Chiang Mai J. Sci. 2019; 46(5) : 975-986http://epg.science.cmu.ac.th/ejournal/Contributed Paper

Application of Smartphone as a Digital Image Colorimetric Detector for Batch and Flow-based Acid-Base Titration Janejira Chanla [a], Miki Kanna [a], Jaroon Jakmunee [b,c] and Sarawut Somnam*[a][a] Department of Chemistry, Faculty of Science and Technology, Chiang Mai Rajabhat University, Chiang Mai

50300, Thailand.[b] Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.[c] Center of Chemistry for Development of Health Promoting Products from Northern Resources, Faculty

of Science, Chiang Mai University, Chiang Mai 50200, Thailand.*Author for correspondence; e-mail: sarawut_som@cmru.ac.th, wut_080@hotmail.com

Received: 10 March 2019Revised: 23 April 2019

Accepted: 24 April 2019

ABSTRACT Inthisresearch,wehavedevelopedthebatchandflow-basedsystemof titrimetric

analysisbyusingamobilephoneasadetector.Thedigitalimagecolorimetricdetectionsystemwassetupwitheconomicdevicesandtobeeasytousebytakingphotographwithmobilephonecamera,thentheRGBsignalswerereadfromtheRGBcolorpickerapplicationtocalculatetheRGB-basedvalueandplottitrationcurveforevaluatingtheequivalencepoint.Thismethodwasappliedtoanalyzesamplesof acid-baseondailybasis,comparedwiththepotentiometricandphotometrictitrationsthatusingpHmeterandspectrophotometerasadetector,respectively.Themethodwashighlyreproduciblewiththerelativestandarddeviationof 1.14%(n=11)for0.5%w/vof aceticacidstandardsolution.Theproposedmethodwasappliedtothedeterminationof aceticacidinvinegarandtitratableacidityinfruitjuices.Concentrationsof aceticacidwerefoundtobeinarangeof 5.23-5.35%w/v.Concentrationsof titratableacidityinthejuicesampleswerefoundtobeinarangeof 0.27-0.50%w/v.Thereafter,ananalyticalapplicationinvolvingthedeterminationof thetotalalkalinityinmineralwaterswasperformed,anditwasfoundintherangeof 11.50-18.50mg/Lof CaCO3 which were in good agreement withtheresultsobtainedfromthestandardmethodatthe95%confidencelevel.

Keywords: titration,flow-basedanalysis,smartphone,RGBcolorsystem,applicationRGBcolorpicker

1. INTRODUCTIONTitrationisapowerfulquantitativechemical

analysisthatbaseduponthemeasurementof thereagentvolumewithobservingasuddenlyphysicalchangeinasolutionthatso-calledendpoint.Indicatorsareoftenusedforthisnoticeabletransformationincludingtheappearance

ordisappearanceof color;achangeincolor,ortheoccurrenceorvanishmentof turbidity.Therefore,theaccuracyinchangeobservationwithbareeyescouldalsosubsequentlyaffectthereliabilityof theanalyticalresults.Apartfromthechangeincolorof the indicator,

Chiang Mai J. Sci. 2019; 46(5)976

usingof anelectrodetomeasurethechangein potential or a spectrophotometer to observe the absorbance that responded to a reagent or analyteconcentrationinordertoconstructatitrationcurveisanalternativewaytoobtainthe endpoint. However, the higher expense of theinstrumentsincludingthemaintenancecost,comprisedof itssophistication,shouldbe considered.

Adigital image-basedmethodservedforthequantitativechemicalanalysisisnow

popularlyusedashasbeenproposedinmanypiecesof literature.Digitalimagingbecomesaninterestingalternativewayasadetectorforthevariousanalyticalmeasurementstomanyanalytesdueto itsrapid,cheapanddirectdeterminationsasexemplifiedinTable1.

Adigitalimagewhichisanarrayof pointsor pixels (the smallest color unit), could be captured via the digital camera, webcam, or flatbedscannerthatthosebasedupontheuseof charge-coupleddevices (CCD)or

Table 1.Theexamplesof theapplicationof digitalimagemethodforthevariousanalyticalmeasurements.

Analytes Samples Analytical techniquesDigital

imaging devices

References

Al(III)andFe(III) Syntheticalloys ColorimetryusingthechromeazurolSasachromogenicreagent

Digitalcamera [1]

HCl, H3PO4 and totalalkalinity

Aqueoussolution,mineral and tap

water

Titrationusingphenolred,bromocresolgreen,andmethyl

orange as indicators

Webcam [2]

Li,NaandCa Anti-depressivedrug,physiologicalserum, and water

Flameemissionspectrometry Webcam [3]

Ti(IV) Plastics ColorimetryusingH2O2 and H2SO4toformanorange

complex

Digitalcamera [4]

Totalacidity Red wines Titration(withoutindicator) Webcam [5]

Ca hardness Citynet,mineral,and natural water

ColorimetryusingGBHAinalkalinemediaasachromogenic

reagent

Digitalcamera [6]

Fooddyes Commercial product

Spottedthedyesonfilterpaperandsubsequentlymeasuredthe

RGB value

Flatbedscanner [7]

Al(III)andCr(VI) Naturalwater ColorimetryusingCTABandDPCasthechromogenic

reagentforAl(III)andCr(VI),respectively

Webcam [8]

Variousorganiccompounds

- Colorimetrybythereactionof theazocouplingof diazotizedpolyurethanefoams(PUFs)with

organic substances

Digitalcamera [9]

Estrone, 1-Naphthylamine,4-Aminophenol

- Colorimetrybythereactionof theazocouplingof diazotizedPUFswithorganicsubstances

Aneye-onepro mini-

spectrometer and a monitor

calibrator

[10]

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complementarymetal-oxidesemiconductors(CMOS)toprovideRGBcolordata[6,11-12].TheRGBcolorsystemconsistsof threeprimarycolorcomponents;red(R),green(G),andblue(B),of whichthemixingof thesecolorsineachpixelisutilizedinadisplayorcomputergraphicapplications[12-13].TheRGBcolorsarecombinedindifferentintensitieswithvaluesfromsensorreadingvaryfrom0to255(8bits)percolor[2,14-15].Thus,thetotalnumberof possiblecolorsfromtheprimarycolor combination is 28×28×28=16,777,216colors[6,13].Withthesenumerousvalues,theconstructionof analyticalcurvesfromRBG-based signal that response to the change in analyticalmeasurements,e.g.,calibrationcurve[16-18]andtitrationcurve,isfeasible.

Hence, inthiswork,thedigital image-based colorimetric method is applied to the acid-basetitrationbyusingtheRGB-basedvaluesobtainedfromasmartphonecameratobuildatitrationcurve.Thecaptureof thedigital imageof indicatorchangeincludingto the RGB data assessment is achieved via a high-resolution camera coupled with a costless downloadable application which installed in multipurpose,easilyportable,anddailyusagedevices,i.e.,smartphone.Moreover,aflow-basedtechniqueisalsoappliedtothisworkinorderto decrease the chemical consumption, increase thesamplethroughput,aswellastofacilitatehigher automation in detection procedure. Therefore,therequirementof thepreviouscomplicatedinstrumentaltechniquesseemstobereducedbythenovelproposedmethod.

2. MATERIALS AND METHODS2.1 Chemicals

Allsolutionswerefreshlypreparedwithde-ionizedwater(DIwater)andanalyticalgrade chemicals.

Primarystandardsolutionsof KHC8H4O4 orKHP(RFCL)andNa2CO3(Labscan)werepreparedforthestandardizationprocedure.

About0.1MNaOH(Labscan)wasstandardizedbeforeuseasthetitrantforthetitrationof strongacidof HCl(Merck)andweakacidof CH3COOH(Labscan)tobuildatitrationcurve,includingthedeterminationof CH3COOHinvinegarandacidityinjuice.Thetitrationcurveof thestrongacid-weakbasictitrationwasalsodoneusingtheexactconcentrationof HClandNH3solution(Labscan).TotalalkalinityinnaturalwatersampleswasdeterminedbyusingastandardizedH2SO4 as the titrant.

About1.0%w/vof bromothymolblue(Ajax),methylorange(Labscan),methylred(Labscan)andphenolphthalein(Labscan)wereused as indicators in the titration.

BuffersolutionsateachpHusedforobservationof colorchangeof indicatorswerepreparedbymixingthesesolutionsof differentvolumesasfollow;0.2MKCl(Ajax)and0.2MHCl(pH1and2),0.1MKHPand0.1MHCl(pH3and4),0.1MKHPand0.1MNaOH(pH5-7),0.1MKH2PO4 and 0.1 MNaOH(pH8),0.1MHCland0.0025MNa2B4O7(Ajax)orborax(pH9),0.1MNaOHand0.0025Mborax(pH10),0.1MNaOHand0.05MNa2HPO4(Ajax)(pH11and12),and0.2MKCland0.2MNaOH(pH13)

2.2 Apparatus and Detection Procedure2.2.1 RGB-detection box for a conventional titration setup and detection procedure

First,amanualconventional titrationsetupwasbuilt.Titrantwasreleasedfromburettewiththedefinedvolumeintoabeakerwhich contained titrand and indicator that werebeingcontinuouslystirredbyamagneticstirrer(DragonLaboratory).Then,aportionof 2.00mLof mixedsolutioninthebeakerwas pipetted and discharged into a test tube. AnRGB-detectionbox(10cm×11cm×17cm)wasmadeof balsawoodasillustratedinFigure1inordertoplacetesttubeandalsoavoidtheinterferingof ambientlightwhilemeteringtheRGBadditivecolor.Alightbulb

Chiang Mai J. Sci. 2019; 46(5)978

3W(Lumax)wasattachedatthetopof thebox.Theinternalwallsof theboxwereallcoveredwithwhitepapertoprovideuniformillumination.Atthefrontof thebox,oppositetothepositionof thetesttube,wascircularlydrilledwitharadiusof 2.0cm.Aplasticclampwasalsoadheredonoutsidewallforholdingasmartphone(AsusZenFone2)byplacedthecameralensontotheholetofocusthesolutionin the test tube and then captured a picture to obtainR/G/Bvalues.AftermonitoringRGBvalues, the measured solution in the test tube wastransferredbacktothetitrationbeakerprioradditionof thenextportionof thetitrant.

2.2.2 RGB-detection box for a flow-based titration setup and detection procedure

Inordertoavoidtheleakageof thechemicalduringtransferredfrombeakertotesttube,and to reduce time in R/G/B value detection procedure,aflow-basedtechniquewasappliedtoatitrationsetupasillustratedinFigure2.

Afteraportionof adefinedtitrantvolumewasaddedtothetitrandinabeakerwhichwascontinuouslystirred,amixedsolutionwasdrawnupthroughPTFEtubing(i.d.0.795mm)withaflowrateof 5mL/minusingaperistalticpump(Ismatec,Switzerland).Three-wayvalvewasemployedforcontrollingaflow

Figure 1.Aschematicof RGB-detectionboxforaconventionaltitrationsetup.

Figure 2.Schematicdiagramof aflow-basedtitrationsetupwithRGB-detectionbox,B=burette,PP=peristalticpump,MB=magneticbar,MS=magneticstirrer,TV=three-wayvalue,RGB-DB=RGB-detectionbox,andSPEC=UV-Visspectrophotometer.

direction. Solution was propelled through a valve at position 1, RGB-detection box and spectrophotometer,respectively,beforeflowbacktobeakerbyspendingthecirculationtimeof 45seconds.Thedetectionstepwascarriedoutbyswitchingthree-wayvaluetoposition2inordertostoptheflowinthedetectionbox

andspectrophotometerforrecordingRGB-basedvaluesandanabsorbance,respectively.

More robust RGB-detection box was builtemployingtheblackopaqueacrylicsheet(thicknessof 3.00mm)replacingtothebalsawood.Theinternalof theboxwasalsocoveredwithawhitepaperandattacheda3Wlight

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bulbonthetop.Theboxwasdrilledfortwosmall-sizeholesattherightsidetoinsertPTFEtubingforflowinletandoutlet,respectively.Aglassflowcellwithaninnervolumeof 715µLasshowninFigure3(a)wasputintotheboxatthesamepositionof thetesttube.The

holewitharadiusof 2.0cmwasdrilledattheoppositetotheflowcell.Asmartphonewasheldontheboxwithaplasticclampbyplacingthelensonthedetectionhole.TheRGB-detectionboxfortheflow-basedtitrationsetupwasillustratedinFigure3(b).

for two small-size holes at the right side to insert PTFE tubing for flow inlet and outlet,

respectively. A glass flow cell with an inner volume of 715 µL as shown in Figure 3(a) was

put into the box at the same position of the test tube. The hole with a radius of 2.0 cm was

drilled at the opposite to the flow cell. A smartphone was held on the box with a plastic

clamp by placing the lens on the detection hole. The RGB-detection box for the flow-based

titration setup was illustrated in Figure 3(b).

(a)

(b)

Figure 3. A schematic of (a) flow cell and (b) RGB-detection box for a flow-based titration

setup.

2.2.3 Acquisition of RGB-based value

The RGB-based values were assessed via a costless downloadable application,

namely “RGB color picker”, which could be downloaded from the “Play Store” application.

The application provided a multipurpose utility by the caption of color at real time with

Figure 3.Aschematicof (a)flowcelland(b)RGB-detectionboxforaflow-basedtitrationsetup.

2.2.3 Acquisition of RGB-based value TheRGB-basedvalueswereassessed

via a costless downloadable application, namely“RGBcolorpicker”,whichcouldbedownloadedfromthe“PlayStore”application.Theapplicationprovidedamultipurposeutilitybythecaptionof coloratrealtimewiththephonecameraandflash.Themainscreenof this application is a small window (1.7 cm×2.5 cm)whichcouldbemanuallyadjustedonthetouchscreentoselectthesuitableareaforthepicturecaption.Thecolorwasdisplayedwiththemostcommoncolormodels;i.e.,CYMK,HSL,HSV,RGBandYUV,andevengaveanametothecolor.ThecapturedcolordatawerealsoavailablefortheSDcard.Inthiswork,aftertheapplicationwasstandby,thecolorcapturewasdonewhenplaced/flowedthesolutiontothemarkedpositioninthebox.ThenselectedRGBmode,eachof valuesof R,G,andBwereimmediatelyshownwithoutanyassessmentbytheoperator.Thevaluesof R, G, and B were reported with the number intherangeof 000-255.TogainRGB-based

value,alldataof R,G,andBweremultipliedtoenhancetheresolutionof thetotalnumberof possiblecolorsfromtheprimarycolorcombination.However,becausethevalueof zeroof R,GorBmightbeobtainedinsomecases,andthenaffectedinmultiplicationsteptogainthezeroatlast,everydisplayedvaluesof R,G,andBmustbeplusbyonebeforemultiplying.

2.3 Preliminary Test of R/G/B Value of the Color Change of Indicators

Thepreliminaryestimationof R/G/Bvalueswasmonitoredbyobservingthechangeincolorof theindicatoratthevariouspH.Threetypesof indicator;phenolphthalein,bromothymolblue,andmethylredwereaddedthreedropsinto10mLof differentbuffersolutionmediumateachpHfrom1-13.TheportionswerecontainedintesttubesbeforemanuallydetectedtheR/G/BvaluesusingabalsawoodRGB-detectionbox.Theobtainedvalues were plotted versus the pH to obtain characteristicgraphsforeachof theindicators.

Chiang Mai J. Sci. 2019; 46(5)980

2.4 Acid-base Titration Based on RGB-Based Value Detection2.4.1 Accuracy evaluation of RGB detection for titrimetric analysis

Fromthepreliminarytest toobservethe relationship between the change in color of eachindicatorandRGB-basedvalue,theanalyzerwasthenappliedtoacid-basetitrations.However,theaccuracyof RGBdetectionshouldbe investigated to ensure that it is appropriate tobothof thebatchandflow-basedtitrationsetups.Threecategoriesof titrationweredoneconsistedof;strongacid-strongbase,weakacid-strongbase,andstrongacid-weakbase,byusingtheknownconcentrationof standardacidic and basic solutions as the titrant and titrandassummarizedinTable2.Incaseof NaOHandHClwhichusedasthetitrant,NaOH

wasstandardizedwithKHPandthenusedasthetitranttostandardizeHCl,respectively.Thetitrandof 25.00mLwaspipettedintoabeaker(100mL)andmixedwiththreedropsof indicator.R/G/Bvaluedetectionprocedurewas carried out as mentioned in the previous subjectof RGB-detectionboxforaconventionaltitrationsetupanddetectionprocedure.Thetitrationcurveswereconstructedbyplottingthe titrant volume versus RGB-based value to gaintheequivalentpointfromtheinflectionpoint.Concentrationsfoundof titrandwerecompared to theknownconcentrations.Moreover, all results were compared with those of potentiometrictitrationmethodbythemonitoringwithapHmeter(VernierSoftware&Technology).

Table 2.Standardsolutionsusedfortheaccuracyevaluationof RGBdetection.

Categories of titration Titrant Titrand Indicator

Strong acid-strong base 0.1045MNaOH HCl Bromothymolblue

Strongacid-weakbase 0.1032MHCl NH4OH Methylred

Weakacid-strongbase 0.1045MNaOH CH3COOH Phenolphthalein

2.4.2 Determination of acetic acid and total titratable acidity

Threebrandsof distilledvinegarandfourbrandsof fruitjuice(guavaandorange)wereboughtfromaconveniencestoreinChiangMai.Theknownvolume(1.00mL)of vinegarwaspipettedtomakeaten-folddilution.Thejuiceswerefilteredthroughafilterpaper(WhatmanNo.5)beforepipettedat10.00mLof samplefortitration.Threedropsof phenolphthaleinwere added to all prepared samples and then titratedwithastandardizedNaOH(0.1060M) [14]. R/G/B value detection procedure was carried out as mentioned in the previous subjectof RGB-detectionboxforaflow-basedtitrationsetupanddetectionprocedure.Thetitrationof thesesampleswasalsocomparedwith those methods that using a pH meter and

a spectrophotometer as detectors to indicate theaccuracyof theproposedmethod.

2.4.3 Determination of total alkalinityThreebrandsof mineralwaterwerealso

obtainedfromaconveniencestore.Threedropsof methylorangewereaddedto100.0mLof eachsample.Standardsolutionof 0.0100NH2SO4 was used as the titrant [15]. RGB detection procedure was also carried outasdoneinthedeterminationof titratableacidity.Theresultswerealsocomparedtothatbeobtainedfromaphotometrictitrationusingspectrophotometer as the detector.

2.5 Precision of the RGB DetectionOneof vinegarsamplewasrandomto

the11replicatedtitrationsastheprocedureof

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theconventionalandtheflow-basedmethodwiththestandardizedsolutionof NaOHusingphenolphthalein as the indicator. Percent relative standarddeviation(%RSD)wascalculatedtoestimate the precision.

3. RESULTS AND DISCUSSION3.1 R/G/B Value Assessment of Color Change of Indicators

Bromothymolblue,phenolphthaleinandmethylredwerechosenduetothedifferenceof

colorchangeatthedifferenttransitionrangesof pH.Fromtheexperiment,basedonusingtheRGBdetectionusingthesmartphoneforaconventional titration setup (a static measurement), thechangeof R/G/BandRGB-basedvaluesof eachindicatorintherangeof pH1-13wereplottedasshowninFigure4(a-f).

Assuggestedfromthetheoreticalaspect,the pH transition range and the color change of bromothymolblue,phenolphthaleinandmethylredwere6.2-7.6(yellowtoblue),8.2-

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10.0(colorlesstopink)and4.4-6.2(redtoyellow),respectively.Figure4(a)showedthatRandGvaluesweresimilarintherangeof pHof 1-6whileBvaluewasmuchlower.Itcould be described that the mixture between theadditivecolorof red(R)andgreen(G)providedtheyellowinaccordancewiththecolorof bromothymolblueatthepHlowerthan6.AfterpHraisedover7,thecolorturntoblue,Bvaluethenobviouslyincreasedthatwasoppositetothechangeof RandGvalues.

Inthecaseof phenolphthalein(Figure4(c)),becauseof theclearsolutionatpHlowerthan 8, then the captured color was the white colorof thecoveredpaperinthedetectionboxandaffectedtothesimilarvaluesof R/G/B.AfterthecolorturntopinkatpHhigherthan8, R value showed a constant while G and B valuesdecreasedsuddenly.

Forthechangeof R/G/Bvaluesof methylredasshowninFigure4(e),Rvaluewashigher than the other at pH less than 7. When pH surpassed 7, G value also increased due to thecolortransformationtoyellowinthesamewayof thechangeinbromothymolblue[19].Additionally,asFigure4(b,d,f),thechangeof RGB-basedvaluesof eachindicatorprovidedtheinflectionpointof thegraphthatcorrespondedtotheindicatorcolortransformation.Themorenumerousvaluesfrommultiplyingof R/G/Bcolors,themoreresolutionsof analyticalsignalcontributetothehigherresponsibilityinanalyticalmeasurements.Therefore,themonitoringof RGB-based value during titrimetric process could be applied to construct the titration curve as well. 3.2 Acid-base Titration Curve Using RGB-Based Value

Fromtheapplicationof smartphonetodetect RGB values using a batch setup in real titrationof;strongacid-strongbase(NaOHastitrant),weakacid-strongbase(NaOHastitrant),andstrongacid-weakbase(HClastitrant),a

collectionof pointsof addedtitrantvolumeswiththeobservedsignalsfrombothintheRGB-based and in the pH measurement values were recorded.Thepreviouslymentionedindicators,i.e.,bromothymolblue,phenolphthalein,andmethylred,wereusedinthetitrationof thestrongacid-strongbase,weakacid-strongbase,andstrongacid-weakbase,respectively,duetotheappropriatecolortransformationatendpointforeachtitration.Secondderivativesof bothdatawerefurthercalculated.Twocategoriesof titration curve, normal and second derivative werealsoconstructedtoobservetheequivalencepointasillustratedinFigure5-7. Fromtheresults,evenif thesetitrationsinvolveddifferentchangedpatternsof pH,provideddifferentpHatequivalencepointanduseddifferentindicators,butitwasfoundthattheabruptchangeof RGB-basedvalueof allnormaltitrationcurvescorrespondedtotheabruptchangeinpH.Theseaffectedtolocalizethesimilarequivalencepointinthesecondderivativetitrationcurve.Therefore,the RGB detection using a smartphone could beeffectivelyusedforacid-basetitrationandbefurtherappliedtorealsampleanalysis.

3.3 Application of RGB Detection Using the Smartphone in Real Sample Analysis3.3.1 Determination of acetic acid in vinegars and total titratable acidity in juice

RGBdetectionusingasmartphoneforaflow-basedtitrationsetupwasappliedtorealsampleanalysisbycomparingtheanalyticalresultswiththetitrationusingof pHmeterandspectrophotometer.Thevolumesatequivalencepointfromsecondderivativetitrationcurveof eachtitrimetricmethodwerecalculatedinordertoassaytheamountsof aceticacidinvinegarsandtotaltitratableacidity injuicesasshowninTable3.TheanalyticalresultsfromRGBdetectionusingasmartphonewerestatisticallycomparedbypairedt-testtotheassayof pHmeter(tstat=1.48,tcritical=2.45)

Chiang Mai J. Sci. 2019; 46(5) 983using a smartphone could be effectively used for acid-base titration and be further applied

to real sample analysis.

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Figure 5. Normal and second derivative titration curves of strong acid-strong base model

titration using (a-b) RGB-detection box (bromothymol blue as an indicator) and (c-d) pH

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Figure 6. Normal and second derivative titration curves of weak acid-strong base model

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Chiang Mai J. Sci. 2019; 46(5)984

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Figure 7. Normal and second derivative titration curves of strong acid-weak base model

titration using (a-b) RGB-detection box (methyl red as an indicator) and (c-d) pH meter.

3.3 Application of RGB detection using the smartphone in real sample analysis

3.3.1 Determination of acetic acid in vinegars and total titratable acidity in juice.

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Figure 7.Normalandsecondderivativetitrationcurvesof strongacid-weakbasemodeltitrationusing(a-b)RGB-detectionbox(methylredasanindicator)and(c-d)pHmeter.

Table 3.Determinationof aceticacidandtotaltitratableaciditybytitrationusingthreedetectioninstruments.

SampleFound amount (%w/v)

RGB-detection box pH meter Spectrophotometer

1. Vinegars

SampleA 5.23±0.09 5.69±0.07 5.17±0.07

Sample B 5.35±0.10 5.69±0.07 5.29±0.08

Sample C 5.23±0.08 5.60±0.06 5.17±0.08

2. Juices

GuavajuiceA 0.27±0.01 0.26±0.01 0.27±0.01

Guava juice B 0.33±0.02 0.31±0.01 0.34±0.01

OrangejuiceA 0.50±0.02 0.48±0.02 0.49±0.02

OrangejuiceA 0.50±0.03 0.50±0.02 0.49±0.02

Chiang Mai J. Sci. 2019; 46(5) 985

and spectrophotometer (tstat=0.284,tcritical=2.45),respectively,andfoundthatnosignificantdifferencebythosemethods.Therefore, itmight be indicated that a smartphone could be effectivelyemployedtotheacid-basetitrationforthecoloredsample.

3.3.2 Determination of total alkalinity. Apartfromtheaciddetermination in

realsamples,theassayof base intermof totalalkalinityinmineralwatersampleshavealsosucceededwiththestatisticallyagreeableresults(pairedt-testat95%confidencelevel;

tstat=0.99,tcritical=4.30)usingthesamesetupasproposedinTable4whencomparingtothe photometric titrimetric standard method.

3.3.3 Precision of the monitoring with RGB-detection box

Fromthestudy,0.5%w/vof CH3COOHwasevaluatedfor11replicationsforbothof batch,andflow-basedtitration,thepercentrelativestandarddeviation(%RSD)valueswere1.20%and1.14%,respectively.Theflow-basedtitrationhadadetectionfrequencyabout80cycles/hwithaflowrateof 5mL/min.

Table 4.Determinationof totalalkalinitybytitrationusingtwodeterminationinstruments.

Mineral water sampleFound amount (mg/L of CaCO3)

RGB-detection box Spectrophotometer

1 11.50±0.55 12.00±0.50

2 16.50±0.30 16.00±0.45

3 18.00±0.50 18.75±0.40

4. CONCLUSIONSTheexperimentalresultsindicatedthatthe

developed RGB detection using a smartphone couldbeappliedforthebatchandflow-basedtitration.RGB-basedvaluecouldbesuccessfullyapplied to build a titration curve which gave the agreeableresultscomparingtotheuseof pHvalue or absorbance. Moreover, the proposed analyzershowedobviousadvantages,e.g.,concise,portable,inexpensive,fastandcheapanalysis,whichshouldbeappropriateforthedeterminationof acidandbase invariousbeverages despite the colored sample.

ACKNOWLEDGEMENTSTheauthorswould like to thankthe

Departmentof Chemistry,Facultyof ScienceandTechnology,ChiangMaiRajabhatUniversityandPhayaoPittayakhomSchoolforpartialsupportof instruments.WealsogratefullyacknowledgetotheNationalResearchCouncil

of Thailand(NRCT)forthefinancialsupport,andChiangMaiUniversityforpartiallysupport.

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