Continuous hydride generation

Lab method using continuous flow or flow injection analysis hydride generation and atomic absorption spectrometry... 

Other techniques used for organotin speciation comprise GC-FAAS, GC-GFAAS, GC-ICP-MS, HPLC-FAAS, HPLC-GFAAS, HPLC-DCP (after continuous on-line hydride generation), HPLC-ICP-AES, HPLC-ICP-MS, etc. [555], Whereas ICP-AES does not provide an adequate response for ng levels of tin, ICP-MS can detect sub-ng to pg levels. GC-ICP-ToFMS... 

Hydride generation systems (a) batch mode operation (b) continuous mode operation. 

Hydride generator PS Analytical continuous flow hydride generator. 

Reductant A solution of 1% w/v sodium borohydride (NaBHJ should be freshly prepared in 0.1 M sodium hydroxide (NaOH), and placed in the reductant reagent compartment of the PS Analytical continuous flow hydride generator. 

Because MIPs are formed at low temperatures, liquid samples cannot be introduced because they extinguish the plasma, even small amounts of organic vapour. However, the on-line coupling of HPEC to MIP-OES has been described for the speciation of mercury and arsenic compounds. Continuous cold vapour (CV) or hydride generation (HG) techniques were used as interfaces between the exit of the HPEC column and the MIP, held in a surfatron at reduced pressure [24]. 

A sample treatment device composed of continuous hydride generation, pre-redissolution with thiourea and preconcentration by coprecipitation with La in a knotted reactor was studied... 

Figure 7.7. Schematic diagram of the continuous flow hydride generation system, showing the two positions of the four-port valve (A) for analysis of the test solution and (B) for blank integrations used for changing the test solution. From [115]...

Mohammad, B., Ure, A.M., Reglinski,J. and Littlejohn, D. (1990) Speciation of antimony in natural waters the determination of Sb(III) and Sb(V) by continuous flow hydride generation-atomic absorption spectrometry. Chem. Spec. Bioavail., 3, 117-122. 

A flame AAS (FAAS) detector can monitor the GC effluent continuously to provide on-line analysis. However, as the gas flow rates for the flame are quite high, the residence time in the flame is short, and this can adversely affect the detection limits. Detection limits in the microgram range are usually achieved. Improved detection limits can be obtained if the additional techniques of hydride generation or cold vapour mercury detection are used as described in Section 4.6. 

Cobo-Fernandez, M.G., Palacios, M.A. and Camara, C. (1993) Flow-injection and continuous-flow systems for the determination of Se (VI) and Se (IV) by hydride generation atomic absorption spectrometry with on-line prereduction of Se (IV) to Se (VI). Anal. Chim. Acta, 283, 386-392. 

Total tin was determined by continuous on-line hydride generation followed by direct current plasma emission spectroscopy. Interfacing the hydride generation-DC plasma emission spectrometric system with high performance liquid chromatography allowed the determination of tin species. Detection limits, sensitivities and calibration plots were determined. 

Continuous, batch, and flow injection modes of hydride generation have been used successfully [39-41]. In the commonly used continuous mode the sample and sodium borohydride solutions are pumped by using a dual-channel peristaltic pump into a mixing chamber. The volatile hydride gas and hydrogen are carried into the plasma with a flowing argon gas and the excess liquid is directed to the drain. 

D. Velez, N. Ybanez, R. Montoro, Analysis of geological materials for bismuth, antimony, selenium and tellurium by continuous flow hydride generation inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 12 (1997), 91-97. 

Liquid samples are typically analyzed, gaseous phase from hydride generation is easily accepted, and solids can be introduced as slurries or after appropriate pretreatment procedme aimed at solubilization and/or preconcentration of the analytes. However, laser ablation techniques continue to increase in popularity. 

Anderson R. K., Thompson M., and Culbard E. (1986) Selective reduction of arsenic species by continuous hydride generation Part II. Validation of methods for application to natural waters. Analyst 111, 1153-1157. 

Figure 2.17 Schematic diagram of continuous flow hydride generator. (Reproduced with kind permission from PSAnalytical, Orpington BR5 31 IP, UK)...

The benefit of sample preparation techniques using microwave acid digestion and bomb combustion is that the sample is totally enclosed during the decomposition. These methods remove matrix interference and generate aqueous solutions, which can be analysed using ICP-OES. Sub-trace concentrations can be detected when hyphenated attachments are used, e.g. ultrasonic nebuliser, hydride generation or continuous cold vapour method. These methods are essential where trace levels of toxic elements are present that need to be identified and quantified. 

Figure 28-5 Continuous sample introduction methods. Samples are frequently introduced into plasmas or flames by means of a nebulizer, which produces a mist or spray. Samples can be introduced directly to the nebulizer or by means of flow injection (FIA) or high-performance liquid chromatography (HPLC). In some cases, samples are separately converted to a vapor by a vapor generator, such as a hydride generator or an electrothermal vaporizer.

In electrolytic hydride generation, a cell as shown schematically in Fig. 55 can be used [158]. It is made of PTFE rings and disks and can be easily disassembled for cleaning. The electrodes are platinum sheets with a surface of 10 cm2 each. The compartments of the anode (10 cm2) and the cathode (2 cm2) both have a solution inlet and outlet and are separated by a Nation membrane. The cell is held together with six screws. Solutions of the sample acidified with HC1 are used as the catho-lyte and dilute H2S04 as the anolyte. At a cell current of a few amperes, the solutions are continuously fed through the cell compartments, and on the cathodic... 

In a flow injection system the sample flow and a reagent flow are continuously brought together so as to allow a chemical reaction to take place. This reaction produces a gaseous compound, which has to be separated off as in hydride generation, or forms a complex, which can be adsorbed onto a solid phase to be isolated and preconcentrated. In the latter case, elution with a suitable solvent is carried out and the analytes are led on-line into the AAS system. 

Fig. m. Gas sampling glow discharge (A) and continuous-flow hydride generation system (dimensions in mm) (B), (a) reaction column, (b) fritted glass disk, (c) gas-.liquid separator and (d) condenser (Reprinted with permission from Ref. [488].)... 

A. C. and Hieftje G. M. (1994) Direct coupling of continuous hydride generation with microwave plasma torch atomic emission spectrometry for the determination of arsenic, antimony and tin, Spectrochim Acta, Part B 49 59-73. 

Tao H. and Miyazaki A. (1991) Determination of germanium, arsenic, antimony, tin and mercury at trace levels by continuous hydride generation-helium microwave-induced plasma atomic emission spectrometry, Anal Sci 7 55-59. 

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