Selective ion determn. in aq. soln. - by electrical conductivity measurement before and after reacting with selective complexing agent

摘要

Measurement of the concn. of ions or ion gps. in aq. solns. involves (a) measuring the electrical conductivity of a sample stream taken from the soln., (b) adding a reagent (I) selective for the ions concerned, which changes the conductivity according to the ion concn., (c) measuring the conductivity at the same temp. as in (a) after the reaction and (d) representing the difference in conductivity values as an index for the absolute content of the ion concerned in the sample stream. (I) is pref. a complexing agent forming inclusion cpds. with the ions, esp. 4,7,13,16,21-pentaoxa-1.10-diazabicyclo-(8,8,5 -tricosane, 4,7,13,18-tetraoxa-1,10-diazabicylco-(8,5,5)-eicosane or 4,7,13, 16,21,24-hexaoxa-1,10-diazabicyclo-(8,8,8)-hexaconsane. The method is suitable for the selective determn. of very small concns. in aq. solns. , e.g. monitoring breakthrough of Na ions in the ion exchange treatment of salt water. It is suitable for continuous long-term operation with great maintenance or calibration intervals.