Laboratory sampling

Time, Cost, and Equipment Automated chemical kinetic methods of analysis provide a rapid means for analyzing samples, with throughputs ranging from several hundred to several thousand determinations per hour. The initial start-up costs, however, may be fairly high because an automated analysis requires a dedicated instrument designed to meet the specific needs of the analysis. When handled manually, chemical kinetic methods can be accomplished using equipment and instrumentation routinely available in most laboratories. Sample throughput, however, is much lower than with automated methods. 

There are several methods to determine and compare the resistance to partial discharges. Some tests are done on finished cables, such as the U-bend test, and others are done on laboratory samples molded from the insulation, that are subjected to partial discharges created by sharp objects, such as needles under high voltages. The tests compare either the energy required or the length of time required to erode or fail (short circuit) samples of similar thickness. 

Of laboratory samples prepared identicaUy from different raw materials. 

Samples may separate into two or more phases as they cool in the sample line precipitate, coagulate, and freeze. Laboratory sampling may result in nonrepresentative compositions. Heat tracing may be required and may not be installed on the nonroutine sample locations. 

Analysis of environmental and laboratory samples for eyanobaeterial toxins falls into a number of eategories sereening for the presenee of the toxins, identiheation of toxins present and qiiantiheation of toxieity and/or toxins. Sereening should provide an indieation of the presenee, in all eases, of the toxin sought it should... 

This sort of nucleation - where the only atoms involved are those of the material itself - is called homogeneous nueleation. It cannot be the way materials usually solidify because (usually) an undercooling of 1°C or less is all that is needed. Flomogeneous nucleation has been observed in ultraclean laboratory samples. But it is the exception, not the rule. 

Bad laboratory analyses are not always the fault of the laboratory.. Sampling plays a big role. One plant superintendent investigated every instance of suspect analyses in his plant using elaborate around-the-clock methods over a considerable period. His results revealed that over one half of the bad analyses were not the fault of the laboratory. We are all human and bad analyses will result from time to time. Rather than resubmit samples, it may be well to spend a few minutes using the following methods as referees to evaluate the reasonableness of the results. 

In some laboratories samples are heated for prolonged periods in a press at a suitably elevated temperature. Such results may frequently fail to correlate with oven-heated samples since oxygen is largely excluded from the samples. 

TNT and HMX were from highly purified laboratory samples and the nitrogen contents listed are calcd values for the pure compds. Precision and accuracy as indicated by the FNAA data for these compds are excellent and most likely represent the optimum that can be achieved by this technique... 

After the seed crystals had arrived it was found that crystallization practically always occurred when amounts of 100 g of any laboratory sample were slowly warmed over a period of a day, after cooling to liquid-air temperatures. This occurred even when great precautions were taken to exclude the presence of seeds. However, it was found readily possible, by temperature manipulation alone, to produce crystalline or supercooled glycerol at will. 

Sample shelves also become overcrowded quickly, but it is often required to keep samples for extended periods of time. Older samples can be stacked into cardboard cartons, clearly identified by laboratory project references or quality control numbers, and stored at a convenient location away from the laboratory. Periodically they should be inspected and the out of date ones eliminated. One word of caution, however. Under current pollution control rules, laboratory samples may not be indiscriminatly disposed of as garbage. The laboratory operator should call in a waste disposal service when in doubt. 

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])...

Once the target number of samples was defined, the frequency of collection and the number of samples to be collected on each collection date were determined, based on an overall total sampling period of 1 year. The sampling plan specified collection every other week, primarily to accommodate the workload at the analytical laboratories. Sampling had to occur early in the week to preclude problems with shipping samples over the weekend. With these considerations in place, specific dates for collection of commodity samples could readily be set. 

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. 

Exclusions for laboratory samples and waste treatability studies... 

Quality control laboratories are a necessary part of any plant, and must be included in all cost estimates. Adequate space must be provided in them for performing all tests, and for cleaning and storing laboratory sampling and testing containers. 

Sampling is a crucial step of the analytical process, particularly in cases where there are large differences between the material under investigation and the test sample (laboratory sample) with regard to both amounts and properties, especially grain size, fluctuations of quality and inhomogeneities. 

Near-infrared spectroscopy is quickly becoming a preferred technique for the quantitative identification of an active component within a formulated tablet. In addition, the same spectroscopic measurement can be used to determine water content since the combination band of water displays a fairly large absorption band in the near-IR. In one such study [41] the concentration of ceftazidime pentahydrate and water content in physical mixtures has been determined. Due to the ease of sample preparation, near-IR spectra were collected on 20 samples, and subsequent calibration curves were constructed for active ingredient and water content. An interesting aspect of this study was the determination that the calibration samples must be representative of the production process. When calibration curves were constructed from laboratory samples only, significant prediction errors were noted. When, however, calibration curves were constructed from laboratory and production samples, realistic prediction values were determined ( 5%). 

Laboratories sampling/ Hydrowires Samplers analytical precisions... 

This chapter gives an introduction to sampling. Devising a sampling plan or procedure may apply to your current position but it is more likely that the only sampling you are involved with is taking a test sample from the laboratory sample which has been submitted for analysis. However, you should be aware of the complete sampling process because this allows you to discuss sensibly the previous history of the material which comes into the laboratory. This will help to ensure that you measure the correct parameter. 

The sampling plan should specify the number and size of primary samples which need to be obtained from the lot/batch. It should also describe how the laboratory sample is to be obtained. These issues may well be outside of the analyst s control, but it is important to consider how the validity of any analysis will be affected. 

In addition to the sampling that goes on external to the laboratory, the analyst must also address issues such as the size and number of test portions which will be taken from the laboratory sample for analysis. 

The total variance in the final result (,v2ita ) is made up of two contributions. One is from variation in the composition of the laboratory samples due to the nature of the bulk material and the sampling procedures used ( ample). The other (Tanalysis) is from the analysis of the sample carried out in the laboratory ... 

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. 

A subsample is a portion of a sample, prepared in such a way (hat there is some confidence that it has the same concentration of analyte as that in the original sample. The laboratory sample may be a subsample of a bulk sample and a test sample may be a subsample of the laboratory sample. Because of inhomogeneity, differences may occur between samples but there should not be any significant inhomogeneity between subsamples. 

If the laboratory sample has been prepared in a particular way to pass a specific mesh size, the coefficient of variation of the result for one component varies inversely with m, where m is the mass of the test portion. A sampling constant (Ks) can be defined by the following ... 

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