Fluoride Failing low

[icctberk]

Hi everyone,

We are having a problem with our Dionex ICS-2000. It use to have a CR- TC Tower, but our calibrations were not passing for any of the anions, so changed it over to a Carb/Bicarb eluent late last year. Essentially it is has become an ICS-1000. Recently, we cannot get the analyte fluoride to pass when we are calibrating the instrument. The ICV (initial calibration validation) for fluoride keeps failing low, all the other anions are passing.

We have AS22/AG22 2 mm columns installed with a 300 ASRS 2mm suppressor. Flow rate is 0.30 mL/min. Pressure and conductivity are at ~1614 psi and ~20.2 µs. We buy the 100x of our eluent pre-made from Dionex/Thermo Scientific.

Here is what we have tried and it has not worked:
1. Changed our calibration standard three times, we can get fluoride to pass on our other instrument, a DX-120, so we know it is not our standard.
2. Added eluent to the vials to get rid of the water dip.
3. Lowered our mA on our suppressor to 50.
4. Both our columns were changed a month ago.
5. Changed our suppressor.
6. Changed the injection valve components.

Would anyone have any other suggestions that we have not tried? We would really like to get fluoride to pass on this instrument again since the run time is 15 minutes compared to 25 minutes on our DX-120.

Thank you

[James_Ball]

Hi everyone,

We are having a problem with our Dionex ICS-2000. It use to have a CR- TC Tower, but our calibrations were not passing for any of the anions, so changed it over to a Carb/Bicarb eluent late last year. Essentially it is has become an ICS-1000. Recently, we cannot get the analyte fluoride to pass when we are calibrating the instrument. The ICV (initial calibration validation) for fluoride keeps failing low, all the other anions are passing.

We have AS22/AG22 2 mm columns installed with a 300 ASRS 2mm suppressor. Flow rate is 0.30 mL/min. Pressure and conductivity are at ~1614 psi and ~20.2 µs. We buy the 100x of our eluent pre-made from Dionex/Thermo Scientific.

Here is what we have tried and it has not worked:
1. Changed our calibration standard three times, we can get fluoride to pass on our other instrument, a DX-120, so we know it is not our standard.
2. Added eluent to the vials to get rid of the water dip.
3. Lowered our mA on our suppressor to 50.
4. Both our columns were changed a month ago.
5. Changed our suppressor.
6. Changed the injection valve components.

Would anyone have any other suggestions that we have not tried? We would really like to get fluoride to pass on this instrument again since the run time is 15 minutes compared to 25 minutes on our DX-120.

Thank you

With the shorter runs on this instrument you may want to compare the chromatograms between the two instruments and see if there is a tiny peak on the one with the longer run time just after the Fluoride peak. We have had a similar problem on our Metrohm instrument. The longer run may be separating that peak from the fluoride peak while the faster run may not, and it is adding to the areas of your lower standards causing them to be artificially high. We believe this peak could be an acetate peak that is a contaminate in one of the stock standards since one source will pass while the other will fail. Look at the curves and see if the areas for the low standards on the failing instrument seem slightly higher than they should be compared to the higher standards.

[mattmullaney]

Hi Icctberk,

I agree with James_Ball, I have observed a similar phenomenon using both Dionex ICS-3000 as well as a Shimadzu Prominence instruments. With two vendors' standard solutions, both mixed anions as well as fluoride standard solution, decreasing the hydroxide concentration in the eluent allowed us to observe as many as two additional peaks eluting after fluoride ion. Our thoughts at the time were that the source of the peaks might be contaminants unintentionally introduced with preservatives in the standard solutions.

Good Luck!

[Markus Laeubli, Metrohm]

Dear All

yes, it's not insrtument depending. Its standard solution depending. You miht go for certified standards e.g. from Sigma-Aldrich http://www.sigmaaldrich.com/analytical- ... ge=9639432.