A plasticizer is a substance intendent to increase flexibility and softness of the material to which it is added, , in order to improve its susceptibility to further processing. A plasticizer compound in the simplest sense is considered to be an organic solvent. There are many types of such compounds, such as animal fats, petroleum fractions, or all kinds of plant extracts. Plasticizers are used in the membranes of ion-selective electrodes and optodes forming their physical structure, however affecting as well the analytical performance of the sensors. Plasticizers can be also used in the process of creating microspheres that are incorporated with chemical indicators. With the change of environmental conditions, such structures can change their optical properties, becoming optodes in the microscale. In this work, the influence of two plasticizers - polar 2-Nitrophenyl octyl ether (o-NPOE) and non-polar bis(2-ethylhexyl) sebacate (DOS), on the optical response of microspheres sensitive to lipophilic ions was investigated. In addition, studies were also carried out considering the impact of the amount of plasticizer on the created microspheres properties - systems were prepared with a standard amount of the compound, its five-fold amount and without a plasticizer. The obtained results prove that in the case of the tested sensory system, the non-polar plasticizer works best, ensuring the obtaining of optodic microspheres with the highest linearity range of the calibration curve and the best sensitivity. When the amount of the selected plasticizer was adjusted, it was found that the best results can be obtained using the intermediate content of this ingredient. These result show, that plasticizer type and amount significantly influences analytical performance of optode microspehers.
This work was financially supported by National Science Centre (Poland) within the framework of the SONATA BIS project No. UMO-2018/30/E/ST4/00481. Aleksandra Kalinowska acknowledges financial support from IDUB project (Scholarship Plus programme).
