The stability of the produced acid-base indicator paper from Catharanthusroseus flower extract was conducted and a potentiometric titration method in four cases of titration was done to test the suitability of the extract indicator.
Extraction was done by reflux method using water as extracting solvent. The color of the extract was gray, and it turned light pink when added to an acidic solution and yellow green when added to basic solution. Potentiometric data were used to construct a plot that was pH as a function of the volume of titrant added to determine the transition error of the four (4) cases of titration. Results showed that the extract can be used as an indicator in the titration of a strong acid against a strong base which had the lowest percent minimal transition error (2.91%) with a pH range of 3.09-9.10 and volume range of 10.60-10.92 ml.
The stability of the acid-base indicator paper produced was done in terms of its effect on: the type of matrix used, temperature, and storage time. Results showed that the acid-base indicator paper that used bond paper as its matrix gave a stable color in four (4) weeks observation, and more stable when stored at lower temperature (7-10ºC) compared when it was stored at room temperature (28-33ºC). Furthermore, the acid-base indicator paper that used bond paper as its matrix showed lesser amount of cost per strip compared to a litmus paper (standard). From the study, the kind of matrix used, time of storage and temperature of storage really matters in the stability of an acid-base indicator paper.