Derivatisation hydride generation

The most frequently used methods for elemental analysis in plastics (certainly in the past) deal with digestions of some kind. Also, some derivatisation methods (e.g. hydride generation for element analysis, or the equivalent TMAH treatment for molecular analysis) may be used to generate volatile species which are more easily separated from each other by chromatography. Derivatisation reactions are often far from being well controlled. 

The techniques used were based on solvent extraction (e.g. with pentane), complexation (e.g. with diethyldithiocarbamate, EDTA), derivatisation (e.g. hydride generation, propylation or ethylation), and capillary GC separation followed by a range of detection techniques (e.g. QFAAS, ICPMS, MIP-AES, MS) DPASV has also been successfully used. In the frame of this project, two new techniques were also developed and successfully applied, namely supercritical fluid extraction followed by CGC/MS and isotope dilution ICPMS after ethylation and CGC separation. A full description of the techniques is given elsewhere (Quevauviller, 1998b). 

Several methods have been developed for the determination of arsenic species, involving different extraction, derivatisation, separation and detection steps [13] these include hyphenated techniques based on liquid chromatography coupled to detectors such as ICP-MS or ICP-AES, and hydride generation in line with QFAAS and UV degradation followed by ICP-AES detection. The techniques that were selected in the certification campaign are listed in Table 7.8. 

The methods using hydride generation and AAS as final determination were, however, in considerable difficulty with this complicated matrix, due to unknown interferences either at the derivatisation step or in AAS detection, or determination limits that were too low. As observed by the participants, the laboratories using gas chromatographic separation and detection either by FPD or MS tended to agree which would confirm that these methods would be more suited to the determination of TBT in this particular material. 

The majority of species present in aqueous or solid samples will be ionic, and must be derivatised to non-polar, volatile compounds, accessible for GC analysis. Extraction and derivatisation can be accomplished simultaneously or sequentially, as described in the following sections. The derivatisation techniques most often applied are hydride generation with NaBHa, ethylation with NaBEt4 or Grignard alkylation, and were recently reviewed by Morabito et a/. ... 

Ionic species must be derivatised into volatile compounds. These may be purged from the water phase into a cryogenic trap, an approach which is mainly appUed after hydride generation for methylated species of As, Sn, Ge and Sb in urine, landfill condensates, seawater or geothermal... 

Ethylation using NaBEt4 has, for example, heen shown for the derivatisation of mercury and germanium species prior to purging and trapping, and is favourahle over derivatisation with hydride generation. 

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