Sample gross

Upper sieve size (cm) Lower sieve size (cm) Mass % in class (lOOw/) Sample weight required 

Determine the minimum sample of quartz p = 2.65 g em ) to give an expected sampling error o = 0.05 (= 5%) if the coarsest size range of 105 to 75 pm contains 10% of the total weight. 

Since is proportional to cfi it increases rapidly with increasing particle size. 

This equation is applicable when the coarsest class covers a size range of not more than 2 1 and W is less than 50% of the total sample. 

Assume that a sieve analysis of the above powder is carried out, with the results shown in Table 1.7 and the tolerable sampling error for each fraction is 5%. The amount required for each fraction, in order to keep within this limit, equation (1.15) is given in column 4. 

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The initial sample is called the primary, or gross sample and may be a single increment drawn from the target population, or a composite of several increments. In many cases the gross sample cannot be analyzed without further treatment. Processing the gross sample may be used to reduce the sample s particle size, to transfer the sample into a more readily analyzable form, or to improve its homogeneity. 

Sample Preparation Most analytical methods can be applied to analytes in a liquid or solution state. For this reason a gross sample of a liquid or solution does not need additional processing to bring it into a more suitable form for analysis. 

Illustration showing the method of coning and quartering as a means of reducing a gross sample for subsampling, (a) The gross sample is first piled into a cone and... 

Sample taken into the lab for analysis after processing the gross sample. 

Two samples taken from a single gross sample and used to evaluate an analytical method s precision. 

Analysis of Duplicate Samples An effective method for determining the precision of an analysis is to analyze duplicate samples. In most cases the duplicate samples are taken from a single gross sample (also called a split sample), although in some cases the duplicates must be independently collected gross samples. The results from the duplicate samples, Xi and X2, are evaluated by determining the difference, d, or the relative difference, d) between the samples... 

British Standard Methods for the Determination of Particle Sis e Powders, Part I, Subdivision of Gross Sample Down to 0.2 Milliliters, BS3406 Part I, British Standards, London, 1961. 

Sampling. A sample used for trace or ultratrace analysis should always be representative of the bulk material. The principal considerations are determination of population or the whole from which the sample is to be drawn, procurement of a vaUd gross sample, and reduction of the gross sample to a suitable sample for analysis (15) (see Sampling). 

There are various types of samples within given sampling schemes, e.g., bulk samples > primary samples > gross samples > subsamples > test samples > measuring samples —Fig. 2.4... 

Consider the case of two single (methine) protons HA and Hx attached to adjacent carbon atoms and with quite different chemical shifts (Figure 9.32(a)). The field experienced by HA is increased or decreased slightly by the two allowed spin states of Hx, designated and l, and which in the gross sample are virtually equally populated. This results in the absorption band for HA splitting into a doublet whose peak intensities are in the ratio 1 1. The effect is mutual in that the two almost equally populated spin states of HA cause the Hx absorption to split into an identical doublet. The spacing... 

Reduction of the gross sample to a suitable sample for analysis. 

To take 1/50 to 1/100th of the total bulk for gross samples. 

To take larger gross samples for products having larger particle size. 

Either separate aliquots of liquid may be analyzed individually and the results combined duly, or the various aliquots may be first combined into one gross sample and replicate analysis carried out. However, the latter method is preferred for obvious reasons since the analysis shall have a better hold on the accuracy and precision of the analysis. 

Aliquot that quantity of material of proper size for measnrement of the property of interest test portions may be taken from the gross sample directly, but often preliminary operations such as mixing or further reduction in particle size are necessary. 

Gross sample. (Also called bulk sample, lot sample.) One or more increments of material taken from a larger quantity (lot) of material for assay or record purposes. 

Subsample. A portion taken from a sample. A laboratory sample may be a subsample of a gross sample similarly, a test portion may be a subsample of a laboratory sample. 

ASTM D-2234-76 Standard Methods for Collection of a Gross Sample of Coal," American Society for Testing and Materials Philadelphia, 1976. 

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