Medium Selection

For batch-to-batch quality testing, selection of the dissolution medium is based, in part, on the solubility data and the dose 

Basket, paddle, reciprocating cylinder, or flow-through cell Paddle Paddle 

Basket, paddle, or reciprocating cylinder with glass beads Paddle over disk Franz cell diffusion system Paddle, modified basket, or dual chamber flow-through cell Special apparatus [European Pharmacopoeia (PhEur)] Flow-through cell (powder/granule sample cell) 

Modified flow-through cell Modified flow-through cell 

The dissolution characteristics of oral formulations should be evaluated over the physiologic pH range of 1.2-6.8 [1.2-7.5 for modified release (MR) formulations]. During method development, it may be useful to measure the pH before and after a run to see if the pH changes during the test, 

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All filters require a filter medium to retain solids, whether the filter is for cake filtration or for filter-medium or depth filtration. Specification of a medium is based on retention of some minimum parficle size at good removal efficiency and on acceptable hfe of the medium in the environment of the filter. The selection of the type of filter medium is often the most important decision in success of the operation. For cake filtration, medium selection involves an optimization of the following factors ... 

Filter-medium selection embraces many types of construction fabrics of woven fibers, felts, and nonwoven fibers, porous or sintered solids, polymer membranes, or particulate solids in the form of a permeable bed. Media of all types are available in a wide choice of materials. 

The difficulty becomes accentuated by several other requirements that cannot be achieved through the selection of a single filter medium. Therefore, selection is often reduced to determining the most reasonable compromise between different, mutually contradictory requirements as applied to the filter medium at a specified set of filtration conditions. Because of this, some problems should be solved before final medium selection. For example, should attempts be made to increase filtration rate or filtrate purity Is cost or medium life more important In some cases a relatively more expensive filter medium, such as a synthetic cloth, is only suitable... 

One can to outline a general approach for medium selection along with a test sequence applicable to a large group of filter media of the same type. There are three methods of filter media tests laboratory- or bench-scale pilot-unit, and plant tests. The laboratory-scale test is especially rapid and economical, but the results obtained are often not entirely reliable and should only be considered preliminary. Pilot-unit tests provide results that approach plant data. The most reliable results are often obtained from plant trials. 

Proper filter medium selection is based on understanding these mechanisms and analyzing the impact each has on the filtration process. 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

Increased determined by growth on salinised medium. Selected plants were hexaploid (5)... 

Figure 3 Root fingerprints of Pseudomimets sp. associated with barley seedlings showing the production of siderophore by actively growing bacteria located in the zone of elongation behind the root tips. Root.s were pressed on to an iron-deficient minimal medium selective for Pseudomonas. After growth of the colonies, the production of siderophore was visualized by exposure of the agar plate to ultraviolet light, which causes the siderophore to Huoresce.

Tables 3.4 and 3.16 show the main characteristics of SFE. The technique has important advantages especially in cases where loss or degradation of target analytes is likely to occur. The generation of oxidation products will not present any problems. Some authors have claimed that selectivity can be introduced in modern SFE instrumentation [320]. Extraction selectivity and efficiency can be controlled by the nature of the supercritical medium (Selectivity 1). Another opportunity for selectivity concerns the density of the...

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

The medium selected for the dissolution test must consider the drug solubility. Aqueous media with a typical plT range between 1 and 7 to mimic the human gastrointestinal tract are preferred over organic solvents. The operating parameters of the dissolution setting should be optimized to ensure complete dissolution. ... 

Selectivity is more important than efficiency (AO in determining resolution because Rs is directly proportional to selectivity, but is proportional only to the square root of efficiency (see Fig. B4.2.5 along with Equation B4.2.1 and Equation B4.2.2. Hence, a four-fold increase in efficiency is required to double resolution, as compared with a two-fold increase in selectivity. In practice, selectivity depends partly on the chromatographic technique employed but can usually be controlled by manipulating experimental conditions, such as the pH and ionic strength of the mobile phase. Because this can be done easily and predictably, selectivity is the factor that is exploited to achieve maximum resolution in column chromatography rather than efficiency, which is fixed by the particle size and uniformity of the medium selected. 

Polyhedra bioactivity can be compromised due to nutrient limitations, causing abnormalities in virion development and occlusion within polyhedra (Rollinson et al., 1965 Slavicek et al., 1995 Belloncik et al., 1997). The most important aspects of culture medium selection are pH, osmolar-ity, and organic salt components. Components such as amino acids, vitamins, and carbon source (glucose for example), are typically found in the basal culture medium formulation. However, these simple formulations cannot promote cell growth themselves, unless supplemented with animal serum, normally 5-20% (v/v) fetal bovine serum (FBS) (Schlaeger, 1996). 

TABLE 11.2 Dissolution Medium Selection—Solubility of Active Component... 

The lactone (464) was reduced with lithium aluminium hydride to the (20/ )-18,20-diol. Regeneration of the A -3-keto-group afforded the keto-diol (465). Catalytic hydrogenation in alkaline medium selectively reduced the double bond at C(4) and gave the desired configuration of 5)5-H. Acetylation at C(18) was followed by oxidation, which provided the diketo-pregnane (466). Hydroxy-la tion of the -double-bond of (466) with osmium tetroxide gave the 3a,9a-... 

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