Anal. Chem. 1981, 53, 916-917
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Table I. Comparison of Thin-Layer Chromatography (TLC) and Column Chromatography (CC) Results Aa SHC + UHC ARO %
NSO % recovery % a
Crude oil.
BQ
Db
Ca
EC
TLC
CC
TLC
cc
TLC
cc
TLC
cc
TLC
cc
66.7 21.7 5.6 94.0
54.7 21.4 3.8 80.9
60.0 30.0 8.8 99.7
59.1 30.6 6.7 96.4
63.9 20.2 14.9 98.5
62.6 14.7 13.7 91.0
9.9 28.2 62.2 100.3
6.0 32.5 48.5 87.0
21.9 25.0 48.6 95.2
20.4 27.6 50.4 98.4
Pyrolysis oil.
Rock extract.
SHC+UHC
I
b
C
the column chromatography is not quantitative for SHC + UHC since the heaviest alkanes are eluted with the aromatic fraction. In such a case the TLC technique is more suitable because there is no overlap between the saturated hydrocarbons and the aromatic compounds bands (Figure 4). Another advantage of the technique is that the TLC can be performed without a previous deasphalting which is required when carrying out a column chromatography on petroleum compounds. On occasion, in recent sediments and sometimes even in ancient sediments, unsaturated hydrocarbons are present. As previously quoted, in the described procedure the unsaturated hydrocarbons (UHC) show the same chromatographic behavior as the saturated hydrocarbons and thus provide an interference with the latter. A way to solve this problem is to carry out a second quantitative TLC in order to discriminate between the two types of hydrocarbons (5) (Figure 5). The layers are prepared by using a mixture of silica gel (50 g of silica gel, G Type 60, Merck, for five layers with a coating thickness of 0.5 mm, 5 g of silver nitrate, and 120 mL of water). When dried the plates are activated (1 h at 140 “C) and stored in a dark container until use. Cyclohexane is used again as developing solvent. The resulting bands of saturated hydrocarbons (Rf= 0.7) and unsaturated hydrocarbons (Rf 0-0.5) appear after spraying the layer with berberine sulfate in methanol solution. The recovery of the compounds is carried out by using the method previously described. In this case the adsorbent is extracted with ethyl ether.
LITERATURE CITED CARBON NUMBER-
Figure 5. Discrimination between saturated (SHC) and unsaturated (UHC) hydrocarbons (bitumen).
has a higher boiling point than the chloroform. So, in many cases we have observed a more important loss of the lighter hydrocarbons with the column chromatography procedure. Another difference is seen when samples are rich in high molecular weight saturated hydrocarbons. In some samples
(1) Huc, A. Y.; Roucach6, J.; Bernon, M.; Calllet, G.; da Silva, M. Rev., Inst. Fr. Pet. 1976, 3 1 , 67-98. Chem. Abstr. 1976, 85, 145438~. (2) Castex, H.; RoucachB, J.; Boulet, R. Rev., Inst. Fr. Pet. 1974, 29(1), 3-40. Chem. Abstr. 1074, 8 1 , 17253111. (3) Monln, J. C.; Peiet, R.; FBvrler, A. Rev., Inst. Fr. Pet. 1078, 33, 223-240. Chem. Abstr. 1978, 89, 165852e. (4) Oudin, J. L. Rev., Inst. Fr. Pet. 1970, 25, 3-15. Chem. Abstr. 1970, 73, 68661k. (5) RoucachB, J.; Bouiet, R.; da Silva, M.;Fabre, M. Rev., Inst. Fr. Pet. 1977, 32(6), 981-994. Chem. Abstr. 1078, 89, 11346111.
RECEIVED for review September 29,1980. Accepted January 22, 1981.
Chromatographic Identification and Quantitation of Dimethyl Sulfoxide Wayne A Morris Sanford Regional Crime Laboratory, Florida Department of Law Enforcement, Sanford, Florida 3277 1
As of October 1,1980, the State of Florida has allowed those people licensed to prescribe medication to prescribe dimethyl sulfoxide (Me2SO)for bladder cystitis. As of this time, only one product is approved by the Food and Drug Administration (FDA) for such use. However, so-called “Arthritis Clinics” have begun to dispense MezSO as arthritis pain relievers.
Some of these clinics are dispensing the approved MezSO product improperly, while others are dispensing Me2S0 which is not approved for human use. The author received several such submissions at the Sanford Regional Crime Laboratory with a request to differentiate the approved product from the other products.
0003-2700/61/0353-0918$01.25/00 1981 American Chemical Society
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Anal. Chem. 1981, 53, 917-919
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Table I. Quantitation Results Me,EIO
av % Me,SO
accuracy,
sample
% (w/w)
A1 A2
79.99 81.516 79.910 77.57 79.84 88.41 86.60 87.94 88.08 87.47 47.95 50.45 49.49 49.20
80.78 80.78 79.10 79.10 79.10 87.65 87.65 87.65 87.78 87.78 49.27 49.27 49.27 49.27
0.98 0.97 1.01 1.93 0.94 0.87 1.20
B1 B2 B3 c1 c2 c3
D1 D2 El E2 E3 E4
%
0.33 0.34
0.35 2.68 2.40 0.44 0.14
Preliminary results indicated that refractometry may be used to quantitate the MezSO in solution and that quantitation could distinguish the samples (I). As refractometers are not available a t all crime laboratories, an attempt to quantitate MezSO with readily available instrumentation was made by this writer. This paper reports the results of that work.
EXPERIMENTAL SECTION Reagents. Spectrograde dimethyl sulfoxide, obtained from Eastman Chemicals (Rochester, NY) was used as the standard sample. The FDA-approved Me2S0 solutioin was obtained from Research Industries Corp. (Salt Lake City, 'UT). The methanol and toluene used in this work were analytical reagent grade quality. A 2% aqueous !solution of cobalt(I1) thiocyanate was prepared with 98% cobalt(I1) thiocyanate from Alfa Products (Danvers, MA). A methaiiolic solution of 2 parts of this aqueous cobalt thiocyanate solution to 1part of methanol was used as the visualizing reagent. Apparatus. A Hewlett-Packard (Palo Alto, CA) 5930A mass spectrometer connected to an H/P 5700 gas chromatograph by a membrane separator and equipped with a 6 ft long, coiled glass column prepacked with 3(%OV-1 on 100/120 Gas Chrom Q was used. Data were collected by an H/P 5933A data system coupled to a Tektronix 4012 CRT display and a Tektieonix 4610 hardcopy unit. Thin-layer Chromatography was accomplished with Whatman (Clifton, NJ) LK6DF plates precoated with 250-bm silica gel. Gas chromatography was performed by using a Varian 2700 chromatograph equipped with a dual flame ionization detector and a 6 ft long, coiled glass column prepacked with OV-1 on 100/120 Gas Chrom Q. During operation of this system, nitrogen gas flow was approximately 30 mL/min. The injection port temperature was 250 "C, ithe detector temperature was 270 "C, and the column over temperature was 60 OC. Data were collected and displayed by a Shimadzu CRlA integreting recorder.
Procedure. The identification of Me2S0 was accomplished by using gas chromatography (GC), thin-layer chromatography (TLC), and gas chromatography-mass spectrometry (GC-MS). It was found that addition of a 2% CO(CNS)~ solution to a solution of MezSOresulted in a light blue color and that the prior addition of 1 or 2 drops of methanol heightened this color. TLC was run with a developing solution of 1.5:lOO ammonia/methanol with a run time of 30 min. Methanolic cobalt thiocyanate was used to visualize the chromatogram. The samples used for thin-layer chromatography were diluted with methanol to form a solution of 6 parts MezSOsolution to 100 parta methanol. GC was used for both qualitative and quantitative analyses. The samples were prepared by mixing 1 mL of the Me2S0 solutions and 20 mL of internal standard solution. The internal standard solution was prepared by diluting 2 mL of toluene to 1000 mL with methanol. The integrating recorder was set to perform internal standard quantitation and to determine the weight percent of Me2S0. Mass spectral identification was performed on the samples prepared for TLC. The spectra were obtained by scanning between m / e 40 and 150 at a rate of 108.3 amu/s.
RESULTS AND DISCUSSION The analytical scheme presented is a fairly rapid procedure for differentiating the FDA-approved MezSO solution from other preparations of Me2S0. It had been hoped that some impurity would become obvious with either of the chromatographic schemes employed but this was not the case. This left only quantitation as the means of differentiation. The results of the gas chromatographic quantitation are shown in Table I. As can be seen from the high reproducibility of results, the procedure is reliable. Sample E, the FDA approved solution, is labeled as a 50% by weight solution. The average value of 49.27% represents a 1.46% accuracy. Samples A, B, C, and D were taken from the suspected bottles. The TLC resulted in one spot only which was of a light blue color. Although the background is also blue, a differentiation of colors can be easily made. Furthermore upon drying overnight the background becomes a pinkish red color. In all cases, an approximate R, value of 0.49 was obtained. The retention time from GC a t 60 "C was 1.5 relative to toluene. Although a small amount of water was present in all samples, due to the fact that no extraction was performed on the MezSO solutions, no effect was observed in either the thinlayer or gas chromatography results.
LITERATURE CITED (1) Estes, Dick, Tampa Regional Crlme Laboratory, Florida Department of Law Enforcement, Tampa, FL, Oct 1980.
RECEIVED for review December 1,1980. Accepted February 12, 1981.
Gas Chromatographic Determination of Acids Derived from Phosphorus by Trimethylsilylationi with N ,0-Elis( trimet hylsilyl)trifluoroacetamide Georg Bauer"' and Walter Vogt Instltut fur organische Cheniie der Universitat Mainz, Johann-JoachimBecher- Weg 18-20, D 6500 Mainz, BRD
In many cases, a mixture of acids derived from phosphorus is produced on the hydrcdysis of their polyesters with water ( 1 , Z ) . To get information about the structure of the original polymers, we developed an analytical method which allowed Present address: Boehr inger Mannheim, Control Department,
D 6800 Mannheim 31, BRDl.
the determination of all acids present in the hydrolysates. For that purpose gas chomatography is especially suitable. Yet the direct gas chromatographic analysis is not accessible for multibasic acids derived from phosphorus. Getty, Stone, and Hanson (3) and Wiese and Hanson ( 4 ) reported the gas chromatographic determination of phosphate after its conversion to the corresponding trimethylsilyl derivate with a
0003-2700J81/0353-0917$01.25/0 0 1981 Amerlcan Chemical Soclety
