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Potassium test

>> Paul Lesniak wrote:

>>  I had noticed over the past couple of months that it
>> was stated by different people that  'we' don't have a way
>> of testing for potassium in water. I looked around at our
>> lab at work and I found a couple of different methods; one
>> was using an Atomic Absorption unit ( we don;t have the
>> right bulb for this test though), the other was using the Hach
>> spectrophotometer. The spectrophotometer test is the
>> Tetraphenylbotrate method and measures up to a concetration
>> of 7ppm. I am wondering  if anyone has heard of this type
>> of potassium test and if so is it the kind of test that would
>> give the information an aquarist would be looking for.

> Paul Krombholz wrote:
> This is very interesting.  I had a chemist tell me that only
> atomic absorbtion could be used because potassium didn't form
> any colored complexes.  I think it would be useful for aquatic plant
> hobbyists to be able to test for potassium as long as the test isn't
> very complex and doesn't use expensive chemicals.

Your potassium test has arrived!  The LaMotte I recently ordered is
a two reagent test using using Tetraphenylboron powder and Sodium
hydroxide ( 6% ).  It is not a color reactive test but rather a
"turbidity" test.  It is LaMotte model 3138-KIW. The cost was $40 or
$50 dollars.  I have just received this so it has not been used.  It
produces results in mg/L of K in values of 6, 8,10, 20, 30, 40, and 50;
it would appear that above 20 mg/L distinction is more difficult. Before
ordering the test technical support indicated that at the higher levels,
the eyes ability to distinguish between increasing amounts of turbidity
weakened;  It would also appear ( based on the scale imprinted on the
"turbidity tube" ) that at would be possible to interpolate results easily
below 20 mg/L,  allowing practical results of 6, 7, 8, 9, 10, 15 and 20

One additional, interesting note: while it is a turbidity test,  I believe
they sell similar reagents for use in their "Colorimeter"  ( photometer )

Christopher Coleman
christopher.coleman at worldnet_att.net