Forensics C

[megan_scioly]

Where is a good place to start with soil identification? What kind of soil are possibilities?

[Tailsfan101]

Where is a good place to start with soil identification? What kind of soil are possibilities?

I don't know if this is the same for Forensics, but in Crime Busters we have four soils to identify: sand, loam, silt, and clay. In Forensics they might add peat, but I'm not the expert here.

[Stefannli]

Do invitational competitions like Princeton require competitors to identify real hairs under a microscope?

[pikachu4919]

Do invitational competitions like Princeton require competitors to identify real hairs under a microscope?

They generally should, but they may also give microscope images if unable to obtain the hairs specified in the rules.

[alleycat03]

I was wondering if somebody could please explain the differences between different chromatography solvents?

At tournaments, I have used acetone, isopropyl alcohol, and simple DI water, depending on what the proctor provided. Which one of these is usually the best to use, and why? If, for example, DI water and isopropyl are both provided, is it better to use one of them over the other?

[Stefannli]

I was wondering if somebody could please explain the differences between different chromatography solvents?

At tournaments, I have used acetone, isopropyl alcohol, and simple DI water, depending on what the proctor provided. Which one of these is usually the best to use, and why? If, for example, DI water and isopropyl are both provided, is it better to use one of them over the other?

Acetone is non polar and is a good chromatography solvent for non polar ink like permanent marker.

[pikachu4919]

I was wondering if somebody could please explain the differences between different chromatography solvents?

At tournaments, I have used acetone, isopropyl alcohol, and simple DI water, depending on what the proctor provided. Which one of these is usually the best to use, and why? If, for example, DI water and isopropyl are both provided, is it better to use one of them over the other?

Acetone is non polar and is a good chromatography solvent for non polar ink like permanent marker.

Acetone is actually a polar aprotic solvent, as it is miscible in water but also in many nonpolar solvents as well such as diethyl ether. It is only partially polar, as the methyl groups on either side of the ketone are responsible for its nonpolar properties, while the ketone in the middle is responsible for its polar properties. But yes, acetone does work well on inks that are not water soluble.

[alleycat03]

I was wondering if somebody could please explain the differences between different chromatography solvents?

At tournaments, I have used acetone, isopropyl alcohol, and simple DI water, depending on what the proctor provided. Which one of these is usually the best to use, and why? If, for example, DI water and isopropyl are both provided, is it better to use one of them over the other?

Acetone is non polar and is a good chromatography solvent for non polar ink like permanent marker.

Acetone is actually a polar aprotic solvent, as it is miscible in water but also in many nonpolar solvents as well such as diethyl ether. It is only partially polar, as the methyl groups on either side of the ketone are responsible for its nonpolar properties, while the ketone in the middle is responsible for its polar properties. But yes, acetone does work well on inks that are not water soluble.

First, there usually isn’t a fast way to tell if a pen’s ink is or isn’t water soluble, right? Unless it says it is water soluble right on the pen, but from my experience that isn’t usually what happens. Usually event supervisors only provide the exact # of chromatography strips needed (like 1 strip for each pen), so it most likely wouldn’t be feasible to try and run the chromatography with water first, and then, if an ink isn’t water-soluble, use a different solvent.

Second, in a competition, should we use acetone if available? And if it’s not provided, should I use isopropyl (since it is usually provided for plastics float tests) or should I use water?

[pikachu4919]

Acetone is non polar and is a good chromatography solvent for non polar ink like permanent marker.

Acetone is actually a polar aprotic solvent, as it is miscible in water but also in many nonpolar solvents as well such as diethyl ether. It is only partially polar, as the methyl groups on either side of the ketone are responsible for its nonpolar properties, while the ketone in the middle is responsible for its polar properties. But yes, acetone does work well on inks that are not water soluble.

First, there usually isn’t a fast way to tell if a pen’s ink is or isn’t water soluble, right? Unless it says it is water soluble right on the pen, but from my experience that isn’t usually what happens. Usually event supervisors only provide the exact # of chromatography strips needed (like 1 strip for each pen), so it most likely wouldn’t be feasible to try and run the chromatography with water first, and then, if an ink isn’t water-soluble, use a different solvent.

Second, in a competition, should we use acetone if available? And if it’s not provided, should I use isopropyl (since it is usually provided for plastics float tests) or should I use water?

If the ink doesn't separate in water, then you should use either acetone or IPA. Acetone would probably be better tho, as IPA is more polar than nonpolar, while acetone has significant enough nonpolar properties that it will be able to separate the nonpolar components of that ink.

And it wouldn't be a terribly wise decision to use the IPA from the plastics. competitors will probably be dropping plastics in and out of it all day, and by then, it might have some traces of oil and salt in it from other solutions, and that might mess up your chromatography.

[alleycat03]

Acetone is actually a polar aprotic solvent, as it is miscible in water but also in many nonpolar solvents as well such as diethyl ether. It is only partially polar, as the methyl groups on either side of the ketone are responsible for its nonpolar properties, while the ketone in the middle is responsible for its polar properties. But yes, acetone does work well on inks that are not water soluble.

First, there usually isn’t a fast way to tell if a pen’s ink is or isn’t water soluble, right? Unless it says it is water soluble right on the pen, but from my experience that isn’t usually what happens. Usually event supervisors only provide the exact # of chromatography strips needed (like 1 strip for each pen), so it most likely wouldn’t be feasible to try and run the chromatography with water first, and then, if an ink isn’t water-soluble, use a different solvent.

Second, in a competition, should we use acetone if available? And if it’s not provided, should I use isopropyl (since it is usually provided for plastics float tests) or should I use water?

If the ink doesn't separate in water, then you should use either acetone or IPA. Acetone would probably be better tho, as IPA is more polar than nonpolar, while acetone has significant enough nonpolar properties that it will be able to separate the nonpolar components of that ink.

And it wouldn't be a terribly wise decision to use the IPA from the plastics. competitors will probably be dropping plastics in and out of it all day, and by then, it might have some traces of oil and salt in it from other solutions, and that might mess up your chromatography.

Thank you for your helpful responses!

Just to clarify, at most competitions we attend, there’s usually a large container of IPA and we just pour our own for the plastics tests. Same with the other salt solutions and such. So there shouldn’t really be any contamination. That is, if the competition actually has a real forensics test that actually follows the event rules and not just a multiple choice test, but I digress.