Uniformity of weight

Quahty control during manufacture and of the final product assures batch-to-batch consistency and reflabiUty. Bioavadabihty is checked in early batches produced for clinical testing. Other tests include uniformity of weight and contents, hardness (qv), disintegration rate, dissolution rate, and friabihty. 

Often it is thought that the effectiveness of a riffler can be demonstrated by the uniformity of weight accumulated in each collector. This reasoning is incorrect if one considers that each collector will necessarily acquire a slightly different amount of sample if the collector diameters vary slightly. The only correct test for the effective performance of a riffler is to compare the contents of each collector in terms of particle size distribution or specific surface area. 

The effect of the active ingredient on flow properties can be determined at the same time by calculating the uniformity of weight of the tablets used to prepare pressure-strength profiles. 

No such uniformity of weights and measures existed on the European continent. Weights and measures differed not only from country to country but even from town to town and from one trade to another. This lack of uniformity led the National Assembly of France during the French Revolution to enact a decree (May 8, 1790) that called upon the French Academy of Sciences to act in concert with the Royal Society of London to deduce an invariable standard for all of the measures and all weights. Having already an adequate system of weights and measures, the English... 

Uniformity of weight (e.g. for tablets, single-dose powders, suppositories, capsules and herbal tea in sachets), disintegration time (for tablets, capsules, suppositories and pills), hardness and friability (for example, uncoated tablets), viscosity (for internal and external fluids), consis-... 

The importance of powder flow was emphasised in the section on Powder Flow. The formulation should have sufficient flowability to ensure that the appropriate quantity of powder flows into the dies of the tablet machine on a consistent basis. While the tests described for powder flow are useful development tools, the ultimate test of a formulation is the uniformity of weight of tablets manufactured on a production tablet machine. 

Table 11.6 European Pharmacopoeia uniformity of weight limits. ...

The fundamental requirements of a formulation to be filled on a dosator type machine are good flow properties, compressibility and lubricity. Plow is important in the powder bed when the dosator dips into the powder, it leaves a void which must be closed with material of the same bulk density prior to the next dosator entering that area of the hopper. Irwin et al. (1970) investigated the effect of powder flow on the uniformity of weight achieved on a Zanasi filling machine and concluded that the better the rate of flow the better the uniformity of fill. 

Some liquid oral medicines are dosed in drops. This may be practical but the doses that are administered in the form of drops should meet the requirements for uniformity of weight and content. For pharmacy preparations the requirements for oral drops of the Ph. Eur. cannot be achieved with the available dropper devices. See further Sect. 24.4.19.4—6. 

Capsules content, uniformity of weight, content uniformity, appearance, disintegration time, dissolution rate. 

In any application of a copolymer the rate of formation of the product, its molecular weight, and the uniformity of its composition during manufacture are also important considerations. While the composition of a copolymer depends only on the relative rates of the various propagation steps, the rate of formation and the molecular weight depend on the initiation and termination rates as well. We shall not discuss these points in any detail, but merely indicate that the situation parallels the presentation of these items for homopolymers as given in Chap. 6. The following can be shown ... 

In a solution of molecules of uniform molecular weight, all particles settle with the same value of v. If diffusion is ignored, a sharp boundary forms between the top portion of the cell, which has been swept free of solute, and the bottom, which still contains solute. Figure 9.13a shows schematically how the concentration profile varies with time under these conditions. It is apparent that the Schlieren optical system described in the last section is ideally suited for measuring the displacement of this boundary with time. Since the velocity of the boundary and that of the particles are the same, the sedimentation coefficient is readily measured. 

Uniformity of the rate of feed will be ensured by a constant-weight feeder density control may be automatically obtained through a measuring probe on the media-return line that adjusts delivery of the nec-essai y volume of media from the densifier or media thickener the viscosity can be controlled automatically by continuously testing a predetermined volume of return media and adjusting the divider under the drainage screen for media cleaning as needed pH control can be automated by conventional methods. 

The foregoing are volume integrals evaluated over the entire volume of the rigid body and dw is an infinitesimal element of weight. If the body is of uniform density, then the center of gravity is also called the centroid. Centroids of common lines, areas, and volumes are shown in Tables 2-1, 2-2, and 2-3. For a composite body made up of elementary shapes with known centroids and known weights the center of gravity can be found from... 

It is significant that most of the data from which a remarkable uniformity of attack is deduced are derived from small isolated panels. This is the most convenient form of specimen for measurements of corrosion rates by loss of weight but it eliminates the important effect of galvanic currents passing between remote parts of a large structure. It is believed that the experience of civil engineers and other users would not support the conclusion suggested by panel tests that corrosion is no faster in tropical than in temperate waters. 

Corrosion rates in normal industrial atmospheres measured as loss of weight over a period are extremely uniform among the various alloys. Table 4.19, last column, gives the corrosion rates (in g m d" ) for a number of alloys determined at Clifton Junction in recent years. The highest value recorded (0-4 g m d ) is equivalent to a rate of penetration of 0-076 mm/y, which is appreciably less than that of mild steel. 

The corrosion rate of a metal in terms of weight loss per unit area (g m" d ) or rate of penetration (mm y" ) can be calculated from Faraday s law if the current density is known. Conversely, the corrosion current density can be evaluated from the weight loss per unit area or from the rate of penetration. The following symbols and units have been adopted in deriving these relationships in which it is assumed that corrosion is uniform and the rate is linear ... 

Polymerization of t-butyl methacrylate initiated by lithium compounds in toluene yields 100% isotactic polymers 64,65), and significantly, of a nearly uniform molecular-weight, while the isotactic polymethyl methacrylate formed under these conditions has a bimodal distribution. Significantly, the propagation of the lithium pairs of the t-Bu ester carbanion, is faster in toluene than in THF. In hydrocarbon solvents the monomers seem to interact strongly with the Li+ cations in the transition state of the addition, while the conventional direct monomer interaction with carbanions, that requires partial dissociation of ion-pair in the transition state of propagation, governs the addition in ethereal solvents. 

A special case of the internal stabilization of a cationic chain end is the intramolecular solvation of the cationic centre. This can proceed with the assistance of suitable substituents at the polymeric backbone which possess donor ability (for instance methoxy groups 109)). This stabilization can lead to an increase in molecular weight and to a decrease in non-uniformity of the products. The two effects named above were obtained during the transition from vinyl ethers U0) to the cis-l,2-dimethoxy ethylene (DME)1U). An intramolecular stabilization is discussed for the case of vinyl ether polymerization by assuming a six-membered cyclic oxonium ion 2) as well as for the case of cationic polymerization of oxygen heterocycles112). Contrary to normal vinyl ethers, DME can form 5- and 7-membe red cyclic intermediates beside 6-membered ringsIl2). 

The dose uniformity of tablets can be determined by two different general approaches the weight variation between a specified number of tablets or the extent of drug content uniformity. The USP permits the latter approach in all cases. Moreover, drug content uniformity must be measured for coated tablets because... 

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