Hydride generation reduction methods

A method for tributyltin in sediments consists of extraction with anhydrous acetic acid, hydride generation, cold trapping and end analysis by GC-AAS using a quartz furnace75. Reduction with NaBFLi followed by solvent extraction, concentration and GC-FPD was proposed for simulaneous determination of di- and tributyltin residues in sea water LOD 10 ng/L for 1 L sample, with 87.1-98.4% of Sn recovery76. 

To implement an easy and automated means for chemical vapour generation procedures (hydride generation for arsenic, selenium, etc., and cold vapour mercury), which allows for a reduction on the interferences caused by first-row transition metals (such as copper and nickel). FI methods may be readily coupled with almost all the atomic-based spectroscopic techniques (including graphite furnace atomisers). 

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 ability to monitor trace levels of a number of heavy metals in a variety of samples is an important feature of modern environmental chemistry. Hence, sensitive analytical methods are required. When faced with the task of analyzing very low concentrations of antimony, bismuth and tin the hydride generation method is the first choice because of the improved sensitivity and lower detection limits as compared to many other techniques. The hydride generation technique includes the use of a reductant, such as a NaBH4 solution, to separate the volatile metal hydrides from the sample solution and the subsequent determination with atomic absorption after decomposition of the hydrides in a heated quartz cell. 

Hydride generation methods involve three or four successive steps depending on the technique used (i) The hydride is generated by chemical reduction of the sample (ii) The formed hydride may be collected in the batch type methods (iii) The hydride is entrained in a gas stream into the atomizer (iv) The hydride is decomposed in the atomizer to form the atomic vapour, and the absorption signal is measured. A number of methods in use are based on this principle, but they differ in the means of reduction, atomization, and sample introduction. 

M is the analyte and m may be equal to n or not (for example, As and As are both reduced to AsHs). Hydrides were collected in U-tubes in a nitrogen trap or in rubber balloons. Titanium(iii) chloride—hydrochloric acid and magnesium-zinc reductants were used to extend the hydride method to bismuth, antimony, and tellurium. For some elements, especially tin, lead, and tellurium, the hydride formation reaction is relatively slow and hence the collection vessel is necessary. In addition, arsenic(v) must be reduced to arsenic(iii) by tin(ii) chloride or potassium iodide before the actual hydride generation when a metal-acid reduction is employed. 

Sodium borotetrahydride is now generally used as the reductant in various hydride generation methods. The reduction may be illustrated by the following reactions ... 

Mercury can be determined in plasma AES by reducing it first to elemental mercury and then transporting the mercury vapour into the plasma. The same reduction methods may be used as for AAS. Commercial hydride generation systems can be adopted to the cold vapour method. The detection limit is about 0.02 mgP ... 

The quest for tin-free reductive methods led the same authors to develop the use of indium(lll) hydride ClalnH, generated in situ from triethylsilane and InCla. Aromatic and aliphatic azides as well as sulfonyl azides and acyl azides are reduced in moderate to excellent yield to the corresponding amines and amides. Azido nitriles are efficiently converted to the pyrrolidin-2-imines (Scheme 8.45). 

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