2.5. Characterization of formulation

Unless otherwise referred, the physico-chemical properties of the encapsulated PO formulations were tested as per the Collaborative International Pesticides Analytical Council (CIPAC) and Indian Standard (IS) specifications (BIS, 1997). All the experiments were done in triplicate.

The pH value of PO formulation was measured by immersing the electrode directly into the emulsion using a pH meter (Systronics, Model 335, Gujarat, India) at 25 ± 1 °C (CIPAC MT75.3, 2000). Before recording the value, pH meter was calibrated using pH 4.0, 7.0 and 9.2 buffer solutions (Merck).

For stability study, formulated PO was subjected to different tests viz., centrifugation, heating-cooling cycle and freeze-thaw stress. Initially, the formulations, which passed the thermodynamic stress tests, were considered for further characterization.

Encapsulated PO formulations were centrifuged (Eltek, TC-4100D, India) at 3000 rpm for 30 min and observed for any phase separation. Stable samples without separation were analyzed for heating-cooling cycles and freeze-thaw stress.

Heating-cooling cycle was performed by placing PO formulation at 4 °C and 40 °C, alternating at each temperature for 48 h. The cycle was repeated thrice. For freeze-thaw stress, the botanical formulation was kept alternatively at 25 °C and -21 °C for 48 h twice. All tests were carried out as per the standard methods outlined in the CIPAC Handbook (CIPAC MT46.3, 1995).

The morphology of the synthesized microcapsules was examined by Optical Microscope (Nikon, CIS, Tokyo, Japan) equipped with the image capturing (Nikon, DS-Ri2) and image analyzing device (NIS-Elements, BR 4.30.00). An optimized image of microcapsules was captured by exposure adjustments.

The mean droplet size and zeta potential of bio-formulation were measured by Zetasizer (Nano-ZS90, Malvern, Worcestershire, UK) based on the principles of Dynamic Light Scattering (DLS).