Ph conductivity meter

A detailed procedure for the determination of the swelling degree (S_w) was previously described [44 (link)]. S_w was calculated using the equation: $${\mathrm{S}}_{\mathrm{w}}=\frac{{\mathrm{w}}_{\mathrm{t}}-{\mathrm{w}}_0}{{\mathrm{w}}_0}\times 100$$
where w_t is the weight of the swollen microspheres and w₀ is their initial weight.
In vitro release studies of microspheres were carried out at room temperature in the system formed by putting 4 g of microspheres in 100 mL of distilled water, as previously described [45 (link)]. The concentrations of released K, Ca, and Mg were determined by atomic absorption spectrometry (ASS) (HRN ISO 11466:2004). The results are presented as the fraction of potassium (f_K), calcium (f_Ca), or magnesium (f_Mg) using the equation: $$\mathrm{f}=\frac{{\mathrm{R}}_{\mathrm{t}}}{{\mathrm{R}}_{\mathrm{tot}}}$$
where f represents the fraction of cumulatively released calcium, potassium, or magnesium, R_t is the calcium, potassium, or magnesium released at time t, and R_tot is the total amount of calcium, potassium, or magnesium loaded in the microsphere formulation. The concentration of released cations was determined by an atomic absorption spectrometer (Solar, Thermo Scientific, Abingdon, UK).
During release, the pH and conductivity changes were measured by the Mettler Toledo pH/Conductivity meter (Zagreb, Croatia). The results were statistically analyzed with Microsoft Excel 2016 and the XLSTAT statistical software add-on. The data are shown as mean values ± standard deviations.