There are quite a number of metal ions like Zn^2, Ca^2, F^2, Mg^2 and Pb^2 etc. which are present in plants and almost all of them can be quantitatively estimated by UV. A brief method to estimate Zn^2 is given below.

[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 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 long time . Filter the chloroform layer to obtain dark CHERRY RED color*.

[E]Take eight  cleaned washed dried test tubes(20ml capacity) 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 solution 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 prepare the extract of the specific portion of the plant in distilled water or methanol or ethanol or chloroform etc using suspension extraction and column extraction. 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 in a cleaned dry test tube and note its absorbance at 525 nm.Draw a straight line from the point representing this value of absorption on Y-axis so that it meets the curve at a certain point. Now draw a perpendicular from this point on the curve on the X-axis. Note this value to obtain the molar concentration of Zn(II).

* The color does not fade at all even after 11-12 hrs.

all metals can adsorb uv here i am having the estimation of copper

Fast Sulphone Black – F indicator – Prepared by dissolving 0.5g in

100 cm3 of de-ionized water.

0.01M EDTA – 3.7224g disodium salt of ethylenediaminetetraacetic acid by dissolving in 1000 cm3 de-ionized water.

Ammonia solution (32%)

Sample solution - The sample solution was prepared by dissolving the copper complex (0.1g) in water by adding 2-3 drops of HNO3 to make 100 cm3 of the solution.

Procedure

The sample solution (10 cm3) was taken in a titration flask. It was diluted to 100 cm3 with distilled water. To this ammonia solution (5 cm3) about 4 drops of the indicator were added. The solution was titrated with 0.01 M EDTA to a dark green end point. Percentage of copper(II) was calculated by using the formula.

1 mole EDTA = 1 mole Cu2+

Cu (%) = (63.54 / weight of the complex) X 100

wish you good luck