Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Joeay on May 16, 2006, 05:20:39 PM
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Hello, I'm not sure if this is the section for this question, however I'll try anyhow.
I was wondering how one would detect if the presence of gasoline would be located in a soil sample? I would also need to know the level of concentration, or atleast approximately. I have been reading a little about gas chromatographs but am not sure if this would be the answer, or the only answer. I am also hoping there is a cheaper alternative. Thanks a lot!
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what do you need to detect it for, one method would be to wear gloves and non-flammable things and light a small flame near it to see if it ignites, tho i would avoid this
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what do you need to detect it for, one method would be to wear gloves and non-flammable things and light a small flame near it to see if it ignites, tho i would avoid this
lol, fire isn't the answer to everything... and even if you did get soil to ignite that wouldn't insure that gasoline was the cause nor would it tell the concentration
hell, smelling the ground would be a better idea... if it smells like gas then it probably contains some gasoline, the stronger the smell the higher the concentration (and this would definitely be the cheapest approach)
on a more serious note, couldn't you do a mass spec. or something like that
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i was just trying to keep the cheap approach to it
if it does ignite, it wouldn't be spontaneous but you could move around the flame to catch everywhere and when you're done, there is no concentration. unless you need the numbers for something then just ignore what i said
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on a more serious note, couldn't you do a mass spec. or something like that
Could you perhaps expand on that idea? Sorry, I'm no chemist.
I am trying to find a way to do this on my own, because going through a lab cost 1500$ per test. All I need is an approximate of the amount of gas so that I don't have to trial and error and take multiple tests, doesent have to be exact although the more precise the better.
I am willing to do whatever it takes to learn what I need. Like I said, I've been searching on the net for some time, but have not had luck. Any help is really appreciated.
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http://www.psigate.ac.uk/roads/cgi-bin/redir.pl?url=http://www.mfe.govt.nz/publications/hazardous/sampling-protocols-oil-may99.pdf
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on a more serious note, couldn't you do a mass spec. or something like that
Could you perhaps expand on that idea? Sorry, I'm no chemist.
I am trying to find a way to do this on my own, because going through a lab cost 1500$ per test. All I need is an approximate of the amount of gas so that I don't have to trial and error and take multiple tests, doesent have to be exact although the more precise the better.
I am willing to do whatever it takes to learn what I need. Like I said, I've been searching on the net for some time, but have not had luck. Any help is really appreciated.
i wish i could but i have to be honest and say i really don't know much about that particular area either... i am pretty sure however that there is no way to do this without doing a lab test
here's about the extent of my knowledge:
mass spec. means mass spectrometry which dictionary.com defines as:
"an instrumental method for identifying the chemical constitution of a substance by means of the separation of gaseous ions according to their differing mass and charge called also mass spectroscopy"
http://dictionary.reference.com/search?q=Mass%20Spectrometry
most labs, at least the good ones, have machines that do this but i don't know if it would work on soil since it isn't a gas... perhaps a mod could give us some more information on this or lead you in a different direction ;)
also, mike's website appears to give a very detailed description of how to solve your problem
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Mikes website was not exacly what i needed however it did point me in the good direction such as the right terminology to search.
it seems i must use a TPH 1,2 test method. After searching this I found an ebook named Analytical Methods For Petroleum Hydrocarbons. As I stated before, I'm no chemist. But I'm hoping this book could teach me a thing or two. If this is totally the opposit from what i need let me know. I'd still like help from the experts ;)
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Mikes website was not exacly what i needed however it did point me in the good direction such as the right terminology to search.
That was the idea ;)
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I don't know if it would work on soil since it isn't a gas...
Doesn't matter - you can heat up the sample and volatile substances will become gaseous...
that's the way you do it.
Whoever will continue lyrics gets a snack ;)
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..money for nothing and chicks for free....
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+1 :)
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I don't know if it would work on soil since it isn't a gas...
Doesn't matter - you can heat up the sample and volatile substances will become gaseous...
I suppose that would work if there is a small sample. I also read that this is how the gas chromatograph (i believe thats the word) works this way, however gives a detailed output. Is there an instrument that would detect and calculate the amount of the fumes from the gas?
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Problem is - most analytical methods give you information about individual compounds. Gasoline is a mixture of different hydrocarbons and it is not clear to me how to translate individual compounds into "gasoline amount". Additionally, these different hydrocarbons have different volatility, so they will evaporate from the soil with different speeds - so their composition in soil will change with time, making problem even more complex.
I suppose that there are some norms and methods defined by gov agencies that allow for such measurements, but the result is - at least partially - a matter of convention (just like soil pH (http://www.ph-meter.info/pH-measurements-other-procedures) is). As long as you follow the convention you may compare results of measurements done in the different places, but measurement doesn give exact answer to the "gasoline amount" question, as the question is not exact. Perhaps if you will ask for "total hydrocarbons" it will be much easier - it will be enough to add all HC concentrations to get some number of more or less well defined meaning.
I suppose that would work if there is a small sample.
You always work this way - you get small sample to analyze.
Is there an instrument that would detect and calculate the amount of the fumes from the gas?
What do you mean by "amount of the fumes from the gas"? But perhaps I have already answered your question above?
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how about fractional distillation? u can check the boiling temperature of the liquid mixture at different intervals after cooling down the soil sample to produce a liquid which composes of those HCs
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The usual way to do what you want is to use a GC. The analyst will extract the soil with some solvent, and run that sample on the GC. He then compares the GC response for the sample that was extracted from the soil to the response from a standard (known concentration) sample to estimate the concentration in the original soil sample. For gasoline hydrocarbons, this is never an exact number because the "standard" that the analyst has will not be exactly the same as the gasoline contamination in the soil (different origin, partially degraded by soil bacteria, partially evaporated from soil, etc.)
The least expensive way to do it is with your nose (a very sensitive detector indeed). Smell the soil.
If the contamination is high. You may be able to send a sample of the contaminated soil along with some clean soil from a nearby location to a soil testing lab for organic carbon analysis. This test is performed frequently for agricultural soils and is not too expensive ( surely less than $50). I'm not sure how the lab will feel about the gasoline contamination as they usually only do agricultural soils. You could also try to do this on your own if you have a really hot oven. The soil is first heated to 110C for 24 hours to remove all of the water, then weighed. Then it is heated to a very high temperature to burn off all of the carbon and weighed again. This will give you percent organic carbon. If the gasoline contamination was large, you should see a difference between the clean and contaminated soils.
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The soil is first heated to 110C for 24 hours to remove all of the water
...and you have just lost all volatile HCs from gasoline. Bad idea.
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Perhaps if you will ask for "total hydrocarbons" it will be much easier - it will be enough to add all HC concentrations to get some number of more or less well defined meaning.
That would be even better actually. I am assuming you were talking about the heating the soil method, ssince you were speaking of different volatilities.
Idea 1:
I suppose this could be done with a heating element, and a top sealed box. Since the vapours are lighter than the air, they would go up, being trapped in the top sealed box. Any extra oxygen would be forced down, where there would be an opening. Now, how do I measure the total hydrocarbons which were evapourated?
If the amount of oxygen would need to be known, I would be able to have a pilot light, heating a thermocouple in which would result in creating a very little voltage. This could control a solenoid, which would either let oxygen in, or close.
Idea 2:
This one is much more basic. A heater element, the soil, and a pressure sensor would be placed in a completely sealed box. The pressure of the trapped air would be taken before the soil is heated, then compared after. This would have to be done a few times and tested at a real lab to create our own scale. (ex. 10 psi of air, 15 psi after heated, 15-10 = 5psi difference, send to lab, find out that 5 psi is equal to so much.) I suppose a pressure release valve could also be included for safety reasons, though I do not imagine that much extra pressure would be created.
Would these ideas work? Or am I just dreaming?
Thanks for the replies so far guys. I really appreciate it
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Would these ideas work? Or am I just dreaming?
I am afraid they won't.
Don't expect vapours separation in small box, I doubt in separation even if the box will be two meters high.
Second method sounds more reasonable, but the pressure will build up not only because of gasoline, but becasue of water too. Thus you will measure some combination of gasoline, water and probably even humus decomposition. Hardly precise.
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Well, you said it would be a lot simpler if I would detect all hydrocarbons. Which method were you speaking of when you said this? Or is there a way to improve on my second idea?
Anything to do with he electrical would not be a problem for me as my carreer is being an electrician, perhaps eventually leading to electrical engineer.
I'm sorry if I'm being a bother, I've been searching and reading on the net for some time now, and this seems to be the only place I could get answers for exacly what I need.
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Well, you said it would be a lot simpler if I would detect all hydrocarbons. Which method were you speaking of when you said this?
Perhaps there are methods of detecting sum of HC that I am not aware off. Simplest way seems to be GC or GCMS plus addition of individual concentrations/amounts.
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What do you want to determine exactly? Are you looking to analyse the soil where there is an expected gasoline contamination? or are you looking to find an oil field?
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What do you want to determine exactly? Are you looking to analyse the soil where there is an expected gasoline contamination? or are you looking to find an oil field?
I want to analyse the soil where there is a gasoline contamination, however hydrocarbons in general would probably be even better.
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"Detection of Hydrocarbon fuel spills using distributed fibre optic sensor"
MacLean et al. Sensors and Actuators A 109 (2003) 60-67
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WOW! That's impressive! Would of never thought of using an OTDR for this! I'm VERY impressed! Only downside is the price, however it is possible to take a long length of tests instead of individually! I'm impressed if it works as easily as it explains in the article.
I think everyone should google that article. Definately a good read!
I'm still for a look out for a cheapter method. If anyone has information please post it.
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...and you have just lost all volatile HCs from gasoline. Bad idea.
Yeah, didn't think about that. We were doing oil and diesel fuel contamination where volatilization wasn't so much of a problem.
Maybe you could extract the soil with something like pentane. Then let pentane evaporate and weigh the residue. If you compare the residue to that of a clean soil, you should get some idea of contamination. Pentane is a weak solvent and should extract much from the soil except for the gasoline hydrocarbons. Of course evaporation of the gasoline is still something of an issue, but maybe you could evaporate at low temp and catch it before too much gasoline evaporates. Still not as quantitative as GC, but it's cheap!
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You could also artificially contaminate some soil and try the pentane extraction to see how much gas you recover in the residue. Probably not the most environmentally friendly way, but like I said it's cheap ;D
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"Detection of Hydrocarbon fuel spills using distributed fibre optic sensor"
MacLean et al. Sensors and Actuators A 109 (2003) 60-67
This one?
http://cmp.eee.strath.ac.uk/detection%20hydrocarbon%20fuel%20spills.pdf
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Pentane is a weak solvent and should extract much from the soil except for the gasoline hydrocarbons.
Quite contrary - I would rather expect pentane to extract most of the gasoline.
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I would rather expect pentane to extract most of the gasoline
That was my point. Pentane will only extract the gasoline from the soil and not much else.
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Up to date, the fiber optic sensor seems to be the most useful for my needs. However, the GC seems to give more precise measures which could be given as a plus.
However I have one question. I was talking with a chemist and he said they use to detect hydrocarbons with some sort of chemical, sugar and some color dye. The darkness of the color dye would determine the amount of hydrocarbons within the soil. Anyone know which chemical this could be? I almost seem to believe this is a old folk story because he says he "forgot" how they did it. However he said he had 2 small jars of this mixed substance left. He offered to give them to me. Perhaps this could be used to duplicate, or learn from. Please let me know your inputs.