Development of Cellulosic Paper-Based Test Strips for …with mercury(II) and the coordination...

Research ArticleDevelopment of Cellulosic Paper-Based Test Strips forMercury(II) Determination in Aqueous Solution

ShoujuanWang1ZhenXu2Yongyi Fang2ZhongmingLiu1XinZhao 1GuihuaYang 1

and Fangong Kong 1

1State Key Lab of BiobasedMaterial and Green Papermaking Key Laboratory of Pulp and Paper Science and TechnologyMinistryof Education Qilu University of Technology (Shandong Academy of Sciences) Jinan Shandong 250353 China2Xuancheng Product Quality Supervision and Inspection Institute Xuan Cheng Anhui 242000 China

Correspondence should be addressed to Xin Zhao zhaoxin_zixi126com Guihua Yang ygh2626126com and FangongKongkfgwsj1566163com

Received 11 June 2018 Revised 21 August 2018 Accepted 2 September 2018 Published 1 November 2018

Academic Editor Chih-Ching Huang

Copyright copy 2018 Shoujuan Wang et al 7is 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 isproperly cited

Titration method (dropping-on method) was introduced as an efficient approach for determining the mercury ion (Hg2+)concentration in aqueous solution by using fabricated cellulosic paper-based test strips In this study dithizone used as a rec-ognition reagent was physically loaded on cellulosic paper-based test strips for Hg2+ selective recognition7e sensing mechanismwas established on the spectral absorption rate of the coordination compound that was formed by dithizone and Hg2+ understrong acidic conditions 7e calibration curve was obtained by the absorbency of Hg2+-dithizone complexes from different Hg2+

concentration solutions and the correlation coefficient (R2) reached 09971 7e detection range of the test trip for Hg2+ wasobtained at 01 μgmL to 30 μgmL Moreover these superior cellulosic paper-based test strips have a rapid color-forming time(15min) and low volume demand (37 μL samples at 00127 gL dithizone recognition concentration) 7is portable paper-basedtest strip can give potential applications for field screening or on-site semiquantitative analysis

1 Introduction

Mercury is one of the most toxic elements to human healthcausing several symptoms related to polyneuropathy mer-curialis neurasthenia etc [1] Mercury ions can persistentlyexist in water environments and accumulate easily in or-ganisms Moreover it has high toxicity even in low con-centrations [2] 7erefore mercury pollution is animportant issue that demands an ongoing development ofanalytical procedures to ensure its reliable determination[3 4] To fulfill the demands of the environmentally sus-tainable oriented goal for determining mercury in variousmatrices and at various levels of concentration an essentialtool is needed to assure accuracy and establish the trace-ability of the measured results A lot of approaches have beenused to develop optical or visual disposable sensors formercury ion determination 7e most common approaches

are methods with spectrometric detectors [5ndash7] Meanwhileseveral compounds have been shown as selective for metalanalysis and used as receptors for the design of sensingsystems ranging from alloys and amalgam [8] and syntheticmetal ionophores [9 10] to biological receptors [9 11]

A fluorescence-based paper test strip is developed byusing N-alkylaminopyrazole ligands for mercury detectionin water and a linear range from 10 μgmL to 100 μgmLmercury ion concentration ([Hg2+]) was achieved [2]Meanwhile pyrazole-derived ligands have been determinedto be suitable for the coordination of metal ions [12ndash14] Apolyester sheet with a sensing area containing plasticizedpolyvinyl chloride (PVC) was made by incorporating tet-raarylborate salt as a selective recognition reagent anda porphyrin proton-selective fluoroionophore as the opticaltransducer for Hg2+ [15] Later Yallouz et al incorporatedcuprous iodide (Cu2I2) carboxymethyl cellulose membranes

HindawiJournal of Analytical Methods in ChemistryVolume 2018 Article ID 3594020 7 pageshttpsdoiorg10115520183594020

on paper for Hg2+ in fish samples [16] Shi and Jiang useda pH indicator color for Hg2+ in waters with a detection limitof 02 ngmL under the inhibition of the different types ofenzymes [17] Capitan-Vallvey et al developed an irre-versible optical test strip for mercury determination basedon an ion-exchange mechanism [18] A circular sensing zonecontaining the essential reagents was used to produce a se-lective response for Hg2+ and consisted of plasticized PVCincorporating the cation-selective neutral ionophoreChandio et al also developed a PVCmembrane ion selectiveported to determine the Hg2+ in waste water [19] Gurrsquoevaet al developed a test method for the mercury(I II) de-termination by putting an intensely colored insolublecompound on a polycaproamide membrane surface in weakacid solutions depending on the reaction between mercury(I II) and 5-chloro-2-hydroxy-3-[(tetrahydro-24-dithioxo-13-thiazin-5-yl) azo] benzenesulphonic acid [20] Howevermost of these methods require expensive chemicals andinstruments and the treating procedure is complex and noteasy to handle In addition most of these test strips are basedon the plastic membrane technology 7e used test strips arenot reusable and biodegradable after disposal Also as thediffusion of Hg2+-containing solution in the plastic mem-brane is very slow even there are plasticizers in the mem-brane the color-forming time usually needs a few minuteseven a few hours which is not suitable for on-site screeninganalysis7erefore great emphasis still needs to be placed onthe development of a low cost and convenient method formercury determination

Dithizone as a kind of color-forming agent has low costand efficiency advantages which can produce coloredcomplexes between the color-forming agent in the paperstrip and Hg2+ in the sample [21] Based on the reactionbetween the dithizone and Hg2+ in the trichloromethaneunder strongly acidic conditions the paper-based test stripfor determining the concentration of Hg2+ in aqueous so-lutions could be developed 7e test strip reacted rapidlywith Hg2+ could lead to color formation of the test stripSubsequently the test color liquid diffused in indefinitedirections due to liquid diffusivity For the dipping-inmethod the absorbency value continued to increase withthe reaction time and it was difficult to determine the resultof color forming due to the reaction of the test strip andHg2+or liquid diffusivity

7e aim of this work is to introduce an efficient andsimple approach to fabricate cellulosic paper-based teststrips by physically impregnating paper strips in dithizone-containing solution to load dithizone into strips for de-termining the Hg2+ in aqueous solution 7is preparation ofthe dithizone-loaded test strip is very simple and easilyoperated using biodegradable materials paper strips at lowcost compared with other plastic-based test strips In thisstudy dithizone is used as a recognition reagent to achieveselective recognition by Hg2+ with dithizone under strongacidic conditions 7e calibration curve and pertinence areobtained by the absorbency from different concentrations ofHg2+ Furthermore all the experiments are performed to-wards the detection linear range of the test strip system andsuperior test conditions of cellulose paper-based test strips

2 Experimental

21 Materials 7e paper sample used for the test strip wasquantitative filter paper of medium porosity which wasobtained from Fisher Scientific (Jinan China) Dithizonewas obtained from Sigma-Aldrich (Jinan China) Mercurysolutions with various concentrations were freshly pre-pared by dissolving a certain amount of mercury nitrate innitric acid solution with pH 20 Other solutions includingmercury ions (Hg2+) potassium ions (K+) calcium ions(Ca2+) sodium ions (Na+) manganese ions (Mn2+)magnesium ions (Mg2+) copper ions (Cu2+) barium ions(Ba2+) aluminum ions (Al3+) iron ions (Fe3+) zinc ions(Zn2+) phosphate ions (PO4

3-) chloride ions (Clminus) andsulfate ions (SO4

2minus) were prepared by using analyticalreagent-grade chemicals and nitric acid solution with pH20 7e pH of solutions was adjusted by adding eitherdiluted sodium hydroxide (NaOH) or nitric acid (HNO3)solution 7e spiked water sample of Hg(II) was preparedby adding Hg(II) into tap water with its pH adjusted to 20

22 Apparatus A UV-Vis spectrophotometer (UV-2550Shimadzu Nagoya Japan) was used to determine the ab-sorption of the colored complex solutions A reflect spec-trophotometer (i1Basic Pro2 X-Rite Agilent Foster CityCalifornia USA) was used for the measurement of colorintensity formed on the test strip

23 Preparation of Cellulosic Paper-Based Test Strip 7edithizone was dissolved in trichloromethane (Fisher Sci-entific Jinan China) with a concentration of 00127 gL 7efilter paper was then immersed into this solution for 2min atroom temperature 7e filter paper with dithizone was driedat 50degC in a nitrogen protected environment 7e dried filterpaper was then cut into 5 cmtimes 1 cm strips sealed in a plasticbag and kept until further use 7e paper strip immersed in00127 gL dithizone solution had a 033mgcm2 dithizoneloading amount

3 Methods

31 Spectral Reflectivity Measurement 7e Hg2+ solutionwas dropped on the paper-based test strip After the color-forming reaction finished the color intensity developed onthe test strip was measured using the reflect spectropho-tometer at a fixed wavelength of 490 nm

7e color forming depended on the dithizone reactionwith mercury(II) and the coordination compound(dithizone-mercury complex) was formed and the linearrelationship between the absorbency value and differentHg2+ concentrations was tested by spectrophotometer ata fixed wavelength of 490 nm [22]

32Hg(II)DeterminationUsingUV-VisSpectroscopyMethodA 250mL mercury solution with 10 μgmL concentrationwas put into a separatory funnel (500mL) by adding 1mLsodium sulfite (20) After mixing 10mL dithizone-trichloromethane solution was added and the solution

2 Journal of Analytical Methods in Chemistry

layered after 1min 7e mercury solution after contactingwith the dithizone was dissolved in the trichloromethaneand was transferred to a cuvette of the spectrophotometricmeasurements A UV-Vis spectrophotometer (UV-2550Shimadzu Nagoya Japan) was used to measure the ab-sorbance value of the dithizone-mercury complex in thesolution [22] 7en the concentration of Hg(II) was cal-culated based on the calibration curve obtained in this study

Y 00558X + 00391

R2

09932(1)

where Y is the absorbance value and X is the mercury ionconcentration (μgmL)

4 Results and Discussion

41 Development of Paper-Based Test Strip Due to the highspecific surface area and plenty of capillary pores papersheets such as filter paper have high absorbability of in-organic or organic liquids [23] By loading the effectivechemicals onto a paper sheet a paper-based test strip specificfor the determination of Hg(II) concentration is expected tobe portable user-friendly and handy From this viewpointthe selection of a suitable reagent to extract the Hg(II)content puts emphasis on the following considerations 7ispaper-based test strip would have specific features of (i)giving a color response so that the test strip to be used witha color chart or miniature device can quantitatively de-termine the Hg(II) concentration in the field screening oron-site semiquantitative analysis without excessive labora-tory instruments and (ii) having a selectivity for Hg(II) sothat the sample pretreatment steps would be minimizedBecause of the high stability constant of the Hg(II)-dithizonecomplex the dithizone formed a much more stable complexwith Hg(II) 7e extraction process of Hg(II) was performedusing dithizone with a high selectivity to avoid any in-terfering elements in the extraction process

7e detection principle for the mercury assay of this teststrip method is shown in Figure 1 [24] Dithizone is one ofthe foremost extractants that is recognized as a sensitivereagent for the determination of Hg(II) in acidic media It iscapable of forming primary and secondary dithizonates withHg(II) [25 26] Meanwhile due to a higher absorptivitycoefficient and solubility in the organic phase the primarymercury-dithizonate chelate is preferred in the spectro-photometric determination as well

7e dissolved diatomic mercury ions Hg(II) are thecommon form in aqueous solution 7e Hg(II) could reactwith dithizone under acidic condition and the complex iscolored In addition the colored complex and the con-centration of the Hg(II) ion are in accordance with theLambertndashBeer law

A lg1T

1113874 1113875 kbc (2)

where A is the absorbency (L(mollowastcm)) T is the trans-missivity (degC) and b and c are the concentration of the light-absorbing material (molL) and the thickness of theabsorbed layer (cm) respectively

Figure 2 shows the characteristic absorption of themercury-dithizone complexes in aqueous solution 7eabsorbency gradually increased as the wavelength increasedto 490 nm Afterwards the absorbency gradually decreasedas the wavelength continued to increase 7e results showedthe maximum absorption peak of this Hg(II)-dithizonecomplex was at 490 nm Subsequently the measurementof spectra reflectivity was measured at 490 nm7e apparentmolar absorptivity at 490 nm was 06 Lmiddotmolminus1middotcmminus1

Figure 3(a) shows the linear relationship between theabsorbency value and different reaction times of the test stripand Hg2+ via the dipping-in method which is that the paper-based test strip is dipped directly into the Hg2+-containingsolution firstly and then pulled it out from the solution tomeasure the absorbency In this process the test strip reactedrapidly with Hg2+ in solution which led to color formationof the test strip However in this process the Hg2+ containedin solution can continuously react with dithizone whichloaded in the paper-based test strip which caused the colorabsorbency of mercury-dithizone complexes formed onpaper-based test strip increase with the prolongation ofdipping time as shown in Figure 3(a) 7e dipping-in timeof the test strip needs to be strictly and accurately controlledif this dipping-in method was used in determining Hg2+concentration which is very difficult to operate by handespecially in on-site screening analysis To solve this issuethe dropping-on method was chosen to use In this methodcertain amount of Hg2+-containing solution was dropped onthe dithizone-loaded paper-based test strip Subsequentlythe absorbency of the test strip colored by mercury-dithizone complexes was measured using spectrophotom-eter During the measurement of using this dropping-onmethod it was found that the colored liquid (mercury-dithizone complexes) diffused in indefinite directions dueto liquid diffusivity For the dropping-on method althoughthe absorbency value does not continued to increase with thereaction time it was still difficult to accurately determine theresult of color forming due to nonuniformity of coloredcomplexes on the paper strip due to the Hg2+ or liquiddiffusivity

To overcome this diffusivity phenomenon a horizontalcircle 9mm in diameter was made on the paper-based teststrip [27]7is marker circle served as a hydrophobic barrierto prevent the dropped mercury solution from dispersingand the uniform color is displayed in Figure 3(b) 7e teststrip shows a light green color at the absence of mercurysolution When a drop of test solution was placed on the teststrip as shown in Figure 3(b) the test strip turned into pinkat the presence of mercury solution According to a series oftrials 37 μL was a suitable volume to be placed in the circlefor preventing the mercury solution drop from dispersingand forming a uniform color In addition it should be notedthat the dithizone loaded in this 90mm circle test strip115mmol is much higher 10 times higher than that re-quired for reacting with Hg2+ 15ndash35mmol in 37 μLsolution

After solving this diffusivity phenomenon of mercurysolution on the paper-based test strip this dropping-onmethod could be used to determine the Hg2+

Journal of Analytical Methods in Chemistry 3

concentration in solution In this method the Hg2+-con-taining solution was quanticationally dropped on thesurface of circled paper-based test strip and then the Hg2+ in

the dropped solution reacts with dithizone loaded in the teststrip to form mercury-dithizone complexes which is coloredin pinke color intensity formed on the test strip is mainly

025

030

035

040

045

050

Abso

rben

cy (L

(m

ollowastcm

))

15 30 45 60 75 90 1050Time (s)

(a) (b)

Figure 3 Dishyerent images of dipping-in method and dropping-on method (a) the linear relationship between absorbency value anddishyerent dipping time of test strip and Hg2+ by dipping-in method and (b) test strip with marker circle and mercury-dithizone coloredcomplexes forming by dropping-on method

NH

HN N

S

N

NPh

H

N

NN

Ph

S

H

N Ph

H

N

NN

Ph

S

H

Hg2+

+ Hg2+ H+

Figure 1 e detection principle for the mercury assay

040

045

050

055

060

065

070

Abso

rben

cy (L

(m

ollowastcm

))

420 440 460 480 500 520 540400Wavelength (nm)

Figure 2 Characteristic absorption of the mercury-dithizone complexes in aqueous solution


ashyected by the reaction time between Hg2+ and dithizonehere namely color-forming time e test strip absorbency(color intensity) served as a standard function of color-forming time e absorbency at 490 nm of coloredcomplexes formed using 30 μgmL mercury solution to reactwith dithizone-loaded test strip at dishyerent color-formingtime (05 to 10min) is presented in Figure 4 As shown inFigure 4 the absorbency of the test strip after dropping ofHg2+ solution gradually increased with color-forming timeranging from 05min to 15min and then the absorbencyvalue tended to stabilize between 15min and 35min eabsorbency further reduced as the color-forming timeprolonged beyond 35mine absorbency increase at color-forming time from 05min to 15min is due to formation ofmore mercury-dithizone complexes through the reaction ofHg2+ with dithizone When the color-forming time reached15min the absorbency stabilized illustrating all the Hg2+ inthe dropped solution reacted completely with dithizoneloaded in test strip and formed the colored complexes andthis color intensity kept at a constant value for a while up to35min After 35min the decrease of absorbency is at-tributed to the water evaporation of the test strip emaximum and most stable absorbency value (0282)appeared at a 25min color-forming time e resultsshowed that the reliable absorbency measurement of this teststrip should be carried out in 15ndash35 minutes after droppingof Hg2+-containing solution on the test strip

42 Calibration Curve To establish the calibration curvemercury solutions with various concentrations were pre-pared and used (Figure 5) Under the optimum conditionspH 20 and reaction time 25min a linear calibration curvewas constructed for Hg(II) determination over the range of01 μgmL to 30 μgmL e correlation coecient (R2) was09971 which showed an acceptable linearity of the cali-bration curve rough the data analysis presented in Fig-ure 5 it is found that the upper and lower detection limits ofthis paper-based test strip method are 30 μgmL and01 μgmL respectively Although this lower detection limitwas not enough for detection of Hg2+ ions in drinking watersor lake waters it could be used for determination of wastewaters from industry e paper-based test strip with muchlower detection limit suitable for detecting lake waters ordrinking waters is our another research work which is goingand will be reported in detail in our another paper

43 Selectivity of Paper-Based Test Strip In practice Hg2+

cannot exist alone because large numbers of anions andcations also exist However the dithizone is eshyective onvarious ions As shown in Figure 6 the test strips haveabsorbency for the dishyerent ions (Hg2+ K+ Ca2+ Na+Mn2+ Mg2+ Cu2+ Ag+ Ba2+ Al3+ Fe3+ Pb2+ Zn2+PO4

3minus Clminus and SO42minus) Furthermore Hg2+ displayed

excellent absorbability due to the test strips having bettersensitivity and selectivity with the Hg2+ in the solutionOccasionally Mn2+ Mg2+ Pb2+ Cu2+ Ag+ Clminus andSO4

2minus interfered a little with mercury [2] and according to

y = 00543x + 02815R2 = 09971

010

015

020

025

030

035

040Ab

sorb

ency

(L(

mol

lowastcm

))

ndash15 ndash10 ndash05 00 05 10 15 20ndash20lg (Hg2+)

Figure 5 Working range of paper-based test strip (pH 20 color-forming time 25min)

Abso

rben

cy (L

(m

ollowast

cm))

022

024

026

028

030

032

034

036

038

Pd2+

Ag+K+

Na+

Cu2+

Mg2+

Mn2+

Ca+

Ba2+

PO43ndash

Zn2+ Cl

ndash

Al3+

SO42ndash

Hg2+

Fe3+

Blan

k

Figure 6 Absorbency of various metals in contact with thedithizone-loaded test strip shown are the responses from blank(MilliQ water) 20mgL of Hg2+ K+ Ca2+ Na+ Mn2+ Mg2+ Cu2+Ag+ Ba2+ Al3+ Fe3+ Zn2+ PO4

3minus Clminus and SO42minus and the con-

centration of other ions were one thousand times of Hg2+ (color-developing time 25min)

Abso

rben

cy (L

(m

ollowastcm

))

024

025

026

027

028

029

15ndash35 min

15 30 45 60 75 9000Time (min)

Figure 4 Absorbency of colored complexes formed using 37 μL30 μgmL Hg2+ solution and dithizone-loaded test strip at dishyerentcolor-forming time


the calibration curve the deviations resulted from theinterference of these ions are all less than 5 which isacceptable usually for analysis [1 9]

44 Verification of the Method with Spiked Water SamplesIn this study a high-efficiency test strip was developed in thecircle with 37 μL of the mercury solution by pipette thecolor-forming time was fixed at 25min and compared withthe reference method UV-Vis spectroscopy method bydetermining same mercury concentrations [18] 7e meanvalues from three replicate samples and the standard de-viations of these measurements are shown in Table 1 7emeasured concentrations of Hg(II) using the test strip weresimilar as these from the reference method (29 and 31 62and 60 91 and 88 and 135 and 137) 7e results exhibiteda good sensitivity and selectivity and also the deviation ofthis test-strip method was similar as that of referencemethod even better than the reference method at high Hg(II) concentration (005 and 005 021 and 018 025 and030 and 019 and 032) 7emeasured data denoted that theproposed method can be satisfactorily applied to the de-termination of trace Hg(II) in real samples

5 Conclusions

A cellulosic paper-based test strip for specially determiningHg2+ was developed 7e color-forming reagent dithizonewas physically loaded into the quantitative filter paper byimpregnation process and the mercury-dithizone com-plexes have a characteristic magenta color at acidic condi-tion 7e high-efficiency test strip method was developed bydropping 37 μL of the mercury solution via pipette ona circle test strip and the color-forming time was fixed at25min Furthermore the paper-based test strips have a highselectivity to Hg2+ ion

7e developed method offered a good sensitivity andselectivity for the determination of Hg(II) in the concen-tration range of 01 μgmL to 30 μgmL Although this lowerdetection limit was not enough for detection of Hg2+ ions indrinking waters or lake waters it is enough to be used fordetection of Hg2+ ion in waste waters from industry

7is paper-based test strip method when applied tosamples spiked with Hg2+ ions gave accurate results incomparison with the conventional method for the de-termination of Hg2+ 7erefore it can be concluded that thepaper-based test strip method developed in this study isa simple effective and reliable way of determining the Hg2+ion concentration in aqueous sample

Data Availability

7e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

7e authors declare that they have no conflicts of interest

Authorsrsquo Contributions

Zhen Xu was contributed equally

Acknowledgments

7e authors are grateful to the National Natural ScienceFoundation of China (Grant Nos 31570566 3150048931800499 and 31600472) the Natural Science Foundation ofShandong (ZR2017LEM009 and ZR2018BEM026) the KeyResearch and Development Program of Shandong Province(No 2017GSF17130) the Foundation of Guangxi KeyLaboratory of Clean Pulp and Papermaking and PollutionControl of China (KF201717) the Shandong Taishan ScholarProgram and the Foundation of Key Laboratory of Pulp andPaper Science and Technology of Ministry ofEducationShandong Province of China (Nos ZR201707and ZR201710) National Key RampD Program of China (No2017YFB0308000) and Joint Research Fund for YoungDoctor of Qilu University of Technology (ShandongAcademy of Sciences) (No 2017BSH2010)

References

[1] J Chen Y Li W Zhong H Wang P Zhang and J Jiang ldquoAhighly selective fluorescent and colorimetric chemosensor forHg2+ based on a new rhodamine derivativerdquo AnalyticalMethods vol 8 no 9 pp 1964ndash1967 2016

[2] M Kolb M Bahadir and B Teichgraber ldquoDetermination ofchemical oxygen demand (COD) using an alternative wetchemical method free of mercury and dichromaterdquo WaterResearch vol 122 pp 645ndash654 2017

[3] G Aragay H Monton J Pons M Fontbardıa andA Merkoccedili ldquoRapid and highly sensitive detection of mercuryions using a fluorescence-based paper test strip with anN-alkylaminopyrazole ligand as a receptorrdquo Journal of Ma-terials Chemistry vol 22 no 13 pp 5978ndash5983 2012

[4] J H Richard and H Biester ldquoMercury removal from con-taminated groundwater performance and limitations ofamalgamation through brass shavingsrdquo Water Researchvol 99 pp 272ndash280 2016

Table 1 Determination of Hg(II) concentration in a spiked tap water sample based on the test strip method

Sample IDTest strip method Reference method

[Hg2+] (μgmL)lowast Standard deviation (μgmL) [Hg2+] (μgmL)lowast Standard deviation (μgmL)1 29 005 31 0052 62 021 60 0183 91 025 88 0304 135 019 137 032lowastAverage value (n 3)


[5] D A Deeds A Ghoshdastidar F Raofie E A GueretteA Tessier and P A Ariya ldquoDevelopment of a particle-trappreconcentration-soft ionization mass spectrometric tech-nique for the quantification of mercury halides in airrdquo An-alytical Chemistry vol 87 no 10 pp 5109ndash5116 2015

[6] A Fashi M R Yaftian and A Zamani ldquoElectromembraneextraction-preconcentration followed bymicrovolumeUVndashVisspectrophotometric determination of mercury in water and fishsamplesrdquo Food Chemistry vol 221 pp 714ndash720 2017

[7] K Ma X Li B Xu and W Tian ldquoA sensitive and selectiveldquoturn-onrdquo fluorescent probe for Hg2+ based on thyminendashHg2+ndashthymine complex with an aggregation-inducedemission featurerdquo Analytical Methods vol 6 no 7pp 2338ndash2342 2014

[8] H Tao Y Lin J Yan and J Di ldquoA plasmonic mercury sensorbased on silverndashgold alloy nanoparticles electrodeposited onindium tin oxide glassrdquo Electrochemistry Communicationsvol 40 pp 75ndash79 2014

[9] L Farzin M Shamsipur and M A Tabrizi ldquoBiomagneticseparation and pre-concentration of trace amounts of Hg2+ inbiological samples based on T-rich oligonucleotide modifiedmagnetic beadsrdquo Analytical Methods vol 7 no 20pp 8947ndash8953 2015

[10] B Silwana D H C Van E Iwuoha and V SomersetldquoAmperometric determination of cadmium lead and mer-cury metal ions using a novel polymer immobilised horse-radish peroxidase biosensor systemrdquo ournal of EnvironmentalScience and Health Part A vol 49 no 13 pp 1501ndash15112014

[11] A Scheuhammer B Braune H M Chan et al ldquoRecentprogress on our understanding of the biological effects ofmercury in fish and wildlife in the Canadian Arcticrdquo Science oflte Total Environment vol 509-510 pp 91ndash103 2015

[12] M Cegłowski andG Schroeder ldquoRemoval of heavymetal ionswith the use of chelating polymers obtained by graftingpyridinendashpyrazole ligands onto polymethylhydrosiloxanerdquoChemical Engineering Journal vol 259 pp 885ndash893 2015

[13] M Tomas-Gamasa M S S Serdjukow M S M SuMMuller and P T Carell ldquoRemoval of heavymetal ions withthe use of chelating polymers obtained by graftingpyridinendashpyrazole ligands onto polymethylhydrosiloxanerdquoAngewandte Chemie International Edition vol 54 no 3pp 796ndash800 2015

[14] C Pettinari A Tabacaru and S Galli ldquoCoordination poly-mers and metalndashorganic frameworks based on poly(pyrazole)-containing ligandsrdquo Coordination Chemistry Re-views vol 307 pp 1ndash31 2016

[15] C Cano-Raya M D Fernandez-Ramos J Gomez-Sanchezand L F Capitan-Vallvey ldquoIrreversible optical sensor formercury determination based on tetraarylborate de-compositionrdquo Sensors and Actuator B Chemical vol 117no 1 pp 135ndash142 2006

[16] A V Yallouz D C R Calixto and S Paciornik ldquoA low-costnon instrumental method for semiquantitative determinationof mercury in fishrdquo Freseniusrsquo Journal of Analytical Chemistryvol 366 no 5 pp 461ndash465 2000

[17] G Q Shi and G Jiang ldquoA dip-and-read test strip for thedetermination of mercury(II) ion in aqueous samples basedon urease activity inhibitionrdquo Analytical Sciences vol 18no 11 pp 1215ndash1219 2002

[18] L F Capitan-Vallvey C C Raya E L Lopez and F RamosldquoIrreversible optical test strip for mercury determinationbased on neutral ionophorerdquo Analytica Chimica Actavol 524 no 1-2 pp 365ndash372 2004

[19] Z Chandio F Talpur H Khan H Afridi G Khaskheli andM Mughal ldquoOn-line preconcentration and determination ofultra trace amounts of mercury using surfactant coated alu-mina modified by dithizone with cold vapor atomic ab-sorption spectrometryrdquo RSC Advances vol 4 no 7pp 3326ndash3331 2014

[20] R F Gurrsquoeva S B Savvin and A V Mikhailova ldquoSorptionand determination of vanadium(IV V) and Mercury(I II) astheir colored complexes of organic reagentsrdquo Journal ofAnalytical Chemistry vol 58 pp 623-624 2003

[21] R Sedghi S Kazemi and B Heidari ldquoNovel selective andsensitive dual colorimetric sensor for mercury and lead ionsderived from dithizone-polymeric nanocomposite hybridrdquoSensors and Actuators B Chemical vol 245 pp 860ndash8672017

[22] S S Yamamura and J H Sikes ldquoUse of Citrate-EDTAmasking for selective determination of iron with 1 10-phe-nanthrolinerdquo Analytical Chemistry vol 38 no 6 pp 793ndash795 1966

[23] S Carrera G Santiago and M Vega ldquoSpectrophotometricdetermination of dithizonendashmercury complex by solid phasemicroextraction in micropipette tip syringe packed with ac-tivated carbon xerogelrdquo Microchemical Journal vol 129pp 133ndash136 2016

[24] Z Zhang J Li X Song J Ma and L Chen ldquoHg2+ ion-imprinted polymers sorbents based on dithizonendashHg2+ che-lation for mercury speciation analysis in environmental andbiological samplesrdquo RSC Advances vol 4 no 87pp 46444ndash46453 2014

[25] M Mudasir K Karelius N H Aprilita and E T WahyunildquoAdsorption of mercury(II) on dithizone-immobilized nat-ural zeoliterdquo Journal of Environmental Chemical Engineeringvol 4 no 2 pp 1839ndash1849 2016

[26] D Zhang M Sun and L Zou A Review on Spectrometer of Pb(II) in Water Springer Berlin Germany 2016

[27] A Y Satoh J E Trosko and S J Masten ldquoMethylene blue dyetest for rapid qualitative detection of hydroxyl radicals formedin a fentonrsquos reaction aqueous solutionrdquo EnvironmentalScience and Technology vol 41 no 8 pp 2881ndash2887 2007


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on paper for Hg2+ in fish samples [16] Shi and Jiang useda pH indicator color for Hg2+ in waters with a detection limitof 02 ngmL under the inhibition of the different types ofenzymes [17] Capitan-Vallvey et al developed an irre-versible optical test strip for mercury determination basedon an ion-exchange mechanism [18] A circular sensing zonecontaining the essential reagents was used to produce a se-lective response for Hg2+ and consisted of plasticized PVCincorporating the cation-selective neutral ionophoreChandio et al also developed a PVCmembrane ion selectiveported to determine the Hg2+ in waste water [19] Gurrsquoevaet al developed a test method for the mercury(I II) de-termination by putting an intensely colored insolublecompound on a polycaproamide membrane surface in weakacid solutions depending on the reaction between mercury(I II) and 5-chloro-2-hydroxy-3-[(tetrahydro-24-dithioxo-13-thiazin-5-yl) azo] benzenesulphonic acid [20] Howevermost of these methods require expensive chemicals andinstruments and the treating procedure is complex and noteasy to handle In addition most of these test strips are basedon the plastic membrane technology 7e used test strips arenot reusable and biodegradable after disposal Also as thediffusion of Hg2+-containing solution in the plastic mem-brane is very slow even there are plasticizers in the mem-brane the color-forming time usually needs a few minuteseven a few hours which is not suitable for on-site screeninganalysis7erefore great emphasis still needs to be placed onthe development of a low cost and convenient method formercury determination

Dithizone as a kind of color-forming agent has low costand efficiency advantages which can produce coloredcomplexes between the color-forming agent in the paperstrip and Hg2+ in the sample [21] Based on the reactionbetween the dithizone and Hg2+ in the trichloromethaneunder strongly acidic conditions the paper-based test stripfor determining the concentration of Hg2+ in aqueous so-lutions could be developed 7e test strip reacted rapidlywith Hg2+ could lead to color formation of the test stripSubsequently the test color liquid diffused in indefinitedirections due to liquid diffusivity For the dipping-inmethod the absorbency value continued to increase withthe reaction time and it was difficult to determine the resultof color forming due to the reaction of the test strip andHg2+or liquid diffusivity

7e aim of this work is to introduce an efficient andsimple approach to fabricate cellulosic paper-based teststrips by physically impregnating paper strips in dithizone-containing solution to load dithizone into strips for de-termining the Hg2+ in aqueous solution 7is preparation ofthe dithizone-loaded test strip is very simple and easilyoperated using biodegradable materials paper strips at lowcost compared with other plastic-based test strips In thisstudy dithizone is used as a recognition reagent to achieveselective recognition by Hg2+ with dithizone under strongacidic conditions 7e calibration curve and pertinence areobtained by the absorbency from different concentrations ofHg2+ Furthermore all the experiments are performed to-wards the detection linear range of the test strip system andsuperior test conditions of cellulose paper-based test strips

2 Experimental

21 Materials 7e paper sample used for the test strip wasquantitative filter paper of medium porosity which wasobtained from Fisher Scientific (Jinan China) Dithizonewas obtained from Sigma-Aldrich (Jinan China) Mercurysolutions with various concentrations were freshly pre-pared by dissolving a certain amount of mercury nitrate innitric acid solution with pH 20 Other solutions includingmercury ions (Hg2+) potassium ions (K+) calcium ions(Ca2+) sodium ions (Na+) manganese ions (Mn2+)magnesium ions (Mg2+) copper ions (Cu2+) barium ions(Ba2+) aluminum ions (Al3+) iron ions (Fe3+) zinc ions(Zn2+) phosphate ions (PO4

3-) chloride ions (Clminus) andsulfate ions (SO4

2minus) were prepared by using analyticalreagent-grade chemicals and nitric acid solution with pH20 7e pH of solutions was adjusted by adding eitherdiluted sodium hydroxide (NaOH) or nitric acid (HNO3)solution 7e spiked water sample of Hg(II) was preparedby adding Hg(II) into tap water with its pH adjusted to 20

22 Apparatus A UV-Vis spectrophotometer (UV-2550Shimadzu Nagoya Japan) was used to determine the ab-sorption of the colored complex solutions A reflect spec-trophotometer (i1Basic Pro2 X-Rite Agilent Foster CityCalifornia USA) was used for the measurement of colorintensity formed on the test strip

23 Preparation of Cellulosic Paper-Based Test Strip 7edithizone was dissolved in trichloromethane (Fisher Sci-entific Jinan China) with a concentration of 00127 gL 7efilter paper was then immersed into this solution for 2min atroom temperature 7e filter paper with dithizone was driedat 50degC in a nitrogen protected environment 7e dried filterpaper was then cut into 5 cmtimes 1 cm strips sealed in a plasticbag and kept until further use 7e paper strip immersed in00127 gL dithizone solution had a 033mgcm2 dithizoneloading amount

3 Methods

31 Spectral Reflectivity Measurement 7e Hg2+ solutionwas dropped on the paper-based test strip After the color-forming reaction finished the color intensity developed onthe test strip was measured using the reflect spectropho-tometer at a fixed wavelength of 490 nm

7e color forming depended on the dithizone reactionwith mercury(II) and the coordination compound(dithizone-mercury complex) was formed and the linearrelationship between the absorbency value and differentHg2+ concentrations was tested by spectrophotometer ata fixed wavelength of 490 nm [22]

32Hg(II)DeterminationUsingUV-VisSpectroscopyMethodA 250mL mercury solution with 10 μgmL concentrationwas put into a separatory funnel (500mL) by adding 1mLsodium sulfite (20) After mixing 10mL dithizone-trichloromethane solution was added and the solution



Y 00558X + 00391

R2

09932(1)






A lg1T

1113874 1113875 kbc (2)









025

030

035

040

045

050

Abso

rben

cy (L

(m

ollowastcm

))

15 30 45 60 75 90 1050Time (s)

(a) (b)


NH

HN N

S

N

NPh

H

N

NN

Ph

S

H

N Ph

H

N

NN

Ph

S

H

Hg2+

+ Hg2+ H+


040

045

050

055

060

065

070

Abso

rben

cy (L

(m

ollowastcm

))

420 440 460 480 500 520 540400Wavelength (nm)










y = 00543x + 02815R2 = 09971

010

015

020

025

030

035

040Ab

sorb

ency

(L(

mol

lowastcm

))



Abso

rben

cy (L

(m

ollowast

cm))

022

024

026

028

030

032

034

036

038

Pd2+

Ag+K+

Na+

Cu2+

Mg2+

Mn2+

Ca+

Ba2+

PO43ndash

Zn2+ Cl

ndash

Al3+

SO42ndash

Hg2+

Fe3+

Blan

k




Abso

rben

cy (L

(m

ollowastcm

))

024

025

026

027

028

029

15ndash35 min

15 30 45 60 75 9000Time (min)





5 Conclusions




Data Availability






Acknowledgments


References






































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





Y 00558X + 00391

R2

09932(1)






A lg1T

1113874 1113875 kbc (2)









025

030

035

040

045

050

Abso

rben

cy (L

(m

ollowastcm

))

15 30 45 60 75 90 1050Time (s)

(a) (b)


NH

HN N

S

N

NPh

H

N

NN

Ph

S

H

N Ph

H

N

NN

Ph

S

H

Hg2+

+ Hg2+ H+


040

045

050

055

060

065

070

Abso

rben

cy (L

(m

ollowastcm

))

420 440 460 480 500 520 540400Wavelength (nm)










y = 00543x + 02815R2 = 09971

010

015

020

025

030

035

040Ab

sorb

ency

(L(

mol

lowastcm

))



Abso

rben

cy (L

(m

ollowast

cm))

022

024

026

028

030

032

034

036

038

Pd2+

Ag+K+

Na+

Cu2+

Mg2+

Mn2+

Ca+

Ba2+

PO43ndash

Zn2+ Cl

ndash

Al3+

SO42ndash

Hg2+

Fe3+

Blan

k




Abso

rben

cy (L

(m

ollowastcm

))

024

025

026

027

028

029

15ndash35 min

15 30 45 60 75 9000Time (min)





5 Conclusions




Data Availability






Acknowledgments


References






































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls






025

030

035

040

045

050

Abso

rben

cy (L

(m

ollowastcm

))

15 30 45 60 75 90 1050Time (s)

(a) (b)


NH

HN N

S

N

NPh

H

N

NN

Ph

S

H

N Ph

H

N

NN

Ph

S

H

Hg2+

+ Hg2+ H+


040

045

050

055

060

065

070

Abso

rben

cy (L

(m

ollowastcm

))

420 440 460 480 500 520 540400Wavelength (nm)










y = 00543x + 02815R2 = 09971

010

015

020

025

030

035

040Ab

sorb

ency

(L(

mol

lowastcm

))



Abso

rben

cy (L

(m

ollowast

cm))

022

024

026

028

030

032

034

036

038

Pd2+

Ag+K+

Na+

Cu2+

Mg2+

Mn2+

Ca+

Ba2+

PO43ndash

Zn2+ Cl

ndash

Al3+

SO42ndash

Hg2+

Fe3+

Blan

k




Abso

rben

cy (L

(m

ollowastcm

))

024

025

026

027

028

029

15ndash35 min

15 30 45 60 75 9000Time (min)





5 Conclusions




Data Availability






Acknowledgments


References






































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls











y = 00543x + 02815R2 = 09971

010

015

020

025

030

035

040Ab

sorb

ency

(L(

mol

lowastcm

))



Abso

rben

cy (L

(m

ollowast

cm))

022

024

026

028

030

032

034

036

038

Pd2+

Ag+K+

Na+

Cu2+

Mg2+

Mn2+

Ca+

Ba2+

PO43ndash

Zn2+ Cl

ndash

Al3+

SO42ndash

Hg2+

Fe3+

Blan

k




Abso

rben

cy (L

(m

ollowastcm

))

024

025

026

027

028

029

15ndash35 min

15 30 45 60 75 9000Time (min)





5 Conclusions




Data Availability






Acknowledgments


References






































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls






5 Conclusions




Data Availability






Acknowledgments


References






































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls

































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




Development of Cellulosic Paper-Based Test Strips for …with mercury(II) and the coordination...

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