Methamphetamine Misidentified

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Case Summary: Defendant tested positive for methamphetamine in a urine sample, but assured the public defender they did not use the drug.  An expert was tasked with building a credible, defensible, and reliable opinion on the basis that Defendant was using a commercially available inhaler for breathing relief.

Expert Analysis: Methamphetamine consists of two enantiomers, or optical isomers.  These molecules have the same number of constituent elements (i.e., carbon, hydrogen, and oxygen), but the arrangement of these atoms around one of the carbons can be in two different orientations.  The left-handed methamphetamine molecule has medicinal properties and can be an ingredient in commercially available inhalers, such as what Defendant was using.  The right-handed methamphetamine molecule is the drug of abuse.

Mass spectrometry is typically used to identify drugs, by comparing a sample scan to a reference scan in a computerized library.  Since the left-handed and right-handed molecules have the same numbers of constituent elements, the resulting mass spectra of one is indistinguishable from the other.  Optical isomers can be distinguished from one another with specialized instrumentation that measures the changes in direction of polarized light when interacting with such molecules.

The analytical laboratory that the county used did not have the specialized instrumentation needed to make this distinction.  As a result, what the lab (and the county) considered to be a positive test for the right-handed methamphetamine molecule was actually a measurement of the total amount of both molecules.  Without the additional specialized instrumentation testing, it is impossible to know if the sample was all left-handed molecules, all right-handed molecules, or some mixture of the two.

Result: When the expert’s report was disclosed to the prosecutor, they recognized that the county needed to utilize an analytical laboratory with the specialized instrumentation required to distinguish between the two methamphetamine molecules.  This case was dismissed.