[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

pH Meters and Electrodes (long, as usual)



I have read 2 schools of thought on this.  One is that pH changes slightly
but proportionally with increasing temperature.  At 25C, 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 0C and pH 6.5 at 60C. (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