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MathSimard
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[*] posted on 6-6-2017 at 10:45
NH4+ determination


Hi everyone,

I am working on a method to determine the amount of NH4+ in soil extracts. I am using a standard method which is supposed to work but surprisingly it doesn't. I put sodium nitroprusside with a hypochlorite buffer solution and it turns yellow when it's supposed to be colorless. I guess that the sodium nitroprusside loses a ligand and replace it with OCl or maybe NH3 and thi is why I the solution is colored. After adding this I add my soil extract (in 2 M KCl) and EDTA (that does not react with anything just make sure that polyvalent anions don't precipitate). and dilute it in 11 mL of dionized water. It is supposed to be emerald green in theory but it stays yellow. I have tried everything. First I thought that Cl- ions were interferating so I treat the solution with sodium thiosulfate but doesn't change the color. If someone was able to help me I would be very grateful. :) Thank you so much
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Melgar
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[*] posted on 6-6-2017 at 12:04


Do you need to use a method besides reacting with sodium nitrite and measuring the volume of nitrogen gas produced? I suppose in something like soil analysis, there would be more that can go wrong, since nitrite is capable of oxidizing and reducing a number of different things, and many of the products would be gases.

Chloride ions don't react with sodium thiosulfate, chlorine in the +0 oxidation state does, is that what you meant? And how is hypochlorite a buffer solution? It's a strong, basic oxidizer, no? The yellow is likely from hypochorite oxidizing your nitroferrocyanide ion to iron (iii) chloride and whatever species in the oxidation products of cyanide that it can, which is something I'm guessing you don't want. Try adding a base to a sample of the yellow solution, and see if rusty-looking iron precipitate doesn't form.
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feacetech
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[*] posted on 6-6-2017 at 15:41


I havent done any soil analysis

But do you need N-NH3 or N-NH4+ or both

or would TKN work as well (digest with sulphuric and catalyst and steam distill) or TKN minus N-NH3 would this be usefull?

What about ISE analysis?

I use to do a blue colormetric test with N-NH3 in water i cant remebetr but i could look it up in the APHA, i think it involved bleach and phenol + some other stuff.

Would direct distillation (add strong base (40-50% NaoH) and steam distill into boric acid with indicator and titrate) work or does the soil matrix interfere (N-NH3). this would convert N-NH4+ into N-NH3 and volataise.

When he/she says hypocholrite buffer it wont be hypocholrite by it self it will be some sort of solution required by the method.

What is your source of hypo for the buffer solution and how old is it? Is it comerical bleach? if it is it could be weak off the shelf if its old, check the dates.

I guess the hypo buffer is to digest the soil and you are doing colormetric analysis?

If you cant use another method trouble shooting would be: get new chems and make new solutions and see if you can get the colourless nitroprusside/buffer solution mix.

What is the conductivity of your DI water maybe your resine is bad and it is spoiling your solutions(unlikely)?

If its colourmetric analysis can you succesfully make standards and blanks or is it some other form of analysis?

do you have a reference we can read?

I only have a limited amount of ATSM (no soil), APHA water (adaptions could be made if you can sucessfully digest your soil), and AOCS (fats and oils).

I found a similar reference online is this what you are doing?
http://www-personal.ksu.edu/~jblair/nh4.html

the yellow could be that your old over conc hypo (strong hypo is yellow) you may only need weak bleach like houshold stuff?

[Edited on 6-6-2017 by feacetech]
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AJKOER
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[*] posted on 7-6-2017 at 05:40


New test to consider:

Mix a water solution of the soil sample with say NaOH.

Heat and drive fumes into a larger vessel in which sits a beaker of fuming HCl.

Collect the condensed NH4Cl smoke and use to estimate ammonia content.

I would suggest calibrating this method with a known amount of an NH4+ salt. Repeat several times to arrive at a yield correction factor and its standard deviation.

Target the range of values normally expected for ammonia content.

Interestingly, if the calibrating is performed using the soil in question which may have compounds that confound the normal chemistry, this procedure would reveal this and may still indicate (via a statistical correction factor) the likely true underlying ammonia content.

[Edited on 7-6-2017 by AJKOER]
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feacetech
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[*] posted on 7-6-2017 at 15:35


that would be similar to direct distilation.

except you add NaOH in excess and steam distill and scrub into boric acid with a mixed indciator and back titrate.

matrix interferance can be over come with doping or standrad addtions.

My bet is the OP made the reagents wrong or used hypo that was too strong or weak expired household bleach and will not return to update us on what went wrong

[Edited on 7-6-2017 by feacetech]

[Edited on 7-6-2017 by feacetech]
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Melgar
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[*] posted on 8-6-2017 at 03:30


Quote: Originally posted by feacetech  
My bet is the OP made the reagents wrong or used hypo that was too strong or weak expired household bleach and will not return to update us on what went wrong

That sounds depressingly likely. Hey OP, prove us all wrong. What if someone finds this thread and they have exactly the same problem as you? And you never responded to say what the problem was? You'd look like kind of an asshole, wouldn't you?
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MathSimard
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[*] posted on 9-6-2017 at 10:01


Well, I am using a buffer solution of hypochlorite which is make with solid NaOH, commercial NaOCl solution (not that old) and some sodium salicylate. The main goal of this reaction is to produce a diazonium compound that is colored. I tried to put some concenrated NaOH but it has not turned red it just dilute the yellow color more.
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[*] posted on 9-6-2017 at 16:50


Quote: Originally posted by MathSimard  
Well, I am using a buffer solution of hypochlorite which is make with solid NaOH, commercial NaOCl solution (not that old) and some sodium salicylate. The main goal of this reaction is to produce a diazonium compound that is colored. I tried to put some concenrated NaOH but it has not turned red it just dilute the yellow color more.

Glad to see you back! Anyway, now you've given us enough information to figure out that you seem to be using this procedure:

http://monitoringprotocols.pbworks.com/f/USGS-Method-I-2522-...

Unfortunately, that's not a procedure I'm familiar with, although the PDF contains a lot of warnings regarding what to do and what not to do. A lot of ions apparently interfere, including bromide, nitrite, and sulfide. But you're saying that something is wrong before you even get to adding the extraction from your sample? I guess first, we should make sure that the procedure I've posted is the one that you're using.




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feacetech
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[*] posted on 11-6-2017 at 13:49


if you cant even get standards and blanks for it to change to the correct colour something is wrong with the reagents or the tech has made mistake making up the reagents.

this is the same method i have used to check water for ammonia containination (blue from memory)

FYI comerical bleech has NaOH added

try another bleech
try all new chemicals

do you get the blue colour once you develop the standards?

you will be doomed to failure if you cant even make the standards!

IMHO commerical bleech will be the weak spot.

Can you determine the FAC of the bleech, i would just buy a new brand thats has a recent manufactutre date


[Edited on 12-6-2017 by feacetech]
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feacetech
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[*] posted on 11-6-2017 at 14:10


APHA 2005
45000-NH3 F. Phenate Method

Reagents

Phenol solution
Mix 11.1 mL of Liquified Phenol (<=89%) with 95% v/v ethyl alcohol to a final volume of 100 mL (prepare weekly)

Sodium nitroprusside 0.5 w/v
Dissolve 0.5 g sodium nitroprusside in 100 mL of D.I water, store in an amber bottle (and in the dark or wrapped in foil) (1 month shelf life)

Alkaline citrate
Dissolve 200 g trisodium citrate and 10g sodium hydroxide in D.I water, dilute to 1000 mL

sodium hypochlorite
Commerical solution, about 5%. this solution slowly decomposes once the seal is broken, repalce every 2 months

Oxidizing solution
Mix 100 mL alkaline citrate soltuion with 25 mL sodium hypochlorite prepare fresh daily

Ammonium stock and working solutions for standard curves


From memory many years ago I kept all bottles wraped in foil and in a dark cupboard

I used janola bleech

My pheol solution used solid phenol and absolute ethanol

Once again make it all up and see if you can get a standard curve going of increasing blue conc

Procedure
To a 25 mL of sample in a 50 mL flask, add, with thorough mixing after each addtion, 1mL phenol solution, 1mL sodium nitroprusside solution and 2.5 mL oxidizing solution. Cover samples develop at room temperature (22-27C) in subddued light for at least 1houre. Color is stable for 24 hours

[Edited on 12-6-2017 by feacetech]
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[*] posted on 13-6-2017 at 12:05


thank you for the answers!

I effectively use the same technic than the one on the pdf file. I tried to make the reagents by myself but I have the same problems with it nothing has changed. I bet that the problem comes from the commercial bleach I use.
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feacetech
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[*] posted on 13-6-2017 at 12:14


try making some standards with the APHA method and see if they turn blue
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