Injecting sample with buffer salts

[cody841]

Hey, I'm trying to do residual solvents on a sample that has citrate buffer in it by direct inject. I don't have much options for sample prep or using headspace.
Some more info: My standard is acetaldehyde, ethanol, acetone, ACN, dibromomethane and DMSO in water at ICH limits. Samples are radioactive, so I am only supplied with a very small amount ~ 50 µL.

I've found that at low injector temp ~200 C the citrate does not affect the chromatography, however I have a lot of carryover of DMSO from my standard (in water). At 230 C and higher, the citrate does something in the liner (degrades and stays) and all injections following have high tailing and almost a shoulder on the peaks at which point changing the liner fixes the problem. I'm using a straight liner with wool that is "ultra inert". Injecting 0.5 µL with a 30 split. Flow at 5 mL/min. I've tried a pressure pulse to get the sample on faster with no luck.

Does anyone have any experience dealing with something similar or any suggestions? Some sample prep maybe, or a guard column, specific liner? A way to get the DMSO out at lower temp?

Thanks

[rb6banjo]

What detection limit for the analytes in your mixture?

[cody841]

<1% of the limit for each. I haven't calculated actual values yet.

[mbreslav]

Hi Cody,
I am struggling with the same problem: carry-over of the DMSO. I am using cold direct injector with stainless steel sleeve as a liner. My carryover is up to 10% of DMSO. I tried different injector temperatures from 65 to 100C - same problem. I installed guard column - did not help. I tried inlet temperature ramp after injection to 220C - no changes. Still struggling...

[Peter Apps]

Hi Cody,
I am struggling with the same problem: carry-over of the DMSO. I am using cold direct injector with stainless steel sleeve as a liner. My carryover is up to 10% of DMSO. I tried different injector temperatures from 65 to 100C - same problem. I installed guard column - did not help. I tried inlet temperature ramp after injection to 220C - no changes. Still struggling...

Why not use a glass inlet liner ??

Peter

[mbreslav]

But would be the difference, if DMSO is trapped by the sample matrix?

[Peter Apps]

But would be the difference, if DMSO is trapped by the sample matrix?

If DMSO is trapped by the sample matrix, and only by the sample matrix, then the liner will make no difference. It is very likely that the DMSO interacts with the stainless steel liner you use, as well as with the matrix.

Peter

[mbreslav]

I will be able to check it by injecting the sample without salts. Thank you for the suggestion.

[RogerBardsley]

Hi All,

I work for Teledyne Tekmar with their headspace instrumentation. You state that headspace is not an option, and I agreee that the instrumentation can be difficult to justify for a short term project. However Forensics labs have been doing headspace analysis for accelerants for many years using paint cans. If there are only a few samples, a heater block at a constant temperture, a sealed glass vial, an internal standard and a heated gas tight syringe can provide some good results. This will keep the buffer and some of the solvents out of the injector.

[mbreslav]

Here is what I found by running system suitability samples without salts, with NaCl only and with NaCl+ascorbate: ascorbate in my drug product formulation is responsible for trapping residual DMSO. There is nothing that can be done about it using direct injection. The only way - is to remove ascorbate using an anion-exchange cartridge before analysis.

[Peter Apps]

Thanks for the feedback - headspace might be the way to go.

Peter

[mbreslav]

Headspace would be the way to go. But unfortunately it is cost prohibitive taking into account a great number of sites that will be using this method. However I am going to validate this residual solvents method without using ascorbate in working standards, so the contamination load on a column is minimum. Then I will do robustness studies finding out how many samples I can analyze until system suitability fails and there is a need to clean the injector and trim the column.
Thank you for the participation in this discussion.