I was recently tasked with an interesting challenge by a client and it had me exercising spectral interpretation muscles I have not used in a long time. They sent me a dozen unknown mixture spectra to analyze prior to my teaching an on-site course on the topic at their facility (for the advantages of on-site FTIR training, including free customization, click here http://www.spectros1.com/course_custom.html ). These spectra are perhaps the most difficult to interpret because they are unknowns and because in mixture spectra it can be difficult to figure out what functional groups give rise to what peaks. As I was wading through these spectra I became conscious of the process I was following, and since I had some success I thought I would share that process with my readers.
In my Infrared Spectral Interpretation I course (outline here: http://www.spectros1.com/c-spectral-i.html ) I teach attendees a 12-step program for successfully interpreting spectra. I followed the 12 steps for each spectrum, but in several cases I got to the end of the process without having made much progress. This is when Step 12, "Get Help", comes into play. I found the first thing I did after completing my analysis of a difficult unknown mixture spectrum was to do a library search. In one case the search was of high quality and allowed me to identify the main component in an unknown.
In a few other cases the library search was inconclusive. This is when I hit the literature. I have published a book on Infrared Spectral Interpretation (more info here: http://www.spectros1.com/books.html) and I also have on my bookshelf a number of IR spectral interpretation books by other authors, some of which are more far ranging than my introductory text. Between these books I was able to narrow down some of the unknowns to categories of molecules. For instance, that several of the samples contained carboxylates.
After this I looked up reference spectra of possibilities in a specific chemical class in an infrared spectral atlas. Such an atlas is a collection of infrared spectra organized by functional group. My favorite infrared spectral atlas is the comprehensive 3-volume collection published by Aldrich Chemical (more info here: http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=Z286001ALDRICH&N5=SEARCH_CONCAT_PNOBRAND_KEY&F=SPEC). This compendium contains over 18,500 spectra organized into 53 functional groups. The beauty of this atlas is that you can look at many spectra of the same type of molecule together and quickly learn the pattern of peaks that is diagnostic for that functional group. I did this with a few of the unknowns to become more familiar with the spectra of functional groups that the library search suggested were present in a sample. If I wanted to look up a specific reference spectrum the Aldrich Spectral Atlas could be used for that. However, Aldrich also sells the Aldrich Spectral Viewer (details here: http://www.sigmaaldrich.com/labware/learning-center/spectral-viewer.html). This is an electronic collection of 11,000 infrared spectra that can be searched by compound name or functional group. I find that if I have to look up the spectrum of a specific compound the Spectral Viewer is faster than the Spectral Atlas. The spectral viewer is nice because the spectra are in color, the display limits can be altered, and peaks can be picked and marked. By looking up spectra of functional groups I made progress, and in a few cases by looking up specific spectra I was able to identify specific compounds in a mixture. In the end, I was able to identify specific molecules in a number of the unknowns. However, in a few cases I was only able to suggest what functional groups might be present in a sample.
So, the key then to analyzing unknown mixture spectra is to execute the first 11 steps of the 12-Step interpretation strategy I have discovered. Then exercise the "Get Help" step by using library searches, spectral atlases, and the spectroscopy literature. Using these techniques unknown mixture spectra can be convinced to yield some of their secrets.
Monday, April 20, 2009
Monday, April 13, 2009
Where CSI Gets it Wrong
Where CSI Gets it Wrong
I recently had the privilege of teaching my FTIR Analysis of Controlled Substances course at a well known forensics lab; one of the ones they make TV shows about (course outline is here: http://www.spectros1.com/c-forensic.html). The simple act of writing the letters "CSI" on the board elicited a chorus of groans and laughter from the roomful of forensic scientists taking the course. For those of you who don't watch much TV, the letters "CSI" stand for "Crime Scene Investigation", a series of shows about how forensic scientists help solve crimes. The chorus of groans and laughter is based on the fact that the science on these shows is so inaccurate as to be laughable.
The first thing CSI gets wrong is the role of forensic scientists in crime fighting. They portray lab workers donning bullet proof vests, carrying guns, and chasing down and arresting bad guys. Now in some states forensic scientists may go to the occasional crime scene, but there are no forensic lab workers that I am aware of that carry a gun and arrest people. In many forensics labs there is a strict division of labor between the police, who arrest the bad guys and collect evidence at crime scenes, and the civilian scientists who analyze crime scene evidence and testify about it in court.
Another thing CSI gets wrong is the speed of the analyses performed in a forensics lab. In the world of CSI it apparently only takes a few minutes to run a DNA analysis and identify the bad guy. In the real world it usually takes days or weeks to get DNA results back, and although DNA is a powerful forensics tool it may not be definitive because you can not identify someone who is not in your DNA database.
It is true of CSI, and most movies and TV shows, that the actors and actresses are exceedingly good looking. Now, I have great respect and admiration for the professionalism of forensic scientists and the important role they play in promoting public safety. However, I can tell you that they all don't look like supermodels :-).
But what CSI really gets wrong is the way it portrays the use of FTIR in forensic labs. If you watch the show closely you may have noticed there is a Thermo Nicolet FTIR on the set of one of the CSI shows. Several years ago a Nicolet salesman told me the story of how this came to be. The producers of the show approached Nicolet and asked them for a free FTIR in return for the free publicity Nicolet would enjoy by having the instrument appear on TV. The folks at Nicolet were a little leery of handing over an instrument worth tens of thousands of dollars for free. They had the intelligence to ask the producers of CSI, "Will you ever use the FTIR to perform an analysis?". The answer was no. So, instead of giving the show a complete instrument Nicolet proposed giving them the plastic shell that covers the instrument but with nothing inside of it. This was acceptable to the producers, and that is how a Nicolet "FTIR" came to be featured on a TV show.
Several years ago an episode of CSI featured the use of the FTIR in one of their shows, and they got it terribly wrong. On TV they showed a red visible light laser, apparently a He-Ne laser, as the light source of the FTIR As I teach in my Fundamentals of FTIR course all FTIRs contain a visible light laser that is used to measure the optical path difference of the interferometer. However, this laser is NOT the infrared source because you can't measure an infrared spectrum with visible light. Also, because a laser gives off only one wavelength of light it is impossible to use it to measure a spectrum, which requires many wavelengths of light. Another thing I teach in my Fundamentals of FTIR course is that FTIR is a form of molecular spectroscopy. Individual atoms are not chemically bonded to anything, do not possess vibrations, and hence generally don't have a mid-infrared spectrum. This makes FTIR inappropriate for elemental analysis. On the same show mentioned above they were using the FTIR to perform an atomic analysis on a sample. This is more than I could take, and I have not watched an episode of the show since.
These scientific inaccuracies may seem amusing, but they can have a negative effect upon the public safety of our country. A number of forensic scientists and police officers that I have talked to have said there exists a "CSI effect". Potential jurors, defense attorneys, and even some prosecutors have been so swept up into the imaginary world of the TV show that they have totally unrealistic expectations of what a crime lab can do. Prosecutors expect DNA test results back in hours and get cranky when they do not get what they want. But the scariest story I heard involved a juror. This person had watched so much CSI that he fancied himself an expert in the field. When the police did not run the tests that this juror thought they should have run, he assumed the police were hiding something and as a result voted to acquit a person who may very well have been guilty. So, as entertaining as these shows may be, there is always a cost to portraying things that are not true.
I recently had the privilege of teaching my FTIR Analysis of Controlled Substances course at a well known forensics lab; one of the ones they make TV shows about (course outline is here: http://www.spectros1.com/c-forensic.html). The simple act of writing the letters "CSI" on the board elicited a chorus of groans and laughter from the roomful of forensic scientists taking the course. For those of you who don't watch much TV, the letters "CSI" stand for "Crime Scene Investigation", a series of shows about how forensic scientists help solve crimes. The chorus of groans and laughter is based on the fact that the science on these shows is so inaccurate as to be laughable.
The first thing CSI gets wrong is the role of forensic scientists in crime fighting. They portray lab workers donning bullet proof vests, carrying guns, and chasing down and arresting bad guys. Now in some states forensic scientists may go to the occasional crime scene, but there are no forensic lab workers that I am aware of that carry a gun and arrest people. In many forensics labs there is a strict division of labor between the police, who arrest the bad guys and collect evidence at crime scenes, and the civilian scientists who analyze crime scene evidence and testify about it in court.
Another thing CSI gets wrong is the speed of the analyses performed in a forensics lab. In the world of CSI it apparently only takes a few minutes to run a DNA analysis and identify the bad guy. In the real world it usually takes days or weeks to get DNA results back, and although DNA is a powerful forensics tool it may not be definitive because you can not identify someone who is not in your DNA database.
It is true of CSI, and most movies and TV shows, that the actors and actresses are exceedingly good looking. Now, I have great respect and admiration for the professionalism of forensic scientists and the important role they play in promoting public safety. However, I can tell you that they all don't look like supermodels :-).
But what CSI really gets wrong is the way it portrays the use of FTIR in forensic labs. If you watch the show closely you may have noticed there is a Thermo Nicolet FTIR on the set of one of the CSI shows. Several years ago a Nicolet salesman told me the story of how this came to be. The producers of the show approached Nicolet and asked them for a free FTIR in return for the free publicity Nicolet would enjoy by having the instrument appear on TV. The folks at Nicolet were a little leery of handing over an instrument worth tens of thousands of dollars for free. They had the intelligence to ask the producers of CSI, "Will you ever use the FTIR to perform an analysis?". The answer was no. So, instead of giving the show a complete instrument Nicolet proposed giving them the plastic shell that covers the instrument but with nothing inside of it. This was acceptable to the producers, and that is how a Nicolet "FTIR" came to be featured on a TV show.
Several years ago an episode of CSI featured the use of the FTIR in one of their shows, and they got it terribly wrong. On TV they showed a red visible light laser, apparently a He-Ne laser, as the light source of the FTIR As I teach in my Fundamentals of FTIR course all FTIRs contain a visible light laser that is used to measure the optical path difference of the interferometer. However, this laser is NOT the infrared source because you can't measure an infrared spectrum with visible light. Also, because a laser gives off only one wavelength of light it is impossible to use it to measure a spectrum, which requires many wavelengths of light. Another thing I teach in my Fundamentals of FTIR course is that FTIR is a form of molecular spectroscopy. Individual atoms are not chemically bonded to anything, do not possess vibrations, and hence generally don't have a mid-infrared spectrum. This makes FTIR inappropriate for elemental analysis. On the same show mentioned above they were using the FTIR to perform an atomic analysis on a sample. This is more than I could take, and I have not watched an episode of the show since.
These scientific inaccuracies may seem amusing, but they can have a negative effect upon the public safety of our country. A number of forensic scientists and police officers that I have talked to have said there exists a "CSI effect". Potential jurors, defense attorneys, and even some prosecutors have been so swept up into the imaginary world of the TV show that they have totally unrealistic expectations of what a crime lab can do. Prosecutors expect DNA test results back in hours and get cranky when they do not get what they want. But the scariest story I heard involved a juror. This person had watched so much CSI that he fancied himself an expert in the field. When the police did not run the tests that this juror thought they should have run, he assumed the police were hiding something and as a result voted to acquit a person who may very well have been guilty. So, as entertaining as these shows may be, there is always a cost to portraying things that are not true.
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