272
P.J. Craig· S.N. Forster· R.O. Jenkins· D.P. Miller· N.Ostah . L.M. Smith· T.-A. Morris
compounds boiling points. Table 14.2 illustrates conditions which have been utilized
for successful separation of organoantimony compounds.
14.2.4
Detection Systems
14.2.4.1
Atomic Absorption Spectrometry
Atomic absorption spectrometry (AAS) is the most commonly utilized detection technique, owing to its selectivity, sensitivity and relatively low running costs, together with
the speed and ease of operating the instrument. The characteristic source emission is
generated by one of two types of lamp. Hollow cathode lamps are commonly used,
however Andreae et al. (1981) reported an improvement by a factor of three when using an electrode discharge lamp. This power source also needs to be replaced less frequently than the former, although the cost of initial installation is higher. Principal
resonance lines for antimony are found at 217.6, 206.8, and 231.2 nm. The 217.6 nm line,
which is the most sensitive, should be used with a spectral band-pass of less than
0.2 nm to isolate this line from two non-absorbing lines at 217.0 nm and 217.9 nm.
Without this, reductions in sensitivity and linearity will occur. An electrically heated
quartz furnace offers the most sensitive method of introduction of the organoantimony
compounds into the light beam, owing to its long path length. The quartz furnace also
facilities the use of a hydrogen-air flame, which improves sensitivity, owing to a complex series of reactions between hydrogen and oxygen radicals as the sample passes
through. Using an AAS quartz furnace, detection limits as low as 30-60 pg have been
observed (Andreae et al. 1981).
14.2.4.2
Mass Spectrometry
The use of mass spectrometry (MS) in conjunction with hydride generation (HG) and
gas chromatography (GC) allows for the characterization of the antimony compounds
based on their retention times and mass spectral data. However, it should be noted
that this detection system is less sensitive than atomic absorption spectroscopy. Antimony has two stable isotopes: 121Sb (relative abundance 57%) and 123Sb (43%), hence,
the mass spectra will be more complex than those of arsenic, for example, which has
only one stable isotope. The occurrence of these two stable isotopes provides a useful
signature for the detection of antimony compounds by MS in the natural environment.
Dodd et al. (1996) used a semi-continuous HG-GC-MS with a detection limit of -15 ng
of antimony in the narrow scan mode (m/z 117-170). Jenkins et al. (1998 a,b,c) used
GC-MS to analyse the headspace of cultures for organoantimony compounds (Fig. 14.2).
Here, the culture headspaces were initially preconcentrated onto Tenax -TA tubes and
a thermal-desorption unit was used to introduce sample into the GC-MS instrument.
Giirleyiik et al. (1997) also used GC-MS to sample headspaces from cultures, but this
was by direct gas injection, undertaken by sampling the headspace using a gas-tight
syringe
P.J. Craig· S.N. Forster· R.O. Jenkins· D.P. Miller· N.Ostah . L.M. Smith· T.-A. Morris
compounds boiling points. Table 14.2 illustrates conditions which have been utilized
for successful separation of organoantimony compounds.
14.2.4
Detection Systems
14.2.4.1
Atomic Absorption Spectrometry
Atomic absorption spectrometry (AAS) is the most commonly utilized detection technique, owing to its selectivity, sensitivity and relatively low running costs, together with
the speed and ease of operating the instrument. The characteristic source emission is
generated by one of two types of lamp. Hollow cathode lamps are commonly used,
however Andreae et al. (1981) reported an improvement by a factor of three when using an electrode discharge lamp. This power source also needs to be replaced less frequently than the former, although the cost of initial installation is higher. Principal
resonance lines for antimony are found at 217.6, 206.8, and 231.2 nm. The 217.6 nm line,
which is the most sensitive, should be used with a spectral band-pass of less than
0.2 nm to isolate this line from two non-absorbing lines at 217.0 nm and 217.9 nm.
Without this, reductions in sensitivity and linearity will occur. An electrically heated
quartz furnace offers the most sensitive method of introduction of the organoantimony
compounds into the light beam, owing to its long path length. The quartz furnace also
facilities the use of a hydrogen-air flame, which improves sensitivity, owing to a complex series of reactions between hydrogen and oxygen radicals as the sample passes
through. Using an AAS quartz furnace, detection limits as low as 30-60 pg have been
observed (Andreae et al. 1981).
14.2.4.2
Mass Spectrometry
The use of mass spectrometry (MS) in conjunction with hydride generation (HG) and
gas chromatography (GC) allows for the characterization of the antimony compounds
based on their retention times and mass spectral data. However, it should be noted
that this detection system is less sensitive than atomic absorption spectroscopy. Antimony has two stable isotopes: 121Sb (relative abundance 57%) and 123Sb (43%), hence,
the mass spectra will be more complex than those of arsenic, for example, which has
only one stable isotope. The occurrence of these two stable isotopes provides a useful
signature for the detection of antimony compounds by MS in the natural environment.
Dodd et al. (1996) used a semi-continuous HG-GC-MS with a detection limit of -15 ng
of antimony in the narrow scan mode (m/z 117-170). Jenkins et al. (1998 a,b,c) used
GC-MS to analyse the headspace of cultures for organoantimony compounds (Fig. 14.2).
Here, the culture headspaces were initially preconcentrated onto Tenax -TA tubes and
a thermal-desorption unit was used to introduce sample into the GC-MS instrument.
Giirleyiik et al. (1997) also used GC-MS to sample headspaces from cultures, but this
was by direct gas injection, undertaken by sampling the headspace using a gas-tight
syringe