Ion Chromatography

Created by Monica Z. Bruckner, Montana State University

Please visit our website for more information on this topic.

What is Ion Chromatography?

Ion chromatography is used for water chemistry analysis. Ion chromatographs are able to measure concentrations of major anions, such as fluoride, chloride, nitrate, nitrite, and sulfate, as well as major cations such as lithium, sodium, ammonium, potassium, calcium, and magnesium in the parts-per-billion (ppb) range. Concentrations of organic acids can also be measured through ion chromatography.

How Does Ion Chromatography Work?

Ion chromatography, a form of liquid chromatography, measures concentrations of ionic species by separating them based on their interaction with a resin. Ionic species separate differently depending on species type and size. Sample solutions pass through a pressurized chromatographic column where ions are absorbed by column constituents. As an ion extraction liquid, known as eluent, runs through the column, the absorbed ions begin separating from the column. The retention time of different species determines the ionic concentrations in the sample.

Applications

Some typical applications of ion chromatography include:

• Drinking water analysis for pollution and other constituents
• Determination of water chemistries in aquatic ecosystems
• Determination of sugar and salt content in foods
• Isolation of select proteins

How to - Sample Collection, Preparation and Concerns

Liquid Samples:

Liquid samples should be filtered prior to evaluation with an ion chromatograph to remove sediment and other particulate matter as well as to limit the potential for microbial alteration before the sample is run. Aqueous samples should be collected using a sterile syringe or bottle rinsed three times with sample water and then filtered through 0.45um (or smaller) filters. The collection vial should likewise be rinsed three times with filtrate before being filled brim-full of sample filtrate. Samples should be stored cold until they can be processed. The minimum sample required for analysis is approximately 5mL, with no maximum limits.

Link to Orun

Solid samples and Organic Liquids

Solid samples can be extracted with water or acid (cations) to remove ions from the sample surface. Liquid samples must also be filtered and stored cold until analysis can be performed. The minimum sample required for a solid sample is approximately 2-3 cm2 for solids, with no maximum limits.

Data Output and Analysis

The diagram on the upper left shows how an ion chromatograph works to output data. Each peak represents a separate ion from the sample solution. The elution time, or time it takes for the ion to move through the column, varies for each ion species as they elute from the column separately as the pH and/or ionic strength of the eluent is increased. The concentration of ions moving through the column at a particular time is represented by the height and the breadth of the peaks and can be correlated to the concentration of a particular species in the sample solution.

The graphs on the upper right display typical data output from an ion chromatography run. The upper graph shows cation concentrations and the lower graph depicts anion concentrations from dilute glacial waters. Ion concentrations can be calculated using the area under each peak, where a larger area correlates with a higher concentration of a particular ion species. Most ion chromatography machines provide software that calculates this area, which users can convert to ppm or other quantity using calibration standard solutions.

Literature

For more detailed information regarding the theory and practice of ion chromatography, please see:

• Joachim Weiss, Tatjana Weiss (Translated by) (). Handbook of Ion Chromatography, Third, Completely Revised and Enlarged Edition. John Wiley and Sons, Inc. 931p. ISBN: 3-527--9.
• Prof. Yuri Kazakevich and Prof. H. M. McNair () The Basic Liquid Chromatography (more info) from the Analytical Sciences Digital Librarycollection.
• Chromatography Forum (more info) : An online public discussion group where you can post questions, news, or messages of interest to chromatographers everywhere.

Related Links

• For more information about other types of chromatography, please visit theNational Sciences Digital Library Collection.
• For more information about ion chromatography applications, clickhere.
• For ion chromatography distributors, please visit theMetrohm orDionex websites.

Teaching Activities

For teaching activities, labs, and resources, please visit:

Want more information on IC Ion Chromatography? Feel free to contact us.

Hi all,

I'm not going to lie, this is 100% a question on a take-home final.  However, the book that we use, coupled with the professor, means I've not solved most of the problems on the take-home final through pouring over the book, but by google and doing my own research.  Anyway, after 9/10 questions successfully solved and answered, I'm stumped beyond all attempts to solve this last question.

This question is in regards to Ion-Exchange chromatography with Eluent Suppressor Columns.  We're told to view a figure in our book.  It shows the separation of the group I and group II metals using ion-chromatography.  The group I elements come off the column first and they're grouped into one peak.  Then individually the group II elements come off the column in the order, Mg, Ca, Sr, Ba.  We are then asked to explain why:
a)  The group I metals elute faster than group II metals
b) The group II metals elute in reverse order of their atomic numbers

First thoughts that came to mind were Zeff, Ionic size, polarizability, and such.  However, when I was thinking about that, I realized that group I ions would probably have the largest Zeff and would bind most tightly to the column.  So that idea was shot, polarizability...we've got bigger, more polarizable elements at the bottom, so..I'd think that they would probably elute slower, so that might be a reason why the group II metals elute in the order they do.  After googling everything I can imagine with regards to this question, and trying to find scholarly articles, I'm giving up.  I've got other finals to study for (PChem, ugh), and after this many hours, I'm just frustrated with this professor's exam.

Now, reading the rules, I fully realize that "my professor is bad.." and such isn't an excuse.  I understand that, and that's not my excuse, just one of the reasons I've decided to finally stop googling in vain, and come here in hopes someone can point me in the right direction.

I'm thinking A-Chem is the most appropriate section for this question, but if it isn't Mods, feel free to move this to the appropriate forum.

Thanks for your time.

BTW, take-home final is due on wednesday by noon (CST), just for reference. Hi macman:

Elution order in ion exchange chromatography is determined by the charge density (charge/radius) of the hydrated ion. In organic acids and bases the elution order is determined by their pKa or pKb (strength of acid or base)

For ion exchange selectivity, we need to consider the hydrated radius of the ions and not just the bare ionic radii.

The hydrated radius of an ion is the effective size of the ion or a molecule plus its tightly bound sheath of water molecules, which are attracted by the positive or negative charge of the ion. Smaller bare ions have larger hydrated radii because they attract water molecules more strongly

- Lager radius of naked ion -> more diffuse electric charge -> fewer water molecules
  surrounding the ion

- Greater ion charge -> increased solvent attraction -> greater the hydrated radius

More information: The Selectivity and retention time in Ion Chromatography depends on:

1- Valence of ions ( Retention time increases with increasing ionic charge )

2- Radius of hydrated ions ( Retention time increases with decreasing hydrated ionic radius,
   and increasing naked ionic radius )

3- Polarization of ions ( Ion Which can be polarized easily has longer retention)
4- Concentration of the mobile phase
5- Column Temperature
6- pH of the mobile phase

(Information from Shimadzu Power Point File)

Regards,

Chiralic