Fluoride is a naturally occurring ionic compound (or salt) that is found in low levels in most bodies of water. The concentration of fluoride in water is affected by: climate, geology, contact with fluoride minerals and groundwater chemical composition. Fluoride is dissolved into water from the surrounding soils and rocks.
The Fluoride sensor is an Ion Selective Electrode (ISE). It measures charged fluoride ions found in the water.
Our fluoride sensors can be fitted to many of our probes, below are some examples.
To see all of the probes that feature fluoride please visit the Products section.
The Aquasonde-2000 has 2 spare ports. They can house either 1x ISE sensor and 1x Optical sensor. Or it can house 2x ISE sensor.
This is a solid state sensor in that it is not gel filled, the advantage of this kind of sensor over those offered by other manufacturers is that the sensor will not deteriorate over time so long as its dry. A new dry sensor can be stored for years without degradation. Gel filled sensors are different and have a finite life from the point of manufacture.
Successful calibration of an ISE is fairly complex. On its initial use, a three-point calibration is required. For the fluoride sensor, this is at 0.5ppm and 5ppm of the sensor’s specific calibration solution, with the third point intended to characterise the effect of temperature on that specific sensor. The third point is a second calibration at 0.5ppm however, this calibration point must be at least 10 degrees colder than the initial point. This is because the measured concentration varies with temperature as well as the actual concentration of the ion.
The good news is that once this calibration is complete, subsequent calibrations do not require the third point to be re-done making future calibrations much simpler to perform.
An ideal ISE sensor would only allow the ion in question to be passed through the membrane. However, in practise all ion selective electrodes suffer from interference from ions which are similar in nature to the target ion. For this reason, ISE Electrodes are not recommended for use in brackish or salt water due to the high level of interfering ions.
Installing the Fluoride sensor into an Aquaprobe is a very simple process. Simply unscrew the blanking plug from an appropriate aux socket, apply some silicon grease to the thread of the sensor (grease provided) and screw in the sensor. After installation full calibration is required.
In unpolluted ocean waters the natural fluoride level is in the range of 1.3 to 1.4 mg/L. The levels are usually lower in estuarine areas due to dilution by fresh water, unless fluoride pollution is occurring upstream. Measuring fluoride in water is important as fluoride is toxic to humans and aquatic life. Fluoride is accumulated in the hard tissues of fish and shellfish, and then enters the food chain when the organisms are eaten.
Marine organisms can accumulate fluoride even at ambient ocean levels, and this accumulation increases noticeably when there are higher fluoride levels are present. As fluoride moves up the food chain, biomagnification occurs at about 1 order of magnitude per level.
To use Aquaread’s fluoride sensor, first install it into your probe of choice, then perform a full calibration using dilutions from the stock calibration solution. Once calibrated it’s good to go. Simply put the probe into the body of water, allow the reading to stabilise and take your measurement.
One might want to monitor fluoride levels in water to determine the ambient level of fluoride in a water body. Once the base level is known, continued measuring of fluoride in water will allow any pollution to be identified by any spikes in fluoride concentrations.
Measuring fluoride in water close to industrial areas, for example aluminium smelting plants, is necessary to carefully monitor the levels of fluoride in drinking water that is produced in water processing plants. High concentrations are dangerous for humans and can cause dental fluorosis, or skeletal fluorosis in extreme cases.