Ion chromatography (IC) is a variant on HPLC where the stationary phase interaction is based on ion exchange. It is, therefore, applied to separate ions or charged species. Anions and cations are separated on separate columns. Unlike HPLC where much of the focus is on separating similar compounds, in IC the separations tend to be standard and the emphasis is on accuracy and sensitivity. Due to the different properties of ions, conductivity detectors are often used; to improve sensitivity the background conductivity of the eluent is removed before detection of the ions. To achieve much higher sensitivity the ions may be preconcentrated on a short ion exchange column and then eluted into the eluent stream for separation. This offers a very effective way of determining trace levels of many anions. IC is often used to complement the ICP-MS determination of metals in a sample.