GC-MS false positives happen in drug testing
As we blogged before, both in Stereoselectivity matters in methamphetamine: The Science of Breaking Bad cook makes both D and L forms of meth and in GC-MS is not perfect: The case study of methamphetamine there is a large issue in the ability of the Gas Chromatography with Mass Spectrometry is not perfect. It can provide for GC-MS false positives.
From that second post:
Both L-methamphetamine (levo-isomer referred to as the R-isomer) and D-methamphetamine (dextro-isomer referred to as the S-isomer) have the same chemical formula C10H15N. They have the same boiling point at 215 degrees Celsius at 760mmHG. They have the same molecular mass of 149.233 g/mol. They are stereoisomers.
And later on we make the following observation:
126.96.36.199 The L form has very little pharmacodynamic effect; whereas, the D will really make you have an interesting series of days.
188.8.131.52 The L-Form is known as Levomethamphetamine (other names include l-methamphetamine, levodesoxyephedrine, l-desoxyephedrine, levmetamfetamine).
184.108.40.206 The problem is that the L form is completely legal under certain circumstances, and is present in Vicks VapoRub® Inhaler which is over-the-counter for example (In fact, it has 50 mgs of the L for in a typical commercially available package). It is a common sympathomimetic vasoconstrictor. Per 21 CFR 1308.21 and 1308.22 the l-methamphetamine in VapoRub® Inhaler is non-narcotic. However, if one were to extract and collected from the inhalers and possessed with the intent to use, it would be impermissible (illegal) per the CFR.
Here is yet another example of how GC-MS is not perfect and can provide for real world false positives:
GC-MS false positive most likely was an interpretive error by the analyst rather than an instrument error. But error is error. This was the proficiency test where these GC-MS false positives happened.
Can you imagine losing your entire career in the Army, Navy, Air Force, Marines or Coast Guard because of a false positive that is thought to be impossible because the analysis was conducted on a GC-MS machine? It would be devastating.
The defense bar is waking up. It is starting to understand that even the “forensic gold standard” testing method is not without error. Defense attorneys need to continue to be better educated so they can issue spot errors in the data themselves.