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ESTIMATION OF TOTAL POTASSIUM IN PLANT SAMPLES
Aim:
To estimate the total K content in plant samples by flame photometer.
Principle
When liquid samples containing potassium is burnt in the flame, K emits photons characteristics of its wavelength. The intensity of the emission is proportional to the K content. By measuring the intensity in a flame photometer the K content of the plant samples is determined.
Materials required
(i). Ammonium hydroxide (ii). Flame photometer (iii). Volumetric flask 25 ml and (vi). Pipette
Procedure
v Pipette out 5 ml of triple acid extract into a 25 ml volumetric flask and add 5 ml of ammonium hydroxide.
v Make up the volume to 25 ml with water.
v Transfer the content to an injection vial and feed to a flame photometer after adjusting the flame photometer to read zero with distilled water and 100 with 100 ppm K solution.
v Note the meter reading and calculate the K content by referring to the standard curve prepared
PREPARATION OF STANDARD CURVE
Dissolve 1.907 g of AR grade KCl in one litre of water. This gives 1000ppm of K (1000 micro gram/ml). 100 ml of 1000 ppm K is diluted to one litre which gives 100 ppm K. From this main stock solution, various standards ranging from 10 to 100 ppm are prepared.
Conc. required
Volume to be pipetted out from 5 ppm stock solution
Volume to be made upto
10 ppm
10 ml
100 ml
20 ppm
20 ml
100 ml
30 ppm
30 ml
100 ml
40 ppm
40 ml
100 ml
50 ppm
50 ml
100 ml
60 ppm
60 ml
100 ml
70 ppm
70 ml
100 ml
80 ppm
80 ml
100 ml
90 ppm
90 ml
100 ml
Record the flame photometer reading for the above K solutions.
Plot the meter reading against the corresponding concentration of K.
Use this standard curve for finding out the concentration of K in the plant extract.
Calculation
Weight of the sample taken = W g
Volume of triple acid prepared = 250 ml
Volume of aliquot pipetted = 5 ml
Volume of the solution made up = 25 ml
Concentration of K as read from
Standard curve = A ppm
100
(100- M)
100
w
25
5
A
106
Content of potassium in the sample on moisture free basis
= X 250 x X
(M = moisture content of the sample).
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