Journal of Fluorescence

https://doi.org/10.1007/s10895-020-02503-4

ORIGINAL ARTICLE

Fluorescence “Turn On–Off” Sensing of Copper (II) Ions Utilizing

Coumarin–Based Chemosensor: Experimental Study, Theoretical
Calculation, Mineral and Drinking Water Analysis
Fatma Nur Arslan 1,2 & Gonul Akin Geyik 1 & Kenan Koran 3 & Furkan Ozen 4 & Duygu Aydin 1 & Şükriye Nihan Karuk Elmas 1 &
Ahmet Orhan Gorgulu 3 & Ibrahim Yilmaz 1

Received: 13 January 2020 / Accepted: 27 January 2020

# Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract
Herein, we report the preparation of a fluorescent sensor based on coumarin derivative for copper (II) ion sensing in CH3CN/
HEPES media. 6,7–dihydroxy–3–(4–(trifluoro)methylphenyl)coumarin (HMAC) sensor was fabricated and analyzed by spec-
troscopic techniques. The sensor demonstrates “turn on–off” fluorescence quenching in the presence of copper (II) ions at 458 nm.
A clear complex between the chemosensor HMAC and copper (II) ions was characterized by ESI–MS as well as the Job’s
method. Also, the limit of detection (LOD, 3σ/k) value was determined as 24.5 nM in CH3CN/HEPES (95/5, v/v) buffer media
(pH = 7.0). This value is lower than the admissible level of copper (II) ions in drinking water (maximum 31.5 μM) reported by EU
Water Framework Directive (WFD) and World Health Organization (WHO) guidelines. The theoretical calculations (density
functional theory, DFT) have been performed for the geometric optimized structures. As a final stage, real sample analyses have
successfully been performed by using HMAC, as well as ICP–OES method. The relative standard deviation for copper (II) in
mineral and drinking water samples has been determined to be below 0.15% and recovery values are in the range of 95.48–
109.20%.

Keywords Fluorescence sensor . Copper . Coumarin . Drinking water . Mineral water . DFT

Introduction many fundamental physiological and biological processes, for

instance, mitochondrial electron transport, enzyme functions,
Copper ion is the most abundant d–block metal ion in the producing red blood cells, acting as a catalyst for the production
human body behind iron and zinc ions. It is a crucial agent in of melanin, and also serving to be neurotransmitters [1–3]. The

Electronic supplementary material The online version of this article

(https://doi.org/10.1007/s10895-020-02503-4) contains supplementary
material, which is available to authorized users.

* Ibrahim Yilmaz Şükriye Nihan Karuk Elmas

iyilmaz@kmu.edu.tr snihankaruk@gmail.com
Fatma Nur Arslan Ahmet Orhan Gorgulu
arslanfatmanur@gmail.com aogorgulu@firat.edu.tr
Gonul Akin Geyik 1
gnlakin@gmail.com Department of Chemistry, Kamil Ozdag Science Faculty,
Karamanoglu Mehmetbey University, 70100 Karaman, Turkey
Kenan Koran 2
Van’t Hoff Institute for Molecular Sciences, Analytical–Chemistry
kenan.koran@gmail.com
Group, University of Amsterdam, Amsterdam, Netherlands
Furkan Ozen 3
Department of Chemistry, Firat University, Science Faculty,
furkanozen@akdeniz.edu.tr 23119 Elazıg, Turkey
4
Duygu Aydin Department of Mathematics and Science, Akdeniz University,
duyguaydin@kmu.edu.tr Faculty of Education, 07058 Antalya, Turkey
 J Fluoresc

human body may intake copper ions through food, drinking chemosensors based on coumarin derivatives for copper (II)
water, environmental and biological sources, as well as through ion sensing with high accuracy and recovery values is notice-
skin contact to copper containing compounds. However, main- ably urgent.
taining the copper level within a particular range below toxic In an effort to contribute towards the above issues, a
concentrations is a challenge [4–6]. It is well known that high new 6,7–dihydroxy–3–(4–(trifluoro)methylphenyl)coumarin
level of copper ions in human body causes the disturbance of (HMAC) sensor based molecular system is fabricated for
cellular homeostasis leading to oxidative stress and disorders the sensitive and selective sensing of copper (II) ions.
such as brain and neurodegenerative diseases such as Coumarin has been employed to be a fluorophore due to
Parkinson’s and Alzheimer’s diseases, and also leads to liver its high fluorescence quantum yield, high chemical stabil-
or kidney damages [1–10]. For drinking water samples, the ity, large Stoke’s shift and moderately high water solubil-
maximum admissible level of copper ions is 2 mg.L−1 accord- ity. Besides, coumarin derivatives are less toxic to envi-
ing to the WHO and EU–WFD [4, 6–10]. Since copper ions ronment and the livings [31–33]. Herein, we reported the
can accumulate into the human body through drinking water, preparation of a fluorescent “turn on–off” chemosensor
the detection of its levels in mineral or drinking water samples based on coumarin derivative for copper (II) monitoring
is vital to control its impact on the human health. in mineral and drinking waters with a quite simple oper-
Although a wide range of traditional methodologies for ation. Firstly, HMAC fluorescent sensor was synthesized
example inductively coupled mass atomic emission spectrom- and then successfully characterized by 13C–NMR, 1H–
etry (ICM–AES) [11], plasmon resonance sensor [12], graph- NMR and FT–IR techniques. Afterwards, it was evaluated
ite flame atomic absorption spectrometry (AAS) [4, 13], elec- for the selective determination of copper (II) ions in
trochemical assays [14], Rayleigh scattering spectroscopy CH3CN/HEPES media (95/5, v/v) at pH = 7.0. The theo-
(RSS, plasmon–resonance) [15], inductively coupled plasma retical calculations, DFT, were also carried out for the
optical emission spectroscopy (ICP–OES) [16], and etc. have geometric optimized structures. In the last part of study,
been employed to monitor copper (II) ions, as a consequence, the sensor HMAC was applied for the various real min-
fluorescence chemosensors based techniques remain attrac- eral and drinking water samples. Fabricated sensor
tive, because of their high efficiency, operational simplicity, HMAC presents low detection limits and shows a good
sensitive detection and non–destructiveness [1, 2, 4–7, 9, 10, performance for a series of mineral and drinking water.
17]. Recently, thousands of investigations have been placed
on the development of novel, highly selective and sensitive
fluorescent chemosensors for the determination of copper ions
[18–27]. For this purpose, various organic molecules such as Materials and Methods
rhodamine, BODIPY, coumarin, fluorescein and cyanine are
widely used to monitor copper (II) ions in different media Chemicals and Instruments
[20]. Among these organic molecules, fluorescent sensors
based on coumarin derivative in the literature offer the selec- All chemicals were of analytical reagent grade and pur-
tive and sensitive monitoring of copper (II) ions as well as chased from VWR international (Poole, UK), Sigma–
high accuracy. However, the studies based on the fluorescent A l d r i ch (Ly on , F r an ce ) a n d M er ck ( D a r m s t a d t ,
chemosensor based on coumarin derivative for copper (II) Germany) chemical companies. Perchlorate salts of differ-
monitoring in real drinking and water samples are quite lim- ent metal ions (Cu2+, Zn2+, Cd2+, Ca2+, Sr2+, Ba2+, Mg2+,
ited. For example, a fluorescent chemosensor based on cou- Mn2+, Fe2+, Fe3+, Co2+, Na+, Hg2+, Pb2+and Al3+) were
marin derivative for the efficient monitoring of copper (II) used. Ultrapure water was supplied by Millipore water
ions in wine samples was successfully developed by Wu and purification system (Millipore Corp., Billerica, MA). 1H
coworkers [28], and the limit of detection was found as and 13C NMR spectra were obtained on a Bruker DPX
62 nM. In another study, Yan and coworkers designed a novel 400 MHz spectrometer. A spectrum 100 FT–IR spectrom-
FRET ratiometric sensor for the monitoring of copper (II) ion eter (Perkin Elmer Inc., Wellesley, MA) was employed to
in tap and lake water samples with satisfactory recovery ratios, measure the FT–IR spectra of compounds. Fluorescence
and the limit of detection was found as 210 nM [29]. Duan and spectra were recorded on a Varian Cary Eclipse fluores-
coworkers presented a novel fluorescent chemosensor based cence spectrophotometer (Agilent Technologies Inc.,
on coumarin derivative for sensing copper (II) ion present in Santa Clara, CA, USA). A mass spectrum was obtained
deionized water samples. The detection limit was measured to on a Bruker Mass Spectrometer (Daltonics Microflex)
be 52 nM [30]. However, detection limits in the mentioned equipped with an ESI source. An inductively coupled
studies are still above the legal acceptance values reported by plasma–optical emission spectroscopy (ICP–OES,
WHO and EU–WFD guidelines for drinking water samples Agilent 720) system (Agilent Technologies, Wilmington,
(31.5 μM). Hence, the fabrication of novel fluorescent USA) equipped with an axial plasma torch was used.
J Fluoresc

Preparation of the Chemosensor HMAC Procedure of Copper (II) Ion Determination

by Fluorescence Spectroscopy
The compounds 6,7–dihydroxy–3–(3–
methylphenyl)coumarin (probe HMAC) and 2–(2,4,5– Following the centrifugation and filtration procedures, the
trimethoxyphenyl)–1–(3–(methylphenyl))acrylonitrile spectroscopic measurements were carried out by the following
(HMAN) were fabricated and purified according to the liter- procedure. Briefly, 5.0 μM of ligand (probe HMAC) solution
ature [17, 34, 35]. The procedures are given in supporting was freshly prepared in 95/5, v/v, CH3CN/HEPES buffer me-
information file. dia (pH = 7.0) before analysis. For each experiment, 3 mL of
the ligand solution was added to fluorescence cuvette and
spectra were recorded. Then, 15 μL of real sample was added
Fluorescence Studies of Probe HMAC to this solution and it was mixed for a few seconds.
Fluorescence spectra of the mixed solution (probe HMAC +
The stock solution of HMAC (10 mM) was prepared in real sample) were taken again at room temperature (λexc =
CH3CN and diluted to appropriate concentration (5.0 μM). 364 nm, λemm = 458 nm with 5 nm of slit size). Also, to eval-
The emission intensities of the probe HMAC system uate the method accuracy, standard addition method was per-
(5.0 μM) were performed in CH3CN/HEPES (95/5, v/v) at formed by adding 15 μL of copper (II) solutions (0.1 μM and
pH = 7.0 buffer media, and the excitation wavelength was 0.2 μM) into the mixed solution.
364 nm. 1.10−3 M of perchlorate salts of the metal ions was
prepared in ultrapure water. The excitation and emission Procedure of Copper (II) Ion Determination
wavelengths were adjusted as 364 nm and 458 nm (slit width by ICP–OES
5 nm), respectively.
The fluorescence titration experiments were carried out Before the ICP–OES analyses, the pre–treatment procedure
triplicate at 458 nm, and the LOD value of the chemosensor for real samples was done according to the method proposed
HMAC was calculated using the 3σ/k equation. (σ = standard by Mendil et al. [41]. Briefly, the mineral and drinking water
deviation of blank solution, k = the slope of the calibration samples were acidified with 1% of nitric acid and the solutions
curve between the amount of copper (II) and fluorescence were adjusted to pH = 9 by NH3/NH4Cl buffer solution. They
intensity of chemosensor HMAC). The interference behav- were kept approximately 10 min and then the solutions were
iours were tested by excitation at 364 nm, in the presence of centrifuged at 8.000 rpm for 15 min. The upper layers were
various metal ions [10–fold excess solutions, suspended and the precipitates were dissolved with 0.5 mL of
M(ClO4)nxH2O)] and copper (II) ion. concentrated nicric acid. Finally, the samples were diluted to
2.5 mL of HPLC grade water and analyzed by ICP–OES in
Theoretical DFT Calculation triplicate. The operating parameters of system were given in
Table S1. The measurement results were reported as mean
The calculations were performed using the Gaussian 09 soft- value ±SD.
ware (Gaussian, Inc., Wallingford CT) with B3LYP and 6–
31 g(d) basis sets [36–40]. The theoretical calculations were
carried out for the geometrically optimized structures, the en- Results and Discussion
ergy levels (HOMO and LUMO) of the probe HMAC and
complex of the HMAC–Cu2+. Fabrication and Characterization of HMAN and Probe
HMAC

Sensing of Copper (II) Ions in Real Samples Synthesis and purification of HMAN were done according to
previous literatures [17, 34, 35]. After filtering the synthesized
To demonstrate the applicability of the probe HMAC in real phenylacrylonitrile compound, it was washed with ultrapure
samples, various mineral and drinking water samples were water until the neutral pH. HMAC was synthesized in a non–
analyzed. Samples were obtained from local markets solvent silica gel condition under microwave irradiation at
(Karaman city, Turkey). As an initial step, the waters were high yield in the presence of HMAN with pyridinium hydro-
degassed to remove the carbonate present in the samples; chloride, and column chromatography was chosen to purify
and then they were put on an ultrasonic bath and sonicated the crude product. The general procedure for synthesis is pre-
for 15 min. Afterwards, tested samples were centrifuged at sented in Scheme 1.
8.000 rpm for 10 min, and then filtered using a 0.45.0 μM Silica gel was used as a solid support for the synthesis
pore–size membrane filter to get rid of suspended species or step of HMAC. This support material reduced formation
contamination. of side products and has been effective for obtaining the
 J Fluoresc

Scheme 1 Synthetic scheme of

HMAN and HMAC

main products with high yields. Pyridinium hydrochloride spectrum of the compound HMAC. Also, the disappear-
was used to transform hydroxyl groups of methoxy ance of methoxy and formation of –OH stretching vibra-
groups in the compound HMAC. Therefore, the lactone tions are clearly monitored at 3190 and 3412 cm−1 in the
ring was formed and resulted in a changing from the hy- HMAC spectrum. The lactone ring of the coumarin com-
droxyl groups to nitrile carbon. FT–IR, 1H–, 13C– and pound has specific –C=O stretching vibrations monitored
APT–NMR techniques were used to confirm the structure at 1661 cm−1. The disappearance of methoxy protons and
of synthesized compounds. When comparing the NMR formation of –OH proton peaks prove that there is a clear
and FT–IR spectra of HMAN and HMAC, it is easily product formation. All of the characterization data is giv-
seen that the –C ≡ N peaks of HMAN do not exist at en in Fig. S1 to S7.

Fig. 1 (a) Fluorescence intensity changes of probe HMAC (5.0 μM) in of probe HMAC in the presence of various metal ions in ACN/HEPES
the presence of various cations (50 μM) in ACN/HEPES buffer solution buffer solution (95/5, v/v, pH = 7.0) (λemm = 458 nm, λexc = 364 nm)
(95/5, v/v, pH = 7.0), (b) Changes in the fluorescence intensity ratio (Io/I)
J Fluoresc

Fig. 2 (a) Selectivity of the HMAC–Cu2+ sensor over the different metal copper (II) in ACN/HEPES buffer solution (95/5, v/v, 5.0 μM, pH =
ions in ACN/HEPES buffer solution (95/5, v/v, 5.0 μM, pH = 7.0) (b) the 7.0) (λemm = 458 nm, λexc = 364 nm)
fluorescence spectra of HMAC with the increasing concentrations of

Fluorescence Studies obtained results were presented in Fig. S8. In the presence of
copper, an increase in the absorbance intensity of the sensor
Selectivity is one of the most important performance parame- HMAC at 230 nm was observed, while the peak at 370 nm
ters for fluorescent sensors. In this study, the ability of the was shifted to 300 nm, in other words towards the blue wave-
chemosensor HMAC for the detection of copper (II) in the length. Thus, chemosensor HMAC demonstrated a high se-
existence of 10–fold excess of various cations (Mg2+, Mn2+, lectivity for copper (II) ions over tested metal ions.
Ca2+, Sr2+, Co2+, Ba2+, Fe2+, Hg2+, Cu2+, Zn2+, Fe2+, Pb2+, To study the impact of the other metal cations on the rec-
Cd2+, Al3+ and Na+) was evaluated. As shown in Fig. 1, when ognition of probe HMAC system to copper (II) (10.0 eq.),
these ions were added into the HMAC solution, only copper each of the other metal cations (10.0 eq.) was added into the
(II) ions result in a significant fluorescence quenching at probe HMAC–copper (II) solution, respectively (Fig. 2a).
458 nm. None of the other metal cations generated obvious The selectivity studies of probe HMAC (5.0 μM) were per-
impact on fluorescence intensities. In addition to fluorescence formed at 458 nm in CH3CN/HEPES buffer media (95/5, v/v)
emission study, UV–Visible experiments were performed, and at pH = 7.0. As depicted in Fig. 2a, the fluorescence emission

Fig. 3 (a) The plot of emission intensities of probe HMAC versus various Cu2+ concentrations, (b) Benesi–Hildebrand plot of 1/(I–I0) vs 1/[Cu2+] based
on 1:1 association stoichiometry between probe HMAC–Cu2+ complex (λemm = 458 nm, λexc = 364 nm)
 J Fluoresc

Fig. 4 ESI–MS spectrum of

probe HMAC–Cu2+ complex

intensity of probe HMAC–copper (II) solution changed only to be 24.5 nM on the basis of 3σ/k and the linearity range was
a little when adding the tested cations, which proposed that the so extensive. The LOD value of probe HMAC enables the
recognition process of copper (II) was scarcely influenced by copper (II) ion monitoring in nanomolar levels, and therefore
tested cations. Consequently, probe HMAC system had high it is lower than the acceptable limit of the drinking water
selectivity on monitoring copper (II) ion. To obtain quantita- guidelines of WHO and EU–WFD (31.5 μM) [4, 6–10].
tive relation of probe HMAC (5.0 μM) solution on sensing Furthermore, the correlation constant value was calculated to
copper (II) ion, the fluorescence titration experiments in be 9.00 × 104 M−1 using the Benesi–Hildebrand equation
CH3CN/HEPES buffer media (95/5, v/v) at pH = 7.0 were based on the data of fluorescence titration (Fig. 3b). Thus,
performed (Fig. 2b). As can be seen from Fig. 2b, the fluores- these results showed that the probe HMAC system had good
cence emission intensity at 458 nm gradually decreased with sensitivity on copper (II), and the standard curve with good
the copper (II) concentration (0 to 50 μM) increased. After the linearity (R2 = 0.9916) could be used to quantify.
addition of 2.0 equivalent of copper (II) ion, quenching of the During detecting copper (II) ion with probe HMAC system
fluorescence intensity reached a constant value. This as fluorescent probe, fluorescence quenching occurred, which
quenching which resulted from the formation of the meant copper (II) ion interacted with probe HMAC system. To
HMAC–Cu2+ complex, may be attributed to the paramagnetic investigate the structure of HMAC–Cu2+ complex, ESI–MS
effect and heavy atom effect of transition metals [42]. Hence, spectra were obtained (Fig. 4). The formation of a complex
the probe HMAC could be employed as a “turn–on–off” fluo- between HMAC–Cu2+ (Scheme 2) was verified by the ESI–
rescent chemosensor for sensing copper (II) ions. MS technique. As can be seen from MS spectrum, the peak at
Based on the fluorescence titration experiments, the cali- m/z = 405.8 corresponds to the [HMAC+ Cu + Na+] was in-
bration curve of the quantitative correlation between the emis- dicated 1:1 ratio in Fig. 4.
sion value and metal concentration was y = −3.56 × 107x + Also, to detect the stoichiometric ratio of copper (II) ion
366.38 (R2 = 0.9916) (Fig. 3a). The detection limit of the and probe HMAC in HMAC–Cu2+ complex, Job’s graph was
chemosensor HMAC for copper (II) ion sensing was found plotted based on fluorescence titration data (Fig. 5). As shown

Scheme 2 The proposed binding

mechanism of probe HMAC and
copper (II) complex in ACN/
HEPES buffer solution (95/5, v/v,
5.0 μM, pH = 7.0)
J Fluoresc

Fig. 5 Job plots of HMAC–Cu2+

complex in ACN/HEPES buffer
solution (95/5, v/v, 5.0 μM, pH =
7.0) (λemm = 458 nm, λexc =
364 nm)

in Fig. 5, the stoichiometry of the HMAC–Cu2+ complex was with EDTA, and the obtained results were presented in
found to be 1:1 ratio, due to the maximum of relative intensity Fig. S10.
was about 0.5 value.
The response time of the probe HMAC were also per- Computational DFT Studies
formed for real–time monitoring of copper (II) ion, and
presented in Fig. S9. The emission intensity of HMAC– To support the experimental results, DFT calculations were
Cu2+ complex was balanced within only 1 min, and it was performed on probe HMAC and HMAC–Cu2+. Molecular
proved that the extraordinarily rapid reaction between orbital (MO) energies and figures of HOMO and LUMO
chemosensor HMAC and copper (II) ion was occurred. levels are given in Fig. 6. The HOMO and LUMO of probe
Moreover, the reversibility experiments were performed HMAC were spread over the molecules, but the electronic

Fig. 6 Frontier molecular orbital

profiles of probe HMAC and
HMAC–Cu2+complex
 J Fluoresc

Table 1 The analysis of Cu2+ in

various mineral and drinking Cu (II) found (μmol L−1) difference of t test statistics (df = 2)
water samples by probe HMAC the means
and ICP–OES HMAC ICP–OES t probability > |t|
Statistic

mineral water samples

mineral 1.18 ± 0.003 1.18 ± 0.001 0.0056 3.2095 0.0849 t calculated < t
water–A tabulated
mineral 0.29 ± 0.006 0.30 ± 0.002 −0.0090 −2.0718 0.1740 t calculated < t
water–B tabulated
mineral 1.23 ± 0.002 1.23 ± 0.001 −0.0016 −0.9351 0.4484 t calculated < t
water–C tabulated

mineral 0.24 ± 0.003 0.25 ± 0.001 −0.0053 −2.0276 0.1797 t calculated < t
water–D tabulated
mineral 0.55 ± 0.003 0.56 ± 0.004 −0.0059 −1.4388 0.2868 t calculated < t
water–E tabulated
drinking water samples
drinking 0.25 ± 0.003 0.25 ± 0.003 0.0048 2.6381 0.1186 t calculated < t
water–A tabulated
drinking 0.50 ± 0.002 0.49 ± 0.001 0.0056 2.9099 0.1005 t calculated < t
water–B tabulated
drinking 0.31 ± 0.007 0.31 ± 0.002 0.0045 1.3326 0.3141 t calculated < t
water–C tabulated

drinking 0.20 ± 0.002 0.20 ± 0.001 −0.0027 −1.3361 0.3132 t calculated < t
water–D tabulated
drinking 0.21 ± 0.004 0.21 ± 0.004 −0.0002 −0.0841 0.9406 t calculated < t
water–E tabulated
drinking 0.10 ± 0.003 0.10 ± 0.001 0.0044 3.0072 0.0950 t calculated < t
water–F tabulated

† Null Hypothesis: mean1–mean2 = 0

†† Alternative Hypothesis: mean1–mean2 <> 0
††† At the 0.05 level, the difference of the population means is NOT significantly different with the test difference
(0)

distribution weren’t the same for the HMAC–Cu2+ complex. LUMO for probe HMAC and HMAC–Cu2+ is found as
Although the LUMO of HMAC–Cu2+ complex was localized 3.87 and 1.17 eV. Probe HMAC provides a suitable molecular
over the copper (II) ion and the coumarin moiety, HOMO of structure to coordinate with the copper (II) ion. After complex-
HMAC–Cu2+ complex was distributed around the molecules ation, the interaction energy (Eint = Ecomplex – EHMAC – ECu2+)
and copper (II) ion. The energy gap between HOMO to is lowered by −11.94 eV (−275.348 kcal/mol), which proves

Table 2 Comparison of the performance of coumarin–based fluorescent probes reported in literature and probe HMAC

fluorescent probe method performance application reference

linear range LOD λex/ λem

coumarin 7–yl picolinate based probe 0.1–0.9 μM 35 nM 325 nm/ 454 nm tap water, deionized water [29]
4,7–dihydroxy–3–aminocoumarin based probe 1.0–3.2 μM 256 nM 350 nm/ 475 nm tap water, river water [30]
CQP, (E)–ethyl–7–hydroxy–8–[[2–[2–(quinolin–8 0.0–15.0 μM 52 nM 365 nm/ 410 nm deionized water [45]
–yloxy)acetyl] hydrazono] methyl]–coumarin–3
–carboxylate based probe
7–diethylaminocoumarin–3–carbohydrazide 0.0–10.0 μM 210 nM 340 nm/ 458 nm tap water, lake water [46]
(HCM) based probe
6,7–Dihydroxy–3–(4–(trifluoro)methylphenyl) 0.0–30.0 μM 24.5 nM 365 nm/ 458 nm drinking water, mineral water this work
coumarin based probe

† LOD; limit of detection

J Fluoresc

the high affinity of probe HMAC towards copper (II) ions and 24.5 nM and it was below the current literature [29, 30, 45,
the formation of a stable complex between probe HMAC and 46] fluorescent probe’s detection levels used for analysis of
copper (II) ions. Thus, the obtained results indicate that the copper (II) ion in drinking water samples (Table 2). Overall, it
stabilized complex between probe HMAC and copper (II) ion is clear that the obtained results were accurate and had good
has a lower HOMO–LUMO energy gap when compared to recovery values, which confirm the reliability of the proposed
probe HMAC. This emission quenching response of probe assay, and could be applied to trace copper (II) ion sensing in
HMAC was carried out due to the strong interaction between real beverage samples quantitatively.
copper (II) ions and –OH as a result of the charge transfer
process from the variation of electronic structure of probe
HMAC [43, 44].
Conclusion
ICP–OES Analysis of Mineral and Drinking Water
Samples A fluorescent chemosensor based on coumarin derivative for
copper (II) ion sensing with signal “turn–on–off” has been
To prove the applicability of the probe HMAC, we performed developed. The fabricated probe HMAC is a quite simple
analyses for copper (II) ion detection in various mineral and operation and offers a realistic potential for the trace copper
drinking water samples. The amount of copper (II) ion in (II) ion monitoring in the presence of other cations. The cali-
tested samples was directly analyzed with a simple operation bration plot of 1/(I–I0) versus concentration of 1/Cu2+ was
and quantitatively determined using the calibration curve. linear with a correlation coefficient of 0.9875. The LOD was
Also, a standard addition method was carried out (final con- found as 24.5 nM on the basis of 3σ/k. The stoichiometry of
centrations = 0.1 μM and 0.2 μM). The satisfactory recovery the HMAC–Cu2+ complex was established by Job’s method
and relative standard deviation (RSD) values were obtained (1:1 ratio) and ESI–MS technique. In mineral and drinking
for all tested samples (Table S2). The recovery values of the water samples, copper (II) ions can be detected with excellent
method were obtained within a range of 95.48% to 106.01% recovery values (95.48–109.20%). Furthermore, the ICP–
for drinking waters and 96.18% to 109.20% for mineral wa- OES results confirmed the results of HMAC for copper (II)
ters, respectively. The results show the great potential and ion sensing. Consequently, the presented approach is expected
feasibility of the developed probe HMAC for the sensing of to have a great potential application for safety copper (II)
copper (II) ion in mineral and drinking water samples (Table monitoring in various drinking samples including water used
S2). in agriculture and environmental applications as well as in
The ICP–OES analyses were also performed (Table S3). commercial distribution of beverages.
Before ICP–OES measurements, the calibration curves were
Acknowledgments The authors are grateful to the Research Fund of the
constructed by standard copper (II) ion solutions prepared in TUBITAK for their support (for the synthesis of compound) with the
the concentrations from 10 to 1000 μg.L−1. Besides, two dif- project No–110 T652. The authors would also like to thank Scientific
ferent concentrations (10 and 20 μg.L−1) of the standard so- Research Project Center of Karamanoglu Mehmetbey University with
lutions were spiked to the tested samples. The good agree- the project 30–M–16 and for providing the financial support to use
Gaussian 09 (Gaussian, Inc., Wallingford CT) program.
ments were obtained between the spiked and found amounts
of copper (II) ion. The recovery values were between
91.05%–109.57% and the relative standard deviation (RSD)
values were also obtained as lower (0.05%–2.78%) from ICP–
OES measurements. The accuracy values of the probe
HMAC and ICP–OES procedures were evaluated (Table 1).
Moreover, the results were statistically evaluated employing References
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fidence level = 95%). As a result, the results of probe HMAC 1. Wang S, Liu C, Li G, Sheng Y, Sun Y, Rui H, Zhang J, Xu J, Jiang
and ICP–OES were in good agreement (Table 1). Therefore, D (2017) The triple roles of glutathione for a DNA-cleaving
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chemosensor HMAC for copper (II) ion sensing present in water. ACS sensors 2:364–370. https://doi.org/10.1021/acssensors.
various mineral and drinking water samples. 6b00667
Consequently, studies on the fluorescent chemosensor 2. Yang S, Jiang W, Tang Y et al (2018) Sensitive fluorescent assay for
based on coumarin derivative for metal ion sensing in various copper(II) determination in aqueous solution using quercetin–
cyclodextrin inclusion. RSC Adv 8:37828–37834. https://doi.org/
drinking water samples are limited, and most of them are not 10.1039/C8RA06754F
related for copper (II) ion monitoring. The LOD for the 3. Gao J, Yin J, Tao Z, Liu Y, Lin X, Deng J, Wang S (2018) An
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