PERMEATION TUBES FOR CALIBRATION IN FLOW-INJECTION ANALYSIS

The use of a permeation tube for the production of liquid stream calib ration standards in the flow injection determination of ammonia was in vestigated. By varying the flow rate from 0.5 to 4.0 ml min-1, calibra tion standards over the range 1.5-0.18 ppm could be produced. The rela tionship between concentration of the resulting solution and the recip rocal of the flow rate was shown to be linear. The inherent high tempe rature dependence of the release rate necessitated the tubes being use d under thermostated conditions. The release rate was found to vary be tween 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 relea se rate varied between 12.0 and 16.2 ng min-1 cm-1 over the same 7 d p eriod. The device was used in a manifold for the determination of ammo nia in pond water in which the method of standard additions was employ ed.