Anyone who is good with chemistry or chemical analysis

[AutoEuphoria]

I know this is a LONG shot, but right now I need all the help I can get. Me and a partner have been given the task to figure out how to do the following problem:

Determination of the Hydrocarbon Content from a Crime Scene. You will be given a sample that was obtained from a crime scene and will need to identify which of three compounds is present. You will also need to determine how much of the compound is present. The sample will be a specific weight of absorbent (sand) that contains a certain amount (mass) of the organic compound. The three possible aromatic contaminants from the crime scene are xylene, aniline and chlorobenzene. Only one compound will be present in a sample. You will need to quantitatively extract the organic compound from the sand and proceed with an analysis (one or multiple methods) that can provide both qualitative and quantitative information. The precision of the measurement will be important to determine (n=3). Report your answer in mg of organic compound per mg of sand.

have a few ideas, but we (I have a lab partner) don't know how to get the compound out of the sand, and then we are unsure of the method that would best analyze it. We have at our disposal a UV-Vis spectrometer, Infared Spectrometer, HPLC, and GC machines. Any help would GREATLY be appreciated!

Tyler

 

[TyraNSX]

I'm guessing you would have to do an extraction of the sand (maybe more than 1) to get the compound out of the sand & maybe by choosing the right solvents you get to separate the compounds somewhat which would delineate what you had based on which fraction it partitioned into. Would xylene & chlorbenzene separate together in a good organic solvent but aniline wouldn't? I'm not a chemist, just asking.

 

[Autophile]

Cool, organic chemistry.

Quantitative:
1) Tare a weigh boat, zero the scale, weigh the entire sample (sand + unknown)
2) Tare a new weigh boat, zero the scale
3) Separate out a smaller, usable sample
4) Weigh the new smaller sample, note the ratio of entire sample weight to small sample weight
5) Remove sample from scale, leave sample in boat, rinse sample lightly with benzene, collect rinse fluid for analysis
6) Transfer the rinsed/wet sand onto a drying oven safe boat, and place sample in a drying oven to dry
7) When the sand is dry, tare a new weigh boat, zero the scale, weigh the sand
8) Multiply the dry sand weight by the ratio found in step 4. This is the dry entire sample weight. Subtract the dry entire sample weight from the weight found in step 1. This is the weight of the organic compound.

Qualitative
1) Run a sample of pure benzene through the IR
2) Run a portion of the sample from step 5 of the quantitative section through the IR
3) Compare the benzene IR to the sample IR, note where new absorption peaks appear in the sample IR
4) Compare new peaks with absorption tables to see which functional group is attached to benzene (xylene: methane, aniline: amine, chlorobenzene: chlorine)

That's it. Have fun. If you mess up, it's ok, that's why you don't use your whole sample all at once.

 

[peiserg]

my spouse took a chemistry course in college. She may be able to help. I'll ask. the only potential issue i could see from the above suggestion is if the benzene alters the sample.

 

[nchopp]

PM or e-mail me if none of the above posts helped - me mum's a Pharmacist, could probably help.

 

[Autophile]

my spouse took a chemistry course in college. She may be able to help. I'll ask. the only potential issue i could see from the above suggestion is if the benzene alters the sample.

Benzene won't alter the sample. I say this from taking ~ 15 chemistry courses in college.

 

[peiserg]

Benzene won't alter the sample. I say this from taking ~ 15 chemistry courses in college.

I'll still ask my spouse. She mumbled something once about how her masters in organic and PhD in Analytical chemistry makes her smarter than me. I was smart enough not to argue.

 

[Autophile]

Since no one else is speaking up, I'll give some extra advice. With reference samples, you could use any of the other mentioned methods. Some reference-free methods would be refractive index, GC-MS, EDX, and H1/C13 NMR, among others. Any other chemists want to discuss?