Unknown Identification - Not as easy as TV leads on

By Wayland Rushing, Ph.D.

Senior Scientific Advisor

ABC Laboratories

www.abclabs.com

As an analytical chemist one portion of crime dramas which has always frustrated is the ease at which they make the analytical chemistry seem. If you have ever watched the program CSI (or other related TV show/movie), you could easily get the impression that identifying an unknown is an easy and straightforward process that any lab tech can accomplish.   Here is the scenario:  The victim was poisoned via their herbal supplements.  Their prime suspect is about to leave the country in a few hours. The investigator takes a sample of the supplement, dissolves it and preps the sample.  Switch to the inevitable scene of the GC autosampler arm picking up the vial and transferring it for injection.  30 seconds later a nice chromatogram is printed off with all the peaks identified. The poison is quickly identified with name and structure.  They greet the bad guy at the airport and he goes to jail……If only it were so easy.

Unfortunately, the real world is much more complicated.  Let’s take a more realistic journey using the same scenario.

1)      The analyst, using a method from the supplier of the supplement, preps the sample and analyzes it to look for any potential unknown peaks.  We will assume that an unknown is observed in the supplement method via HPLC.

2)      An evaluation of the method is performed: is it mass spec compatible?  One of the challenges is that many HPLC methods used for analysis of products are not compatible with MS.  If the method is not compatible then a new compatible method will need to be developed.  This method luckily is MS friendly.

3)      Analysis by MS occurs, but by which MS system?  There are a multitude of systems available today which all give slightly different information: single-Quad MS, Ion-trap, MS/MS, QTof, Orbitrap, etc. The key is to ensure that the right system is chosen to provide the best data.  Since we have limited time in the episode I will skip the discussion on the possible different sources used in the various MS systems.

4)      The analyst choses well and analyzes via Orbitrap-MS.  Unfortunately, the unknown does not give a great response in the MS system, so no good structural data is collected.

5)      Enter the isolation montage, semi-prep equipment is used to isolate the unknown, injection after injection and then it is carefully concentrated.

6)      Re-analysis of the sample yields good structural data.  I.e. high resolution mass and fragmentation data.  No nice printout yet with the name and structure.

7)      Concurrently the sample is analyzed by NMR.

8)      Deconvolution of the MS and NMR data is performed by a highly skilled scientist, piecing together the various masses and fragments to build the structure of the molecule used.

9)      We now have identified the poison used after 2 weeks of hard work.

Unfortunately, our bad guy is now sitting on a beach in a tropical island since he boarded the plane two weeks earlier.

Unknown identification is a complicated and time intensive process that requires the correct combination of the right equipment and highly trained scientists.  While I find the real world scenario to be more scientifically interesting it doesn’t translate as well for modern TV.  But we need to give credit where credit is due, the experts performing the work.  Unfortunately it appears that the public doesn’t find this work as enthralling as I do.