Frequently Asked Questions about Ion Chromatography

How long are working standards stable?

This will depend on your analytes and their concentrations. We would recommend that you establish an in-house stability assessment program by measuring aged working standards against freshly prepared working standards. If you wish to improve stability then you can add dilute acid or base to your standard matrix.

I’m having trouble analyzing brine solutions, any tips?

High concentrations of total dissolved solids can cause issues with analysis. Dilution of your sample is a good approach if you are not looking for low concentrations. If diluting the sample is not an option you could try switching to a smaller injection loop. Finally, you can modify your sample preparation to include filter your sample with specialty filters that strip major matrix components from your sample matrix. These filters can be either added to a syringe, included in your IC vial cap, or be plumbed in-line before your injection valve.

Can you perform Chromium speciation analysis with IC?

Yes, there are several application notes that detail the use of IC partnered with mass spec or IC instruments with UV/VIS detectors to perform Cr speciation. Here at IV, we use a combination of anion IC to measure Cr +6 as Chromate and ICP to measure total Cr.

Are there any ways to extend the life of high-cost consumables?

This will depend a lot on your sample type and how clean they may be. Investigate in-line filters and guard columns that can help prevent wear on your analytical column. Also, check the system pressure frequently as spikes in pressure may indicate a filter that needs to be replaced.

What is the best way to determine eluent concentration?

If you are starting from scratch then we would recommend referencing sample chromatograms that are available from column manuals, white papers, and application notes by IC instrument manufacturers. That should get you close to a final concentration, then you can tweak the concentration by running control samples to finalize your method. Thermo also has a good virtual column tool that can help estimate how eluent concentration will impact retention times and separation.

I’m having trouble with contamination in my blanks.

Try segregating your IC lab equipment, including your diluent, as much as possible to be used for IC applications only. You may also see a benefit from leaching your IC vials with DI H2O, especially if you are seeing cation contaminants.

We are having trouble achieving low detection limits.

We would recommend trying to get your background conductivity as low as possible. Use freshly prepared eluent, kept under a nitrogen purge, as compared to using an eluent generator. During sample preparation, try to utilize specialty filters that remove major matrix components from your sample. Finally, you can Increase the sample amount loaded onto your column by switching to a larger injection loop.

In what way does methanol or acetonitrile improve performance?

If your analytes are non-polar then you may benefit from adding methanol or acetonitrile to your eluent. The addition of these organics may also increase the solubility of your analytes. We would suggest referencing application notes, white papers, and column manuals that are available from ion chromatography instrument manufacturers to get a starting point on the concentrations of methanol or acetonitrile to add to your eluent.

Could you suggest a method for separating organic acids (acetic, formic, butyric, & propionic)?

For this method you will want to investigate ion exclusion columns that are better suited for separating weak organic acids. Both Metrohm and Thermo have application notes available and the column manual for the IonPac ICE-AS6 is a good resource for sample chromatograms that you can reference for method development.

If an IC is connected to ICP-MS, what would be a good sample flow rate and what nebulizer should I use?

This is a great question. We would recommend validating the ion chromatography separation portion of your method before selecting a nebulizer based on that flow rate. There are a wide range of nebulizers available that can handle a slow flow rate or a fast flow rate. Thermo has some good application notes available on instrument settings used for various methods.

What biocide would you recommend to stabilize phosphate?

Unfortunately, the biocide we use in our certified reference material products is held as a trade secret. There are a wide variety of anti-microbial agents on the market, and we would suggest adding the agent at a very low concentration to your standards to prevent “bug growth”. The concentration that we add to our standards is 0.01% by volume. However, make sure to run a sample of your biocide at your working concentrations and higher to check for any possible interferences that may be present from the addition of the biocide.

Is there a method developed for separating isomers of organic acids? Like valeric and iso-valeric acids.

Yes, there are applications for separating valeric and iso-valeric acid. The methods include the use of ion exclusion columns. Thermo published an application note (AN 291) using their IonPac ICE-AS1 column to separate these analytes along with some other organic acids.

How can I separate Fluoride and Iodate peaks?

There is a recent paper that was published that may help with this application. It appears to require a hydroxide gradient method with an IC instrument equipped with a conductivity and UV detector. Please see this paper for full details:

Das, M. K., Mishra, V. G., Umadevi, K., Jeyakumar, S., & Saxena, M. K. (2023). Simultaneous determination of fluoride, iodate and iodide by ion chromatography in caustic off-gas scrubber of nuclear recycle facilities by employing dual detectors. Separation Science and Technology, 58(15–16), 2867–2873. https://doi.org/10.1080/01496395.2023.2222226