Capillary Ion Chromatography Gains Momentum

Jul 07, 2014

Since the introduction of ion chromatography over 30 years ago, there has been much progress in the development of innovative IC systems. Capillary IC was introduced to provide a technique that is always ready and provides excellent eluent and waste economy. The first commercial capillary IC systems became available in 2010, but uptake of the technique has been slow, even though it has many benefits. This article assesses these benefits and presents selected application areas where capillary IC is proving especially useful.

There are a number of benefits to capillary ion chromatography (IC):

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Continuous Operation: A capillary IC system is always ready to run samples. Column size, injection volumes, and flow rates are scaled down by a factor of 10 to 100 in capillary IC compared to conventional flow systems, thereby improving system stability and reducing the need for recalibration. A continuous mode of operation is possible because capillary IC systems only consume 15 mL of water per day or 5.2 L a year.

Less Waste: The waste produced in a capillary IC system is minimized, thereby reducing disposal costs. When operated as a "reagent-free" ion chromatography (RFIC) system, the eluent generation cartridge can last for 18 months of continuous operation. When using eluent generation, only water flows through the pumps, extending the life of seals and decreasing the cost of maintenance compared to other mobile phases. Advances in eluent generation and electrolytic suppression technologies enable a wider variety of applications and increased productivity. RFIC systems combine automated eluent generation and electrolytically regenerated suppression technology to create the required eluents and regenerants used for IC applications. Laboratories using RFIC systems spend less time on equilibration, calibration, method verification, troubleshooting, and consistency checks because the technology minimizes unintentional variations in the preparation of eluents and regenerants.

Lower Sample Volume: Capillary IC operated as a RFIC system can provide trace-level determinations using sample volumes of up to 250 µL. One approach is to perform a large-volume direct injection that is suitable for samples with low levels of matrix ions. A 10 µL injection onto a 0.4-mm i.d. column in a capillary IC system is equivalent to a 1000 µL injection onto a 4-mm i.d. column. An alternative approach is to load a 250 µL sample onto a capillary concentrator rather than loading a 25-mL sample onto a 4-mm concentrator. Capillary IC can offer significant benefits in trace analysis where sample volumes might be limited.

Higher Resolution: Capillary IC can be performed under high pressure at up to 5000 psi when configured as an RFIC system. These high-pressure capillary IC systems can support higher back pressure 4-µm particle ion exchange columns. The advantage of using a 4-µm particle ion exchange column is improved chromatographic efficiency because of the smaller particle size. A 150-mm length column can be used at higher flow rates to increase productivity; a 250-mm length column can provide higher resolution separations of complex sample matrices.