Ion Bar Graph
Ion Bar Graph
The ion bar graph is presented by Davis and DeWeist (1966) and reprinted in many other publications including Freeze and Cherry (1979) and Zaporozec (1972) where it is referred to as the Collin’s Bar Graph
The ion bar graph displays two bars for each sample. The left bar displays cations. The right bar displays anions. Cations include Ca, Mg, Na, and K. Anions include CO3, SO4, and Cl. The axis is scaled in percent of total for the units of measure. The typical units are meq/l.
The total meq/l of cations should theoretically equal the total meq/l of anions in each sample. However, for various reasons explained in the references, this is commonly not the case. Some references present ion bar graph with both cations and anions displayed up to 100% regardless of whether the cations and anions are equal in meq/l. ChemPoint can display the graph in this manner. However ChemPoint can also display the graph such that 100% is the larger of meq/l for cations or anions. In this fashion, it is possible to discern for each sample if the cations and anions are equal in meq/l.
The ChemPoint implementation displays the ion bar graph with the following characteristics.
- Multiple samples are plotted on a single graph. You can specify how many samples to display on a graph.
- Concentrations for seven parameters are plotted. The seven parameters can not be changed. However, you can choose to group sodium and potassium.
- The graph can be displayed using any concentration units, however meq/l is the typical unit. Charge balance can only be discerned when using units of meq/l.
- The data for the graph can be limited by sample date or sampling location.
- You can use field names to specify custom graph titles and axis labels.
- You can select custom colors and fill patterns for the bars.