Hydride interference

Crain, J. S. and Alvarado, J., Hydride interference on the determination of minor actinide isotopes by inductively coupled plasma mass spectrometry,. /. Anal. At. Spectrom., 9, 1223-1227, 1994. 

Hydride techniques, however, can suffer from many interferences (see Section 3.3). In AAS these interferences can not only occur as a result of influences on the hydride formation reaction but also as a result of influences of concomitants on the thermal dissociation of the hydride. Interferences from other volatile hydride forming elements can also occur [291]. Recently it has been found that still more elements can form volatile hydrides, as demonstrated e.g. by Cd. Here the hydride... 

An illustrative example of this is shown in Figure 5.11 in which hydride interferences experienced by the Si and °Si secondary ions from a Phosphorus-doped Silicon wafer are derived as the difference in the signals recorded relative to the natural abundance of the isotopes. From this, an expected value for the interference can be estimated. This can then be used to derive an interference-free signal from P . The fraction subtracted from the intensity at 31 m/q would represent the interference introduced by the °Si H ions. This fraction would either be defined by the relative intensity of some other secondary ion related to the secondary ions responsible for the interference, or would be derived to produce the expected result. Note Caution must be exercised when using this approach to ensure the validity of the faction subtracted. Indeed, this approach should only be used as a last resort. 

Figure 5.11 A mass spectrum of the negative secondary ion emission from a Silicon wafer. The solid line represents the collected signal and the dashed lines represent the peak stripped spectra, i.e. the spectra not suffering the hydride interferences. This mass spectrum was collected on a Quadrupole-based SIMS instrument at unit mass resolution (from Figure 5.1).

HaU, G. E. M., and Pelchat,. C. (1997). Analysis of geological materials for bismuth, antimony, selenium and tellurium by continuous flow hydride generation inductively coupled plasma mass spectrometry. Part 1. Mutual hydride interferences.,/. Anal. At. Speetrom. 12(1), 97. 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

A flow-injection system with electrochemical hydride generation and atomic absorption detection for the determination of arsenic is described. This technique has been developed in order to avoid the use sodium tetrahydroborate, which is capable of introducing contamination. The sodium tetrahydroborate (NaBH ) - acid reduction technique has been widely used for hydride generation (HG) in atomic spectrometric analyses. However, this technique has certain disadvantages. The NaBH is capable of introducing contamination, is expensive and the aqueous solution is unstable and has to be prepared freshly each working day. In addition, the process is sensitive to interferences from coexisting ions. 

A-ring conjugated ketones do not normally interfere with the epoxidation reaction, but hydride reduction will reduce any ketone groups to alcohols. These can be reoxidized by conventional means. 

The cross metathesis of vinylsilanes is catalyzed by the first-generation ruthenium catalyst 9. This transformation has been extensively investigated from both preparative and mechanistic points of view by Marciniec et al. [86]. Interestingly, the same vinylsilanes obtained from cross metathesis may also result from a ruthenium-hydride-catalyzed silylative coupling and there might be some interference of metathesis and nonmetathesis mechanisms [87]. 

AFS instruments are mainly used to detect the vapour-forming elements, such as those that form hydrides (As, Bi, Ge, Pb, Se, Sb, Sn and Te). AFS is less prone to spectral interferences than either AES or A AS. Detection limits in AFS are low, especially for elements with high excitation energies, such as Cd, Zn, As, Pb, Se and Tl. In recent years, the use of AFS has been boosted by the production of specialist equipment that is capable of determining individual analytes at very low concentrations (at the ng L-1 level). The analytes have tended to be introduced in a gaseous form. AFS methods and instrumentation have been reviewed [214-216], see also ref. [17]. 

Negative interferences by transition metal cations such as nickel and copper and nitrite were observed. However, these interferences have also been reported for the hydride generation atomic absorption method, and are due to... 

Willie et al. [17] used the hydride generation graphite furnace atomic absorption spectrometry technique to determine selenium in saline estuary waters and sea waters. A Pyrex cell was used to generate selenium hydride which was carried to a quartz tube and then a preheated furnace operated at 400 °C. Pyrolytic graphite tubes were used. Selenium could be determined down to 20 ng/1. No interference was found due to, iron copper, nickel, or arsenic. 

Braman et al. [34] used sodium borohydride to reduce arsenic and antimony in their trivalent and pentavalent states to the corresponding hydrides. Total arsenic and antimony are then measured by their spectral emissions, respectively, at 228.8 nm and 242.5 nm. Limits of detection are 0.5 ng for antimony and 1 ng for arsenic, copper, and silver. Oxidants interfere in this procedure. 

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