Laboratory sample calculations

Fig. 3.23 Left-. Calculated relationship between the thickness of an alteration rind and/or dust coating on a rock and the amount of 15.0-keV radiation absorbed in the rind/coating for densities of 0.4, 2.4, and 4.0 g cm [57]. The bulk chemical composition of basaltic rock was used in the calculations, and the 15.0 keV energy is approximately the energy of the 14.4 keV y-ray used in the Mossbauer experiment. The stippled area between densities of 2.4 and 4.0 g cm is the region for dry bulk densities of terrestrial andesitic and basaltic rocks [58]. The stippled area between densities of 0.1 and 0.4 g cm approximates the range of densities possible for Martian dust. The density of 0.1 g cm is the density of basaltic dust deposited by air fall in laboratory experiments [59]. Right Measured spectra obtained on layered laboratory samples and the corresponding simulated spectra, from top to bottom 14.4 keV measured (m) 14.4 keV simulated (s) 6.4 keV measured (m) and 6.4 keV simulated (s). All measurements were performed at room temperature. Zero velocity is referenced with respect to metallic iron foil. Simulation was performed using a Monte Carlo-based program (see [56])...

In the laboratory, soil samples collected in the held are mixed thoroughly and reduced in size to laboratory samples. The air-dried soils are passed through a 2-mm sieve in order to remove stones and roots, then the water content of the soil is calculated after drying at 105 °C for 5h. If the analytical samples cannot be analyzed immediately after drying and sieving, they should be stored at about —20 °C in glass or Teflon bottles fltted with screw-caps. 

The analytical variance can be determined by carrying out replicate analysis of samples that are known to be homogeneous. You can then determine the total variance. To do this, take a minimum of seven laboratory samples and analyse each of them (note that Sample characterizes the uncertainty associated with producing the laboratory sample, whereas sanalysis w h take into account any sample treatment required in the laboratory to obtain the test sample). Calculate the variance of the results obtained. This represents stQtal as it includes the variation in results due to the analytical process, plus any additional variation due to the sampling procedures used to produce the laboratory samples and the distribution of the analyte in the bulk material. 

Personnel working in some programs at the Los Alamos National Laboratory (LANL) may handle radioactive materials that, under certain circumstances, could be taken into the body. Employees are monitored for such intakes through a series of routine and special bioassay measurements. One such measurement involves a thermal ionization mass spectrometer. In this technique, the metals in a sample are electroplated onto a rhenium filament. This filament is inserted into the ion source of the mass spectrometer and a current is passed through it. The ions of the plutonium isotopes are thus formed and then accelerated through the magnetic held. The number of ions of each isotope are counted and the amount of Pu-239 in the original sample calculated by comparison to a standard. 

The results of interlaboratory study II are presented in Fig. 4.5.1. Five sets of results were obtained for the LAS exercise, and four sets for the NPEO exercise. For LAS, the within-laboratory variability ranged between 2 and 8% (RSD) for sample III (distilled water spiked with lmgL-1 LAS), 1 and 13% for sample 112 (wastewater influent), and 3 and 8% for sample 113 (sample 112 spiked with lmgL-1 LAS). Between-laboratory variations (calculated from the mean of laboratory means, MOLM) amounted to RSDs of 15, 30 and 30% for samples III, 112 and 113, respectively. The LAS values reported were in the range of 700—1100 p,g L-1 in sample III, 1100-1800 p,g L-1 in sample 112 and 1900-3000 p,g L-1 in sample 113, indicating that even in the matrix wastewater influent, the spiked concentration of lmgL-1 LAS could be almost quantitatively determined by all laboratories. 

Computers were first used in laboratories to calculate results and generate reports, often from an individual instrument. As automated analysers were developed, so the level of computerization increased and computers now play a major role in the modem laboratory. They are associated with both the analytical and organizational aspects and the term Laboratory Information Management System (LIMS) is often used to describe this overall function. Such systems are available that link the various operations associated with the production of a validated test result, from the receipt of the sample to the electronic transmission of the report to the initiator of the request, who may be at a site removed from the laboratory. Other uses include stock control, human resource management and budgets. 

The MSA enables laboratories to calculate the analyte concentration in an interference-ridden sample. In the MSA technique, equal volumes of a digested... 

Laboratories subsample two aliquots of a field sample from the same container and treat them as two separate samples. Typically, laboratory duplicates are prepared and analyzed with every 10 samples in trace element and inorganic analyses. This allows laboratories to calculate the RPD between the two results as a measure of analytical precision. Laboratory duplicates are rarely used in organic compound analysis. 

One of the laboratory procedures that you are expected to know involves the determination of molar mass from gas density. In the sample calculation that follows, you will solve for the density of a gas, but understand that a simple rearrangement of the equation allows you to solve for the molar mass. 

A sample calculation should also be presented as an appendix to an undergraduate laboratory report. This appendix should show how one obtains tlie final results starting from the raw data. In general, the numbers used in the computations should have more significant fignres than are justified by the precision of the final result, in order to avoid mathematical errors due to roundoff. Units should be included with each step of the calculation. Also specify the source of raw data used (e.g., mn 5 on page 14 of notebook). 

To measure the amount of each, the intensity of the color can be measured with a spectrophotometer. The intensity of the color is directly proportional to the amount of the product, and thus to the amount of enzyme in the original sample. This allows the laboratory to calculate the concentration of each isoenzyme in the sample. 

Suppose the laboratory performs measurements of n blank samples, where the blanks simulate real analyte-free samples as nearly as possible and the results. . .,B are expressed as yield-corrected activity. Then the laboratory may calculate the arithmetic mean B and the experimental standard deviation s(Bi) of the values (see Eq. 10.5), and it may blank-correct the absolute activity found in a subsequent measurement of a real sample by subtracting the mean B from it. In this case the critical value Lq for the net absolute activity is calculated as shown... 

A sample of pure polonium-210 is used in a laboratory experiment. Calculate the time it takes for (a) 99%, (b) 99.9% of the mass of the polonium to decay. 

Once the concrete maturity curve has been developed, using the elapsed time-temperature calculated from the heat transfer analysis of the laboratory sample, the compressive strength of the concrete at any time can be estimated. 

X-ray fluorescence spectrometry has been established as the prime analytical technique for cement works control since the early 1970s. During the 20 years that have followed. X-ray spectrometers have been incorporated into complete control systems, which include sample transport from the sampling points to the works laboratory, sample preparation and transport into the spectrometer, analysis, calculation of control moduli, and generation and feedback of control signals to the plant to modify the process when necessary. 

Once this data is generated, it can be used in typical acceleration factor models relating accelerated stress tests to field data. For example, if it is determined that it takes x hours or cycles for an assembled package to fail in a laboratory test, the acceleration factor model can be used to extrapolate expected life of the device in typical field operating conditions. Details on acceleration factor models and sample calculations are provided in the next chapter. 

Therefore in this example (to meet area electrical classification requirements), if the lowest autoignition temperature (i.e., 225°C) were chosen for the commodities in the composition, 200,000 would have to be expended for the light fixtures, but if it was accepted that a mixture of commodities will be constant in the process and a higher autoignition temperature (i.e., 405°C) is acceptable for the composition as demonstrated by the calculation (and possibly collaborated by a laboratory sample test), a 100,000 savings could be realized with the utilization of the higher temperature light fixtures (i.e., 375°C). 

Measuring the gross heating value (mass) is done in the laboratory using the ASTM D 240 procedure by combustion of the fuel sample under an oxygen atmosphere, in a bomb calorimeter surrounded by water. The thermal effects are calculated from the rise in temperature of the surrounding medium and the thermal characteristics of the apparatus. 

The oil and gas samples are taken from the appropriate flowlines of the same separator, whose pressure, temperature and flowrate must be carefully recorded to allow the recombination ratios to be calculated. In addition the pressure and temperature of the stock tank must be recorded to be able to later calculate the shrinkage of oil from the point at which it is sampled and the stock tank. The oil and gas samples are sent separately to the laboratory where they are recombined before PVT analysis is performed. A quality check on the sampling technique is that the bubble point of the recombined sample at the temperature of the separator from which the samples were taken should be equal to the separator pressure. 

In thermoluminescence dating, a sample of the material is heated, and the light emitted by the sample as a result of the de-excitations of the electrons or holes that are freed from the traps at luminescence centers is measured providing a measure of the trap population density. This signal is compared with one obtained from the same sample after a laboratory irradiation of known dose. The annual dose rate for the clay is calculated from determined concentrations of radioisotopes in the material and assumed or measured environmental radiation intensities. 

Scale-up Factors Factors used in thickening will vary, but, typically, a 1.2 to 1.3 multiplier applied to the unit area calculated from laboratory data is sufficient if proper testing procedures have been followed and the samples are representative. 

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