Chromatography Forum

I'm getting high variability in fluoride analysis (AS15 on ICS-5000). Other analytes work fine. Any thoughts?

iceyuser,

High variability of retention time or area?

Chris

Chris, it's variability in the peak area. The retention time is consistent.

iceyuser,

The most likely causes of this are setting the peak width too wide or having the detector data rate too slow. You should be at 5Hz and 0.1 minute minimum peak width.

Chris

Hi iceyuser,

Check your Matrix as well, chelating metals such as Alumina or high Iron concentrations can influence fluoride recovery

Mark Albertson
Thermo Fisher Scientific
Sales Mgr ANZ

On a similar topic, can anyone recommend the best column for improving fluoride resolution from the water dip? Currently using Dionex IC20 with #051786 AS9-HC high capacity column, with a 9mM carbonate eluent. Has anyone had experience with Allsep anion IC columns? Or is there another good way to improve fluoride without the extra step of spiking all the samples with carbonate to eliminate the dip?

You don't say whether you're open to switching to hydroxide mobile phases but, if so, a good choice would be the IonPac AS19. If you want to stick with carbonate eluent systems the IonPac AS23 is roughly equivalent to the AS9-HC but has superior resolution of fluoride from the void.

It's been a while since I evaluated an Allsep column but in my experience this column isn't state-of-the-art. While they still sell IC columns such as the Allsep column, Grace exited the IC instrument business years ago and hasn't done any IC column development work since.

Showdex has a number of competitive products with good fluoride including the IC SI-50 4E that you might consider as well.

A Metrohm ASupp 7 column does a pretty good job of separating Fluoride from the water dip when using a carbonate eluent. I don't remember off hand the eluent concentration but they have several applications posted online there.

Standardeluent for the Metrosep A Supp 7 - 250/4.0 is 3.6 mmol/L sodium carbonate.

See AN-S-256: Thirteen anions separated on the Metrosep A Supp 7 – 250

For faster separations Metrosep A Supp 7 - 150/4.0 is available.

Have had good luck running fluoride with a Metrohm A Supp 5-100 x4mm column with 3.2mM Na2CO3/1.0mM NaHCO3 eluent. Solved a similar reproducibility issue by cleaning the suppressor with 2,6 pyridinedicarboxylic acid to remove chelating metal contamination. Just a thought.