Phyllis Kerridge

And The Miniature Ph Electrode

Barrie Blake-Coleman

Phyllis Kerridge (neé Tookey) will be remembered as the originator of the miniature pH electrode.  Used in early physiology experiments, her design was the forerunner of most of the glass electrodes used today and was central to her PhD thesis completed at University College London in 1927 (Use of the Glass Electrode in Biochemistry).

Her academic studies and career (described as 'brilliant' - UCL Annual Report for 1940) was unusually convoluted in that she was listed as both a UCL staff member (lecturer from 1923) and as a student (from 1919 - until she completed her studies in medicine 14 years later). She was awarded the BSc in Chemistry & Physics (1923) MSc in Chemistry (1924) and, as noted above, completed her PhD in 1927. However, she then took up Part 2 studies in medicine and became a Member of the Royal College of Surgeons, and Licentiate of the Royal College of Physicians  in 1933 (Member RCP 1937).

Phyllis was the daughter of William Tookey of Combe Lodge, Duncombe Hill London. Well known, and well published as an engineer, her father was able to place her in the City of London School for Girls where she excelled in science.

 

She entered UCL as an undergraduate in 1919 and lived at her home address until 1926 when she appears to have married, taking up residence at St Petersburgh Place (W2).  Of the shadowy Mr Kerridge little is known but Phyllis' insistence that she retain her maiden name after marriage (thereafter Phyllis Tookey Kerridge) is, perhaps, an indication of her ideas about women's identity in society and her support for women's causes.  She is recorded as being a committee member of the Women's Union Society in her student days.

 

Her principal work in developing the miniature glass electrode came during her research for her PhD.  Phyllis had the good fortune to be well versed in physical chemistry and this allowed her to contrive a glass electrode design that was insertable into biological membranes.  She was attempting to establish certain biochemical processes in living tissue.  Glass electrodes are able to measure acidity/alkilinity of biological fluids by establishing the potential created when the electrode is screened by glass.  Acidity is denoted by the hydrogen ion (H+) concentration, alkalinity by the hydroxyl (OH-) ion concentration.  The glass/electrode combination works because the glass becomes an hydrogen-ion permeable 'membrane'.

 

An exposed platinum electrode surface absorbs H+ ions particularly well. As it does so, an electron motive force develops and this electrode potential or 'half cell (or 'half electrode pair') if paired with a source of counter potential (the other 'half-cell') creates a 'balanced cell'  and this forms an electric current circuit.  The result is the electrical measurement of the Hydrogen ion concentration and thus a measure of the pH.

 

Phyllis was aware that very small electrode dimensions led to very small potentials - too low to measure - but she needed small dimensions in her electrode to successfully invade very narrow layers in living tissue.  She overcame the problem by maximising the electrode surface area by heat treating the platinum with platinum chloride at red heat.  This created a massively greater surface than hitherto and gave a much larger signal making it possible to measure very small variations in larger fluid volumes, and producing enough signal for accurate measurement in low fluid volumes.  To this day the lessons provided by Phyllis Tookey are still incorporated into the ‘black art’ of glass electrode manufacture.

 

Following her PhD she was appointed as Demonstrator in Physiology At UCL in 1923 (following graduation) and retained this status until 1926 when she was appointed lecturer.  This became a part-time appointment from 1929 until 1935 when she was then given a 5 year appointment as a full time lecturer.  She died, tragically, of an unrecorded illness in June 1940.

 

The work that Phyllis carried out was only recognised retrospectively.  The first major citation for her work appears in 1939. It is unlikely then that she would have known that her electrode work had been acknowledged and recognised, though it would be nice to believe that she did.

A Modern

Ph Electrode