Sension ph31 ph meter

The three fenofibrate-loaded SNEDDSs (i.e. super-SNEDDS solution150, SNEDDS75 and super-SNEDDS suspension150) were separately weighed in a beaker and dispersed in 26 mL of HTP intestinal medium (Table 2). The amount of SNEDDS (i.e. either super-SNEDDS solution150, SNEDDS75 or super-SNEDDS suspension150) added to the beaker was chosen in order to obtain a final fenofibrate concentration of 480 µg/mL for all SNEDDSs and to have the same drug concentration as the one utilized in the in vitro lipolysis experiments performed by Michaelsen and colleagues (2019) . The mixture was stirred at 37 °C for 20 minutes prior to the addition of the pancreatic lipase solution (4 mL) in the case of the presence of lipolysis, or of HTP intestinal medium (4 ml) in the case of sole dispersion (i.e. absence of lipolysis). To obtain the pancreatic lipase solution, the crude lipase extract was mixed with 5 mL of HTP intestinal medium in the absence of calcein, and the mixture was centrifuged for 7 minutes at 6500×g. The supernatant (4 mL) was added to the beaker to initiate the lipolysis (final activity of 550 USP/mL). To simulate physiological temperature, the experiment was performed at 37 °C.
Samples (1 mL), either utilized for the assessment of fenofibrate distribution in the aqueous phase or used for the permeation study, were taken out of the beaker after initial dispersion, after 30 minutes of additional dispersion or after 30 minutes from the initiation of lipolysis. This allowed to study both how the presence or absence of lipolysis affects the distribution of fenofibrate in the HTP intestinal medium on top of the mucus-PVPA barriers, and to evaluate the resulting drug permeation.
To study the distribution of fenofibrate between the aqueous and pellet phase before the start of lipolysis To confirm that the pH conditions were kept constant during dispersion/lipolysis by the buffering capacity of the HTP intestinal medium, the pH was monitored using a SensION TM PH 31 pH meter (HACH, Dusseldorf, Germany). Moreover, the size of the SNEDDSs droplets after dispersion and after initiation of lipolysis was determined using a Malvern Zetasizer Nano ZS (Malvern, Oxford, UK).
Samples were prepared by dispersing the SNEDDS pre-concentrate in HTP intestinal medium (concentration 1.45 mg/mL), and for the investigation on the effect of lipolysis on the droplet size, pancreatic lipase extract was added to the dispersion in order to obtain a final activity of 550 USP/mL.
The operating conditions used for the size determination were the following: viscosity of the sample dispersant 0.8872 cP, temperature 25.0 ºC, measurement angle 173 º backscatter, cell type disposable cuvettes (DTS0012), number of measurements 3.

All chemicals and reagents used were of analytical grade. Solutions were prepared using deionised water (Millipore, resistivity not less than 18.2 MΩ cm at 25 °C). Buffer solutions were prepared using citric acid/sodium citrate for the pH range 2.5-5.0 and monosodium phosphate/disodium phosphate for the pH range 5.0-9.0. All solutions contained 100 mM KCl as supporting electrolyte. The pH values of buffers were measured using a HACH LANGE Sension+ PH31 pH meter calibrated using standard buffers of pH 4.01 ± 0.01, 7.00 ± 0.01, and 10.01 ± 0.01. Defibrinated sheep's blood was purchased from TCS Biosciences Ltd, UK and the pH adjusted using vapour withdrawal carbon dioxide gas (BOC, Guildford UK). Carbon dioxide gas was bubbling into sheep's blood samples for a few seconds to adjust the pH and the pH of the samples was recorded.