nn total Chlorine: 8.5-105
2 I air
I
I
tS Iminl
t,
min
20
10
Figure 3. Sample, 2-1. Compressed cylinder air; detector, FID, gradient tube 25-cm Dexsil GC 300 on Chromosorb AW H M D S . Cryogenic TGC from -80 to 4-150 "C on 4-m column Silicone oil DC 200 on Kieselgur Camag
By eluting a t very limited temperature ranges, the compounds analyzed represent only a fraction of all that have been enriched. Backflushing a t higher temperatures is the clean u p procedure for the gradient tube. This again makes clear that environmental analysis done this way is limited in the type of contaminants measurable.
CONCLUSIONS Micro fog is often produced when cooling flowing gases too suddenly or to too low a temperature even in the ppb-concentration range, where the micro fog cannot be seen. This leads to erratic results. Even when using freshly activated molecular sieves 3 A, 4 A, 5 A, and 13 X in a 4-m column, 4-mm diameter, stainless steel, kept a t the temperature of liquid nitrogen, a gaseous sample contaminated with hydrocarbons flowing a t 2 l./hr, can loose micro fog representing a constant loss of about 10 ppb hydrocarbons in this gas. In other words, this long molecular sieve bed cannot clean up the flowing gas to better than 10 ppb contaminants of hydrocarbon type or: when using such a trap, the analytical result will have a noticeable systematic error. We used a tempera-
30
n 1
20
10 I 4-
Figure 4. River water, 100-gram sample, detector Dohrman coulometer CI, enriched and separated as in Figure 3, contarninants transfer by clean nitrogen 4 lL/hr flow rate for 10 minutes at 20 "C. Blind value as good as in Figure 2
ture gradient system, which helped analyze such a gas behind the 4-m long cold trap. This shows the power of gradient enrichment for preventing micro fog production. By enrichment of many liters of air, one obtains a lo-, or 15-, or 20-minute sample as a medium result. This does not fulfill all requirements in environmental analysis; therefore, high speed sample enrichment methods need to be developed, but often a 15-minute value is useful. The temperature gradient can be combined with a gradient in sorbing materials, thus making the enrichment effective for a wider scale of compounds, but often the few-compound enrichment, the very specific enrichment, coupled with multidimensional separation, again enriched after separation by mini gradient tubes-to achieve high rates of grams per second flow-into specific detectors is a powerful tool for correct environmental analysis a t the concentration level where effects really start to influence life quality.
ACKNOWLEDGMENT The author thanks his former employer, Badische Anilin-& Soda Fabrik AG, LudwigshafenjRhein, Germany, for the agreement to publish parts of these results and W. Stoll for his valuable experimental help. Received for review November 29, 1972. Accepted January 29, 1973.
Gas Chromatographic and Mass Spectrometric Studies of S-Alkyl Derivatives of N,N-Dialkyl Dithlocarbamates Francis I . Onuska and Walter R. Boos UniRoyai (Canada) L t d . , Research Laboratories, Guelph, Ontario
In the past decade, gas chromatography has been used as a very powerful analytical technique in the separation of trace amounts of organic compounds. However, it has the disadvantage of being vague in qualitative interpretation of a chromatogram. Mass spectrometry, on the other hand, has the advantage of being unambiguous in the structural identification of organic compounds in extremely minute quantities. Yet, it loses its potential if mixtures have to be identified. The combination of these two techniques, i.e., the identification of components separated by tandem GC/MS, has become close to the ideal solution for residual analysis.
In the course of our investigations into the identification of S-alkylated N,N-dialkyl dithiocarbamates (DTC) in wastewater, we found that a mixture of these compounds can easily be separated by gas chromatography. Gas chromatography has been recently applied to the separation of S-n-propyl N,N-dialkyl dithiocarbamates ( I , 2) and S-methyl and S-ethyl derivatives as a part of a more extensive investigation. These compounds are technically important as herbicides and rubber chemicals. (1) J Hrivhak and V KoneEny, Collect Czech Chem Cornrnun 32, 4136 (1967) ( 2 ) F I Onuska, lntern J Environ A n a / Chem In press
A N A L Y T I C A L C H E M I S T R Y , VOL. 45, NO. 6 , M A Y 1973
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I
1
I
I
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Table I . Retention Indices for S-Alkyl N,N-Dialkyl Dithiocarbamates on Apiezon L at 250 "C R >-CSz-Rz, Mass spectrum No.
Ri
1 2 3
(CH3)zN(CzH5)zNn-(C4Hg)zN-
5 6 15 20 Time, mirutes
25
10
I
Temperature, "C
190
7 8 9 10
270
Figure 1. Chromatogram of S-methyl- and S-ethyl, N,N-dialkyl dithiocarbamates
100
S-methyl N,N-dimethyl dithiocarbamate; 2. S-ethyl N,N-dimethyl dithiocarbamate; 3. S-methyl N.N-diethyl dithiocarbamates; 4. S-ethyl N,N-diethyl dithiocarbamate: 5. S-methyl N,N-di-n-butyl dithiocarbamate; 6. S-ethyl N. N-di-n-butyl dithiocarbamate 1.
60
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-CH3 -CH3 -CH3 -CZH5 (CH3)zN-CZH5 (CzH5)zN~ - ( C ~ H ~ ) Z N - -CZH5 (CH3)zNn-C3H7 (CzH5)zNn-C3H7 ~ - ( C ~ H ~ ) Z N - n-C3H7 n-(CdHg)zNn-C3 H 7
4
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Time,minutes
15
20
40
60
60
I60
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Figure 2. Chromatogram of S-n-propyl-N,N-dialkyl dithiocarbamates
1-4. impurities: 5. S-n-propyl N.N-dimethyl dithiocarbamate; 6. S-n-propyl N.N-diethyl dithiocarbamate; S. S-n-propyl N,N-di-n-propyl dithiocarbamate: 7.S-n-propyl N, N-di-n-butyl dithiocarbamate
Figure 3. Mass spectra of S-methyl N.N-dialkyl dithiocarbam-
EXPERIMENTAL Gas-liquid chromatography (GC) was carried out using a Varian Model 1800 gas chromatograph equipped with a flame ionization detector. The column, 355 cm long and 2.1-mm i.d. was packed with Varaport 80 (80-100 mesh), coated with 10% Apiezon L. Helium was used as carrier gas. The injector and detector temperatures were adjusted to 270 "C and the oven temperature was kept a t 250 "C. Gas chromatography-mass spectrometry (GC-MS) was carried out using a Varian Gnom M a t 111 GC-MS instrument with a slit separator as reported by Brunnee ( 3 ) . The built-in electron impact detector (EID) records the correct chromatogram. The electron energy in EID is 20 eV. The mass spectrometer detector (MSD) produces the ions for the mass spectrometer and has the electron energy of 80 e v . (3) C. Brunnee, L. Delgman, K. Habfast, and S. Meier, " A New GC/MS System." Proceedings of the 18th Annual Conference of the American Society of Mass Spectrometry, San Francisco, Calif.,June 1970, p 8306. 968
ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, MAY 1973
ates
Operating Conditions of Varian Gnom Mat I11 GC-MS. The same column as above was used. The column temperature was kept isothermal a t 190 "C for four and a half minutes, then it was programmed at 4 "C/min to 270 "C. The injector temperature was 240 "C; separator temperature, 240 "C; interface line temperature, 250 "C; amplifier attenuation, 128; helium flowrate, 28 ml/min; chart speed, 50 cm/hr; and injected amount, 1.0 pl. Methyl esters of N,N-dialkyl dithiocarbamic acids were prepared using diazomethane (4, 5 ) , ethyl esters (6) using iodoethane and n-propyl esters using I -iodopropane. Chromatograms of a synthetic mixture of S-methyl and S-ethyl derivatives (Figure 1) and S-n-propyl derivatives (Figure 2) showed that these compounds were completely alkylated each giving a single reaction product. Impurit!es noted in Figure 2 are not side-reaction products but rather starting material and reagents. (4) J . J . Kirkland, Anal. Chem.. 33, 1520 ( 1 9 6 1 ) . ( 5 ) G. Yip, J. A S S . Olfic. Anal. Chem., 45, 367 (1962). (6) F. I . Onuska, unpublished data, 1972.
Table II. Relative Intensities YS. Mass-to-Charge Ratio (rnle) for the Dithiocarbamates Listed in Table I mle
1
2
3
4
15 27 29 34 38 39 40 41 42 43 44 55 56 57 58 59 60 61 69 71 72 73 76 83 85 88 90 91 97 102 103 105 109 111 116 117 119 120 121 122 128 135 144 145 146 147 148 149 150 163 164 165 172 173 177 178 179 180 191 192 193 204 205 206 207 219 220 221 233 247 248 249
4.9
1.9
1.8
3.0
37.6 8.2 11.2
32.2
15.4
28.7
5
6
...
...
44.7
23.0 20.0 34.5 63.9 24.5 22.2 31.4 9.2 12.2 80.8 7.7 22.2 23.4 26.1 6.9 100.0 16.9 11.9 89.3
43.5 13.6 51.7 41.9 37.2 24.2 100.0 17.7
37.6 10.7
24.2 11.9
19.3 19.3 30.6
13.1 17.7 16.1 , . .
10.8 10.9 19.6 17.9 44.7 7.7 7.4 12.5 2.3 3.1 3.1 3.7 6.9 8.0 6.1 9.8 100.0 5.3 6.4 94.7 6.0
13.2 18.0 18.4 53.2 15.7 23.4 34.0 23.4 10.6 55.3 10.3 10.1 15.9 48.9 11.2 100.0 7.2 7.6 48.9
4.5
5.8
2.6 2.1 2.2 72.4 8.1
5.1
...
4.4 6.8 32.2 3.3
11.2
2.6
11.5 9.7 51.7
8.1
9
10
...
38.0 37.6
31.8
... 60.4 46.6
11.7
... 7.6
...
...
2.0
41.4 100.0
... ...
...
3.7
... 2.1 1.6
...
15 32 2 78 100 0
12.8 1.8 3.3 11.0 62.0 6.9
10 07
27.6 31.1
...
...
34.5 19.8 20.7 ...
...
26.3 2.2 3.7
...
...
100.0 4.4 1.
62.4 4.0 1.9
11 4 15 19 8 10 46 08 49 44
54.1 12.0 51.1 9.0 21.3 ...
... ... ... 25.8
11.1
... 0.6
19.0
7.5 8.0 8.8
2.4
55.3 6.6 2.2 48.2 3.1
100.0 8.4 2.6 1.8
1.2 27.3 10.2
20.7 1.9
2.3
4.5 40.8
1.2 11.0 22.2 36.9
...
25.3 0.6 0.6
8
...
12.8 8.4
7.9 14.6 12.8 25.5 6.9 8.1 10.6 2.4 2.1 2.5 2.8 5.1 7.2 6.0 10.6 100.0 4.0 3.9 84.8 3.6 8.8
39.7
7
6.4 4.2 12.3 37.8 4.0 2.3
10.7
44.7
5.6 53.2 4.6
6.6 34.0 4.0
46.7
2.1
24.6 3.0 3.0 17.7
13.8 46.8
7.6 15.3 2.4 1.7
100.0 12.0 5.1
27.4 11.0 4.0 4.0 8.8
15.9
9.4 4.8 1.7
20.1 34.5 6.3 3.9 4.5 1.2
8.3 30.0 7.2 0.7
ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, M A Y 1973
969
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Figure 4. Mass spectra of S-ethyl N,N-dialkyl dithiocarbamates
Figure ates
RESULTS AND DISCUSSION Gas chromatographic retention data for S-alkylated N,N-dialkyl dithiocarbamates are listed in Table I. A non-polar liquid phase such as Apiezon L is quite suitable for separation. The mass spectral data obtained from the peaks eluted from the gas chromatographic column provided fragmentation patterns of the respective S-methyl DTC, S-ethyl DTC, or S-n-propyl DTC depending on the alkylating agent. Figures 1 and 2 illustrate that these derivatives are easily separated by GC. The relative intensities of t h e compounds are listed in Table 11. A significant feature in the spectra of S-methyl-, is S-ethyl-, and S-n-propyl-N,N-dialkyldithiocarbamates the predictable array of intense peaks a t high values and the molecular ion (M+). As can be seen from Figures 3-5, the molecular ion is obvious in the spectra of all dithiocarbamate esters. The relative intensities of (M + l ) + and (M + 2 ) + peaks indicate the presence of sulfur-containing compounds. The size of the molecular ion peak of S-methyl N,N-dialkyl dithiocarbamates depend upon the nature of the N substituents. The shorter the chain in the N,N-dialkyl moiety of the dithiocarbamates, the more intense are the peaks for the molecular ions. S-methyl derivatives lose a fragment ion (M - 15) corresponding to a methyl radical. An additional significant peak in their spectra is the cleavage product of a [CH3-S]+ ( m / e 47) from the molecular ion and the expulsion of [CS,lf ( m l e 76).
S-ethyl DTCs give essentially the same fragmentation pattern with a few minor exceptions, such as the expulsion of ethyl-fragment ( m / e 29) from the molecular ion. N,N-dimethyl- and the N,N-diethyl dithiocarbamates give the base peak belonging to [CS2]+ ( m l e 76). The N,N-di-n-butyl derivative has the base peak a t mle 57 which represents the butyl fragment. A peak a t 29 mass units results from the fragmentation of the ethyl group and was observed in all S-ethyl derivatives. S-n-propyl esters of N,N-dialkyl dithiocarbamates have a frequently observed peak a t [M - 75]+ due to cleavage between the dialkyl thiocarbamyl ion and [R-SI+. These compounds also yield a characteristic peak which is probably produced by y-cleavage of propyl ( m l e 43) or propylene ( m / e 42) from the molecular ion typical for dibutyl dithiocarbamate. The relatively intense peak at ( m l e 44) is observed for all compounds containing dimethylamine moiety. A similar conclusion was reported for zinc salt of N,N-dimethyl dithiocarbamate by Benson and Damico (7). The electron impact-induced fragmentation of the majority of DTC derivatives is consistent with bond rupture directed by the presence of bivalent sulfur in these molecules. However, it is very difficult to draw a simple decomposition path using tandem GC-MS because N ,N-dialkyl dithiocarbamates are thermally very unstable.
970
ANALYTICAL CHEMISTRY, VOL. 45, NO. C , M A Y 1973
5.
Mass spectra of S-n-propyl N,N-dialkyl dithiocarbam-
(7) W. R . Benson and J, N. Damico, J . Ass. Offfc. A n a / . Chem.. 5 1 , 347 (1968).
spectra scanned a t 20 eV and 70 eV. They are also stable up to 250 "C to thermal decomposition.
For these reasons mass spectra of individual 5'-n-propyl DTC were run (8) a t different temperatures and various electron energies using direct inlet for liquid samples on the Varian CH07 analytical mass spectrometer. It seems that S-n-propyl esters are stable to electron impact since there is no significant difference between
ACKNOWLEDGMENT The authors thank UniRoyal Ltd. for permission to publish these results and are grateful to Varian Associates of Canada Ltd. for recording mass spectra. Received for review November 29, 1972. Accepted January 22, 1973.
(8) F. I . Onuska, unpublished data, 1972.
Polar Silicone-Based Chemically Bonded Stationary Phases for Liquid Chromatography Milos Novotny,' Susan L. Bektesh, and Kenneth B. Denson Department of Chemistry, Indiana University, Bloomington, Ind. 47407
Karel Grohmann2 and Wolfgang Parr Department of Chemistry, University of Houston, Houston, Texas 77004
It had been felt for a long time that the stationary phases bonded chemically to siliceous surfaces of chromatographic supports may alleviate many practical problems encountered in gas-liquid and liquid-liquid chromatography. The past several years were, in particular, marked by increased activity within this area of research. The reactivity of surface silanol groups offers three main possibilities for chemical modification: the formation of Si-0-C bonds (through esterification); Si-C-C bonds (obtained, for instance, by the reaction of chlorinated surfaces with either organolithium or Grignard reagents; and Si-0-Si-C bonds (through silylation). The use of these general methods for the modification of both adsorbents ( I ) and glass capillary columns in gas chromatography (2, 3) has been reported. Halhsz and Sebestian (4) esterified Porasil C and described the chromatographic properties of this new packing material. The hydrolytic and thermal instability of ester packings are great disadvantages when compared to silicones. Locke et al. (5) applied Grignard reactions to cover the surface of siliceous beads with benzyl and naphthyl functional groups. However, too few suitable reagents and the possible formation of magnesium occlusion salts during the bonding process make this approach much less realistic than esterification or silylation. In situ polymerization of silane compounds on various solid supports was studied by a number of investigators T o whom a l l correspondence should b e directed. Present address, D i v i s i o n o f Biology, California Institute o f Technology, Pasadena, Calif. 91109. (1) (2) (3) (4) (5)
(6)
(7) (8) (9) (10)
A. V . Kiselev, Advan. Chromatogr., 113 (1967). K. Grob, Helv. Chim. Acta. 51, 718 (1968). M. Novotny and A. Zlatkis, Chromatogr. Rev., 14, 1 (1971). I . Halasz and I. Sebestian, Angew. Chem., lnf. Ed. Engl., 8, 453 (1969). D. C. Locke. J. J. Schermund, and B. Banner. Anal. Chem., 44, 90 (1972). E. W . Abel, 2. H. Pollard, P. C. Uden, and G. Nickless. J. Chrornatogr., 22, 23 (1966). H. N. M. Stewart and S . G . Perry, J. Chromatogr., 37,97 (1968). C. J . Bossart, /SA Trans., 7, 283 (1968). W . A. Aue and C. R. Hastings. J . Chromatogr., 42, 319 (1969). C. R. Hastings. W. A. Aue, and J. M. Augl, J. Chromatogr., 53, 487 (1970),
(6-15). Stewart and Perry (7) prepared a nonpolar chromatographic material by reacting Celite with octadecylchlorosilane and suggested its value for liquid partition chromatography. Following this approach, several packings became commercially available which can be used for reversed-phase separations. Aue et al. published a series of articles (9-12) dealing with the preparation and gaschromatographic properties of nonpolar chemically bonded silicone phases. These articles present the most detailed studies on the mechanism of polymerization on chromatographic supports. Relatively little has been reported on the prepartion of polar silicone chemically bonded phases. Limited availability of commercial silane compounds possessing selective groups in the side chain seems to explain this situation. Bossart (8) was partially successful in the preparation of polar gas-chromatographic packings using certain trimethoxy- and triethoxysilanes. Kirkland described (13) and studied (14) the polar stationary phases with ether and cyanoethyl functions for both gas and liquid chromatography. It is, however, known that the reactivity of silanes is decreasing in the following order: trichlorosilane > dichlorosilane > monochlorosilane > ethoxysilane (16). Consequently, long reaction times and incomplete bonding found by Bossart (8) are not surprising. More recently, Majors and Hopper (15) investigated bonding of a trichlorosilane, possessing a cyano group in the side chain, to highefficiency liquid chromatographic packings. In their recent work, Parr and Grohmann (17-19) synthetized some novel chlorosilanes for the derivatization of an inorganic silica carrier to form the following structure (11) W. A. Aue, C. R. Hastings, J. M. Augl, M. K. Norr, and J. V. Larsen,J. Chromatogr., 56, 295 (1971). (12) C. R . Hastings, W. A. Aue, and R . N. Larsen. J. Chrornatogr., 60, 329 ( 1 9 7 1 ) (13) J. J. Kirkland and J. J. DeStefano, J. Chromatogr. Sci., 8, 309 (1970), (14) J. J. Kirkland, J. Chromatogr. Sci., 9, 206 (1971). (15) R . E. Majors and M. J. Hopper, 160th National Meeting, American Chemical Society, Chicago, Ill., September 1970, paper No. A42. (16) L. C. F. Blackman and R. Harrop, J. Appl. Chem.. 18, 37 (1968). (17) W. Parr and K. Grohmann, Tetrahedron Lett., 1971, 2633. (18) W. Parr and K. Grohmann, Angew. Chem., Int. Ed. Engl. 11, 314 (1972). (19) K. Grohmann, Ph.D. Thesis, University of Houston, 1972. ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, MAY 1973
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