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IntroductionArticaineHClisawhiteoralmostwhitecrystallinepowder,freelysolubleinwater,methanolandethanol[1].Itisanintermediate-potency, short-acting amide local anesthetic with a fastmetabolismduetoanestergroupinitsstructure.Itiseffectivewithlocalinfiltrationorperipheralnerveblockindentistry,whenadministeredasaspinal,epidural,ocular,orregionalnerveblock,or when injected intravenously for regional anesthesia. Localanestheticdrugsare administeredtotheareasaroundthenervesto be blocked as the skin, subcutaneous tissues, retrobulbar,intrathecal, and epidural spaces. Articaine has a half-life of 60minutesafterenteringthecirculationandisquicklymetabolizedviahydrolysisintoitsinactivemetabolitearticainicacid,whichispartlymetabolizedinthekidneyintoarticainicacidglucuronide.Seventy-fivepercentofarticainicacidisexcretedunchanged;therest is glucuronidatedby the kidneysbefore excretion [2]. It isan amino-amide anesthetic having a thiophene, rather than abenzenering,as wellasanadditionalestergroupthatissubjecttometabolismbyplasmaesterases.Ithasawidespreadpopularityindentalanesthesia,whereitisgenerallyconsideredtobemoreeffective,andpossiblysafer,thanlidocaine,thepriorstandard[3].Epinephrinegreatlyincreasesthe durationofthelocalanesthesia
Literature survey reveals that several different analyticaltechniques have been developed for the determination ofarticaineHClandepinephrineincludinghighperformanceliquidchromatographic methods [5-7], thin layer chromatographicmethods [8], gas chromatographic methods [9] andspectrophotometric methods [10] for articaine HCl and highperformance liquid chromatographic methods [11-15], thinlayer chromatographic methods [16,17], gas chromatographicmethods [18,19], spectrophotometric methods [20-24] andelectrochemicalmethods[25-30]forepinephrine.Carbonbasedelectrodes are currently in widespread use in electroanalyticalchemistry, because of their broad potential window, low cost,rich surface chemistry, low background current and chemicalinertness. Carbon paste electrode (CPE) has some special
Simultaneous Electrochemical Determination of Articaine HCl and Epinephrine
AbstractAsimple,precise,accurateandinexpensivevoltammetricmethodwasdevelopedfor the simultaneous determination of articaine HCl and epinephrine in bulk,pharmaceutical formulations and human urine at carbon paste electrode inBritton-RobinsonbufferofpH7and40µLof10−2molL−1sodiumdodecylsulphate.Several factorswerestudiedsuchasbuffer type,pH, surfactant, scan rate,andaccumulationtime to obtain the optimumconditions for analysis. Themethodshowedlinearityinconcentrationrangeof1.0×10−6-2.6×10-5molL−1.Thelimitsof detection and quantitation were found 2.88 × 10−7 mol L−1 and 8.72 × 10−7 molL−1forarticaineHCland5.10×10−8molL−1and1.56×10-7forepinephrine,respectively. The proposed voltammetric method was successfully applied forsimultaneousdeterminationofarticaineHClandepinephrine inbulk, injectionsand urine. The results obtained from the proposed method were statisticallycomparedwiththoseofareportedmethodandshowednosignificantdifference.Thus,itcanbeusedasqualitycontrolinlaboratories.
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characteristicsandbenefitssuchastheeaseofsurfacerenewal,individual polarizability, and easy to apply modifications. Thedisadvantage of CPE is the tendency of the organic binder todissolveinsolutionscontaininganappreciablefractionoforganicsolvent[31].
In this study articaine HCl and epinephrine were determinedsimultaneously using differential pulse voltammetry (DPV) atcarbonpasteelectrodeinbulk,pharmaceuticalformulationsandhumanurine.
Materials and MethodsExperimental preparationsPure and market samples: Articaine HCl and epinephrinebitartrate were kindly supplied by Inibsa Laboratories, Spain.Theirpuritywas100%asstatedbythesupplier.
Artinibsa ampoules; batch no. K-3, labeled to contain 40 mgArticaineHCland0.01mgEpinephrineperampoule,productofInibsaLaboratories,Spain.
Standard solutions: Standard solutions of articaine HCl andepinephrine bitartarate were prepared in methanol. For cyclicvoltammetry(CV)1.0x10−2molL−1solutionswerepreparedbydissolving32.1mgofarticaineHCland33.3mgofepinephrinebitartarate, each in 10 mL volumetric flask and diluted withmethanol.ForDPV,onemLofeach1.0×10−2molL−1solutionwastakenanddilutedto10mLwiththesamesolventtoobtain1.0×10−3molL−1workingsolution.
Chemicals and reagents: All reagents used were of analyticalgradeandsolventswereofspectroscopicgrade.Distilledwaterwasusedthroughoutthework.
(viii) Britton-Robinson (BR) buffer was prepared by mixing0.04molL−1ofphosphoricacid(Sigma-Aldrich),aceticacid(LobaChemieCo.,India)andboricacid(Sigma-Aldrich).
Phosphatebufferwaspreparedbyadding34.7mLof0.2molL−1 NaOHto50mLof0.2molL−1monobasicpotassiumphosphatesolution (prepared by dissolving 27.22 gmonobasic potassiumphosphate in water and dilute with water to 1000 mL) andcompleteto200mLwithwater[32].
Instruments: All voltammetricmeasurementswere carriedoutusinga computer-drivenanalyticalelectrochemicalworkstation(modelAEW2)withECProg3electrochemistrysoftware(Sycopel,England) in combinationwith a three-electrode configuredC-3stand. The working electrode was a carbon paste electrode(MF-2010,BASmodel),thereferenceelectrodeAg/AgCl/3molL−1 NaCl (MW-2063, BAS model) and a platinum wire counterelectrode (MW-1032, BAS model). A digital pH-meter (JenwaypHmeter,UK)withcombinedglasselectrodewasusedtocarryoutthepHmeasurements.Allelectrochemicalexperimentswereperformedatanambienttemperatureof25±0.2°C.
ProceduresPreparation of working electrode: In a mortar 0.5 g graphitepowder and 0.3 mL paraffin oil were mixed thoroughly witha pestle. The pastewas packed into the hole of the electrodebody and smoothed on a filter paper until it acquired a shinyappearance;thepastewascarefullyremovedandreplacedbyanewoneaftereachmeasurement[33].
Linearity: Aliquots of working standard articaine HCl andepinephrinesolutions(1.0×10−3)wereaddedseparatelytotheelectrolyticcellcontaining5mLofBritton-RobinsonbufferofpH7and40µLof1.0×10−2molL−1SDS,thesolutionswerestirredfor5satopencircuitconditions,voltammetricanalyseswerecarriedoutandvoltammogramswererecordedatascanrate20mVs−1.
Calibrationcurvewasconstructedbyplottinganodicpeakcurrentagainst drug concentrations in molarity; and the regressionequationwascomputed.
Accuracy and precision: ThreedifferentconcentrationscoveringthelinearityrangeofarticaineHClandepinephrinewereanalyzedin triplicates within the same day for intraday and for threesuccessivedaysforinterdayusingtheproceduredetailedunderlinearity part. Accuracy was calculated as precision (Relativestandarddeviation(%RSD)).
Application to pharmaceutical formulationsAnaliquot(0.8mL)containing32.1mgarticaineHCland0.0144mgepinephrinebitartaratewastransferredto10mLvolumetricflask, 33.286 mg pure standard epinephrine bitartarate wastransferredtothevolumetricflaskandvolumecompletedwithmethanoltoobtain1.0×10−2molL−1solutionofeachdrug.OnemL of the prepared 1.0 × 10−2mol L−1 solutionwas taken anddilutedto10mLwiththesamesolventtoobtain1.0×10−3molL−1 workingsolutiontobeanalyzedbytheproposedelectrochemicalmethodusing theproceduredetailedunder linearity part. Thedrug concentrations were calculated from the correspondingregressionequation;theproposedmethodwasfurthervalidatedbyusingthestandardadditiontechnique.
Analysis of articaine HCl and epinephrine in urine: Fortheanalysisof articaineHCl andepinephrine inurine, 1.0mLof urinewasmixedwith9.0mLBRbufferofpH7.0,thensuccessiveadditionsof 1.0 × 10−3mol L−1 working standard solutions (covering thelinearityrange)wereaddedtothevoltammetriccellcontaining5.0mLofthepreviouslydilutedurine.
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Results and DiscussionElectrochemical oxidation of articaine HClThereversibilityoftheoxidationprocessofarticaineHClatCPEwas studied by CV, the cyclic voltammogram showed onewelldefinedanodicpeakinBRbufferofpH7.0(anodicpeakcurrent(I)=19.58µAat1.095V),andthereversescanshowednocathodicpeakindicatingthatarticaineHCloxidationisirreversible(Figure 1a).TheproposedoxidationmechanismwasshowninFigure 1b.
Optimization of experimental conditionsEffect of pH: CVatCPEandscanrateof100mVs−1wasusedtoinvestigatetheeffectofpHupontheoxidationofarticaineHCl.4.5mLofBRbuffer(2-11)and0.5mLof1.0×10-2molL−1articaineHClstandardsolutionwereaddedtotheelectrochemicalcell,andtherespectivevoltammetricresponsewasrecorded(Figure 2a).Thisexperimentwasrepeatedusingphosphatebuffer(Figure 3a) toobtaintheoptimumbufferwiththeoptimumpHvalue.
Figures 2a and 3a showthattheanodicpeakpotential (E)wasshiftednegativelyby increasingpH indicatingthatarticaineHCloxidationatCPEispHdependantandthoseprotonsareinvolvedinthereaction.Figures 2c and 3cshowthathigherpeakcurrentwasachievedusingBRbufferofpH7.0.
The anodic peak current at pH 7 (BR buffer) was found 19.58µA and at pH6.8 (Phosphatebuffer)was 15.10µA. The linearrelationsbetweenpHandpeakpotential(E)observedinthepHrange7-11 (BR)buffer, and6.4-8.0phosphatebufferwasusedtoapplyNernestequationasshown inFigures 2b and 3bwitha regression equation: E(V)=−0.053 pH+1.465, R2 (correlationcoefficient=0.9974 and E(V)=−0.0695 pH+1.548, R2=0.9977 incaseofBRandphosphatebuffers,respectively.ApplyingNernstequation using the formula ∆Ep/∆pH (Slope)=0.059x/n, wherex and n is the number of protons and electrons involved inthe reaction, respectively. It can be concluded that number ofelectronstransferredisequaltothenumberofprotons,thusn=x[34,35].
Effect of surfactant: A surface-active agent (surfactant) isone which tends to accumulate at a surface or interface. Aprerequisiteforsurfactantstobesurfaceactiveisthepropertyof
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thesemoleculestoadsorbattheinterfacebetweenbulkphases,suchasairandwater,oil andwaterorelectrodeand solution.Thedistinct structural featureofa surfactant is thehydrophilicregionof themoleculeor thepolarheadgroupwhichmaybepositive, negative, neutral or zwitterionic and the hydrophobicregion or the tail that consists of one or more hydrocarbonchains,usuallywith6-22carbonatoms,thustheyarealsocalledamphiphiles, i.e., compounds having both polar and nonpolarregionsintheirmolecules.Dependingonthechemicalstructureofthehydrophilicmoietyboundtothehydrophobicportion,thesurfactant may be classified as cationic, anionic, non-ionic orzwitterionic.
Two important properties of surfactants, adsorption atinterface and aggregation into supramolecular structures areadvantageouslyusedinelectrochemistry.Surfactantscanmodifyandcontrolthepropertiesofelectrodesurfaces(Figure 4)[36].
Surfactants were widely used in electroanalytical chemistryto improve sensitivity and selectivity and were applied fordetermination of potassium ferricyanide and dopamine [37],diethylstilbestrol [38], dopamine, uric acid and ascorbic acid[39], uric and ascorbic acids [40], thyroxine [41], moexiprilhydrochloride[33],cefdinir[42],drotaverinehydrochloride[43]andatorvastatin[44].
inpresenceof40µLof1.0x10−2molL−1SDS(Figures 5 and 6) whichenhances thecurrentvalueandshowingcatalyticeffect.SeveralsurfactantsweretriedincludingSDS,DSS,andHSA,whereSDSgavethebestresultswiththehighestanodicpeakcurrentasshowninFigure 6.
Effect of SDS concentration: TheanodicpeakcurrentofarticaineHCl increased gradually upon increasing the concentration ofSDS,howeveritdecreasedwhenSDSconcentrationexceeded8.0×10−5molL−1(40µLof1.0×10−2molL−1SDS),whichwaschosenastheoptimumconcentrationofSDS.TherelationshipbetweenanodicpeakcurrentofarticaineHClandSDSconcentrationwasillustratedinFigures 7a and 7b.
Effect of scan rate: Theeffectofdifferentscanrates(υ)rangingfrom 10 to 250 mV s−1 on the cyclic voltammetric responseof articaine HCl in BR buffer (pH 7.0) was investigated, withincreasing scan rates, the anodic peak was slightly shifted to
5
0
-5
-10
-15
-20
-250.4 0.6 0.8 1.0 1.2 1.4
E/V
pH 6pH 6.4pH 6.8pH 7.2pH 7.4pH 8
l/µA
Figure 3a Cyclic voltammograms of 1.0 × 10−3 mol L−1 articaine HCl in phosphate buffer pH (6-8) atCPE,scanrate100mVs−1.
the positive potential direction and the peak current increasedremarkablywith increasing scan rates (Figure 8a). Itwas foundthatthe logarithmofanodicpeakcurrent (log I) is lineartothelogarithmofscanrate(logυ),withthelinearregressionequationaslogI=0.59logυ+0.421,R2=0.9966.Fromthevalueoftheslope,0.59,itcanbededucedthattheelectrochemicaloxidationprocessof articaine HCl at CPE is diffusion controlled process with an
adsorptioncontribution(Figure 8b)[45].
Effect of accumulation time: Itwasfoundthatthepeakcurrentdependedontheaccumulationtime(Tacc)of1.0×10−3molL−1 articaineHClatCPE inBRbuffer (pH7.0)and40µLSDS (1.0×10−2 mol L−1). Sharp increase was observed at 5 s reaching itsmaximum value, and then decreasedwith increasing time. 5 swaschosenastheoptimumTaccfordeterminationofarticaineHCl(Figures 9a and 9b).
Simultaneous determination of articaine HCl and epinephrineFigure 10a shows the cyclic voltamogramof 1.0 × 10−3mol L−1 epinephrineatCPEinBRbuffer(pH7.0)containing40µLSDS(1.0×10−2molL−1).Figure 10b exhibitstheoxidationmechanismofepinephrine[34].Figure 10cpresentsthecyclicvoltammogramof1.0×10−3molL−1articaineandepinephrineatCPEusingthesame conditions referring to well defined separate peaks ofarticaineandepinephrinewereobtained,thereforethesedrugscanbedeterminedsimultaneously.
Method validationLinearity: Linear relationships were found between the peakcurrentsandconcentrationsofthetwodrugsintherangeof1.0×10−6-2.6×10−5molL−1(0.320-8.34µgmL−1)forarticaineHCland(0.183-4.763µgmL-1) forepinephrineusingtheproposedmethodasshowninFigure 11.Themeanpercentagerecoverieswereof
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98.1±1.96and98.2±1.94 for articaineHCl andepinephrine,respectively. The proposed method is more sensitive thanspectrophotmetricmethod for articaineHCl 10-70µg/mL [10],spectrophotometric methods for epinephrine: 2-20 mg mL-1
[20],1.5-30,3.0-30,and1.5-25μmolL-1[21],0.4-12.8mgmL-1 [22],1.143-142.90μgmL-1 [23],and1.8-35.3μgmL-1 [24],andelectrochemical methods for epinephrine: 3.0-175.0 μmol L−1 [26], and 1.0 × 10−5 to 1.0 × 10−3 mol L−1 [29]. The regressionparameterswerecomputedandpresentedinTable 1.
LODandLOQ:Thelimitsofdetection(LOD)andofquantification(LOQ)weredeterminedaccordingtoICH[46]usingthestandarddeviation of multiple blank samples and the slope of the
0
-20
-40
-60
-80
0.4 0.6 0.8 1.0 1.2 1.4
E/V
zero s5s10 s15 s20 s25 s30 s35 s40 s
50 s55 s60 s
45 s
l/µA
Figure 9a Cyclic voltammograms of 1.0 × 10−3 mol L−1 articaineHClatCPEinBRbuffer(pH 7.0)and40µLSDS(1.0×10−2molL−1)atscanrate100mV s−1 as a function of accumulation timefrom0to60s.
65
60
55
50
45
40
350 10 20 30 40 50 60 70
Tacc/s
l/µA
Figure 9b Plot of the anodic peak current versusaccumulationtime.
Accuracy and precisionIntradayandinterdayaccuracy(%R)rangedfrom99.3%to101.7%andprecision(%RSD)from0.23%to1.49%forarticaineHClandfrom98.3%to101.5%andfrom0.58%to1.78%forepinephrine(Table 3).
Application to pharmaceutical formulationThe proposed method was applied successfully for thedeterminationofarticaineHCLandepinephrineinpharmaceuticaldosage form in thepresenceofexcipientsandadditives in thesame concentration range as in the bulk without interferencewitharecoveryof100.4±0.65and99.2±0.71,respectively.Thestandardadditiontechniquewasfurtherusedtodeterminetherecoveryoftheproposedmethod (Table 4).
25
20
15
10
5
00 5 10 15 20 25
Conc/µ mol L-1
l/µA
Figure 11b Calibration curve of the anodic peak current to thecorrespondingconcentrationofepinephrine.
Table 3 IntradayandInterdayaccuracyandprecisionforthesimultaneousdetermination of articaine HCl and epinephrine by the proposedelectrochemicalmethod.
Statistical analysis of the results obtained by the proposedmethod compared with a reported method [47] revealed nosignificant difference between the proposed and reportedmethods, where the calculated t- and F- values are less thanthe tabulated ones, confirming accuracy and precision at 95%confidence limit [48]. However, the proposed method allowssimultaneousdeterminationofbothdrugs,thereportedmethoddeterminesbothdrugsseparately(Table 5).
The reported method involved determination of articaine HCland epinephrine by HPLC; articaine HCl was determined usingmobilephase(600mLacetonitrileand400mL[1.3mLfrom1.0mol L−1 sodium phosphate+32.5mL from 0.5mol L−1 disodiumphosphatein1000mLwithdistilledwater(pH8.0)],lichrospher100RP-18(5µm×250mm×4mm)ascolumnandwavelengthof240nm.Epinephrinewasdeterminedusinggradientmobilephase [A: methanol, B: 0.42% w/v tetramethylammoniumhydrogensulphate+0.116%w/vsodiumheptanesulfonate+0.21%v/vdisodiumedetateatpH3.5with40%NaOH],KromacilC185µm×4mm×150mmandwavelengthof205nm.
Simultaneous determination of articaine HCl and epinephrine in spiked urine samplesSuccessiveadditionsofarticaineHClandepinephrinesolutions(1.0×10−3molL−1)coveringthelinearityrangeof(1.0×10−6-2.6×10−5mol L−1)wereadded to thevoltammetric cell containing5mL of diluted urine and 40µL of 1.0 × 10-2mol L−1 SDS, thevoltammogramswererecordedatascanrateof20mVs−1usingDPVatcarbonpasteelectrodewithpercentagerecoverieswerecalculatedfromregressionequation(Table 6).
ConclusionIn the present work a simple, sensitive, accurate and preciseelectroanalytical voltammetric method was developed for
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simultaneous determination of articaine HCl and epinephrinein bulk, pharmaceutical dosage forms and spikedhumanurinebasedontheelectrochemicaloxidationofthesedrugsatcarbonpasteelectrodeinBRbufferofpH7.0inthepresenceofsodiumdodecyl sulphate, which allows to use the proposed methodfor routine quality control applications for articaine HCl andepinephrine.
Articaine HCl Epinephrine
Mean ± RSD Standard addition Mean ± RSD Standard addition
Table 5 Results obtained by the proposed electrochemical method compared with the reportedmethod for the analysis of articaine HCl andepinephrineinArtinibsa®carpules.
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