Testing powder stability tests

Aerated powder test, powder stability tests 77... 

Precipitation and Purification. During the hydrolysis, control tests are made by turbidimetric titration of samples taken intermittently. When the desired degree of hydrolysis is reached, the ester is precipitated from the reaction solution into water. It is important for the precipitate to have the proper texture for subsequent washing to remove acid and salts for thermal stabilization. Before precipitation, the reaction solution is usually diluted with additional aqueous acetic acid to reduce the viscosity. If a flake texture is desired, the solution is poured into a vigorously stirred, 10—15% aqueous acetic acid. To precipitate the acetate in powder form, dilute acetic acid is added to the stirred reaction solution. In both cases, the precipitated ester is suspended in 25—30% aqueous acid solutions and finally washed with deionized water. The dilution, precipitation temperature, agitation, and strength of the acid media must be controlled to ensure uniform texture. 

CA 31,5165 (1937) 4)P.Hayard, Vacuum Stability Tests on Solventless Double Base Powders Containing Various Stabilizers OSRD 5959 (20 Nov 1945), 28 Fig 32 5) J.G. Grasselli ed, Atlas of Spectral Data and Physical Constants for Organic Compounds ,... 

The polymer stability upon storage was tested by keeping samples of pure, powdered poly(N-palmitoylhydroxyproline ester) in... 

Silica powder has been studied as a stabilizer for oil well cement at high temperatures [1895]. Tests indicated that silica powder can improve the stability and pressure resistance strength of cement. The manufacture of very-high-strength concrete (after 28 days the compressive strength is greater than... 

The purpose of in-use stability studies is to establish the period for which a product intended to be used on more than one occasion may be used after reconstitution or dilution or the withdrawal of the first dose from the container without adversely affecting the integrity of the product and with the product retaining acceptable quality characteristics. This type of test can be applied to any multiple use product (e.g., sterile products in multiple-use containers, powders or granules including those used to produce oral solutions or suspensions) but is likely to be of particular importance in the case of products that are manufactured with an inert headspace gas, for products containing antioxidants to protect an active ingredient that is liable to oxidative decomposition, and for products that contain a volatile antimicrobial preservative. 

Many methods have been proposed and are used to study the thermal stability of propellants and to ensure the absence of possible autocatalysed decompositions during storage. None are sufficiently reliable to merit individual description. In practice, stabilisers are added, the usual being diphenylamine for nitrocellulose powders and symmetrical diethyl diphenyl urea (carbamate or centralite) for double base propellants. Provided a reasonable proportion of stabiliser remains, the propellant can be assumed to be free from the possibility of autocatalytic decomposition. The best test of stability is therefore a chemical determination of the stabiliser present. 

Perhaps conceptually one of the simplest tests for comparing the stability of related polymer samples is that of measuring oxygen uptake. In such a measurement the amount of oxygen reacting with a polymer sample, at a particular temperature and over a specific time, can be measured either manometrically or volumetrically, by a relatively simple device [1], such as that illustrated in Figure 4 [10]. Whereas such a measurement may be made on solid samples, such as sheet, powder or film, in order to minimise errors, the measurement is preferably made on thin film samples. 

The appearance of tablets and powders during accelerated stability testing can be quantified using tristimulus colorimetry [29]. In this work, various formulations were stored under stress conditions, and the tristimulus parameters... 

The stability of powders can be determined by adiabatic storage tests or Dewar flask tests under an air atmosphere (Section 2.3.2.2). Several other dedicated tests have been developed [10,133-136]. 

In the Bowes and Cameron test [133], the stability of the powder at constant (uniform) ambient temperature is investigated. Cube-shaped baskets, made of wire gauze, are filled with the substance and placed in an oven that is controlled at the desired constant temperature. The temperature in the center of the cube and of the oven are continuously recorded. By testing at different temperatures, and using a number of cube dimensions, the thermal stability of the powder can be established, that is, the determination of the temperature below which the exothermic decomposition of the powder does not result in a runaway. Bowes [133] has given a number of theoretical calculations for scaling up the test results. 

More rudimentary tests to identify the stability of powders are the so-called "hot plate" tests. Here, the substance is placed in a well-defined manner (circular, specified thickness of the layer, and so forth) on a hot plate with a controlled temperature. The temperature in the center of the layer is recorded continuously, and the progress of the self-heating is followed. Observations are made if self-heating of the substance occurs, the induction period of such self-heating, and the extent of the effect such as smoldering or spontaneous ignition. 

The test methods discussed in this context are broad in scope and relate to a variety of applications. In some such tests, a pigment powder is extracted with water and its contents analyzed other procedures reveal the stability of a pigmented system with regard to water, acids, or bases. A number of these tests have developed into industrial standards. 

Various dry powder attributes are assessed at release and on stability. These include physieal eharaeteristies sueh as appearance, content uniformity, delivered dose uniformity, and partiele size distribution. Chemieal attributes that may be assessed include drug eontent, purity, and identity, as well as the water content. Dry powders may also undergo mieroseopie evaluation for foreign particulate matter, unusual agglomeration, and partiele size. Mierobial limits should also be examined, including the total aerobie, yeast, and mold eounts. The presence of specific pathogens should be ruled out. The dry powders may be dissolved to test for pH. 

The inclusion of the a routine microbial limit test in a marketed product stability protocol depends on the pharmaceutical dosage form. Typically, the test would be used only for nonsterile products, especially oral liquids, nasal sprays, and topical liquids, lotions, and creams that have sufficient water activity to support the growth of microorganisms. In contrast, tablets, powder- and liquid-filled capsules, topical ointments, vaginal and rectal suppositories, nonaqueous liquids and inhalation aerosols with a water activity too low to allow for the product to support the growth of microorganisms would not be routinely tested. 

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