Homogeneous samples

The sampling constant for the radioisotope " Na in a sample ( homogenized human liver has been reported as approximate 35 g. (a) What is the expected relative standard deviation fo sampling if f.O-g samples are analyzed (b) How many f.O-g samples need to be analyzed to obtain a maximum sampling error of 5% at the 95% confidence level ... 

Several factors affect the bandshapes observed ia drifts of bulk materials, and hence the magnitude of the diffuse reflectance response. Particle size is extremely important, siace as particle size decreases, spectral bandwidths generally decrease. Therefore, it is desirable to uniformly grind the samples to particle sizes of <50 fim. Sample homogeneity is also important as is the need for dilute concentrations ia the aoaabsorbiag matrix. 

Fig. 2. Electropherogram of real sample (homogenize of Drosophila flies heads). Electrolyte solution 7 mM sodium tetraborate, pH 8.14...

Filey RH, Nguyen S, Campbell S, Bragg A and Grimm CA (1987) Evaluation of sample homogeneity for geochemical standard reference materials used in microanalysis. J Radioanal Nud Chem Artides 110 147-158. 

After sampling, homogenization, extraction, cleanup, concentration and possible derivatization, use a suitable determination method which provides sufficient selectivity or specificity and sufficient sensitivity. 

A 10-g sample of the homogenized dry sample is soaked in 20 mL of distilled water for 2 h. After adding 100 mL of acetone to the soaked sample and shaking vigorously on a mechanical shaker for 30 min, the extract is filtered. After the addition of a further 100 mL of acetone, the sample homogenate is shaken as before and the acetone extract is filtered. The filtrates are combined and acetone is removed with a rotary evaporator. " ... 

An example of adequate sample homogenization is given in Table 4. The experiment was conducted with two replicate treated soil samples. Each replicate was analyzed in duplicate. Three different sample aliquots (2, 5 and 10 g) were used from each replicate. Analyses of controls and fortified samples were also conducted concurrently with treated samples to evaluate method performance (i.e., extraction recoveries). These results show that residue values are the same regardless of sample size. Thus, thorough homogenization of soil samples coupled with mgged analytical methodology provides for satisfactory residue analysis. 

For crop samples, homogenize 10 g of a prepared sample with acetonitrile-water [9 1 (v/v), 100 mL minus the water content of the sample] for 5 min and centrifuge the mixture at 3500 rpm for 5 min. 

Requirement for sample homogeneity clogging by large particles... 

Nondestructive radiation techniques can be used, whereby the sample is probed as it is being produced or delivered. However, the sample material is not always the appropriate shape or size, and therefore has to be cut, melted, pressed or milled. These handling procedures introduce similar problems to those mentioned before, including that of sample homogeneity. This problem arises from the fact that, in practice, only small portions of the material can be irradiated. Typical nondestructive analytical techniques are XRF, NAA and PIXE microdestructive methods are arc and spark source techniques, glow discharge and various laser ablation/desorption-based methods. On the other hand, direct solid sampling techniques are also not without problems. Most suffer from matrix effects. There are several methods in use to correct for or overcome matrix effects ... 

Tissue Weigh sample homogenize in aqueous zinc acetate using a rotostator at 18,000 rpm for 20 seconds dilute with horate buffer convert to methylene blue. Ion-interaction reversed-phase HPLC nmol g 1 NR Mitchell et al. 1993... 

From the most general point of view, the theory of fractals (Mandelbrot [1977]), one-, two-, three-, m-dimensional figures are only borderline cases. Only a straight line is strictly one-dimensional, an even area strictly two-dimensional, and so on. Curves such as in Fig. 3.11 may have a fractal dimension of about 1.1 to 1.3 according to the principles of fractals areas such as in Fig. 3.12b may have a fractal dimension of about 2.2 to 2.4 and the figure given in Fig. 3.14 drawn by one line may have a dimension of about 1.9 (Mandelbrot [1977]). Fractal dimensions in analytical chemistry may be of importance in materials characterization and problems of sample homogeneity (Danzer and Kuchler [1977]). 

The specific analytical techniques discussed in this chapter and their main applications are detailed in Table 2. Sample homogeneity/heterogeneity may need to be addressed when selecting an analytical technique or designing a test method. 

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