2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
tion of negatively charged aluminium complexes in seawater
(e.g. fluoro complexes) and the high ionic strength of the eluent.
The effect of ionic strength has been reported to affect
the retention of ions in chelation IC 8,16 . In an environment
of sufficiently high ionic strength the repulsion between
negatively charged aluminium species and the iminodiacetic
acid functional groups may be reduced. This can result
in a subsequent increase in retention time as observed in our
studies. This response is actually considered favourable as it
allows for additional stabilisation of the baseline between the
minor dip in fluorescence and elution of the aluminium.
Fig. 2. Effect of increasing sample volume on column performance
and fluorescence response
S e a w a t e r S a m p l e s
At this stage, the optimised HPCIC system coupled with
fluorescence detection had been shown to be applicable to the
determination of aluminium in acidified standards prepared
in Milli-Q water. Previous work by us has shown that IDAS
can be successfully applied to the analysis of samples with a
complex matrix but it had not yet been used for the detection
of aluminium in seawater. Seawater is difficult to analyse not
only in terms of the high salt content, but also due to the
number of other potentially interfering ions, such as iron and
magnesium. However, preliminary chromatograms showed
no co-elution problems and there was only one additional
peak (at ~ 8 min) other than aluminium. Based on previous
findings this peak is likely to be due to iron and/or a mixture
other analytes e.g. sodium and calcium.
Calibration of the system using a 500 µl sample loop
was carried out by means of standard addition to an Antarctic
seawater sample containing low levels of aluminium. The
limit of detection was determined from the standard deviation
of clean seawater and determining the signal equivalent to
three times this value (i.e. 3σ). A LOD of 0.39 nM was achieved
using a 500 µl sample loop. Good linearity of the system
was observed between 1.8 and 36 nM.
Chromatograms of Antarctic seawater for different injection
volumes are given in Fig. 3.
s322
Fig. 3. Chromatogram of Antarctic seawater for different injection
volumes
Conclusions
The optimised HPCIC system with fluorescence detection
of the aluminium-lumogallion complex shows
promise for the quantification of aluminium in Antarctic
seawater. The IDAS chromatographic column does not suffer
from issues such as co-elution of species with aluminium and
produces peaks of good efficiency in a reasonable timescale.
The response of the system to standard addition is linear and
is applicable over a concentration range valid to seawater
analysis. Additionally, the LOD achievable with the system
means it should be capable of handling the low concentrations
of aluminium expected in Antarctic seawater.
At this stage, the system has not been successfully
applied to the quantification of aluminium in a seawater
sample. The method currently suffers from an enhanced
fluorescent response most likely due to matix interferences
of seawater. It is difficult to determine the extent of this
enhancement since there is not a certified seawater reference
material for aluminium; but it is believed that, at present, the
system produces a response approximately three times higher
than the true value. Studies are underway to eliminate
this problem and are currently focusing on the removal or
adequate separation of aluminium from the remainder of the
seawater matrix.
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