At 2000-07-14 09:25 +0100, Stuart Robertson wrote:
>I would have thought that most laboratories are now
>using ISE for sodium and potassium determination, and
>the crucial point here surely, is whether ISE is
>direct (on an undiluted specimen) or indirect (on a
>diluted specimen).
There are many sources of error (cf the literature on this matter) when
using ISE, including the effect of liquid junction and streaming
potentials. Dilution will diminish some of these interferances, but it also
disturbs any equilibrium in which the ion is involved and it definitely
changes the ion product and hence also the activity coefficient.
>The former should theoretically be equivalent to ion
>activity in plasma water, but the latter is more of an
>approximation to ion concentration in plasma (or
>serum).
That's correct.
>This is a separate issue from what happens in the
>clotting process, anyway.
Of course, but I none had mentioned that the method of measurement is of
importance when discussing the change in electrolytes in the clotting process.
Sten Öhman, PhD
Elfin Lab & Milieuconsult
P O Box 133
S-590 70 Ljungsbro
Sweden
Tel Nat: 013-368940 Int: +46 13 368940
Fax Nat: 013-368941 Int: +46 13 368941
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