow restrictor. The make-up gas is added in order to maintain a positive pressure a t the splitter. The separator is a glass single-stage jet (Vacumetrics, Inc., Ventura, Calif.) which is attached using Vespel ferrules (Supeltex M-2, Supelco). The valves are Nupro SS-6BW-TWS metal bellows valves (Nupro Co., Cleveland, Ohio). For GC-MS analysis, the carrier gas flow through the micropacked column and make-up gas line were each maintained a t approximately 6 mL/min. The make-up gas flow rate was set so that approximately 10% of the column effluent flowed to the FID detector. The lines between the GC and the mass spectrometer were maintained at 250 "C. Solvent peaks were vented by closing the metal bellows valve to the MS and opening the metal bellows valve to a diffusion pump (see 10 in Figure 1). The mass spectrometer operating conditions were as follows: ion source temperature, 200 "C; electron energy, 70 eV; and emission current, 300 PA. The mass spectrometer was interfaced to a Varian MAT Spectro-system 100 for the acquisition and recording of low resolution mass spectra. This data system consists of a Varian 620/i minicomputer with 8K of core memory, dual 9-track tape drives, a Tektronix 4010-1 graphic display terminal with 4610 hard copy unit, and a Varian MAT NlOl interface unit. The NlOl contains a 50-kHz 14-bit analog-to-digital converter, a Hall-effect probe, and associated electronics. Spectra were acquired using Varian MAT'S KOS I1 software, supplemented with a program written in our lab for plotting spectra on the Tektronix 4010. The mass spectrometer accelerating voltage was set at 8 kV and the

257 119

348 162

123

202

magnet was scanned from m / e 450 to m l e 25 a t 0.074 decade/s, resulting in a 17-s scan time, with another 13 s required for magnet recovery before another scan could be made. For selected ion monitoring, ion beam switching was accomplished electrically. As reported previously (15),the ion accelerator and electric sector power supplies on our instrument can be replaced with computer-controllable power supplies constructed in our laboratory. In this way the 620/i computer can control the focusing of ion beams onto the detector. The signal from the electron multiplier is sent to a current-to-frequency converter and then to an ion counting interface in the computer, as described elsewhere (16). For the work reported here, single ion monitoring traces at masses 372, 386, and 400 were obtained in three separate GC runs, although software for multiple ion monitoring is currently being written. Sample Preparation. Extractions were carried out in a Soxhlet extractor using 3/2 v / v of benzeneemethanol on 100-g samples of the New Albany Shale that were ground to pass a 200-mesh sieve. After removal of the extraction solvent in a stream of nitrogen a t 40 "C, the shale extracts were chromatographed on silica gel columns and/or thin-layer plates (17). The alkane fractions studied in this investigation correspond to either the carbon tetrachloride (CClJ eluates from column chromatograph or the TLC fractions with the largest R, values.

RESULTS AND DISCUSSION Gas Chromatographic Column. T h e liquid phases considered for this investigation of GLSC using GCB are listed with their McReynold's constants (18) in Table I. These phases were selected on t h e basis of their stabilities a t temperatures up to 350 "C or higher. Preliminary thermal stability tests were carried out by coating 1.5% of t h e liquid phases in Table I on Carbopack A, a well studied modification of GCB having a surface area of 15 m2/g. The results indicate that both Dexsil 400 and FPE 20 are almost completely retained on the surface of GCB u p to 380 "C, while OV 17 is

402


t

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2.5

350t

tkt300

1

-

Ikb I-

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liquid

// //

////

////

,I-

///

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1t ELS.C/ a /

0 Carbon number of n-paraffins

Figure 2. Effect of various degrees of liquid coatings on the GLSC elution temperatures of n-alkanes from Carbopack A coated with (a) PPE 20 and (b) Dexsil 400 and a GLC column packed with Chromosorb WAW coated with 3% w / w of (a) PPE 20 and (b) Dexsil 400. Elution temperatures of pristane and phytane are denoted by V and a, respectively rapidly desorbed above 300 "C. T h e effect of the degree of coating on elution temperature of n-alkanes was measured for both Dexsil400 and P P E 20. Amounts of Dexsil400 and P P E 20 corresponding t o 1.5, 2.5, 5, and 8% w/w on GCB were employed in GLSC analyses to determine the effect of the degree of coating on the elution temperatures of n-alkanes. T h e smallest of these amounts (1.570) corresponds to two complete monolayers; whereas the largest amount ( 8 % ) corresponds to approximately 13 monolayers (19). Since GCB is a nonporous adsorbent exhibiting a geometrically homogeneous surface, the 8 7 ~coating closely approaches the amount of liquid phase usually used in GLC. For comparison purposes, GLC columns were constructed using Chromosorb WAW as solid support and this support was separately coated with 3% w/w each of Dexsil 400 and P P E 20. All columns were 2 m long. Figures 2a and 2b are plots of the elution temperatures for alkanes on PPE 20 and Dexsil 400 coated Carbopack A (GLSC) and Chromosorb WAW (GLC). The positions of the reference pristane and phytane peaks relative to the positions of the C17,C18, and CI9 n-alkanes are indicated in these plots because it is difficult to separate these isoprenoid alkanes from C17t o C19n-alkanes on most packed columns. The following information may be deduced from Figures 2a and 2h: (1)GLC columns employing either Dexsil 400 or P P E 20 do not adequately separate pristane and phytane from n-CI7 and n-Cls alkanes; (2) The resolutions determined for the GLC columns indicate that a capillary column approximately 30 m in length would be required to completely isolate pristane and phytane from n-alkanes with comparable boiling points; (3) Pristane a n d phytane can be completely separated on a 2-m packed column by GLSC using Carbopack A coated with either Dexsil 400 or P P E 20; and (4) T h e GLSC elution temperatures decrease as the amount of the polar coating ( P P E 20) is increased, b u t this trend is reversed when a nonpolar liquid phase (Dexsil 400) is employed. Similar observations on the separations obtained using polar and nonpolar coatings on GCB (9, 22) and on Chromosorb W (20) have been reported. These studies have shown that the separations obtained between nonpolar compounds on GCB

Table 11. Reference Hydrocarbons Coinjected with the Mixture of Utah n-Alkanes Branched Chained and Cyclic Alkanes a. cyclohexane b. adamantane c. farnwane d. octylcyclohexane e . C , isoprenoid f pristane g. phytane h. C,, isoprenoid i. androstane j. iso-C,, k. anteiso-C,, 1. heptadecylcyclohexane

m. anteiso-C,, n. squalene 0. squalane p. coprostane q. a-cholestane r. 17a-trisnorhopane s. 17a-trisnormohopane t. lupene u. fernene v. moretane w. 170-homohopane y. 174-homohopane

n-Alkanw C,-C,,

c,, c,, , c,, , c,, and c,, 3

coated with a nonpolar liquid are slightly reduced by increasing the amount of coating; however, a n increase in the amount of polar coating on GCB sharply decreases the retention volumes for nonpolar compounds without a reduction in the separation factor ( a ) . Figure 3 shows a GLSC analysis of n-alkanes isolated by use of 5-A molecular sieves from a Utah (Uinta) crude oil to which were added the reference compounds listed in Table 11. As the chromatogram presented in Figure 3 clearly demonstrates, PPE coated Carbopack A provides a versatile and selective packing for the analysis of alkanes. This packing permits the relatively rapid chromatographic analyses of alkanes with a wide range of carbon numbers and the separation of isoprenoid-type hydrocarbons, steranes, and nalkanes at a preparative scale. The column bleeding of either P P E 20 or Dexsil400 coated GCB is remarkably low a t high operating temperatures. Carbopack C was used in place of Carbopack A after our supply of Carbopack A was exhausted. As previously reported (29), the chromatographic properties of liquid coated Car-


403

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C a r b o n n u m b e r of n - p a r a f f i n s

Figure 3. Chromatogram of a hydrocarbon mixture obtained by adding the reference compounds listed in Table I1 to C13to C, n-alkanes from a Utah (Uinta Basin) crude oil. Column: 2 m X 2 mm. Packing: 100-120 mesh Carbopack A 8 % w/w PPE 20. (6 = 25 mlimin. Temperature programmed at 4 "C/min.

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Time (rnin) . Figure 4. FID trace from GC-MS analysis of alkane fraction of the New Albany Shale extract. (a) C,, isoprenoid, (b) C,, isoprenoid, (c) C,, isoprenoid, (d) C, isoprenoid. Column: 2 m X 1 mm. Packing: 100-120 mesh Carbopack A -k 8 % PPE 20. fi = 6 mL/min. Temperature programmed at 4 OC/min from 170 to 350 O C

bopack C and Carbopack ii are similar, but these GCB's require different amounts of a liquid phase. Carbopack C coated with 470 w / w of P P E 20 is chromatographically equivalent to Carbopack A coated with 8% w / w of P P E 20 for alkane analysis, but Carbupack C columns operate at lower temperatures than do Carbopack .4columns. Specifically, the n-C4,,alkane elutes a t 340 " C and 350 "C, respectively, from chromatographically equivalent P P E 20 coated Carbopack C

and Carbopack A columns. In subsequent discussions, no distinction will be made between applications of Carbopack C and Carbopack A columns. GC-IMS Coupling. Micropacked columns can be operated at high linear gas velocities (0)while maintaining low flow rates (21, 22). This capability enhances the potential of micropacked columns for use in conjunction with mass spectrometry and the low bleed rate and high efficiency of P P E 20 coated

404 100

ANALYTICAL CHEMISTRY, VOL 51, NO 3, MARCH 1970 -peak 2

232 I

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Figure 5. Mass spectra of steranes and triterpanes collected during the GC-MS analysis of the New Albany Shale. Peak numbers correspond to those in the chromatogram in Figure 4

GCB recommend its use in micropacked columns. An original GC-MS coupling shown in Figure 1 joins a micropacked column t o a CEC21-110 B mass spectrometer. This novel coupling permits simultaneous recording of a gas chromatogram using any type of gas chromatographic detector and t h e beam monitor of the mass spectrometer. T h e splitter makes it possible to operate the column exit a t atmospheric pressure, as in standard GLSC, rather than a t a vacuum as is the case for most GC-MS couplings (23). T h e addition of make-up gas may be varied to adjust the split ratio between the GC and MS detectors without changing the linear gas velocity ( U ) of the column. When the flow of the make-up gas is properly set, signals from the two detectors are coincident and the recorded peak widths are equal. The two metal valves, labeled as 10 in Figure 1, permit the isolation of the ion source during the venting of the GC solvent peak. Efficient removal of the carrier gas (He) is achieved by the separator. T h e ion source is maintained a t approximately 9 x lo-' Torr (uncorrected) and the beam monitor gives a stable base-line

signal during operation of the coupled system a t 70-e\' ionization potential.

ANALYTICAL APPLICATIONS GC-MS Analyses of Branched Chain and Cyclic Alkanes from the New Albany Shale. T h e F I D trace, obtained during the GC-MS analysis of the total alkane fraction of the benzeneemethanol extract of a New Albany Shale sample is shown in Figure 4. T h e high abundances of the C I S ,C l i , and CI9 n-alkanes and of pristane indicate t h a t the remains of marine organisms are major constituents of the organic materials in this shale ( 2 4 ) . As suggested above, the analysis of the steranes and triterpanes present in this shale are of special interest because these compounds have been used in investigations of the migration and maturation of petroleum (25,26). The empirical formulas of the compounds for which the peaks are numbered in Figure 4 are listed by these numbers in Table 111. Mass spectra are recorded in Figure 5 for some of the steranes and a triterpace in these


405

8

Table 111. Steranes and Triterpanes Identified in the Alkane Fraction of the New Albany Shale Extract peak numbe r

(Figurp 4)

formula

hydrocarbon type steranes steranes s teranes steranes steranes steranes stwanes steranos s tpranes steranes

1. 2.

3. 4. 5.

6. 7. 8. 9. 10.

11. 12.

steranes

13.

steranes

14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

C: ,H.i? 50-stiemastanp

steranes pentacyclic pentacyclic pentacyclic pentacyclic pentacyclic pentacyclic pentacyclic pentacyclic

2

triterpanes tritprpanes triterpanes triterpanes tritprpanes triterpanps triterpanes triterpanes

alkanes. The peak numbers listed in Figure 3 correspond with those in Figure 4 and Table 111. Marked differences may be observed between the mass spectra of Sa-cholestane, 3a-ergostane and 5a-stigmastane and the mass spectra of other types of steranes in Figure 5. One noteworthy difference is the presence of an intense peak a t m / e 259 coupled with a decreased intensity of the peaks a t m / e 217 and 218. T h e m / e 259 peak is formed as a consequence of the cleavage of the large alkyl side chain a t the 17 position, and the m / e 217 and 218 ions are formed by the cleavage t h a t removes ring D. T h e loss of the side chain fragments is particularly evident in the mass spectra of the steranes in GC peaks 8 and 9 of Figure 5, where large peaks may be observed a t m / e 371, 357, 315, 287, and 273. T h e appearance of the peak at m / e 259 is associated with a general increase in the sizes of the peaks a t m l e 177, 163 and m / e 149 which result from cleavages in ring B. None of the steranes have a base peak a t m / e 231 t h a t is characteristic of the 4-methyl substituted steranes. T h e distributions of Czs, and CZ9steranes may be clearly observed some of the in the single ion monitor traces recorded a t m / e 372, 386, and 400 in Figure 6. T h e shaded area indicates the presence of a compound that has a m / e 259 peak which is >SO% as large as the base peak ( m / e 217). T h e symbols a and $ denote 5 a and $3 isomers of cholestane, ergostane, and stigmastane that were present in these eluates. T h e identifications of these steranes were confirmed by coinjecting standard compounds. T h e single ion monitor traces in Figure 6 indicate similar distributions for the Czi, Czs,and Czgsteranes. Furthermore, the relative concentrations of steranes t h a t have and d o not have intense m / e 259 peaks in their spectra are approximately constant. Steranes with large m / e 259 peaks comprise between 35 and 45% of the total C Z i ,C28,and CZ9steranes in the New Albany Shale extract. As shown by the positions of the shaded areas in the Figure 6 traces, the steranes with large m / e 259 peaks have shorter GC retention times than do the other steranes. Seifert et al. ( 1 4 ) have observed distributions and fragmentation patterns for steranes from California crude oils

$:372

1

4

I

40

I

I

50 t irne(rnin)

Figure 6. Single ion monitor traces for C,,, C,,, and C,, steranes collected during the GC-MS analysis of the New Albany Shale extract. The shaded areas indicate the presence of m l e 259 peaks that are larger than 5 0 % base peak. Peak numbers correspond to those in the chromatogram in Figure 4

which resemble those reported above for the steranes from the New Albany Shale. They propose t h a t the crude oil steranes with intense m / e 259 peaks are rearrangement products of sterols in which the bridge methyl groups are attached to carbon atoms 5 and 14 rather than a t the 10 and 13 positiuns. Laboratory experiments have established t h a t cholestanol undergoes a “backbone rearrangement” (27) under strongly acidic conditions a t 145 “C to yield a 5,14-dimethyl substituted sterol ring system. Seifert et al. ( 1 4 ) cite these experiments and the fact that the mass spectrum of the sterene product has a strong m / e 257 peak as evidence for the presence of the 5,14-dimethyl sterane in the crude oil. This interpretation presumes t h a t hydrogenation of the steranes with a large m / e 257 peak would produce a sterane with an intense m / e 259 peak, and their interpretation is indirectly supported by the similarity in the mass spectra of the stereoisomers of cholestane reported by Mulheirn and Ryback (28). Recently, Ensminger et al. (29) have found backbone rearranged steranes, which they refer to as diasteranes, in the Dontrien Shale. Their identifications of $a- and ap-diasteranes were accomplished by comparisons of the retention times and the mass spectra of the natural products isolated from shales and crude oils with those of diasteranes prepared

406

ANALYTICAL CHEMISTRY, VOL. 51,

NO. 3, MARCH 1979 Time (min)

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Carbon number o f n-paraffins Figure 7 . Chromatogram of a total Devonian crude oil from Lowry Indiana. Column: 2 m X 1 mm. Packing: Carobpack C f 4 % PPE 20. I#I = 10 mL/min. Temperature programmed at 4 'C/min

by synthesis. An intense mle 259 peak was observed in the mass spectra of pa-diacholestanes as reported by these authors. Moreover, the fragmentation patterns of peaks 2 and 3 of Figure 5 closely resemble the d a t a presented for Padiacholestanes (29), and in this respect, some of our mass spectral analyses support the presence of backbone rearranged products in the sterane fractions from the New Albany Shale. However, it is conceivable t h a t rearrangements requiring less severe conditions than methyl group migrations (13)may have been favored relative t o the backbone rearrangement in the New Albany Shale which has a mild thermal history. For instance, Petrov (30) has noted t h a t the cis CD ring fusion in the steroid ring system is the thermodynamically preferred configuration. At equilibrium, up to 90% of cholestanes may be converted to cholestanes with cis CD ring junctures, and similar conversions are observed in the hopanes (31). The mechanism for the formation of the m / e 217 peak in the mass spectra of 5 steranes involves a hydrogen rearrangement from position 14 to 17 and from positions 12, 8, and 13 to position 14 (32). Seemingly, isomerizations a t ring and side chain junctures may reasonably be expected to diminish cleavages in the D ring of steranes. In this regard, it is interesting t o note that m / e 218 is the base peak of 5a,l4/3-cholestane (28). Moreover, a small but detectable increase in m / e peaks 259, 149, 163, and 173 in the mass spectrum of 5a,l4/3-cholestane can be observed relative to these peaks in the mass spectrum of 5a,l4a-cholestane. Although we suggest that structural rearrangements other t h a n those involving methyl group migrations may provide an explanation of the gas chromatographiemass spectrometric analyses of unidentified compounds in the sterane fractions of t h e New Albany Shale and similar geological samples, we recognize that our suggestion cannot be evaluated until suitable reference compounds are available.

Table IV. Compounds Identified in the New Albany Shale Distillate FID T r a c e 1 C,olefin + C n alkane + benzene

16

e5

2 Caalefin + Can alkane + toluene

17

0: @o c 1

3 Cgulefin +

18

Q-6

19

a a.c3

m xylene

4 C901efin + 0 and p xylene

5 6 Calefin

10 7 methylethylbenzene

20.21 22

a4* 0 11 C a l e f i n

a . c 2

+

m'

23

03-c3

24

a

-

25

a

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26

a

27

a

28

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C c

C

4 2

5

12 13

14

0

-

c

3

5

29.30 a . c 4 31

a . C 5

ECD Trace thiophene

c .+ c 2

3

-benzothiophenenes

benzodithiophenes

-

F i n g e r p r i n t Analysis of t h e T o t a l O r g a n i c F r a c t i o n s of Geological a n d Industrial-type Samples. Crude oils and organic extracts and distillates of sedimentary rocks are generally complex mixtures. Definitive analyses of these carbonaceous substances are commonly preceded by sequential


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TIME (rnin) Chromatograms of two equivalent samples of a distillate obtained from the New Albany Shale in a Fischer Retort operated at 500 O C . Column: 2 m X 1 mm. Packing: Carbopack C 4 % PPE 20. 4 = 6 mL/min. Temperature programmed at 4 OC/min from 100 to 340 O C Figure 8.

+

separations which divide these complex mixtures into relatively simple fractions that are amenable to analyses. Unless elaborate precautions are taken, substantial portions of such organic samples are lost during the exchanges of solvent involved in the extractions, chromatographic fractionations, and recoveries of these samples. For instance, the gasoline and kerosene portions of crude oils are lost when crude oil is separated by LSC or TLC. GLSC employing GCB affords a means of resolving complex mixtures composed of organic compounds with widely different molecular weights and functional groups or polarities. For example, the GC analyses of samples of a Devonian crude oil from Indiana and a 500 “C Fischer Retort distillate of the New Albany Shale are presented in Figures 7 and 8. As the GC analyses of a total crude oil in Figure 7 shows, the pristane/phytane, n-C,;/pristane, and n-C18/phytaneratios

as well as the carbon preference indices, which are extensively used in organic geochemical investigations (33), can be measured. GC data acquired with GLSC columns packed with GCB exhibit a large capacity in addition to high resolution. For this reason, these columns may employ multidetection systems ( 3 4 ) thus making it possible to obtain GC “fingerprints” and mass spectral analyses in a single run. Figure 8 shows the FID and ECD traces recorded during two separate GC-MS analyses of the New Albany Shale distillate. Table IV lists the compounds tentatively identified by the GC-MS analysis of this distillate which is predominantly composed of aromatic hydrocarbons ( I 7 ) . Both the intensity of the ECD signal and the distributions of 32Sand 34Scontaining ions in the mass spectra provide evidence relating to the number of sulfur atoms in the thiophenes listed in Table IV.

408


ACKNOWLEDGMENT T h e authors thank G. Eglinton of the University of Bristol (England) for providing some of the reference compounds, W. B. Wimberg for technical assistance. and G. E. Von Unruh and E. Brancaleoni for helpful discussions. We also thank P. J. Arpino of the Ecole Polytechnique (France) for calling to our attention the recent work by Ensminger et al. (29).

(18) (19) (20) (21) (22) (23) (24)

LITERATURE CITED (1) D. M. Young and A. D. Croweli. "Physical Adsorption of Gases", Butterworths, London, 1962, and references therein. (2) S.Ross and J. P. Olivier, "On Physical Adsorption", Interscience, New York. 1969, and references therein. (3) A. V. Kiselev and Y. I. Yashin, "Gas Adsorption Chromatography". Plenum Press, New York, 1969, p 128. (4) G. M. Petov and K. D. Sherbakova, in "Gas Chromatography 1966", A. B. Littlewood, Ed. Institute of Petroleum, London, 1967, p 50. (5) A. V. Kiselev, N. V. Kovaleva, and Y. S. Nikitin, J . Chromatogr., 58, 19 (1971). (6) F. Bruner, P. Ciccioli, G. Crescentini. and M. T. Pistolesi, Anal. Chem., 45, 1851 (1973). (7) A. DiCorcia and A. Liberti. Adv. Chromatogr., 14, 305-363 (1974). (8) F. Bruner, P. Ciccioli, and A. DiCorcia, Anal. Chem., 44, 894 (1972). (9) F. Bruner, P. Ciccioli, and F. DiNardo, Anal. Chem., 47, 141 (1975). (10) C. Vidal-Madjar and G. Guiochon, Nature (London), 215, 1372 (1967). (11) F. Bruner, P. Ciccioli, and F. DiNardo. J . Chromatogr.,99, 661 (1974). (12) C. Vidal-Madjar, S. Bekassy, M. F. Gonnord, P. J. Arpino, and G. Guiochon, Anal. Chem., 49, 768 (1977). (13) W. G. Meinschein, Bull. Am. Assoc. Petrol. Geologists. 43, 925 (1959). (14) W. K. Seifert and J. M. Moidowan. Geochim. Cosmochim. Acta, 42, 77 (1978). (15) K. 8. Denson, S. P. Taylor, and J. M. Hayes, Proc. 24th Annu. Conf. Mass Spectrom. Allled Topics. San Diego Calif., 548 (1976). (16) D. E. Matthews, K. B. Denson, and J. M. Hayes, Anal. Chem., 53, 681 (1978). (17) G. Rinaldi, P. Ciccioli, W. B. Wimberg, and W. G. Meinschein, Paper

(25) (26) (27) (28)

(29) (30) (31) (32) (33) (34)

presented at the "First Eastern Gas Shales Symposium", Morgantown, W.Va., 1977, pp 734-747, in press. W. 0. McReynoid, J . Chromatogr. Sci., 8, 685 (1970). F. Bruner, G. Bertoni, and P. Ciccioli, J . Chromatogr., 120, 307 (1976). P. Urone, Y. Takahashi, and G. H. Kennedy, J . Phys. Chem., 74, 2326 (1970). F. Bruner, P. Ciccioli, G. Bertoni, and A. Liberti, J . Chromatogr. Sci.. 12, 758 (1974). M. Novotny, J. M. Hayes, F. Bruner, and P. G. Simmonds, Science, 189, 215 (1975). F. Bruner, P. Ciccioli, and S. Zeiii, Anal. Chem., 45, 1002 (1973). P. Albrecht and G. Ourisson, Angew. Chem., Int. Ed. Engl., 10, 209. (1971). R. C. Clark, Jr., and M. Blumer, Limnol Oceanogr., 12, 70 (1967). W K. Seifert. Geochim. Cosmochim. Acta, 42, 473 (1978). I . Rubinstein, 0. Sieskind, and P. Albrecht, J . Chem. Soc., Perkin Trans. 7 , 1833 (1975). L. J. Muheim and G. Ryback, "Advances in Organic Geochemistry", (Madrd. 1975), R . Campos and J. Soni, Ed., 1977, p 211. A. Ensminger, G. Joly, and P. Albrecht, Tetrahedron Lett., 18. 1575 (1978). A. A. Petrov, D. S. Pustilnikova, and N. N. Abriutina, "8th International Congress on Organic Geochemistry" held in Moscow 10-13 May, 1977; Volume 1, Abstracts of Reports, p 162. A. Ensminger, P. Albrecht, G. Ourisson, and B. Tissot, "Advances in Organic Geochemistry" (Madrid, 1975), R . Campos and J. Soni, Ed., 1977, p 45. L. Tokes, G. Jones, and C. Djerassi, J . Am. Chem. Soc., 90, 5465, (1968). R. E. Kreider, 1971 Joint Conference on Prevention and Control of Oil Pollution, p 119. P. Ciccioli, G. Bertoni, E. Brancaleoni, R. Fratarcangeli, and F. Bruner, J . Chromatogr., 126, 757, (1976).

RECEIVED July 17, 1978. Accepted December 8, 1978. This work was partially supported by DOE Grant EY-76-C-05-5204 and funding from NSF Grant EAR 76-13463, NASA Grant NGR 15-003-118, and OWRT Grant 14-31-0001-5143contributed to the maintenance of the laboratory facilities used in this study.

Development and Characterization of a Miniature Inductively Coupled Plasma Source for Atomic Emission Spectrometry R. N. Savage and G. M. Hieftje" Department of Chemistry, Indiana University, Bloomington, Indiana

4740 1

these ICP-AES systems has been the high operational cost and complexity associated with the ICP source itself. In addition, the high-power rf equipment required by conventional ICP sources increases their initial cost, requires a lot of laboratory space, and can produce strong radio-frequency interference (RFI), unless proper shielding techniques are employed. Many of these limitations should be overcome merely by shrinking the physical dimensions of the ICP. Such a mini-ICP, if operated a t similar power densities t o its larger counterpart, should exhibit the same high sensitivity, working curve linearity, and freedom from interferences; these desirable features are largely a result of high plasma temperature, which is itself a function of power density (8). In turn, the smaller ICP would require a lower input power to maintain equivalent power density and would consume less coolant gas (argon) during operation. Attendant savings in the cost of the rf power supply, impedance matching device, and transmission lines would be expected. In addition, lower power requirements would reduce necessary laboratory space and expected interference from radiated rf energy. In the present study, such a mini-ICP was developed and its operational characteristics and analytical capabilities were evaluated and compared to a conventional ICP source. The conventional source is a commercially available system containing a 20-mm o.d. torch. This kind of system is found

A miniature inductively coupled plasma source for atomic emission spectrometry is described and a preliminary evaluation of its analytical capabilities is presented. The mini-ICP is very economical to sustain and works well with less than 1 kW of rf power and 8 L min-' of argon coolant gas. I n addition, the new source possesses some unique operating characteristics which simplify sample introduction. I n this paper, detection limits, multielement capabilities, and other analytical features of the mini-ICP are compared with those demonstrated by a conventional ICP source and shown to be comparable. In addition, the two plasmas are shown to exhibit similar excitation temperatures in their respective analyte observation regions (i.e., plasma tail flames). These results suggest that the mini-ICP possesses the same desirable atomization and excitation characteristics as conventional ICP sources.

During the past decade, the radio-frequency inductively coupled plasma (ICP) has emerged as a very promising excitation source for atomic emission spectrometry (AES) and many investigators have examined both the physical nature (1-4) and analytical capabilities (5-7) of ICP sources for simultaneous multielement optical emission analysis. However, one of the main impediments to the acceptance of 0003-2700/79/0351-0408$01 O O / O

C

1979 American Chemical Society

Graphitized carbon in gas-liquid-solid ... - ACS Publications

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