odd question

[lagilman]

Assuming backwash in a soda or a glass of wine, might there be there any way to get a court-admissible saliva/dna sample from it? Or would the sample be tainted (especially from the alcohol).

peggin and I were wondering (don't ask, we have some straaaaange conversations).

Comments

[ilvack.livejournal.com]

I think it would be possible. A little disgusting tidbit to throw in: It's possible to collect DNA from stomach acids which are alot stronger than the stuff they put in soda. The wine, I'm not so sure of.

If nothing else, then the rim of the glass they drank out of would work.

I know it's possible to get fingerprints off of a can with condensation on it, but that's not really the same thing, is it?

[badgermirlacca.livejournal.com]

I think it might even be possible to get the DNA off the rim of the glass, these days. Although given the backup in most labs, and the level of competency of many lab technicians.... what is possible and what is practicable are not always coincident.

[lagilman]

I think it might even be possible to get the DNA off the rim of the glass, these days.

yeah, but that wasn't the question. The question was about the backwash (assume the suspect was savvy enough to clean off the lip of the glass, or the soda can, etc)

[agamisu.livejournal.com]

Hmm, I would worry about organics.

And the 'divided by a common language' thing? I had pictures of drinking from a glass full of soda crystals. Nice. That would certainly screw with the DNA.

[neutronjockey.livejournal.com]

My thoughts are the acid in either would destroy any organic evidence, though the lip marks on the glass/can--whatever certainly.
-=Jeff=-

[kalligraphy.livejournal.com]

As a scientist with experience in laboratories, I would probably have to say the answer is no. Mind you, I am working on guess work here, but it is very valid guesswork. Contrary to what they show on things like CSI, they do not have machines that sniff someone's clothes and tell you ever chemical they have come into contact with in the past month inside of 30 seconds. CSI takes a lot of liberties.

A number of questions come to mind first. Will the dna survive the experience? In reality, it is NOT really the dna that has to survive, it is the cell it is contained within. Once the cell wall is broken, the dna is vulnerable to chemical reaction to the materials it comes into contact with. Some substances can penetrate cell walls easily, some can not. The important factor is that the cell wall has to survive and resist intrusion. DNA testing works by breaking open the cell wall and then cleaving the protien strand at certain bonds within the strand, then you measure how much of what size fragment remains. If the protein strand is exposed to a hostile environment, the strand can break at uncontroled points and give you inaccurate results. This is what happened in the OJ trial when blood samples were left in a hot vehicle, the cell walls broke and the protein strands degraded. Assuming the cell wall has survived, you next come to the next biggest problem there is. How do you get it?

It's not like it comes with a string attached, pull the string and you get the cell pops out in your hand. No, there are a small number of cells in a very large volume of some substance. How do you seperate the two? Typically when substances are mixed together, you can seperate them through mixing with a contrary solvent. For instance, a small amount of an organic substance, suspended in water can often be extracted by mixing an oil like substance with the water. The organic ends up in the oil, everything not soluble in oil, ends up in the water, toss out the water. The problem is that alcohol can actually solvate both organics and inorganics, although it is less efficient with organics because of it's polar nature.

So the biggest problem is how do you seperate a decent number of cells (I assume real life dna tests require more than 1 or 2 cells for accurare results) from a mixture of various substances without damaging the cells. I am not sure it can be done. There are ways of filtering the liquid through an EXTREMELY fine pore sieve, but that is extremely slow and also involves exposing the whole mess to vacuum, which may damage the cell wall. Besides, assuming it is more than a few drops (say half a glass of wine), filtering 5 or 6 oz of wine through such a filter could take days.

Now I could be wrong, because I am not an expert in this field. However, I am a physical chemist with 10 years of research experience (not to mention college training) with a strong background in instrumental methods of analysis.