Weight of sample required

The weights of sample required for the determination of nitrogen in compounds containing between 1% and 90% of nitrogen are shown in Table 2.6. Also shown is the normality of the hydrochloric acid required for the titration of ammonia at the end of the determination. 

Example 1 Sample Quantity for Composition Quality Control Testing An example is sampling for quality control of a 1,000 metric ton (VFg) trainload of-Ks in (9.4 mm) nominal top-size bentonite. The specification requires silica to be determined with an accuracy of plus or minus three percent for two standard errors (s.e.). With one s.e. of 1.5 percent, V is 0.000225 (one s.e. weight fraction of 0.015 squared). The problem to be solved is thus calculating weight of sample to determine sihca with the specified error variance. 

It is vital that sufficient weight of sample is taken for the planned analyses, extra being added in case further unforeseen tests are required. Plant materials... 

Calculation. Divide the weight lost by the weight of sample and multiply by 100 to obtain the percentage oil in the seed sample. A separate sample for moisture content must be weighed at the same time as the sample for oil extraction if the percentage oil in seed DM is required. 

Analysis of errors [234] indicated that the optimal conditions for standard addition experiments correspond to values of Ga/Gr and m/m, of unity. The main limitation of the method is, obviously, the relatively large amounts of sample required (about 1-2 mg) for weighting in conventional analytical balances. This is a... 

Calculate the minimum weight of Na2C03 required to dissolve a0.500-g sample of an ore which analyzes 19.1% silica (SiC>2). 

Recall that NK and N are the numbers of atoms in the mixture due to sample and tracer, respectively. To convert them to weight requires use of the familiar Avo-gadro relationship and involves multiplying both sides of the equation by 1.0 twice, thereby introducing the atomic weights of sample and tracer (i.e., multiply each side by A JAS and A/At). Note that Avogadro s number appears on both sides of the equation and cancels out. As and Ar on the other hand, are not equal and do not cancel. The resulting equation is one form of the isotope dilution equation. 

Precipitation of the dissolved carbon species and their extraction from 50 200 1 is preferably done in the field. This procedure requires experience (guided by the laboratory staff or, preferably, carried out by a trained hydrochemist). Precipitation in the field is time consuming, but it reduces the volume and weight of samples that have to be transported to the laboratory. 

What are the limits to collection in terms of (i) time frame (how long does an approval last ) (ii) local involvement (is there a requirement for local personnel to accompany a collector ) and (iii) amount (weight) of sample being collected ... 

The amount of sample required to obtain a spectrum is of the order of 0.01 mg (direct sample introduction system) to 1 mg (indirect sample introduction system). Purity of the sample is desirable, but in many cases not essential. Usually up to 10% of impurity (much more even of low molecular weight compounds) does not seriously interfere with the interpretation. In some instances, information about the structures of the different compounds may be obtained even from mixtures. 

V = ml of Fischer Reagent required for sample F =equivalency factor for Fischer Reagent, in mg of water per ml of Reagent, and W = weight of sample in grams... 

Powdered material is poured into a cone and divided into four equal parts. One quarter is recovered and the process was repeated until the required weight of sample is obtained. This method is prone to operator bias, as finer particles tend to remain in the center of the cone because of size segregation. Symmetry of the cone is also quite difficult to achieve but is necessary for accuracy, so this method is not recommended. ... 

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