Mass Spectrometry is only computer assisted pattern recognition

On July 27, 2010, in Analysis, Equipment, Identification, Metrology, by Justin J. McShane

In our prior post, CRMs:  Ref­er­ence mate­ri­als and stan­dards, we saw how the library is impor­tant in ana­lyt­i­cal chem­istry.  It enables the ana­lyst to com­pare the unknown to a known to arrive at an opin­ion that is often expressed as a con­clu­sion.  We saw that there are many dif­fer­ent com­mer­cial sources for these libraries.  In fact, some sys­tems allow the ana­lyst to exer­cise his/her dis­cre­tion in employ­ing his/her own stan­dards as opposed to the com­mer­cially avail­able ones that are CRMs.

Elec­tron Ion­iza­tion (EI) based Mass Spec­trom­e­try has been so fan­tas­ti­cally removed from the base of the sci­ence, that it has been sim­pli­fied to accom­mo­date the masses.  In the mod­ern crime lab, it has been reduced to sim­ple computer-assisted pat­tern recog­ni­tion.

Sadly gone are the days of acid-based chem­istry to elu­ci­date mass spec­tral pat­terns.  Instead, just let the com­puter do it.  Com­put­ers are never, wrong are they?

This is what one of the NIST 08 library screen­shot looks like:

Science has been reduced to computer-assisted pattern recognition

Sci­ence has been reduced to computer-assisted pat­tern recognition

But what if it is not a trace­able source?  What if it is not a per­fect match mean­ing 100% prob­a­bil­ity?  As we can see from this screen­shot there is a list of probabilities.

What a minute! You mean there is a possibility that it is not the analyte of interest?

What a minute! You mean there is a pos­si­bil­ity that it is not the ana­lyte of interest?

There is a judg­ment call that is made even in GC/MS.

At what probability percentage, does the analyst get to call it a specific compound to the exclusion of all others?

At what prob­a­bil­ity per­cent­age, does the ana­lyst get to call it a spe­cific com­pound to the exclu­sion of all others

Why are state sci­en­tists allowed to come in and present a con­clu­sion that is really an opin­ion that an unknown is def­i­nitely a known sub­stance?  Why aren’t court’s forc­ing the truth be pre­sented?  Why the cover up?

 
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Justin J. McShane

Harrisburg DUI attorney Justin J. McShane is the President/CEO of The McShane Firm, LLC - Pennsylvania's top criminal law and DUI law firm. He is the highest rated DUI attorney in PA as rated by Avvo.com. Justin McShane is a double Board certified attorney. He is the first and so far the only Pennsylvania attorney to achieve American Bar Association recognized board certification in DUI defense from the National College for DUI Defense, Inc. He is also a Board Certified Criminal Trial Advocate by the National Board of Trial Advocacy, a Pennsylvania Supreme Court Approved Agency. Justin McShane is the first and so far the only Pennsylvania attorney to achieve American Bar Association recognized board certification in DUI defense from the National College for DUI Defense, Inc.

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1 Response » to “Mass Spectrometry is only computer assisted pattern recognition”

  1. Ethan Strauss says:
    July 26, 2011 at 12:20 pm

    It is true that Mass Spec involves com­puter assisted pat­tern recog­ni­tion and there is some uncer­tainty, but there is uncer­tainty in every­thing. Per­haps results of this type of analy­sis should be pre­sented as opin­ion, but it is informed opin­ion, not ran­dom opinion.

    How should this data be reported?
    An astronomer, a physi­cist and a math­e­mati­cian are on a train in Scot­land. The astronomer looks out of the win­dow, sees a black sheep stand­ing in a field, and remarks, “How odd. Scot­tish sheep are black.” “No, no, no!” says the physi­cist. “Only some Scot­tish sheep are black.” The math­e­mati­cian rolls his eyes at his com­pan­ions’ mud­dled think­ing and says, “In Scot­land, there is at least one sheep, at least one side of which appears to be black from here.”

    Ethan

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