In a series of posts, we are going to talk about Mass Spectrometry.

1. Introduction-The dif­fer­ent con­fig­u­ra­tions and the Elec­tron Impact process
2. What types of mass ana­lyz­ers are there?
3. What type of detec­tors are there?
4. What types of analy­sis can be done?
5. How do you read the output?
6. How do they come to a qual­i­ta­tive mea­sure using software?
7. How do they quan­ti­tate the results?
8. Do you need chro­matog­ra­phy if you are using Mass Spectrometry?
9. Other top­ics of inter­est about GC-MS

There seems to be a debate, more like a sci­en­tific war, between spec­tro­scopists and chro­matog­ra­phers. It boils down to this fun­da­men­tal question:

Does co-elution mat­ter if one uses Mass Spectrometry?

Well, the answer is yes, of course. Here is why…

1. If it were indeed true that we do not need well resolved (sep­a­rated) and spe­cific peaks before we use mass spec­trom­e­try (i.e., co-eluting peaks don’t mat­ter), then we would not waste our time with the chro­matog­ra­phy aspect of the gas chro­mato­graph. The GC part of the GC-MS method takes the most amount of time using this tech­nique, and if we could cut that out com­pletely and per­form instead what is called a direct intro­duc­tion (DI) or direct inter­face (DI) probe into the MS alone, then we would increase through­put tremen­dously. We could test so many more sam­ples. But we don’t and for good rea­son. One of the rea­sons that we just do not per­form DI and we need chro­matog­ra­phy with need well resolved peaks is that it is very easy to use too much sam­ple in the DI method system.
   

   DI to the MS

2. If you are test­ing pure com­pounds, then DI may be a very use­ful tech­nique. It is fast and rugged requir­ing very low sam­ple size. How­ever, in our world, the foren­sic world, the chances of either get­ting a pre-consumption unknown drug in pure form is extremely rare. Fur­ther if the sam­ple is in post-consumption matrix (e.g., blood, tears, sweat, urine, blood), then we know that the sam­ple is not pure.
3. Pro­fes­sors Harold McNair, PhD and Fred W. McLaf­ferty, PhD as well as Dr. Mar­vin C. McMas­ter and Dr. Lee Polite warn against intro­duc­ing into MS analy­sis any­thing other than pure com­pounds (one way to get pure com­pounds is through the use of a GC). Pro­fes­sor McLaf­ferty in Inter­pre­ta­tion of Mass Spec­tra wrote as fol­lows: “If sev­eral com­pounds are present in the sam­ple, the result­ing spec­trum will rep­re­sent a lin­ear super­po­si­tion of the com­pe­tent spec­tra.” Dr. McNair puts even more sim­ply, “Just don’t do it. Use the advan­tages of good chro­matog­ra­phy first, then you have lit­tle chance of error in the report­ing of your results.” Another author­ity in the field Dr. Mar­vin C. McMas­ter writes “A mass spec­trom­e­ter is an excel­lent tool for clearly iden­ti­fy­ing the struc­ture of a sin­gle com­pound, but it is less use­ful when pre­sented with a mix­ture.” He fur­ther writes “A good chro­mato­graphic sep­a­ra­tion based on cor­rect selec­tion of injec­tor type and throat mate­r­ial, col­umn sup­port, car­rier gas and oven tem­per­a­ture ramp­ing, and a prop­erly designed inter­face feed­ing into the ion source can make or break the mass spec­tro­met­ric analy­sis.” He con­cludes, “The mass spec­trom­e­ter is designed to ana­lyze only very clean mate­ri­als.” Another noted inter­na­tional instruc­tor for Agi­lent, Dr. Lee Polite, PhD, MBA writes, “If you want to be sure and you are in the busi­ness of being sure, then sep­a­ra­tion first always before MS work.”
4. The other issue is human integrity. While there are a lot of ana­lysts who have high stan­dards for them­selves. Some really care about what they do and want high qual­ity of their results. How­ever, there are some that do not share that vision or care. In the worst case, there is fraud. The issue of co-elution of the GC into the MS invites issues sur­round­ing human integrity.

It is a ques­tion of could ver­sus should. Could you per­form MS with­out GC or use GC in a way that doesn’t resolve peaks and not prove for a puri­fied com­pound into the MS for analy­sis? Sure. You clearly can. BUT, will you be right in your result? Pos­si­bly not. Clearly best prac­tices would be to use the pow­er­ful tool of GC as it is intended and as it is designed which is to pro­vide for purity and speci­ficity in the efflu­ent. Why would you invite or pro­mote the pos­si­bil­ity of error if you did not have to? Why would you invite or pro­mote the need for human integrity. Why if it is not necessary???

As the video above shows us, there is always clearly a“human fac­tor” in all of this analy­sis. In fact, there is a lot! To a degree, we are left to the dis­cre­tion of a human being. Scary.

The report­ing that is pro­vided is just a small sliver of what can be pro­vided to review­ing indi­vid­u­als. For exam­ple, what review­ing coun­sel and experts typ­i­cally get are a one sheet con­clu­sion piece of paper.

Here is a typ­i­cal con­clu­sory report that a defense attor­ney may get. As you can see no detail, just a conclusion.

Con­clu­sory Report

Con­clu­sory Report

Here is a typ­i­cal auto-report from GC-MSD Agi­lent soft­ware. Again, not a lot of detail is provided.

But we can get a lot more infor­ma­tion from the GC-MSD soft­ware such as these from Agilent:

• The full size TIC print­out, and
• Method print­out

And we can get sig­nif­i­cantly more infor­ma­tion from the NIST search soft­ware sim­ply by right click­ing on the screen below such as these reports:

• The full infor­ma­tion print­out on any­where between the top 1 to 100 results from the NIST spec­tral library. (This one is the top 10.) There are var­i­ous click boxes where you can add or sub­tract information;
• The full unknown mass spec­trum from the dis­play “Bar Graph Dis­play of Searched Spec­trum;”
• The full infor­ma­tion from the dis­play “Text Info for Searched Spec­trum;”
• The full infor­ma­tion from the dis­play “Text Info for Selected Hit Spec­trum;” and
• The full infor­ma­tion from the dis­play fields “Com­pare Win­dow” includ­ing “Sub­tract,” “Side by Side,” “Head to Tail,” and “Dif­fer­ence.”
• Per­haps the most impor­tant is the Hit List with the Library iden­ti­fied, the Match Fac­tor, Rel­a­tive Match Fac­tor and the Prob­a­bil­ity Score.