Chromatography Forum

Hello everyone,

I am having some issues with getting LCOH powder standards into solution. Literature has suggested a heptane:ethanol ( 50:50) solution, but this solvent has not put my standards into solution. I have also tried heptane, acetone, dodecane, and heptane:isopropanol:water (70:20:10).

This is my first time posting and I am getting a little desperate for help now. I greatly appreciate any help or insight that you may have.

How long?

I was using chloroform with C30-OH.

osp001 wrote:
How long?

I was using chloroform with C30-OH.

C24-30.

Prior to running them on the GC, I am making either an acetate or TMS derivative and evaporating it down and resuspending it in dodecane. So, I am also nervous that they will not be in solution in the dodecane once I make the derivative.

The nickel-and-dime test would be to add (say) 1 mL of dodecane, let it equilibrate, and squirt a sample. Then add another 100-200 uL of dodecane, let it equilibrate, and squirt a new sample.

If your peaks are the same, you know your solution is saturated and you have undissolved material. If the peaks are smaller the second time around, your solution is not saturated.

You may need heat, ultrasonication, etc. as part of the glib "let it equilibrate" step. Some of these compounds may not be motivated to full solubility over short time spans.

I got the standard to go into solution with chloroform. I am going to run this standard through our protocol and GC and see how it acts. Thank you for your help.

Hmm - in my business we did octadecanol in solid antiperspirants, rarely higher. We used dimethylformamide as solvent and derivatized with BSTFA for these.

The part that is most confusing about this issue I am having is that multiple lab groups have reported using heptane:ethanol. But, when I try using it, it will not put my LCOHs into solution. Heating the solution to 40-50 C did put the LCOHs into solution, but once cooled back down to room temperature the solution would be "cloudy".

The main issue with the cloudiness in the standard solution that I found is that it leads to inconsistent peak area percentages and this will lead to massive variation in calculated concentration of your samples.

Toluene is one of my favorite solvents for high boilers. Pyridine is another possibility but it stinks stinks stinks and tends to linger through the chromatogram. You might need a bit of DMSO or DMF (20%) if all else fails. I am pretty sure DMSO or DMF should come out before C24 alcohols.

Hi

Without knowing your matrix or analysis problem

a) Literature has suggested a heptane:ethanol ( 50:50) solution, but this solvent has not put my standards into solution. heptane:isopropanol:water (70:20:10).

No , they are too polar, which is why you have the "cloudiness " - DCM or toluene should work if just for solvation

b) But, for that chainlength you will need to derivitise for GC

c) For GC, silylation (as previously suggested) directly with something like TrisilBSA/pyridine or /DMF should work fine