Yes; pls. find the experimental details stepwise as follows:
[A]Zn(II) can be determined colorimetrically using Dithizone by drawing a CALIBRATION CURVE as:
[B]Prepare a standard solution of zinc sulphate solution containg 3.3 μg/ml of Zn(II) ions . Take 50 mL of this solution and to it add about 50 mL (0.1% w/v) of dithizone[ prepared by dissolving 10 mg of dithizone was dissolved in 100 ml of chloroform].
[C] Then add aout the same volume of a buffer solution of an alkaline ammonium citrate [prepared by dissolving 5g of dibasic ammonium citrate in 100ml of 5% ammonia solution].
[D]The mixture solution is shaken vigorously in a separating funnel. It was extracted
with over a total of 85-95 ml of chloroform(3 times). The organic layer was transferred in 250 ml volumetric flask after keeping over anhydrous calcium sulphate for sufficiently. Filter the chloroform layer to obtain dark CHERRY RED color*.
[E]Take eight washed and dried test tubes(20ml capcity) and label them as 1,2,3------8. .
[F] Add 10 ml of the cherry red colored complex solution in tube No:1.
[G] Similarly, add 9 ,8 ,7,6,5,4,3 ml of the cherry red complex in the remaining 7 tubes and make up the volume of each one these 7 tubes to 10ml by adding 1,2,3,4,5,6 and7 ml of chloroform respectively .
[H] Now note the absorbance of each one of these 8 tubes containing the complex solution with the help of the spectrophotometer at 525 nm.
[I] Plot a graph between molar concentration of Zn(II){ along X-axiz} and absorbance {Along Y-axis} to obtain the standard calibration curve.
[J] Now take the given UNKNOWN solution containg the alkaline Zn(II) ions. To it add appxo. the same volume of each of dithizone and buffer solutions and again develop cherry red color by the procedure already followed in [D]
{K}Take 10 ml of this solution and note its absorbance at 525 nm. Match its absorbance on the Y-axis of calibrating curve and note the corresponding reading on X-axis which gives the molar concentration of Zn(II).
* The color does not fade at all even after 11-12hrs.
For Mdm. Esma Senel
It is to bring to kind observation that that Zn(II) can also be estimated spectrophotometrically by another equally efficient method. But here the complexing ligand first need to be prepared in the laboratory.Of course, once prepared, it can be kept to use time and again.
[A]General procedure for the preparation of ligand :
1.0 g of 3-Hydroxybenzaldehyde is dissolved in 25 mL of double distilled water and mixed in a flask with 1.0 g of 4-aminobenzoic acid and refluxed for 3 hrs. A pale yellow colored crystal product having the formula 3-hydroxybenzylaminobenzoic acid formed. After filtering the product, it was dried at room temperature.Finally the very light colored product was recrystallized by using ethanol(M.pt=165C; yield=80-90%).
[B] Now prepare a standard solution of zinc sulphate solution containg 3.3 μg/ml of Zn(II) ions . Take 25 mL of this solution and to it add about 75 mL of buffer solution[pH(5sodium acetate-acetic acid buffer)] and 50 mL of the ligand solution[ prepared by dissolving 20 mg of the ligand was dissolved in 100 ml of chloroform] . Keep for sufficiently long time to obtain yellow colored hydroxybenzylaminobenzoic acid -zinc complex.
[D]The mixture solution is shaken vigorously in a separating funnel. It was extracted
with over a total of 80-90 ml of chloroform(3 times). The organic layer was transferred in 250 ml volumetric flask after keeping over anhydrous calcium sulphate for sufficiently long time. Filter the chloroform layer to obtain the complex in the nonaqueous layer.
Then follow the steps E-K [as given in the first method] while using 460 nm filter.
The complex remains stable for over 12hrs.
[1] My friend,you know that the inorganic salts are expected to to be more soluble in aqueous medium[ Like dissolves like] . So we dissolve the zinc sulphate in aqueous medium.
[2] On the other hand,the ligand 3-hydroxybenzylaminobenzoic acid has very less solubility in aquous medium but is sufficiently soluble in a non- aqueous medium like CHCl3 ( Also EtOH). So dissolve it in CHCl3.
[ 3] Mi x the aquous& nonaquous media. A complex of the ligand with the Zn(II) would form.
[4] The complex formed is more soluble in the non aqueous medium.
[4] You know the basic rule- the partition coefficient. On vi grous shaking of aquous& non aqueous, virtually whole of the complex will come to the noaqueous medium on repeated adding of more of non aqueous medium.
[5] Due to the difference in the densities, the two separate layers would form In the separating funnel.
[6] Since our complex is soluble in the nonaqueos layer, separate it from the aqueous layer.
[7] But this nonaqueos layer contains some water.
[8] In a way , we have 97%( say) nonaqueous layer containg 3%(say) water.
[ 9] You know anhydrous CaSO4, being a non reacting dehydrating agent will take up water[ forms CaSO4.2H2O] while non aqueous layer remain unaffected by CaSO4 . But it has been freed from water.
[10] This pure dry complex will be used further.
Dear Manohar sehgal our formulation contain 7 vitamins, selenium and zinc. All are come out different methods except zinc I try to estimate zinc By UV Spectrometric method ( Method = Zinc- Dithizone Chloroform Method) results are come out but placebo ( With out API's) Interference (10%) is there. That's the problem. Would you suggest any alternative method with out interference. Please tell me
Dear Manohar sehgal, My medium of experiment is aqueous ( Zinc sulphate monohydrate, Soluble in water) . this is tablets one tablet contain vitamins (Like ALA, Benfothiamine, Methyl cobalamine, Folic acid, ) Selenium and zinc. Our placebo ( with out vitamins and selenium, means Only excepments ) interfere. would you suggest how to eliminate interfere. please tell to me
yes. you can anlysed with Zinc pigments.
pleas read ASTM standard D2745
Esma Senel
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