439875

The Scientific World JournalVolume 2012, Article ID 439875, 7 pagesdoi:10.1100/2012/439875

The cientificWorldJOURNAL

Research Article

Stabilizing Agents for Calibration in theDetermination of Mercury Using Solid SamplingElectrothermal Atomic Absorption Spectrometry

Hana Zelinkova, Rostislav Cervenka, and Josef Komarek

Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic

Correspondence should be addressed to Josef Komarek, [email protected]

Received 15 November 2011; Accepted 9 January 2012

Academic Editors: K. Kannan, R. G. Wuilloud, and M. C. Yebra-Biurrun

Copyright 2012 Hana Zelinkova et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Tetramethylene dithiocarbamate (TMDTC), diethyldithiocarbamate (DEDTC), and thiourea were investigated as stabilizing agentsfor calibration purposes in the determination of mercury using solid sampling electrothermal atomic absorption spectrometry(SS-ETAAS). These agents were used for complexation of mercury in calibration solutions and its thermal stabilization ina solid sampling platform. The calibration solutions had the form of methyl isobutyl ketone (MIBK) extracts or MIBK-methanolsolutions with the TMDTC and DEDTC chelates and aqueous solutions with thiourea complexes. The best results were obtainedfor MIBK-methanol solutions in the presence of 2.5 gL1 TMDTC. The surface of graphite platforms for solid sampling wasmodified with palladium or rhenium by using electrodeposition from a drop of solutions. The Re modifier is preferable due toa higher lifetime of platform coating. A new SS-ETAAS procedure using the direct sampling of solid samples into a platform withan Re modified graphite surface and the calibration against MIBK-methanol solutions in the presence of TMDTC is proposed forthe determination of mercury content in solid environmental samples, such as soil and plants.

1. Introduction

Mercury and its compounds belong among the most toxiccontaminants and have the ability to bioaccumulate. Themain sources of mercury are volcanic activity, combustionof coal, and other human activities, through which mercuryis released into water, soil, and sediments, whereby it entersinto the food chain and causes health damages. Hence, thestudy of mercury content in environmental samples is veryimportant [13].

For direct analysis of solid samples over the past years,solid sampling electrothermal atomic absorption spectro-metry (SS-ETAAS) has been used. The solid samples areweighed on a graphite platform, which is inserted intoa graphite tube. The advantages of this method are theuse of a very small amount of sample and little samplepretreatment. The precision and accuracy of the results

depend on the weighing process, distribution of particlesin the sample, and its homogeneity. The disadvantages areincreases in interferences and calibration technique [1, 2, 410].

In SS-ETAAS, the interferences, kinetic of atomization,shape of the signal, and sensitivity depend on the amountof the sample, the form of the analyte, and the matrixcomposition. If the properties of the sample and standardsfor calibration are dierent, an error can occur. Therefore,the right calibration technique is very important. The firstmethod is the application of solid standards, such as certifiedreference materials with properties similar to the analyzedsample. The reference material is weighed on the graphiteplatform in various amounts, and every point of the cali-bration curve corresponds to one weight and measurement[11]. Vale et al. found that a higher amount of the sample hasa depressive influence on the signal and distorts the

2 The Scientific World Journal

calibrationcurve [5]. Maia et al. used five dierent referencematerials and constructed the calibration curve as depen-dence of the normalized absorbance on the certified mercurycontent [11]. The disadvantage of calibration with solidstandards is their low availability, high cost, limited con-centration range, and limited possibility to prepare artificialsamples [5, 6, 11]. If the matrix components interfere, thestandard additionmethodmay be used. Thismethod is basedon the assumption that a change in response for the sampleand the sample with an addition of standard correspondsonly to the change of the concentration. For solid samplestwo techniques can be used: the addition of an aqueous stan-dard or the addition of reference material to the solid sample.A disadvantage of this method is that it is impossible toensure the constant sample mass [7].

Another technique is calibration against aqueous stan-dards. The main problem with the determination of mer-cury in a solution by ETAAS is the high volatility ofthe element and its compounds. Therefore, additions ofthermal stabilizing agents are applied to avoid losses ofmercury. Because inorganic mercury compounds are lessvolatile than the element itself, various oxidizing agentssuch as hydrogen peroxide, permanganate, or dichromatewere used to prevent their reduction [1, 3, 8, 12, 13].Reagents containing sulphur as dithizone, diethyldithio-carbamate (DEDTC), or tetramethylene dithiocarbamate(TMDTC) stabilize mercury by the formation of complexand subsequently mercury sulphide [1, 1315]. A successfulapproach used to stabilize mercury is the application ofmodifiers to the graphite atomizer surface. Gold, platinum,palladium, rhodium, and iridium or their mixtures wereinvestigated. Palladium is applied most frequently. Themodifiers can be deposited onto an atomizer surface bythe thermal or electrochemical method [1, 1013]. In SS-ETAAS, calibration against aqueous standards was applied,utilizing oxidizing agents and modifiers of the graphiteatomizer surface [1, 10]. In [1], a loss-free determinationof mercury in aqueous calibration solutions was reachedonly through the addition of potassium permanganate andby using Pd, thermally deposited on the SS platform. Thisprocedure was satisfactory for mercury determination in ash,sludge, and sediment reference materials. In our previouswork [10], permanganate was used together with a Pdmodifier, electrochemically deposited on the SS platform.However, the use of permanganate has some disadvantages.For technical reasons the dosing of only 3 L of KMnO4solution onto the SS platform with concentration >10 g L1

is possible. By the injection of a volume >3 L, a drop ofsolution with great viscosity is superimposed on the innerspace of the SS platform and the insertion of the SS platforminto to the graphite tube without any spills, using tweezers,is impossible. For the optimal total amount of KMnO4(0.3mg), a concentration of 100 g L1 is required for 3 L ofthe solution. Moreover the preparation of such a solution ofpermanganate is dicult [10].

Therefore, the aim of this work was to select anothersuitable stabilizing agent for calibration solutions. For thispurpose, the influence of thiourea, tetramethylene dithio-carbamate, and diethyldithiocarbamate was studied. In our

Table 1: Temperature program for the determination of mercury.

Stage Temperature (C) Ramp (C s1) Hold (s)

Drying 90a, 120b 30 15

Pyrolysis 200 30 40

AZc 200 0 6

Atomizationd 1100 1500 10

Cleaning 1700 200 4aDrying temperature for aqueous solutions, bdrying temperature for MIBKcalibration solutions in the presence of TMDTC and DEDTC, cauto zero,dgas stop.

previous work [10], the electrodeposition from a drop ofa modifier solution proved to be suitable method of prepa-ring the Pd surface for the determination of mercury bySS-ETAAS. Because palladium has a relatively low boilingpoint, another metal for coating the SS platform was tested.On the basis of our previous results by the determinationof gold with the complete electrochemical coating of thegraphite tube surface, rhenium was chosen [16]. Palladium,and newly, rhenium were used as modifiers of the graphiteplatform surface for the determination of mercury in solidenvironmental samples as soil and plant.

2. Experimental

2.1. Instrumentation. A ZEEnit 650 atomic absorption spec-trometer (Analytik Jena, Germany) with a transverselyheated graphite tube and a solid sampling system SSA61Z was used for all measurements. The spectrometer wasequipped with a Zeeman-based and deuterium backgroundcorrector. The magnetic field of an electromagnet wasapplied to the graphite atomizer by the 2-fieldmode. Zeemancorrections were used throughout the work, and a deuteriumdevice was used only in special cases. A mercury hollowcathode lamp at current 4.5mA was used as the radiationsource. Measurements were performed in the peak areamode at 253.7 nm using a spectral bandwidth of 0.5 nm.Calibration solutions were applied manually onto an SSgraphite platform (Analytik Jena, Part no. 407-152.023) andintroduced into the graphite tubes without a dosing hole(Analytik Jena, Part no. 407-152.316) in the same way as thesolid samples. The calculated integrated absorbance per mgof the sample is introduced as the normalized absorbance.The temperature program for the determination of mercuryis presented in Table 1.

For comparison purposes, the mercury content in envi-ronmental materials was also determined using the AMA254 analyzer (Altec, Czech Republic). The measurement inthis single-purpose atomic absorption spectrometer is basedon the combustion of a sample in a flow of oxygen andthe subsequent capture of mercury by a gold amalgamator.After thermal release from amalgamator, the mercury vapouris measured. This pyrolysis approach in AAS is frequentlyused in analysis of environmental and biological materials,for example, marine sediments, soil, citrus and tomatoleaves [17]. Each time, 40100mg of a sample was weighed

The Scientific World Journal 3

mA

V

1

2

3 4

+

Figure 1: Schematic diagram for electrodeposition from a drop. (1)Power supply, (2) SS platform: cathode, (3) Pt wire: anode, (4) dropof modifier solution.

or 10200 L of solution was dosed in nickel boats. Thesolid samples were dried at 120C for 60 s and decomposedat 650C for 150 s. The AMA 254 analyzer was regularlycalibrated using standard solutions of 11000 gL1 ofmercury for the first (06 ng Hg) and second (0200 ngHg) calibration intervals. The calibration solutions wereprepared by diluting the stock standard solution with 0.05%(m/v) K2Cr2O7 and 0.6% HNO3 to improve their stability.The accuracy of the results was controlled by analysis ofthe standard reference material GBW 07405. The relativestandard deviation (RSD) was 3.2% (at 0.29mgkg1 Hg,n = 10).

2.2. Chemicals and Solutions. Hg(II) solutions were preparedfrom the stock standard solution for mercury (1.000 0.002 g L1 Hg, Analytika, Czech Republic) in 2% HNO3by dilution with 5% (v/v) HNO3. Thiourea p.a. (SigmaAldrich), ammonium tetramethylene dithiocarbamate p.a.(TMDTC, Sigma Aldrich), acetic acid p.a. (Fluka), sodiumacetate p.a. (Fluka), sodium diethyldithiocarbamate p.a.,(DEDTC, Lachema), acetylacetone p.a. and methyl isobutylketone p.a. (MIBK, Lachema) were used for the preparationof calibration solutions. A stock solution of 110 g L1

KMnO4 (Merck) was prepared as in [10] with the supportof an ultrasonic bath and added to the calibration solutionsfor a final concentration of 100 g L1. PdCl2 (Merck, Darm-stadt, Germany) and NH4ReO4 (Analytika, Czech Republic)standard solutions containing 10 g L1 Pd or Re were used tomodify the graphite platform surface.

2.3. Samples and Their Treatment. A Certified reference ma-terial (CRM) soil GBW 07405 (National Centre for StandardMaterials, Beijing, China) and the environmental samplesof soil II and plant Scirpus from the Hg-polluted area wereused. The environmental samples were ground in a millFritsch Pulverisette 7 with balls from Si3N4 and passedthrough a nylon sieve for a particle size of 56 m. The

Table 2: Temperature program (according to study [1]) fortreatment of platform after the electrodeposition of modifiers froma drop of solutions.

Stage Temperature (C) Ramp (C s1) Hold (s)

Drying 90 30 15

Pyrolysis 250 20 35

AZa 250 0 6

Atomization 1000 1000 10

Cleaning 2000 200 5aAuto zero.

aliquots of environmental samples between 0.1 and 0.5mgor CRM GBW 07405 210mg were weighed directly ontothe SS platforms and inserted into a graphite tube. Beforeeach weighing on the SS platform, these ground sampleswere carefully stirred. The residues of solid samples afteratomization were easily removed from the platform.

2.4. Electrodeposition of Palladium and Rhenium from a Dropof Solutions. The surface modifiers were applied to thegraphite platform using 7 injections of 20 L of solutionof 2 g L1 Pd or Re. The graphite platform with a dropof modifier solution served as the cathode and a Pt wirewas used as the anode (Figure 1). Electrodeposition of everydrop proceeded by the current 10mA for 5min. After eachdeposition, the surface of the SS platform was rinsed withwater, dried, the SS platform was inserted into the graphitetube, and the temperature program started according toTable 2. The amount of Pd or Re electrodeposited ontothe SS platform was calculated from the dierence of itscontent in the solution before and after electrolysis. Duringelectrodeposition 250 g Pd or Re was deposited.

2.5. Preparation of Calibration Solutions of Hg(II) in thePresence of TMDTC and DEDTC. Calibration solutions ofHg(II) in the presence of TMDTC and DEDTC wereprepared using two methods:

(i) The extraction of mercury with chelating agents intoMIBK or acetylacetone.1mL of mercury(II) solution, 2mL of 2.5 g L1

TMDTC or DEDTC aqueous solution and 1mL ofacetate buer (pH 5) were pipetted into the extrac-tion tube. After shaking, 4mL acetylacetone or MIBKwas added. The chelates were extracted into theorganic phase on the shaker at a speed of 300 RPMfor 1 h. The extraction eciency was checked bymeasuring the absorbance of the aqueous phase.

(ii) The preparation ofMIBK-methanol solution from anaqueous methanol solution refilled by MIBK.The calibration solutions of Hg(II) in the presence ofTMDTC were prepared from 0.5mL of Hg(II) aque-ous solution, 1mL of 25 g L1 TMDTC in methanoland 1mL of 1mol L1 sodium acetate in methanol.After shaking, the solution was diluted with MIBK to10mL to formation of single phase.


Table 3: Maximum pyrolysis temperatures for the determination ofmercury in calibration solutions with the stabilizing agents.

Temperature/C

Agents Pd Re

Potassium permanganate 250a 280

Thiourea 280

TMDTC 200 200

DEDTC 200 230a[10].

3. Results and Discussion

3.1. Stability of Surface Modifiers. The modifier of the graph-ite platform surface has a limited lifetime. To its investiga-tion, the solution of a constant concentration of mercury wasalways applied after the 10 atomization cycles, and mercuryabsorbance was measured. In our previous work [10], thelifetime for the Pd modifier was found to be 100120atomization cycles. In case of the Re, a sensitivity decreaseof 10% was observed after 200 cycles. The Re modifier ismore stable due to a higher boiling point than Pd. Thesurface of the platforms was always recoated with optimalmass of 250 g Pd or Re after 100 or 200 cycles. By usingthe less mass of modifier, lower sensitivity was observed.The electrodeposition from a drop proved to be a suitableway for graphite surface modification with rhenium as well.This technique does not require a special cell, the electrolysisspans a short time (35min), and the electrochemical coatingof the SS platform is ensured.

3.2. Stabilizing Agents for Hg(II) in Solution. The pyrolysiscurves (Figures 2 and 3) and the influence of the amounts ofstabilizing agents on mercury absorbance were investigatedfor both surface modifiers and all stabilizing agents. Thesolutions were injected in a volume 20 L. For comparisonthe results obtained for solutions of mercury(II) only indiluted nitric acid without a stabilizing agent are shown.The integrated absorbance for mercury is low and indicatesthat part of mercury was lost, probably already during thedrying stage. The investigated graphite surfacemodifiers thushave little stabilizing eect for mercury in a diluted nitricacid solution during the drying stage. Therefore, the additionof a stabilizing agent into calibration solutions is necessary.Maximum usable pyrolysis temperatures for solutions ofmercury(II) with stabilizing agents are shown in Table 3. Inthis table, the data for potassium permanganate with Pdmodifier [10] and newly measured with Re modifier arementioned.

The aqueous calibration solutions in the presence of1 g L1 thiourea were prepared at pH 1.5.With Zeeman back-ground correction for both Pd and Re modifiers, an over-correction of the signal was observed and the absorbancerecord was made impossible. A change of pH in range1.55, similarly to the concentration of thiourea in range0.130 g L1, did not eliminate this eect. With deuteriumbackground correction and Pd modifier, a dual-split peak

100 150 200 250 300 350 4000

0.2

0.4

0.6

0.8

1

1.2

1.4

0

0.02

0.04

0.06

0.08

0.1

0.12

Pyrolysis temperature (C)

Inte

grat

ed a

bsor

ban

ce (

s)

Inte

grat

ed a

bsor

ban

ce (

s)

Figure 2: Pyrolytic curves for Hg(II) solutions in the presence ofstabilizing agents and Pd surface modifier. left axis: DEDTC, TMDTC; right axis: without stabilizing agent.

100 150 200 250 300 350 400 4500

0.2

0.4

0.6

0.8

1

1.2

0

0.02

0.04

0.06

0.08

0.1

0.12


Inte

grat

ed a

bsor

ban

ce (

s)

Inte

grat

ed a

bsor

ban

ce (

s)

Figure 3: Pyrolytic curves for Hg(II) solutions in the presence ofstabilizing agents and Re surface modifier. left axis: thiourea(deuterium background correction), DEDTC, TMDTC; rightaxis: without stabilizing agent.

was observed. By using the graphite platform, modified withRe and with deuterium background correction, the determi-nation of mercury was possible with RSD = 3.54.1% for 510 ng Hg (n = 5). The calibration curve was linear to 10 ngHg (R2 = 0.9955).

TMDTC forms with Hg(II) stable chelate, which maybe extracted in an organic solvent. Acetylacetone and MIBKwere selected for this purpose. The use of an acetylacetoneas a solvent was not appropriate, because overcorrectionof the signal was observed. Preevaporation of acetylacetoneunder an infralamp did not eliminate this eect. By usingMIBK as a solvent, mercury was stabilized to 200C for bothsurface modifiers. However, the overcorrection of the signalwas observed with the use of a Pd modifier and Zeemanbackground correction at pyrolysis temperatures 260340C.This eect was not observed by using deuterium backgroundcorrection. The presence of 0.014mg TMDTC in 20 L ofcalibration solution had no influence on the mercury signal,and the amount of 0.05mg TMDTC was chosen as optimal.Both methods of preparation of the calibration solutions,with the use of extract in MIBK and with aqueous methanolsolution refilled by MIBK, yielded the same results. TheRSD values for the measurements with extracts by pyrolysistemperature 200C were 1.32.4% for 1015 ng Hg (n = 5)


Table 4: Results obtained for mercury content in environmental materials using SS-ETAAS with modification of platform surface andcalibration against calibration solutions.

Material

Obtained value SD/mg kg1 (n = 5) Certified anddetermined

value SD/mg kg1TMDTC/MIBK TMDTC/methanol/MIBK KMnO4

a

Pd Re Pd Re Pda Re

Soil II 37.2 1.8 37.7 1.9 38.9 1.3 38.3 1.4 38.8 1.6 36.6 2.1 38.1 0.7Plant 35.7 1.7 37.5 1.8 37.4 1.6 37.7 1.4 37.7 2.0 36.5 1.8 37.6 0.5GBW 07405 0.25 0.02 0.27

0.020.30 0.02

0.29 0.02

0.30 0.01

0.27 0.02

0.29 0.03aAccording to procedure in [10].

90 130 150 180 200 230 250 280 300 3300

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

Nor

mal

ized

inte

grat

ed a

bsor

ban

ce

Nor

mal

ized

inte

grat

ed a

bsor

ban

ce


Figure 4: Pyrolytic curves for solid samples in presence Pd surfacemodifier. left axis: plant, soil II; right axis: CRMCBW 07405.

with Pd modifier and 1.9-2.0% for 1015 ng Hg (n = 5) withRe modifier. The RSD of mercury determination in MIBK-methanol solution was 1.92.4 for 1015 ng Hg (n = 5)with Pd modifier and 2.02.5% for 1015 ng Hg (n = 5)with Re modifier. Calibration curves were linear to 15 ng Hg(R2 = 0.9975 or R2 = 0.9994 for extracts with Pd or Remodifier and R2 = 0.9976 or R2 = 0.9994 for MIBK-methanol solution with Pd or Re modifier). By using the Pdmodifier, the detection limit, 128 pg Hg, acquired through6 repetitive firings of the platform with TMDTC enables thedetermination of 0.43mg kg1 Hg for an optimum samplemass of 0.3mg. By using the Re modifier, the detection limitwas 120 pg Hg and 0.40mg kg1 Hg.

DEDTC as the chelating agent was not suitable for sta-bilization of mercury in calibration solutions, because dual-split peaks were obtained for both types of modifiers andbackground corrections. The change of the concentrationof DEDTC in a range of 0.014mg DEDTC in 20 L ofsolution or modification of the temperature program had noinfluence on the shape of peak.

The use of 100 g L1 of permanganate in combinationwith the Re modifier of the graphite platform surfaceprovided better results than those in combination with Pdmodifier. The disadvantage of permanganate is the necessityof dosing only 3 L of KMnO4 solution and diculty inpreparing the stock solution of permanganate. The RSD ofmercury determination was 4.04.9% for 1015 ng Hg (n =5) with the Pd modifier [10] and 3.55.0% for 1015 ng

130 150 170 200 230 250 2800

0.3

0.6

0.9

1.2

1.5

1.8

2.1

0

0.005

0.01

0.015

0.02

0.025

Nor

mal

ized

inte

grat

ed a

bsor

ban

ce

Nor

mal

ized

inte

grat

ed a

bsor

ban

ce


Figure 5: Pyrolytic curves for solid samples in presence Re surfacemodifier. left axis: plant, soil II; right axis: CRMCBW 07405.

Hg (n = 5) with the Re modifier. Calibration curves werelinear to 15 ng Hg (R2 = 0.9991 for the Pd modifier andR2 = 0.9998 for Re modifier). By using the Pd modifier, thedetection limit, 120 pg Hg, was acquired from 10 repetitivefirings of platform with KMnO4 and enabled determinationof 0.40mg kg1 Hg for an optimum sample mass of 0.3mg.By using the Re modifier, the detection limit was 110 pg Hgand 0.37mg kg1 Hg.

3.3. Analytical Results. The pyrolytic curves (Figures 4 and 5)were investigated for solid samples by using both surfacemodifiers and from their shape maximum usable pyrolysistemperature results for soil II 280C with Pd or 230C withRe, for plant 200C with Pd or 230C with Re, and for CRMGBW 07405 200C with both surface modifiers. The resultsobtained for mercury content in soil II, plant, and CRMGBW 07405 using SS platforms modified with palladiumor rhenium electrolytic from a drop of modifier solutionsand calibration against MIBK extracts or MIBK-methanolsolutions in presence of TMDTC are given in Table 4. Forcomparison the results obtained for permanganate with thePd modifier presented in [10] or with the Re modifier newlymeasured in this paper are also mentioned. In all cases,the results are in good agreement with the certified valueand with those obtained by measurement on the AMA 254analyzer. The RSD values are dependent on the numberof platform firings and consequently on the state of the


platform surface. According to the results, the switch fromthe calibration solutions to the samples on the modifiedsurface can also play a certain role. It can be connected withincreased precision of mercury determination using calibra-tion solutions in the presence of TMDTC.

4. Conclusion

Agents such as TMDTC, DEDTC, and thiourea were in-vestigated for complexation of mercury in calibration solu-tions and its thermal stabilization in a solid samplingplatform in the determination of mercury using SS-ETAAS.The calibration solutions were used in the form of MIBKextracts or MIBK-methanol solutions for the TMDTC andDEDTC chelates and aqueous solutions for the thioureacomplexes. Only calibration with TMDTC was successful.MIBK-methanol solutions in the presence of TMDTC areeasier to prepare than MIBK extracts. Therefore, calibrationwith MIBK-methanol solutions in the presence of TMDTCwas preferred. Higher precision in calibration and easiermanipulation with the solutions makes the calibration withMIBK-methanol solutions preferable to the heretofore usedpotassium permanganate [1, 10]. The use of standardsolutions for calibration also provides the best precision andlowest uncertainty prior to the use of reference materials.The surface of the graphite platforms for solid sampling wasmodified with palladium or rhenium using electrodepositionfrom a drop of solutions. This process of electrochemicalcoating of the SS platform surface is promising for the prepa-ration of graphite surface modifiers in SS-ETAAS. The Remodifier is preferable due to the higher lifetime of platformcoating. The use of the SS-ETAAS method with a modifiedsurface of the SS platform and calibration against stabilizedcalibration solutions reduces the time of analysis comparedwith the mercury determination after the sample digestion.Sample preparation requires only routine grinding andhomogenization. The new SS-ETAAS procedure using directsampling solid samples into a platform with an Re modifiedgraphite surface, and the calibration against MIBK-methanolsolutions in the presence of TMDTC is proposed for thedetermination of mercury content in solid environmentalsamples, such as soil and plants. With calibration againstMIBK-methanol solutions in the presence of TMDTC, thedetection limit was 120 pg and with a sample mass of 0.3mgit was 0.4mg kg1 Hg.

Acknowledgments

This work was supported by the project MSM 0021622412 ofthe Ministry of Education, Youth and Sports of the CzechRepublic and the project MUNI/A/0992/2009 of MasarykUniversity in Brno.

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