Chromatography Forum

I have to measure Log D. It it ok to inject 10ul of Octanol in RP hplc? Would it affect my peak shape a lot?

Compounds are in small amount it would be difficult to extract them from octanol and then dissolve them for hplc?

I doubt... unless you use a lot of organic. I'd set up a series of small test tubes with ~1 ml water:ACN ranging from 80:20 to 20:80, place a drop of octanol. At some point it will dissolve. This would be your mobile phase.

Or.. use normal phase, GC, GC-MS if the compound is amendable.

One can obtain this quantity directly, using a countercurrent chromatograph. With our 200 ml one it will take quite a lot of compound.

We can help..

You can evaporate a small amount of your octanol sample and re-dissolve the residue in the same volume of HPLC-compatible solvent, I have used the reverse of this method in normal phase HPLC.

I agree evaporate the octanol off. If the analytes are volatile you are better off using GC or GC/MS.

People still shake flasks?

Since you already have a liquid chromatograph and likely a C18 column, I would seriously look into logP/logD via HPLC.

People still shake flasks?

Since you already have a liquid chromatograph and likely a C18 column, I would seriously look into logP/logD via HPLC.

There are still analytes where the HPLC method is not appropriate (logP < 0). If you want a value more exact than "logP smaller than smallest available standard" you have to shake flasks. Or what reference standard do you use < 0 ?
Joerg

People still shake flasks?

Yes. I'm currently doing alcohol solubles on 36 samples of competitive fabric softener liquids.

Never mind that on these formulations that oven solids = cationic softener level. Never mind that like 8 samples of Gain are all the same except for fragrance and color, and similar for other brands groupings. The product development scientist (woman PhD) insisted to my boss that I pushed-back when I suggested to her that oven solids would provide the same information, but she wanted them done the same way a different analyst - her friend - had done a few in the past. So I got in trouble from my boss for using my experience and knowledge; we're not supposed to let others with less knowledge/experience dictate to us "how" we do such assays, that is our business. But in today's world of political correctness, things are different, and that PhD did not discuss with me, instead tattled to my boss.

So way more labor is now required, plus at least 2 gallons of alcohol, plus two gallons of alcohol volatilized into the atmosphere, and yet we also have big sustainability and environmental goals...

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Hey: that's a thread steal!

But very funny, and true too often. Good saying: just mutter "it's a living"

People still shake flasks?

Yes. I'm currently doing alcohol solubles on 36 samples of competitive fabric softener liquids.

KM: I don't know how many years of experience you have with products like this, but I agree that on this type of product that oven solids relates very well to alcohol solubles for cationic softener determination.

And wait until you get to Snuggle, Downy non-Ultra and Down Free & Sensitive, Gain non-Ultra, WalMart Great Value, and Final Touch Ultra, and find out that they are 100% alcohol soluble anyway, so solids must equal alcohol soluble solids by definition.

People still shake flasks?

Yes. I'm currently doing alcohol solubles on 36 samples of competitive fabric softener liquids.

Never mind that on these formulations that oven solids = cationic softener level. Never mind that like 8 samples of Gain are all the same except for fragrance and color, and similar for other brands groupings. .

I never considered measuring logP for detergents. I'd wonder if micro-emulsions would make this measurement problematic?