[danavuia.1987]

Does anyone have  the procedure?
I have tried this way:
50 of sample in a small berzelius, 1 drop of
phenolphthalein ,1 ml H2So4 2.5 M and 0.4 ammonium persulfate.
Boil for 45 minutes oe until the volume reaches 10 ml.
Then this volume is diluted to 30 ml with distilled water , add 1 drop of
phenolphthalein
Then add 1 M NaOH to fade pink.
Then dilute this to 100 ml with distilled water.
From this volume i take 50 ml , add 1 drop of
phenolphthalein and 8 ml
combined reagent and after 10 minutes read on 880 nm.
I did a calibration curbe and table with formula included.
I found online a way of working that indicates that the result(the result from table according the standards praparated-8 standards of known concentration) will  be multyplicated with 2 .
It is correct?
Sorry for my english .I'm from Roumania.
Have a nice day!

[Arkcon]

I found online a way of working that indicates that the result(the result from table according the standards praparated-8 standards of known concentration) will  be multyplicated with 2 .
It is correct?
Sorry for my english .I'm from Roumania.
Have a nice day!

If this is your question, then yes, that seems correct.  Each quantity of H₂SO₄ does neutralize twice the NaOH, because you can see in the chemical formula for sulfuric acid -- there's two H+ there.  So the calculations will tell you to double the amount, to get your answer.

If you've found that procedure, you should be following it exactly, and you should get the answers you want.  You've built calibration curve samples, so you can build some extra sample, to test that your calculations still fit the cal curve.

I don't recognize the procedure, but I don't know everything.  But here in the Analytical sub-forum, we like to talk about using techniques to effectively follow established procures.

If you have tons of samples, people will soon tell you, "Submit for ISP-MS and get the results to 4 decimal places."  And you will soon tell us you can't afford that.  But if you want answers, those are the suggestions you'll get.