under these conditions a chemical reaction takes place between H?O?,H+, and NO?- (the radiation yield of NOz- was higher than that of H?Od and all the hydrogen peroxide was consumed. I n the absence of NOn- the peak height of HzOn peaks was always proportional to the H202concentration, obtained when NH4HS04 was used as the eluent. The elution curves of reference solutions of NaNOn, H 2 0 2 , and CH3NOr in N a N 0 3 obtained with 0.1M ("&SO4 are shown in Figure 2. Corresponding curves with 0.1M NH4HS04 are shown in Figure 3. The data obtained indicate that NOn- ions are sorbed only
after neutralization to undissociated "02 molecules. The and radiolytic products-Hz02, NO*- (in the form of "02) CH3NOz-are sorbed o n strongly acid Dowex 50 W-X8 (cationite), and their desorption proceeds in the order of increasing molecular weights as in the case of homologous series of nitroparaffins. The results indicate that chromatopolarography is applicable for the determination of radiolytic products. RECEIVED for review January 5 , 1969. Accepted March 5 , 1969.
Separation of Isotopic Methanes by Gas Chromatography Fabrizio Bruner, G . Paolo Cartoni, and Massimiliano Possanzini Istituto Chimica Analirica, Uniuersita Roma, Rome, Italy
DIFFERENT isotopic molecules can be separated by gas-solid o r gas-liquid chromatography. The partition liquid or the adsorbing medium of the column should be properly selected in order to achieve the best separation in the minimum time of analysis. The required column efficiency for a complete separation of a given pair of isotopic molecules can be theoretically calculated as shown in a previous paper (/). Many hydrocarbons such as paraffins and aromatics have been separated from the corresponding deuterium substituted species (/), and recently some polar deuterated compounds such as C D 3 0 H , C Z D ~ O HCD3COCD3 , have been resolved from the fully protonated ones (2). The separation of methane and deutero-methane has been achieved by several authors. One method consists of a recycling system on a column packed with molecular sieves operating approximately at room temperature (3). An almost complete separation was achieved after a large number of cycles. Gant and Yang (4) reported a partial separation of methanes, partially substituted with deuterium or tritium, o n a long column with activated charcoal in a temperature range between -3.5 and 150 "C. Under the working conditions of all these authors, the retention times decrease, increasing the number of deuterium o r tritium atoms on the molecules. O n the other hand, we have shown ( I ) that, working at very low temperature, the elution order is reversed and the heavier molecules are more retained. An enrichment of carbon isotopes (12C and l a c ) was obtained by Blanc et al. ( 5 ) by gas chromatography of carbon monoxide o n a column packed with molecular sieves. In this paper we report the separation, o n adsorption glass capillary columns, of all isotopic methanes either when the substitution takes place on the carbon atoms o r when the hydrogen is partially or completely substituted by deuterium or tritium. Because, under the selected working conditions, the separation factor between C H I and C H I D is very large, it is shown that the determination of the monodeuteromethane in natural methane is feasible. (1) F. Bruner, G. P. Cartoni, and A. Liberti, ANAL.CHEM., 38,298
(1966). (2) G. P. Cartoni, A. Liberti, and A. Pela, ibid.,39, 1618 (1967). (3) J. W. Root, K. C. Lee, and F. S. Rowland, Science, 143, 676
(1964). (4) P. L. Gant and K. Yang, J . Amer. Chem. SOC.,86,5063 (1964). (5) C. Blanc, C. T. Huynh, and L. Espagno, J. Chromatog., 28,
177 (1967). 1122
ANALYTICAL CHEMISTRY
EXPERIMENTAL
All of the measurements were carried out on a gas chromatographic apparatus prepared for working at low temperatures. The glass capillary column is coiled around an aluminum case and held to a brass plate where the injector with a splitter and the detectors are located. Hydrogen flame and ion chamber detectors have been used, the former as a general detector and the latter for the detection of radioactive compounds. Both detectors are connected to the column outlet through a T-tube. To avoid the effect on peak shape caused by the large ionization chamber volume, nitrogen is added as scavenging gas to the column effluent. The ion detector is a 100-ml chamber operating at room temperature with a flow rate of about 100 mlimin and con.- .. nected to a vibrating electrometer (Applied Physics Corp., Model 31). The glass capillary column was prepared from soft glass tubing and etched, as previously described (6), by passing a 10% solution of NaOH through the capillary which was heated o n a water bath at about 100 "C for 8 hours. After washing with water, alcohol, and ether, the column is dried in an oven at 120 "C under nitrogen. After this treatment a thin layer of active silica is formed inside the capillary column. I n order to deactivate this adsorbing medium to a constant grade, a flow of wet nitrogen, saturated with water vapor from a trap maintained at 0 "C, is passed through until a constant value of the retention volumes is observed. In this way columns of high efficiency are obtained (for a column 47 meters long, 70,000 theoretical plates), and methane shows symmetrical peaks even at very low temperature. A mixture of 7 0 x Np and 3 0 x H e was employed as carrier gas. A mixture of this composition is recommended because use of helium alone at liquid nitrogen temperature, causes a very strong retention of methane. With this mixture some nitrogen is adsorbed o n the silica layer of the column, as can be inferred from the adsorption isotherm of N? on etched glass previously reported (7). At values of the relative vapor pressures pipo between 0.7-0.9 a plurimolecular layer of N2 cFvers all of the surface, and pores with a radius below 80 A are filled. In this way the most active sites of the adsorbent, which are located in the small pores, are blocked, and as a consequence retention volumes are decreased and symmetrical peaks are obtained. (6) F. Bruner and G. P. Cartoni, ANAL.CHEM., 36, 1522 (1964). (7) A. Liberti, "Gas Chromatography 1966," A. B. Littlewood, Ed., The Institute of Petroleum, London, 1967, p 106.
-TIME
(min]
Figure 1. Gas chromatographic separation of a mixture of deuterated and tritiated methanes on a glass capillary adsorption column (47 meters, 0.22-mm i.d.) Temperature: 77 "K; carrier gas: N B70%, He 30z; pressure: 21 cm Hg; flow rate: 1 ml/min; detectors: flame ionization and ion chamber Materials. CD4 and 13CH4( S O X enrichment) were purchased from Merck, Sharp, and Dohme Co., Ltd., Montreal, Canada; CH3D was prepared by the Grignard reaction of CH31 with D 2 0 . The mixture of the other partially deuterated methanes was obtained by X-ray irradiation of a mixture containing 4SX D1, 4SX Xe, and 10% C H I . CT4 was prepared according to the procedure described by White, Campbell, and Payne (8). 14CH4was prepared according to Jordan ( 9 ) . RESULTS
The separation of all isotopic methanes obtained with the glass capillary column at liquid nitrogen temperature is shown in Figure 1. In the upper part of the chromatogram are the (8) D. F. White, I. G. Campbell, and P. R. Payne, Nature, 166, 628 (1950). (9) P. Jordan, Nucleonics, 23, 46 (1965).
radioactive compounds detected by the ion chamber and in the lower part are the stable isotopes monitored by the flame ionization detector. The two chromatograms are not referred to the same injection because the large amount of methane contained in the tritiated methane mixture and IC-methane would have hidden the 13C-methane peak. Methanes with the carbon isotopes 12C, l a c , and l4C are eluted according to their mass, and separation is very small compared with the deuterated and tritiated molecules. This clearly indicates that the isotope effect is very different when the isotopic substitution takes place on the central carbon atom rather than on the peripheral hydrogen atoms. Differences in the retention volumes between the carbon isotopes are consistent with the mass differences. For the deuterated
l
o
c
(
l
'
+
l
/
IrJ I ;,:SO 1350 2.170 233 7,050
!
7,100
1:;l
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I
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-71
Figure 2. Plots of logarithm X lo3of relative retention volumes for consecutive isotopic methanes cs. their mass ratio
__+
TIME (hours)
--
Figure 3. Plots of per cent concentration of deuterated methanes cs. X-ray irradiation time VOL. 41, NO. 8, JULY 1969
1123
species, as previously shown (IO),the elution order is largely affected by temperature; at high temperature there is a n inverse isotope effect and the deuterated species are eluted first. At low temperature (as in our experiments at liquid nitrogen) there is a normal isotope effect and the retention volumes increase by increasing the number of deuterium atoms o n the molecules. The separation between a consecutive pair of deuterium- or tritium-substituted molecules decreases as the mass ratio between each pair approaches unity. There is a linear relationship between the logarithm of the relative retention volumes of consecutive pairs cs. their mass ratio, as shown in Figure 2. Comparing the elution order of the deuterated and tritiated species, one can see that the tritium substitution has a larger effect on the retention volumes than expected from the simple mass effect. In fact, molecules such as CH3T and CH2TZ merge from the column later than the corresponding CH2D2 and CD4of the same mass. Many interesting applications can be found from the gas chromatographic separation of isotopic methanes. One is the purity control of various isotopic molecules, another is the possibility of studying the kinetics of isotope exchange reactions, For instance, the mixture of partially deuterated methanes was prepared by exchange of Dz with CH4 induced by X-rays. By means of consecutive Chromatographic analyses one can follow the relative abundances of the deuterated molecules at different irradiation times (Figure 3).
Another interesting application is the determination of the monodeuterated methane in natural methane (Figure 4). In the upper part of the chromatogram the separation of CHID/ C H 4 in the same amount is shown; in the lower part, by injecting a large amount of CH4, one can observe the small peak of CH,D and measure the isotopic abundance (CHID = 0.06
(10) A. Liberti, G. P. Cartoni, and F. Bruner, “Gas Chromatography, 1964,” A. Goldup, Ed., The Institute of Petroleum, London, 1965, p 312.
RECEIVED for review January 14, 1969. Accepted February 28, 1969. The authors thank the Consiglio Nazionale delle Ricerche for providing funds to support this investigation.
C-------a-alOO
257
259
-p
261
263
Figure 4.
265
267
269
271
273
I
275 TlME(min)
Separation CHd-CH3D
Upper chromatogram: same amount Lower chromatogram : natural isotope abundance
x).
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Assay for Heroin in Illicit Preparations Using Partition Chromatography George R. Nakamura’ and Herman J. Meuron Alcohol, Tobacco and Firearms Laboratory, Internal Revenue Service, Box 36075, San Francisco, Calif 94102
THEQUANTITATIVE ESTIMATION OF HEROIN (diacetylmorphine) in most illicit preparations by the classical solvent extraction methods ( I ) proved to be tedious and time-consuming while that by direct ultraviolet absorption measurement was inapplicable because of the effects of adulterants and dark colored resinous impurities. Since the end of World War 11, a large number of adulerants have been added to heroin powder and the heroin itself often times has not been carefully purified by the clandestine laboratory. Thus, the Mexican, o r brown colored heroin, which appears on the West Coast seems to contain dark resinous matter, possibly some residual constituent of opium. I n addition, this brown heroin is generally very intimately mixed with procaine, and then coarsely mixed with other adulterants or diluents such as lactose and starch. 1 Present address, Bureau of Narcotics and Dangerous Drugs, San Francisco Regional Laboratory, Box 36075, 450 Golden Gate Ave., San Francisco, Calif. 94102
(1) “Methods of Analysis,” Internal Revenue Service Publication No. 341, (Rev 6-67), Internal Revenue Service, U. S. Treasury Dept., Washingion, D.C., June 1967. 1124
ANALYTICAL CHEMISTRY
The presence of the dark resinous matter as well as procaine, also interferes with a number of identification tests, such as the formation of microcrystals with platinic chloride ( I ) and with quantitative procedures. The assay method employing gas-liquid chromatography developed by Grooms (2) in this laboratory was not affected by the common adulterants except quinine. However, it was considered desirable to develop an alternate method for use by laboratories not having a gas chromatograph and the choice was some foim of rapid column chromatography procedure. Levine (3) showed that many alkoids, such as heroin, can be extracted as ion pairs by chloroform and other chlorinated hydrocarbons. The principles underlying the phenomenon are discussed by Doyle and Levine (4) and by Higuchi e[ al., (5) and are used as a basis for the separation of a wide range of pharmaceutical amines under various conditions. The application of ion pair elution presented here affords ~(2) (3) (4) (5)
J. 0. Grooms, J. Assoc. Off: Anal. Chem., 51, 1010 (1968). J. Levine, J. Pharm. Sci., 54, 485 (1965). T. D. Doyle and J. Levine, ANAL.CHEM., 39, 1282 (1967). T. Higuchi, A. Michaelis, T. Tan, and A. Hurwitz, ibid., 39,
974 (1967).
