Total nitrogen

Estimation of total Nitrogen (Micro Kjeldahl Method)

Aim

         To estimate the total nitrogen content in the given organic manure sample.

Principle

         A known weight (1g / 0.5 g) of the powdered sample is treated with diacid mixture so as to oxidize the organic matter and bring the mineral elements into solution.

Materials required

         1. 100 ml conical flaks   2. 250 ml volumetric flask  3. Funnel 4. Sand bath 5. Diacid mixture 6. Boric acid 2 % 7. Standard N/10 sulphuric acid 8. Double indicator (Bromocresol green and methylred) 9. Sodium hydroxide 40 %.

Procedure

A. Preparation of Diacid Extract

         Weigh 0.5 gram of a sample and transfer into a 100 ml conical flask. Add about 10-15 ml of diacid mixture (Sulphuric acid, perchloric acid in the ratio of 5:2) and cover the mouth of the flask with 5 cm funnel. Digest the contents of the flask, over a sand bath till a clear solution is obtained. Transfer the contents of the flask into a 100 ml volumetric flask using minimum quantity of water and make up the volume to 100 ml.

B. Estimation of total Nitrogen

         Pipette out 10 ml of the diacid extract and transfer into the distillation flask. Pipette out 25 ml of 2 % boric acid into an ice tumbler/beaker and add two drops of double indicator (bromocresol green and methyl red) and keep it at the delivery end of the distillation set. Add 10 ml of 40 % sodium hydroxide to the distillation flask and distil the contents collecting the distillate in 2% boric acid. Test the completion of distillation with a moistened red litmus paper. Absence of blue colour indicates that all ammonia has been distilled. Then wash the delivery tube with distilled water and collect the washing in ice tumbler. Nitrate the contents with N/10 sulphuric acid. The end point is the change of colour from green to pink.

Observation and calculation

Weight of the sample taken

=

'W' g ( 0.5/1.0)

Volume of diacid extract prepared

=

250 ml (100)

Volume of diacid extract pipetted out for analysis

=

10 ml

Volume of N/10 H2SO4 used

=

'X' ml

1 ml of N/10 H2SO4

=

0.0014 g of N

This is present in 10 ml of the diacid extract

=

This is present in 'W' g of the sample

=

Percentage of nitrogen

=