Soil Extraction of Total and Aromatic Hydrocarbons

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

10 posts Page 1 of 1
Hello i am developing a method for extraction of hydrocarbons from soil.
I took 5 gram of soil mix it with 20mL of hexane and 20mL of acetone. I put the samples on shaker for 30 min. Then i Centrifuged the vials and took the supernatant and mixed it with DI water then passed it through a separatory funnel to take acetone out. Then i passed the extract through Sodium Sulfate and then i ran the extract on the GC i only got decane out in quantitative analysis and the peaks are weird. The retention time for decane is not matching the calibration curve. The RT shifted a little bit. I dont know if i am doing this wrong. Can anybody help me with better extraction technique and i dont have soxlet appratus. Can anyone help me

For the PAH. Is it necessary to pass the soil extract through Silica gel column? If it is how would it be done. Thank you very much
Why are you reinventing the wheel? Use the EPA's method 8310.
sohaib1 wrote:
Hello i am developing a method for extraction of hydrocarbons from soil.
I took 5 gram of soil mix it with 20mL of hexane and 20mL of acetone. I put the samples on shaker for 30 min. Then i Centrifuged the vials and took the supernatant and mixed it with DI water then passed it through a separatory funnel to take acetone out. Then i passed the extract through Sodium Sulfate and then i ran the extract on the GC i only got decane out in quantitative analysis and the peaks are weird. The retention time for decane is not matching the calibration curve. The RT shifted a little bit. I dont know if i am doing this wrong. Can anybody help me with better extraction technique and i dont have soxlet appratus. Can anyone help me

For the PAH. Is it necessary to pass the soil extract through Silica gel column? If it is how would it be done. Thank you very much


I would do a simple evaporation instead of the water step to remove the acetone. Warm water bath and gentle stream of nitrogen bring it to less than 1ml, then add another 10ml hexane and again bring to less than 1 ml to help remove all of the acetone, then bring to final volume of 1ml. It will remove the acetone and give 20x more sensitivity due to the lower final volume.
The past is there to guide us into the future, not to dwell in.
HPLC chemist wrote:
Why are you reinventing the wheel? Use the EPA's method 8310.

I don't have a sonication probe or soxhlet
James_Ball wrote:
sohaib1 wrote:
Hello i am developing a method for extraction of hydrocarbons from soil.
I took 5 gram of soil mix it with 20mL of hexane and 20mL of acetone. I put the samples on shaker for 30 min. Then i Centrifuged the vials and took the supernatant and mixed it with DI water then passed it through a separatory funnel to take acetone out. Then i passed the extract through Sodium Sulfate and then i ran the extract on the GC i only got decane out in quantitative analysis and the peaks are weird. The retention time for decane is not matching the calibration curve. The RT shifted a little bit. I dont know if i am doing this wrong. Can anybody help me with better extraction technique and i dont have soxlet appratus. Can anyone help me

For the PAH. Is it necessary to pass the soil extract through Silica gel column? If it is how would it be done. Thank you very much


I would do a simple evaporation instead of the water step to remove the acetone. Warm water bath and gentle stream of nitrogen bring it to less than 1ml, then add another 10ml hexane and again bring to less than 1 ml to help remove all of the acetone, then bring to final volume of 1ml. It will remove the acetone and give 20x more sensitivity due to the lower final volume.


So how would i do PAH and total hydrocarbons with GC. How would I extract soil for Total Hydrocarbons and How to do it for PAH? Are the extraction method same for both?. How did you do a soil extraction?
sohaib1 wrote:
James_Ball wrote:
sohaib1 wrote:
Hello i am developing a method for extraction of hydrocarbons from soil.
I took 5 gram of soil mix it with 20mL of hexane and 20mL of acetone. I put the samples on shaker for 30 min. Then i Centrifuged the vials and took the supernatant and mixed it with DI water then passed it through a separatory funnel to take acetone out. Then i passed the extract through Sodium Sulfate and then i ran the extract on the GC i only got decane out in quantitative analysis and the peaks are weird. The retention time for decane is not matching the calibration curve. The RT shifted a little bit. I dont know if i am doing this wrong. Can anybody help me with better extraction technique and i dont have soxlet appratus. Can anyone help me

For the PAH. Is it necessary to pass the soil extract through Silica gel column? If it is how would it be done. Thank you very much


I would do a simple evaporation instead of the water step to remove the acetone. Warm water bath and gentle stream of nitrogen bring it to less than 1ml, then add another 10ml hexane and again bring to less than 1 ml to help remove all of the acetone, then bring to final volume of 1ml. It will remove the acetone and give 20x more sensitivity due to the lower final volume.


So how would i do PAH and total hydrocarbons with GC. How would I extract soil for Total Hydrocarbons and How to do it for PAH? Are the extraction method same for both?. How did you do a soil extraction?


You can use the same extraction you are doing now, just skip the water extraction step and instead use a simple blow down step to remove the acetone. Since acetone has a lower boiling point than hexane, you have to evaporate it multiple times to reduce the acetone. But if acetone does not elute within the target analytes of your method then you should be able to inject the acetone/hexane mixture, just make calibration standards in the same mixture ratio.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
sohaib1 wrote:
James_Ball wrote:

I would do a simple evaporation instead of the water step to remove the acetone. Warm water bath and gentle stream of nitrogen bring it to less than 1ml, then add another 10ml hexane and again bring to less than 1 ml to help remove all of the acetone, then bring to final volume of 1ml. It will remove the acetone and give 20x more sensitivity due to the lower final volume.


So how would i do PAH and total hydrocarbons with GC. How would I extract soil for Total Hydrocarbons and How to do it for PAH? Are the extraction method same for both?. How did you do a soil extraction?


You can use the same extraction you are doing now, just skip the water extraction step and instead use a simple blow down step to remove the acetone. Since acetone has a lower boiling point than hexane, you have to evaporate it multiple times to reduce the acetone. But if acetone does not elute within the target analytes of your method then you should be able to inject the acetone/hexane mixture, just make calibration standards in the same mixture ratio.


Oh ok do i have to use the silica to clean the sample (like lets say i am analyzing wet soil sample after mixing with hexane/acetone do i have to run the extract through silica gel? Does the wet soil have to be mixed with Sodium Sulfate? if so then how much Thank you
Normally for wet soil you mix with sodium sulfate until the soil become a dry powder, also you can allow the soil to dry at room temperature overnight before extraction. There will be some moisture in the extract but if you pass it through some sodium sulfate it will remove the moisture before you begin the evaporation steps.

Silica Gel is used if you need to further clean up the extract of interferences.

https://www.epa.gov/hw-sw846/sw-846-compendium

Look here in the 3500 series methods to find information on the silica gel cleanup procedure and on different extraction methods. The preparation of samples for the sonication method should be similar to what you are doing and also the microwave methods would be similar also.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
Normally for wet soil you mix with sodium sulfate until the soil become a dry powder, also you can allow the soil to dry at room temperature overnight before extraction. There will be some moisture in the extract but if you pass it through some sodium sulfate it will remove the moisture before you begin the evaporation steps.

Silica Gel is used if you need to further clean up the extract of interferences.

https://www.epa.gov/hw-sw846/sw-846-compendium

Look here in the 3500 series methods to find information on the silica gel cleanup procedure and on different extraction methods. The preparation of samples for the sonication method should be similar to what you are doing and also the microwave methods would be similar also.


Thank you very much james for your help. i really appreciate it. Thanks
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