CHAPTER 14 • Occurrence, Formation and Fate of Organoantimony Compounds
ethyl compounds has resulted in the formation of insoluble polymers (Dodd et al.1992).
Only trimethylantimony compounds have been successfully synthesized and isolated
as standards by a number of researchers (Giirleyiik et al. 1997; Dodd et al. 1992; Craig
et al. 1999; Gates et al. 1997). A further problem has been that on hydride generation
of these trimethylantimony standards (i.e. (CH3hSbC12), many researchers have detected four peaks relating to the one standard compound, irrespective of the detector
used. The structures of the compounds corresponding to each of the four peaks have
been elucidated, using GC-MS, as (CH 3 hSb and the expected dismutation products
SbH 3 , (CH 3 )SbH 2 and (CH 3 hH. These are eluted in order of their boiling points on
non-polar chromatographic columns. Some researchers have attributed this
dis mutation to the influence of pH on the derivatization system (Koch et al.1998), while
others have thought that it may be due to a very fast oxidation rate of trimethylantimony in the gaseous phase (Giirleyiik et al. 1997). Conversely, this rearrangement has
been used to good effect in headspace analysis (Jenkins et al.1998a, 1998b, 1998c), with
hydride generation of a single standard under conditions that will deliberately cause
rearrangement being utilized. The identification of inorganic, monomethyl-, dimethyl, and trimethylantimony compounds by comparison with retention times, achieved
through chromatographic separation, can therefore be utilized for standards work. It
is clear from a review of the literature (see for example Andreae et al. 1981; Dodd et al.
1996) that great care must be taken in performing hydride generation of methylantimony compounds from environmental matrices. For both quantitative and qualitative analysis, consideration must be given to reaction conditions. Koch et al. (1998) have
shown that environmental matrices directly affect molecular rearrangement, and they
recommend that only the standard additions method be used as a calibration technique in the hydride generation of organoantimony compounds from environmental
samples. Table 14.1 illustrates the various hydride generation conditions utilized in the
literature and the subsequent rearrangement observed.
It should be noted that hydride generation precludes analysis as such of large
organoantimony molecules, such as the stibnolipid suggested by Benson (1988). These
(from the As precedent) are not expected to be hydride derivatised under normal conditions. Only if techniques such as microwave digestion or ultraviolet photolysis are
included on-line before the borohydride step (in order to breakdown these molecules),
can these compounds be detected. Even so, the organic counter-ion species would be
destroyed and only the methylantimony portions detected, i.e. there would not be a
full molecular speciation.
14.2.3
Gas Chromatographic Separation
Both gas chromatography and cold trap methods have been utilized in conjunction
with hydride generation to ensure the gaseous species produced are adequately separated. Essential to the problem of partially alkylated compounds is the requirement
that measurement be capable of both rapid and non-destructive molecular separation. To reach this goal the preconcentrated sample must be separated without strong
interactions between the volatile metal compound and the stationary phase of a chromatographic system. This is generally achieved at relatively low temperatures, in comparison with more conventional GC, on a non-polar column with elution according to
ethyl compounds has resulted in the formation of insoluble polymers (Dodd et al.1992).
Only trimethylantimony compounds have been successfully synthesized and isolated
as standards by a number of researchers (Giirleyiik et al. 1997; Dodd et al. 1992; Craig
et al. 1999; Gates et al. 1997). A further problem has been that on hydride generation
of these trimethylantimony standards (i.e. (CH3hSbC12), many researchers have detected four peaks relating to the one standard compound, irrespective of the detector
used. The structures of the compounds corresponding to each of the four peaks have
been elucidated, using GC-MS, as (CH 3 hSb and the expected dismutation products
SbH 3 , (CH 3 )SbH 2 and (CH 3 hH. These are eluted in order of their boiling points on
non-polar chromatographic columns. Some researchers have attributed this
dis mutation to the influence of pH on the derivatization system (Koch et al.1998), while
others have thought that it may be due to a very fast oxidation rate of trimethylantimony in the gaseous phase (Giirleyiik et al. 1997). Conversely, this rearrangement has
been used to good effect in headspace analysis (Jenkins et al.1998a, 1998b, 1998c), with
hydride generation of a single standard under conditions that will deliberately cause
rearrangement being utilized. The identification of inorganic, monomethyl-, dimethyl, and trimethylantimony compounds by comparison with retention times, achieved
through chromatographic separation, can therefore be utilized for standards work. It
is clear from a review of the literature (see for example Andreae et al. 1981; Dodd et al.
1996) that great care must be taken in performing hydride generation of methylantimony compounds from environmental matrices. For both quantitative and qualitative analysis, consideration must be given to reaction conditions. Koch et al. (1998) have
shown that environmental matrices directly affect molecular rearrangement, and they
recommend that only the standard additions method be used as a calibration technique in the hydride generation of organoantimony compounds from environmental
samples. Table 14.1 illustrates the various hydride generation conditions utilized in the
literature and the subsequent rearrangement observed.
It should be noted that hydride generation precludes analysis as such of large
organoantimony molecules, such as the stibnolipid suggested by Benson (1988). These
(from the As precedent) are not expected to be hydride derivatised under normal conditions. Only if techniques such as microwave digestion or ultraviolet photolysis are
included on-line before the borohydride step (in order to breakdown these molecules),
can these compounds be detected. Even so, the organic counter-ion species would be
destroyed and only the methylantimony portions detected, i.e. there would not be a
full molecular speciation.
14.2.3
Gas Chromatographic Separation
Both gas chromatography and cold trap methods have been utilized in conjunction
with hydride generation to ensure the gaseous species produced are adequately separated. Essential to the problem of partially alkylated compounds is the requirement
that measurement be capable of both rapid and non-destructive molecular separation. To reach this goal the preconcentrated sample must be separated without strong
interactions between the volatile metal compound and the stationary phase of a chromatographic system. This is generally achieved at relatively low temperatures, in comparison with more conventional GC, on a non-polar column with elution according to