Ind. Eng. Chem. Res. 1994,33, 1259-1263
1259
Absorption Processes of n-Butenes in Sulfuric Acid. 1. Determination of Di-sec-butyl Sulfate, Di-sec-butyl Ether, and sec-Butyl Alcohol by High-Resolution Gas Chromatography Jose L. Mazzei, Francisco R. de Aquino Neto,' and Jose L. F. Monteiro Programa de Engenharia QutmicalCOPPE, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco G, Sala 115, CEP 21949-900 Rio de Janeiro, Brazil
The n-butene derivatives, di-sec-butyl sulfate, di-sec-butyl ether, and sec-butyl alcohol, ordinarily present in the process of olefin absorption in sulfuric acid solutions, were determined by highresolution gas chromatography (HRGC)with SE-54as the liquid phase and flame ionization detection. The application of this chromatographic procedure is very important to the study of industrial catalytic processes which involves absorption stages as in the alkylation of isoparaffins with n-butenes and in the indirect acid hydration to sec-butyl alcohol.
Introduction Di-sec-butyl sulfate (DBS) is obtained in processes involving the absorption of n-butenes in sulfuric acid at high concentrations. Other n-butene derivatives such as sec-butyl ether and alcohol are also formed. Indirect hydration of n-butenes to sec-butyl alcohol (Lacy, 1931; Engs and Moravec, 1932; Katsuno, 1941; Robey, 1941; Nippon, 1969; Jorn, 1971; Schmidt, 1981) and alkylation of isoparaffins with these olefins (Goldsby, 1971;Albright et al., 1977; Albright et al., 1988) are examples of such processes. The formation of DBS is favored at low temperatures (-20-0 "C) (Albright et al., 1977) and with an excess of olefin (Engs and Moravec, 1932; Katsuno, 1941;Albright et al., 1988;Pardini, 1991). Over the 1980s the world-wide consumption of n-butenes to produce secbutyl alcohol by the indirect hydration process was around 600 thousand metric tons per year. The formation of DBS and di-sec-butyl ether (SBE) as byproducts in these industrial processes is undesirable. Therefore, their quantitation would allow investigation on optimization of these processes as well as gathering of DBS toxicological data. Albright et al. (1977) tried to characterize, by gas chromatographic analysis (GC), the residual n-butene content in the organic phase after absorption in concentrated sulfuric acid at -20 "C, but DBS (also contained in the organic phase) decomposed to n-butenes during the GC run (Albright et al., 1988). The samples were not previously treated. DBS decomposition takes place through hydrolysis to the corresponding monoester, according to reaction 1,which further decomposes to HzS04 and n-butenes (Katsuno, 1941). Also, dimethyl sulfate (RO),SO,
+ H,O
.sROH
+ ROS0,H
(1)
R = alkyl radicals (DMS) hydrolysis by atmospheric moisture has been observed, upon its collection from the atmospheric air by solid sorbenta (Lee et al., 1980). DBS determination by an indirect titrimetric procedure was reported by Albright et al. (1988). On the other hand, GC procedures have been used for the determination of dimethyl and diethyl (DES) sulfates.
* T o whom correspondence should be addressed Departamento de Qufmica Orgllnica-Instituto de Qufmica Universidade Federal do Rio de Janeiro, CT, B1. A, Sala 607, Ilha do FundAo, Rio de Janeiro 21949-900, Brasil.
Table 1. Packed Chromatographic Columns Used To Determine Dimethyl (DMS) and Diethyl (DES) Sulfatee phase support compd detectop re@ DESGSE Chromosorb W DMS MS 1 ov-101 Supelcoport DMS, DES FPD 2 FID 3 Apiezon L Chromosorb P DMS FPD 4 Ucon Chromosorb HP DMS TCD 5 XE-60 Inerton AW DMS FIDand 6 Gas Chrom Q DMSC OV-17 and Unisole 400 MS OV-330 Chromosorb W AW DMS FIDand 7 FPD a FID, flame ionizationdetector; FPD, flame photometric detector selectiveto sulphur; TCD, thermal conductivity detector; MS, mass spectrometer. 1, Ellgehausen, 1974, 1975; 2, Gilland and Bright, 1980; 3, Sidhu, 1981; 4, Toro, 1981; 5, Zheltukhin et al., 19&1; 6, Masuokaetal.,1988;7,Fukuietal.,1991. Thissulfatewasobtained from derivatization of sulfuric acid by silver oxide and methyl iodide.
*
Table 2. Capillary Chromatographic Columns Used To Determine Dimethyl (DMS) and Diethyl (DES) Sulfates ahase laver (um) comDd detectop refb 0.35 DMS FID, FPD, and MS 1 SE-52 1.5 DMS,DES FID and FPD 2 J&W DB-1 J&W DB-1 5 DMS FID 3 Megabore ~~~~
a Acronyms defined in previous Table. b 1,Lee et al., 1980;2,Diiblin and ThBne, 1988; 3, Seymour, 1989.
The high toxicity of these sulfates demands strict control of their concentrations in the workplace and atmospheric environments. These GC procedures are sensitive enough to detect the threshold limit values adopted by the American Conference of Governmental Industrial Hygienists (Gilland and Bright, 1980,Fukui et al., 1991;Sidhu, 1981), the Environmental Protection Agency (Lee et al., 1980),or their European counterpart (Diiblin and ThBne, 1988). The methods usually involve the enrichment of these sulfates by thermal desorption (Diiblin and ThBne, 1988) or by extraction with solvents (Ellgehausen, 1974, 1975;Lunsford, 1978, Gilland and Bright, 1980;Lee et al., 1980; Sidhu, 1981; Toro, 1981; Fukui et al., 1991) after trapping on solid adsorbents; the target compounds were then analyzed by GC. Chromatographic columns used in those studies are given in Tables 1(packed columns) and 2 (capillary columns). As a matter of fact only two studies were performed by high-resolution gas chromatography (HRGC)(Lee et al., 1980;Dublin and ThBne, 1988). These tables also show the detectors used to quantitate DMS and DES by GC. Both external calibrations (Zheltukhin et al., 1984; Dublin and Thone, 1988; Fukui et al., 1991)
0888-5885/94/2633-1259$04.50/00 1994 American Chemical Society
1260 Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994
solvent peak (methanol or methyl isobutyl ketone) due to their small retention time difference, whereas determination by FPD resulted in a sharp peak for this sulfate (Lee et al., 1980;Fukui et al., 1991). The present work introduces a quantitation procedure, by HRGC, of DBS obtained by the absorption of n-butenes in concentrated sulfuric acid at low temperatures. Prior removal of the monoester, water, and acid contaminants eliminates DBS decomposition. SBE and sec-butylalcohol are also analyzed.
Experimental Section IC)
I (d)
p.
If'
and internal standards (Masuoka et al., 1988;Seymour, 1989)have been used. The higher sensitivity of the flame photometric detector (FPD) selective to sulfur on identification of DMS, when compared to that of the flame ionization detector (FID),was reported by Lee et al. (1980) and by Fukui et al. (1991). The lower sensitivity of the FID is due to the low ponderal contents of carbon and the high oxidation state of that compound. This detector should have an increased relative molar sensitivityto larger aliphatic sulfates, as indicated by the minimum detectable quantity presented for DMS and DES by Diiblin and Thiine (1988). Some GC methods for DMS determination by FID resulted in the DMS peak overlapped with the
1 " ' ' 5.5
5.6
""~""'""~""~"" w4.
4.0
3.
Reagents. Concentrated sulfuric acid was obtained from Pro-Analysi (analytical grade, 9598% 1. Sec-butyl alcohol was purchased from Grupo QuImica (analytical grade, 95 % ). Analytical-reagent grade dimethyl sulfate (VETEC) and diethyl sulfate (MERCK) were twice distilled at reduced pressure over calcium carbonate and analyzed by HRGC coupled to a mass spectrometer (HRGC-MS). Analytical-reagent grade carbon tetrachloride (Pro-Analysi) was washed with KOH in ethanol, washed with concentrated sulfuric acid until the washings became colorless, neutralized, and then dried over anhydrous calcium chloride and distilled. SBE was obtained from an industrial effluent together with several lower alcohols. The effluent was collected from a sec-butyl alcohol production plant (Oxiteno Ind. Com.) by absorption of n-butenes in sulfuric acid solution. 43% w/w, neutralThe effluent was washed with ized, and distilled in spinning-bandcolumns. The distillate was analyzed by infrared spectroscopy and by HRGC-MS presenting 98% w/w purity of SBE. It was also characterized by 'H-NMR. A mixture of 2-butenes was prepared by acid dehydration of sec-butyl alcohol with HzS04 60% (Young and
I
3.
2.:
I
I
I
I
0.
I
I
0.
m
Figure 2. 'H-NMFt spectrum of di-sec-butylsulfate standard diseolved in CDCk. Varian VXR-300 magnetic resonance spectrometerat 7.05 T magnetic field (300MHz to lH nucleus). Note the hqh chemical shift of (a) the proton of the methine group adjacent to the sulfate group, (b)the methylene group signal, (c) the methyl group signal in the @-position,and (d) the methyl group signal in the yposition relative to the sulfate group (Albright et al., 1988).
j,
Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994 1261
41
195
i
P
3R
115
m/z
46
30
lee
'
d 0
161
.
8
0
I
8
16
. -0
195 It0
2R0
Figure 3. Mass spectrum of di-sec-butyl sulfate on a HRGC-MS run. Hewlett-Packard5880gaschromatographconnectedtoHewlettPackard 6987 mass spectrometer. Chromatographic conditions are described in the Experimental Section. The mass spectrometer was operated at an ionizingenergy of 70 eV and was continuously scanned from 50 to 500 atomic mass unit (u) at 300 u/s. Probable fragmenta are illustrated.
Lucas, 1930) under reflux. According to these authors, this mixture contains around 42% of cis-2-butene and 58% of the trans-isomer. This 2-butenes mixture was kept in the liquid state in a lecture bottle. Another mixture of 2-butene isomers (The Matheson Co. Inc.) was used as a chromatographic standard. DBS was synthesized according to a procedure reported in the literature (Katsuno, 1941; Pardini, 1991): The lecture bottle with 2-butenes was cooled with dry ice, and the olefin was slowly added to concentrated sulfuric acid, at 0-5 "C, in a round bottom flask with magnetic stirring. A cold finger condenser with a dry ice/ethanol mixture kept the 2-butenes under reflux. The absorbate so obtained was stirred for 1h between -40 and -30 "C and then washed with saturated sodium sulfate solution until neutrality and stored at -1O/O "C over anhydrous sodium carbonate. Washing with water was avoided due to the formation of a stable emulsion. This treated absorbate is exempt of acid contaminants, permitting the analysis by HRGC. Elimination of light contaminants in the treated absorbate was performed by simple volatilization a t 60 OC under reduced pressure (1mmHg) over anhydrous calcium carbonate, resulting in a yellowish raw sulfate with 9798% DBS. The DBS standard was obtained through distillation of the raw sulfate a t 65 "C/0.35 mmHg, resulting in acolorless liquid, characterized by its FTIR spectrum (Figure 1)as compared to Albright et al. (1988), Pardini (1991), and band assignment following Detoni and Hadii (1957). 'HNMR (Figure 2) and HRGC-MS (Figure 3) completed the identification. Di-seobutyl Sulfate Standard Solutions. DBS standard solutions ranging in concentration from 38 pg/ mL to 3.70 mg/mL in carbon tetrachloride (CCl4) were prepared gravimetically in 10.00 mL glass volumetric flasks. Similarly, SBE standard solutions were prepared ranging in concentration from 57 pg/mL to 2.50 mg/mL. Instrumentation and Analytical Conditions for Calibration. The gas chromatographic analyses were conducted in a Hewlett-Packard 5890 gas chromatograph coupled to a Hewlett-Packard 339611 integrator. The column was a glass capillary one (13.5 m long, 0.33 mm i.d.) coated with SE-54 stationary phase (0.3-pm film thickness), with deactivated fused silica retention gaps (30cm long) at both ends of the column. Conditions: flame ionization detector at 260 "C, with air at 2.8 kg/cm2 and
I 16
Figure 4. Chromatograms of (a) a mixture of treated absorbate, dimethyl, and diethyl sulfates, (b) di-sec-butyl sulfate, (c) di-secbutyl ether, (d) sec-butyl alcohol standards, and (e) typical treated absorbate. Analytical conditions as described in the experimental section except for the chromatogram in part a that was obtained at 10 OC/min heating rate. The marked peaka correspond to (S)CC4 as solvent, (M) dimethyl sulfate, (E) diethyl sulfate, (1) di-sec-butyl sulfate, (2)di-sec-butyl ether, (3)sec-butyl alcohol, and (4) 2-butene isomers. Table 3. Chromatographic Analysis of Homologous Sulfates. sulfuric diester dimethyl diethyl di-sec-butyl di-n-butyl
tR t R (min)
nb 1 2 4 4
- tRDM8)
n - nDm
2.018 3.881 1.863 7.630 -1.871 7.607e 1.863 a Conditions are described in Experimental Section. Where n corresponds to the general molecular formula of aliphatic sulfates: (C,Hb+l)zSO,. Calculated from the h e a r relationship of t R versus n(Ciola, 1973;Jennings, 1980).
*
hydrogen at 1.8 kg/cm2;a split/splitless injector at 260 OC with split ratio of 1/20, with an empty splitless-type liner. Hydrogen was used as carrier gas a t 50 cm/s. The oven was programmed from 40 to 50 "C at 2.5 "C/min then to 150 "C a t 8.0 "C/min. Injection volume: 0.8 pL. Attenuation: 25; amplifier range: 2". Results and Discussion
Preliminary Analyses. The stability of DBS under HRGC was checked through GC analyses of the raw sulfate solution in n-heptane, by cold on-column injection at low temperature oven programming (40-100 OC at 2.5 "C/ min), and by the routine conditions above-with split/ splitless injector at 260 "C. Identical results of these analyses demonstrated no DBS decomposition for the treated samples used in this work, contrary to the results
1262 Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994 A t R (Elo/Ell)
= 4 . 9 9 min
AtR (Ell/Elz)
= 4 . 8 2 min
T
0.00 0.00
I .oo
2.00
3.00
4.00
mg/mL in C C l l
Figure 6. Calibration graph of di-sec-butyl sulfate (DBS) and disec-butyl ether (SBE). For analytical conditions see Experimental Section. Table 4. Calibration Curves and Repeatability Parameters of HRGC Di-sec-butyl Sulfate and Ether Determination. parameter DBS SBE 1.27 X 105 angular coefficient (mg/rnL)-l 2.28 X 106 -1.02 x 102 5.45 x 103 linear coefficient correlation coefficient 0.9996 0.9998 0.038/3.70 concentration range (mg/mL) 0.057/2.50 repeatability: 1.4 concentration (mg/mL) 0.60 k0.039 h0.014 standard deviation (mg/mL) (2.8% ) (2.3%) 4 4 number of determinations a
Wll2(El0)
= 0.10 mm
W,,2(Ell)
= 0.1 1 mm
U,/2(El,)
= 0.11 mm
u
u1
C 0
eu
D
L
k
J
0
u u
J
v
JL
Conditions are described in the Experimental Section.
of Albright et al. (1977)whose samples of the organic phase after absorption contained acid contaminants. The DBS peak was identified by analysis, under the analytical conditions proposed but at 10 OC/min heating rate, of a mixture of treated absorbate, DMS,and DES in CC4(Figure 4a). Retention times (tR) are shown in Table 3. From the quasi linear tRversusnumber of carbon atoms relationship (Ciola, 1973; Jennings, 1980) the retention time for di-n-butyl sulfate was calculated. Table 3 shows a good agreement between the retention time of peak 1 (Figure 4a) and the calculated one. Therefore, this peak should be a C4 disubstituted sulfate. This was later confirmed by comparison with the t~ of standard DBS-Figure 4b. With this proposed chromatographic method, it is possible to analyze DBS as well as lower sulfates as symmetric peaks without overlapping with the solvent (CC4) (Figure 4a), contrary to what occurred on analyses of lower sulfates by other chromatographic methods with application of FID (Lee et al., 1980; Fukui et al., 1991). Insufficient separation of the diastereoisomeric sulfates (Figure 4b), formed on absorption, contrasts with the resolution of the diastereoisomeric ethers (Figure 4c). HRGC analysis of the treated absorbate solution in C C 4 (Figure 4e) showed that sec-butyl alcohol (Figure 4d) was not present, possibly due to its extraction by the acid phase during absorption. SBE, found in the treated absorbate (Figure 4e), can be formed in the olefin absorption stage (Nippon, 1969; Schmidt, 1981) or can originate from the 2-butenes production stage (Drake and Veitch, 1935).The olefin was characterized by its tR determined from analyticalgrade 2-butene (cis- and trans-isomers) solutions in CClr. In these analytical conditions, separation of 2-butene isomers does not occur.
i,
i'0
d0
1
30
tR (min) Figure 6. Chromatogram of the Grob-teat solution of the SE-54 column used. Composition of the Grob-testsolution and respective symbols, 2,3-butylene glycol, D; decane, Clo; 1-octanol, ol; 2,6dimethylphenol, P; 2-ethylhexanoic acid, S; 2,6-dimethylaniline,A; dodecane, (212; methyl caprate, 4 0 ; dicyclohexylamine,am;methyl undecanoate,Ell; and methyllaurate,El2 (Grob et al., 1981;Cardoso and Aquino Neto, 1986).
Calibrations. Calibration graphs for DBS and SBE (both diastereoisomers taken together) were prepared by plotting peak area versus concentration in mg/mL. The regression lines were fitted by the least-squares method. As shown in Figure 5, the calibration graphs are linear over the concentration range presented in Table 4. The standard deviations and regression coefficients are also listed in Table 4. The results obtained for both DBS and SBE revealed that they can be determined by HRGC on SE-54 using a FID. The low relative standard deviations show the good precision of this method. The correlation coefficients demonstrate the linear relationship between concentration in CC4 and detector response for the concentration range studied. At low concentrations, the correlation Coefficients are also representative (0.9991 for DBS in 0.038-0.380 mg/ mL range and 0.9982 for SBE in 0.057-0.570 mg/mL range). This HRGC method also determines sec-butyl alcohol, which is the most important byproduct in acid hydration processes of n-butenes. Evaluation of Column Performance Along the Analyses. The evaluation of column performance is important to verify possible sample effects over the inertia and activity of the stationary phase during the GC runs.
Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994 1263 To evaluate the column performance, Grob-test solutions (Grob et al., 1981; Cardoso and Aquino Neto, 1986) were injected, periodically,always after conditioning the column at 300 OC for 15 min. A typical chromatogram is shown in Figure 6, and the initial value of Trennzahl (TZ, "separation number") has not changed after 31 injections of DBS-containing samples. The shape of the peaks was also unmodified. These results highlight the stability of the chromatographic stationary phase during the GC runs with DBS.
Conclusion The analyses of di-sec-butyl sulfate, di-sec-butyl ether, and sec-butyl alcohol, in absorbates obtained from the reaction of n-butenes with sulfuric acid at low temperatures, may be performed by HRGC with excellent resolution and precision. The method also encompasses the analysis of lower carbon number sulfates. A cleanup procedure was developed to avoid the decomposition of di-sec-butyl sulfate during the GC run, as reported by previous authors. This method should be of great help on process control and studies for process development.
Acknowledgment We are grateful to Petrobrhs Qulmica (Petroquisa) for the literature survey, to Oxiteno Ind. Com. for the supply of industrial effluents, to Rosane A. S. San Gil, and the Divisgo de Quimica do Centro de Pesquisas e Desenvolvimento Leopoldo A. Miguez de Mello (DIQUIM/CENPES/ Petrobrb) for the analyses of 'H-NMR. Registry No.: The following registry numbers were supplied by the author: DBS, 63231-73-2; SBE, 6863-587; 2-butene, 107-01-7;1-butene, 106-98-9;sec-butyl alcohol, 78-92-2; sulfuric acid, 7664-93-9;DMS, 77-78-1; DES, 6467-5.
Ellgehausen, D. Bestimmung von Dimethylsulfat in Luft in ppbBereich durch Gekoppelte Gas-Chromatographic/Massenspektrometric (Determination of Dimethylsulphate in the Air in the p p b h g e by Coupled Gas Chromatography/MaasSpectrometry). Fresenius' Z. Anal. Chem. 1974,272, 284. Ellgehausen, D. Determination of Volatile Toxic Substances in the Air by Means of a CoupledGas Chromatograph-MassSpectrometer System. Anal. Lett. 1975,8,11. Engs, W.; Moravec,R. Z.Production of Dibutyl Sulphate. US. Patent US 1854581, 1932. Fukui, S.; Morishima, M.; Ogawa, S.; Hanazaki, Y. Determination of Dimethyl Sulphate in Air by Gas Chromatography with Flame Photometric Detection. J. Chromatogr. 1991,541, 459. Gilland,J. C., Jr.; Bright, A. P. Determination of Dimethyl and Diethyl Sulfate in Air by Gas Chromatography. Am. Znd. Hyg. Assoc. J. 1980,41,459.
Goldsby,A. R. Separate Recovery of Diisopropyl and Dibutyl Sulfate in an Alkylation Acid RecoveryProcess. US. Patent US 3742081, 1971.
Grob, K.; Grob, G.; Grob, K., Jr. Testing Capillary Gas Chromatographic Columns. J. Chromatogr. 1981,219, 13. Jennings, W. Gap Chromatography with Glass Capillary Columns; Academic Press: New York, 1980. Jorn, E. Improvements in the Manufacture of Alcohols. British Patent Brit 1373211, 1971. Katauno, M. Synthesis of Secondary Butyl Alcohol from Normal Butylenes. I 11. Kogyo Kagaku Zasshi 1941,44,275. Lacy, K. B. Process of Reacting Olefins with Sulphuric Acid. U.S. Patent US 1991948,1931. Lee, M. L.; Later, D. W.; Rollins, D. K.; Eatough, D. J.; Hansen, L. D. Dimethyl and Monomethyl Sulfate: Presence in Coal Fly Ash and Airbohe Particulate Matter. Science 1980, 207, 186.Lunsford, R. A. Determination of Dimethyl Sulfate in Air. Presented at the American Chemical Society's 175th National Meeting, Anaheim, 1978. Masuoka, N.; Ubuka, T.; Kinuta, M.; Yoshida, S.; Taguchi, T. Gas Chromatographic Determination of Sulfuric Acid and Application to Urinary Sulfate. Acta Med. Okayama 1988,42,247. Nippon Oil Company. Improvements in or Relating to Process for the Production of Alcohols. British Patent Brit 1174387, 1969. Pardini, V. L. Personal Communication, Instituto de QuImicdUSP,
-
1991.
Robey, R. F. Reaction Product of Olefins with Sulfuric Acid. Znd. Eng. Chem. 1941,33,1076. Schmidt, R. J. Hydration of Olefins. U.S.Patent US 4393256,1981. Literature Cited Seymour, M. Determination of Residual Dimethyl Sulphate in a Lipophilic Bulk Drug by Wide-Bore Capillary Gas ChromatogAlbright, L. F.; Doshi, B.;Ferman, M. A.; Ewo, A. Two-step Alkylation raphy. J. Chromatogr. 1989,463,216. of Isobutane with Cd Olefins: Reactions Of C4 Olefinswith Sulfuric Sidhu, K. S. Gas Chromatographic Method for the Determination Acid. In Recent Advances in Alkylation; Albright, L. F.; Goldsby, of Dimethyl Sulfate in Air. J. Chromatogr. 1981,206,381. A. R., Co-chairmen; Preprints, Division of Petroleum Chemistry Toro, P. Analisis de Algunos Compuestos Organicos con Azufre por 22; American Chemical Society: Washington, DC, 1977, p 369. Albright,L.F.;Spalding,M.A.;Nowinaki,J.A.;Ybarra,R.M.;Eckert, Cromatogrdia Liquido-Gas (FPD-Detector) (Analyses of some Organic Compounds Containing Sulphur by Gas-Liquid ChroR. E. Alkylation of Isobutane with Cd Olefins. 1. First-Step matography). Bol. SOC.Chil. Quim. 1981,26, 59. Reactions Using Sulfuric Acid Catalyst. Znd. Eng. Chem. Res. Young, W. G.; Lucas, H. J. The Composition of Butene Mixtures 1988, 27, 381. Resulting from the Catalytic Decomposition of the Normal Butyl Cardoso, J. N.; Aquino Neto, F. R. Testes de AvaliaGBo de Colunas Alcohols. J. Am. Chem. SOC.1930,52, 1964. Capilares para Cromatografia com Fase Gasosa de Alta ResoluMo Zheltukhin, I. A,; Glybochko, N. I.; Sobolev, A. S.; Maslakova, T. S. (Evaluation Testa of Capillary Columns for High Resolution Gas Gas-Chromatographic Determination of Dimethyl Sulfate. Znd. Chromatography). Quim. Nova 1986, 9,58. Lab. 1984, 50, 132. Ciola, R. ZntroduGBo a Cromatografia em Fase Gasosa (Introduction to Gas Phase Chromatography); EDUSP: Silo Paulo, 1973. Received for review August 12, 1993 Detoni, S.; Hadki, D. Infra-red Spectra of Some Organic SulphurRevised manuscript received January 6, 1994 Oxygen Compounds. Spectrochim. Acta 1957,19,601. Accepted January 25, 1994. Drake, N. L.; Veitch, F. P. Jr. The Action of Sulfuric Acid on Butanol2. J. Am. Chem. SOC.1935,57,2623. DOblin, T.; ThBne, H. J. Thermal Desorption-Capillary Gas Chromatography for the Quantitative Analysis of Dimethyl Sulphate, Abstract published in Advance ACS Abstracts, March 15, Diethyl Sulphate and Ethylene Oxide in the Workplace. J. Chromatogr. 1988,456, 233. 1994. @
