216
Phytoplankton
both as oven-dried-only samples (sonifier method), and after ashing them (ashing
method), the results reported in Table 9.2 are obtained.
These errors (which contain all the previous ones) are generally higher for samples
with a lower metal content; moreover, the variability is strongly enhanced for the
samples of smaller size. The comparison of the two methods demonstrates that the
ashing of the samples introduces some additional scattering, and the mean values are
generally lower with this method than for the dried-only samples (with the exception
of freshwater plankton samples). As the mass of particulate matter samples is generally lower than those used in this test, it is very likely that the variability of the sample
dissolution step introduces an even greater error than those estimated using the
reference materials.
Filtration reproducibility was estimated by fIltering sub-samples of candidate reference
material suspensions and Lake Maggiore water. From the data shown in Table 9.3, it is
evident that the fIltration yield (on a mass basis) is more variable when the particles are
larger. However, the removal of the larger particles by a pre-fIltration step significantly
reduces the mass of particulate matter collected on the fIlters, and the subsequent
analyses have a proportionally higher bias as the sample signal decreases.
Table 9.2
ReprodUcibility of sample dissolution for different materials and differenc sample sizes
(from [625])
Fe
Mn
Cu
Cr
Zn
A. Ashing method - Platihypnidium riparioides
2000 mg X ppm
9480
3900
660
550
640
RSD, %
5
1
11
4
10 mg ppm
7080
3470
640
520
700
RSD, %
7
4
2
9
16
Olea europea
2000 mg X pm
340
57
50
20
RSD,%
1
16
Lagarosiphon major
200 mg X ppm
2300
1800
50
40
410
RSC, %
3
3
2
2
2
Freshwater plankton
10 mg X ppm
3800
250
40
70
RSD,%
9
6
5
7
B. Sonifier method -
Platihypnidium riparioides
200 mg X ppm
9720
4170
690
630
640
RSD,%
3
2
Olea europea
200 mg X ppm
340
60
50
20
RSD,%
2
3
3
7
Lagarosiphon major
200 mg X ppm
2430
1880
50
40
360
RSD, %
3
Freshwater plankton
10 mg X ppm
3700
230
40
60
RSD, %
5
16
19
25
a X = mean
b RSD = relative standard deviation
Phytoplankton
both as oven-dried-only samples (sonifier method), and after ashing them (ashing
method), the results reported in Table 9.2 are obtained.
These errors (which contain all the previous ones) are generally higher for samples
with a lower metal content; moreover, the variability is strongly enhanced for the
samples of smaller size. The comparison of the two methods demonstrates that the
ashing of the samples introduces some additional scattering, and the mean values are
generally lower with this method than for the dried-only samples (with the exception
of freshwater plankton samples). As the mass of particulate matter samples is generally lower than those used in this test, it is very likely that the variability of the sample
dissolution step introduces an even greater error than those estimated using the
reference materials.
Filtration reproducibility was estimated by fIltering sub-samples of candidate reference
material suspensions and Lake Maggiore water. From the data shown in Table 9.3, it is
evident that the fIltration yield (on a mass basis) is more variable when the particles are
larger. However, the removal of the larger particles by a pre-fIltration step significantly
reduces the mass of particulate matter collected on the fIlters, and the subsequent
analyses have a proportionally higher bias as the sample signal decreases.
Table 9.2
ReprodUcibility of sample dissolution for different materials and differenc sample sizes
(from [625])
Fe
Mn
Cu
Cr
Zn
A. Ashing method - Platihypnidium riparioides
2000 mg X ppm
9480
3900
660
550
640
RSD, %
5
1
11
4
10 mg ppm
7080
3470
640
520
700
RSD, %
7
4
2
9
16
Olea europea
2000 mg X pm
340
57
50
20
RSD,%
1
16
Lagarosiphon major
200 mg X ppm
2300
1800
50
40
410
RSC, %
3
3
2
2
2
Freshwater plankton
10 mg X ppm
3800
250
40
70
RSD,%
9
6
5
7
B. Sonifier method -
Platihypnidium riparioides
200 mg X ppm
9720
4170
690
630
640
RSD,%
3
2
Olea europea
200 mg X ppm
340
60
50
20
RSD,%
2
3
3
7
Lagarosiphon major
200 mg X ppm
2430
1880
50
40
360
RSD, %
3
Freshwater plankton
10 mg X ppm
3700
230
40
60
RSD, %
5
16
19
25
a X = mean
b RSD = relative standard deviation