Representative samples and sample storage

Representative Samples and Sample Storage. Sample Concentration and Clean-up Solid Phase Extraction. 

For cases of sample storage where losses cannot be excluded a priori, some sort of check is required. This should be done under conditions representative of the actual sampling, sample storage, and sample analysis. As this study indicates, the use of radiotracers is helpful in making such checks. 

Field samphng, sample transport, and laboratory sampling are the three steps that must be carried out before sample analysis in the laboratory. Not getting a representative sample in the held, transport, and storage under nonideal conditions, and improper sampling in the laboratory can all cause dramatic changes in the results of an analytical procedure and thus alter its accuracy. The effect of these factors on variation in the data obtained is always larger than the inherent accuracy of the actual chemical procedure. 

XRF characteristics that can limit its usefulness are the surface area observed and surface contamination. In XRF, the surface area measured is small, meaning that a large number of determinations must be made in order to obtain a representative sample of the elements present. In addition, transport and storage of uncovered soil samples can lead to surface contamination that will subsequently appear as part of the soil constituents. 

For the basic calibration we will use sufficiently pure material which is free from interfering compounds. We have to ensure the homogeneity of the samples and the representativeness regarding the characteristics described in the slide. Of course the samples have to be sufficiently stable for the time period within which they are intended to be used. If necessary, we have to preserve the samples. Storage of the samples has to be organised in such a way that the integrity of the sample is not influenced. 

Figure 11 Physical changes occurring to SQ-33600 disodium salt during solid-formulation processes as described using PXRD analysis. Sample A represents the initial wet-granulated amorphous material. Samples B and C represent samples following storage at 52% RH and 75% RH, respectively.

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