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pH Probe

Submitted by sat on 24 July 2015

There are many pH probes commercially available to use in schools. See the School science suppliers for more information on suppliers of general science equipment, and also those that specialize in data loggers. Science ASSIST does not specifically recommend any one brand of data loggers. It does, however, provide the following information for consideration when selecting a pH probe for use with a data logger. It is also recommended that the references listed are consulted for more detailed information.


Background Information


The pH of a solution is a measure of the hydrogen ion (H+) concentration of the solution. Solutions with a high concentration of H+ have a low pH (i.e., acidic) and solutions with a low concentration of H+ ions have a high pH (i.e., basic).


The pH probe measures the pH of a solution on a scale from 0 to 14, with 0 being the most acidic, 7 being neutral and 14 being the most basic. The probe consists of a pH electrode that requires special attention regarding its use and storage. Also, as pH is dependent upon the temperature, probes usually have an in-built temperature sensor.  For those pH probes with a data logging capability, the measurements are continuously recorded and displayed by a connected computer, iPad, tablet or dedicated data logger. The selection of a pH probe will depend upon physical aspects of the probe as well as the specifications of the probe and the data logger that it will be connected to. Consideration should also be given to the ongoing care and maintenance of the probe.


Physical Aspects


Science ASSIST recommends that, before purchasing a pH probe, the following physical aspects should be taken into consideration.


Recommended Specifications


Science ASSIST also recommends that pH probes with the following specifications should be considered:


Care and Maintenance of the pH probe


One of the most common reasons for a pH probe to not work properly is that it is not properly calibrated or because it is dirty, clogged or coated with sample. Regular cleaning and calibration of the probe will restore performance and prolong the useful life of the electrode. The probe should be stored in the recommended pH storage solution between measurements. The glass bulb can be cleaned by soaking it in warm deionised water. Read the manufacturer’s user manual for long-term storage and calibration.


Note: It should not be stored in distilled or deionised water and should not be allowed to dry out. Long-term exposure to pure water may damage the special glass membrane/bulb.


Probes should be rinsed after each reading and between samples with distilled or deionised water. To remove excess water, the end of the probe should be blotted gently with lint-free paper. The glass membrane of the probe should never be directly touched, as oils from the skin will damage the electrode.


Note: It is best to avoid the use of multiple probes in the same solution as they can electrically interfere with one another and result in erroneous readings. In addition, the probe should never be wiped, as wiping can create a static charge, which may also result in erroneous readings.


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References


Frost, Roger 2002. The IT in Science book of Data logging and control. IT in Science, Cambridge http://oer.educ.cam.ac.uk/w/images/a/a0/Data_Logging_and_Control.pdf


Lovatt, P 2009. Data logging: Applications, advantages and disadvantages. Physog website: https://web.archive.org/web/20170121064310/http://physog.co.uk/pluginfil... (Original web page not available, this copy made available by the Internet Archive's Wayback Machine, April 2018)


‘PASPORTpH Sensor-PS-2102’ Pasco website http://www.pasco.com/prodCatalog/PS/PS-2102_pasport-ph-sensor/#overviewTab (Accessed July 2015)


‘pH Electrodes Information’ HIS Engineering360 website https://www.globalspec.com/learnmore/sensors_transducers_detectors/analytical_sensors/ph_orp_electrodes (Accessed July 2015)


‘PH/ORP Sensor Primer’ Phidgets website, https://www.phidgets.com/docs/PH/ORP_Sensor_Primer (Accessed 17 June 2015)


‘pH Sensor’ Vernier Software & Technology website https://www.vernier.com/products/sensors/ph-sensors/ph-bta/ (Accessed July 2015)


‘pH Sensor’, Vernier website http://www2.vernier.com/booklets/ph.pdf (27 December 2006)


Roberson, Peter 2004. Using date loggers Uniserve, University of Sydney website https://web.archive.org/web/20180319233723/http://science.uniserve.edu.a... (Link updated February 2019 with a copy from the Internet Archive).


‘The Best pH Electrode for Your Application’, Hanna Instruments website http://www.hannainst.com/usa/electrode_choosing.cfm (Accessed July 2015)