Electrolyte is the medical term for a salt or ion in the blood or other bodily fluid that carries a charge.

The dissolution of some biological polymers such as DNA or synthetic polymers such as polystyrene sulfonate gives a solution of electrolytes that are referred to as polyelectrolytes and these contain charged functional groups. Placing a salt into a solvent (such as water) also results in an electrolyte solution, as the components in the salt dissociate in a process called solvation. When sodium chloride or table salt is added to water, for example, the salt dissolves and breaks down into its component ions sodium (Na+) and chloride (Cl-). Similarly, when the gas carbon dioxide is dissolved in water, it produces the carbonate ions, hydrogen carbonate ions and hydronium ions. Melted salts can also be electrolytes. For example, molten sodium chloride becomes a liquid that can conduct electricity.

The electrolyte in a solution is termed concentrated if it has a high number of ions and dilute if it has a low number. Therefore, if a large amount of the solute dissociates to give free ions, the electrolyte is strong whereas if a small proportion of the solute dissociates, the electrolyte is weak. Electrolytes have several properties that can be utilized in the process of electrolysis as a means of separating and extracting the elements and compounds present in a solution.

In biological systems, the main electrolytes are:

• Sodium (Na+)
• Potassium (K+)
• Calcium (Ca2+)
• Magnesium (Mg2+)
• Chloride (Cl−)
• Hydrogen phosphate (HPO42−)
• Hydrogen carbonate (HCO3−).

The plus or minus symbol indicates the ionic nature of the substance that its either positive or negative charge as a result of dissocation. These electrolytes are essential to various bodily functions and an electrolyte imbalance can be dangerous and even life threatening, depending on the clinical scenario. The balance of electrolyte levels is therefore carefully maintained in the body and may be checked in the blood or urine as a measure of health. Electrolyte loss is common in cases of excessive vomiting, diarrhea or sweating but may be replaced using isotonic drinks or in some cases, oral rehydration solution (ORS).