Sulphur content

ESTIMATION OF SULPHUR

Aim

         To estimate the sulphur content in plant sample.

Principle

         Sulphur is estimated in a suitable aliquot of the diacid extract, using BaCl2 which reacts with SO4 in diacid extract and precipitates the SO4 as BaSO4 and the turbidity developed is measured colorimetrically.

Reactions

         BaCl2                                   Ba 2+ +  2Cl-

         Ba2+ + SO4 2-                     BaSO4 precipitate

Equipments and Apparatus

         Colorimeter, 100 ml conical flask, 5 ml pipette, 25 ml volumetric flask.

Reagents

1. Diacid (Nitric acid and perchloric acid, 2:1 ratio)

2. Barium Chloride - grind BaCl2 crystals in a mortar, until they pass through a 30 mesh sieve and are retained on a 60 mesh sieve.

3. Gum acacia (0.25 %): Dissolve 0.25 g of gum acacia in a distilled water and dilute to 100 ml.

Procedure

         Weigh 0.5 g of powdered plant sample and transfer into a 100 ml corning conical flask. Add 12 ml of diacid mixture (Nitric acid and perchloric acid 2:1 ratio (Aulakh and Dev, 1978) and digest it over on electric sand bath till a clear solution is obtained. Cool the content and the volume is make upto 100 ml using distilled water. Pipette out 5 m of diacid digested extract in to a 25 ml volumetric flask and add 10 ml of distilled water and shake it well. Add 1 gm of BaCl2 crystals and shake for 1 minute. Then add 1 ml of 0.25% solution of gum acacia and shake for 1 minute. Make up the volume of volumetric flask with distilled water and shake for 1 minute. Make turbidity measurements within a period of 5 to 30 minutes, following of formation of precipitate, using a colorimeter at 420 nm wave length using a blue filter. (Chesnin and Yein, 1951). From the standard graph the content in ppm of the plant sample is obtained and from this calculates the S content of the plant sample.

Preparation of standard curve

         Dissolve 0.5434 g of AR grade K2SO4 in distilled water and dilute to one litre. This is the 100 ppm stock solution of S.

         Pipette out 0.25, 0.5, 1.0, 2.5, 5,0 and 7.5 ml of the stock solution in a series of 25 ml volumetric flask. Add to each flask, 10 ml of the extracting solution, followed by about 1 g of BaCl2 crystals and shake it for 1 minutes. Then add 1 ml of 0.25 % solution of gum acacia. Make up the volume of each flask with distilled water and shake for 1 minute. Make turbidity measurements within 30 minutes in a colorimeter at 420 nm wave length. Plot curve showing the relationship between the concentration of S and the turbidity readings (% T or A).

Observation and Calculation

Weight of the sample

=

0.5 gm

Volume made up

=

100 ml

Volume pipetted out

=

5 ml

Volume made up

=

25 ml

Colorimeter reading

=

O.D.

Corresponding reading in ppm from standard graph

=

x ppm

Therefore S content in plant sample

=