Drug Substance and Excipient Characterization
Dilip M. Parikh in Handbook of Pharmaceutical Granulation Technology, 2021
Gas adsorption is carried out by placing a powder sample in a chamber and evacuating the air within. The latter process is commonly referred to as degassing. Upon achieving a very high vacuum, known volumes of an adsorbing gas are introduced. From the knowledge of pressure and temperature before and after the introduction of the adsorbing gas, usually nitrogen, calculations of total sample surface area can be made. The surface area determined by gas adsorption is based on a simple principle. From Avogadro’s number, a known volume of air at a certain temperature and pressure contains a determinable number of molecules. When various volumes of gas are introduced to a degassed sample, the small pressure changes in the chamber are recorded and using a calculation technique known as the Brunauer, Emmett, and Teller or BET method, the initial amount of gas molecules which are adsorbed onto the surface forming a monolayer can be calculated. Thus, the surface area covered by the gas molecules can be determined by multiplying the number of molecules needed with the surface area occupied per molecule. Samples are usually cooled to a low temperature using liquid nitrogen. There are variations in the technique for gas adsorption by different instrument manufacturers.
Nanocarrier Technologies for Enhancing the Solubility and Dissolution Rate of Api
Debarshi Kar Mahapatra, Sanjay Kumar Bharti in Medicinal Chemistry with Pharmaceutical Product Development, 2019
Structural Characterization: Structural characterization is a factor which plays a significant role in determining various properties like shape, size, structural arrangement, morphology, spatial distribution, geometric feature, density etc. of a nanosystem. Advancement of electron microscopy helps in increasing ease of access and feasibility to determine these properties at the nanometer scale. Scanning electron microscopy (SEM) shows the image of even as small as 10 nm sizes particles and provides important information about surface morphology, spatial distribution as well as structural arrangement of nanoparticles. Even more dominant imaging tools are Transmission electron microscopy (TEM) and high resolution TEM which give meticulous geometrical characteristics and information like crystal structure and orientation of nanoparticles. Also, tools like scanning tunneling microscope (STM), scanning thermal microscopy and electrical field gradient microscopy (EFM), in combination with atomic force microscopy (AFM) can be employed to exemplify structural, magnetic, electronic and thermal characteristics along with topographical characteristics of nanosystems. Laser diffraction is the general technique used to measure particle sizes for bulk samples along with powder X-ray diffraction. Surface area can be determined by using techniques based on BET isotherm like the nitrogen adsorption technique. The morphology of nanoparticles can be analyzed by its shape and aspect ratio that is evaluated by analysis of images produced through electron micrographs.
Pharmacokinetic-Pharmacodynamic Relationships of Cardiovascular Drugs
Hartmut Derendorf, Günther Hochhaus in Handbook of Pharmacokinetic/Pharmacodynamic Correlation, 2019
Similar equations and models have been used to describe a variety of biochemical processes (e.g., protein binding, enzyme kinetics) since they all reflect reversible binding of a ligand to a receptor. The classic Michaelis-Menten equation, which relates the rate of a chemical reaction to the concentration of substrate, the maximum velocity (Vmax) and the Michaelis constant (Km), is in the form of Equation 7. The equation is also analogous to the Langmuir adsorption isotherm, which is used to describe the adsorption of gases to solid surfaces.5 Similarly, the association of oxygen and hemoglobin was described by Hill6 in 1910 using the equation:
Optimization of Swiss blue dye removal by cotton boll activated carbon: response surface methodological approach
Published in Toxin Reviews, 2022
Rekha Rani, Summaiya Tasmeem, Anju Malik, Vinod Kumar Garg, Lakhvinder Singh, Sanju Bala Dhull
The mechanism of adsorption is commonly investigated through graphical representation known as adsorption isotherm. Isotherms illustrate the dispersal of dye among solid and liquid stage at certain temperature (Aljeboree et al.2017). The adsorption equilibrium of dye on AC was assessed in adsorption experiments. Different models have been applied in literature to express preliminary adsorption data in the isotherm. Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich (D–R) are the generally applied models (Pathania et al.2017, Hasan et al.2019, Shakya et al.2019, Kıvanç and Yönten 2020). Equilibrium sorption isotherms prove to be incredibly important for efficiency determination of an adsorbent. In the present investigation, four types of isotherms, viz. Langmuir, Freundlich, Temkin, and D–R were applied to the adsorption data. Thermodynamic parameter – Gibbs free energy change (ΔG0ads) was also computed and used for describing the results.
Synthesis and characterization of water stable polymeric metallo organic composite (PMOC) for the removal of arsenic and lead from brackish water
Published in Toxin Reviews, 2022
Khalil Ahmad, Habib-Ur-Rehman Shah, Hafiza Ammara Nasim, Asif Ayub, Muhammad Ashfaq, Abdul Rauf, Syed Shoaib Ahmad Shah, Muhammad Mahboob Ahmad, Haq Nawaz, Ejaz Hussain
Adsorption process is proceeded by various procedures as reported in literature. Some of these are (i) surface area and volume, (ii) electrostatic interactions, (iii) hydrogen bonding, (iv) adsorbents having active sites, (v) chemical and porous nature of the adsorbent, (vi) π–π interaction, and (vii) acid–base interaction. Adsorption process takes place by physically or chemically; chemically based upon functional group and physically be influenced by the surface of adsorbents. Before and after the adsorption process, FTIR spectrum was accomplished to elucidate the adsorption mechanism of Co-MOF/PANI composite. From the FTIR spectrum, it was calculated that the spectra after adsorption indicated peaks at 542, 921.71, and 832.71 cm−1 which are due to the interaction of composite with arsenic and lead, and these peaks are not present in the spectrum before adsorption as shown in Figure S1. From this FTIR spectrum, it was revealed that the hydroxyl group is responsible for adsorption of Pb(II), As(III), As(V), and DMA upon the surface of adsorbent. Moreover, the peaks in FTIR spectrum at 542, 921.71, and 832.71 cm−1 were presented owing to As–O and Pb–O bond, respectively (Li et al.2020). Adsorption mechanism is also represented schematically in Figure 7.
Mesoporous silica particles as potential carriers for protein drug delivery: protein immobilization and the effect of displacer on γ-globulin release
Published in Drug Development and Industrial Pharmacy, 2020
Adejumoke Lara Ajiboye, Vivek Trivedi, John Mitchell
In general, the adsorption isotherms for silica particles were a better fit to Langmuir model suggesting monolayer coverage of γ-globulin at most pH conditions on the surface of studied adsorbent particles [19,39]. The Langmuir isotherm describes a dynamic protein adsorption process where it is assumed that (i) a monolayer is formed at the adsorbent surface (ii) there are no interactions amongst adsorbed molecules, and (iii) no conformational change occurs to the protein structure upon adsorption [39]. On the other hand, Freundlich’s isotherm can be used to certify several immobilization processes permitting for one or more interactions either between adsorbed molecules or between the adsorbed molecules and sorbent surface [39].
Related Knowledge Centers
- Absorption
- Activated Carbon
- Atom
- Chemisorption
- Heterogeneous Catalysis
- Molecule
- Solvation
- Sorption
- Ion
- Surface Science