This is one reason why lcms confirmation is actually useful. No false positives where one drug masquerading as another drug. Only false positives from all the lab personnel having no idea how to read lcms data and relying on software
I don't think standard LCMS alone wouldn't discriminate dextromethorphan from levormethorphan which IS an opioid.
I'm pretty sure NMR wouldn't spot it either. It would require polarimetry.
I am aware that a number of more modern techniques are now also able to spot enantiomers but I'm uncertain if they are generally applicable. All seem to have specific limitation such as growing a crystal of the compound or so forth.
I did a quick Google for dextromethorphan and I understand that they appear to rely on the two drugs being metabolized at different rates.
It's mad that someone got funding to work out such a test, but if you start dragging in tests for the chirality of one medicine at a time, that would be costly.
I would also argue that due to every person having genetic differences, it's hard to know if outliers exist who would present different rates of metabolism. I am reminded that people of African-American ancestry are often 'super metabolizers' which may be why 'lean' is popular among certain groups. I was gutted to learn DJ Screw had died from a 'codeine overdose'. Possibly his liver was converting almost all of that codeine into morphine.
Has nobody sat these people down and explained that there are still literally tens of thousands of novel compounds of every class of psychoactive that the determined abuser might be pushed into using but that these novel compounds are largely untested in man and so would represent the greater risk?
Recently I talked to a retired prison officer who noted that MDTs had been a disaster in UK prisons. Before then convicts would smoke a bit of puff and have the odd drink. So chilled prisoners who don't cause hassle. Now UK prisons are infamous for the most obscure RCs turning up to avoid MDT detection. It's turned out very badly for everyone concerned.
I just think the US system is geared towards making money and controlling people. I'm sorry to say this but it looks like fascism from where I'm sitting. British people have an abiding liking for US citizens - we just think some of your politicians are mental. So please don't take it as an insult to you guys.