Atomic emission spectroscopy accuracy

Chapters 7 and 8 describe two major techniques for the monitoring of trace elements in environmental samples atomic absorption (AA) and inductively coupled plasma-atomic emission spectroscopy (ICP). AA is most ideally suited for analyses where a limited number of trace metal concentrations are needed with high accuracy and precision. ICP has the advantage of multielement analysis with high speed. 

Inductively coupled plasma, ICP, atomic emission spectroscopy has made the determination of wear metals very easy and used oils can be scanned for the presence of at least 20 elements in less than 1 min. Wear trends can be obtained by comparing wear metals from a series of samples. However, it should be noted that the accuracy of the determination can be limited by the particle sizes present. 

Since the mid-1960s, a variety of analytical chemistry techniques have been used to characterize obsidian sources and artifacts for provenance research (4, 32-36). The most common of these methods include optical emission spectroscopy (OES), atomic absorption spectroscopy (AAS), particle-induced X-ray emission spectroscopy (PIXE), inductively coupled plasma-mass spectrometry (ICP-MS), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray fluorescence spectroscopy (XRF), and neutron activation analysis (NAA). When selecting a method of analysis for obsidian, one must consider accuracy, precision, cost, promptness of results, existence of comparative data, and availability. Most of the above-mentioned techniques are capable of determining a number of elements, but some of the methods are more labor-intensive, more destructive, and less precise than others. The two methods with the longest and most successful histoty of success for obsidian provenance research are XRF and NAA. 

The method of standard additions is widely used in atomic spectroscopy (e.g. determination of Ca2+ ions in serum by atomic emission spectrophotometry) and, since several aliquots of sample are analysed to produce the calibration graph, should increase the accuracy and precision of the assay... 

Argon plasma offers a number of advantages as a source for emission spectroscopy. Argon is an inert gas and will not react with the sample so chemical interference is greatly reduced. At plasma temperatures, atomization is complete and elemental spectra do not reflect molecular components. Detection limits are high for most elements. Accuracy and precision are excellent. In addition, ICP/OES requires less sample preparation and less sample amount than other techniques. 

These relatively high concentrations measured by FDMS can also be detected by other methods with adequate accuracy, although the FD method has the advantage that tissues need no pretreatment. Parallel measurements of the same preparations by atomic absorption and emission spectroscopy have revealed no significant deviations from the authors results. 

The uncertainties Ay/yhave been calculated taking into account the errors on Io/Iat and L (thickness of the recombination boundary layer) but also on the flow parameters the diffusion coefficient Do,air determined using the Chapman-Enskog theory, the mean square atomic velocity V determined using the gas kinetic theory (rarefied gas). The accuracy on these two last values is due essentially to that of the gas temperature, measured by emission spectroscopy (N2 rotational temperature), this leads to a total accuracy of 35%. 

The sensitivity, accuracy, and precision of solid sample analysis were greatly improved by coupling of LA with ICP-OES/MS. The ablated species are transported with a carrier gas (usually argon) into the plasma torch. Additional atomization. excitation and ionization of the ablated species in a stationary hot plasma provide a dramatic increase in the sensitivity of emission detection (LA-ICP-OES) or detection of ions (LA-ICP-MS). The efficiency of the transport of ablated species into an ICP strongly depends on the size of the particles. The optimal conditions for ablation in the ca.se of LA-ICP differ significantly from the optimal conditions for LIBS because the efficient transport of the ablated matter to an ICP requires a fine aerosol (with solid particle diameters less than a few micrometers), whereas direct optical emission spectroscopy of the laser plume needs excited atoms and ions. 

Evaluation of accuracy requires comparing results against standard materials or the results obtained using other independent techniques. Figure 11.9 illustrates the correlation for iron in orchard leaves determined by atomic-absorption, DC-arc, and x-ray-fluorescence spectroscopy, and ICP-emission spectrometry. The standard deviations are also indicated. 

Mossbauer spectroscopy is based on the observation that nuclei held rigidly in a lattice can undergo recoil-free emission and absorption of X-radiation the separation of nuclear energy levels can be measured with great accuracy, and it is possible to detect weak interactions between a nucleus and its electronic environment. This may reveal the chemical state of the atom or ion, but only a few nuclei are susceptible to the effect, most work having been done with iron ( Fe) and tin Sn) and a little with ruthenium... 

Analytical schemes concerned with the determination of blood ions and gases can be divided into two categories analyses done in vivo and those done in vitro. By far the most common method of determining blood ions in vitro involves atomic spectroscopy. Atomic absorption and flame emission have both been used although the latter is the most popular. In the clinical lab nearly all of the remaining determinations (both in vivo and in vitro) are performed with ion-selective (for ions, NH3 and CO2) or amperometric electrodes (O2 and H2). Two important characteristics of ion-selective electrodes, sensitivity and selectivity, should be mentioned. The applicability of a specific electrode in any particular situation can be determined by considering, on one hand, the ionic constituents of the solution to be measured and, on the other hand, the sensitivity and specificity of the electrode in question. Proper consideration of these points will allow an investigator to determine the accuracy and validity of the measurement. 

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