Analysis of PEG 400 in a matrix containing Dextrose

[Alfred88]

Hello,
We are trying to analyze PEG (Polyethylene Glycol) 400 in an aqueous matrix, using SEC and RI detector, but we have strong interference from Dextrose in the matrix. The matrix also has buffer, salts, and glycerin.
We have tried with the Waters’ Ultrahydrogel 120 column (120A), and the PolyLC column (60A) but got no good separation.
Could anyone give us some advice? Thanks

[Uwe Neue]

The Utrahydrogel 120 should do fine for this purpose. Something else is wrong. Please describe in detail the remainder of your conditions... Column length, i.d., flow rate, injection volume, mobile phase, temperature, sample solvent etc.

[Alfred88]

Dear Sir:
The conditions are below:

Column: Ultrahydrogel 120 column; dimension is 7.8x300.
Mobile phase is 0.05M NaCl in water, and flow rate is 1 mL/min.
Column oven is at 40C, and detector cell temp is set at 35C.
Inject vol. 20uL, up to 40 uL.
Sample is injected neat (no dilution).
Tubing is 0.010''.

The difficulty here is that PEG400 displayed a broad peak that overlapped with Dextrose (MW of PEG range may be ~ 350-450 D, and MW of Dextrose is ~200).

[Alfred88]

I forgot to mention that we have tried to improve the resolution of the separation, by connecting 3 columns (Ultrahydrogel 120) in series, but that did not help. That set up could resolve about 40% of the overlapping peaks. Should we try some extraction of Dextrose (glucose) first?

[Uwe Neue]

I understand now. You may not be able to do this cleanly, unless you use a lot of columns in series. If you can think of a way to selectively remove the dextrose, you should try this first. A boronate column or SPE could do this for you.

[XL]

Hello,

Please check this link to see if Acclaim Surfactant column is helpful for your application. Analyses of PEG 300, 400, 600 are listed in Figure 17 with chromatographic conditions.

http://www1.dionex.com/en-us/webdocs/25 ... et_V24.pdf

In the event that matrix interferes with some early eluting peaks of the PEG, you might still be able to quantify its content based on the rest well separated peaks.

X.L.

[Uwe Neue]

Actually, XL is correct. If you do your PEG analysis by reversed-phase, the dextrose will always elute as an unretained peak. Such a solution is superior to trying to solve the problem with GPC.

[rhaefe]

This might be useful:

Determination of Polyethylene Glycols by High Performance Liquid Chromatography-Thermospray Mass Spectrometry.
Auriola, S.; Ronkko, K.; Urtti, A. Journal of Pharmaceutical & Biomedical Analysis, 1993, 11, (10), 1027.

It is a reversed phase separation of PEGs in the size range 238 to 590 using a PRP-1 column and ammonium acetate/acetonitril mobile phase.

best regards

[Alfred88]

Thanks to all the suggestions!
We have tried with the Acclaim Surfactant column (Dionex), and used isocratic elution of 5% MeCN (gradient elution does not work with our RI detector). The result: Dextrose is retained (but eluted early), so it is not interfering with PEG400. But PEG400 gave many tiny scattered peaks (just like in figure 17 in the Dionex's brochure, but here we don't have ELSD), so it is very hard to quantify.
If the amount of MeCN is higher (e.g 20%), both Dextrose and PEG would not be retained by the column.
Robert H. (Hamilton Co) gave info about another LC method for PEG. But we could not find this article in the library. Could you describe about the system and operating conditions in this forum? Thanks.
We are looking into the possibility to couple two columns: one amino column, and one SEC. One limit: there is no switching valve for this LC system.
Any suggestions would be appreciated.
Alfred

[Uwe Neue]

You made a large jump in the solvent composition. A smaller change might get you to a better spot (5%->7%->9% etc.)

You do not need to quantify the individual PEGs, just integrate the total area.

[rhaefe]

Alfred88:
Determination of Polyethylene Glycols by High Performance Liquid Chromatography-Thermospray Mass Spectrometry.
Auriola, S.; Ronkko, K.; Urtti, A. Journal of Pharmaceutical & Biomedical Analysis, 1993, 11, (10), 1027.
Compound:
PEG 238 Rt: 2.3
PEG 282 Rt: 2.5
PEG 326 Rt: 2.9
PEG 370 Rt: 3.5
PEG 414 Rt: 4.2
PEG 458 Rt: 5.3
PEG 502 Rt: 6.9
PEG 546 Rt: 8.9
PEG 590 Rt; 11.8
Column: PRP-1, 150 x 4.1mm, 10µm.
Conditions: 85 : 15 0.1M Ammonium Acetate, pH6 : Acetonitrile. 1 mL/min. Thermospray ionization mass
spectroscopy.

[XL]

I agree with Uwe. Using a mobile phase containing around 10% acetonitrile should give better result (the peak height is taller and the run time is reasonable). I expect by intergrating either second half of peaks or an individual peak (say, the tallest one) of PEG-400, you can obtain satisfactory results.

X.L.

[Alfred88]

Thanks to Uwe, Robert H., and X.L.
We will try to make it works.
Alfred.