Sampling considerations

Any water analysis method is only as good as the sample used to represent the effluent stream. Sampling of a continuously flowing stream containing two or more phases (e.g., oil and water) is difficult unless the mixture is completely emulsified or is a very fine stable dispersion. Since the sampling techniques for oil concentration measurement and particle size distribution differ in some aspects, they are described separately here. 

In the enthusiasm for a particular technique or method, it is sometimes the case that the appropriateness of sample size is overlooked. Even though the sampling process outlined in Chapter 3 has been followed, it is essential that the size of the test sample and its relationship to the sizes of the test portion and the test solution are considered. These factors need to be considered during method selection. 

For example, is a 2 g test sample from a 1000 kg consignment or bulk batch adequate for the purpose It may be under appropriate circumstances. If not, how much material needs to be taken Recent draft guidance to the pharmaceutical industry from the FDA recommends that for blend uniformity sample sizes no more than three times the weight of an individual dose should be taken. 

Equally, consideration needs to be given to sample presentation. Is it more appropriate to test non-destructively to gain physical and chemical information or by solution/extraction processes to separate the analyte(s) of interest  

The most important aspect here is that these questions have been asked and documented answers given as part of the User Requirements Specification. 

It is essential to remember that whilst any test result may be method-dependent it is always sample-dependent. 

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Surface phases have low Debye temperatures. As a result, the recoil-free fraction may be low at room temperature (see Fig. 5.2). Thus, measuring at cryogenic temperatures will increase the Mossbauer intensity of such samples considerably. But there can also be other circumstances which call for low temperature experiments. 

In point source sampling, consideration of the topography, in this case (Figure 7.6) the slope and soil type, will be important. Discussion of soil types and sampling is presented in the next section. 

Wages SA, Church WH, Justice JB Jr. 1986. Sampling considerations for lin-line microbore liquid chromatography of brain dialysate. Anal Chem 58 1649-1654. 

As to the method of preparing our catalyst samples, considerable work was devoted to the various methods of preparation by which the ferroferrioxide (Fea04) can be obtained from metallic iron, in view of the... 

APPENDIX III SAMPLING CONSIDERATIONS AND TOOLS Homogenous Systems... 

IR spectra were recorded with a Beckman Acculab 6 spectrophotometer. Pellets were prepared by torque pressing a finely ground mixture composed of 1-2 mg of sample and 100-500 mg of spectroanalytical KBr. The pellets were translucent brown and showed good dispersion of the sample. Considerable attention was given to prevent moisture interference. The spectrum of a polystyrene film was recorded prior to the sample for QA purposes. 

Amides have a very strong tendency to self-associate by hydrogen bonding, and the appearance of the spectrum is very much dependent on the physical state of the sample. Considerable shifts in band positions can occur on passing from a dilute solution to a solid, thus N—H and C=0 stretching bands show a marked shift to lower frequency while the N—H bending (amide II) band moves to higher frequency. 

As above mentioned, the presence of CMI units within the PMMA chain backbone makes the sample considerably more brittle. Such an effect is already reflected in the type of deformation micromechanisms more and more crazes when the CMI content increases. 

Figure 18.2 shows the scanning electron microphotograph of the fractured surface of the sample. Considerable featureless material, possibly amorphous or microcrystalline, is visible. Due to the very fine starter powders used in this material, it is likely that the resulting crystals of magnesium potassium phosphate are also very fine and, hence, are not easily visible in the micrograph. The elongated crystals of calcium silicates are embedded in this amorphous mass. Also notice the crack due to fracture of the material, which is diverted by... 

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