Sampling species

Static Secondary Ion Mass Spectrometry (SIMS) involves the bombardment of a sample with an energetic (typically 1-10 keV) beam of particles, which may be either ions or neutrals. As a result of the interaction of these primary particles with the sample, species are ejected that have become ionized. These ejected species, known as secondary ions, are the analytical signal in SIMS. 

Note that the distribution coefficient depends only on pH, pKa values, and P (not on concentration of sample species). Equation (4.7) is applicable to all lipophilicity calculations. Special cases, such as eq. 4.9, have been tabulated [275],... 

Electron beams Particle-matter interactions > (a) Inelastic interactions (energy transfer with sample species) SPECTROSCOPY (b) Elastic interactions (energy transfer) DIFFRACTION, MICROSCOPY... 

The genesis of signals is directly connected with the interaction between the entities of the sample (see Fig. 2.13) and the form of matter and energy represented in Fig. 3.2. This interaction produces the signal as a result of a chemical reaction, an electrochemical, physicochemical or physical process, e.g. by a neutralization or precipitation reaction, an electrolytical process, or by interactions between radiation and particles on the one hand and the sample species on the other. 

The low mobility of lead is reflected in the vertical concentrations of lead in the soil and the distribution of lead within the plant system. Lead seems to preferentially concentrate in roots rather than aerial parts of the sampled species. This is agreement with the frequent behaviour of most species in relation to this heavy metal. 

Size exclusion chromatography (SEC) separates molecules based on size in a short analysis time. Unlike other chromatographic techniques, SEC does not retain sample species in the column, the analysis time is fixed, and everything loaded onto the column elutes within a fixed time frame. The application of SEC is limited only to the solubility of the sample in a solvent. Since tetrahydrofuran (THE) is a good solvent for coal liquids, the separation of coal liquids by SEC can be easily achieved. 

Each genus involved may include one or more samples (species or plant organs). Each sample contains one or more of the listed anthocyanins. 

Native Zone Electrophoresis. In some cases, good resolution between sample species can be obtained with little or no sample pretreatment. In these eases, the gels arc said to he native gels. In this method, the charge on the individual sample component is primarily responsible for its differential migration. 

Sample Species Petal width Petal length Sepal width Sepal length... 

We have recently investigated another type of mobile matrix - a liquid metal [100, 102]. Here, we discovered that ion bombardment of the liquid metal surface, upon which sample particles were deposited, resulted in movement of the sample species towards the primary ion beam where they were desorbed and finally detected by the mass analyzer. 

With biological samples, species which cannot be determined by in situ techniques (see Table 2.2) are usually extracted, concentrated and separated by chromatographic methods, with subsequent determination of the element in the separated fractions. 

This relation can be expanded for a two-step electrolysis involving two sample species. Because the first species continues to diffuse to the electrode even after the first transition time, the expression is more complex than a simple additive relation ... 

Another significant challenge remains in further increasing the efficiency with which sample species are utilized through increased ion throughput and duty factor. Currently many of the ions generated by continuous ionization sources are lost because of the pulsed nature of the instrument. Realization of higher duty factor and the unit transmission efficiency of which TOF-MS is capable could propel the TOF-MS into a sensitivity realm well beyond that of current mass analyzers. 

Sample/Species Flavonoids Ionization mode Reference... 

Sample Species MW k Peak Area Mole Fraction Mass Fraction... 

Flow field-flow fractionation (flow FFF) is a separation method that is applicable to macromolecules and particles [1], Sample species possessing hydrodynamic diameters from several nanometers to tens of microns can be analyzed using the same FFF channel, albeit by different separation mechanisms. For macromolecules and submicron particles, the normal-mode mechanism dominates and separation occurs according to differences in diffusion coefficients. Flow FFF s wide range of applicability has made it the most extensively used technique of the FFF family. 

The characteristic feature of flow FFF is the superimposition of a second stream of liquid perpendicular to the axis of separation. This cross-flow drives the injected sample plug toward a semipermeable membrane that acts as the accumulation wall. The cross-flow liquid permeates across the membrane and exits the channel, whereas the sample is retained inside the channel in the vicinity of the membrane surface. Sample displacement by the cross-flow is countered by diffusion away from the membrane wall. At equilibrium, the net flux is zero and sample clouds of various thicknesses are formed for different sample species. As with other FFF techniques, a larger diffusion coefficient D leads to a thicker equilibrium sample cloud that, on average, occupies a faster streamline of the parabolic flow profile and subsequently elutes at a shorter retention time t,. For well-retained samples analyzed by flow FFF, t, can be related to D and the hydrodynamic diameter d by... 

A summary of the mean, minimum, and maximum tissue concentrations of mercury detected for two of the sampled species with the widest geographical distribution the largemouth bass and the channel catfish are given in Tables 5-8 and 5-9. As Table 5-8 shows, the maximum mercury residues reported for the largemouth bass exceeded the FDA action level (1 ppm) in 15 of the 25 states that collected and analyzed tissue samples for this species. The highest maximum mercury concentration reported for this species was 4.36 ppm, reported by Florida. Table 5-9 shows the maximum mercury residue reported for another widely distributed species, the channel catfish. While the maximum mercury residues reported for this species are not consistently as high as those for the largemouth bass, maximum residues in... 

Electrochemical detection depends on a catalytic oxidation or reduction at the surface of an electrode located in the column effluent stream. This reaction produces a net charge transfer at the electrode surface. The resulting current is measured and provides a basis for quantirication of sample species. 

Sometimes called secondary electrochemical detection, this technique is useful when the sample species of interest is not electroactive. A reagent is mixed with the column effluent to transform the sample, M, into an clcclroactive species. An example is shown by Eq. 4.11 ... 

ICP-AES is often used to determine the concentrations of various elements in a sample. However, an element may be present in a variety of chemical forms or species. By coupling an ICP-AES detector to an ion-chromatographic column, a more complete description of the sample species can be obtained. Such a coupling generally requires a nebulizer to introduce the column effluent into the ICP. Conventional pneumatic nebulizers operate at about 1 mL/min sample flow and may introduce as little as 1 % of the sample into the plasma. A newer direct-injection nebulizer (DIN) operates at sample flow rates only 5 to 10 % that of a conventional nebulizer [2. >). 

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