Combustion ion chromatography (CIC) is an interesting variation on IC that enables the analysis of certain kinds of samples that would be otherwise difficult to manage. To understand the method, it is advantageous to strip away the different layers of the technique. At its heart is chromatography, a basic separations method that makes use of the chemical interactions between the different analytes in the sample and the stationary phase in the chromatographic column to separate the analytes. Different chemical interactions cause the analytes to elute from the column at different times, where they can then be identified and quantified by a detector.

IC uses the overall charge of the analytes, rather than their chemistry, to make the separation. IC is commonly used for environmental water analysis and other industrial uses. IC is most easily performed on samples that are readily dissolved. This presents difficulties with some samples, such as plastics, polymers, petrochemicals and fuels, as well as solid samples, such as soil. CIC adds an additional sample preparation step that, for certain specific applications, allows the use of IC on these kinds of samples without manual sample preparation.

In CIC, the sample is oxidized, or combusted, under controlled conditions so that the combustion gases are collected. Burning the sample changes the chemical molecules; however, the individual elements are still present in the gas. Thus, CIC is an elemental analysis technique. The next module in the sequence absorbs the combustion gases into a liquid. Finally, this prepared solution is introduced into the ion chromatograph.

Common applications focus on the analysis of halogens and sulfur in plastics, fuels and soil samples. Some testing is mandated by environmental laws, as well as various laws relating to the EU’s Restrictions on Hazardous Substances (RoHS) law for commercial products. Both of these application areas have seen strong growth in recent years, and CIC has benefited greatly as a technique, particularly as the ASTM and other bodies have approved official methods using CIC.

There are two main varieties of CIC instruments. The sample preparation stages can either be an integrated part of a complete unit, or they can be separate modules that interface with a standard lab IC. This latter configuration has been the most common since their introduction in the early 2000s. The primary vendor in this area is Mitsubishi Chemical Analytech (formerly DIA Instruments). Mitsubishi offers a modular combustion system with combustion, absorption and optional autosampler modules. Mitsubishi has partnered with Dionex and Metrohm, the leading IC vendors, to develop complete systems that were released this year (see page 9). PAC, a Roper Industries company, offers an all-in-one integrated system. Under its Antek brand, PAC released the Multitek system in October (see page 9). The total market for CIC reached about $7 million in 2009 and is expected to grow rapidly in the short term.

Combustion Ion Chromatography at a Glance:

Leading Suppliers

• Mitsubishi Chemical

• Dionex

• Metrohm

Largest Markets

• Plastics

• Petrochemicals

• Biofuels

Instrument Cost

• $40,000–$80,000