268
P.J. Craig· S.N. Forster· R.O. Jenkins· D.P. Miller· N.Ostah . L.M. Smith· T.-A. Morris
14.2
Analysis of Organoantimony Compounds
The advent of highly sensitive analytical instruments has resulted in a variety of techniques that can be employed for the speciation of organoantimony compounds. Many
workers have simply adapted techniques already developed for similar elements, such
as arsenic, and applied the knowledge gained for use with antimony. Although this has
not always been straightforward, our understanding of these organoantimony compounds is continually increasing.
14.2.1
Sample Preparation
The type of analytical instrument( s) used for the detection and speciation of antimony
compounds will dictate the necessary sample preparation needed. Often samples to
be analysed are of a biological or environmental nature, and the vast array of auxiliary chemical species present usually necessitates a cleanup stage to remove potential
interferents. Also, in these complex matrices there is sometimes a need to derive the
antimony species into a form that is suitable for analysis (e.g. volatile). Processes such
as freeze-drying, homogenisation and acid digestion are common examples of sample
preparation. Samples to be analysed by inductively-coupled plasma mass spectrometry (ICP-MS) must not contain solid material larger than 20 microns or the risk of
blocking the nebulizer is introduced and hence acid digestion followed by filtration is
required. Once in an acceptable physical form, the sample can be analysed using one
or a combination of sensitive techniques. A selection of the most commonly utilized
techniques is outlined below.
14.2.2
Hydride Generation
Derivatisation of organoantimony species by hydride generation with sodium tetraborohydride (NaBH4) has proved to be a useful technique for their speciation. Gaseous hydride species can be produced directly from environmental samples, thus providing a relatively simple cleanup and matrix separation process and avoiding any
pretreatment steps. Generally hydride generation only provides information about the
oxidation state of an inorganic compound, by inference from previous knowledge of
the reaction conditions under which a metal in a known oxidation state is successfully derivatised. With respect to alkylated compounds, hydride generation can only
provide information about the degree of organic substitution of the compound, and
this only in conjunction with gas chromatographic methods. It cannot provide information about the full molecular nature of an environmental compound, even in conjunction with techniques such as GC-MS. For this liquid chromatographic techniques
and standards are required. There is a total lack of environmental organoantimony
standards. This may be due to the instability of the methylhydrides to oxygen (reported
as 10 3 m- I S-I) (Parris and Brinckman 1976) and partially due to the difficulty of synthesizing pure mono- and dimethyl compounds. It is not even certain which methylSb species should be synthesized! Recent attempts to prepare both mono- and dim-
P.J. Craig· S.N. Forster· R.O. Jenkins· D.P. Miller· N.Ostah . L.M. Smith· T.-A. Morris
14.2
Analysis of Organoantimony Compounds
The advent of highly sensitive analytical instruments has resulted in a variety of techniques that can be employed for the speciation of organoantimony compounds. Many
workers have simply adapted techniques already developed for similar elements, such
as arsenic, and applied the knowledge gained for use with antimony. Although this has
not always been straightforward, our understanding of these organoantimony compounds is continually increasing.
14.2.1
Sample Preparation
The type of analytical instrument( s) used for the detection and speciation of antimony
compounds will dictate the necessary sample preparation needed. Often samples to
be analysed are of a biological or environmental nature, and the vast array of auxiliary chemical species present usually necessitates a cleanup stage to remove potential
interferents. Also, in these complex matrices there is sometimes a need to derive the
antimony species into a form that is suitable for analysis (e.g. volatile). Processes such
as freeze-drying, homogenisation and acid digestion are common examples of sample
preparation. Samples to be analysed by inductively-coupled plasma mass spectrometry (ICP-MS) must not contain solid material larger than 20 microns or the risk of
blocking the nebulizer is introduced and hence acid digestion followed by filtration is
required. Once in an acceptable physical form, the sample can be analysed using one
or a combination of sensitive techniques. A selection of the most commonly utilized
techniques is outlined below.
14.2.2
Hydride Generation
Derivatisation of organoantimony species by hydride generation with sodium tetraborohydride (NaBH4) has proved to be a useful technique for their speciation. Gaseous hydride species can be produced directly from environmental samples, thus providing a relatively simple cleanup and matrix separation process and avoiding any
pretreatment steps. Generally hydride generation only provides information about the
oxidation state of an inorganic compound, by inference from previous knowledge of
the reaction conditions under which a metal in a known oxidation state is successfully derivatised. With respect to alkylated compounds, hydride generation can only
provide information about the degree of organic substitution of the compound, and
this only in conjunction with gas chromatographic methods. It cannot provide information about the full molecular nature of an environmental compound, even in conjunction with techniques such as GC-MS. For this liquid chromatographic techniques
and standards are required. There is a total lack of environmental organoantimony
standards. This may be due to the instability of the methylhydrides to oxygen (reported
as 10 3 m- I S-I) (Parris and Brinckman 1976) and partially due to the difficulty of synthesizing pure mono- and dimethyl compounds. It is not even certain which methylSb species should be synthesized! Recent attempts to prepare both mono- and dim-