Linear and nonlinear approaches to study transient signals of a flow-through bulk optode

The transient signals obtained with an anion flow-through bulk optode based on a lipophilized pH indicator dissolved in a plasticized poly(vinyl)chloride membrane and entrapped in a cellulose support in response to different concentrations of NO3−, Br−, I−, BF4−, ClO4− and PF6− were studied using a flow injection system. The transient signals presented different shapes for each anion. The signal shapes were characterized by means of appropriate parameters, and were found to be dependent on the size and concentration of the anion, providing information that could be used for their identification and quantification. A characteristic portion of the signal was also studied using nonlinear analysis. The results show the existence of chaos and the K2-entropy (an approximation for the Kolgomorov K-entropy) was seen to be dependent on the size and concentration of anion.