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.
Quantitative ultrasound
C M Langton, C F Njeh in The Physical Measurement of Bone, 2016
Preparation of bone samples is also governed by the study objectives, specimen size and shape. Most sample preparation for QUS investigation has three phases: cutting, defatting and degassing. Cutting. The samples should be cut under constant water irrigation. This prevents heating and possible damage to the samples. Both soft tissue and the cortical endplates should be removed to leave purely cancellous bone.Degassing. Air pockets in bone samples are detrimental to QUS measurement because they are highly reflective. All air bubbles in a sample must be removed to improve the reliability of the measurement. This can be achieved by degassing the samples submerged in water using a vacuum desiccator over a period of time.Defatting. Cancellous bone has pores filled with bone marrow, which might make degassing take longer. Most studies are carried out on samples with marrow removed (defatted) to speed up the degassing process. Njeh et al [48] defatted bone samples using the following procedure: the sample is subjected to a high speed jet of water, and then compressed air. This process is repeated until no fat is visible. The sample is then tumbled overnight in excess of 2:1 chloroform : methanol mixture. The sample is finally dried in air and stored in a vacuum desiccator.
Practical Implementations And Technology Of Measurement Devices*
Marvin C. Ziskin, Peter A. Lewin in Ultrasonic Exposimetry, 2020
As shown in Figure 5, radiation force measurements are performed in water. Since minute air bubbles in water can lead to significant measurement errors, acoustic power measurements using the radiation force phenomenon require the use of degassed water. At high-level measurements, for example, approximately 1 W or more, acoustic power should always be carried out in degassed water in order to prevent cavitation. One of the most effective degassing procedures is to boil water for approximately 30 min and allow it to cool under vacuum. Several other water degassing procedures are described in Reference 40. Also, water is a highly nonlinear medium and, therefore, the axial distance between the measured acoustic source and the target should be minimized, while maintaining free-field conditions in the measurement container. Often a thin, acoustically transparent membrane separating target and the source is used in order to minimize errors due to such second-order phenomena as acoustic streaming.47 In addition, for frequencies above approximately 5 MHz, corrections should be made to account for the absorption of ultrasound in water.48
Development and optimization of self-nanoemulsifying drug delivery systems (SNEDDS) for curcumin transdermal delivery: an anti-inflammatory exposure
Published in Drug Development and Industrial Pharmacy, 2019
Mohammad A. Altamimi, Mohsin Kazi, Mshaan Hadi Albgomi, Abdul Ahad, Mohammad Raish
Chromatographic separation was achieved with high accuracy and precision of the method. The analysis of THQ and CUR employed a highly sensitive UHPLC system obtained from Thermo scientific, Bedford, MA, that consisted of a Dionex® UHPLC binary solvent manager equipped with an autosampler and (PDA) eλ detector. Isocratic method was used and the mobile phase was prepared as CH3OH:H2O (60:40% v/v). Water contained 0.25% fumaric acid to adjust pH. Selected flow rate was 0.3 ml/min and the used column was (BEH C18, 2.1 × 50 mm, 1.7 µm). Temperature was maintained at 35 °C. Run was completed in 4 min. mobile phase was prepared prior to experiment and was filtered using 0.20 µm filter. The system was equipped with automatic degassing ability. Selected wavelength was 254 nm for THQ and 428 nm for CUR, respectively. The injection volume was 1.0 µL.
Soft, chewable gelatin-based pharmaceutical oral formulations: a technical approach
Published in Pharmaceutical Development and Technology, 2018
Morten J. Dille, Magnus N. Hattrem, Kurt I. Draget
A solution was prepared with gelatin and water (deionized) at 55 °C. Xylitol, sucralose, trisodium citrate, and malic acid were added to the sample vessel and mixed for 5 min giving a final pH of 4.5. Thereafter, a homogenous dispersion of sorbitol and ibuprofen was added to the mixture. The sample was stirred until all ingredients were dissolved or dispersed, and excess air was removed by degassing the mixture in a vacuum chamber. Finally, an amount of water was added to the sample vessel corresponding to the amount lost due to evaporation during processing. The composition of the ibuprofen soft-chew formulation used for dissolution, rheological measurements, and microbial stability is described in Table 1. The ibuprofen soft-chew used for chemical stability used an older and slightly different recipe, with the same concentration of ibuprofen, but with only citric acid as acidity modifier (pH 4.5), and 1% added strawberry flavor. Before gelling the mixture was transferred to petri dishes and fully sealed.
The impact of gestational sac size on the effectiveness and safety of high intensity focused ultrasound combined with ultrasound-guided suction curettage treatment for caesarean scar pregnancy
Published in International Journal of Hyperthermia, 2018
Yuqi Zhang, Cai Zhang, Jia He, Jin Bai, Lian Zhang
Strict three-day diet preparation before HIFU treatment was required for bowel safety. Patients were asked to start the diet preparation with a bland diet (no fibre and no milk) 3 days prior to HIFU treatment, followed by semi-liquid and liquid food in the next two days, respectively. At least 12-h fasting was required the night before treatment day, followed by 1–3 times of enema performed on the morning of treatment day. Shaving the lower abdominal area, from the umbilicus to the upper margin of the pubic symphysis, was performed. In addition, degreasing and degassing were perfomed using 75% ethanol and a vacuum device prior to HIFU treatment. Catheterization was also performed to control bladder size and help push the bowel away from the acoustic pathway for bowel safety.
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