CARBON BY PERSULFATE OXIDATION-ACID TITRIMETRY

Scope
This test method covers the determination of soluble carbon in uranyl nitrate solution in sample aliquots containing 10 t0 15 g 0f uranium.

Summary of test method
The carbon in the uranyl nitrate solution is oxidized to carbon dioxide by potassium persulfate and silver nitrate. The carbon dioxide (CO2) produced is reacted with a measured quantity of barium hydroxide- barium chloride solution. The solution is then titrated with standard hydro chloric acid to a thymolphthalein end point. A reagent blank is olso determined in the same manner as the sample. The difference between the two is equivalent to the carbon present.

Interferences
· Persulfate oxidation is eneffective for water insoluble compounds and may be unsatisfactory for some stable ring compounds.
· The recovery of carbon from ethyl and methyl amines is only about 75%.
· Sulfure, nitrogen and chlorine do not interfere.

Apparatus
· Oxidation apparatus. 250 mL round bottom flask connected to a reflux condenser with a standard taper joint. A gas inlet is provided in the flask. The top of the condenser is connected to a fritted disk which can be submerged in a 50 mL test tube containing Ba (OH)2 solution.
· Heating mantle, controlled by a variable transformer.
· Buret, class A, 10 mL.

Reagents
· Argon compressed.
· Barium Chloride Solution (1 M). Dissolve 122 g of BaCl2.2H2O in water and dilute to 500 mL.
· Barium Hydroxide Solution ( 0.08 N in 1 M BaCl2 solution). Dissolve 6.3 g of Ba(OH)2.8H2O in 500 mL of 1 M BaCl2 solution and filter.
· Arbon Standard Solution ( 1 mL = 10 mg C). Dissolve 2.375 g of sucrose in water and dilute to 100 mL. Make fresh weekly.
· Hydrochloric Acid standard (0.05 N). standardize against a standard sodium hydroxide solution which has been standardized against potassium hydrogen phthalate.
· Potassium persulfate (K2S2O8), reagent grade.
· Silver Nitrate Solution (40 g/L). Dissolve 4 g of AgNO3 in water and dilute to 100 mL.
· Thymolphthalein Solution (5 g/L). Dissolve 0.5 g of Thymolphthalein in 100 mL of 95% ethyl alcohol.

Procedure
· Transfer a weighed 30 to 50 mL sample aliquote to a 250 mL round bottom flask.
· Add 5 g of potassium persulfate and enough water to give a total volume of 100 mL
· Add a fewdrops of dilute H2SO4 and swirl to liberate any carbonate present.
· Add 4 drops of AgNO3 solution and mix.
· Transfer 10 mL of 0.08 N Ba(OH)2 solution to a 50 mL test tube and dilute to 40 mL with water. Add 3 drops of thymolphthalein solution. Insert the glass frit into the solution in the test tube.
· Start the flow of argon sweeps gas, and adjust to give a slow but continuous stream of fine bubbles from the glass frit.
· Bring heat up to 70 oC and hold for 30 min.

Note 1. The content of the flask darhen upon heating When oxidation is complete, the dark color will disappear.. oxidation is usually complete within 30 min.
Note 2. There is denger of incomplete oxidation if the potassium persulfateis decomposed too rapidl. The reaction temperature should be held bedween 70 and 75 oC

· Titrate the solution in the test tube to a colorless end point with 0.05 N HCl.
· Run a series of reagent blanks to establish the titer of the Ba(OH)2 solution.
· Carry 1 mL of carbon standard solution through the procedure step 1 to step 10

Note 3. The purpose of the standard is to determine the efficiency of the test method in terms of carbon recovery.


Calculation
Calculate the efficiency as follows :

F = (B-A) x C x 6000 / E

Calculate the carbon content as follows :

Carbon, µg/g = (B-A) x C x 6000 / D x F


Where
A = standard HCl used in sample or standard titration, mL.
B = standard HCl used in blank titration, mL.
C = normality of HCl
D = uranium contained in the sample aliquote, g.
E = carbon in standard carbon solution, µg
F = efficiency factor for the method,
6000 = equivalent weight of carbon.

Precision
The limit of error at the 95% confidence level for a single determination is ± 5%.

Literature
ASTM-C799, Standard Methods for “Chemical, Mass Spectrometric, Spectrochemical, Nuclear, and Radiochemical analysis of Nuclear-Grade Uranyl Nitrate solution”