Metals, determination applications

Fortunately, inelastic X-ray scattering can provide a means of determining semi-empirically g(q) from (q, to) measurements of simple metals. The application of g(q) to x° according to Equation (6) tends to shift x° on the energy loss scale to lower energy losses. 

Taste characteristics in general determine applicability of intense sweeteners. A time-intensity profile of sweetness perception similar to sucrose is desirable, and a delay in sweetness onset or a lingering sweetness are generally perceived as less pleasant. Side-tastes like bitter, liquorice or metallic taste are disadvantages which limit the applicability of some sweeteners. 

The potential applications of NIR OFCD determination of metal ions are numerous. The detection of metal contaminants can be accomplished in real-time by using a portable fiber optical metal sensor (OFMD). Metal probe applications developed in the laboratory can be directly transferred to portable environmental applications with minimal effort. The response time of the NIR probe is comparable to its visible counterparts and is much faster than the traditional methods of metal analysis such as atomic absorption spectroscopy, polarography, and ion chromatography. With the use of OFMD results can be monitored on-site resulting in a significant reduction in labor cost and analysis time. 

Other applications of supported liquid membranes have been related to metal speciation. For example, recently a system for chromium speciation has been developed based on the selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two SLM units connected in series. Aliquat 336 and DEHPA were used respectively as carriers for the two species and graphite furnace atomic absorption spectrometry used for final metal determination. With this process, it was possible to determine chromium in its different oxidation states [103]. 

We see that the factor (G5E)N (t2 vq vm E)n represents the probability of tunneling of N electrons or holes from the grain to the metal with 5E being the typical energy of one electron (hole) excitation in the metal. Determination of the factor (3 in (95) requires an application of the instanton method which is capable of careful description of quantum tunneling process between... 

It is seen that the amperometric technique is more used for heavy-metal determination in comparison to potentiometric techniques. The research published during the last 5 years concerning heavy-metal determination has shown the applications especially for water samples (Table 14.1). 

S. Munro, L. Ebdon, Application of inductively coupled mass spectrometry (ICP-MS) for trace metal determination in foods, J. Anal. Atom. Spectrom., 1 (1986), 211-221. 

Atomic absorption spectrometry has been applied to the analysis of over sixty elements. The technique combines speed, simplicity and versatility and has been applied to a very wide range of non-ferrous metal analyses. This review presents a cross section of applications. For the majority of applications flame atomisation is employed but where sensitivity is inadequate using direct aspiration of the sample solution a number of methods using a preconcentration stage have been described. Non-flame atomisation methods have been extensively applied to the analysis of ultra-trace levels of impurities in non-ferrous metals. The application of electrothermal atomisation, particularly to nickel-based alloys has enabled the determination of sub-part per million levels of impurities to be carried out in a fraction of the time required for the chemical separation and flame atomisation techniques. 

The number of applications of atomic techniques based on solid or slurry sampling is so large that only a comparatively minute fraction is discussed in this section. Interested readers are referred to the biannual reviews of Analytical Chemistry and the atomic spectroscopy update in the Journal of Analytical Atomic Spectrometry, among other sources, for more extensive information. A specific review of the uses of graphite atomizers modified with high-melting carbides has been published by Volynsky that includes virtually all metals determined in this manner [74]. 

Several efforts have been carried out to develop a new aqueous derivatization reagent. Phenylation with sodium tetraphenylborate is a promising procedure for the speciation of several metals. Its application for organomercury analysis has been comprehensively studied [10]. Sodium tetrapropylborate is another reagent that has been investigated for determining organolead, tin, and mercury compounds [1]. However, its application is limited because it is not commercially available. 

Only recently have devices been introduced which are capable of precise measurements of some trace elements their application is limited because the sensitivity of sensors is not adequate to determine trace metals at concentrations present in oceanic areas. A submersible probe for trace metal determination in the water column has been described by Tercier et al. (43) and used to determine Cd, Cu, Pb... 

For chemical monitoring, a list of priority substances has been established that includes metals such as cadmium, lead, and nickel. As far as metals are concerned, voltammetric techniques and more precisely electrochemical stripping analysis has long been recognized as a powerful technique in environmental samples. In particular, anodic stripping voltammetry (ASV) coupled with screen-printed electrodes (SPEs) is a great simplification in the design and operation of on site heavy metal determination in water, for reasons of cost, simplicity, speed, sensitivity, portability and simultaneous multi-analyte capabilities. The wide applications in the field for heavy metal detection were extensively reviewed (Honeychurch and Hart, 2003 Palchetti et al., 2005). 

Of course, the procedure introduced here for analyzing heavy and transition metals is applicable not only to the investigation of strong bases such as sodium hydroxide or potassium hydroxide, but to all those matrices in which traces of heavy metals are to be determined in the presence of high alkali metal excess. These matrices include alkali salts, saline waters, and sea water [109], and also salt-rich tissue samples and urine. 

There are many methods for metal determination (Standard Methods, 1998 section 3000). Some, for example as gravimetric, titrimetric or colorimetric methods, are most effective at high metal concentrations. Others, for example atomic absorption (AA), inductively coupled plasma (ICP) or inductively coupled plasma mass spectrometry (ICPMS) are far more sensitive. The latter are used for typical textile applications, such as compliance testing for water quality or detection of trace impurities in high-volume raw materials. 

For flow analysis incorporating electrolytic dissolution, very small characteristic masses, often below the ng level, are reported for metal determinations. This is a consequence of the analytical sensitivity and the small sample volume required, and is an attractive feature of in-line electrolytic dissolution. As a very small dissolved mass is required, rapid electrolysis (a few seconds) under a moderate current (mA) is sufficient. This was demonstrated in the flow-based spectrophotometric determination of aluminium in steels [29]. The analyte was oxidised and dissolved in a flowing acidic electrolytic solution that also acted as the sample carrier stream of the flow analyser. This innovation was further applied to the spectrophotometric determination of molybdenum in alloys [30]. In both applications, the anode was the polished metallic sample, and the cathode was a gold or silver coated electrode placed at the bottom of the electrolytic chamber (Fig. 8.4). A silicone rubber sheet (adapter) was placed between the solid sample and the chamber walls in order to avoid leakage and to define the sample surface area to be dissolved. This classical geometry is the most commonly used. 

S. Barabas, S.G. Lea, Application of anodic dissolution technique to automated analysis of metals. Determination of phosphorus in copper, Anal. Chem. 37 (1965) 1132. 

Some metals determined by electrogravimetric methods and their deposition potentials are given in Table 11.3.1. Detailed discussions of the methods and applications of electrogravimetric methods are available (1, 3, 19, 20). Electrogravimetry can also be carried out with the quartz crystal microbalance as described in Section 17.5. 

In the 1980s, research has been performed on laser-induced AFS (LI-AFS) after electrothermal atomization of metals. No application of this technique for the determination of mercury seems to have appeared, but for several other metals, detection limits 1-2 orders of magnitude lower than for GF-AAS have been reported (Dougherty et al., 1989 Ome-netto, 1989, general review). However, the application of this technique on mercury in biological samples may cause problems, due to the volatility of mercury compounds (see Graphite furnace ). 

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