Microdetermination of organic halogens by argentometric titration using Gran's plot.

Abstract

Halogens in microamounts of organic compounds were determined using the flask combusion method and the potentiometric titration with a silver nitrate standard solution. A silver wire electrode treated in a saturated silver halide solution for more than 24 h was employed for measuring the electrode potential in a sample solution containing the same halide ion. An aliquot of 0.005 M halide solution was accurately pipetted into a 50 ml beaker and made up to the mark with water. The silver electrode and a double junction reference electrode were inserted into the solution, which was titrated with a 0.005 M AgNO3 standard solution. The electrode potential was measured at 2 min after each addition of the titrant. The end point of the titration was determined by using Gran's plot for two data points on a personal computer. When the titration fraction was taken at two data points of 40% and 60%, the relative standard deviations of the volume of end points were 0.49% for Cl-, 0.44% for Br-, and 0.71% for I-. This method was applied to microdetermination of organic halogens after flask combusion as follows: A sample weighing about a few mg on a piece of filter paper was ignited in an oxygen flask containing 5 ml of water and 5 drops of 5% hydrazine hydrate solution as an absorption liquid. After standing for 30 min, the solution was transferred to a 50 ml beaker. After the addition of 4 ml of 0.1 M HNO3 solution to adjust pH around 5, the solution was finally made up to 50 ml with water. The solution was then titrated with 0.005 M AgNO3 standard solution. The end point was determined using the Gran's plot method as described above. Micro determination was carried out for several organic halogen compounds and the relative standard deviation of the determinations was 0.21%.