滋賀大学教育学部紀要
人文科学・社会科学・自然科学
67
No. 62, pp. 67-76, 2012
Determination of Total Dissolved Aluminum
in Seta River Water by Flow Injection Fluorometry with
Aluminum-Lumogallion Complex after Acid Digestion
Hirokazu HARA*, Sakura OKUNI, Yosuke KOEBISU
and Naomichi NISHIKAWA
Faculty of Education, Shiga University, Otsu, Shiga 520-0862, Japan.
Abstract
The total dissolved aluminum in the Seta River water was determined by flow-injection fluorometry
using the aluminum-lumogallion complex after its digestion by a mixture of nitric acid and hydrofluoric
acid. The sample decomposition system, which was hard to be contaminated by aluminum from the air,
was constructed and used successfully to produce reproducible values. By subtracting the concentration
of dissolved reactive aluminum, the concentration of the non-reactive aluminum was estimated. The
concentration change in the total dissolved aluminum from the Seta River water for one year was
reported, together with that of the dissolved reactive aluminum. The concentration of total dissolved
aluminum was usually between 0.2 and 0.5 μM, however, it increased to 1.87 μM after typhoon no. 12 of
2011 has passed through the Shiga prefecture. Unexpectedly, hydrofluoric acid was not necessary for the
complete decomposition of the aluminum species in the Seta River water. However, hydrofluoric acid
was indispensable for the complete recovery of aluminum from a clay mineral, i. e., montmorillonite. We
found that even the small amount of fluoride (about the same concentration as that originally present in
Seta River water) was effective for the decomposition of the montmorillonite. The determined values of
the total dissolved aluminum showed a good correlation to the results obtained from GFAAS.
Keywords : Seta River water, dissolved aluminum, fluorometry, lumogallion, acid digestion
Aluminum is the most abundant metal
Thus, the speciation of aluminum in water has
element in the earthʼs crust. It is well known
been the subject of research in the field of
that aluminum is toxic to the human nervous
analytical chemistry and environmental chem-
system when it enters the human brain through
istry [3, 4].
the Brain Blood Barrier [1].
The toxicity
The largest lake in Japan, Lake Biwa, is
depends on its chemical form. The monomeric
located in the Shiga prefecture. The lake water
aluminum ion Al3+ is believed to be more toxic
is the source of drinking water for Otsu City
than the Al complex with organic ligands [2].
and other cities in the Shiga prefecture. The
speciation of aluminum in Lake Biwa has been
* Corresponding author : Fax+81 077 537 7840.
E-mail address : [email protected]
studied [5, 6]. Hori et al. reported that the
seasonal variation in the concentration of
68
Hirokazu HARA, Sakura OKUNI, Yosuke KOEBISU and Naomichi NISHIKAWA
dissolved reactive aluminum in Lake Biwa
We tried to precisely measure the concentra-
water and also the correlation of the concentra-
tion of dissolved non-reactive aluminum in the
tion were relatively high versus the pH
Seta River water.
measured one month before sampling [5, 6].
concentration of the total dissolved aluminum
The dissolved total aluminum concentration did
should be precisely measured, because the
not show such a clear seasonal variation as that
concentration of dissolved non-reactive alumi-
of the dissolved reactive aluminum [5].
num was determined by subtracting the
For this purpose, the
The lake water flows out from the Seta River.
concentration of dissolved reactive aluminum
We have been examined the concentration
from that of the total dissolved aluminum. The
change in the dissolved aluminum in the Seta
total dissolved aluminum could be measured by
River water and also found its seasonal
GFAAS, however, its precision is not very good
variation, i. e., high in the summer and low in the
for the precise determination of the dissolved
winter [7, 8], as was reported previously for
non-reactive aluminum [9].
Lake Biwa [5, 6]. The seasonal variation in the
In this study, we developed a sample
concentration of the dissolved aluminum corre-
decomposition system, in which the acid-
sponded well with that of the pH on the
digestion of the Seta River water samples could
sampling day of the Seta River water [7].
be done without contamination. The concentra-
We noticed that the concentration of dissolved
aluminum
measured
by
tion of aluminum after acid digestion was
GFAAS
determined by the FIA method, because of its
(Graphite Furnace Atomic Absorption Spec-
high precision. The experimental conditions of
troscopy) was usually higher than that meas-
the acid digestion were examined in detail.
ured by flow injection fluorometry using the
aluminum-lumogallion complex [9]. The differ-
Experimental
ence means the existence of non-reactive
aluminum with the complexing agent, lumogal-
Reagents and solutions. Ultrapure water
lion, in the FIA short time scale. We also
was prepared from once-distilled water using a
compared the concentration of dissolved reac-
Millipore Simplicity UV system.
tive aluminum with the FIA method and batch
nitric acid (ca. 14.9 M (1 M=1 mol/L)) and
method in which the reaction temperature and
hydrofluoric acid (ca. 27 M) were purchased
time were higher and longer than the FIA
from Tama Chemicals (Kanagawa, Japan) as
method, respectively [10]. Although a slightly
Tamapure AA-100. Calcium nitrate tetrahy-
higher concentration was observed with the
drate (Cat. no. C4955, SigmaUltra) was pur-
batch method, the difference was very small, at
chased from Sigma (St. Louis, MO, USA). The
least measured on the sampling day. This
carrier solution was a 0.015 M calcium nitrate
Ultrapure
result means that the concentration difference
solution, of which the pH was adjusted to 4.0 by
between the FIA and GFAAS is caused not by
adding 0.1 M nitric acid. (This eluent was first
the difference in the reaction time but by the
used by Sutheimer and Cabaniss in order to
fact that non-reactive aluminum with lumogal-
separate aluminum species in acidic lake water
lion really existed in the Seta River water, even
using a cation-exchange resin column [11].
after filtering using 0.45 μm membrane filter.
The divalent calcium ion was added to promote
Hori et al. reported that the concentration of the
the eluting capability.) The post-column re-
non-reactive aluminum in the southern part of
agent solution was 0.05 mM lumogallion
Lake Biwa was usually in the range of 0 to 0.4
(Tokyo Chemical Industry, Tokyo, Japan)
μM [5].
dissolved in 0.2 M acetate buffer (pH 5.2).
Determination of Total Dissolved Aluminum in Seta River Water
Acetic acid (Cat. no. 01021-1B, for the atomic
69
ic bath for 60 min [12].
absorption spectrometry) was purchased from
All other chemicals were of analytical
Kanto Chemical Co., Ltd. (Tokyo, Japan). Its
reagent grade obtained from Nacalai tesque
aluminum concentration was certified to be
(Kyoto, Japan).
below 0.01 mg/kg.
A stock aluminum standard solution (10−2
M) was prepared by dissolving 0.4744 g of
AlK (SO4)2･12H2 O into 0.1 dm
−3
−3
of 10
Apparatus. Fig. 1 is a schematic diagram of
the FIA system.
The basic scheme was
M
developed by Sutheimer and Cabaniss [13]. A
nitric acid. This standard solution was diluted
Shimadzu LC-10AD double-plunger type chro-
to 10−4 M from which the final standard solu-
matographic pump was used to deliver the
tions of 0-1 μM aluminum were prepared. The
calcium nitrate carrier solution. The sapphire
pH of the standard solutions was adjusted to 3.0
plungers were replaced by zirconia ceramic
by adding 0.1 M nitric acid for the determina-
plungers in order to decrease the possibility of
tion of the dissolved reactive aluminum and to
aluminum elution from the pump. The flow
2.0 for the determination of total dissolved
rate of the carrier solution was set at 0.9 mL
aluminum. These solutions were kept in the
min−1. Dissolved gases were removed by a
plastic volumetric flasks after their preparation.
degassing unit (DEGASYS DG1210) produced
The buffer capacity of the acetate buffer was
by Uniflows Co., Ltd. (Tokyo, Japan).
so high that the pH after mixing with pH 3 Al
In order to remove the residual aluminum
standard solutions or river water samples was
ions from the carrier solution, a precolumn of
confirmed to be 5.2.
TSK-gel on which 8-quinolinol was covalently
The standard sample of montmorillonite
fixed, was placed before the injection valve.
(JCSS-3101) was purchased from the Clay
The TSK-gel (TOYOPEARL HW-65F) was
Science Society of Japan. The size distribution
purchased from Tosoh (Tokyo, Japan). The
was 0.02-0.2 μm and 0.3-5 μm [12]. It was
chelating resin was prepared by a method
reported that the size distribution became
reported by Landing et al. [14]. This column
0.01-0.04 μm after the treatment in an ultrason-
was occasionally washed with 0.1 M HNO3 in
Fig. 1
Schematic diagram of flow injection system. Eluent : 0.015M Ca (NO3)2 adjusted to pH 4 by HNO3,
Lumogallion : 0.05 mM lumogallion dissolved in 0.2 M acetate buffer (pH 5.2)
70
Hirokazu HARA, Sakura OKUNI, Yosuke KOEBISU and Naomichi NISHIKAWA
order to recover its capability. (For the
reactive aluminum without any contamination,
efficient removal of the residual aluminum in
PTFE
the carrier solution, it is desirable that its pH
were constructed and used. Fig. 2 shows the
should not be too acidic.)
front view of the vessel. The vessel consists of
(poly (tetrafluoroethylene))
vessels
A stainless steel injection valve (Rheodyne
two parts. The upper part has a side pipe from
(IDEX Health & Science, WA, USA) Model
which the water and acid vapor went out. The
7010) was used. The rotor seal was Tefzel. A
lower part was screwed into the upper part.
0.5 mL PEEK (poly(ether-ether-ketone)) loop
The gap was closed with an O-ring made of
(Parts. No. 9055-026) was used for flow-injec-
fluorine rubber.
tion method.
diagram of the decomposition system. Ten
Fig. 3 shows a schematic
A peristaltic pump (ATTO Co., Tokyo,
vessels were put on a steel tray, in which five
Japan, Model SJ1211H) was used to deliver just
vessels were placed side by side on both sides of
1 mL of a sample solution into the 0.5 mL
the tray. The side pipe of the vessel was
sample loop at the flow rate of about 1.8-1.9 mL
located on the side part of the stainless steel
−1
min
[15].
cover and connected using a PFA (copolymer
A single plunger pump (Nihon Seimitsu
of tetrafluoroethylene and perfluoroalcoxyethy-
Kagaku Co., Ltd., Tokyo, Japan, Model SP-T-
lene) tube. (Some of the side pipes were wound
2501U) was used to deliver the lumogallion
with a thin copper film in order to cool the hot
solution. The pulse was effectively damped
vapor coming from the vessel.) The steel tray
using a damper (GL Science, Tokyo, Japan,
was placed on a hotplate. The temperature of
Model HPD-2). The flow rate was fixed at 0.4
the steel tray was controlled by a temperature
−1
mL min
. A back-pressure coil was prepared
controller. The harmful vapors of the nitric and
using a PTFE (poly(tetrafluoroethylene)) tube
(0.2 mm i. d., and 2 m long).
Two PEEK mixing coils (0.5 mm i. d., 5 m
long) were used, the first maintained at 60℃ in
a water bath, while the second remained at
room temperature. PEEK tubing of 0.5 mm i. d.
was mainly used in the entire system, otherwise
PTFE tubing was used.
The fluorescence was detected by a JASCO
(Nihonbunkou, Tokyo, Japan) FP2025 detector
equipped with a 150 W Xenon lamp, a 16 μL
quartz flow cell, and a photomultiplier tube.
The excitation and emission wavelengths were
500 and 595 nm, respectively. The detector
signals were transmitted every 0.5 s and recorded by a microcomputer using JASCO
ChromNAV software. It took 10 min for the
measurement of one sample. Three reasonable
results were selected and the average was
calculated after several repeated measurements.
In order to decompose the dissolved non-
Fig. 2
A front view of the PTFE vessel used for the
decomposition
The vessel was made from a PTFE rod (30mm diameter). A PTFE pipe was screwed
into the upper part after binding the end part
with a thin PTFE seal tape at an angle of 30
degrees. The lower part had threads which
was connected to the upper part. A PTFE Oring was used in order to stop acid vapors
from leaking from the sample solution during
heating. The sample solutions were filled in
the lower part by a micropipette.
Determination of Total Dissolved Aluminum in Seta River Water
71
was used for the wall atomization. Argon gas of
99.99% purity was used.
The instrumental
conditions were the same as stated in a
previous paper [8]. Magnesium nitrate solution (1000 ppm) without nitric acid was used as
the matrix modifier. When the concentration of
total dissolved aluminum was about 0.5 μM or
higher, the wavelength was changed to 396.2
nm in order to decrease the sensitivity to one
half that of 309.3 nm [9].
Sampling of river water. Sampling was
carried out on the river side (E. L. : 135.91°,N.
L : 34.95°) of the Seta River, about 3.5 km from
the boundary between Lake Biwa and the Seta
River. The air and water temperatures were
measured. The sampled water was brought
back to the laboratory within 15 min and was
filtered using a polysulfone funnel equipped
Fig. 3
Schematic diagram of the sample decomposition system. Front and top views are shown.
The reaction vessels were stored in the steel
container. A sample solution in the vessel in
Fig. 2 was heated to ca. 98℃ by a hot plate. A
laboratory-made aspirator was used to wash
the acid vapor. The acid vapor was first
absorbed by the 0.1 M NaOH solutions and
then 10 M NaOH solutions. Air was filtered
through a 0.2 μm membrane filter in order to
prevent any unexpected contamination.
with a 0.45 μm cellulose acetate membrane
filter (Type HAWP, Millipore, MA, USA) in
order to remove any suspended particulate
matter. For the measurement of the dissolved
reactive aluminum, the filtrate was delivered to
the injection loop without any further treatment. Measurements were sequentially done
several times and the average of three reasonable values was calculated.
hydrofluoric acids formed during the decompo-
Determination of total dissolved aluminum
sition process, were first dissolved into a 0.1 M
by acid digestion
NaOH solution and then neutralized by passing
Four milliliters of Seta River water was
through a 10 M NaOH solution. A laboratory-
placed in the reaction vessel after filtration. A
made aspirator in which water was circulated,
0.4 mL aliquot of nitric acid and 0.2 mL of
was used to remove the vapor. Filters in the
hydrofluoric acid were added, unless otherwise
figure were Milex FG filter units (SLFG 05010,
noted. Five of the ten vessels were used for the
pore size : 0.2 μm) purchased from Merk-
determination of the acid blank, i. e., the same
Millipore.
amount of acids were added to 4 mL of
The GFAAS measurement was performed
ultrapure water. They were heated to 98℃
along with the measurement of dissolved
until all of the sample solutions were completely
reactive aluminum on the sampling day. A
dried. It took 3 to 4 days until the heating
Model Z5710 Hitachi polarized Zeeman graph-
process was finished.
ite furnace atomic absorption spectrometer was
After cooling the vessels, the residue was
used. A pyrolytic graphite cuvette (type A)
dissolved in 0.4 mL of 0.1 M nitric acid, and then
72
Hirokazu HARA, Sakura OKUNI, Yosuke KOEBISU and Naomichi NISHIKAWA
3.6 mL of ultrapure water was added to the
were then added to the residue and heated
vessel. The vessel was put into warm water at
again, because the decomposition efficiency was
about 50℃ for 25 min, then immersed in an
expected to be higher than that when these
ultrasonic bath for 5 min in order to promote
acids were initially added.
the complete dissolution of the aluminum. The
reproducibility of five determinations was so
concentration of dissolved aluminum was
poor that this method was concluded to be
measured by the FIA system described above.
inappropriate. Thus, these acids were added
However, the
from the beginning.
Determination of aluminum in montmorillonite
We first examined the effect of the quantity
A 100 mg sample of the standard montmoril-
of nitric acid as shown in Fig. 4. The dissolved
lonite powder was dispersed in 100 mL of
aluminum concentration became almost con-
ultrapure water. This solution was placed in an
stant when 200 μL to 400 μL of nitric acid was
ultrasonic bath for 2 hours, then diluted to
added to 4 mL of the filtered sample solution.
1/10000 by two dilutions of 1 mL to 100 mL.
We concluded that 400 μL of nitric acid was
The diluted solution was filtered through a 0.45
enough for the complete recovery of the
μm membrane filter.
dissolved aluminum.
Three milliliters of the filtered solution was
We next examined the effect of the quantity
placed in the decomposition vessel and 300 μL
of hydrofluoric acid as shown in Fig. 5.
of nitric acid was added. Hydrofluoric acid (150
Unexpectedly, the dissolved aluminum concen-
μL) was also added to 4 of the 10 vessels and
tration was almost constant irrespective of the
not to 4 vessels for the sake of comparison.
quantity of added hydrofluoric acid. It was
Last two vessels were used to estimate the acid
confirmed that non-reactive aluminum was
blanks. The aluminum in the montmorillonite
contained in dissolved aluminum, because the
was measured after the same decomposition
determined value of the total dissolved alumi-
process as that applied to the Seta River water.
num was always higher than that of the
In order to examine the effect of fluoride, a
dissolved reactive aluminum. If aluminosilicate
small amount of sodium fluoride solution was
added to the filtered montmorillonite solution,
so that the fluoride concentration was about the
same as that present in Seta River water (about
0.1 mg/L all year round) [16, 17]. The aluminum in the montmorillonite solution with and
without fluoride was then measured.
The
results were compared to that of the complete
elution obtained by adding hydrofluoric acid
(150 μL).
Results and Discussion
Decomposition conditions of Seta River water
During the beginning of the decomposition
experiment, a Seta River water sample was
first acidified to pH 4 with nitric acid and dried
by heating. The nitric and hydrofluoric acids
Fig. 4
Effect of the quantity of nitric acid on the
determination of total dissolved aluminum in
4 mL of Seta River water sampled on Oct. 10,
2011. Hydrofluoric acid was not added. The
blank aluminum contained in the nitric acid
was not subtracted from the measured
concentration of the total dissolved aluminum.
Determination of Total Dissolved Aluminum in Seta River Water
73
non-reactive aluminum.
It was reported that the suspended matter in
Lake Biwa consisted of phytoplankton and
microparticles of terrigenous origin, including
clay minerals [18]. It is reasonable to suppose
that some of the microparticles smaller than
0.45 μm are aluminosilicate clay minerals, and
therefore contained in the filtered Seta River
water samples.
Decomposition conditions of montmorillonFig. 5
Effect of the quantity of hydrofluoric acid on
the determination of total dissolved aluminum
in 4 mL of Seta River water sampled on Sept.
20, 2011. Nitric acid was added (400 μL). The
blank aluminum contained in the acids was
not subtracted from the measured concentration of the total dissolved aluminum.
ite solution.
In order to verify that the aluminosilicate
clay mineral can be completely decomposed
without hydrofluoric acid, the typical aluminosilicate, i. e., montmorillonite, was decomposed
after being dispersed in the water and filtered
through a 0.45 μm membrane filter. First, it
was confirmed that montmorillonite hardly
dissolved in ultrapure water, since the dissolved
reactive aluminum concentration before decomposition was about 0.006 μM.
The total dissolved aluminum concentration
after decomposition was 0.23 μM±0.011 μM
(n=4) with hydrofluoric acid, and 0.19 μM±
0.0046 μM (n=4) without hydrofluoric acid.
The quantity of the hydrofluoric acid, i. e., 150
μL in 3 mL of the sample solution, was confirmed to be sufficient for the complete decom-
Fig. 6
Effect of the quantity of hydrofluoric acid on
the determination of total dissolved aluminum
in 4 mL of Seta River water sampled on Sept.
05, 2011. Nitric acid was added (400 μL). The
blank aluminum contained in the acids was
not subtracted from the measured concentration of the total dissolved aluminum.
position of the montmorillonite microparticles
as shown in Fig. 7. Although about 80% of the
montmorillonite microparticles was decomposed by only heating with nitric acid, it was
confirmed that hydrofluoric acid was indispensable to completely decompose the aluminosili-
particles smaller than 0.45 μm are the main
cate particles ; even its size was less than 0.45
portion of the non-reactive aluminum, hydro-
μm.
fluoric acid should be added in order to
Apparently, this result was inconsistent with
decompose them. The effect of hydrofluoric
that of the Seta River water. In order to solve
acid was again examined with the sample
this inconsistency, the effect of a small amount
having a very high concentration of dissolved
of fluoride (which was about the same concen-
aluminum as shown in Fig. 6. The addition of
tration as present in Seta River water) on the
hydrofluoric acid seems to be unnecessary
montmorillonite decomposition, was examined
again for the complete decomposition of the
by adding a sodium fluoride solution.
The
74
Hirokazu HARA, Sakura OKUNI, Yosuke KOEBISU and Naomichi NISHIKAWA
addition of hydrofluoric acid is concluded to be
due to the fact that the fluoride present in Seta
River water was sufficient.
However, hydrofluoric acid was added to
ensure the complete decomposition of the
aluminosilicates in the microparticles in the
Seta River water.
Speciation of dissolved aluminum in Seta
River water for one year.
We divided the dissolved aluminum in the
Seta River water into two types, i. e., dissolved
Fig. 7
Effect of the quantity of hydrofluoric acid on
the decomposition of non-reactive aluminum
in the montmorillonite solution. The volume
of the sample solution was 3 mL. The blank
aluminum contained in the acids was not
subtracted from the measured concentration
of the total dissolved aluminum.
reactive aluminum and dissolved non-reactive
aluminum, which was obtained as the difference
of the former from the total dissolved aluminum. Fig. 8 shows the temporal variation in the
dissolved aluminum in the Seta River water
from September, 2011 to September, 2012. The
average aluminum concentrations in the mont-
data of water temperature etc. are shown in
morillonite solutions with and without sodium
Table 1. Unfortunately, a reliable value of the
fluoride were 0.295±0.027 μM and 0.259±
sample pH was not available.
0.0098 μM (acid blank was not subtracted).
The seasonal variation in the concentration of
The difference was statistically significant
dissolved reactive aluminum, i. e., high in the
(p<0.05). It was concluded that the decompo-
summer and low in the winter, was observed as
sition of montmorillonite was promoted when
reported in a previous paper [7, 8]. However,
the small amount of fluoride was present in the
such a clear seasonal variation was not
solution.
observed for the non-reactive aluminum. On
Thus, the reason why aluminum in the
the contrary, the concentration of the non-
microparticles contained in the Seta River
reactive aluminum was usually within the
water was completely eluted without the
narrow range, 0.1-0.2 μm and occasionally
Fig. 8
Concentration change of dissolved aluminum in Seta River water for one year.
Determination of Total Dissolved Aluminum in Seta River Water
Table 1
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Data of Seta River water samples used for
the total dissolved aluminum analysis
Sampling
date
Sept.
Sept.
Sept.
Oct.
Nov.
Nov.
Dec.
Jan.
Feb.
Feb.
Mar.
Mar.
Apr.
May
June
July
July
Aug.
Sept.
75
5,
12,
20,
10,
7,
21,
12,
9,
20,
27,
5,
19,
9,
7,
11,
2,
30,
21,
10,
2011
2011
2011
2011
2011
2011
2011
2012
2012
2012
2012
2012
2012
2012
2012
2012
2012
2012
2012
Water
Air
Sampling
temperature temperature
time
/℃
/℃
h : min
10 : 06
10 : 32
11 : 05
10 : 29
9 : 53
9 : 12
10 : 20
9 : 48
10 : 05
8 : 56
9 : 15
9 : 06
9 : 28
9 : 04
9 : 03
9 : 10
9 : 15
9 : 20
8 : 30
26.8
33.7
23.0
23.3
18.7
12.8
11.0
7.5
8.7
7.9
9.2
7.5
18.0
17.5
26.5
27.5
34.2
30.0
30.8
24.8
25.0
27.1
18.1
19.1
15.5
11.8
7.6
6.6
3.2
9.0
9.4
9.8
16.1
20.8
23.6
27.0
28.1
28.0
Fig. 9
Correlation of the total dissolved aluminum
measured by FIA fluorometry after acid
digestion and GFAAS. Unit of concentration
is μM.
became high due to the large amount of rainfall
the GFAAS was rather poor, thus it cannot be
in the Shiga prefecture before the sampling day.
used for a precise measurement [8]. However,
An extremely high concentration of dissolved
the correlation with the FIA measurement
non-reactive aluminum found on September 5,
results after acid digestion was good (r>0.90)
2011, was due to typhoon no. 12 which produced
as shown in Fig. 9, because the variation in the
a high amount of rainfall for several days before
concentration of the total dissolved aluminum
the sampling throughout the Shiga prefecture.
was high enough. (The data obtained on
Over 400 rivers flow into Lake Biwa. When the
September 5, 2011 was omitted, because the
typhoon reached the Shiga prefecture, an
data was too high to obtain a reliable data with
enormous amount of sediment from these
GFAAS.)
rivers flowed into Lake Biwa and then went
Conclusion
into the Seta River.
An exceptionally high concentration (0.231
μM) of dissolved reactive aluminum on Feb. 20
In order to precisely determine the concen-
was observed. It had snowed two days before
tration of the non-reactive aluminum in the Seta
sampling even in Otsu City. This snow fall
River water, flow-injection fluorometry was
might affect the concentration of dissolved
used because of its high precision.
reactive aluminum.
precision of the determination mainly depended
The
The relative standard deviation of the four or
on the reproducibility of the decomposition
five total dissolved aluminum values was in the
process, not on the final determination method.
range between 1.3% and 5.3%, with some ex-
For the purpose of improving the reproducibil-
ceptions. The blank value was 0.04 μM on ave-
ity, we developed a special decomposition
rage with the standard deviation of ±0.01 μM.
system in which the contamination of aluminum
from the air and surrounding environment was
Correlation of the result with GFAAS.
The total dissolved aluminum was also
measured by GFAAS. The reproducibility of
minimized. The vessels were slowly heated
below 100℃ so that the explosive boiling was
avoided.
Thus, reproducible results were
76
Hirokazu HARA, Sakura OKUNI, Yosuke KOEBISU and Naomichi NISHIKAWA
obtained, although the time needed for the
evaporation process was very long.
We examined the concentration of the nonreactive aluminum in the Seta River water for
almost one year. It was found that the concentration of the non-reactive aluminum in the
Seta River water did not show a clear seasonal
variation, which was observed for the concentration of reactive aluminum. Occasionally, it
became high as a result of the weather
conditions such as a typhoon and/or long and
hard rainfall.
Further study will be necessary to elucidate
the chemical composition (s) of the non-reactive aluminum in Seta River water.
Acknowledgement
A part of this work was financially supported by
the Shiga University in 2011. Some of the data of
dissolved reactive aluminum were taken by Hiroko
Okuda who was a student in our laboratory in 2011.
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