RE:pH paper vs. meter

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To:"J. A. Kiernan" <>
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The latter of your post is a good reason alone for implementing the use of

I think we all have had the experience of working with people who do not
maintain pH meters properly and have had to replace electrodes too frequently
for this reason.  In labs with many hands working with equipment these
conditions are not strange or isolated, I'm sure.

How many times have people gone to a pH meter and found the electrode is not
working properly and no one has told them the spare electrode was the one in use
and than your left running around looking for one that does work.
Unfortunately, this is life in a histology lab where the pH meter is used by 3
or 4 areas of surg path such as immunos, muscle histochemistry, EM , etc. .

pH strips are a fast, accurate, and reproducible means to  pH solutions and
would virtually eliminate this type of situation.

In addition,  EM ColorpHast strips work in colored or turbid samples all you
have to do is dip the strip, rinse and read.  They REMOVE many sources of error
in colorimetric pH measurement.

Salt Error:
 When salt concentrations are above 0.2N, indicator equilibrium can shift ,
causing the pH to shift higher.

Indicator Error:
 In unbufferd and weakly buffered solutions ,errors as high as 1pH unit can
occur if the free acid or base of the indicator is used for pH measurement.

Protein error:
Because proteins are amphoteric, they bind to indicator acids through their
basic groups, and to indicator bases through their acidic groups, Essentially ,
the simpler the structure of the indicator , the less interference.
EM ColourpHast strips do not exhibit protein error and therefore, can be used
for measuring body fluids.

Alkaloid Error.
Essentially , alkaloids interfere with pH measurements in much the same way as

Alcohol Error.
The addition of organic solvents to an aqueous solution changes the dissociation
constants with a corresponding shift in the acid base equilibrium. In
aqueous-Methanol and aqueous -Ethanol solutions above 70% the shift can be as
much as 1.5pH units

I hope I don't sound like a salesperson, I'm just trying to state some facts on
a product that should be fine for using in histology labs definitely for
checking buffers and other things, has reproducible results and would help to
make working life easier.

Rande Kline, HT (ASCP)
Technical Services
EM Science/BDH

"J. A. Kiernan" <> on 04/09/2000 11:47:29 PM

To:   Histonet <>, Rande Kline/EMI/Merck@EMI
Subject:  RE:pH paper vs. meter

On Fri, 7 Apr 2000 wrote:

> pH strips are highly accurate in weak buffers, subsequent to waiting 5-10
> minutes for an indicator on a meter to reach equilibrium.

   If a pH meter takes 5-10 minutes to give a steady reading, whatever
   it's immersed in, it needs a new electrode. The only exception
   would be an older meter that uses an electrometer tube (=valve) in
   its amplifier (rather than all solid-state electronics). An older
   meter may take an hour or so to "warm up" and it should then be
   left switched on all the time. (Current consumption is almost
   zero.)  Modern meters, including those with "digital" displays,
   do not need a warm-up time. These statements are certainly true
   of the three electrometer-type and four digital-type pH meters
   that I've had in my lab over the years. It's the electrodes that
   get broken or wear out - sometimes because of neglect.

> ...  We sell strips ...

> If anyone is interested in trying strips, send me your address.  I can have
> samples sent out.

  Please!  (Address below)
                                    John Kiernan.  London, Canada.
 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1

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