A Fluorescent Chemosensor Based on Schiff Base for the Determination of Zn2+, Cd2+and Hg2+

Article abstract of DOI:10.1007/s10895-020-02563-6

Metal complexes were obtained by the reaction of zinc, cadmium and mercury(II) salts with Schiff base HL (N(salicylidene)benzylamine). HL was synthesized by the condensation reaction of benzylamine and 2-hydroxybenzaldehyde. The fluorescence properties of the Schiff base and its metal complexes were studied in ethanol-water solutions. HL was examined for its utility as a fuorescent chemosensor for the determination of Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous samples. The HL chemosensor was found to be sensitive to Zn²⁺, Cd²⁺ and Hg²⁺ than some metal ions and its complexes emitted strong fluorescence at 452 nm for Zn²⁺ at 474 nm for Cd²⁺ and at 491 nm for Hg²⁺, respectively. It was determined that HL forms complexes with a ratio of 2:1 for Zn²⁺ and Hg²⁺ and with a ratio of 1:1 for Cd²⁺ by Job plots. For the detection of Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous samples, pH, solvent type and ligand concentration were optimized for an analytical method based on HL chemosensor. HL gave a wide range of linearity with Zn²⁺, Hg²⁺ and Cd²⁺, the limit of detection was found to be 2.7 × 10^-7 M, 7.5 × 10^-7 M and 6.0 × 10^-7 M, respectively.

Full text of DOI:10.1007/s10895-020-02563-6

Journal of Fluorescence
https://doi.org/10.1007/s10895-020-02563-6
ORIGINAL ARTICLE
A Fluorescent Chemosensor Based on Schiff Base
for the Determination of Zn2+, Cd2+and Hg2+
E. K. İnal1
Received: 23 February 2020 /Accepted: 25 May 2020
#
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Metal complexes were obtained by the reaction of zinc, cadmium and mercury(II) salts with Schiff base HL
(N(salicylidene)benzylamine). HL was synthesized by the condensation reaction of benzylamine and 2-hydroxybenzaldehyde.
The fluorescence properties of the Schiff base and its metal complexes were studied in ethanol-water solutions. HL was examined
for its utility as a fuorescent chemosensor for the determination of Zn2+, Cd2+ and Hg2+ in aqueous samples. The HL
chemosensor was found to be sensitive to Zn2+, Cd2+ and Hg2+ than some metal ions and its complexes emitted strong
fluorescence at 452 nm for Zn2+ at 474 nm for Cd2+ and at 491 nm for Hg2+, respectively. It was determined that HL forms
complexes with a ratio of 2:1 for Zn2+ and Hg2+ and with a ratio of 1:1 for Cd2+ by Job plots. For the detection of Zn2+, Cd2+ and
Hg2+ in aqueous samples, pH, solvent type and ligand concentration were optimized for an analytical method based on HL
chemosensor. HL gave a wide range of linearity with Zn2+, Hg2+ and Cd2+, the limit of detection was found to be 2.7 × 10-7 M,
7.5 × 10-7 M and 6.0 × 10-7 M, respectively.
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Keywords Schiff base Transition metal complexes Fluorescent sensor Chemosensor Zn(II) Cd(II) Hg(II)
Introduction
applications in medical and environmental research fields,
their practical use, high sensitivity and accuracy, different
biological functions of targeted metal ions [12, 19–32].
Hence, many selective fluorescent chemosensors have
been developed for detecting transition metals [33–49].
Zinc, mercury and cadmium draw attention due to their
biological benefits or harm. However, selective determi-
nation of zinc, cadmium and mercury ions is difficult due
to the fact that they have a closed shell d10 electron con-
figuration [50–54].
Zinc exists naturally about 0.0075% in the Earth’s crust,
making it one of the most abundant elements [25–27, 38, 41,
43–45, 53, 55]. Zinc is one of the indispensable elements for
the metabolism of all living organisms due to its diverse roles
in many biological, physiological and pathological processes
[24, 39, 56–58]. Infertility, acrodermatitis, neuropsychiatric
disorders, breast and prostate cancer, digestive disorders and
sluggish immune system are clinically caused by zinc defi-
ciency [59].
In recent years, transition metal complexes produced
from Schiff base ligands have a wide field of study
because of their importance in coordination chemistry,
especially as analytical, biochemical and antimicrobial
reagents [1–6]. Schiff bases are compounds with
azomethine (-CH=N) groups and their complexes obtain-
ed with different transition metals often exhibit extraor-
dinary structural properties [7–10]. Many of the Schiff
base ligands and metal complexes are used as a model
for metal bioactive site modeling, metalloenzyme reac-
tion centers, nonlinear optical materials, homogeneous or
heterogeneous catalysts for many reactions and lumines-
cent materials [3, 7, 11–16].
The development of luminescent sensors is related to
supramolecular chemistry [17, 18]. Fluorescent sensors
have become an important research topic due to their
Mercury is one of the most dangerous pollutants that
can be found in the aquatic environment [60–62].
Mercury is toxic to human health, especially threatening
the development of fetuses and infants. Different forms of
mercury (elemental, inorganic and organic) have a
* E. K. İnal
inal@science.ankara.edu.tr
1
Department of Chemistry, Faculty of Science, Ankara University,
Ankara 06100, Turkey

J Fluoresc
different level of toxic effects on cardiovascular diseases,
infertility, kidney damage and cancer. Exposure to mercu-
ry occurs in different ways: inhalation of elemental mer-
cury vapors released in industrial processes, ingestion of
fish and shellfish that contain methylmercury, misuse and
excessive use of mercury-containing products such as skin
lighteners, fungicides, antiseptics [60, 63, 64].
Equipment, Australia). pH measurements were carried
out using Mettler Toledo pH-meter equipped with a com-
bined pH electrode.
Synthesis of Chemosensor
Among the various transition metals, cadmium requires
special attention due to its excessive toxicity in nature
[17, 33, 35, 61]. The United States Enviromental
Protection Agency (EPA) has determined that cadmium
is a probable human carcinogen. Due to anthropogenic
activities, its concentration in nature gradually increases
over time and once absorbed by a human, cadmium accu-
mulates in the human body throughout life [38, 44].
In this study, an ON type Schiff base ligand (E)-
2-((benzylimino)methyl)phenol has been synthesized and
it was investigated whether it can be used as a fluores-
cence chemosensor in the determination of Zn2+, Cd2+
and Hg2+ in aqueous samples. Although studies related
to the synthesis of (E)-2-((benzylimino)methyl)phenol
have been found in the literature, the investigation of the
fluorescent properties of metal complexes of this Schiff
base has been the subject of the study. Parameters affect-
ing the fluorescent properties of the prepared metal com-
plexes were examined and the most appropriate values
were determined. The results obtained in the study show
that the (E)-2-((benzylimino)methyl)phenol can be used
as a selective chemosensor for the Zn2+, Cd2+ and Hg2+
in aqueous solution.
HL was prepared by the 1:1 condensation of
salicylaldehyde with benzylamine (Fig. 1). To a stirred
solution of salicylaldehyde (2.44 g, 0.02 mole) in 50.0
mL of hot ethanol, benzylamine (2.14 g, 0.02 mole) in
25.0 mL of ethanol was added. The reaction mixture
was heated to the boiling point. After cooling, the Schiff
base crystals were filtered. The synthesized HL was
stored in the dark and at room temperature.
The interaction between HL and the metal ion takes
place with the covalent bond established on phenolic ox-
ygen and the coordination bond based on iminic nitrogen
[65, 66].
Fluorescence Studies
The stock solution of HL chemosensor was prepared at a
concentration of 3.0 × 10-3 M in ethanol. Metal ion stock
solutions of Zn2+, Cd2+, Hg2+, Fe3+, Ni2+, Cu2+ and Co2+ were
prepared at a concentration of 3.0 × 10-3 M in double distilled
water from their chloride or nitrate salts. Working solutions at
the desired concentration were prepared by diluting the stock
metal ion solutions in double distilled water and diluting HL
in ethanol.
Fluorescence spectra were recorded 40 minutes after
mixing an equivalent volume of metal ion solutions (3.0 ×
10-3 M) and HL (3.0 × 10-4 M) and excitation and emission
wavelengths were determined. HL-M (M: Zn2+, Cd2+ and
Hg2) complex formation stoichiometry was determined by
measuring the fluorescence intensities corresponding to the
varying molar fractions of HL.
Materials and Methods
Reagents and Instruments
Ethanol, methanol and acetone were purchased from
Sigma-Aldrich, N,N-dimethylformamide was purchased
from Riedel-de Haen and Zn(NO3)2.6H2O, HgCl2,
CdCl2, FeCl3.6H2O, CoCl2.4H2O, NiCl2.6H2O and
CuCl2.2H2O were purchased from Merck. All chemicals
and solvents were used without further purification.
Electron ionization mass spectra (EI-MS) were obtain-
ed using the direct inlet (DI) unit of the Shimadzu
QP2010 Plus gas chromatography-mass spectrometer
(Shimadzu, Japan). Ion source and interface temperature
were set at 200 °C. Fluorescence spectra measurements
were carried out using a PerkinElmer LS50B lumines-
cence spectrometer (PerkinElmer, USA). Excitation slit
and emission slit widths were set as 10 nm and 5 nm,
respectively. GBC Avanta flame atomic absorption spec-
trometer (AAS) equipped with acetylene-air (2 L/min:10
L/min) was used for the analysis (GBC Scientific
Analysis of Zn2+, Cd2+ and Hg2+ in Synthetic Aqueous
Sample
To construct the calibration graph, after mixing 6.0 mL of 3.0
× 10-4 M HL solution with increasing concentrations of metal
ion solutions, the total volume was completed to 9.0 mL with
double distilled water.
Fluorescence intensities were measured at 452, 474 and
491 nm emission wavelengths after adding 2 times the
volume of 3.0 × 10-4 M HL on the portion taken from
the synthetic aqueous sample. The amount of Zn2+, Cd2+
and Hg2+ in synthetic sample were determined from the
calibration graph.

J Fluoresc
Fig. 1 Synthesis of Schiff base ligand (HL)
Results and Discussion
wavelength scan was performed. For this purpose, HL solu-
tion in ethanol at 3.0 × 10-4 M was mixed with the equivalent
volume of metal ion solution (3.0 × 10-3 M in double-distilled
water) (Fig. 3).
EI-MS Studies
Electron ionization mass spectrometry was employed for
structural characterization of the Schiff base ligand. Mass
spectra were obtained by using 70 eV electrons in a quadru-
pole mass analyzer. The pattern of the mass spectra shows the
sequential degradation of the ligand. In the mass spectrum, the
fragment at m/z = 211 corresponding to the molecular weight
of the Schiff base and the fragment at m/z = 91 corresponding
to [C7H7]·+ are dominant (Fig. 2). The ions at m/z = 194 and
m/z = 120 were attributed to [C14H12N]·+ and [C7H6NO]·+,
respectively. The fragment at m/z = 194 was thought to be
formed by the removal of the hydroxyl group. The loss of
C7H7NO (2-(iminomethyl)phenol) group from the ligand
caused the formation of a fragment at m/z = 91.
As can be shown in Fig. 4, there is a weak peak at 464 nm
in the fluorescence emission spectrum of HL. The weakness
of the peak indicates that the fluorescence intensity of HL is
very low. The excitation spectra obtained gave a peak at 369
nm.
Fluorescence responses of HL with some metal ions
were examined to assess whether HL could act as a fluo-
rescent chemosensor. As a result of reaction with HL,
significant fluorescence emission was seen for Zn2+
,
Cd2+ and Hg2+. These peaks were observed at 452 nm
for Zn2+, at 474 nm for Cd2+ and at 491 nm for Hg2+ in
the emission spectra (Fig. 5).
Determination of Binding Stoichiometry
Fluorescence Measurements
The binding stoichiometry of HL-M (M: Zn2+, Cd2+ and
Hg2+) complexes was determined from the Job’s plots.
The fluorescence intensity at 452 nm for Zn2+, at
474 nm for Cd2+ and at 491 nm for Hg2+ was measured
by varying the molar fraction of HL with a total
Fluorescence studies were carried out to assess the potential
use of HL as a fluorescent chemosensor for the determination
of Zn2+, Cd2+ and Hg2+. Since excitation and emission wave-
lengths of HL and ligand-metal complexes were not known, a
Fig. 2 Electron ionization mass
spectra of HL obtained with
70 eVelectrons

J Fluoresc
Fig. 3 Synthesis of HL-metal
complexes a. M: Zn2+ and Hg2+
b. M: Cd2+, X: Cl-
,
concentration of the sensor and metal ion solutions. A
series of a solution containing HL (3.0 × 10-4 M in etha-
nol) and Zn2+, Cd2+, Hg2+ (3.0 × 10-4 M in double-
distilled water) were prepared, in which the total volume
of HL and metal ion solution was kept constant at 4 mL.
The molar fraction at maximum emission intensity gives
the binding stoichiometry. Maximum emission intensity
was observed at 0.675 for Zn2+, 0.428 for Cd2+and
0.667 for Hg2+ (Fig. 6). This result shows that
chemosensor HL forms 2:1 complex with Zn2+ and Hg2+
and forms 1:1 complex with Cd2+.
(3.0 × 10-4 M in ethanol) with the same concentration of metal
ion solutions (3.0 × 10-4 M in double-distilled water) the pH
was adjusted between 5 and 9 with Britton-Robinson buffer.
Fluorescence spectra were recorded after 40 minutes at
452 nm for Zn2+, at 474 nm for Cd2+ and at 491 for Hg2+
(Fig. 7). Fluorescence is very weak in the acidic media due
to the protonation of the nitrogen in the imine bond of HL.
This situation was interpreted as the ligand coordination with
metal ions becomes difficult due to protonation [27]. Since
metal hydroxides precipitated at pH above 9, higher values
of pH scanning were not performed. Fluorescence emission
was found to be quite high at pH 8 to 9. Since the pH values of
the HL-metal complexes are between 8.0 and 8.5, there is no
need to adjust the pH.
Optimization Studies
pH Effect
Solvent Effect
In order to determine the optimum pH in the determination of
zinc, cadmium and mercury(II) ions with the chemosensor
HL, pH scan was performed. After mixing the HL solution
Since most of the Schiff bases are insoluble in water, different
solvents should be used. Therefore, the experiments were
Fig. 4 Excitation and emission
spectra of HL (3.0 × 10-3 M in
ethanol)

J Fluoresc
180
150
120
90
60
30
0
0.15
0.35
0.55
0.75
0.95
[HL] / ([M2+] + [HL])
● HL-Zn2+ ♦ HL-Cd2+ ▲ HL-Hg2+
Fig. 6 Job plots for determination of binding stoichiometry of HL-M (M:
Zn2+, Cd2+ and Hg2+) complexes
the structure of complexes. However, due to its practical use,
ligand dissolved in ethanol was used in the experiments.
Ligand Concentration
There is an equilibrium between HL and metal ion in free form
and HL-metal complex (Fig. 3). The increase in the amount of
ligand shifts the equilibrium reaction to the right in favor of
the complex, resulting in an enhancement in the intensity of
fluorescence. In order to determine optimum ligand concen-
tration, HL solutions were prepared in ethanol at 3.0 × 10-3 M,
3.0 × 10-4 M and 3.0 × 10-5 M, respectively. After adding
metal ion solutions (3.0 × 10-3 M) to each chemosensor solu-
tion (1:2 for Zn2+ and Hg2+, 1:1 for Cd2+), fluorescence spec-
tra were recorded at 452 nm for Zn2+, at 474 nm for Cd2+ and
at 491 for Hg2+. It was observed that 3.0 × 10-3 M metal ion
solution with 3.0 × 10-4 M HL solution caused much more
fluorescence intensity compared to the signals obtained from
other HL concentrations (Fig. 9). Subsequent experiments
were performed with a 3.0 × 10-4 M HL solution.
Fig. 5 Excitation and emission spectra of HL-M complexes ([HL]=3.0 ×
10-4 M, [M]=3.0 × 10-3 M) a. M: Zn2+, b. Cd2+, c. Hg2+
180
160
140
120
100
80
carried out using organic solvents that can be mixed with
water because the purpose of the study was to determine zinc,
cadmium and mercury(II) ions in aqueous solutions. The li-
gand was dissolved in ethanol, methanol, acetone, acetonitrile
and N,N-dimethylformamide (3.0 × 10-5 M) to determine the
fluorescent emission behavior of HL-M (M: Zn2+, Cd2+ and
Hg2+) complexes in different solvents. Ethanol, methanol, ac-
etone, acetonitrile and dimethylformamide showed
strengthening and attenuating effects on fluorescence intensity
(Fig. 8). It is thought that fluorescence intensity significantly
increases due to the fact that the molecules become more
stable, especially when dimethylformamide is coordinated to
60
40
20
0
4
6
8
10
pH
● HL-Zn2+ ♦ HL-Cd2+ ▲ HL-Hg2+
Fig. 7 The effect of pH on the fluorescence emission of HL-metal
complexes

J Fluoresc
140
120
100
80
100
90
80
70
60
50
40
30
20
10
0
60
40
20
0
Ethanol
Methanol Acetonitrile Acetone
DMF
HL +
HL + Co HL + Ni HL + Cu HL + Fe
Zn2+ Cd2+ Hg2+
Water
HL-Zn2+ HL-Cd2+ HL-Hg2+
Fig. 10 Effects of interfering ions on the selectivity of HL for Zn2+, Cd2+
Fig. 8 Fluorescence intensity of HL-metal complexes in different
solvents
and Hg2+
Interference Effect
zinc, cadmium and mercury. As shown in Table 1, HL gave a
linear response for Zn2+, Cd2+ and Hg2+ in the range of 0.6 –
9.0 × 10-5 M, 0.3 – 3.0 × 10-5 M, 0.6 – 7.8 × 10-5 M with a
correlation coefficient of R2 = 0.9932, 0.9952 and 0.9938
(n=5), respectively. Limit of detection (LOD) were deter-
mined by using the equation LOD =3 Sb/m. In this equation,
m refers to the slope of the calibration graph and Sb refers to
the standard deviation of 10 different fluorescence intensity
recorded for the lowest metal ion concentration in the calibra-
tion graph. LOD was found to be 2.7 ( 0.2) × 10-7 M, 6.0 (
0.5) × 10-7 M and 7.5 ( 0.4) × 10-7 M, respectively (Table 1).
Errors were calculated by dividing the standard deviation by
the square root of number of measurements.
The high selectivity of a fluorescent sensor for detecting
analytes in the presence of other ions is one of the most im-
portant characterization parameters [28]. The selectivity of HL
for Zn2+, Cd2+ and Hg2+ over other metal ions such as Ni2+,
Cu2+, Co2+ and Fe3+ was investigated. Equivalent volume of
each metal ion solution (3.0 × 10-3 M) was added separately to
Zn2+, Cd2+, Hg2+ solutions (3.0 × 10-4 M) and then the solu-
tions were mixed with HL (3.0 × 10-4 M). Fluorescence spec-
tra were recorded at 452 nm for Zn2+, at 474 nm for Cd2+ and
at 491 nm for Hg2+ after 40 minutes (Fig. 10). In the presence
of Fe3+ and Cu2+, the intensity of HL-M (M: Zn2+, Cd2+ and
Hg2+) decreases considerably. Co2+ and Ni2+ also have a neg-
ative effect on the selectivity of HL for Zn2+ and Cd2+. This
effect can be explicated by the fact that Cu2+ and Fe3+ have
more affinity in the ligand than Zn2+, Cd2+ and Hg2+.
A comparison of limit of detection and working range with
the previously reported sensors for Zn2+, Cd2+ and Hg2+ is
presented in Table 2. The proposed method displays compa-
rable detection limits with the reported sensors.
According to EPA standards, the maximum contaminant
level (MCL) for inorganic chemical contamination in ground
water and drinking water is 0.005 mg L-1 for Cd2+ and
0.002 mg L-1 for Hg2+. Using available organoleptic data,
Calibration Studies
After the optimum conditions were determined, calibration
curves were established for the quantitative determination of
80
60
40
20
0
Table 1 Calibration parameters of fluorescent sensors prepared
HL-Zn2+
HL-Cd2+
HL-Hg2+
Wavelength, nm
λ
exc=398
ems=452
0.6 – 9.0 × 10-5 0.3 – 3.0 × 10-5 0.6 – 7.8 × 10-5
λ
exc=385
λ
exc=366
λ
λems=474
λems=491
Linear working
range, M
Slope
7.7 × 106
97.47
7.6 × 106
80.49
5.2 × 106
121.77
Intercept
Limit of detection, M 2.7 × 10-7
6.0 × 10-7
2.0 × 10-6
7.5 × 10-7
2.5 × 10-6
HL (3 × 10-5 M)
HL (3 × 10-4 M)
HL (3 × 10-3 M)
Limit of
quantification, M
9.1 × 10-7
Zn2+ Cd2+ Hg2+
Correlation
coefficient
0.9932
0.9952
0.9938
Fig 9 Fluorescence intensity of HL-M complexes prepared with different
concentrations of HL (M: Zn2+, Cd2+ and Hg2+; [M]=3.0 × 10-3 M)

J Fluoresc

J Fluoresc
Table 3 Comparison of the results obtained by proposed HL fluorescent sensor and AAS
Sample
Zn2+ (mg L-1)
Proposed sensora
0.655 0.015
Cd2+ (mg L-1)
Proposed sensora
1.748 0.031
Synthetic sample
AASb
AASb
1.596 0.002
0.639 0.069
a The mean of five measurements, b The mean of three measurements
for controlling taste and odor quality of water, the estimated
level of Zn2+ is 5 mg L-1 [67, 68].
Conclusions
In order to examine the applicability of HL as a fluorescent
sensor, Zn2+, Cd2+ and Hg2+ were determined in synthetic
aqueous samples that contain known amounts of metal ions.
Fluorescence spectra were recorded 40 minutes after mixing
5.0 mL of the aqueous sample with 10.0 mL The results were
compared with those obtained with AAS method and present-
ed in Table 3. As can be seen, the results of zinc and cadmium
selective fluorescent sensors and AAS are in agreement. The
accuracy was tested by t-test. The texperimental was found as
1.18 for HL-Zn2+ and 1.03 for HL-Cd2+ at 95% confidence
level (tcritic = 2.45). The t-test shows that there is no significant
difference between the results of the two methods.
In order to test the accuracy of the method based on HL
proposed as a chemosensor, recovery experiments were per-
formed. For this purpose, known amounts of Zn2+, Cd2+ and
Hg2+ solutions were added to the synthetic aqueous sample.
Fluorescence intensities were measured 40 minutes after
mixing 5.0 mL of the synthetic sample with 10.0 mL of 3 ×
10-4 M HL solution. The recoveries of Zn2+, Cd2+ and Hg2+
from the spiked sample are given in Table 4. The recovery
values are in the range from 101 to 108% for zinc, 103 to
104% for cadmium and 101 to 105% for mercury. The results
show that the accuracy of the HL chemosensor is quite good.
In this study, an ON type Schiff base, (E)-
2-((benzylimino)methyl)phenol, was synthesized and its
fluorescence properties against zinc, cadmium and
mercury(II) ions were investigated. This ligand was found
to have good selectivity to zinc, cadmium and mercury(II)
ions. Optimization studies were carried out to improve
sensitivity and selectivity. It was observed that some ions
have decreasing effects on the fluorescence sensitivity of
these ions investigated. Zn2+, Cd2+ and Hg2+ can be de-
termined quantitatively in neutral aqueous samples. For
samples containing a known amount of metal ions, the
results obtained with the fluorescence spectrometer are
compatible with the results obtained with AAS, indicating
that the accuracy of the method based on HL chemosensor
is very good. The method based on HL exhibits a wide
linear range, good accuracy and low detection limits.
Emission of HL-M (M: Zn2+, Cd2+ and Hg2+) complexes
at different wavelengths also made it possible to deter-
mine these ions simultaneously. As a result, it was con-
cluded that the HL ligand can be used as a chemosensor
in determining zinc, cadmium and mercury ions in aque-
ous samples.
Authors’ Contributions Not applicable
Funding Information This research did not receive any specific grant
from funding agencies.
Table 4 Recoveries of Zn2+, Cd2+ and Hg2+ from spiked sample
Zn2+ (mg L-1)
Founda
Availability of Data and Material Available
Calculated
1.24
Recoverya
1.32
105.99 0.02
100.94 0.02
107.92 0.02
Compliance with Ethical Standards
1.44
1.45
Conflicts of Interest The author declares that there is no conflict of
2.22
2.41
Cd2+ (mg L-1)
Founda
2.79
interest.
Calculated
2.70
Recoverya
103.4 1.1
103.8 1.4
103.8 1.5
Code Availability ChemBioDraw Ultra 14.0
Adobe Photoshop CC (64 Bit)
3.02
3.13
4.29
4.45
Hg2+ (mg L-1)
Founda
1.64
Calculated
1.60
Recoverya
104.5 2.3
101.3 3.0
103.1 1.9
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