Hydride generation, continuous method

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

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. 

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.

Alverez GH, Capar SG. 1991. Continuous hydride generation-atomic absorption method for the determination of selenium and arsenic in foods. Analytical Letters 24(9) 1695-1710. 

Menendez Garcia et al.[50] combined on-line liquid-liquid extraction separation with hydride generation gas-liquid separation for the determination of arsenic with ICPES. Arsenic in the aqueous sample is extracted as ASI3 into xylene which is continuously mixed on-line with sodium borohydride in dimethylformamide and acetic acid solutions. Arsine is generated in the organic phase and separated in a gas-liquid separator which prevents most of the xylene vapour from entering the plasma. The method was used to improve the sensitivity and to remove interferences from transition metals in the determination of low levels of arsenic in white metal, cast iron, cupro-nickel etc.. 

Initially hydride generation and cold vapour techniques were developed for the quantitative determination of the hydride-forming elements and mercury by atomic absorption spectrometry (Chapters, Sections 6.2 and 6.3), but nowadays these methods are also widely used in plasma atomic emission spectrometry. In the hydride generation technique, hydride-forming elements are more efficiently transported to the plasma than by conventional solution nebulization, and the production and excitation of free atoms and ions in the hot plasma is therefore more efficient. Spectral interferences are also reduced when the analyte is separated from the elements in the sample matrix. Both continuous (FIA) and batch approaches have been used for hydride generation. The continuous method is more frequently used in plasma AES than in AAS. Commercial hydride generation systems are available for various plasma spectrometers. 

Continuous Hydride Generation. In the continuous or FIA hydride generation method the sample and reagent solutions are continuously pumped, usually by a multi-channel peristaltic pump, into a mixing chamber where... 

Table 1 summarizes the limits of detection of a number of hydride forming elements reported for the various generation-detection methods. For comparison with continuous sampling techniques, a 10 ml sample volume has been assumed for in situ trapping in the graphite furnace (although larger volumes are easily accommodated) and a 500 pi volume for FI approaches. It is clear that, despite the small sample... 

Nonchromatographic continuous separation techniques involving gas-liquid interfaces (e.g., gas diffusion, hydride generation, pervaporation) prior to detection by an atomic spectrometer have frequently been coupled to FI manifolds to develop excellent methods of interest, mainly to the clinical and industrial fields. 

Metalloid compounds are usually determined by flowing-stream techniques hyphenated with hydride generation (HG)-atomic absorption or atomic fluorescence spectrometry. The continuous operation mode inherent to flow injection is specially suited for the latter detection technique as the tetrahyd-roborate reagent is a potential source of hydrogen for supporting the flame. Analyte preconcentration is frequently needed to detect the typical levels of metalloid species found in water matrices. In this context, cold trap collection of generated hydrides, sorbent extraction microcolumn methods, sorption... 

Tao et al. [658] have described a procedure in which antimony and arsenic were generated as hydrides and irradiated with ultraviolet light. The broad continuous emission bands were observed in the ranges about 240-750 nm and 220 - 720 nm, and the detection limits were 0.6 ng and 9.0 ng for antimony and arsenic, respectively. Some characteristics of the photoluminescence phenomenon were made clear from spectroscopic observations. The method was successfully applied to the determination of antimony in river water and seawater. The apparatus used in this technique is illustrated in Fig. 5.16. 

---