Rheological Additives
Laba Dennis in Rheological Proper ties of Cosmetics and Toiletries, 2017
J. M. Huber Listed in decreasing order of thickening efficiency and oil absorption— Zeothix® 265.Zeosyl® 200.Zeodent® 163.Zeofree® 153.Silica Gel
Pitfalls and Practical Solutions
Joseph Chamberlain in The Analysis of Drugs in Biological Fluids, 2018
Traces of water can be removed from organic phase by the adding a pinch of anhydrous sodium sulfate. Even visible amounts of water can be mopped up by this reagent and the dried solvent can be readily poured off, the hydrated salt sticking in clumps to the sides of the vessel. Alternatively the organic extract can be simply filtered through anhydrous sodium; if there are only trace amounts of water, simply passing the phase through dry filter paper will be adequate with less potential of losing drug by adsorption to the solid salt. For example, calcium chloride added to the extract was shown to cause loss of oxprenolol in an assay for this compound.1406 Immediate storage of dried-down samples in a desiccator is recommended to remove last traces of water or to preserve the anhydrous condition of samples. Reid1407 suggests that silica gel, rather than phosphorous pentoxide, should be used as a desiccant; the latter reagent will overdry the atmosphere and cause volatilization of drug from the sample. A similar effect may also be noted in freeze-drying procedures; during the process of freeze-drying the sample will remain cold, but if the process is allowed to continue after the water has been removed, the temperature of the sample will rise to ambient and loss of sample may occur.1408
Sampling Techniques
Jacques Derek Charlwood in The Ecology of Malaria Vectors, 2019
Mounted material is then kept in a tightly sealed specimen box. Care must be taken, particularly in the tropics, to dry the specimens; if this is not done, they will become mouldy and covered with fungus, making them worthless for study. It is advisable to keep a bag of silica gel crystals in the box so that the crystals are not loose and to protect the stored material from insect pests, particularly ants. For this, a strip of slow-release insecticide (such as a Vapona strip or a dog’s flea collar) can be placed in the box.
A comparative evaluation of resin- and varnish-based surface protective agents on glass ionomer cement – a spectrophotometric analysis
Published in Biomaterial Investigations in Dentistry, 2020
Shreya Tyagi, Abi M. Thomas, Neeta Devi Sinnappah-Kang
The setting reaction of GIC involves neutralization of the polyacid by the basic glass leading to the formation of metal polyacrylate units [2]. The setting reaction involves the following stages: decomposition of the powder, gelation, hardening and maturation [3]. When the acid attacks the surface of the glass it leads to decomposition of the powder and the release of metallic cations into the solution. A silica gel is then formed and this surrounds the unreacted glass particles. The ions that are released from the glass powder are Na+ and Ca2+ (or Sr2+), followed quickly by Al3+ ions. These cations react with the polymer chains of carboxylate groups and thus increase the viscosity and contribute to the gelation reaction. Hardening of the cement occurs as a result of formation of crosslinks between the polymer chains and metal cations. Initially there is formation of calcium polyacrylate within 45 s followed by aluminium polyacrylate formation in 10 min and this continues for approximately a day. After the initial hardening, further reactions continue for more than 24 h and this is known as maturation [3–5]. With maturation of the cement, the physical properties change, i.e. there is an increase in strength and translucency of the GIC.
Evaluation of Pistia stratiotes fractions as effective larvicide against Anopheles mosquitoes
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Jincai Ma, Yunusa Adamu Ugya, Asma’u Isiyaku, Xiuyi Hua, Tijjani Sabiu Imam
Isolation of pure compounds was performed by column chromatography of the extract on silica gel. Silica gel with 60–200 mesh size (product of Lobachemie Laboratory Reagents and Fine chemicals, Mumbai, India) was used as a stationary phase in the column. To prepare the column, a glass tube of 5.0-cm diameter and 87-cm length was clamped vertically. The lower end of the column was fitted with a stopper and plugged with cotton wool as a support. Slurry of silica gel was prepared in solvent used for separation (250 g silica gel in 500 ml chloroform). The slurry was added to the column gradually and with gentle tapping to avoid cracks. This process was continued till a uniform column of desired length was obtained. The crude extract (40.42 g) was mixed with 25 g of silica gel to obtain homogenous mixture. This mixture was poured into the column and different fractions were eluted with different solvents viz. chloroform, ethyl acetate and formic acid. The extracted fractions were collected separately and the solvent of the collected fractions was evaporated at room temperature [3,22–24].
In-use stability studies: guidelines and challenges
Published in Drug Development and Industrial Pharmacy, 2021
A model for in-use stability of tablets and powders in bottles is presented by Waterman et al. [67] for determining the an in-use period when a drug in tablets/powders filled in bottle will remain within its specification limits. In this study a heat-induction sealed bottle was opened for fixed time periods and tablets were removed at fixed time points. This model determines the impact of relative humidity as a function of time on rate of degradation for the dosage forms under in-use conditions by combining it with the Accelerated Stability Assessment Program. Here assumptions were made that during periods when the bottle remains open, the air inside bottles with broached heat-induction seals completely exchanges with the external environment. During these openings the solid dosages were assumed to sorb water at estimable rates. When the bottles are capped, the rate of moisture vapor transmission can be estimated by determining the changing RH inside the bottles between opening events. The presence of silica gel desiccant has impact and can also be included in the modeling.
Related Knowledge Centers
- Adsorption
- Alkali
- Desiccant
- Gelatin
- Oxygen
- Silicon Dioxide
- Agar
- Silicon
- Decomposition
- Gel