sanjaygeorge

Nickel estimation in Chocolate

15 posts in this topic

Hi guys.....
i urgently need a damm gud chemistry project for my school assignment.......
Recently i got a idea abt estimation of nickel content in food.......especially in chocolates...........but didn't get any methods to find so.......Do any one of u know....anyway to do this???>........i have to estimate the amount of nickel......or test the presence in excess in chocolate.....
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your 1`st port of call will be to burn the choc to Ash, and then proceed from there.
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I'd choose almost any other transition metal first. Ni can get lost as the carbonyl when you ash it. This isn't an impossible problem to deal with but why make life more difficult than you need to. Measure Cu or Mn or whatever.
You can get round the problem by wet ashing (effectively boiling with acids untill all the organics are destroyed) but that's messy and you need high purity acids.
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[quote name='YT2095']your 1`st port of call will be to burn the choc to Ash, and then proceed from there.[/quote]
that's blasphemy, sir!
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Indeed, However it is somewhat Practical to get to the "crux" of the matter (some pun intended).

remove the volatile parts and leave the metals (and salts).

(I`ll email you the Choc stash he overlooked ;))
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I couldnt find a method for Ni in Cacao products in the AOAC.

but ther is for Tea which could be applied but of no use for a school assigment since it requires AA.

basicly wetash(wet oxidation using HNO3(69-72%) then HClO4(70-72%), caution not for the inexperianced:eek: ) a well mixed sample(either by freezeing and graiting or heating to 50C and mixing then take test sample) then intial dilution then filter and dilute to known volume then detect with AA at (232.00 nm for Ni) with matrix matched stadard solutions to avoid interferance from Na and K.

Now the APHA stadard methods for water and waste water has two chemical methods for determination of Ni these could be applied to the wet ash diltuion.

The Heptoxime Method and the Dimethylglyoxime Method.

in these methods the (water) sample is HNO3-H2SO4 digested with H2O2, so i dont know if wet ashing with HNO3 & HClO4 would be classed as the same or you would to do the extra digestion step after or just the Nitric Sulphuric digetsion instead :confused:

these are both colourmetric(heptosime and Dimethylglyoxime used for colour development, heptoxime method of choice) so you would need a spectrophotometer capable of 445 nm or you could do crude comparison by eye.

It involves treating a portion of the sample
(containg 50-250 ug of Ni) to seperate Cu and Fe then separation of Ni followed by the colour devolping step. then compared to standard curve.

If you want exact details I can post them tomorrow.
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And what is wrong with going to an university or something and ask if you can use their AAS?
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"failing that, Blast it with a M.S :)"
Yeah, 'cos everyone knows that they work really well for volatile things like metals. I'm not saying it's impossible- just that it wouldn't be my first port of call.

BTW, before you use nitric or (God help you) perchloric acid make sure you boil the sample down with sulphuric. That takes out the easilly oxidised components (also known as fuel) before you add the oxidant.
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[quote name='John Cuthber']
BTW, before you use nitric or (God help you) perchloric acid make sure you boil the sample down with sulphuric. That takes out the easilly oxidised components (also known as fuel) before you add the oxidant.[/QUOTE]

thats what the nitric is for

AOAC 935.13
wet ash

"weigh 2.5g sample into 500 or 800mL Kjeldahl flask. add 20-30 mL HNO3 and boil gently for 30-45min to oxidize all easily oxidizable material(aka fuel). cool soln somewhat and add 10 mL of 70-72% HClO4. Boil very gently until soln is colourless or nearly so and dense white fumes appear. use particular care not to boil to dryness(Danger!) at any time. Cool slightly, add 50mL H2O, and boil to drive out any remaining NO2 fumes . Cool, dil., filter into 250mL vol. flask, dil to vol and mix thoroly."
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i just need some method for testing the presence of nickel

hi.....
i am also in search of presence of Ni in chocolate.....so if u get any way 4 this pls send me tooo
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this is my que too ...Ni content in chocolates ...I couldn't find it !!!
Shreya I guess we'll have to mix some chemicals or some sort Cation anion detection thing !
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google is your friend, guys. Try searching for "nickel determination" or "titration for nickel" or "nickel gravimetric analysis" or something along those lines.
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