product of this additive having the same retention time
(21)
(19).
(22) (23) (24) (25) (26) (27) (28) (29)
ACKNOWLEDGMENT The 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, 131 1 (1970).
(30) (31) (32) (33) (34) (35) (36) (37) (38) (39) . , (40) (41) (42) (43) (44) (45)
S. Banerjee
and S. K. Bhatnager, Rubber Chem. Techno/., 42, 1366 (1969). G. Erben and W. Kleeman. Rubber Chem. Techno/., 37, 204 (1964). S. Banerjee and S.P. Manik, Rubber Chem. Techno/., 42, 744 (1969). S. Banerjee and S. P. Manik, Rubber Chem. Techno/., 43, 1294 (1970). H. Krebs, Rubber Chem. Techno/., 30, 962 (1957). M. Cherubim and W. Schlee, Rubber Chem. TechnoL, 31, 286 (1958). K. H. Brugel and K. T. Potts, Rubber Chem. TechnoL, 45, 169 (1972). M. J. Brock and G. 0. Louth, Anal. Chem., 27, 1575 (1955). K. Goda. S. Murakami, and J. Tsurugi. Rubber Chem. Techno/., 44, 857 (1971). W. R. Haipin and F. H. Reid, J. Am. Ind. Hyg. Assoc., 29, 390 (1968). K. Grob and G. Grob, J. Chromatogr., 62, 1 (1971). N. A. Gibson, B. Sen, and P. W. West, Anal. Chem., 30, 1390 (1958). C. L. Fraust and E. R. Herrmann, J. Am. Ind. Hyg. Assoc.. 30, 494 (1969). L. D. White, D. G. Taylor, P. A. Mauer, and R. E. KuDel, J . Am. Ind. Hya. .Assoc., 31, 225 (1970). W. G. Jennings and C. S. Tang, J . Agric. Food Chem., 15, 24 (1967). G. 0. Nelson and C. A. Harder, J. Am. lnd. Hyg. Assoc., 35,391 (1974). G. Guiochon and A. Raymond, Environ. Sci. Techno/., 8, 143 (1974). J. A. Miller and F. X. Mueiler, Am. Lab., 6, 49 (1974). F. W. McLaffertv. "lnteroretation of Mass Smctra: An Introduction". 2nd ed., W. A. Benjamin, New York, N.Y., 1972. F. W. McLafferty, "Mass Spectral Correlations", American Chemical Society, Washington, D.C., 1963. H. Budzikiewicz, C. Djerassi, and D. H. Williams, "Mass Spectrometry of Organic Compounds", Holden-Day, San Francisco, Calif., 1967. H. Budzikiewicz, C. Djerassi, and D. H. Williams, "Interpretation of Mass Spectra of Organic Compounds", Holden-Day, San Francisco, Calif., 1964. S. Abrahamson. F. W. McLafferty, and E. Stendagen, "Atlas of Mass Spectral Data", Vol. 1-3, John Wiley and Sons, New York. N.Y.. 1969. American Society for Testing and Materials, "Index of Mass Spectral Data", Philadelphia, Pa., 1969. "Handbook of Chemistry and Physics", 55th ed., Robert C. West, Ed.. C.R.C. Press, Cleveland, Ohio, 1973, p '2-350.
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 that 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
481
in hexane. The samples were injected into the upstream end of the sample tube with respect to helium flow through the tube. Desorption was carried out a t 300 "C with helium flow rate of 20 ml/min for 5 min. T h e transfer line temperature was 300 "C. The phenol was cryogenically trapped (see discussion) and then the chromatograms were obtained by programming from ambient a t 20°/min. The device was also tested using a simple distillate of crude oil containing a typical mixture of aliphatics, aromatics, and heterocyclics. The oil was injected by syringe into the upstream end of a Tenax-GC sample tube and then desorbed for 5 min with the desorption device and transfer line a t 300 "C. T h e transferred material was cryogenically trapped and then the chromatogram obtained by programming from ambient to 300 "C a t 20°/min. A repeat of this experiment with a desorption time of 10 min gave identical results. Figure 1. Thermal desorption device
placed directly into this injector port, sealed off and desorbed a t 300 O C into a cooled precolumn trap. After complete desorption the precolumn trap is warmed and the material transferred via a value to a GC column and analyzed. A number of other related procedures have also been reported (3-7). The present authors were interested in developing a system which would meet the criteria already mentioned and in addition: 1) would result in little or no modification of an existing GC-MS, 2) would allow the use of conventional packed glass or metal columns, 3) would not require any valving on the GC column side of the injector, and 4) would allow rapid exchange of normal injection and desorption capabilities.
EXPERIMENTAL T h e desorption device is constructed of stainless steel stock. The helium inlet and outlet lines are lk-inch stainless steel tubing and are connected to the device via conventional compression fittings. T h e probe-to-barrel seal is accomplished with a 'h-inch Teflon ferrule obtained from Varian Aerograph. In the prototype, tolerances between interrelated parts, such as the probe and barrel, were made only as close as convenient with no special attempt being made to minimize the values. The capillary crossover consists simply of a length of stainless steel capillary tubing mounted on a circular metal plate. The plate is sealed against the injector port and against the surrounding pipe fitting to compression fitting adapter using Teflon bushings. The bushings were constructed from inch Teflon sheet using a cork borer. T h e desorption device and inlet line are heated by a single heating cord, the output of which is controlled by a Variac. Sample tubes for the probe consists of '/B-inch 0.d. X 23/d-inch long Pyrex tubes holding an appropriate adsorbent. For the adsorbent TenaxGC (Applied Science Laboratories, Inc.), these tubes hold about 30 mg of adsorbent. (A recently added larger i.d. probe uses sample tubes 5-mm 0.d. by 23/4-inches long which hold about 300 mg of Tenax-GC.) T h e device is fitted on a Varian-MAT 111 gas chromatographmass spectrometer (Serial No. 3166). The system was equipped for this study with a f/4-inch 0.d. by 2-mm i.d., 10-ft Pyrex GC column. T h e GC column was packed with 3% OV-17 on Gas Chrom Q (Applied Science Laboratories, Inc.). T h e column was mated to the mass spectrometer via a Teflon "0" ringed 12/2 ball joint (Quartz General Corp.) and a capillary ball joint crossover'. T h e capillary crossover was constructed from the 12/2 ball joint socket of a Varian %-inch detector insert and a 7.5-cm segment of 0.008-inch i.d. X 6-mm 0.d. capillary tubing (Ace Glass Inc.). The capillary crossover allows the elimination of the gold choke which normally throttles the inlet of the slit separator. Problems of inlet clogging around the gold choke, which are common when running compounds of fairly high molecular weight (>300) are completely eliminated using this modification. Gas chromatographic traces were recorded directly from the output of a 20-eV pressure measuring source integral with the mass spectrometer. A full scale deflection on this detector a t the attenuator setting used corresponds to a sample flow through the instrument of -0.6 pg/sec for the calibration compound methyl stearate. A study of transfer efficiency was carried out using Tenax-GC as adsorbent. Samples of phenol were transferred by syringe to prepurged '/s-inch sample tubes as a solution of concentration 1 pg/pl 482
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
DISCUSSION The device which has been constructed to meet the aforementioned criteria is shown in Figure 1. I t consists of a heated sleeve equipped with a helium inlet and heated helium outlet line. The outlet line leads to the gas chromatograph. Into this sleeve fits a probe bearing a glass sample tube containing adsorbent. The probe has holes in its wall such that, when in place, helium enters the probe from the helium inlet in the sleeve and travels axially down the probe across the adsorbent held in the sample tube. The helium then exits the probe via a second hole and then exits the sleeve via the heated helium outlet line. This line is connected via a capillary crossover to the injection port of the gas chromatograph. When an adsorbent tube held in the probe is introduced into the heated barrel, it is rapidly heated to the temperature of the barrel resulting in desorption of the adsorbed organics. The helium flow axially through the probe removes these organics in the vapor phase and transfers them via the heated line to the injection port. Exchange of adsorbent tubes is accomplished by slightly loosening the Teflon ferruled compression fitting sealing the probe where it enters the barrel and pulling back the probe until only the blank-off plug is left in the compression fitting. The compression fitting is then firmly retightened on the blank-off plug (plug will blow out if not tightened firmly) and the probe itself unscrewed from the blank-off plug at the threaded joint. The old adsorbent tube is then removed and, after the probe itself cools, a second tube can be inserted as shown in Figure 2. With the new adsorbent tube in place, the probe is screwed back onto the blank-off plug, the compression fitting is loosened, and the probe is reinserted into the barrel. Indexing lines scribed on the probe and barrel allow accurate alignment of the respective probe and barrel helium ports. Note that as the probe enters the barrel, the helium inlet hole in the wall of the probe enters first allowing a momentary flow of helium across the sample tube and out into the atmosphere. This flow effectively purges the probe and adsorbent tube of air, thereby preventing this air from reaching the GC column and the mass spectrometer. During a transfer, the normal carrier gas supply is valved off and helium to the GC column comes only via the desorption device. This auxiliary helium supply is simply pressure-regulated and not flow-controlled. The back pressure presented to the GC column is, therefore, almost instantly restored when interrupted momentarily by exchange of samples. The back pressure used corresponds to that known to result in a column flow rate of about 20 ml/min under normal conditions. Desorptions are carried out with the GC column directly interfaced with the mass spectrometer. Even a t 300 "C, desorptions of some materials are not instantaneous, but instead appear a t the injection port as relatively broad distributions. I t has been found necessary in some cases, therefore, to trap the desorbed materials in
ADSORBENT TENAX-GC COMPOUND PHENOL LOADING ( 1 ~ 4 10 0 0 3 3 % 5MlNS D TIME D TEMP 300' D FLOW 25 rnl/mln COLUMN 3 % OV-17 CRY TRAP LIP N p PROGRAM 30°- ZOOo 20'//min DETECTOR E I D
II-
-5
9-
S k-
a 7S Y
= U
, I
I
5-
3i l-
.; ,
0
2
I
3
i
1
4
5
6
7
0
1
Fg Figure 3. Curve obtained for transfer of phenol from Tenax-GC
Figure 2. Procedure for exchanging adsorbent tubes
PETRC?EUW 31STILLATE n - C , C TC n - C 3 , COLUMN 3 % C V - 1 7 , I O ' X 2 r n - , P Y R E X PROGRAM 2 0 ° / N 8 h F%CM 2 0 " - 3 C O o
order to obtain a sharp injection-like band. Zlatkis and coworkers used a special precolumn trap for this purpose (1). We find that, for packed columns, such a precolumn is not necessary, and trapping can be accomplished simply by cooling the first 2 inches of column with liquid nitrogen held in a small aluminum boat. This procedure is necessary only for materials which can reasonably be expected to move significantly down the GC column a t room temperature. After the desorption is complete, the liquid Nz trap is removed and the column oven is programmed up in the usual manner to obtain the gas chromatogram and/or the GC-MS data. For our particular application, which often ranges from permanent gases to large polymer decomposition products, it was decided that an external sample loop as an alternative to cryogenic trapping for holding the desorbed sample would not be appropriate. This is because the temperature required to maintain the heavier materials in the gas phase would lead to considerable losses and/or artifacts due to thermal cracking. An external loop which included the adsorbent itself would be especially undesirable because part of the samples could potentially be lost by incomplete removal from the adsorbent due to equilibration with the adsorbent.
RESULTS Although the original design criteria did not specify that this device should be capable of quantitative work, it was of interest to demonstrate that desorbed materials were transferred reasonably reproducibly and efficiently. Accordingly, the transfer of samples of phenol in the 1-5 bg range from Tenax-GC was studied. Details appear in the Experimental Section. The results are summarized in Figure 3. Since an extrapolation of the curve in Figure 3 very nearly passes through zero, these results clearly demonstrate a reasonable efficiency of transfer. Further, the rather small scatter of the points suggests that the transfer is acceptably reproducible. Since materials of rather high molecular weight can potentially be components of adsorbent trapped samples, it was also of interest to determine roughly how large a molecule could be expected to be desorbed under a given set of conditions. Tenax-GC was chosen as the adsorbent and 300 "C was arbitrarily chosen as the desorption temperature. The sample chosen was a crude oil distillation fraction
FLOB 3C K L / H l N , HE,lUK 3E'E:TaR El3
0
2
4
~-E
~
_
____.~_ 8 IO I2 4 IE
TIME
~
~
NhT
Figure 4. Comparative study of injection vs. thermal desorption for a crude oil distillate
which, when injected on the same GC column, gave spikes for the normal paraffins from about (2-10 to C-31. In addition to these alkane spikes, the chromatogram exhibits the continuum characteristic of oils and resulting from the very large number of components present. This continuum is observed as a general base-line elevation during the entire course of the chromatogram. The base-line drift on this column due to bleed is negligible. A cessation of paraffin spikes and a return of the chromatogram to base line a t a point earlier than the C-31 paraffin peak would indicate, therefore, that neither n-paraffins nor other aliphatic, aromatic, or heterocyclic components of the oil have been transferred beyond this point. Figure 4 shows the results of this experiment. Part of the reduction in spike height starting around C-16 is a characteristic of this particular oil as can be seen in the injection trace a t the top of Figure 4.The drastic reduction in spike height starting around C-22 is due, however, to reduced transfer efficiency and the transfer cut-off appears to occur a t about C-25. Extending the desorption time from 5 to 10 minutes does not extend this limit. I t should be noted that some species with molecular ANALYTICAL CHEMISTRY, VOL. 48,
NO. 3,
MARCH 1976
483
_
weights greater than the equivalent of C-25 can nevertheless be expected to transfer if they have especially high volatilities. The most common example of this is the general family of silicon derived materials. A compilation of a number of these appears in reference (2). At present, this device has been used to run over 100 samples from sources as diverse as missile guidance system head spaces and the components of a wintergreen mint as found on the breath of one of the authors. In addition, the samples have been desorbed from a number of substrates including porous polymers, charcoal, and Fiberglas.
LITERATURE CITED (1)A. Zlatkis, H. A . Lichtenstein, and A. Tishbee, Chrornatographia, 6, 67 (1973). (2) W. Bertsch, A. Zlatkis, H. M. Liebich. and ti. F. Schneider. J. Chromatogr., 99,673 (1974). (3)J. P. Mieure and M. W. Dietrich, J. Chromatogr. Sci., 11, 559 (1973). (4)T. A. Beliar, M. F. Brown, and J. E. Sigsby, Jr., Anal. Chem., 35, 1924 (1963). (5) R. E. Kaiser, Anal. Chem., 45, 965 (1973). (6)A. Raymond and G. Guiochon, Environ. Sci. Techno/., 8, 143 (1974). (7)F. Bruner, P. Ciccioli, and F. DiNardo, J. Chromatogr., 99, 661 (1974).
RECEIVEDfor review August 15,1975. Accepted November 24. 1975.
N-per methylation of Polyamines for Gas Chromatographic and Mass Spectrometric Analyses Angelo G. Giumanini,' Giuseppe Chiavari, and Franco L. Scarponi Centro di Gascromatogra fia-Spettrometria di Massa and lstituto Chimico G. Ciamician, University of Bologna, 40 126 Bologna, /taly
A method of derivatization of primary and secondary polyamines in aqueous solutlon employing the formaldehydesodium borohydride system to yield N-permethylated polyamines suitable for GLC/MS analysls Is reported. It offers a set of important advantages over traditional procedures for polyamine analyses. First, the method uses well known, inexpensive, and relatively safe reagents and trivial laboratory procedures, which do not require specially tralned personnel. Second, the possibility of performing the derivatiration directly in aqueous solution exists. Moreover, the workup of the reactlon mixture would automatically eliminate compounds such as amino acids and any nonbasic material. Third, the gas chromatographic properties of the N-permethylated polyamines are Ideal. They are volatile and therefore do not require high temperatures and do give nicely shaped peaks on most stationary phases. Finally, the mass spectra of N-permethylated polyamlnes exhibit parent ions at 70 eV of low but detectable intensity. There are peaks of great intensity which can be used for selected ion recording of the GLC profile.
The biochemistry of polyamines with primary and secondary amino groups and especially their roles in normal and neoplastic growth of tissues is now experiencing a high tide of interest among biological and biomedical workers ( I ) . Unfortunately, the present methods for the qualitative determination and the quantitative assay of polyamines rest on a complicated extraction of these extremely hydrophilic compounds with an organic solvent, which, however, is far from being efficient and selective. In fact, the solution obtained must be further manipulated extensively to obtain a mixture suitable for derivatization to compounds amenable to gas chromatographic analysis. Common derivatizations are accomplished with trifluoroacetic anhydride or, less frequently, with trimethylsilyl chloride. Both reactants are costly and must be handled with special precautions because of their reactivity with moist air and their dangerous properties. The compounds to be reacted with them must be absolutely dry and the derivatives themselves are water sensitive. Derivatization provokes a rather large increase in the molecular weight and introduces polar 484
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
bonds: a decrease of the volatility can be expected. These problems become acute with N-dansylation (2-4), whose derivatives cannot usually be chromatographed. N-Silyl and N-trifluoroacetyl polyamines generally do not exhibit visible parent ions. In view of these drawbacks, which clearly demand quicker and more accurate methods for polyamine analysis, which would definitely speed up research in the field, we looked for a procedure of d i r e c t derivatization in water, followed by s e l e c t i v e extraction with an organic solvent suitable for GLC and, eventually, GLC-MS analyses. The derivatives of choice to ensure low molecular weight, stability to water and air, volatility and excellent GLC and MS properties were expected to be the N-permethyl polyamines.
EXPERIMENTAL Instruments. A variety of gas chromatographs equipped with flame ionization detectors, employing single column systems and temperature programming was used. Injector temperature was kept about 280 "C. Nitrogen was used as a carrier gas and helium replaced it in the GLC-MS analyses. The following stationary phases were used: A) Versamid 900 5%-KOH 5%, B) Carbowax 20 M 10%-KOH 5%, C) OV 17 3%, D) Carbowax 20 M lo%, and E) SE 52 5%, all supported on Chromosorb W (80-100 mesh). Mass spectra were recorded in the range 15-70 eV with an LKB 9000 gas chromatograph-mass spectrometer with chamber temperature of ca. 290 O C and separator temperatures of 280-310 "C. Analyses. All synthetized products were isolated by conventional techniques, compared with specimens obtained by a different route, when feasible, and identified with the usual spectroscopic and chemical analyses, which agreed with reported characteristics, whenever available. A full report with the properties of all the permethylated polyamines will be published later. Materials. All polyamines 1-9 were purchased from Merck (Darmstadt, DBR), sodium borohydride and other common reagents and solvents were obtained from J. T. Baker, and the stationary phases and supports were available from C. Erba (Milan, Italy). Procedures. T h e experimental details about the N-methylation tests with reagents other than sodium borohydride-formaldehyde will be reported elsewhere. This is the typical procedure for the N-permethylation of polyamines 1-9. A solution of the amine (1 equiv NH) to be methylated and 40% aqueous in 3 M aqueous sulfuric acid (0.55 mol/") formaldehyde (3.5 mol/") was treated with solid sodium borohydride (2.1 fw/NH) added in small lots with accurate temperature
