Atoms detectors

Exclusion of gas-diffusion systems integrated with atomic detectors [12-15] for the above-mentioned reasons leaves very few sensors that rely on integrated diffusion and detection as gaseous analytes lending themselves... 

Nowadays, the outstanding advantages of using flow manifolds as sample preparation systems for atomic detectors have been demonstrated for a variety of techniques. Characteristic examples of the instrumentation required and typical applications are presented in a comprehensive monograph dedicated to FI and atomic spectrometric detectors [21]. 

Conversion into hydrides was required in several procedures to increase detectability of most trace metalloids because of their low expected levels in beer samples. Even though HG techniques combined with atomic detectors have been widely used for the determination of elements in food, relatively few publications are devoted to the analysis of beer samples. 

The digestion conditions to be used may aiter some species, inciuding the target analytes. Any such aiterations which may resuit in anaiyte iosses shouid be avoided. Some alterations have no effect on the finai resuit thus, atomic detectors provide the total concentrations of the target eiements irrespective of their chemical form. 

Ultrasound assisted aerosol formation or nebulization prior to sample insertion into an atomic detector is dealt with in Chapter 8 on the grounds of its close relationship to the instrument in spatial and temporal terms. Also, as a step of spray drying, known as "atomization ", is discussed in Chapter 2 inasmuch it can be used for sample conservation purposes and hence as an analytical operation preceding sample preparation. This section is concerned with other non-analytical uses of US-assisted aerosol formation that are closely related to the analytical field and can open new avenues for the development of previously unexplored analytical uses. 

The analytical performance of atomic detectors in terms of sensitivity, selectivity and resolution has been markedly improved by the use of USNs. However, the utility of these nebulization systems is not exclusive of atomic detectors as, in fact, USNs have been successfully implemented in electrospray formation devices, which are employed as inter-faoes between separation techniques such as CE or HPLC and mass detection [8]. 

Most on-line microwave-assisted digestions of these types of samples have been done by introducing them as acid slurries and coupling the manifold to a suitable atomic detector [24,49,51,52,54]. 

Both molecular and atomic detectors have been used in combination with SF extractors for monitoring purposes. 

Both molecular and atomic detectors have been used in combination with SCF extractors for monitoring purposes. Thus, the techniques used in combination with SFE are infrared spectroscopy, spectrophotometry, fluorescence spectrometry, thermal lens spectrometry, atomic absorption and atomic emission spectroscopies, mass spectrometry, nuclear magnetic resonance spectroscopy, voltammetry, and piezoelectric measurements. 

Thus, the picture of measurement in the atom-detector system of two identical atoms is compatible with Mandel s operational approach to the photon localization. For example, the multipole photon statistics in finite volume can be examined in the same way as in Refs. 14 and 20. The commutators for different t can also be constructed in analogy to Ref. 20. 

An FIA system consists of four basic parts a pump or pumps for regulation of flow, an injection valve to insert sample volumes accurately and reproducibly into the carrier stream, a manifold, and a flow-through detector. A manifold is the term used for the tubing, fittings, mixing coils, and other apparatus used to carry out the desired reactions. The flow-through detector in AAS is the atomizer/detector combination in the spectrometer. 

Atomic detectors monitor the presence of specific atoms that are contained in the components of each eluting peak. This can be extremely useful when the analytes contain less common elements such as the halogens or metals. Simultaneous monitoring of several elements, even of the very common elements carbon, hydrogen, sulfur, oxygen, and sulfur, can also help identify the component molecules. 

Notwithstanding the fact that a continuous or online coupling is desirable for speciation purposes, there are examples of the usefulness of both discontinuous nonchromatographic (e.g., ultrafiltration) and continuous separation techniques (e.g., chromatography), which have been coupled offline with atomic detectors to solve important problems requiring speciated information. 

Nonchromatographic and chromatographic separation methods coupled online with the atomic detector used exhibit great advantages compared with offline systems, including less sample manipulation,... 

Figure 3 Possibilities of hyphenation of different separation techniques to different types of atomic detectors for speciation analysis. FAAS = Flame atomic absorption spectrometry QC = quartz tube concentrator.

Nonchromatographic separation coupled to atomic detectors Flow injection analysis (FIA) strategies may provide an efficient, continuous, and automatic method for preconcentration and/or separation of the sought species from a complex matrix, prior to its final determination. Furthermore, FIA systems can be interfaced easily with atomic detectors making them very convenient in speciation analysis. A typical application is selective preconcentration on... 

In this vein, many appHcations have appeared in the literature on speciation of oxidation states, such as Cr(m)/Cr(VI), Fe(n)/Fe(m), As(III)/As(V), Se(IV)/ Se(VI). Also, FIA techniques have been used to preconcentrate Sn, Hg, and Pb organometallics mainly from natural waters, sediment, and soil extracts. In particular great interest has been focused into the speciation of chromium oxidation states in water samples at very low level (nanograms per liter). A FI system with a minicolumn of acidic preconcentration and inductively coupled plasma optical emission spectrometry (ICP-OES) for final detection was developed for a rapid speciation of Cr(VI) and Cr(III) in waters. On sample injection, Cr(VI) is retained in the alumina column whilst Cr(III) is not passing directly to the atomic detector. Afterwards, the retained Cr(VI) is eluted by injection of ammonium hydroxide, as shown in Figure 5, and its analytical signal of emission in the ICP-OES is registered. 

Chromatographic separation coupled to atomic detectors Chromatographic separation techniques, both gas chromatography (GC) and LC, have been... 

In recent years, many analytical strategies for elemental speciation analysis, particularly in (bio)medi-cal speciation, make use of LC-atomic detector hybrid techniques. Most frequently studied elements include As, Pb, Cd, Sn, Hg, Se, Cr, and A1 both in biological and environmental samples. The capability for multielemental detection of ICP-MS can be most useful in such analysis. An illustrative example of multielement trace-element speciation is metal-lothionein proteins (MT) from rabbit liver by LC-ICP-MS. Comparative profiles for Cd, Zn, Cu, and S obtained for MTs from rabbit liver, using a fast protein liquid chromatography (FPLC) column coupled to ICP-MS are shown in Figure 7, using molecular and specific detectors. 

Three essential components of an FI system are shown in Figure 1, which also shows different possible modifications, simple or complex, that could be made depending on the problem to be solved. The fourth essential unit - the detector - is not part of FI manifolds, as it can be coupled to any type of molecular detector - provided the appropriate flow cell is available - or atomic detector. 

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