Rapid photometric determination of phosphine in acetylene

Abstract

In order to determine phosphine in acetylene rapildy, method to determine the light absorbancy of molybodenum blue has been investigated. A gaseous sample of 2550 ml contained in a 100ml capacity injector is introduced into an absorption vessel, large sized test tube, containing 20ml of 0.3% bromine water in 1 min. The sample is oxidized and transferred into a 50 ml measuring flask after 10% sodium sulfite is added dropwise for reduction of the excess bromine, 5 ml of a mixture of 6.5 N H₂SO₄-1.5% ammonium molybdate and 0.25 ml of 2% SnCl₂ are added to the solution. The sample solution is allowed to stand for 10 min at 25°C and the absorbancy of blue colored solution is measured with photoelectric colorimeter. The calibration curve was prepared by using a solution of a standard phosphate solution containing an equal amount of bromine and sodium sulfite to the sample solution and by developing a molybedenum blue after reduction with SnCl₂. Acetylene evolved from calcium carbide is collected in a gas holder and the phosphine content is determined by this method and by the JIS method. Good agreements are observed between the results of both methods. In order to avoid the loss of phosphine in acetylene while standing for long time, an apparatus indicated in Fig. 1 was made. By this method, phosphine can be determined in 15 min. This method is also applicable for rapid determination of phosphine in acetylene in plant operation.