Analytical strategy for an ether compound

[Mattias]

Hi,

I have been asked to determine this compound by any possible analytical technique: polyoxyethylene (12) tridecyl ether.

http://www.chemspider.com/Chemical-Structure.34882.html.

No chromophores, no useful groups for LC/MS detection and I do no have GC/MS. I was thinking of derivatisation, but there are no obvious options for this either. On top of this, the idea is to look for trace amounts of this substance in a water solution. I will be very glad if any of you have some smart ideas!

[Consumer Products Guy]

Mattias - I think your link does not show the same material. Look at http://www.sigmaaldrich.com/catalog/pro ... &region=US

So what you have is essentially a fatty alcohol ethoxylate mix, average 12 moles EO, a nonionic surfactant.

Since you'd be looking at trace levels, I think I'd run through a mixed-bed ion-exchange column (gravity) and blow off the water, leaving the nonionic residue. Since your levels may be too small to do gravimetrically, I might suggest dissolving such residue in DMF and make trimethylsilyl derivatives and look for by capillary GC, such as a specialty high temperature column. You will get separate peaks for each parent fatty alcohol chain, and also for each with the different number of EO. Your quantitation might have to be by area summation.

So what else is present except water and nonionic? If nothing, how about good old solids?

[Vlad Orlovsky]

Do derivatization with arormatic derivatizing agent (benzoyl chloride, p-nitrobenzoyl chloride, 3,5-dinitrobenzoyl chloride, anthracene-9-carbonyl chloride, phenyl isocyanate) in presence of pyridine or other base to create UV active molecules and analyze by UV HPLC. You will be able to detect only starting material or mono ester. You will need to do sample prep - liquid/liquid extraction to concentrate your sample (be prepare to fight very tough emulsions). You will probably need to dry your extract in order to avoid wasting derivatizing agent.

[Mattias]

Thank you both for good suggestions! I do not have GC at all in my lab,so this must be done be HPLC, LC/MS or CE. Fluorescence is an option for the HPLC.

This molecule looks quite hydrophobic. The solution contains (besides water) only sodium chloride and some acetic acid. How about loading the solution on a C18 SPE cartridge and then elute the compound with a solution of aromatic and/or fluorescent derivatisation agent dissolved in acetonitrile?

I understand that I will get multiple peaks, but that is OK. This is only to prove absence or presence of these kind of molecules. I have ordered the chemical in Consumer Product Guy's link!

[chromatographer1]

One procedure to determine 'less than x amount present' would be to trap the Poly EG ether on a reverse phase cartridge and and release it with ethanol or methanol, then remove alcohol carefully, reconstitute in known volume and perform TLC or HPLC with RI detection.

A simple comparison with a known preparation of the analyte could give you an easy and fairly quick, cheap procedure for a less than x amount test. Spiked sample recovery validation should be done in parallel of course.

I have done this for analytes that would take a long time to elute on HPLC and would separate the homologs, making a trace LOD difficult to attain. Don't forget, there is the problem of unknown losses through the derivitization step. If you can avoid this, all the better.

A simple iodine TLC detection can be Zeroxed for documentation purposes and a prepared sample for recovery validation can be done at the same time, again for documentation purposes. TLC strips are quite inexpensive.

But whatever works best for you. Sometimes, the old simple lab tests can be cheaper and quicker, or EVEN better when you want to prove that 'less than x ppm of analyte is present in the sample'.

Indeed, I completed tests like this before the HPLC could be equilibrated and the column changed, with multiple samples analyzed all the same time with a duplicate spiked samples for validation purposes.

best wishes,

Rod

[Mattias]

Thanks!

I have never used TLC, not even in university... I will stick to something I know = HPLC.
I like the idea of evaporation of the sample after elution from the cartridge. The sample will come in 1 ml aqeuous portions and I would prefer not to use more than one sample per cartridge. It is also not so good to inject 100% acetonitrile on the column afterwards.

My first attempt will look like this:
Dissolve N-METHYLISATOIC ANHYDRIDE (called M-25) in acetonitrile to 0.1 mg/ml
Add the 1 ml portion of water to a conditioned 100 mg C18 cartridge (Supelco)
Wash of the salts with water and dry the cartridge with vacuum
Elute the cartridge with 1 ml of M-25 in acetonitrile
Inject on LC with fluorescence detection (350/446 nm), gradient elution.
(if necessary evaporate eluate in RotoVac and reconstitute in water)

By using an anhydride in a non-aqueous solution, the esterification of the hydroxyl group should be fairly easy I hope? Do I need to add base? The reason for using M-25 is that we already have it and that it is quite cheap (1 g costs about 100 Euro).

thanks

[Consumer Products Guy]

We have also used RP with refractive index detector to determine nonionic surfactants. Typically 2 to 4 peaks are obtained, several components in each. OK if your nonionic samples are concentrated enough. This doesn't provide the detail or chain length distributions that capillary GC can provide though.

Interesting, a lab without any GC.

[chromatographer1]

CPG,

also interesting is that they don't bother with TLC in schools anymore.

Cheap, easy, quick, isn't good enough anymore. You have to buy a space shuttle to go to the corner store and buy milk.

I remember testing for 4 components of a synthesis of a drug which had a wide solubility and polarity range. By HPLC it took 16 hours to complete (isocratic analysis) to do ONE sample. (lots and lots of mobile phase of high purity solvents)

By TLC-RP I was able to test 16 samples in only one hour of work: sample preparation, spotting, development, staining, and photocopying, followed by writing up the report. It was a "less than 100 ppm present" test which was easily achieved.

For some strange reason the drug company preferred to use TLC.

But this was in the days where drug companies made a profit.

best wishes,

Rod

[Consumer Products Guy]

Myself: I haven't done TLC in 25 years now.

[chromatographer1]

(showing my age:) and don't get me started on slide rules !