Peak Tailing

[waclaskil]

Hello fellow ion chromatographers,

I'm having an issue with peak tailing on an IC, that I can't seem to resolve. It is a Dionex ICS-2000 with a KOH eluent generator cartridge, being used to analyze anions. The tailing is most noticeable on fluoride, nitrite, and ortho phosphate. So far I've replaced the columns, both guard and analytical, didn't fix it (I took them apart to look at the packing and replaced the frits, no dead space was observed.) I've tried a different suppressor from another system, which was not experiencing the same issue, and this also did not correct the problem. I've tried bypassing the carbonate removal device, also doesn't appear to be the problem. There has also been complete preventative maintenance performed on the AS autosampler by Dionex, replacing the needle assembly, transfer line, etc.

I would really appreciate any suggestions. I feel like there has to be some dead space somewhere in the system, just not sure where it's coming from. The system is still usable for the most part, but the problem is really exaggerated at low concentrations for said anions.

By the way, I'm using AS-18 and AG-18 2mm microbore columns and isocratic elution.

[Markus Laeubli, Metrohm]

Dear waclaskil

From your test results only the detector itself seems to have a problem. Did you try to use a detector from another system?

[mattmullaney]

I'm afraid the only thing I can think of other than Markus' suggestion is that did the data acquisition rate somehow get changed? The slower the data rate, the broader peaks will become, tailing will be exacerbated and these two effects will be more noticeable at lower analyte concentrations.

If both suppressors are truly well--and I think your troubleshooting is good here--and if no alteration to the system volume (dead volume) has been made such as replacing tubing with larger ID tubing by accident, only the data acquisition and the detector itself remain as causes for the observed ills.

Matt

[bluejay]

As a last resort on our (now retired) DX500 I've unscrewed, inspected, and replaced as necessary fittings and ferrules. This has sometimes taken care of mysterious tailing problems for me.

[malbertson]

Hi waclaskil,

There are a few things you can check if you have not solved this issue already, as pointed out dead volume is an issue in 2 mm IC especially if you have tubing/fittings that are not seated in valve or column connections. Tubing that is not cut perpendicular will also cause tailing. However this sort of tailing tends to be universal across all peaks and not analyte specific. Analyte specific causes that affect halides and some oxides are transitional metal contamination of the column. If you have injected samples that are high in Iron or Alumina these can be bad actors. In this case refer to the column manual for clean up procedures. Other causes with monovalent eluants are carbonate. Low grade water or a poorly service DI Water system can introduce Carbonate contamination. As Carbonate is a divalent anion it will raise background, cause tailing and apparently reduce column capacity. In these cases eliminate the problem at the source i.e. the DI Water system and/or replace/clean your CR-ATC if it is over 2 years old. Remember 2mm columns have the same linear velocity as 4 mm columns, however they do not flush as effectively, so addition care is required in this mode of separation. Let me know if you need any more advise

Regards,

Mark Albertson
Thermo Fisher Scientific
Sales Mgr ANZ.
HPLC, IC, Sample Prep