Kjeldhal method
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The document outlines Kjeldahl's method for nitrogen estimation in organic compounds, detailing the steps of digestion, distillation, and titration. It describes the procedure, required reagents, and equipment needed to analyze nitrogen content, emphasizing the method's limitations with certain nitrogen-containing compounds. Overall, it provides a comprehensive understanding of quantitative analysis using Kjeldahl's technique.
Kjeldhal method
- 1. NAME :- ANURAG PANDEY COUSRE :- B.PHARM YEAR :- 2ND YEAR (IVTH SEMSTER) PRESENTED DATE :- 19-JANUARY-2015 PRESENTATION GIVEN BY :- MR. SUNIL SINGH (ASST. PROFESSOR AT INVERTIS INSTITUTE OF PHARMACY)
- 2. INTRODUCTION THEORY DIGESTION DISTILLATION TITRATION PROCEDURE REAGENTS MATERIAL AND EQUIPMENT METHOD CYCLIC PROCESS OF THE PROCEDURE CALCULATION LIMITATION
- 3. Introduction Kjeldahl's method is a faster method than Dumas' method. However, this method is used only for those organic compounds that are converted quantitatively to ammonium sulphate on heating strongly with concentrated sulphuric acid. As the determination of the relative proportions (as percentage) of various elements present in an organic compound is termed as quantitative analysis. Theory :- Kjeldahl's method involves three steps: Digestion A known mass (0.3 to 0.5 g) of the given organic compound is digested with concentrated H2SO4, in presence of a small quantity of potassium sulphate and copper sulphate in a Kjeldahl's flask. Potassium sulphate raises the boiling point of sulphuric acid and copper sulphate catalyzes the digestion. In 3 to 4 hours, the organic compound is completely decomposed to form ammonium sulphate. Reaction :- Distillation The digested reaction mixture, on cooling, is transferred to a round bottomed distillation flask, and distilled with a concentrated alkali solution (NaOH). Ammonia produced is absorbed in a known volume of HCl solution of a known strength. Reaction :- Kjeldhal’s method of Nitrogen estimation 1. Digestion 2. Distillation 3. Titration
- 4. The un-neutralised HCl is then back-titrated against a standard alkali. From the acid consumed, the amount of ammonia produced and hence the mass of nitrogen is calculated. Titration Titration quantifies the amount of ammonia in the receiving solution. The amount of nitrogen in a sample can be calculated from the quantified amount of ammonia ion in the receiving solution. The are two types of titration :- 1. Back titration 2. Direct titration Fig:16.17 Apparatus for the estimation of nitrogen by Kjeldahl's method Procedure:- Reagents :- Mercuric oxide, reagent grade. Potassium sulphate or anhydrous sodium sulphate, reagent grade. Sulphuric acid (98%), nitrogen free. Paraffin wax. 40% solution of sodium hydroxide; dissolve 400 g of sodium hydroxide in water and dilute to 1,000 ml.
- 5. 4% sodium sulphate solution. Boric acid indicator solution; add 5 ml of a solution with 0.1% methyl red and 0.2% bromocresyl green to a saturated boric acid solution. Standard solution of 0.1N chlorhydric acid. Material and equipment:- Kjeldahl digestion and distillation apparatus. 500 ml Kjeldahl flasks. 250 ml Erlenmeyer flasks. Glass beads. Method i. To milligram precision, weigh out 1 g of sample and place in the Kjeldahl flask; add 10g potassium sulphate, 0.7 g mercuric oxide and 20 ml concentrated sulphuric acid. ii. Place the flask tilted at an angle in the digester, bring to boiling point and retain until the solution is clear; continue to heat 30 minutes more. If foam is too abundant, add a little paraffin wax. iii. Leave to cool, gradually adding approximately 90 ml distilled, de-ionized water. When cold add 25 ml sodium sulphate solution and stir. iv. Add one glass bead and 80 ml of 40% sodium hydroxide solution, keeping the flask tilted. Two layers will form. v. Quickly connect the flask to the distillation unit, heat and collect 50 ml of distillate containing ammonia in 50 ml of indicator solution. vi. At the end of distillation, remove the receptor flask, rinse the end of the condenser and titrate the solution with the standard chlorhydric acid solution. Cyclic process of the procedure
- 6. Figure:- Determination of Nitrogen by Kjeldahl's method. Calculation :- Let, Mass of the organic compound = W g Volume of the standard acid required for complete neutralization of the evolved ammonia = V mL Normality of the standard solution of acid = N From the law of equivalence (normality equation), 1000 mL of 1 N acid = 1000 mL of 1 N NH 3 = 17g NH 3 = 14 g nitrogen Then, V mL of N acid = V mL of NH 3 NV milli equivalent of acid = NV milli equivalent of ammonia Therefore, Then, Percentage of nitrogen in the sample = Or, % of the nitrogen in the sample = 1.4 V*N W Where: V = Acid used in titration (ml) N = Normality of standard acid W = Weight of sample (g)
- 7. Limitation Kjeldahl's method cannot be used for the organic compounds :- Containing nitrogen in the ring, e.g., pyridine, quinoline etc. Containing nitro (-NO 2) and diazo (-N = N-) groups.