A New Approach for the Determination of Benzocaine and Procaine in Pharmaceuticals by Single-Sweep Polarography

Home , Cinchocaine, Trimecaine

Hindawi International Journal of Electrochemistry Volume 2018, Article ID 1376231, 10 pages https://doi.org/10.1155/2018/1376231

Research Article A New Approach for the Determination of Benzocaine and Procaine in Pharmaceuticals by Single-Sweep Polarography

Serhij Plotycya,1 Oksana Strontsitska,1 Solomiya Pysarevska ,2 Mykola Blazheyevskiy,3 and Liliya Dubenska 1

1 Ivan Franko National University of L’viv, Department of Analytical Chemistry, 79005, Kyryla i Mephodia Str. 8, L’viv, Ukraine 2Ivan Franko National University of L’viv, Department of Life Safety, 79000, Doroshenka Str. 41, L’viv, Ukraine 3National Pharmaceutical University, Department of Physical and Colloid Chemistry, 61168, Bljuhera Str. 4, Kharkiv, Ukraine

Correspondence should be addressed to Liliya Dubenska; [email protected]

Received 25 May 2018; Revised 13 August 2018; Accepted 19 August 2018; Published 12 September 2018

Academic Editor: Shengshui Hu

Copyright © 2018 Serhij Plotycya et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A new polarographic method for the determination of benzocaine and procaine based on the polarographic reduction of their chemically obtained oxidation products with potassium peroxymonosulfate is developed. Experimental conditions afecting quantitative yield of benzocaine and procaine oxidation products such as aH, oxidation time, reagents’ concentration, and temperature are explored. It is shown that the reduction current changes in a linear fashion (R=0.999) with increasing concentration −6 −5 −1 of anesthetics over a concentration range of 1⋅10 -5⋅10 mol L . Te calculated limits of detection (LOD) for benzocaine and −6 −6 −1 procaine are found to be 5.6⋅10 and 6⋅10 mol L , respectively. In the present study, quantitative polarographic determination of benzocaine in Farisil tablets and “Septolete Plus” lozenges and procaine in solution for injections is performed. Te results of the analysis are in good agreement with the product specifcations described in the quality certifcates. Te possibility of quantitative determination of benzocaine and procaine in pharmaceuticals is confrmed.

1. Introduction lozenges, and as teething formulations for young children [1]. Local anesthetics (LA) are the group of natural and synthe- However, these drugs have many side efects, in par- sized substances that have the ability to cause a reversible, ticular, cardiovascular, allergic reactions, even capable of temporary blocking/interruption of the excitability, and causing anaphylactic shock [1, 2]. Terefore, the quantitative conductivity of nerve receptors and conductors in direct determination of local anesthetics in pharmaceuticals, blood, contact with them. Terefore, they induce a local loss of and other biological materials is crucially important. sensitivity and eliminate the sensation of pain or so-called pain sensitivity. Te structural basis of modern anesthetics is Te chemical structure of LA makes it possible to use paraaminobenzoic acid. It exhibits a high biological activity. diferent methods for qualitative and quantitative determina- Esters of p-aminobenzoic acid have anesthetic efect and are tion of these analytes. British and European Pharmacopoeia synthetic substitutes for cocaine, which historically was the [3, 4] suggests the use of the nitritometric titration method frst anesthetic. to determine the content of the substance in the BC and PC Benzocaine (BC) and procaine (PC) (Figure 1) are substrates. widely used local anesthetics. Tey are active constituents Te most selective are chromatographic methods. Tey of many drugs and medications. PC is used for local, allow simultaneous quantifcation of LA and their metabo- infltration, spinal anesthesia, and in therapeutic blockade lites in the same mixture and can be used for the analysis [1]. Te main area of BC application is as a component of biological objects and foodstufs. However, these meth- of some free-sale formulations for topical use, for example, ods are not always available and require expensive equip- in skin creams, as a dry powder for skin ulcers, as throat ment and reagents [5–7]. Tere are also simple and cheap 2 International Journal of Electrochemistry

O O （2． N HCl （2． O O＃2（5 (a) (b)

Figure 1: Structure formulas of procaine (1) and benzocaine (b). spectrophotometric methods [8–12] that are signifcantly less or impurity. Tus, polarographic analysis gives very highly selective and sensitive than chromatographic ones. reproducible results. In the case when the substance cannot A good alternative is electrochemical methods that are be reduced at DME, the molecule of this compound is increasingly used in the pharmaceutical industry. In prin- modifed by introducing electrochemically active functional ciple, they are easier, quicker, and cheaper in performance groups, which in fact is used in further analysis. In particular, than chromatographic methods. In addition, the sensitivity for the quantitative determination of compounds containing of electrochemical methods is ofen higher than of the the amino group, it is proposed that they are previously spectrophotometric ones [13–15]. However, they are not very oxidized by strong oxidants to form corresponding azo-, commonly employed techniques for the LA determination. azoxi-, nitroso, and nitroderivatives and N-oxides, which Plasticized ion-selective electrodes exhibit selectivity to are easily reduced on DME. Tus, a universal and simple cations of procaine and lidocaine. Tese electrodes work technique for determination of LA belonging to the amide based on the formation of ion associates, i.e., anesthetic— group was successfully developed [34–36]. tetraphenylborate ion [16]. Simultaneous determination of We investigated the products obtained afer BC and PC procaine and lidocaine in mixtures with cefriaxone and oxidation using KHSO5 and their reduction on a mercury −2 −5 −1 cefazolin was performed in the range of 10 -10 mol⋅L drop. Te aim of this study is to develop a simple electro- [17]. However, these electrodes have some limitations, such as chemical method for the quantitative determination of BC a short lifetime and, in addition, their response time depends and PC in pharmaceuticals. on the analyte’s concentration in the probe. Te authors of [18] developed a sensor for the deter- 2. Material and Methods mination of the procaine and lidocaine content in aqueous solutions and dosage forms, whose analytical signal is the 2.1. Reagents. Benzocaine (ethyl ester of 4-aminobenzoic Donnan potential (DP sensor). Concentration range for acid) was purchased from Changzhou Sunlight Pharmaceu- −4 −2 −1 procaine was 1.0 ⋅ 10 -7.3 ⋅ 10 mol⋅L . tical Co., Ltd., China. Te BC stock solution was prepared by Voltammetric methods for determination of LA are dissolving its appropriate amount in double-distilled water −1 signifcantly more sensitive and more selective than poten- with addition of 1 ml 0.25 mol⋅L hydrochloric acid (p.a., tiometric ones. Te authors of works [19–25] used various Sfera sim, Ukraine). carbonaceous modifed electrodes. For instance, in short Procaine (�-diethylaminoethyl ester of 4-aminobenzoic communication [21] Komorsky-Lovricetal.showedthepos-´ acid hydrochloride) was purchased from Guangxi Shentai sibility of local anesthetics (namely, benzocaine, cinchocaine, Chemical Co., Ltd., China. Te PC stock solution was lidocaine, and procaine) detection and their semiquantitative prepared by dissolving its appropriate amount in double- determination by immobilization of solid microparticles distilled water. of anesthetics on parafn impregnated graphite electrode. Te concentration of both anesthetics stock solutions was −3 −1 Also, the results of high-performance liquid chromatography 1⋅10 mol L . (HPLC), fow injection analysis (FIA) [24], and batch injec- Aqueous solutions of BC and PC possess acidic reaction tion analysis (BIA) [25] with amperometric determination and are stable during storage. Te working solutions of both were shown. Earlier we applied the miniaturized thick-flm anesthetics were obtained by diluting stock solution with boron-doped diamond electrode as advanced and facile elec- double-distilled water. trochemical sensor for simple, sensitive, and reliable quantif- Borate, carbonate, phosphate, and Britton-Robinson cation of BC [26]. However, stationary electrodes have some bufer solution were used for preliminary studies. In further disadvantages, particularly, their utilization require labor- investigations phosphate bufer solution was used. It was intensive renewing of electrode surface. Te brief description prepared in the following way: 15.00 g of KH2PO4 (p.a., of some methods of BC and PC determination is presented in Sfera sim, Ukraine) was dissolved in a 250 mL volumetric −1 Table 1. fask; then 2.5 mol⋅L of sodium hydroxide (p.a., Sfera sim, Polarography is also used today in many control labora- Ukraine) was added to achieve the necessary pH and, fnally, tories as a simple, commercially available, highly sensitive, the fask was flled with double-distilled water up to the and selective method for the determination of therapeutically mark. Phosphate bufer is available to maintain pH value in − 2− active substances in medications and biological fuids; see for wide ranges: at pH 4.8–8.0 H2PO4 /HPO4 bufer system 2− 3− instance [27–33]. Te main advantage of dropping mercury works and at pH>8.5 – HPO4 /PO4 system. In addition, electrode (DME) against stationary electrodes is the high the nature of ions and ionic strength does not change repeatability of measurements since each drop has a smooth substantially. Tis is an important feature in voltammetric and uncontaminated surface free from any adsorbed analyte analysis. Te bufer capacity at pH 8.0–9.0, which is relatively International Journal of Electrochemistry 3

Table 1: Brief description of some methods for determination of BC and PC.

Objects Anesthetic Method Linear range LOQ LOD References analyzed PC HPLC-UV 0.05 – 5.0 �g /mL 0.05 �g/mL – human plasma [6] serum of human PC HPLC – MS – ESI 10 – 100 ng / mL 10.0 ng/mL 0.100 ng/mL [7] blood BC SP 10 – 25 �g/L – – [8] commercial PC DPV 3 – 50 �V –0.91�V pharmaceutical [22] samples commercial PC DSWV 1 – 250 �V 1.35 �V 0.4 �V pharmaceutical [22] samples pharmaceutical BC 1.0 – 100 �V 0.83 �M0.25�M [23] products BC FIA–AD 0.2 – 100 – 0.19 [24] HPLC–AD 0.2 – 100 �M – 0.20 �M BC BIA–AD 0.1 – 8 �M – 0.0302 �M [25] pharmaceutical DPV 0.1 – 400 �M 0.27 �M 0.08 �M BC samples, spiked [26] SWV 0.4 – 200 �M 0.32 �M 0.1 �M urine samples BIA–AD: batch injection analysis with amperometric detection; DPV: diferential pulse voltammetry; DSWV: diferential square wave voltammetry; FIA–AD – fow injection analysis with amperometric detection; HPLC: AD with amperometric detection; HPLC–MS–ESI: high-performance liquid chromatography–tandem mass spectrometry with electrospray ionization; HPLC-UV: high-performance liquid chromatography with ultraviolet detection; SP: spectrophotometry. low, can be increased by increasing the bufer concentration 2.3. Voltammetric Procedure and Sample Preparation. Afer [38]. optimization of the experimental parameters for the pro- “Extra pure” commercial triple potassium salt of Caro’s posed method, the analytical curve was obtained in the −1 acid–Oxone was purchased from Acros Organics and used following way: 2 mL of 1.25 mol L phosphate bufer as oxidizing agent. Te active ingredient of Oxone is potas- with pH 9.0 was introduced into 25 mL volummetric fask, −3 −1 sium peroxymonosulfate, KHSO5 (PMS) (CAS 10058-23-8), and then 2.5 mL of 10 mol L PMS and aliquot of commonly known as potassium monopersulfate, which is anesthetic were added to the fask. Te concentration of −5 −5 present as a component of a triple salt with the formula anesthetic must be in the range from 1⋅10 to 5⋅10 mol −1 2KHSO5⋅KHSO4⋅K2SO4 potassium hydrogen peroxymono- L .Teobtainedsolutionshouldstayduring5-6min.Ten −1 sulfate sulfate (CAS 70693-62-8). Tis reagent was chosen 1.25 mL of 2.5 mol L H3PO4 was added to obtain pH because of its availability, sufcient solubility in water, high 4.0 (should be checked with pH-meter). Finally, the fask − − ± oxidative ability (EHSO5 /HSO4 changes from 1.82 0.03 V at was flled with double-distilled water up to the mark. Te aH0to1.44VataH 11 [39]), and sufcient durability obtained working solutions were introduced into the cell, 5 during exploitation and storage [DuPont6 Oxone Techni- and deoxygenated with argon for 10 min. Te voltammogram cal Attributes] [37, 40, 41]. Stock solution of Oxone was was recorded by applying a linear potential scan from 0.0 to prepared by dissolving its appropriate amount in 70 mL of -1.5 V. double-distilled water in a 100 mL volumetric fask; then it was flled with double-distilled water to the mark and 2.4. Preparation of Pharmaceutical Samples and Procedure for shaken. Teir Analysis. Te working investigated sample (WIS) was Purifed argon was used to remove dissolved oxygen. prepared as follows: four tablets were dissolved in 4 mL of −1 0.25 mol⋅L hydrochloric acid, and then the double-distilled 2.2. Apparatus. Voltammetric measurements were carried water was added to the mark followed by continuous stirring out on digital device equipped with personal computer [41] the solution with an electromagnetic stir bar. Te solution was and temperature-controlled three-electrode cell, volume 10 then fltered through the flter paper (the pore size of 1-2.5 mL. An indicator dropping mercury electrode (DME), a nm) in order to remove insoluble excipients. Te precipitate −2 −1 saturated calomel reference electrode, and platinum wire was washed on the flter in several portions of 10 mol⋅L auxiliary electrode were used. Te employed DME had the −4 −1 hydrochloric acid and then with double-distilled water. Te following characteristics: m=5.94⋅10 g⋅s ; �k=10 s in 0.2 −1 contents were quantitatively transferred to a 200.0 mL fask mol L NH4Cl with open circuit. and the double-distilled water was added to the mark. Te Te pH of the solutions was measured potentiometrically concentration of anesthetic in such WIS, according to quality −4 −1 using MV 870 DIGITAL-pH-MESSERAT¨ pH-meter. certifcate, is 6.053⋅10 mol L . 4 International Journal of Electrochemistry

Table 2: Te equations of linear dependence of E, V on pH on a phosphate bufer.

Anesthetics Peak aX range Equation Correlation coefcient, R 2.1-4.3 E=(-0,047±0.007)+(0.082±0.002)⋅aH0.9984 `1 ± ± ⋅a `b 5.0-9.1 E=(0.021 0.002)+(0.065 0.003) H0.9961 `3 5.0-8.1 E=(-0.16±0.02)+(0.069± 0.003)⋅aH0.9971 `4 5.0-8.1 E=(0.011±0.020)+(0.078±0.003)⋅aH0.9977 2.0-4.5 E=(-0,018±0.009)+(0.071±0.002)⋅aH0.9957 jb `1 5.0-9.0 E=(0.03±0.03)+(0.062±0.004)⋅aH0.9951

electrolytes. For further experiments phosphate bufer was 2.0 selected as the supporting electrolyte since it is more appropriate to change pH and to adjust weakly acidic medium A)

 1.0 required for polarographic measurement. I ( TeshapeofpolarogrammsofBCandPCderivatives reduction signifcantly depends on pH of polarographic 0.0 scanning (pHpol)(Figures3and4). 0.0 0.2 0.4 0.6 0.8 1.0 1.2 At pH < 4.5 oxidation products of PC are reduced yielding -E (V) two peaks: -0.13 – -0.3 V (frst peak P1) and approximately - 1 1.15 V (second peak, P2) (Figure 3). Peak P2 is broad and the 2 maximum is blurred. At > 4.5 the peak P1 current dropped 3 down and the two new peaks P3 and P4 appeared near P1. Figure 2: Polarogramms in a PMS solution without BC or PC (1) On the polarogramm of BC on a phosphate bufer, one and the solutions of BC (2) and PC (3) afer oxidation at pH 9 and distinct peak P1 was observed within the studied pH region ∘ −3 −1 −5 −1 > heating to 60 C. CPMS =10 mol⋅L ,CBC=CPC =5⋅10 mol⋅L . (Figure 4). At pH 8, this peak splits similarly to PC. Te Phosphatebuferwasusedassupportingelectrolyte,bbufer=0.2 peak, which corresponds to P2 for the PC, was not observed −1 mol⋅L and aH=4. on the polarogramms of BC derivative. Te maximum value of the reduction current for P1 derivatives of BC and PC is observed at pH about 4.0; An aliquot of 1.00 mL of the dosage solution was taken therefore, this value was selected for all further experiments. intoa25.0mLvolumetricfask,andthen2mLofa1.25 Since the process is rather complicated, the potentials −1 mol⋅L phosphate bufer solution with pH 9 and 2.5 mL of of the reduction peaks of the corresponding derivatives are −2 −1 10 mol L of PMS were added and stirred. Te obtained shifed to a negative direction with increasing the pH. Tis ∘ mixture was heated for 10 min at 40-60 Candcooled. behavior demonstrates that the electrochemical reduction of Ten the pH was adjusted to the value 4.0 by adding a 2.5 BC and PC involves proton transfer stage. Te dependence of −1 mol⋅L solution of H3PO4. Finally, double-distilled water -E vs. pH of the bufer was found to be linear in the whole was added to the mark. Te obtained solution was introduced pH range. Te obtained dependences can be expressed by the into the cell and deoxygenated with argon for 10 min. Te equation presented in Table 2. polarogramm was recorded by applying a linear potential scan from 0.0 to -1.5 V. 3.2. Efect of Temperature, Oxidation Time, and Reagents’ Concentration. Te colorless products of oxidation of the 3. Results and Discussion BC and PC were always obtained, regardless of the reaction conditions used. ⋅ −5 −1 Te polarogramms of 5 10 mol L BC and PC oxidation Te oxidation reaction is slow at room temperature. products in a phosphate bufer solution at DME are depicted Te maximum current can be reached afer 60 minutes of in Figure 2. Te reduction process of both BC and PC oxidation, which is too long. Terefore, all studies were oxidation products is irreversible. performed with the heating of solutions during oxidation. It afects the rate of the oxidation reaction. All the reagents 3.1. Efect of pH and Supporting Electrolyte. Oxidation prod- were mixed (phosphate bufer with pH 9, BC or PC, and ucts of amines are formed in alkaline medium. Acidifcation PMS) in the appropriate ratio in a glass, and then the of reaction mixture leads to stop the oxidation process. An glass was immersed in a water bath until an appropriate optimum pH for oxidation (pHox) of BC and PC is in the temperature was established. Te temperature of the solution range from 8.7 to 9.3. was additionally controlled by a thermometer. Afer reaching Phosphate, borate, carbonate, and Britton-Robinson theappropriatetemperature,phosphateacidwasaddedto bufer solutions were investigated as electrolytes for the pH 4 and cooled to room temperature. For the BC oxidation ∘ oxidation reaction. Higher reduction currents of oxidation product, the optimal heating temperature is 40-60 C(Fig- products were obtained using phosphate bufer as supporting ure 5(a)) and for the oxidation product of PC (Figure 5(b)), International Journal of Electrochemistry 5

I (A) -E (V) I (A) 4.0 4 0.6 3.5 3.0 0.5 3 2.5 0.4 2.0 2 0.3 1.5

1 1.0 0.2 0.5 0.1 0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 12345678910 -E (V) pH pH=2.0 pH=6.1 pH=4.1 pH=8.1 (a) (b)

Figure 3: Polarogramms PC (a) and dependence of polarographic characteristics of derivatives at diferent pH (b) using phosphate bufer, −5 −1 −4 −1 −1 ∘ CPC=5⋅10 mol⋅L ,CPMS=10 mol⋅L ,Cbufer=0.2 mol⋅L ,durationofoxidation10min.,andT=70b.

 I ( A) -E (V) I (A) 3.0 0.6 3 2.5 0.5 2.0 0.4 2 1.5 0.3 1.0 1 0.2 0.5 0.1 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 12345678910 -E (V) pH pH=2.0 pH=6.1 pH=4.1 pH=8.1

(a) (b)

−5 Figure 4: Polarogramms jC (a) and polarographic characteristics of derivatives at diferent pH (b) using phosphate bufer, CBC=5⋅10 −1 −4 −1 −1 ∘ mol⋅L ,CPMS=10 mol⋅L ,Cbufer=0.2 mol⋅L ,durationofoxidation10min.,andT=60b.

∘ −3 −1 within 70-100 C. All further studies were performed in these should not exceed 10 mol⋅L because of PMS reduction temperature ranges. leading to the residual current increase and polarogram An important factor afecting the quantitative yield of background line distortions. the corresponding oxidation products is the oxidation time. Its efect on the yield of the derivative occurs within frst 3.3. Efect of Scan Rate. Te scan rate (]) was changed from 0.1 −1 10 minutes and afer the amount of the oxidation product to 1.0 V⋅s .Withincreasing] the peak height also increases does not change. Terefore, further anesthetics were oxidized and the potential shifs to the cathodic region (Figure 7). within 10 minutes (Figure 6(a)). Te slope of log � versus log ] for P1 of BC (Figure 7) For the maximal yield of BC derivatives a 2-fold excess in various conditions is in the range from 0.33 to 0.54 and of PMS is sufcient. For the oxidation of PC a larger excess indicates the difusion-controlled current with minor kinetic of oxidant should be used (Figure 6(b)). Figure 6(b) shows issues that increase with increasing pH of the solution. Te a fragment of these dependencies. Te reduction current of slope of log � versus log ] for P1 of PC (the data are not shown anesthetic derivatives does not change up to a 200-fold excess here) under diferent conditions at aHlessthan5is0.50 of PMS. However, the concentration of PMS in the solution and also suggests the difusion-controlled current. At pH 7.5 6 International Journal of Electrochemistry

  I ( A) I ( A) 3.0 1.6

1.5 2.5

1.4 2.0 1.3

1.2 1.5

1.1 1.0 1.0 0.5 0.9

0.8 0.0 20 30 40 50 60 70 80 20 30 40 50 60 7080 90 100 ∘ ∘ T ( C) T ( C) (a) (b) −3 −1 −5 Figure 5: Efect of temperature on the oxidation product yield (for peak P1) of BC (a) and PC (b) CPMS =10 mol⋅L ,CBC =CPC =5⋅10 −1 −1 mol⋅L ;Cbufer ∼0.2 mol⋅L ,andaH=4.0.

I (A) I (A) 5 2.8 2 2 2.4 4 1 1 2.0 3

1.6 2

1.2 1

0.8 0 0 10 20 30 40 50 60 0 5 10 15 20

t (min) ＃PMS /＃！．

(a) (b) −3 −1 Figure 6: Dependence of the peak P1 current of BC (1) and PC (2) derivatives on the oxidation time (a), CPMS =10 mol⋅L ,andonthe −5 −1 molar excess of PMS (b), CBC =CPC =5⋅ 10 mol⋅L ,pH4.0. for three peaks `1, `3, and `4for`b the slope is close to 1 Te current reaches a maximum with an excess of oxidizing indicating the adsorption efect. agent, so no further oxidation of this group occurs. Te sof Te linear relationship between �p and the square root oxidation of primary amines with peroxide compounds gives 1/2 ofthescanrate(V )clearlyrefectsadifusion-driven hydroxylamine as the initial product followed by its further mechanism of the electrode reaction at this pH. oxidation to nitroso compounds. Under more stringent conditions, in particular when heated, primary amines can 3.4. Te Possible Mechanism of Electrochemical Reaction. Te be oxidized to nitro compounds. It is also known that, in the polarogramms for derivatives of BC and PC have an anal- concentrated sulfuric acid medium, the BC can be oxidized ogous shape, and various factors afect their characteristics to the formation of colored products. in a similar way. Tis indicates the participation of the From the quantitative parameters of the polarogramm same functional groups in electrochemical reactions and the one can calculate the number of electrons � that participate same mechanism of transformation. Such a joint group for in the electrode process [42]: the BC and the PC is the primary amino group. In the 47.7 �� = − (mV) , case of excessive use of the oxidizing agent the peak of P1 ( − ) (1) appears on the polarogramms within some period of time. Ep Ep/2 International Journal of Electrochemistry 7

I (A) I (A) 4 2.2 2.0 1.8 1.6 1.4 3 1.2 1.0 0.4 0.5 0.6 0.7 0.8 0.9 1.0 / - / v ((Vs ) log I 2 0.4 0.3 0.2 0.1 0.0 1 −0.1 −0.2 −1.0 −0.8 −0.6 −0.4 −0.2 0.0 log v 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -E (V)

−5 −1 −1 Figure 7: Polarogramms of 5⋅10 mol⋅L BC in the potential range from 0.0 to -1.4 V for the scan rate values from 0.1 to 1.0 V s ,CPMS= −3 −1 −1 1/2 1⋅10 mol⋅L ,pH4.0,andCbufer=0.2 mol⋅L . Insets: the dependences of �p vs. V and log �p vs. log V. where � the charge transfer coefcient and � the number 4. Determination of Analytical Parameters of electron transferred in a stage of electrode process. Te coefcient � for irreversible systems equals 0.5. Te previously optimized experimental parameters were Te number of electrons can also be determined from the employed to record the corresponding analytical curves for dependence of �� =�(log V) (not shown here): the slope BC and PC on the phosphate bufer. Tus, the analytical of this dependence equals (2.3RT/�nF). Te results of both parameters obtained by proposed methods are summarized calculations are consistent with each other (Table 3). in Table 4. Te limits of detection (LOD) and quantifcation + + Te number of H ions (zH ) participating in electro- (LOQ) were estimated taking three and ten times the stan- chemical process can be estimated from the slope of the peak dard deviation of the blank (3.3S�/b, 10S�/b), respectively (S�: potential vs. pH (Table 2) according to the following equation residual standard deviation or standard deviation of the y- + dE/pH = (2.3RT⋅zH ) /�nF. Te results of these calculations intercept, n = 9) [46]. are presented in Table 3. We assume that in the presence of the excess of oxidant 4.1. Analysis of Pharmaceutical Dosages. Based on the ob- and heating the complete oxidation of the primary amino tained results, we have developed a polarographic technique group of anesthetics to the nitro group occurs. Ten, the for the determination of BC in “Farisil” tablets (manufactured nitro group gaining four electrons is reduced to the hydrox- by Alcala Pharma, SL, Spain), “Septolete Plus” (KRKA dd, ylamine on the electrode. Tis is in good agreement with the Novo mesto, Slovenia), and `b in solution for injections data reported in the literature [43–45]. On the other hand, (“Darnytsya”, Ukraine). we do not exclude that the amino group is frst oxidized Presence of other compounds in solution for injection to the nitroso compound and then reduced back to the does not afect the determination of `b.Tematrixof amino group on the electrode. In the alkaline medium, the tablets is complex; in particular, it contains a lot of sugar. reduction is stepwise and also complicated by adsorption for Matrix substances slightly infuence the double electric layer PC. leading to a minor change in shape of the polarogramm and Cathodic peak P2 of PC derivative can be caused by the the reduction current of the PC and BC derivatives by less reduction of N-oxide of tertiary amine, but this peak does than 10% in comparison to the pure solution. However, the not have a well-defned profle shape, which makes its precise dependence of the current on the concentration of BC on measurements rather difcult. Tus, it was not used in further the background of the matrix of the tablets remains linear 5 experiments. (Figure 8). Tus, the content of BC in “Farisil ” tablets and 5 For a detailed elucidation of the oxidation mechanism of “Septolete plus ” lozenges was determined using the method the BC and PC and the reduction of their oxidation products, of standard addition. Preparation of the samples is described the spectral analysis (NMR or mass spectrometry) and in detail in the Section 2.4. In the same way the procedure coulometry are recommended for the future investigations. with addition from 0.10 mL to 0.80 mL of standard BC 8 International Journal of Electrochemistry

+ + Table 3: Te calculated number of electrons (n)andionsofH (zH ) involved in electrochemical reduction of BC and PC derivatives at −3 −1 −5 −1 −1 −1 various pH CPMS=1⋅10 mol⋅L ,CBC =CPC =5⋅ 10 mol⋅L , phosphate bufer Cbufer=0.2 mol⋅L ,and]=0.5 V⋅s .

n + Anesthetic aHPe1k zH According to formula [37] by Ep =�(log V) 4.0 `14 43 ` `b 12 –1 6.1 `33 –3 `42 –1 ` jb 4.0 14 43 7. 5 `12 21

Table 4: Characteristics of quantitative polarographic determina- according to Quality Control Methods No. UA/L 48565 ⋅ −3 ⋅ −1 ] −1 tion of BC and PC, pH 4.0. CPMS=110 mol L =0.5 Vs . and No. UA 16/6052-L8 (Ukraine). Te characteristics we determined are in the range from 97.0 to 102.6%. Tese results Analytical parameter BC PC prove that our technique does not sufer from any signifcant Peak potential, V -0.24 -0.51 −1 −6 −5 −6 −5 matrix efects. Linear concentration range, mol⋅L 1⋅10 -5⋅10 1⋅10 -5⋅10 4 4 Te developed method is simple and cheap and has a Slope (�A⋅L/ mol) 4.1⋅10 9.1⋅10 −2 −2 wide linear range. Sensitivity of our method is comparable Intercept (�A) 1.7⋅10 4.2⋅10 to that of chromatographic method. Tus, this work extends Correlation coefcient, R 0.9996 0.9996 the possibility to select the appropriate method among the RSD (%) 2.12 1.13 available ones for determination of the PC and the BC in −1 −6 −6 Limit of quantitation (LOQ), mol⋅L 1.8⋅10 1.9⋅10 specifc real objects such as drugs. −1 −6 −6 Limit of detection (LOD), mol⋅L 5.6⋅10 6⋅10 5. Conclusions I (A) 0.8 Modern voltammetric methods provide reliable and reproducible quantitative determination of substances in a com- 0.7 7 plex matrix. In earlier reported works stationary bare elec- 0.6 trodes and chemically-modifed electrodes were used for 0.5 local anesthetics quantitations. Te procedure of modifca- tion and surface renewing of such electrodes is time consum- 0.4 1 ing and labor-intensive. In this regard the mercury electrodes 2.01.00.0 3.0 have advantages. Tus our methods are instrumentally simple ＃ 10-5 0 ＂＃ ( M) and portable and have moderate cost, high reproducibility 0.5  A and are comparable in sensitivity to other methods. Tere- fore, we have developed a new polarographic method for the determination of BC and PC based on the electrochemical reduction of their chemically oxidized products obtained by the reaction with PMS. Moreover, the achieved results 0.20.10.0 0.3 0.4 0.5 0.6 0.7 0.8 show that this method can be successfully applied for -E (V) quantitative polarographic detetmination of anesthetics in pharmaceuticals, in particular, BC in tablets “Farisil”and Figure 8: Polarogramms for the pharmaceutical dosage Septolete “Septolete plus,”aswellasPCinafreshlypreparedsolution plus analysis with declared content of 5 mg BC using standard for injections. Consequently, the presented method paves the addition method. Te corresponding standard additions: from 0.10 ⋅ −3 −1 way for accurate and reliable quantitative analysis of local mL to 0.80 mL (CBC =110 mol L ). Te quantifcation of BC by anesthetics in medicinal products. standard addition method is depicted in the inset. Te developed technique is universal. Previously, we reported the determination of three other amide anesthetics, namely lidocaine, mepivacaine, and trimecaine, using solution was performed. Te results of quantitative determi- the same approach. Althought these anesthetics were oxi- nation of BC in “Farisil” tablets and “Septolete plus”lozenges dized by PMS, the reduction process was diferent. Tus, and `b in solution for injections are presented in Table 5. our technique is also capable of identifying other drugs We compared our results with the data obtained by the containing the amine functional groups. Obviously, some control laboratories of the State Administration of Ukraine selectivity issues can occur in the real samples, for example, in on Medicinal Products, which provided us the quality cer- patients’ urine afer taking medication. Ten, it is necessary tifcates. In certifcation procedure analysis was carried out to use extraction procedures or HPLC. Nevertheless, the International Journal of Electrochemistry 9

Table 5: Te analysis of the pharmaceutical dosages using the proposed method (n =3).

Declared in Relative Anesthetic Pharmaceutical Requirement of Declared quality Determined determina- dosage ND, mg (%) amount, mg certifcate, amount, mg tion error, mg % 4.75-5.25 “Farisil5” 5.00 5.10 4.9±0.3 3.03 jb (95-105) 4.50-5.50 “Septolete plus5” 5.00 4.98 5.11±0.23 2.54 (90-110) Solution for 4.75-5.25 `b 5.00 4.97 4.9± 0,4 1.62 injections (95-105) proposed electrochemical detection will improve analytical [8] H. A. Merey, “Simple spectrophotometric methods for the performance. simultaneous determination of antipyrine and benzocaine,” Bulletin of Faculty of Pharmacy, Cairo University,vol.54,no.2, pp. 181–189, 2016. Data Availability [9] L. R. Paschoal and W.A. Ferreira, “Simultaneous determination Te [polarogramms, dependences of analytical signal on of benzocaine and cetylpiridinium chloride in tablets by frst- derivative spectrophotometric method,” Farmaco,vol.55,no.11- variety factors (pH, temperature, concentration of reagents, 12, pp. 687–693, 2000. oxidation time, and scan rate)] data used to support the [10]L.P.Savchenko,V.O.Vrakin,V.O.Grudko,T.V.Krutskikh, fndings of this study are included within the article. V.K.Yakovenko,andV.A.Georgiyants,“Selectivespec- trophotometric method for the hydrocortisone butyrate quan- Conflicts of Interest titative determination in compounding ointment in presence of nitrofural and procaine hydrochloride,” Journal of Applied Te authors declares that they have no conficts of interest. Pharmaceutical Science,vol.7,no.8,pp.062–068,2017. [11] E. M. Adamova and V. M. Ivanov, “Methods for the determination of local anesthetic agents,” Journal of Analytical Chemistry, Acknowledgments vol. 71, no. 12, pp. 1169–1181, 2016. Tis work was supported by the Ministry of Education and [12]T.N.Al-Sabha,M.A.Hasan,andH.A.Ibrahim,“Spectropho- Science of Ukraine [Grant no. 0116U001541]. tometric Assay of some Nitrogen Containing Drugs in Phar- maceutical Formulations using p-Chloranilic Acid Reagent,” Journal of Advances in Chemistry,vol.9,no.1,pp.1798–1809, References 2014. [13]Q.Xu,A.-J.Yuan,R.Zhang,X.Bian,D.Chen,andX.Hu, [1] J. K. Aronson, Meyler’s Side Efects of Drugs (Sixteenth Edition) “Application of electrochemical methods for pharmaceutical Te International Encyclopedia of Adverse Drug Reactions and and drug analysis,” Current Pharmaceutical Analysis,vol.5,no. Interactions,16thedition,2016. 2, pp. 144–155, 2009. [2] O. Suzuki and K. Watanabe, “Drugs and poisons in humans,”in [14]L.O.Dubenska,M.Y.Blazhejevskyj,S.I.Plotycya,M.Y. A Handbook of Practical Analysis, pp. 378-379, Springer-Verlag Pylypets, and O. M. Sarahman, “Voltammetric methods for Berlin, Heidelberg, Germany, 2005. the determination of prarmaceuticals,” Methods and Objects of [3] British Pharmacopoeia. Her Majesty’s Stationary Ofce. Lon- Chemical Analysis,vol.12,no.2,pp.61–75,2017. don, UK, 2010. [15]S.A.OzkanandB.Uslu,“Frommercurytonanosensors:Past, [4] “European Pharmacopoeia Online 9.2,” http://online6.edqm present and the future perspective of electrochemistry in phar- .eu/ep902/. maceutical and biomedical analysis,” Journal of Pharmaceutical [5] P. Pérez-Lozano, E. Garc´ıa-Montoya, A. Orriols, M. Miñarro, and Biomedical Analysis,vol.130,pp.126–140,2016. J. R. Ticó, and J. M. Suñé-Negre, “A new validated method for [16] E. G. Kulapina and O. V. Barinova, “Ion-selective electrodes the simultaneous determination of benzocaine, propylparaben for the determination of nitrogen-containing medicinal sub- and benzyl alcohol in a bioadhesive gel by HPLC,” Journal of stances,” Journal of Analytical Chemistry,vol.56,no.5,pp.457– Pharmaceutical and Biomedical Analysis,vol.39,no.5,pp.920– 460, 2001. 927, 2005. [17] \.V.Varygina,R.P.Chernova,and\.Y.Koblova,“Obtaining [6] W.-W. Qin, Z. Jiao, M.-K. Zhong et al., “Simultaneous deter- and use in the analysis of ion-selective electrodes for some mination of procaine, lidocaine, ropivacaine, tetracaine and local anesthetics,” Izvestiya Saratovskogo Universiteta Series bupivacaine in human plasma by high-performance liquid Chemistry, Biology, Ecology,vol.12,no.3,pp.18–25,2012 chromatography,” Journal of Chromatography B,vol.878,no.15- (Russian). 16, pp. 1185–1189, 2010. [18] \.V.Bobreshova,P. 0.Polumestnaya,0.V.Parshina,P. [7]K.Tonooka,N.Naruki,K.Honmaetal.,“Sensitiveliquid Y. Yankina, and b. V. Timofeev, “PD sensor for detecting chromatography/tandem mass spectrometry method for the novocaine, lidocaine in aqueous solutions and dosage forms, simultaneous determination of nine local anesthetic drugs,” Industrial laboratory,” Diagnostics of Materials,vol.78,no.24, Forensic Science International, vol. 265, pp. 182–185, 2016. pp. 22–25, 2012 (Russian). 10 International Journal of Electrochemistry

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