[sharonr]

Hi All

My name is Sharon and i live in Israel.
I am a research student in marine biology.
As part of my research I have to measure low PO4-levels (0.01-0.1 mg/l) and I've found the Ammonium molybdate / tin chloride reduction method very usefull.
I've prepared the reagents by myself for the last 8 months and everything went well, unfortunately during the last preparations I am not able to get proper colorimetric readings.

I am not able to detect any reaction (blue color) when the phosphate levels are below 0.12 mg/l (i was able to detect levels below 0.04 mgl)

I am using the same reagents from the same stock I've used before (all of them ACS accept the picric acid), same pr duction protocol,etc.

I am not familiar with the characteristics of ammonium militate and tin chloride, but are there any interference or any conditions that can interfere with their reaction.

Thanks in advance for all the help

p.s.

sorry about my English


i

[Borek]

Can you try to prepare reagents again? Simple mistake could lead to unpredictable problems.

[sharonr]

Hi Borek

Thanks for the prompt reply.

I prepared  the reagents several times during the last week, and I made 3 repetitions together with one of my colleague just as an "extra eye", and had the same results.
Does the Tin Chloride has a "shelf life" so its reduction capability is diminished?
Its just strange, 3 weeks ago everything worked almost perfect

 

[Borek]

SnCl₂ in solutions can be oxidized to SnCl₄ by atmospheric oxygen, I don't remember if the same may happen to solid. If the jar was left open or not closed tight, in high humidity - I would be not surprised if something wrong happened, but it doesn't mean something had to happen.

[sharonr]

Hi Borek,

The SnCl2 is dissolved in glycerol to prevent oxidation...

[Golden_4_Life]

I observed that:
1) the Sensitivity of your Phosphate Assay has decreased by a factor of 3-fold
2) your Reagents, at least not the titration solution, has been prepared fresh.
3) your eyesight's ability to discern the color change has not been affected.4)

It is concluded that they Indicator solution may be faulty--please re-make it from stock powder.