Loss of weight

Historically this is the first method which appeared in flie pharmacopoeias, performed either at normal pressure or under vacuum. This is, of course, an easy method, particularly for routine control but there are several drawbacks  

This determination can now be done by thermogravimetric analysis (TGA) which makes the method more sensitive (possible LOD 100 ppm) and less product demanding (5 -20 mg). It can also be used as a hyphenated method linking TGA to a mass spectrometer, allowing the identification of the desorbed solvents (specificity). However, whilst this kind of equipment exists, there are no signs of it replacing gas chromatography (GC) in die near future. 

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Loss of weight on heating. NF T 66-011 and ASTM D 6. The loss of weight on heating can also be measured during the RTFOT test. 

The thermodynamic properties of Tefzel 200 and 280 are shown in Table 2 the annual rate of loss of weight with thermal aging for Tefzel 200 ranges from 0.0006 g/g at 135°C to 0.006 g/g at 180°C after an initial loss of absorbed gases of 0.0013 g/g at elevated temperature. The excellent thermal stabihty of ETEE is demonstrated by aging at 180°C at this temperature, the annual weight loss of six parts per 1000, or a 1% weight loss, takes almost two years. 

With respect to the action of the enzyme itself, a loss of weight on account of cellulose hydrolysis, as well as loss in strength properties, occurs. Therefore, control of concentrations, temperature, and other processing conditions is important to achieve a product having the proper balance of properties. 

The simplest analytical procedure is to oxidize a sample in air below the fusion point of the ash. The loss on ignition is reported as graphitic carbon. Refinements are deterrninations of the presence of amorphous carbon by gravity separation with ethylene bromide, or preferably by x-ray diffraction, and carbonates by loss of weight on treating with nitric acid. Corrections for amorphous carbon and carbonates are appHed to the ignition data, but loss of volatile materials and oxidation may introduce errors. 

Moisture measurements are important in the process industries because moisture can foul products, poison reactions, damage equipment, or cause explosions. Moisture measurements include both absolute-moisture methods and relative-humidity methods. The absolute methods are those that provide a primaiy output that can be directly calibrated in terms of dew-point temperature, molar concentration, or weight concentration. Loss of weight on heating is the most familiar of these methods. The relative-humidity methods are those that provide a primaiy output that can be more direc tly calibrated in terms of percentage of saturation of moisture. 

FIG. 21-34 Loss-of-weight-type scale used with a hag-packaging machine for non-free-flowing products. (Coutiesy of H. K Henderson IndusMes, Inc., Caldwell,... 

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. 

By the use of many commercial abrasive processes, the corrosion resistance of magnesium alloys can be reduced to such an extent that samples of metal that may lie quiescent in salt water for many hours will, after shot blasting, evolve hydrogen vigorously, and the corrosion rate, as measured by loss of weight, will be found to have increased many hundred-fold. The effect in normal atmospheres is naturally much less, yet the activation of the surface is an added hazard and is the opposite of passivation which is essential if later-applied paint finishes are to have proper durability. 

A sample ground to 40-mesh is dried in the oven for a long time (100 hours or more) at a temperature where decomposition is not too rapid at the end of this time the sample is assumed to be essentially dry. A drying curve is determined from the loss of weight at various time intervals. The sample is then permitted to absorb in a humidistat a known amount of water which can be accurately determined by weighing before and after the absorption. Drying is then repeated under conditions identical with those of the... 

A comparison of the drying curves for lyophilized and unlyophilized sweet potatoes is shown in Figure 7. It is seen that the same and constant loss of weight (8.2%) was reached with the lyophilized samples at both 60° and 70° C. No such indication is shown by the unlyophilized samples at either temperature. 

Hyperthyroidism (thyrotoxicosis), defined as excessive thyroid activity, causes a state of thyroid hormone excess (thyrotoxicosis) characterized by an increased metabolic rate, increase in body temperature, sweating, tachycardia, tremor, nervousness, increased appetite and loss of weight. Common causes of hyperthyroidism are toxic multinodular goiter, toxic adenoma or diffuse toxic goitre ( Graves disease). Antithyroid diugs (methimazol, carbimazole, propylthiouracil) block thyroid hormone production and are hence suitable for the treatment of hyperthyroidism. 

Rory1 did not allow for this loss of weight as long as the conversion p was not too low, without explaining this assumption, p is given by the classical relation ... 

Water permeability is tested by transmission permeation tests, standard test ASTM E 96 being widely used. The water which permeates is absorbed in a desiccant and its weight—or alternatively, the loss of weight of the water supply from a container (or permeation cup ) sealed by the sheet test sample—is determined. The same procedure is applied for the transmission of volatile liquids in standard ISO 6179 (BS 903 A46)—see Eigure 23.7. 

Cardiac cachexia Physical wasting with loss of weight and muscle mass caused by cardiac disease a wasting syndrome that causes weakness and a loss of weight, fat, and muscle. 

Symptoms of thyrotoxicosis include nervousness, anxiety, palpitations, emotional lability, easy fatigability, heat intolerance, loss of weight concurrent with an increased appetite, increased frequency of bowel movements, proximal muscle weakness (noted on climbing stairs or arising from a sitting position), and scanty or irregular menses in women. 

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