volume cell at the right height (see Fig. 1). The latter may be
replaced by any adequate thickness of a plastic material.
A dramatic change in the purging procedure and time was an
unexpected outcome of the reduction in sample volume. Preliminary
experiments showed that the purging procedure could be extremely
simplified: the purge tubing entering the sample was removed and
nitrogen blown into the headspace from the lid covering the standard
cell. The possibility to purge the headspace only is due to the high
surface/volume ratio of the sample, being the sample height and
diameter 1.6 mm and 20 mm, respectively. This feature ensures a fast
diffusion of the gases to and from the sample volume: actually, early
experiments in which the purge time was systematically changed
demonstrated that 150 s are enough to achieve a satisfactory baseline
with negligible changes observed for longer purge time. A two-fold
reduction in the purge time was accordingly achieved with respect to
the normal 300 s required by the 10 mL sample. For copper determinations,
an even lower 120 s purge time could be used: a slightly
higher baseline was registered although it did not interfere with the
determinations.
The procedure to transfer the sample to and from the cell is the
last modification introduced to the standard procedure. The
removal of the sample was performed by a 100–1000 μL micropipette,
ensuring a faster and more reliable procedure. Higher,
random blanks were conversely obtained when the sample was
poured out of the cell as usually done: actually, incomplete sample
removal and/or contact of the specimen with the rims of the cell
could lead to contamination.
3.2. Freshwater
data refers to triplicate readings of the same sample (i.e. it is an
estimate of the short term repeatability).
No statistically significant difference was evidenced for all of
the sample and analytes but in four cases (two tailed t test,
p¼0.05). Three of these differences were lower than 25% (or
0.1 μg/L in absolute figures), whereas the difference in nickel
concentration in sample 5 was highly significant and possibly
due to the contamination of the aliquot used for AdSV.
volume cell at the right height (see Fig. 1). The latter may be
replaced by any adequate thickness of a plastic material.
A dramatic change in the purging procedure and time was an
unexpected outcome of the reduction in sample volume. Preliminary
experiments showed that the purging procedure could be extremely
simplified: the purge tubing entering the sample was removed and
nitrogen blown into the headspace from the lid covering the standard
cell. The possibility to purge the headspace only is due to the high
surface/volume ratio of the sample, being the sample height and
diameter 1.6 mm and 20 mm, respectively. This feature ensures a fast
diffusion of the gases to and from the sample volume: actually, early
experiments in which the purge time was systematically changed
demonstrated that 150 s are enough to achieve a satisfactory baseline
with negligible changes observed for longer purge time. A two-fold
reduction in the purge time was accordingly achieved with respect to
the normal 300 s required by the 10 mL sample. For copper determinations,
an even lower 120 s purge time could be used: a slightly
higher baseline was registered although it did not interfere with the
determinations.
The procedure to transfer the sample to and from the cell is the
last modification introduced to the standard procedure. The
removal of the sample was performed by a 100–1000 μL micropipette,
ensuring a faster and more reliable procedure. Higher,
random blanks were conversely obtained when the sample was
poured out of the cell as usually done: actually, incomplete sample
removal and/or contact of the specimen with the rims of the cell
could lead to contamination.
3.2. Freshwater
data refers to triplicate readings of the same sample (i.e. it is an
estimate of the short term repeatability).
No statistically significant difference was evidenced for all of
the sample and analytes but in four cases (two tailed t test,
p¼0.05). Three of these differences were lower than 25% (or
0.1 μg/L in absolute figures), whereas the difference in nickel
concentration in sample 5 was highly significant and possibly
due to the contamination of the aliquot used for AdSV.
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