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Gulf Coast Repository

Ion Chromatograph (IC)

Overview

Thumbnail image of Ion Chromatograph Ion chromatography is a form of liquid chromatography used for water chemistry analysis. Measures of the chemical composition of interstitial (porewater), surface, and other waters can be critical in determining diagenetic, geochemical, and biological processes. At the Gulf Coast Repository (GCR), the ion chromatograph (IC) can be used to determine concentrations of major cations (e.g. –Na+, K+, Mg2+, and Ca2+) and anions (e.g. –Cl–, Br–, SO42–) in liquid samples.

Instrument Make & Model

Metrohm 940 Professional IC Vario with 858 Professional Sample Processor
Metrohm 850 Professional Ion Chromatograph with 850 Professional Autosampler

Estimated Measurement Time

  • Sample Preparation: ~3 hours
  • Sample Measurement: ~1–2 samples/hour

Quantity of Sample Material

100 uL–10 mL; dependent on dilution

Principles & Analytical Capabilities

Each ion set is separated and detected in its own flow path. Sample is directed from the anions and cations sample loops into their respective chromatographic columns in which dissolved ions absorb to a stationary phase resin. A unique eluent flows through each column and competes with sample ions for adsorption sites. This causes a gradual separation of sample ions into discrete bands within the column—ordered by each ion’s strength of adsorption (influenced by ionic radius and ionic charge). The separated analyte bands are carried off by the eluent from the column into a conductivity detector, which integrates each analyte’s signal over a short time interval. Analyte concentrations in the samples are calculated based on calibration curves created prior to each sample sequence by analyzing a set of known standards and blanks.

Table Caption
Cation/Anion Measurement Range [ppm]
Br– 0.05–100
Ca2+ 0.1–200
Cl– 0.1–200
F– 0.02–50
K+ 0.05–100
Mg2+ 0.05–200
Na+ 0.05–200
NH4+ 0.05–100
NO2– 0.05–100
NO3– 0.05–100
SO4 0.1–200

In order to maintain a consistent retention time for each ion, the columns are housed in a temperature-controlled chamber and the eluent flowrate is kept constant. For reduced background conductivity and better detection of the analytes, the anions flowpath employs a chemical suppressor and a CO2 exchange membrane between the column and the detector. These suppressors remove sodium and bicarbonate (as CO2) from the eluent solution and convert anions to their more conductive acid counterparts.

Data Generated

Data components:

  • Br-
  • Ca2+
  • Cl-
  • F-
  • K+
  • Mg2+
  • Na+
  • NH4+
  • NO2-
  • NO3-
  • SO4
  • Available upon request: retention time (min), peak height (uS/cm), and peak area [(uS/cm) x min]

Data files:

  • Concentration (CSV): cation and anion concentrations in umol/kg or ppm
  • IC Report (PDF): Metrohm MagIC measurement results and ion chromatogram report for a single sample.

Data Example

Interstitial water sample measurements of sodium, chloride, potassium, and bromide from Hole U1607A of IODP Expedition 400 in the northwest Greenland glaciated margin.
Interstitial water sample measurements of sodium, chloride, potassium, and bromide from Hole U1607A of IODP Expedition 400 in the northwest Greenland glaciated margin.1

Procedures & Manuals

References

1  Knutz, P. C., Jennings, A. E., Childress, L. B., Bryant, R. M., Cargill, S. K., Coxall, H. K., Frank, T. D., Grant, G. R., Gray, R. E., Ives, L., Kumar, V., Le Houedec, S., Martens, J., Naim, F., Nelissen, M., Özen, V., Passchier, S., Pérez, L. F., Ren, J., … Zimmermann, H. H. (2025). IODP Expedition 400 Ion chromatography [Data set]. International Ocean Discovery Program. https://doi.org/10.5281/zenodo.15366869