Sample introduction hydride generation

In ICP-AES and ICP-MS, sample mineralisation is the Achilles heel. Sample introduction systems for ICP-AES are numerous gas-phase introduction, pneumatic nebulisation (PN), direct-injection nebulisation (DIN), thermal spray, ultrasonic nebulisation (USN), electrothermal vaporisation (ETV) (furnace, cup, filament), hydride generation, electroerosion, laser ablation and direct sample insertion. Atomisation is an essential process in many fields where a dispersion of liquid particles in a gas is required. Pneumatic nebulisation is most commonly used in conjunction with a spray chamber that serves as a droplet separator, allowing droplets with average diameters of typically <10 xm to pass and enter the ICP. Spray chambers, which reduce solvent load and deal with coarse aerosols, should be as small as possible (micro-nebulisation [177]). Direct injection in the plasma torch is feasible [178]. Ultrasonic atomisers are designed to specifically operate from a vibrational energy source [179]. 

There are several sample introduction methods that are used in conjunction with ICP, including nebulization, electrothermal evaporation, gas chromatography, hydride generation, and laser ablation [30]. Laser ablation combined with ICP (LA-ICP) is useful for analysis of solids. In such a source the sample is positioned in a chamber prior to the ICP source, the ablation cell. Argon gas at atmosperic pressure flows through the cell towards the ICP source. The sample is irradiated by a laser beam and... 

In this manner an argon flow could be used to strip the generated hydride from solution and carry it out of the top of the cell where it was directed, via a 1mm i.d. xl.5mm o.d. quartz tube, into the sample introduction port of a... 

An automatic system using the hydride generation technique requires attention to (a) chemistry (b) automatic sample preparation and (c) introduction of the hydride into the... 

Various efficient devices have been utilized for sample introduction into an inductive plasma source, for example the application of several nebulizers, hyphenated techniques, hydride generation, laser ablation and electrothermal vaporization. The role of the solution introduction system in an inductively coupled plasma source is to convert the liquid sample into a suitable form (e.g.,... 

In analogy to sample introduction by hydride generation, mercury trace analysis is possible by reducing Hg compounds to the metal using the cold vapour technique or the determination of iodine at the ultratrace level (after oxidation with 70 % perchloric acid of iodide to iodine) via the gas phase. 

Hydride generation for analytical use was introduced at the end of the 1960s using arsine formation (Marshal Reaction) in flame atomic absorption spectrometry (FAAS). A simple experimental setup for a hydride generator is shown in Figure 5.18. Today, hydride generation,91,92 which is the most widely utilized gas phase sample introduction system in ICP-MS, has been developed into... 

Azad et al. [ 186] used a similar technique for the determination of selenium in soil extracts using a nondispersive spectrometer, with which it was possible to observe fluorescence from the 196.1, 214.3 and 204.0 lines simultaneously, thus enabling a detection limit of 10 ng/ml to be observed using discrete sample introduction via the hydride generation technique. In this method, soil... 

Compared with the ICP, other atomic spectrometric detectors are not widely coupled to HPLC. Several interfaces have been described for AAS detector. Methods include a rotating platinum spiral collection system (Ebdon et al., 1987) and a flow injection thermospray sample introduction system (Robinson and Choi, 1987). Post-column hydride generation is also popular with AAS detection as will be described later. Pedersen and Larsen (1997) used an anion-exchange column to separate selenomethionine, selenocysteine, selenite and selenate with both FAAS and ICP-MS. The detection limits for the FAAS system were lmg H1 compared with 1 fig l-1 for ICP-MS. HPLC-MIP systems have been described to an even lesser extent. These either use elaborate interfaces to overcome the problems of quenching the low-power plasma (Zhang and Carnahan, 1989) or use a modified argon/oxygen mixed gas plasma (Kollotzek et al., 1984). 

Olson, L.K., Vela, N.P. and Caruso, J.A. (1995) Hydride generation, electrothermal vaporisation and liquid-chromatography as sample introduction techniques for inductively-coupled plasma-mass spectrometry. Spectrochim. Acta B, 50, 1095-1108. 

Laborda, F., E. Bolea, and J.R. Castillo. 2007. Electrochemical hydride generation as a sample introduction technique in atomic spectrometry Fundamentals, interferences and applications. Anal. Bioanal. Chem. 388 743-775. 

The role of the sample introduction system is to convert a sample into a form that can be effectively vaporized into free atoms and ions in the ICP. A peristaltic pump is typically used to deliver a constant flow or sample solution (independent of variations in solution viscosity) to the nebulizer. Several different kinds of nebulizers are available to generate the sample aerosol, and several different spray chamber designs have been used to modify the aerosol before it enters the ICP Gases can be directly introduced into the plasma, for example, after hydride generation. Solids can be introduced by using electrothermal vaporization or laser ablation. 

Several elements (including As, Bi, Ge, Pb, Sb, Se, Sn, and Te) form volatile hydrides when reacted with sodium borohydride at room temperature. By introducing the analyte as a volatile hydride, high-transport efficiencies, and therefore improved detection limits, can be achieved. Often as importantly, much of the sample matrix is not introduced into the ICP because those species do not form volatile compounds. Commercial hydride generation sample introduction systems are available. 

It should be pointed out that few elements are present in most natural waters at concentrations where flame spectroscopic techniques are directly applicable. Those that are include calcium, magnesium, sodium, potassium, and, in some samples and if conditions are very carefully optimized, manganese, iron, and aluminium. Zinc, and sometimes cadmium, may be determined directly by AFS. Mercury and hydride-forming elements may be determined if cold vapour and hydride generation sample introduction techniques are employed, as discussed in... 

Analyzer Q = quadrupole, CC = collision cell, DRC = dynamic reaction cell, MC = multicollector, SF = sector field. Analytical details CV = cold vapor, ETV = electro-thermal vaporization, FI = flow injection, HG = hydride generation, ID = isotope dilution, LA = laser ablation, UN = ultrasonic nebulization. Sample introduction in liquid or slurry (si) form. 

M. Segura, Y. Madrid, C. Camara, Evaluation of atomic fluorescence and atomic absorption spectrometric techniques for the determination of arsenic in wine and beer by direct hydride generation sample introduction, J. Anal. Atom. Spectrom., 14 (1999), 131-135. 

H. Matusiewicz, M. Mikolajczank, Determination of As, Sb, Sn, and Hg in beer and wort by direct hydride generation sample introduction - electrothermal AAS, J. Anal. Atom Spectrom., 482 (2001), 652-657. 

Hydride generation is a sample introduction technique exclusively for elements that form volatile hydrides (e.g. As, Se, Sn). An acidified sample solution is reacted with sodium borohydride solution, liberating the gaseous hydride in a gas-liquid separator. The generated hydride is then transported to... 

T. Nakahara, Hydride Generation, in Sample Introduction in Atomic Spectroscopy, J. Sneddon Ed., Elsevier, Amsterdam (1990). 

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