Organic compounds in non-saline sediments 149
overlapping higher homolog fragments do not interfere with the quantitation of
lower homologs. The method was demonstrated for extracts in small samples (
∼ 750–
1000 mg) from seven different freshwater biota species (n = 20) to illustrate a wide
range of matrix-induced shifts. Application of the method resulted in more accurate
quantitation, correcting an average 5.3% relative error (false positive bias) in observed
concentration.
All of the parent and daughter ions are trapped in the mass analyser, whether they
are from the homolog of interest at the retention time or from fragments of a higher
homolog that has lost one or more chlorine atoms that is eluting in that same retention
window. The parent ion is then subjected to collision-induced dissociation (CID) and
produces the daughter ions that are used for quantitation. Without correcting for the
contribution from higher homologs that may have formed daughter ions during electron impact ionisation, inaccurate quantitation of the congener of interest may occur
for the lower homolog. In contrast, if a lower order congener concentration is significantly higher than a co-eluting higher homolog, the contribution made the higher
homolog is negligible. For example, a trichlorobiphenyl can form dichlorobiphenyl
and monochlorobiphenyl daughters during electron impact ionisation. During conventional GC-MS/MS of a sample containing a trichlorobiphenyl, lower homologs are
indeed observed (Figure 6.5). Ruddy et al [131] investigated the extent of this type of
EI-induced artefact formation on all 10 homolog classes.
6.3.3 Organohalogen concentration techniques
Lea et al [134] have described an in-situ procedure for qualifying and inorganic chlorine concentrations in environmental samples based on X-ray absorption near edge
structure (XANES) spectroscopy. Cl 1s XANES spectra reflect contributions from all
chlorine species present in a sample, providing a definitive measure of total chlorine concentration in chemically heterogeneous samples. Spectral features near the Cl
K-absorption edge provide detailed information about the bonding state of chlorine,
whereas the absolute fluorescence intensity of the spectra is directly proportional to
total chlorine concentration, allowing for simultaneous determination of chlorine speciation and concentration in plant, soil, sediment and natural water samples. Absolute
chlorine concentrations are obtained from chlorine 1s XANES spectra using a series
of chlorine standards in a matrix of uniform bulk density. With the high sensitivity
of synchrotron-based X-ray absorption spectroscopy, chlorine concentration can be
reliably measures down to the 5–10 ppm range in solid and liquid samples. Referencing the characteristic near-edge features of chlorine in various model compounds,
it was possible to distinguish between inorganic chloride (Cl inorg ) and organochlorine (Cl org ) as well as between aliphatic Cl org and aromatic Cl org with uncertainties in
the range of ∼6%. In addition, total organic and inorganic bromine concentrations
in sediment samples are quantified using a combination of bromine 1s XANES and
X-ray fluorescence (XRF) spectroscopy. Bromine concentration is detected down to ∼1
ppm by XRF, and 1s XANES spectra allow quantification of the inorganic bromine and
organic bromine fractions. These procedures provide non-destructive, element-specific
techniques for quantification of chlorine and bromine concentrations that preclude
extensive sample preparation.
overlapping higher homolog fragments do not interfere with the quantitation of
lower homologs. The method was demonstrated for extracts in small samples (
∼ 750–
1000 mg) from seven different freshwater biota species (n = 20) to illustrate a wide
range of matrix-induced shifts. Application of the method resulted in more accurate
quantitation, correcting an average 5.3% relative error (false positive bias) in observed
concentration.
All of the parent and daughter ions are trapped in the mass analyser, whether they
are from the homolog of interest at the retention time or from fragments of a higher
homolog that has lost one or more chlorine atoms that is eluting in that same retention
window. The parent ion is then subjected to collision-induced dissociation (CID) and
produces the daughter ions that are used for quantitation. Without correcting for the
contribution from higher homologs that may have formed daughter ions during electron impact ionisation, inaccurate quantitation of the congener of interest may occur
for the lower homolog. In contrast, if a lower order congener concentration is significantly higher than a co-eluting higher homolog, the contribution made the higher
homolog is negligible. For example, a trichlorobiphenyl can form dichlorobiphenyl
and monochlorobiphenyl daughters during electron impact ionisation. During conventional GC-MS/MS of a sample containing a trichlorobiphenyl, lower homologs are
indeed observed (Figure 6.5). Ruddy et al [131] investigated the extent of this type of
EI-induced artefact formation on all 10 homolog classes.
6.3.3 Organohalogen concentration techniques
Lea et al [134] have described an in-situ procedure for qualifying and inorganic chlorine concentrations in environmental samples based on X-ray absorption near edge
structure (XANES) spectroscopy. Cl 1s XANES spectra reflect contributions from all
chlorine species present in a sample, providing a definitive measure of total chlorine concentration in chemically heterogeneous samples. Spectral features near the Cl
K-absorption edge provide detailed information about the bonding state of chlorine,
whereas the absolute fluorescence intensity of the spectra is directly proportional to
total chlorine concentration, allowing for simultaneous determination of chlorine speciation and concentration in plant, soil, sediment and natural water samples. Absolute
chlorine concentrations are obtained from chlorine 1s XANES spectra using a series
of chlorine standards in a matrix of uniform bulk density. With the high sensitivity
of synchrotron-based X-ray absorption spectroscopy, chlorine concentration can be
reliably measures down to the 5–10 ppm range in solid and liquid samples. Referencing the characteristic near-edge features of chlorine in various model compounds,
it was possible to distinguish between inorganic chloride (Cl inorg ) and organochlorine (Cl org ) as well as between aliphatic Cl org and aromatic Cl org with uncertainties in
the range of ∼6%. In addition, total organic and inorganic bromine concentrations
in sediment samples are quantified using a combination of bromine 1s XANES and
X-ray fluorescence (XRF) spectroscopy. Bromine concentration is detected down to ∼1
ppm by XRF, and 1s XANES spectra allow quantification of the inorganic bromine and
organic bromine fractions. These procedures provide non-destructive, element-specific
techniques for quantification of chlorine and bromine concentrations that preclude
extensive sample preparation.