Sample Foundation -- GC/MS Identification of Gasoline Used in Arson (Part 1 of 2)
Sample Foundation -- GC/MS Identification of Gasoline Used in Arson. Frederic M. Douglas (C) 1999 Frederic M. Douglas. All rights Reserved. In the following sample foundation, a sample from the charred remains from a suspected arson fire to a residential structure is presented to the witness. The witness explains the GC/MS test results. The examining attorney has already established chain of custody and the scientific theory's validity. Q. What is your occupation? A. I am an analytical chemist at the California Department of Justice. Q. What is an analytical chemist? A. I analyze samples to determine their composition using scientific techniques and instruments. Q. Please tell the jury about the types of samples that you analyze in your work. A. Many of the specimens that we process are suspected of containing narcotics. I specialize in identifying specimens from suspected arson fires and explosives. One example, maybe an investigator gathers a sample from a burnt rafter in a structure fire. We identify the contents of the specimen. Usually, the detectives want to know if an accelerant was used to fuel the fire and if so, what accelerant was used. From time to time I also analyze body fluids and tissues for drugs and their metabolized remnants. Q. Please tell the jury about your formal education. A. I have a Bachelor's and Master of Science degree in Chemistry from M.I.T, and a PhD. in Analytical Chemistry from U.C. Berkeley. Q. Could you tell the jury about the courses you took at U.C. Berkeley? A. Yes, I took many courses in analytical chemistry. I took two semesters of general analytical chemistry. Then there was a survey course on analytical instruments, which included a laboratory component where we operated every device that our course covered. There was a seminar class on analytical instrument troubleshooting techniques where we learned how to identify instrument malfunctions and how to prevent false positives and false negatives. Q. Did any of these courses cover the GC/MS instrument? A. Yes, all of them. The professor for the seminar course, Professor G. See is known as one of the leading experts in the development of the use of the GC/MS instrument in hydrocarbon analysis. Q. How long have you been an analytical chemist? A. For about ten years, all of that time with the California Department of Justice. Q. Have you published anything in the analytical chemistry field? A. Yes, besides my theses I have written twenty articles on analytical chemistry, including a book on the GC/MS analysis. Q. What is "GC/MS"? A. That stands for "gas chromatography and mass spectrometry." It is a two-stage process. The gas chromatography device separates the sample into the different chemicals present by vaporizing the sample. Next the mass spectrometry machine identifies the different chemicals by measuring the mass of each chemical. Q. How many of the articles that you published deal with GC/MS? A. About half or my articles were on GC/MS, using the instrument for arson investigation, drug identification, and bomb blasting powder characterization. Q. Is GC/MS testing reliable? A. Yes, the GC is a superior separation tool and the MS provides specific results. When the GC is combined with the MS, you have an extremely effective analytical tool. Q. What do you mean by "specific results"? A. A specific result is when a test shows that only one brand of gasoline was used, with little likelihood of a false positive result. A nonspecific result is when a test produces a result indicated by more than one brand of gasoline. The nonspecific result gives many false positive results. Q. What is a "false positive" result? A. A false positive is when the test says one brand of gasoline was used when in fact another brand was used. Q. Is GC/MS a specific test or a nonspecific test? A. Specific. The GC by itself is not specific, but using the MS device with the GC gives a specific result. Q. Are you familiar with any research that mentions that using MS with G.C. gives a specific result? A. Yes, that was covered in my instrument lab class at Berkeley. The pioneering research was performed by Professor Ann L. Itical at Wisconsin. I read everything that Professor Itical wrote on the GC/MS combination. Q. Is the GC/MS combination generally accepted in the scientific community as a way to identify the brand of gasoline used in an arson fire? A. Yes, it is the preferred test. At this point, counsel seeks to have the witness describe the GC process with a visual aid. The counsel follows proper courtroom procedure by showing the chart to the opposing counsel and marking the chart as exhibit #3. Q. Your Honor, may the witness step down and approach the exhibit? J. Yes, the witness may step down and approach the item marked exhibit #3 for identification. Q. Thank you, your Honor. Looking at what is marked as exhibit #3 for identification, what is this? A. This is a drawing of the equipment used in gas chromatography. Q. What components does the GC include? The witness points to each component while answering the question. A. The GC has the injection port, the carrier gas, the column, the sample splitter, the detector and the output recorder. Q. A small amount of the sample is dissolved. Then this solution is injected into the injection port, here, with a syringe. The injection port is hot so the sample vaporizes into a gas. The carrier gas pushes the sample, this way, through the column. Each chemical in the sample sticks to parts of the column in different ways; some chemicals stick to the column and do not come back off easily, while some chemicals do not stick at all. Most chemicals act somewhere in between. The greater the chemical sticks, the longer it takes for that chemical to travel through the column. When each chemical eventually leaves the column, the detector, at this end, measures it and the sample splitter sends part of the chemical to the mass spectrometer. While the witness remains near exhibit #3, the counsel properly has another visual aid marked exhibit #4 for identification. The counsel displays exhibit #4 in front of the witness.