Secondary Sampling

Other designations for samples are bulk sample, primary sample, secondary sample, subsample, laboratory sample, and test sample. These terms are used when a sample of a bulk system is divided, possibly a number of times, before actually used in an analysis. For example, a water sample from a well... 

Differentiate between bulk sample, primary sample, secondary sample, subsample, laboratory sample, and test sample. 

Other designations for samples are bulk sample, primary sample, secondary sample, subsample, laboratory sample, and test sample. These terms are used when a sample of a bulk system is divided, possibly a number of times, before actually being used in an analysis. For example, a water sample from a well may be collected in a large bottle (bulk sample or primary sample), from which a smaller sample is acquired by pouring into a vial to be taken into the laboratory (secondary sample, subsample, or laboratory sample), then poured into a beaker (another secondary sample or subsample), before a portion is finally carefully measured into a flask (test sample) and diluted to make the sample solution. 

All Mars rovers to date have carried alpha-particle X-ray spectrometer (APXS) instruments for chemical analyses of rocks and soils (see Fig. 13.16). The source consists of radioactive curium, which decays with a short half-life to produce a-particles, which then irradiate the sample. Secondary X-rays characteristic of specific elements are then released and measured by a silicon drift detector. The Mars Pathfinder APXS also measured the backscattered a-particles, for detection of light elements, but the Mars Exploration Rovers measured only the X-rays. 

SIMS instrumentation enables us to operate SIMS in a scanning mode because it is equipped with an X-Y deflector on the primary ion beam. In scanning mode, a focused primary ion beam scans over a surface area of the sample. Secondary ions emitted in each pixel generate a two-dimensional SIMS image that reveals the distributions of ions on a surface. Formation of SIMS images is quite similar to chemical element mapping by energy-dispersive spectroscopy (EDS) and AES. 

Figure 1. Dendogram of cluster analysis results from phospholipid fatty acid profiles of rhizosphere and nonvegetated soils from the contaminated site. Comparisons of qualitative differences between the groups of microorganisms present in the different samples illustrated the primary clustering of nonvegetated soil samples with Lespedeza cuneata rhizosphere soil samples, and Solidago sp. rhizosphere soil with Firms taeda rhizosphere soil and Paspalum notatum rhizosphere soil samples. Secondary clustering occurred between Firms taeda soil samples and Faspalum notatum soil samples.

It is interesting to note that from each pulse of the ion gun 300 gallium ions strike a spot less than 100 nm in diameter on the sample. Secondary ion yields for organic materials are typically between 10 and 10 secondary ions per primary ion impact. Thus, only a few fragment ions from the polymer surface are produced per pulse. The high transmission of the TOF allows for 50% of these secondary ions to be mass-analyzed. To obtain the final mass spectrum, hundreds of thousands of individual mass spectra are integrated. With TOF-MS, usable static SIMS mass spectra from areas as small as 25 x 25 pm can be obtained from polymer surfaces. 

The FAB experiments described in the previous section use a liquid matrix to ensure a steady secondary ion signal, as is the case with the analysis of discrete samples. The FAB matrix also serves to extract sample material from the chromatogram, whether this is done in a separate extraction outside of the mass spectrometer or during bombardment of the excised sample. Secondary ion mass spectrometry (SIMS) used for the creation of spectra from nonvolatile organic and biological samples also uses the same suite of liquid matrices, and is identical in concept. There are several sputtering methods of ionization that do not require the use of a liquid matrix, and therefore do not involve a liquid extraction of the sample compound from the chromatographic spot. TLC/MS applications and techniques of this kind are reviewed in this section. 

Method Single Sample Time (h) Average Sample Time (h) Labor Time (h/sample) Secondary Waste... 

Starting or Ending Isothermal Baselines. These should be recorded only when and if specific heat capacity data are needed. The isothermal baselines should be stable (i.e., horizontal in appearance, indicating thermal equilibrium) and without evidence of chemical or physical processes. Erroneous heat losses lead to sloping baselines. But baseline slope can also be observed in the case of thermal degradation of the polymeric sample, secondary crystallization, and additional cure. 

The sample environment may influence behaviour in various ways. Degradation in air will usually be more complex than in nitrogen due to additional oxidation reactions. An inert atmosphere is preferred to simplify interpretation of the basic processes induced by heat, but behaviour may differ greatly between a static and a dynamic atmosphere, since if products are not quickly removed from the degrading sample, secondary reactions may occur. The most efficient removal is under continuous evacuation. 

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