Talk:Gas chromatography-mass spectrometry
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This article has been improved by the Cleanup Taskforce to conform with a higher standard of quality. Please see its Cleanup Taskforce page for more details on this process, and possible ideas on how you can further improve this article! |
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[edit] Cleanup?
What does this need before it can be removed from cleanup? Please list here and' on the WP:LO page. Thanks! JesseW 23:54, 19 Oct 2004 (UTC)
--Mmcdougall 16:29, 13 May 2005 (UTC)
Main page is getting pretty close to "ready-to-go" I think. The redacted information (now at the bottom of the talk section), should not be lost. We should find a more appropriate home for it. Similarly, there is detail in that section that should be pushed to CG and MS sections. Sentor material should be editted and moved to Sentor.
[edit] Other comments
Okay, so I admit, it's a bit chatty. It's based on a paper I wrote for a scientic evidence class. It's really just talking about how GC/MS works and what its strengths and limitations are. So there's really nothing that's specific to Scientific Evidence, except towards the end when it starts talking about how it functions under certain legal tests, but that's still relevant.
--Jvraba 10:20, 21 Jul 2004 (UTC)
Okay, so I've started to seperate the legal discussions under seperate headings. The article used to have tons of footnotes, so if things seem like they pop out of nowhere, they might need to be fixed. Actually maybe someone has a better article to adapt for this purpose. But I think it's pretty useful.
--Jvraba 06:30, 23 Jul 2004 (UTC)
If you create a new section, try to use the equal-sign convention (two equals signs for a headline, three for a subhead, four for a sub-sub-head) so it's added to the table of contents rather than just bolding.
Salasks 14:13, 23 Jul 2004 (UTC)
This article has a lot of legal information I was unaware of, but it needs work by someone more familiar with GC/MS. In particulat, I think it poorly describes the technique. One problem with the paper is that it repeatedly refers to mass spectrography. Should be "spectrometry". Cool Hand Luke 23:24, 28 Sep 2004 (UTC)
I'll put a link to the original paper. This version takes out all the footnotes, obviously. Some things which may seem like poor or superficial descriptions may be the product of depending on a footnote that is no longer there. I have no problem with this thing being quite gutted. And maybe I should excerpt the paper to address the legal implications of GC/MS and leave the rest to real scientists. As far as spectrography / spectrometry, it seems to be used interchangibly in certain literature, although this may reflect an artificate of certain periods of development. I began the paper with huge footnotes on the history of GC and MS, so maybe this had a lasting effect on my style throughout.
--Jvraba 03:01, 17 Oct 2004 (UTC)
- Actually, I think I was too harsh on this article. I think it'll require a lot of work, but all of this legal information is actually a very good thing. Although it probably needs to be reorganized and made less verbose, I think most of this information is appropriate. I would imagine lots of folk in chemical sciences would find the article interesting just for the legal aspects of a familiar technique. Unfortunatly, I don't have very much time to work on it now. Cool Hand Luke (Communicate!) 08:29, 17 Oct 2004 (UTC)
- The article shows some promise - I have added links to the text but that in itself took me an hour. It needs de-essaying and things like "needle in a haystack" need to come out. I reckon it would make a really good article if you removed the half of the content that was making it too verbose. I will continue to edit it over the next few weeks, but it will take many revisions as it's too much to do in one go. It probably needs about 10 hours work in total. GregRobson 20:23, 30 Nov 2004 (UTC)
[edit] Proposed introduction
I'm willing to do the cleanup. It will take me quite an effort to eliminate all the wordy "deadwood" in this article. Could the original author provide references so that it will be easier for me to rephrase parts of the article? Allentchang 08:21, 23 Nov 2004 (UTC)
- That's great that you are willing to work on cleaning this up. I assume you've asked at the Talk page of the first contributor(see History)? JesseW 10:31, 23 Nov 2004 (UTC)
- I sent Mr. Chang the artciel. I believe he's working on it now. As a lawyer, I was a bit "cliff's notes" in my understanding of the underlying science, although I tried to do my best to go through all the seminal journal articles. Some things which sound like omissions in the text above are actually nuanced or more clearly explained in the footnotes. Anyway, it seemed like a good idea at the time. But if it doesn't work out, I'm all for completely gutting this entry and starting over again. --Jvraba 02 Dec 2004
- I'll get the cleanup done before Christmas. My background is in electrical engineering, but I've editted technical articles before. allentchang 21:56, 11 Dec 2004 (UTC)
[edit] Legal implications section
The latter third of this article about the implications of GC/MS and related technologies in the American legal system is very interesting. In fact I thought it must have been copied from somewhere else becaue it was very clearly written not as a Wikipedia article. However it seems the author has put it here so it's legit. However, I think it doesn't really fit on this page. I think there should be a page on scientific evidence in the legal system, and this section can serve as the foundation of that article. I'm not going to move it or anything, I just wanted to provide my thoughts and how best to organize this information. I don't think the legal stuff should stay on this page in the current level of detail, but we should keep it somewhere else and link to it. Nohat 00:53, 16 Dec 2004 (UTC)
Probably true. Well, before I pasted in my article there was no GC/MS article, and people kept asking me about GC/MS, so I figured it was better than nothing. I know there are certain problems with the article as it currently stands, because obviously, especially towards the end, its analytical framework is from the scientific evidence (legal) point of view. Was it originally written as a Wiki article? No. It was originally written as a term paper. But it seemed generalized enough to be useful. One of the problems it had, is that some of the more specific scentific quibbles remained in the footnotes which I did not paste in. Allentchang, who is currently working on the article, has the version complete with footnotes. I'm actually looking forward to seeing this reworked. --Jvraba 19:32, 18 Dec 2004 (UTC)
The university library where I'm checking several sources on the subject is closed for winter break so it will take me much longer than I had promised. Allentchang 20:24, 24 Dec 2004 (UTC)
[edit] Clarify this paragraph
"Alternatively, the single-magnet analyzer chamber will deflect the various particles through an electromagnetic field within a long curved tube. The lighter particles traverse the analyzer tube the fastest. The particles emerge from the magnetic region and strike the detector, transferring its charge. This activates the recorder which takes note of the atomic mass through the mass/charge ratio and evaluates concentration of that molecule contained in the sample."
Please clarify the above paragrapgh. So how exactly does the single-magnet analyzer discriminate between particles of different mass to charge ratios? I've read websites that suggest that single magnet is tunned to allow particles of a certain mass to charge ratio to be able to complete the journey through the long curved tube. Particles with a different mass to charge ratio has a trajectory that is incompatible with the pathway offered by the long curved tube and therefore these particles collide on the wall of the tube. Allentchang 20:59, 24 Dec 2004 (UTC)
[edit] I invite anyone to cleanup sections after MS components
I invite anyone to cleanup sections after MS components. There's already a complaint that this article is more than 32k. There are sections of the article after MS compennts that I cannot properly clean up without consulting the book by Giannelli, Paul C. and Imwinkelried, Edward J. The UC Berkeley library does not have that book for some reason. Allentchang 22:43, 7 Jan 2005 (UTC)
[edit] GC/MS analysis
I've looked at the section on GC/MS analysis and got very confused. You said that two kinds of analysis are possible: comparative and original. You then proceed to explain about the comparative analysis in the first paragraph. Then in the second paragraph you vaguely mention about "another analysis." Is this other analysis the "original analysis"? If not, then there is no where in your GC/MS section that talks about original analysis.
Additionally, you later mention "full spectrum" analysis and selective ion monitoring. It seems to me that you are talking at most five different types of analysis instead of two: "comparative," "original," "another," "full spectrum," and "selective ion monitoring." Allentchang 22:54, 7 Jan 2005 (UTC)
[edit] Ruthlessly Excised sections for clarity
Heres the original bits.
[edit] GC components
The gas chromatograph consists of five essential components: a carrier gas supply, a separation column, the inlet/injection port, an oven, a detector, and a data system. The compound sample is vaporized into gaseous form and injected into the separation column. Within the separation column there are two important mediums that control the movement and separation of components from the compound sample: the stationary phase and the mobile phase.
The mobile phase consists of the carrier gas which must be inert (unreactive) to the column materials and the sample to be analyzed. This phase moves all components originating from the compound sample through the separation column to the MS unit. Each component is moved at the same speed.
The stationary phase, which is embedded within the separation column, absorbs the moving components and retains each component for a certain amount of time before releasing it. Because this retention time depends on the type of component being absorbed and because the component is immobile when absorbed, certain types of components move through and exit the column faster than other elements. This results in the sample components separating into identifiable and measurable groups.
Since the sample must be kept in a gaseous state within the column, the column is heated by ovens that maintain a suitable temperature. Sometimes the heating unit will be used to "ramp", or gradually increase the temperature, which can cause the components with lower boiling points to exit the column sooner. Thus, in addition to the stationary phase, another resisting force causing the separation is heat.
[edit] MS components
The MS unit consists of five primary features: an ionizer, the magnetic region, a detector, and a recorder. When the stream exiting the GC unit enters the MS unit, it first goes into the ionizer. The ionizer inundates the sample material with an electron beam, causing it to become positively charged. This results in fission of components into smaller fragments. Every type of component molecule has a unique fragmentation pattern based on properties inherent to that component. The magnetic region may take two forms: a quadrapole magnetic focusing or a single-magnet analyzer tube.
The quadrapole setup uses four magnets to focus specific molecules with a certain mass to charge ratio through a small slot. Molecules that have a different mass to charge ratio would merely bounce around the magnetic region until the time comes for their turn to be successfully focused by the four magnets through the slot. After passing through the slot, the particles hit a detector, which measures the relative amount of particles that have a particular mass to charge ratio.
Alternatively, the single-magnet analyzer chamber will deflect the various particles through an electromagnetic field within a long curved tube. The lighter particles traverse the analyzer tube the fastest. The particles emerge from the magnetic region and strike the detector, transferring its charge. This activates the recorder which takes note of the atomic mass through the mass/charge ratio and evaluates concentration of that molecule contained in the sample.
The MS detector electronics sends the detection data to the computer, which plots a spectrum of the relative abundance of a particle versus the mass to charge ratio.
The EGIS-type can use an 8-pound portable vacuum system that sucks in air around luggage to be analyzed. The vacuum functions as the sampler of the GC-MS system. Alternatively, a cloth can be used to wipe surfaces and the cloth can be inserted directly into an injection port in the GC/MS system. The sample is analyzed with the push of a button. If the unit detects an explosive, it will activate an “audible, LCD, or LED” alarm.
[edit] Sentor: Identifying particles of guilt
Consider the following scenario:
On the morning of March 29, 1993, a United States Navy surveillance aircraft, a P3 Orion, was on a routine drug-interdiction mission in international waters off the coast of the Dominican Republic. Spotting a low-profile vessel in the waters below, the aviators identified the boat to be similar to the type of vessel commonly used in narcotics smuggling. After the Orion made several passes and witnessed the ship's crew members tossing bales overboard into the ocean, small arms tracer rounds came streaming towards the plane. Soon thereafter, Coast Guard officials aboard a Navy frigate, U.S.S. TAYLOR, intercepted and boarded the low-profile vessel. After an exhaustive search, the American officials were unable to locate any contraband on the boat or on the defendants.
Law enforcement officials, attempting to connect the bales of cocaine with the defendants, produced the Sentor, a state-of-the-art electronic device able to detect the faintest molecular traces of cocaine. The officers, using what looked like a large hand-held flashlight, approached the defendants and pointed the device towards their bodies. The machine began to vacuum in a large volume of air around the defendants bodies. The officers then took samples of the air on board the boat. Within thirty seconds, the drug-interdiction officials were able to detect trace amounts of cocaine on both the defendants and the boat. Based upon this and other evidence, the defendants were arrested and later convicted of smuggling narcotics.
Real scenarios like the one presented above are becoming increasingly common, as the drug-sniffing GC-MS-powered Sentor currently is in use by drug enforcement agents, the coast guard, and the border patrol. It both suggests the benefits of such a system, but also elicits worries. This particular scenario inspires the audience to want the test to confirm what we already “knew”: that the boat crew were ejecting bricks of cocaine into the ocean. We already knew they were guilty. In one scene we go from the Coast Guard officials take air samples from the boat and from the bodies of each individual to the happy ending. In a fast time frame for even Hollywood, less than a minute later, the aviators’ visual observations were “proven” through the magic of GC/MS and the machine called Sentor.
The Sentor is actually a derivative of the EGIS machine described in previous section, but instead of being optimized for explosives detection, it is optimized to detect drugs. The following technical description applies also the EGIS hardware.
Consistent with the GC-MS enhancements described earlier (in section 3.1.1), the unit employs high speed GC-MS accompanied by time-of-flight mass spectography. An interesting enhancement is the portable vacuum air auto-sampler, which was described above as resembling a large, handheld flashlight. Unlike traditional GC/MS where samples are injected with a syringe into the mobile state, the auto-sampler directly fits into an auto-intake/injection system.
The operation of the machine is simple. The auto-sampler is inserted into a machine resembling a refrigerator, the GC-MS process begins, and finally it displays the quantity and amount of drugs detected. Unlike the laboratory environment, there is no room to fine-tune. But there is also little possibility of operator error. This principal of operation, in the words of manufacturer Thermedics Detection, Inc., can be described as “simple one-person, one-button operation.” After all, this application was not designed for scientists.
The foregoing description describes Sentor in the criminal context, largely because of the particular agencies involved with the technology at present. However, Pinkerton Security and Investigation Services has entered a marketing agreement to administer the test in the workplace. It would be run by “specially trained Pinkerton guards” who would analyze everything and everyone in a 15,000 square foot (1,400 m²) business for approximately $5,000. In this civil context, Sentor-type technology raises some perplexing issues.
[edit] Reflection: creepy little particles of guilt
The US Supreme Court determined in United States v. Place that sniffs by trained drug dogs did not constitute a "search" within the meaning of the Fourth Amendment. The high-tech sniffing that goes on goes on with GC/MS technology is considerably more powerful than the sniffing ability of dog. But in a certain sense, GC/MS is doing the same thing—“inhaling” certain particles and “alerting” when they are the bad ones. The worry however, is that, given the fact that suspicious particles are in the air and can be inadvertently contracted through others and objects like money, this “dog” could “alert” on anyone. This could give police—should the police begin its widespread use—the power to do a more invasive search and just use the Sentor as a pretext. Perhaps, however, the Sentor may be more like thermal infrared imaging, which the Supreme Court held to be unconstitutional search in Kyllo v. United States.
Another element for this discussion is that of Federal Rule of Evidence 403. Because of the ability to tie people to certain stashes of drugs based on their chemical makeup, there doubtlessly would be some instances where Sentor-type results would be tried to be introduced as evidence in itself. This certainly was the case for the drug traffickers off the coast of the Dominican Republic. The fact that this evidence “magically” discerns the presence of illicit substances might render it substantially more prejudicial than probative. Because the GC-MS configuration in the Sentor-type situation is essentially a “press here, dummy” configuration, one may be left with the impression that because it so simply indicates the presence of some drug residue, then a person who triggers its alarm must be “simply guilty.” The allure of the magic box, in conjunction with the misconception that people with drugs on them (however slight) are drug users, may cause an average juror to become prejudiced. While we know that jurors express a healthy skepticism to scientific evidence and expert testimony, in the case of this situation, it doesn’t necessarily have all the off-putting qualities of scientific machinery. For one, the Sentor and EGIS are very simple when it comes to their interface. However, this prejudice may be cured by effective lawyering on the other side, not in terms of the technicalities of GC/MS, but rather in showing that how common contamination is.
Questions of first impression about GC-MS/MS were raised in United States v. Campbell. In this case, Private Campbell’s urine tested positive for LSD only under GC-MS/MS at Northwest Toxicology Laboratories, but not under conventional tests at Fort Meade which included radioimmunoassay analysis (RIA). The RIA test indicated some LSD in the urine, but did not rise to the 200 picogram standard established by the military. Only with the GC/MS/MS test did the military discover 307 picograms of LSD, enough to convict Campbell for using LSD. The defense successfully maintained that GC-MS/MS is not reliable under MRE 702, primarily arguing that it did not meet the Daubert test. The U.S. Court of Appeal for the Armed Forces (CAAF) reversed the intermediate court, maintaining the trial court had correctly found that it did not meet Daubert standard for reliability:
“Of critical importance is that the Government did not prove the levels or frequency of error, which would indicate: (1) that the particular GC-MS/MS test reliably detected the presence of LSD metabolites in urine; (2) that GC-MS/MS reliably quantified the concentration of those metabolites; and (3) that the DoD cutoff level of 200 pg/ml was greater than the margin of error and sufficiently high to reasonably exclude the possibility of a false positive and establish the wrongfulness of any use. In particular, the Government introduced no evidence to show that it had taken into account what is necessary to eliminate the reasonable possibility of unknowing ingestion or a false positive.”
Falling far short of an in-depth treatment of treatment of Campbell, this introduction serves to highlight the fact that GC-MS/MS is not GC-MS, even though GC-MS/MS relies on GC-MS. While GC-MS’s is nearly-universally accepted as the “gold standard” in a broad array of applications, one ought not to assume that this reverence extends much further.
The code section under which Private Campbell was prosecuted required “knowing use” and this knowing use could theoretically be established upon a certain level of narcotic in the bloodstream. One issue that surfaces in a number of novel GC/MS applications is the meaning of standards. It is troubling that, upon failing to achieve the threshold, one might turn to novel technology which can prove more of a substance is there. It is not automatically clear whether the first test understated the presence of a chemical, or the later test overstated its presence. But it does make sense that, as in Campbell, there should be burden to establish that a test proving the presence of a substance beyond established tests should be required to prove its quantification is reliable in its own regard. Otherwise the application of standards may not be a function of objective testing, but instead a function of “test shopping.”
Sentor, which relies on a technology already proven to be the “gold standard” for drug testing, may be open to a similar attack. Even though High Speed Gas Chromatography (HSGC)/ Time-of-Flight Mass Spectography (TOFMS) upon which Sentor relies is essentially a “suped up” version of first-generation GC-MS, one may question whether it is still essentially GC-MS, based on its hardware. A court may require a separate foundation apart from GC-MS. Adding hardware to increase precision such as an addition MS unit, as above, seems to make GC-MS/MS different enough from GC-MS to warrant independent establishment of its validity. In the case of replacing slower hardware with faster hardware (as with HSG/TOFMS), does that also require a separate showing of reliability from other GC/MS technologies?
The proponent of such evidence may argue that it does not warrant a separate showing because there are many variants among hardware configurations in GC-MS setups that have various characteristics—such as faster or slower speed—and such configurations have always been treated interchangeably in case treatments of GC-MS. Because the procedure is based upon the same essential technology, it could be argued, it should not therefore be treated differently than GC/MS has been. However, perhaps more powerfully, one could argue that Sentor is fundamentally different: HSGC/TOFMS is lower resolution, and while it is widely suggested that it makes up for that fact by performing 500 analyses per second, it remains important that an equivalency be evidenced.
Of course, would Sentor readings really be used for evidence? At first it might not seem so. It might merely be a screening test that gives rise to further confirmatory tests. But think above the scenario detailed above where the Coast Guard employs Sentor to link the accused to bricks of cocaine in the ocean. The fact that the Sentor reported a presence of cocaine, and a mixture of chemicals being identical to that of the cocaine in the bricks is the most incriminating fact in the scenario, as described. Certainly, the analysis of the cocaine in the bricks may be performed later in the laboratory to verify the results of the portable test. However, it is unlikely that the Coast Guard preserved an additional air sample. But this perhaps highlights another point, that even when the identification itself is not very suspect, the source of the sample might be suspect.
The Sentor (and the EGIS for that matter) sample imprecisely, especially when they are analyzing air. To suggest that there is much precision to vacuuming particles from around one’s person is quite suspect. Air is fluid and does not cling to the body like leaves hang on a tree. Contamination with an illicit substance may come from the environment. The particles that cling to someone may be there because they have come into contact with someone else. Individuals are constantly involuntarily and inadvertent bearers of other people’s particles. Along that line of thought, one ought to consider that, in order to activate a Sentor, one need only come in contact with an individual who had handled such drugs recently. Such an individual might be a police officer, a drug dealer, or a pharmacist. Certainly, only a minuscule amount of particles would transfer through casual contact. However, due to Sentor’s use of GC-MS, it is capable of discovering traces of narcotics like cocaine amounting to less than one billionth (0.000000001) of a gram. Moreover, most note-based money in currency is contaminated with cocaine residue. Anyone who constantly handles money could theoretically set off a Sentor.
The concern for incidental contamination is not so far-fetched. It was a concern that was addressed by the Campbell court. Incidental contamination also poses an increasingly monumental danger when the otherwise insignificant contaminants become magnified along with same sample: what was once incidental looms quite large. It is essential to bring this problem into focus before the courts by suggesting, where appropriate, that mountains are being made of molehills. Even in proportional magnification, there is the danger that the sample itself is rather small, and it ceases to be representative of the whole. Imagine a sample from a haystack with a needle in it, consisting of 3 pieces of hay and 1 needle. Bear in mind that unlike a blood or urine sample, some of these more novel sampling techniques will feature clustering of a residue. A gust of wind might “link” someone to a massive drug operation, because a big fragment stuck to your lapel.
Standards can solve some of this problem. A standards-setting organization can determine at what level of reading something can be truly probative. How this would be determined is problematic. But assuming it can be done, perhaps one can come up with a standard that excludes the amount of particles that be merely blown or inadvertently rubbed onto a body. But can the same be said for GC-MS/MS? GC-MS/MS can really look behind a situation that is dominantly “debris” and see the gasoline that was used to burn the house down. But of what probative value is this, when perhaps GC-MS/MS detects not the accelerant in the fire but instead BBQ fluid that had spilled inadvertently into the carpet months ago on the Fourth of July? At some point, detecting too little may be too much for the courts, because alternative explanations can effectively rebut minute samples.
There are more than one type of capillary columns used in a GC-MS system. First there is the Wall Coated Open Tubular (WCOT). This system is the most advanced as there are an infinite number of theoretical plates*. This system coats only the interior tubing with an open center. This system allows for best separation. Another is the Packed or PLOT. This system uses packed plates, which, at its development allowed for an increase in theoretical plates but is not infinite. The third is a Stationary or SCOT. This system uses only a single layer of plating, which is a fairly uncommon way of using a GCMS (now that WCOT exists).
- Theoretical plates: at its development, a separating column was used to separate each component. To do this, the sample moved between literal plates whereby each component could separate (or at least to some degree) on. With a WCOT, the theoretical number of plates is determined by dividing the length of the capillary tube by the number of theoretical plates. Number of theoretical plates is defined as: N=16(tri/Wi)^2
[edit] GC/MS Analysis
Would anyone object to a section in the GC/MS page focusing on some practical observations from someone who works in a lab that does both environmental analysis and drug detection work? We tend to be very focused on supporting the identification with various kinds of quality control samples to show the system is working. We are also always up against the concept of "detection limit". Non-technical clients can't get over the idea that we can't say a sample does not contain a given compound. The best we can do is say we saw no reliable signal above the detection limit. The second question is always "How much is in there?", so quantitation should probably get a mention.
[edit] My suggestion?
I'd add a sentence like "GCMS has a very low detection limit, and can be used to determine how much of blah-de-blah is is present, unlike such-and-such. Then I'd put my insights re: quality controls ect in the detection limit article. Sadly, I'm not an expert on GCMS, so I can't make the "true" statements in good faith.
