Testing concentrations

[gab9681]

Aight, so lets say that someone where to have access to an assortment of analytical equipment. Then lets say that just for fun, one wanted to find out the concentration of their test. What would be the best way to go about this? Could one simply take an absorbance read and get a rough estimate? If so, where would one find the proper wavelengths to read it at? Or would one need to HPLC the sample to determine the concentration? Any ideas and or suggestions guys? Or any websites that might offer such info?

 

[rjl296]

an absorbance wouldnt work, i dont think.
spectrophotometry , i suspect would be the best
omeone else will know more than me, for sure

 

[rjl296]

running a column would work too, i believe

 

[Optimus B]

use GC with an internal standard.

 

[The Shadow]

use GC with an internal standard.

Good idea....but you first need a standard of whatever compound you are testing.

 

[Optimus B]

Good idea....but you first need a standard of whatever compound you are testing.

or you could just use eicosane in MeOH and compare peak heights.

 

[Andy13]

Spectrophotometry (absorbance) would be the most straight forward. The problem with reading the absorbace is that unsaturated fatty acid esters in oil will also scatter light in UV... and this could create an undesirable signal to noise ratio.

HPLC is the choice method.. But unless you have a pure test standard at your disposal and a weekend with the instrument, forget about it.

Either way (reading UV absorbance or HPLC), you will need a standard..

Andy

 

[The Shadow]

or you could just use eicosane in MeOH and compare peak heights.

Not true...as you need total area under the peak...not just the height or the width.......


And you still need a reference standard.....


lets say do a dilute and shoot with mecl2....you get a peak area.....you dont know what concentraion that is unless you have a known amount to compare to.

GC/MS is the way to go

 

[Optimus B]

Not true...as you need total area under the peak...not just the height or the width.......


And you still need a reference standard.....


lets say do a dilute and shoot with mecl2....you get a peak area.....you dont know what concentraion that is unless you have a known amount to compare to.

GC/MS is the way to go

yep, that's correct, my bad.

 

[gab9681]

Hmm, I do have access to a Mass Spec. Any other ideas??

 

[The Shadow]

well.....Like I said,......first and foremost, you must have a known concentration standard

 

[gab9681]

I could make a standard starting with some powders.

 

[The Shadow]

if you know the absolute purity......and account for the difference in the loss of the ester

 

[Andy13]

HPLC is the way to go. Still, need standards. Forget about it unless you have the machine for a weekend.

 

[gab9681]

Let's say i could get a machine for the weekend. Anyone have a good overview of how to set up the method? We run a lot of 55 minute methods here testing for purity of other compounds. I have never dived into the world of juice before though.

 

[Animal]

It might be easier to find a chem which reacts with a structrure on the test and titrate it in.

 

[The Shadow]

HPLC is the way to go. Still, need standards. Forget about it unless you have the machine for a weekend.

How is it batter than gc/ms which is the standard for verification on most analytical testing

 

[Andy13]

How is it batter than gc/ms which is the standard for verification on most analytical testing

The MS is worth its weight in gold..

But when the ID and concentration of the compound (especially non-volatile compounds such as AAS) are desired, HPLC is more high-through put ready, has wider range of compounds that can be applied, and accurate down to ppb.

 

[Andy13]

It might be easier to find a chem which reacts with a structrure on the test and titrate it in.

I've thought about this before but leaned away from it for one reason or another.

Something really cheap and easy would be the bisulfite addition to a ketone. Bisulfite is easy to get, but reacts more with aldehydes than ketones. There's a good chance that testosterone would be quite inert to it.


gab9681-

I still like the idea of precipitating test as a complex, then weighing the complex,( or measuring it some other way) because no equipment is needed. You may want to look into this. There is an old QA book by Vogel. A university library will have it.

As for an HPLC method, search medline. There are chromatography journals where I'm sure you can find several published methods for steroids. It doesn't even need to be fancy because you are not trying to separate it from other steroids, you just want it to show up in the chromatogram with a reasonable RT. If the HPLC is reverse phase, you could probably even use a really straight forward method such as: 80/20 MEOH/H2O, 1mL/min.


As a last resort, get a separatory funnel and extract the test out of the oil with methanol, evap,and weigh it. You will probably get some oil along with it, so you would need to correct for this by running a control group along side that contains oil (only). Evaporate the methanol into pre-weighed vessels and take the difference.

Andy