Ion chromatography – straightforward cation analysis at trace levels

Trace analysis of cations, amines, and transition metals by ion chromatography can be carried out with or without ion suppression. However, some applications require particularly a highly sensitive analysis. Read this article from Issue 9 of the Analytix Reporter, produced by Merck, to find out more.

The highly sensitive analysis required by some applications can only be achieved by sequential suppression as this considerably lowers the detection limits of the analytes. Such analyses are common, for instance, in power plant or pharmaAnalytix_Reporter_Issue9_Article8_Pharmaceutical applications. Moreover, there are several norms and standards that request for a suppressed cation analysis (e.g. the ASTM D6919 - 17 Standard Test Method for Determination of Dissolved Alkali and Alkaline Earth Cations and Ammonium in Water and Wastewater by Ion Chromatography). In short, suppression reduces background conductivity to a minimum and decreases baseline noise. Both effects together improve the signal-to-noise ratio and increase the sensitivity of the measuring system. Thus, whenever the quantification of very low concentrations of cations is required, analysis with sequential suppression is the method of choice.

Analyses that benefit with the use of sequential suppression
Some typical examples of cation suppression are:

• Traces and ultratraces of Na in the presence of monoethanolamine at high concentrations (typical of sample matrices in nuclear power plants).
• Trace and ultratrace concentrations of alkali and alkaline earth metals such as Li, Na, K, Mg, or Ca, and NH₄+ in ultrapure water.
• Traces of transition metals, e.g. Co, Ni, Zn, Mn, and Cd in various types of water samples.
• Aliphatic and aromatic amines in pharmaceuticals, e.g. piperazine in cetirizine·HCl, tetrabutylammonium in atorvastatin, dimethylamine in meropenem, dimethylamine in imatinib mesylate, and meglumine in meglumine salts.

Conclusion
This article demonstrates that the acidic binary IC eluent nitric acid/rubidium nitrate concentrate and the sodium bicarbonate/sodium carbonate suppressor regenerant for use with Metrosep C Supp 2 column, allows for the accurate determination of ammonium in acidic solutions, such as those found in ammonia scrubbers. We also offer a representative range of inorganic cation standards as certified reference materials (CRMs) for IC.

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