Intrasample variance

Precision is measured by making replicate measurements. As mentioned before, it is known to be a function of concentration and should be determined at the concentration level of interest. The intrasample variance can be determined by splitting a sample into several subsamples and carrying out the sample preparation/analysis under identical conditions to obtain a measure of RSD. For example, several aliquots of homogenized fish liver can be processed through the same extraction and analytical procedure, and the RSD computed. The intersample variance can be measured by analyzing several samples from the same source. For example, different fish from the same pond can be analyzed to estimate the intersample RSD. 

The atmospheric variability has also been examined in previous studies. Solomon et al. [32] examined intrasampler variance and found small but consistent differences between the recoveries of four adjacent rotorod samplers and also between the recoveries of three adjacent rotoslide samplers. Although the authors suggested that the intrasampler variance reflected minor differences in... 

Area counts were statistically evaluated for intrasample coefficient of variance and a linear regression analysis for the line of fit for area versus time was prepared. The same evaluation protocol was then used for seven vellum documents and eight parchment documents. 

The intrasample error for paper, vellum, and parchment is summarized in Table 1. Note that the coefficient of variance is significantly higher for vellum and parchment than for paper. The selection of test site was far more difficult on skin than on paper. For paper sampling, a fibril was selected which ran perpendicular to the ink line so that the electron beam would scan the surface of a single fibril without falling into the valley between fibers. With skin, the presence of hair follicles and anomalies in surface texture introduced more sampling error. 

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