A fiber-optic refractive index sensor detects the isoelectric point of gelatin

In the present study, a set-up and a rapid method were developed to determine the isoelectric point (pI) of gelatin based on the combination of an automatic adding solution technique and fiber-optic refractive index sensing. The refractive index of the gelatin aqueous solution was measured as a function of pH and time using a fiber-optic sensor and pH meter. This is a typical acid-base titration process. The peak pH values of the refractive index-pH curve indicate the pI of the gelatins. With the aid of virtual instrument technology, the data acquisition, process and display were automatic, having the advantages of quick and labor saving. Furthermore, this improved analysis efficiency and reduced manual disturbance, which was typically an approximately 15min period. The pI of these two kinds of gelatin, sample 1 and 2 were determined through this method and the pI s were consistent with the values obtained using a rotary viscometer. The test results revealed that this method is rapid, sensitive, accurate, and labor and reagent saving, and has the potential for the rapid determination of the pI of amino acids and proteins.