Do you need to develop an Ion Chromatography (IC) method? Or are you struggling to optimise conditions and not sure where to begin? This list is a summary of tips to help you.
This is based on the free webinar 5 quick tips to develop your IC method, which can be viewed at your leisure here.
Ion Chromatography separations generally follow rules:
Size - small ions elute before larger ions.
Charge - single charged ions elute before multiple charged ions.
Column choice is the place to begin. Check out the column selection guide to find out which column suits your application best. There are also other ways in which you can manipulate IC separations. These quick tips will show you how.
1. Eluent strength
Simply changing the strength of your eluent can alter the elution order of some ions.
Change from isocratic 30mM to 48mM Methanesulphonic acid (MSA) and Magnesium will swap places with Potassium (CS16 column).
0 mM Carbonate/1.0mM Bicarbonate will not resolve Chlorate and Phosphate, 6.0mM/1.0mM will resolve them (AS14 column).
Look at gradient separations, which sharpen peak shapes and resolution of later eluting peaks, plus improving front end separation.
Add additional steps in your gradient to manipulate particular separations further.
The column manuals give great examples, find these and related application notes on the respective column webpage.
Column temperature is important for run and retention time stability.
Find the temperature range for your column in the manual.
Varying the temperature can change the selectivity of the separation.
Monovalent peaks will tend to elute quicker in comparison with divalent as temperature increases.
On a CS16 column at 23°C, magnesium and potassium coelute, separation occurs at 40°C and even more so at 60°C.
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Some applications work better with an alternative detector such as nitrate and nitrite in the high presence of chloride.
Conductivity detection would be swamped with high levels of chloride masking the nitrate and nitrite peaks.
Nitrate and nitrite are UV active, chloride isn’t and switching to a UV detector gives a cleaner response.
Other detectors can be linked to ion chromatographs, such as Mass Spectrometers for unknowns and where higher resolution is required and also ICP-MS for speciation of metals.
4. Method development from your desk
You don’t always need to start a method from scratch with lots of lab work.