pH Meters and Electrodes (long, as usual)

["Kevin Zippel" <kczippel at worldnet_att.net>]

I have read 2 schools of thought on this.  One is that pH changes slightly
but proportionally with increasing temperature.  At 25°C, pH 7.0 is neutral,
as the activity of the hydrogen and hydroxyl ions are equal. The neutral
point (where hydrogen and hydroxyl ions are equal) is temperature dependent,
and is pH 7.5 at 0°C and pH 6.5 at 60°C. (APHA 18th edition, 4-65).  The
other is that pH is temperature independent at 7.0 and increasingly
sensitive above and below (see chart at
http://www.automatedaquariums.com/tecph_3.htm).  In either case, the
temperature induced change is miniscule (1.0 pH unit from 32-140F, so we're
talking about 0.01's difference within the tropical range).  I use the pH
calibration fluid packets at work.  They're quick and easy and single-use
(opening a buffer solution also greatly shortens its life).  I store them in
the fridge but let them warm up in my pocket before calibration, just to be
sure.  Kevin


>> Liquid calibration fluids have a shelflife of 6-12 months, tops.
>> Refrigeration helps.
>>  - - - snip - - -
>> ATC (automatic temperature compensation) is worthless.
>
>Kevin and Everyone -
>Does temperature become an issue if the meter is calibrated in solutions
that are a little/a lot cooler than the aquarium?
>David
>AGA, Paris

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