FOCUS work with molecules containing a keto or aldehyde group. Because we've add ed exactly 134 mass units to the mole cule, we find the molecular ion of this preformed ion at ml ζ 494—360 plus 134—at fairly high intensity and with an order-of-magnitude decrease in its concentration on the surface. So we've
"We' ve picked up an order of magnitude in sensitivity by going with derivatization." Richard Colton picked up an order of magnitude in. sensitivity by going with derivatization. The last spectrum [Figure 3d] shows that we can reduce the concen tration another order of magnitude and still have ample signal to detect this species. This demonstrates the capa bility of using derivatization proce
dures to increase detection sensitivity." Drug-screening applications Why is the NRL interested in derivatiza tion SIMS? The Navy currently has five drug-screening laboratories in the United States that test military per sonnel for drugs such as marijuana, cocaine, LSD, and opiates. The primary screening is done by ra dioimmunoassay. If that result is positive, it is con firmed with a second, in dependent method such as gas chromatography/ mass spectrometry (GC/ MS). According to Colton, "Some species such as LSD are used in such small quantities that, by the time your body me tabolizes them, there is very little left in the urine. Even GC/MS has trouble detecting LSD and some of the design er drugs that are now becoming popu lar. Therefore we undertook a course of study in which we introduced several other techniques, including derivatiza tion SIMS, to demonstrate better sen
sitivity for some of these drugs of abuse." For example, the derivatization SIMS technique has been applied to the detection of a 3-ng mixture of methamphetamine, methadone, qui nine, and propoxyphene in urine. A small amount of CH 3 I is first added to the sample to form methylated quarternary salt derivatives with the four drugs. "We put a few microliters of this sample on a silver substrate and placed it in the SIMS instrument," Colton said. "That was the extent of our sam ple preparation. No extraction or cleanup was needed." Colton and co workers found that SIMS peak intensi ties for the derivatized species were im proved by a factor of 10 over those ob tained from the analysis of an underivatized mixture spiked into urine at the same concentration level. In addition, says Colton, "For LSD, SIMS provides better detection sensi tivity than thin-layer chromatography, liquid chromatography/MS, or direct insertion probe MS, and SIMS detec tion limits are well below the limits of GC/MS. This is important because, when someone is taking LSD, what you find in urine is at the subnanogram level." Stu Borman
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592 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 8, APRIL 15, 1987
Associate of E. Merck, Darmstadt, Germai
