Electrolyte
An electrolyte is a substance (usually a fluid) which contains dissolved ions (electrically charged molecules or atoms), making it electrically conductive, and which allow it to undergo electrolysis. Electrolytes are commonly acidic or alkaline, and salts are also electrolytic. An electrolyte may be strong, having a high concentration of ions; or weak, having a low concentration.
Physiology
In physiology, the main electrolytes are sodium, potassium, calcium, magnesium, chloride, phosphate, and carbonate. All higher lifeforms require a subtle electrolyte balance between the intracellular and extracellular milieu. Nerve and muscle cells in particular benefit from the electrical conductivity this provides.
Electrolyte balance is maintained by oral intake and hormonal regulation, generally with the kidney as effector. In humans, salt homeostasis is regulated by such hormones as antidiuretic hormone, aldosterone and parathyroid hormone. Electrolyte disturbances may lead to cardiac and neurological complications, and most are medical emergencies. Specific electrolyte disturbances include hyper- and hyponatremia (excess and reduced sodium levels), hyper- and hypokalemia (potassium disturbances).
Measurement of electrolytes is a commonly performed diagnostic procedure, done as a blood test or as part of urinalysis. The interpretation of these values is quite meaningless outside the clinical history, and is often impossible without parallel measurement of renal function. Electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except for arterial blood gas interpretation, as they are linked to sodium levels.
Nutrition
Electrolyte drinks containing sodium and potassium salts are used to replenish the body's water and electrolyte levels after dehydration caused by exercise, heat stress, illness, or drought. Giving pure water to a deydrated person is not the best way to restore fluid levels, because it dilutes the salts inside the body's cells and interferes with their chemical functions. This can lead to water intoxication.
Sports drinks are electrolyte drinks with added carbohydrate, such as glucose, to provide energy. The drinks commonly sold to the public are isotonic (containing as near as possible the blood's natural concentration of sugars), with hypotonic (with a low level of sugar) and hypertonic (with a high level of carbohydrate) varieties available to athletes.
Electrolyte and sports drinks can be home-made by using the correct proportions of sugar, salt and water.
Electrochemistry
The behaviour of electrolytes in electrochemistry is discussed further in the electrolysis article.
Electrolytic conductors are used in electronic devices where the chemical action at a metal/electrolyte interface gives useful effects. In batteries the effect is used to store energy as chemical fuel on the surface of metal plates, and the electrolyte also serves as a conductor which connects the plates electrically. In some fuel cells a solid electrolyte or proton conductor connects the plates electrically while keeping the hydrogen and oxygen fuel gases separated. In electroplating tanks, the electrolyte both deposits metal onto the object to be plated, and electrically connects that object in the circuit. In operation-hours gauges, two thin columns of mercury are separated by a small electrolyte-filled gap, and as charge is passed through the device, the metal dissolves on one side and plates out on the other, causing the visible gap to slowly move along. In electrolytic capacitors the chemical effect is used to produce an extremely thin 'dielectric' or insulating coating, while the electrolyte layer behaves as one capacitor plate. In some hygrometers the humidity of air is sensed by measuring the conductivity of a nearly dry electrolyte. Hot, softened glass is an electrolytic conductor, and some glass manufacturers keep the glass molten by passing a large electric current through it.
