METHAMPHETAMINE
One would expect, based on their relative molecular weights, the volatility of methamphetamine to be similar to that of nicotine and considerably greater than that of PCP. Also, as a secondary amine, methamphetamine should be less likely than PCP to undergo thermal elimination to an olefin. it is not surprising then to find that, when methamphetamine is placed in a pyrolysis tube that then is put into a heated furnace, the methamphetamine volatilizes, and at temperatures of 200 to 400°C more than 98 percent of it can be recovered intact. Recovery falls to 88 percent at 600°C and 62 percent at 800°C. At these temperatures, small amounts of amphetamine (0.7 and 1.5 percent) are formed (K.H. Davis, personal communication, July 1990).
Hydrochloride salts of simple amines are also volatile, and 91 percent of methamphetamine hydrochloride is recovered unchanged after volatilization at 300°C in a tube furnace (compared with 5 percent of PCP hydrochloride). Recovery from the hydrochloride drops to 81 percent at 400°C, 62 percent at 600°C, and 38 percent at 800°C. The salt form is more subject to N-dealkylation due to the presence of a protonated nitrogen and a chloride nucleophile, so that even at 400°, 5 percent of amphetamine is formed by N-demethylation (10 percent at 600 C and 9 percent at 800°C) (K.H. Davis, personal communication, July 1990).
Significant amounts of at least four other pyrolysis products were observed but not identified.
The availability of methamphetamine is much reduced by smoking it in a mixture with tobacco. Thus, Sekine and Nakahara (1987) found that from 6 to 17 percent (depending on amount and smoking conditions) of the methamphetamine hydrochloride added to tobacco was recovered from the mainstream smoke of cigarettes. This was confirmed by Davis and colleagues (personal communication, July 1990) who recovered 4.7±1.1 (SD) percent of added methamphetamine hydrochloride in mainstream smoke when cigarettes were smoked in the puff mode and 12.7±2.9 percent when a constant draft mode of smoking was used. Results were essentially the same in the latter study when the freebase was used (4.8±0.6 percent/puff mode and 15.6±1.3 percent/draft mode), again in confirmation of the report of Sekine and Nakahara (1987). Seven significant pyrolysis products (figure 4) were rigorously identified in the tar from methamphetamine/tobacco cigarettes-amphetamine, phenylacetone, dimethylamphetamine, and N-formyl, N-acetyl, N-propionyl, and N cyanomethyl methamphetamine (Sekine and Nakahara 1987), with the N cyanomethyl compound predominating. In a later study, phenylacetone was the predominant product, and trans-ß-methylstyrene also was found. It was shown that formation of the N-cyanomethyl compound required both heat and air and that other amines formed N-cyanomethyl products when smoked with tobacco (Sekine and Nakahara 1990).
The hydrochloride salt of S-(+)-methamphetamine is the form that is smoked as “ice” (Cho 1990). Reports from Hawaii indicate a common method of administration of “ice” is to smoke it in a glass pipe. Interest in studying this phenomenon led to the initiation of human studies using this material smoked in a glass pipe (Cook et al. 1991; Perez-Reyes et al. 1991).
Six informed, healthy, male, paid volunteers familiar with the use of amphetamines were the subjects. Cardiovascular effects of the drug were monitored during the experiment. Heart rate and blood pressure were measured. Other cardiovascular parameters were measured by computeraveraged impedance cardiogram. The subjects gave a subjective rating of drug effect during the study on a scale of 0-100, with 100 representing the most affected they had ever been after taking amphetamines (Perez-Reyes et al.1991).
Smethamphetamine hydrochloride was placed in a glass pipe. The pipe was inserted in a heated aluminum block, and the subjects inhaled the vapor at 1-minute intervals for approximately 4 minutes (Perez-Reyes et al. 1991), Plasma samples were collected at intervals and analyzed for methamphetamine and amphetamine by the procedure shown in figure 5.
Preliminary experiments with the glass pipe were carried out by partially immersing it in a silicone oil bath, making use of a large-volume syringe to simulate the smoker’s lungs and pulling the vapors through a series of acid traps. When methamphetamine hydrochloride was placed in the pipe and the pipe was lowered into an oil bath at 268°C, roughly 9 to 11 mg of the methamphetamine hydrochloride was recovered from the pipe, with the balance being drawn into the traps. The residue remaining in the pipe appeared to be more a function of the area of cooler surface on which it can condense than of the absolute amount placed in the pipe and remained relatively constant with increasing doses placed in the pipe.
For human experiments, the pipe was inserted into an aluminum block heated to 302-308°C on a hot plate. Approximately 30-mg doses of methamphetamine hydrochloride were placed in the pipe. Analysis of pipe residue showed that an average of 7.8±1.0 (SD) mg of methamphetamine hydrochloride remained inthe pipe and pipe stem after the experiments with the volunteers were complete. Thus, the apparent dose of the methamphetamine hydrochloride was approximately 20 to 21 mg, assuming that, as in the in vitro studies, little decomposition occurred during the smoking process.....
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