## 4 Discussions  
Specific surface area of the sorbents was determined, by applying the BET equation, as 1425.5 m\({}^{2}\cdot\)g\({}^{-1}\) for activated charcoal and 112.5 m\({}^{2}\cdot\)g\({}^{-1}\) for Na-montmorillonite. The activated charcoal particle size varies in range 0-18 \(\upmu\)m 93.1% of the particle being less 10 \(\upmu\)m. Furthermore, activated charcoal pore size varies in range 10-100 A over 68% being smaller than 25 A. It can be seen that 92% of natural Na-montmorillonite particles are smaller than 2 \(\upmu\)m and the pore size of the mineral clay varies in range 10-300 A about 35% being in range 10-25 A. The mineral clay contains important quantities of aluminum, silica, sodium, potassium, calcium and iron oxides and other elements in trace amounts in the form of oxides. The active charcoal is rich in surface functional groups C-O like in alcohols, phenols, acids, ethers and esters groups with well characteristics for adsorption. SEM analysis confirms that the pores on the activated charcoal and Na-montmorillonite surface were uniform in the micropore to mesopore size range, but the main difference of both adsorbents is their pore volume, which is nearly 10-times greater for the activated charcoal than for mineral clay. Figure 14: Diazepam adsorption isotherm on Na-montmorillonite from SIF without and with ethanol pH = 6.80 \(\pm\) 0.05; \(T\) = 37.0 \(\pm\) 0.1 °C; \(\blacksquare\) SIF without ethanol; \(\blacklozenge\) SIF with 5% ethanol; \(\bullet\) SIF with 10% ethanol; \(\blacklozenge\) SIF with 15% ethanol. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \(a\) **(mg/g)** & **pH** & **Ethanol(\% p/v)** \\ \cline{2-4} Activated charcoal & 585 & 6.81 & 0 \\ \cline{2-4} Activated charcoal & 560 & 6.85 & 5 \\ \cline{2-4}  & 530 & 6.84 & 10 \\ \cline{2-4}  & 480 & 6.80 & 15 \\ \hline \multirow{3}{*}{Natural Na-montmorillonite} & 11.5 & 6.85 & 0 \\ \cline{2-4}  & 10.1 & 6.82 & 5 \\ \cline{2-4}  & 9.3 & 6.80 & 10 \\ \cline{2-4}  & 8.7 & 6.82 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Maximum amount of diazepam adsorbed from SIF with and without ethanol. For both sorbents, the diazep sorption equilibrium was attained within 2 h, for all values of the drug SIF solutions initial concentrations. The amounts of diazep uptake after 4 h were approximatively the same as the amounts sobbed after 2 h. Thus, we considered that drug adsorption equilibrium was attained in 2 h.  
The amounts of diazep uptake on solid phase increase while the sorbent particle size decreases. Langmuir plots showed excellent coefficient of determination (\(R^{2}\)) for both sorbents. The maximum adsorption capacity for on activated charcoal and natural Na-montmorillonite are 611 mg/g and 13 mg/g, respectively. The pHZPC of natural Na-montmorillonite was determined to 7.3 while for activated charcoal to 7.6. Below the pHZPC, the surface of the sorbents is positively charged and above the point is negative. Diazepam is a weakly basic or neutral drug [24]. The results exhibit that sorption of diazep is higher below this point (Figures 11 and 12), due the neutrality of the drug which adsorbs by weak van der Waals forces, via an attraction of the positively charged surface sites at lower pH [7; 23]. The decreases of sorption capacity above pHZPC could be connected to the gradual ionization of diazep in alkaline medium. The presence of alcohol in SIF influences the diazep sorption. The sorption of diazep from simulated intestinal fluid that contains different amounts of ethylic alcohol (96%) is well described by Langmuir isotherms. It can be observed that increasing the ethanol concentration causes a decreasing of diazep concentration in solid phase. Some previous studies suggest that the water-ethanol solution is less polar than pure water [25] and thus, a solution containing ethanol compared to a pure aqueous solution makes drugs less adsorbable to activated charcoal [26].