Residual gravimetric method

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

Some indirect method of measuring evaporative loss is needed because of the difficulty of direct measurements. Total amounts in random crop samples at various times after spraying can be measured by residue analytical methods (radioactive tracer or otherwise). The rate of loss so determined is subject to large statistical errors and includes losses by chemical and biochemical reaction and perhaps translocation in the crop as well. Exposure of typical test surfaces treated with some model substance, preferably less volatile than water but sufficiently volatile for simple gravimetric procedure, would seem the most suitable. We will see, however, how successful water is as a model for providing rough estimates. 

J. C. May, R. M. Wheeler, and E. Grim, The gravimetric method for the determination of residual moisture in freeze-dried biological products. Cryobiology 26.-277-284(1990). 

The freeze-dried product has to have a residual moisture content (RM) between alj and am, e.g., 0.7-1.1%, measured by a method, e.g., the gravimetric method at +50°C [4]. The dried cake should be white, with no visual shrinkage, and mechanically stable when slightly shaken. It will withstand a maximum tern-... 

Others have used interference microscopic 36> and gravimetric methods 37> to compare the density of the residual polymer on the various steps. 

Flocculating ability was measured as velocity (V) of precipitation of suspended disperse particles of a specific imitator - black copper oxide. Besides, residual suspended materials concentration (turbidity - T) was measured with the use gravimetric method after passing through the front of depositing flakes. 

AOAC enzymatic gravimetric method The samples are dried, with fat extracted if necessary, gelatinized with heat-stable a-amylase and enzymatically digested with protease and amyloglucosidase to remove protein and starch. The soluble dietary fiber is then precipitated using ethanol, the residue filtered and washed, and corrections made for indigestible protein and ash. This method is widely used in the EC and the USA. 

Enzymic-gravimetric methods, which measure a variety of components and give no details of polysaccharide type. In the method of the Association of Official Analytical Chemists for total dietary fibre, samples are gelatinised by heating and treated with enzymes to remove starch and proteins.The total dietary fibre is precipitated with ethanol and the residue is dried and weighed. 

The methods used for determination of fat or oil in food are often based on extraction with either ethyl ether or petroleum ether and gravimetric determination of the extraction residue. These methods may provide unreliable or incorrect results, particularly with food of animal origin. As shown in Table 14.20, where a corned beef sample was analyzed, the amount and composition of fatty acids in the fat residue were influenced greatly by the analytical methods used. In addition to the accessible free lipids, the emulsifiers present and the changes induced by autoxidation affect the amount of extractable lipids and the lipid-to-nonlipid ratio in the residue. The use of a standard method still does not eliminate the disadvantages shown by analytical methods of fat analysis. Therefore, in questionable cases, quantitative determination of fatty acids and/or glycerol is recommended. 

The solvent removal can also be followed by gravimetric analysis of the weight loss. This method is used to determine the time necessary for complete solvent removal. Shown in Fig. 29 are such drying curves for 5 mm diameter cy-hndrical samples prepared with 16 wt % and 20 wt % cyclohexane. It is seen that most of the solvent is removed within the first day. However, the samples are held for an additional four days to achieve a porous structure with minimal amount of residual solvent. 

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