Optimum sampling

A general feature of optimum sample preparation is that maximum recovery of the analyte is observed. Consider a graph of recovery vs. variation in one experimental condition. Figure 5 shows such a graph, with temperature as the experimental variable. The curve exhibits a maximum and a decline on either side of the maximum. The assay will be most reproducible at the point of zero slope, i.e., at the maximum recovery, because small variations in conditions will not affect the result. In hydrolysis of a protein to its constituent amino acids, for example, it will be found that at very high temperatures or long hydrolysis times, degradation of the product amino acids occurs, while at low temperatures or short hydrolysis times, the protein... 

Calculations Absorption Factor, Optimum Sample Thickness... 

The optimum sample thickness for PET of a mass density pp r=l-35 g/cm3 in transmission geometry thus is topt,PET = 1 /Ppet 1 mm. If measured in reflection, the PET sample should be at least 3 mm thick. 

However, that only addresses the limiting case. We are interested in the behavior of the standard deviation of AA/A in this whole intermediate regime, so that we can determine the optimum sample transmittance, just as we did before, for data measured... 

The Tameapa stream sediment orientation survey consisted of 30 sample sites situated down-stream from the Pico Prieto and Venado prospect areas. The primary purpose of the stream sediment orientation survey was to determine optimum sampling and assaying parameters for use in the regional stream sediment survey. 

Alternatives to Optimum Sample Processing. The 20-24 samples/ wk were considered the optimum because that number of samples could be completely analyzed in 5 days, working one 8 -hr shift/day. 

There are numerous ways to prepare a solid sample for XPS-analysis 17K Because of the 360° angle of acceptance, the optimum sample geometry is a cylinder of 11 mm diameter and 2 mm width. However, with a certain loss in sensitivity, flat samples as well as odd shaped samples can be analyzed as well, if they do not exceed the maximum size defined by the vacuum interlock. Sample powders are normally mounted on sticky tape or pressed into a metal grid 17). Excellent results were also obtained by pressing pellets 31) or by subliming the sample directly unto the sample holder. 

Selection of the optimum sample of conjugated protein A and colloid silver... 

How to choose the best tissue preparation technique for every application is a difficult question to address. Sample throughput, analyte recovery, analyte thermal stability, amount of available sample, sample preparation techniques available, precision, accuracy, manual labor involved, and operator safety are only a few of the parameters that must be considered when selecting the optimum sample preparation technique. 

Because it is obvious that optimum sampling must always be a compromise between statistical requirements, economic aspects, and empirical knowledge, only the constructive cooperation of the environmental specialist, the analytical chemist, and the chemo-metrician can substantially improve the results of sampling and analytical programs. 

Which is the required optimum sampling frequency of the different fractions for the representative assessment of the impact of the emissions ... 

Sample Size. - The larger the sample, the more nuclei there are to detect, and hence the stronger the signal. The homogeneity of the magnetic field will, however, deteriorate over the whole sample volume, and resolution will be adversely affected. A further complication with solid samples is that the process of rapid spinning imposes very severe mechanical forces on the sample holder, and destruction thereof can become a problem. An optimum sample size is of the order of a few hundred milligrams. 

Significant Mass Spectrometry operational parameters were as follows ionization voltage, 70 eV ionization current, 200ifA source temperature, 200°C electron multiplier voltage, 1.9 kV integration time, 1 ms/a.m.u.. For optimum sample transfer, a transfer temperature of 200°C was employed. 

For financial, time demand, and logistical reasons, a smaller sample size is preferable to a sponsor than a larger one. There are also ethical factors that need to be borne in mind. It is unethical to choose a sample that can reasonably be considered either too small or too large (see Section 9.2). The optimum sample size can be considered to be the smallest sample size that can reasonably be expected to answer the primary research question, i.e., evaluating the primary objective as stated in the study protocol. 

Thus, the optimum sample arrangement for Raman spectroscopy of crystal pow ders with a low absorption coefficient is a forward-scattering (0°) arrangement of coarse crystallites with an optimum thickness in a multiple scattering arrangement. These are the conditions for the investigation of colorless samples in the visible range of the spectrum. 

One of the most important decisions that is left to the analyst when operating a liquid chromatograph is the choice of detector sensitivity. In some instruments the output from the sensor is monitored continuously over its entire dynamic range and so sensitivity is not an optional experimental parameter. Nevertheless, in this case, the sample size determines the concentration range over which the eluted solutes are monitored and thus an optimum sample size must be chosen. The detector should never be operated at its maximum sensitivity unless such conditions are enjoined by limited sample size or column geometry. Provided that there is adequate sample available, and the sample concentration when eluted is within the linear dynamic range of the detector, the maximum sample size that the column can tolerate should be used. This ensures that the detector noise is always minimal... 

EXAMPLE 27-4 A shipment of oil consists of equal numbers of 1-1 and 5-1 containers. A previous study has led to the expectation that the sulfur content of the 1-1 containers is 10 ppm with a standard deviation of 2 ppm, and that of the 5-1 containers is 15 ppm with a standard deviation of 3 ppm. If the analytical error is negligible, what is the optimum sampling scheme for a total of 24 samples to give an unbiased estimate of the sulfur content of the shipment, with minimum sampling error ... 

The significant result is that the optimum allocation of sampling after the first stage is independent of the desired overall variance In other words, for different values of the modification of the optimum sampling scheme consists of changing the number of strata n sampled while maintaining constant the treatment of the various sections. 

EXAMPLE 27-5 If the standard deviation of sampling strata is 0.07, that of sampling within strata is 0.10, and that of a single determination is 0.21, and if the relative costs are in the ratio 4/2/1, calculate the optimum sampling scheme and minimum cost that will give an overall standard deviation of the mean of 0.08. 

In order to determine the optimum sample preparation conditions, we initially tried several sample preparation methods in the absence of contaminants. The following peptide and protein mixture was prepared (peptides and protein were purchased from Sigma Chemicals, St. Louis, MO) 1 pmol/jul Parathyroid Hormone Fragment 39-68 (PHF), MW = 3285.7, 10 pmol/ul Pigeon Heart Cytochrome C (PHC), MW = 12,173, and 10 pmol/ul Bovine Serum Albumin (BSA), MW = 66,256. A saturated solution of Sinapinic acid in 1 1 ethanol water was used as matrix. 

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