PERMEATION TUBES FOR CALIBRATION IN FLOW-INJECTION ANALYSIS

The use of a permeation tube for the production of liquid stream calibration standards in the flow injection determination of ammonia was investigated. By varying the flow rate from 0.5 to 4.0 ml min-1, calibration standards over the range 1.5-0.18 ppm could be produced. The relationship between concentration of the resulting solution and the reciprocal of the flow rate was shown to be linear. The inherent high temperature dependence of the release rate necessitated the tubes being used under thermostated conditions. The release rate was found to vary between 136 and 158 ng min-1 cm-1 over a 7 d period. Taking all sources of uncertainty into account, the 95% confidence interval for the release rate varied between 12.0 and 16.2 ng min-1 cm-1 over the same 7 d period. The device was used in a manifold for the determination of ammonia in pond water in which the method of standard additions was employed.