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analyzing anions from sample dissolved in DMF or other solvents

IC-man
Involved Contributor II
Involved Contributor II

Hello team,

Analytical instrumentation:

ICS6000

AS19 4um  (4mm)

DRS600 suppressor 

25uL loop

10mM 0-10min  KOH

10-45mM 10-45min KOH

1.0mL/min

conductivity

I tried to analyze MSA in a product dissolved in DMF(polar organic solvent).   The peak of interest was on top of the organic hump.  The back side of peak returning to baseline.   This is not ideal chromatography conditions.  Would reducing the eluent strength to 0mM for the first 5 minutes or more allow an analyst to separate the polar organics from the MSA.  MSA usually comes out around 8minutes with the above conditions.  I know if had other anions the run would have to be extended 5 minutes.  Total runtime is 60minutes.  The separation of acetate and Fluoride might be affected.    Any insights? 

4 REPLIES 4

The_Ion_Lady
Team TFS
Team TFS

@IC-man, interesting. What concentration of anions are you looking at? Also, are you using electrolytic suppression or external water? From experience of using DMF, it's never that clean. Chemical suppression is better for using with higher levels of organic solvents and dirtier matrix in samples.

Let me know the details and I can give you more info.

Look forward to further information 😊

IC-man
Involved Contributor II
Involved Contributor II

Hello,

 

I use electrolytic.   

 So far, I have analyzed samples in 5-8% NMP, sulfolane, and DMAC(polymer world).  Since I inject 25uL the solvent does not seem to bother the suppressor, trap column.  My retention times have stayed steady   LOD stays 0.025ppm to  0.035ppm.   I started running into problems when some samples containing metals(Ni, FE etc..) began to roll in.  These samples coated AS19 column, suppressor, cr-atc.  I cleaned the column with 2 n HCL.    I then cleaned the suppressor and trap column with Oxalic acid.   My retention time shifted 0.6-1.0 minutes earlier.  The suppressor and the trap column were not restored.  I now filtering these samples through SCX SPE.   I analyze cations without the SPE SCX pretreatment.  Removing metals from samples with a polar organic is a must!!!  Especially in recycle mode.

Thanks a million, 

IC-man
Involved Contributor II
Involved Contributor II

If I am looking for methane sulfonate.   I want to calibrate to .050ppm.   Even though I don't care about the other anions I still worry about coelution.  I need to push the polar solventI(DMF)  within 5minutes.  After the DMF is pushed through ramp though with DI water.   Ramp to 10mM to 20mM then to 45mMKOH. 

 

Thanks, 

The_Ion_Lady
Team TFS
Team TFS

@IC-man , let me tell you why the retention time is now earlier. 

1. transition metals have a tendency to stick to the resins and take up capacity in columns and suppressors.

2. 2N HCl through an anion exchange column with have a lot of Cl- anions taking up all the capacity of the column so with need a lot of column flushing with 2N NaOH to clean that column.

 

There are ways to solve some of those problems.

To ensure you have less organic interference, I would recommend a Dionex IonPac NG1 guard column.

 

Overall, I would suggest you flash/clean the system out with manually prepare 2N NaOH  with 50:50 concentrated NaOH for about 2hours before going back to your method.

If you use 100mM from EG to flush/clean, you will need to drop the flow down to 0.5mL/min (keeping backpressure pressure ~2000psi). Do that over a weekend or overnight, slower and longer is the best to clean columns. Unfortunately with 4mm column format there will be a lot of liquid! Don't forget the waste 🙂.

Good-luck.

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