ACKNOWLEDGMENTS

This work was supported in part by research grants from the National Science Foundation, Division of Materials Research, Polymers Program (DMR76-17999) and the American Iron and Steel Institute {66-345). A grant from the Armco Foundation enabled the ellipsometer to be obtained.

1. B. J. Fontana and J. R. Thomas, J. Phys. Chem. 65, 480 (1961). 2. J. A. Herd, A. J. Hopkins, and G. J. Howard, J. Polymer Sci. (Pt. C) 34, 211

(1971). 3. E. Hamori, W. C. Forsman, and R. E. Hughes, Macromolecules 4, 193 (1971). 4. C. Thies, J. Polymer Sci. (Pt. C) 34, 201 (1971). 5. S. Ellerstein and R. Ullman, J. Polymer Sci. 55, 123 (1961). 6. R. Botham and C. Thies, J. Polymer Sci. (Pt. C) 30, 369 (1970). 7. S. A. Francis, and A. H. Ellison, J. Opt. Soc. Am. 49, 131 (1959). 8. R. G. Greenler, J. Chem. Phys. 44, 310 (1966). 9. R. G. Greenler, R. R. Rahn, and J. P. Schwartz, J. Catal. 23, 42 (1971).

10. G. W. Poling, J. Electrochem. Soc. 117, 520 (1970).

11. F. L. McCrackin, E. Passaglia, R. R. Stromberg, and H. L. Steinberg, J. Res. Natl. Bur. Stand. 67A, 363 {1963).

12. F. L. McCraekin and J. Colson, National Bureau of Standards Technical Note 242 (U.S. Government Printing Office, Washington, DC, 1964).

13. F. J. Boerio, L. H. Schoenlein, and J. E. Greivenkamp, J. Appl. Polymer Sci. 22, 203 (1978).

14. B. J. Intorre, T. K. Kwei, and C. M. Peterson, J. Phys. Chem. 67, 55 (1963). 15. J. Glazer, J. Polymer Sci. 13, 355 (1954). 16. J. F. Murphy and H. A. Page, Am. Chem. Soc. Div. Paint Plastics Printing

Ink Chem. Papers 15, 27 (1955). 17. A. B. Winterbottom, J. Iron Steel Inst. 165, 9 (1950). 18. P. C. S. Hayfield and G. W. T. White, in Ellipsometry in the Measurement of

Surfaces and Thin Films, National Bureau of Standards Miscellaneous Publication 256 (U.S. Government Printing Office, Washington, DC, 1964), p. 157.

19. H. Lee and K. Neville, Handbook of Epoxy Resins (McGraw-Hill, New York, 1967, Ch. 4, p. 29.

20. R. N. Jones and C. Sandorfy, in Chemical Applications of Spectroscopy, W. West, Ed. (Interscience, New York, 1956), Ch. 6.

Collection of Gas Chromatographic Fractions on Act ivated Charcoal and Identification by Infrared Spectroscopy

DANIELLA GOLDFARB and CHRIS W. BROWN Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 02881

A nove l m e t h o d for co l l ec t ing gas chromatographic fract ions in c o m m e r c i a l l y ava i l ab l e t u b e s of act ivated charcoal has b e e n d e v e l o p e d and tes ted on a n u m b e r o f o r g a n i c m i x t u r e s . The t rapped fract ions w e r e d e s o r b e d w i t h CS2 a n d i n f r a r e d spectra of the CS2 so lut ions m e a s u r e d to provide pos i t ive ident i f icat ion of t h e e luen t s . The col lec t ion eff ic iency w a s found to be >68% in all but one case , and the reso lut ion of the separat ion and collec- t i on m e t h o d w a s adequate for m a k i n g pos i t ive ident i f icat ions . The a d v a n t a g e s o f us ing computer ized subtract ion of i n f r a r e d spec tra in ident i fy ing the e luents is a lso demonstrated .

Index Headings: I n f r a r e d ; Gas chromatography .

INTRODUCTION

During the past two decades, gas chromatography has proven to be an excellent technique for separating com- ponents in a mixture of volatile organic compounds. Components can be identified by retention times, but this requires measuring retention times of knowns under identical conditions. Furthermore, in complicated mix- tures, two or more components could have the same retention times. Generally, it is advisable to use a sepa- rate analytical technique for identification, e.g., mass, UV-visible, nuclear magnetic resonance, or infrared spec- troscopy.

The instrumentation for identification can be coupled directly to the gas chromatograph such as in GC/MS or GC/IR. Both of these techniques require expensive equipment, and the MS or the IR is generally dedicated

Received 21 August 1978; revision received 20 October 1978.

126 Volume 33, Number 2, 1979

to the GC, i.e., used solely for identifying GC eluents. In many cases, it is not necessary to identify all of the GC eluents or to identify components routinely. For example, it may be necessary to identify only a few components in a GC on a one time basis. Thus, in many cases, a dedicated instrument is not warranted, and an indirect method of collecting GC fractions for later identification is more desirable.

A number of techniques for trapping GC fractions have been tested. These include trapping at reduced temper- atures, 1-6 in solvents, 1 or on absorbing materials. L' ~' 7-:0 The method used in the present study falls in the latter category, i.e., absorbing materials. Activated charcoal in cartridges supplied for OSHA analyses are used to collect GC fractions. The methods for collecting multiple frac- tions, desorbing the fractions, and identifying them by infrared spectroscopy are discussed herein.

I. EXPERIMENTAL

In the present experiments an older gas chromatograph (Hewlett-Packard model 700) was modified for collecting fractions. A 10 ft., 1/8 in. column of 10% SP2250 on 100/ 120 Supelcoport was used for separation. This chromat- ograph is equipped with flame ionization detection (FID) which destroys the eluents. Thus, it was necessary to split the effluent prior to the detector. A Swagelok union T was inserted between the column and the detector (inside the oven) to split the flow. A stop-flow valve was placed between the splitter and the FID detector. An- other stop-flow valve and a fine metering valve (Nupro

APPLIED SPECTROSCOPY

4BM) was installed between the splitter and the collec- tion device. The splitter and all three valves were located in the oven; however, the metering valve could be con- trolled externally. The diagram of the modified oven compartment is shown in Fig. 1.

After the two valves on the collection side of the splitter, the effluent exits the oven compartment through a temperature controlled heated jacket to a "merry-go- round" device shown in Fig. 2. This device was made in- house of Teflon; the eluent enters the device through the center and is directed at a right angle to the front where it enters one of the 20 possible holes containing a charcoal cartridge.

To collect a number of fractions, the GC eluents are monitored by the FID detector (10% going to the detector and 90% to the collection device). When the recorder indicates that a GC fraction is starting to elude the column, the collection device is manually moved to a position containing the desired charcoal cartridge. The eluent is collected and the device is rotated to another position for collecting the next fraction.

The possibility of a single component concentration exceeding the breakthrough level of a charcoal cartridge was investigated for a number of components (acetone, benzene, toluene, and p-xylene) by attaching a second cartridge to the exit of the first cartridge. The compo- nents could not be detected in the solutions of the de- sorbed cartridges; thus, it was concluded that under typical GC conditions the breakthrough level would not be exceeded.

The charcoal cartridges (S.K.C., Inc.) were desorbed with CS2. The charcoal was first cooled to liquid N2 temperature, and 1 ml of CS2 was added. The mixture was then allowed to warm to room temperature. The liquid N2 treatment is necessary to reduce losses due to heat of solution. 11

Infrared spectra of the CS2 solutions were measured in

column c o m p a r t m e n t

f a '

FIG. 1. Schemat ic of spli t ter in GC oven: a, injection port; b, column; c, union T; d, stop-flow valves; e, regulating valve; f, to collector; g, to detector.

• 1 ~ ¸

' \ : - I • ~" i /

Fro. 2. Schemat ic of "merry-go-round" collection device: a, inlet; b, hole for charcoal cartridge; c, rotat ing section.

6 mm AgC1 matched cells on a Beckman model 4260 infrared spectrometer. The spectrometer is directly im terfaced to a NOVA 3/12 computer, and all spectral data were stored digitally in 1 cm -1 increments.

II. RESULTS AND DISCUSSION

A. Col lec t ion Eff ic iency. A number of single com- ponent solutions in CS2 were prepared and injected into the GC to determine the overall efficiency of the system, i.e., collection and extraction efficiency. A known amount of each component was injected into the GC with the splitter previously set so that 90% of the sample was directed to the charcoal tube and 10% to the flame ionization detector. Each component was collected on charcoal and desorbed with CS2, and its infrared spec- trum was measured in CS2. The concentration of" the component in CS2 was determined from a concentration vs absorbance plot for that component. The following bands were used for the quantitative analyses: 1715 cm -2 for acetone; 670 cm -1 for benzene; 720 cm -1 for toluene; 790 cm -1 for p-xylene; and 1740 cm -1 for ethylhexanoate.

The initial concentrations, instrument conditions, and yields are given in Table I. Four benzene solutions had an average yield of 80.75% with a range of 75 to 89%. The efficiency was >75% for all components, except acetone. Since the GC columns were chosen for separating hydro- carbons, the acetone was lost by irreversible absorption on the column. When higher concentrations of acetone in CS2 (90% vol/vol) were injected, the percent yield increased.

B. Reso lu t ion o f S e p a r a t i o n and Col lect ion Method. A mixture of 10% (v/v) of carbon tetrachloride,

APPLIED SPECTROSCOPY 127

thiophene, toluene, p-xylene, and m-xylene in carbon disulfide was prepared; 1.4 /~1 of this solution were in- jected into the GC. The gas chromatogram shown in Fig. 3 contained four peaks (in addition to the solvent peak), the first two peaks were slightly overlapping and one of the peaks represented two components. All four fractions were collected and their IR spectra measured. The IR of the first and the second GC peaks, carbon tetrachloride and thiophene, are shown in Fig. 4. Although the GC peaks were very close, a good separation was obtained and the fractions collected were pretty clean. The IR spectrum of the fourth peak, shown in Fig. 5, was iden- tified as a mixture ofp-xylene and m-xylene.

T A B L E I. Co l l ec t i on and extract ion efficiencies for s ing le com- p o n e n t organics injected into GC and collected on charcoal

Volume in- Conc (v/v) Yield (%) Column C°mp°unda jected (~l) (%) temp (°C)

Benzene (1) 1.8 2 89 80 Benzene (1) 2.0 2 75 80 Benzene (1) 1.3 10 79 80 Benzene (1) 1.3 10 80 80 Acetone (1) 2.0 5 55 80 Acetone (2) 2.1 90 68 80 Acetone (2) 2.1 90 68 80 Toluene (2) 2.1 10 86 80 Toluene (2) 2.1 10 78 80 p-Xylene (2) 2.1 10 83 90 Ethylhexanoate (2) 1.5 10 78 115

" (1), column used was 10% SP-2100 1/8 in. × 10 ft.; (2) column used was 10% SP-2250 1/8 in. x 10 ft.

b.l

Z O Q. CO bJ

0 l--

l.d I" W ¢3

5 0

J Q : o o i - w = m

k.

I i I I I I / I 0 3 6

T I M E , ( M I N )

.J X

I O.

i i

J ) -

X I

I I 9

FIG. 3. GC of a mixture containing carbon tetrachloride, thiophene, toluene, p-xylene, and o-xylene in CS2.

128 Volume 33, Number 2, 1979

C A R B O N T E T , G C

C A R B O N T E T

T H I O P H E N E , GC

1 1300

F R E Q U N C Y . (C M "+)

T H I O P H E N I E

IO J L / I I I I I I I I I 15 0 I000 700 I000 700

FIG. 4. IR spectra of the GC fractions of carbon tetrachloride and thiophene, and pure carbon tetrachloride and thiophene.

(o z

P - X Y L E N E

03 1 M - X Y L E N E

I I I 1 I I I J 1300 I 0 0 0 7 0 0

F R E Q U E N C Y, ( C M -~)

FIG. 5. l a spectrum of the fourth GC peak in Fig. 3, identified as a mixture ofp-xylene and m-xylene.

C. C o m p u t e r i z e d S e p a r a t i o n . A random mixture of benzene, toluene, p-xylene, and o-xylene was prepared. About 1 ml of the mixture was added to 150 ml of sea water and the vapors were collected by pumping air from above the "spill" through a charcoal cartridge.] 2 The charcoal was desorbed with CS2 and the infrared spec- t rum of the solution was measured. Then the mixture was injected into the GC, each fraction was collected, and its infrared spectrum was measured. The gas chro- matogram is shown in Fig. 6. Two methods were em- ployed to obtain infrared spectra of the pure components: (1) the spectrum of each GC fraction was measured; and

W

Z 0

a. o

LIJ

o N F- Z

0 °J W W ~ II1

E l

I I I I I I

o 3

.5 .5 )- >-

X X I j

Q" 0 J

l\ t I I t

6 9

T I ME , (MIN)

FIG. 6. GO of the vapors collected above a simulated spill of benzene, toluene, p-xylene, and o-xylene on sea water.

P E A K I , 3 , 4 " P E A K 3 .

P E A K I , 4

MIX'PEAK 2

PEAK 1,3,4

PEAK 1,4 - PEAHI ,

PEAK4

/

1 13100 I I I0100 I 1 7(~0 1310O I I I0[00 I 7~)0

FREQUENCY, (CM "j)

FIe. 7. IR spectrum of the total mixture (in 0S2) of benzene, toluene, p-xylene, and o-xylene; spectrum of the mixture minus the spectrum for peak 2 (toluene}; the latter spectrum minus peak 3 (p-xylene); the latter spectrum minus peak 1 (benzene}. The lower, right spectrum of peak 4 should correspond to o-xylene.

(2) the spectra of three components were sequentially subtracted from the spectrum of the entire mixture to give the spectrum of the fourth component. 1:~' 14 This lat ter method is demonstra ted in Fig. 7, where the spec- t rum of GC peak 2 (toluene) is first subtracted from that of the mixture, followed by the subtraction of the spec- t rum for GC peak 3 and then 1. The resulting spectrum should be tha t of GC peak 4 or o-oxylene. The computed spectrum of o-oxylene is compared with the spectrum of GC fraction 4 in Fig. 8; the results are identical. The computed and actual spectra of the other three compo- nents were also identical. The purpose of this exercise was to demonstra te the power of computer subtraction in unraveling the identification of components in a mul- t icomponent mixture, e.g., we could have missed collect- ing one of the components and still have identified it by subtracting the spectra of the other components from the spectrum of the complete mixture.

D. A p p l i c a t i o n to a R e a l P r o b l e m . Much of our research is directed toward identifying hydrocarbons in various petroleum samples. The present method is well suited for providing much of the desired information. For example, we have been investigating the chemical com- position of vapors above oil slicks. Vapors are collected by pumping air from above a spill through charcoal cartridges, desorbing with CS2, and measuring GC of the solutions. The gas chromatogram of vapors collected from above a simulated spill of Kuwait crude oil is shown

bJ

Z

F-

(o Z

Q::

O ' X Y L E N E , C O M P U T E R

/

O - X Y L E N E , G C

I I I I I I I 1300 I 0 0 0 7 0 0

F R E Q U E N C Y , ( C M "1)

FIG. 8. IR spectra of o-xylene obtained by subtraction and of the GC fraction.

APPLIED S P E C T R O S C O P Y 1 2 9

hJ

Z 0

03 U.I

o

o uJ

Q

i

0

III

I I i I I I 2 4 6 8 I 0 12 14

T I M E , M I N

FIG. 9. GC of sample collected above a simulated oil spill of Kuwait. Peaks 1 and 2 were collected.

o z <

z <

PEAK 2

e,..gTL,

} ff-xvL

P E A K I TOL ge I~[

l e o , L ~ O O I 2~00, I 20¢00 . . . . . 1700 14100 . . . . . IlO0 8~)0 ' t 500 '

F R E Q U E N C Y , ( C M "~)

FIG. 10. IR spectra of GC peaks 1 and 2 in Fig. 9.

in Fig. 9. We collected various fractions for identification by IR. Spectra of two of the peaks labeled 1 and 2 are shown in Fig. 10. Toluene, o-xylene, and rn-xylene can be identified from the spectra. Both samples also contain a paraffin, possibly branched chain molecules, which we were unable to identify. However, these data satisfied our need to identify the substituted aromatics.

III. CONCLUSIONS

The activated charcoal cartridges supplied for OSHA analyses are ideally suited for collecting GC eluents. In the present report, we have demonstrated that this method provides adequate samples for analysis by in- frared spectroscopy. However, the same samples could be analyzed by UV-visible, nuclear magnetic resonance, and mass spectroscopy. Furthermore, the method could be easily automated by interfacing the GC detector to a laboratory computer and having the computer operate the merry-go-round device.

ACKNOWLEDGMENTS

This research was supported by the Environmental Control Division, Depart- ment of Energy [Contract No. E(11-1)-4047]. The authors wish to express their appreciation to the contract monitor, John M. Cece, and the project director, Mason P. Wilson, for their support. We also express our appreciation to Robert J. Obremski for suggesting the use of charcoal tubes and for helpful discussions.

1. D. Welti, "The examination of gas chromatographic fractions by infrared spectroscopy," in Laboratory Methods in Infrared Spectroscopy, R. G. Miller and B. C. Stace, Eds. (Heyden & Son Ltd., Philadelphia, 1972) p. 186.

2. S. K. Freeman, "Gas chromatography and infrared and raman spectrometry," in Ancillary Techniques of Gas Chromatography, L. S. Ettre and W. H. McFadden, Eds. (Interscience, New York, 1969), pp. 227-268.

3. A. A. Casselman and R. A. B. Bannard, J. Chromatogr. 90, 185 (1970). 4. K. H. Norin, Analyst 99, 717 (1974). 5. V. Devek, Anal. Chem. 43, 1909 (1971). 6. I. S. Degen, G. A. Newman, and J. F. Trigg, Lab Pract. 25, 767 (1976). 7. J. W. Amy, E. M. Chain, and W. C. Baitinger, Anal. Chem. 37, 1265 (1965). 8. M. Cartwright and A. Heywood, Analyst 91, 337 (1966). 9. I. A. Fowlis and D. Welti, Analyst 92, 639 (1967).

10. J. Witiak, G. A. Junk, G. V. Calder, J. S. Fritz, and H. J. Svec, J. Org. Chem. 177, 3066 {1973).

i1. J. D. Rueda, H. J. Sloane, and R. J. Obremski, Appl. Spectrosc. 31, 298 (1977).

12. D. Goldfarb and C. W. Brown, in preparation. 13. C. W. Brown, P. F. Lynch and M. Ahmadjian, Ind. Res/Develop. 20 (5), 122

(1978). 14. P. F. Lynch and M. M. Brady, Anal. Chem. 50, 1518 (1978).

Theory of High Frequency Differential Interferometry: Application to the Measurement of Infrared Circular and Linear Dichroism via Fourier Transform Spectroscopy

LAURENCE A. NAFIE and MAX DIEM Department of Chemistry, Syracuse University, Syracuse, New York 13210

A g e n e r a l m e t h o d fo r t he d i r ec t m e a s u r e m e n t of d i f fe ren t ia l absorption i n t e n s i t i e s u s i n g a F o u r i e r t r a n s f o r m i n f r a r e d spec-

Received 30 June 1978; revision received 3 November 1978.

t r o m e t e r is desc r ibed . The d i f fe ren t ia l i n t ens i t i e s m u s t be h i g h e r in f r e q u e n c y t h a n the i n t e r f e r o g r a m f r e q u e n c i e s a n d m a y a r i s e f r o m a pe r iod i c v a r i a t i o n o f t he a b s o r p t i o n s t r e n g t h o f t he s amp le , o r by d ich ro ic r e s p o n s e o f t he s a m p l e to a l t e r n a t e s t a t e s

130 Volume 33, Number 2, 1979 APPLIED SPECTROSCOPY