Design of a Disposable Solid State Potentiometric

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SENSOR LETTERS Vol. 12, 1341–1346, 2014

RESEARCH ARTICLE

Design of a Disposable Solid State Potentiometric Sensor for Codeine Content Control in Pharmaceutical Preparations Mohammad Reza Housaindokht1 2 , Narges Ashraf1 ∗ , and Elham Sheikhzadeh1 2 1

2

Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, 9177948974, Mashhad, Iran Research and Technology Center of Biomolecules, Ferdowsi University of Mashhad, 9177948974, Mashhad, Iran (Received: 26 August 2013. Accepted: 14 June 2014) In the present research, a novel and simple disposable solid state potentiometric sensor is proposed and used for determination of codeine in pharmaceutical samples. The sensing membrane which contains codeinium-tetraphenylborate ion pair is coated on strip-shaped pencil leads and also on stainless steel spinal needles. Composition of the coated membrane has been optimized to obtain a Nernstian response. The best performance was observed with the strip-shaped pencil lead as the substrate and the membrane composition of 52.5 mg of PVC, 43.2 mg of o-nitrophenyloctylether (o-NPOE), and 4.3 mg of the ion pair for the sensing membrane. The constructed electrode showed a Nernstian slope of 59.1 ± 0.5 mV decade−1 over the concentration range of 1.0 × 10−4 to 1.0 × 10−1 mol L−1 and a limit of detection of 5.0×10−5 mol L−1 of codeine. The electrode has a response Delivered Publishing to: ? electrode has been used time of 15 s and can be applied in thebypH range of 5Technology to 9. The proposed IP: 126.120.22.239 On: Sun, 08 Feb 2015 03:51:07 to measure the codeine contents in pharmaceutical tablets.

Copyright: American Scientific Publishers

Keywords: Codeine, Potentiometric Sensor, Sodium Tetraphenylborate, Pharmaceutical Samples.

1. INTRODUCTION Codeine, which is generally used as phosphate form in pharmaceutical preparations, is a weak opioid often administrated orally to relieve pain, to suppress cough, or to control diarrhea.1 2 The molecular structure of codeine (Fig. 1) with general formula of C18 H21 NO3 was given by Gulland et al.3 It is one of the 40 individual chemical compounds (specifically, alkaloid compounds) found in opium. However, today, it is perceived as a safe and effective analgesic and used as a local anesthetic in many pharmaceutical products.4 Thus, regarding the availability of codeine in the community, the potential for drug dependence and misuse have raised concerns.5 Moreover, besides therapeutic effects, there are several side effects that can develop after codeine is ingested or injected. These include acute toxicities such as sedation, nausea, meiosis, mental clouding, vomiting, itching, dizziness, agitation, low blood pressure, urinary retention, respiratory depression, and chronic toxicities such as tolerance and physical dependence. Also, after a large overdose of codeine, there is a depression of ∗

Corresponding author; E-mail: [email protected]

Sensor Lett. 2014, Vol. 12, No. 9

central nervous system: the patient may be in a stupor or may go into a coma.2 Development of simple, reliable, rapid, inexpensive and accurate analytical procedures for active ingredient quantification of pharmaceutical preparations is of great importance in drug quality control process.6 To date, several analytical methods have been proposed and applied for quantitative determination of codeine in oral formulations including gas chromatography,7 8 high performance liquid chromatography,9–11 chemiluminescence and electrochemiluminescence,4 12 13 electrophoresis,14 and spectrophotometry.15 16 However, there are many drawbacks associated with these methods, such as high cost and complicated sample pretreatments prior to the analysis. In addition, the demands for highly skilled operators often restrict their use in routine analyses.17 Also, there are several electrochemical methods including voltammetry, amperometry, and potentiometry techniques which have been proposed for the detection of codeine.17–24 29 30 Pournaghi-Azar and Saadatirad have developed an aluminum electrode modified by palladium,18 and also a prussian blue film modified-palladized aluminum electrode19

1546-198X/2014/12/1341/006

doi:10.1166/sl.2014.3291

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Design of a Disposable Solid State Potentiometric Sensor for Codeine Content Control

Fig. 1. Structure of codeine.

Housaindokht et al.

(for in vivo measurements) and integration of multiple sensors on a single chip, and the mass fabrication for cost reduction.42 43 However, to our knowledge, there has been no report on the fabrication of a solid state ion selective electrode for detection of codeine. Present paper describes a novel disposable potentiometric solid state sensor based on the codeiniumtetrapheylborate ion pair as the sensing material for determination of codeine to be used in drug quality control process. Here, two novel cost effective solid substrates i.e., strip-shaped graphite pencil leads (which are used generally in calligraphic mechanical pencils) and stainless steel spinal needles, have been introduced as alternatives for platinum and silver wires which are commonly used for construction of CWEs. After the optimization of electrode configuration and the sensing membrane composition, the proposed potentiometric sensor was satisfactorily applied for determination of codeine in pharmaceutical tablets. The results presented in this paper show that the proposed sensor has an acceptable analytical characteristics.

for determination of Codeine by voltammetry. Recently, a composite graphene and nafion film modified glassy carbon electrode,20 a multi-walled carbon nanotubes modified glassy carbon electrode,21 a boron-doped diamond film electrode17 and a single-walled carbon nanotubes modified carbon-ceramic electrode22 have been applied for voltammetric determination of codeine. There is also a report on utilizing a clay-modified screen-printed electrode as a voltammetric and amperometric codeine sensor.23 Zhou et al. have used the carbon-disk electrode for detection of codeine by amperometry.24 These electroanalytical techniques are rapid, simple, applicable to colored and turbid 2. EXPERIMENTAL DETAILS solutions and have relatively low cost; however, they still 2.1. Reagents and Chemicals suffer from several disadvantages such as lack of selecAll reagents were of analytical grade and deionized tivity in complex matrices, unsuitability for routine and water was used throughout the entire experiments. High automated analytical practices, and the demand for promolecular weight polyvinylchloride (PVC), tetrahydrofessional operators. Also, the electrodes are not (THF, Merck, Delivered by disposPublishingfuran Technology to: ? Germany), sodium tetraphenylboIP:for 126.120.22.239 08 Feb 2015 Merck, 03:51:07 able and therefore, there is a risk memory effects.On: OnSun,rate (NaTPB, Germany), o-nitrophenyloctylether Copyright: American Scientific Publishers the other hand, potentiometric ion sensors or ion-selective (o-NPOE, Fluka, USA), dioctylphthalate (DOP, Abtin electrodes (ISEs) are another subgroup of electrochemical resin company, Iran) and dibutylphthalate (DBP, Abtin sensors which are characterized by their simple design and resin company, Iran) were used as plasticizer. A stanoperation, relatively low detection limits, reasonable selecdard solution of 100 mM of Codeine phosphate (Temad, tivity, accuracy, fast response, portability, low-energy concompany, Iran) was prepared by dissolving the proper sumption, low cost and non-destructive operation. Also, amounts of the corresponding compound in deionized these methods can easily be automated and computerized water. Sucrose (Fluka, USA), urea, dextrose, arginine, which are attractive features in practical applications. For phenylalanine, paracetamol (all from Merck Company) these advantages, ISEs have found various applications in were used to determine selectivity coefficients. clinical chemistry.25–27 In comparison with voltammetry, while both techniques offer a similar sensitivity, poten2.2. Apparatus for Potential Measurements tiometry offers higher selectivity in the presence of comThe potential measurements were carried out using a mon interferences.28 Dropsense® (Spain) instrument. The prepared codeine The conventional polyvinylchloride (PVC) membrane selective electrode was immersed in conjunction with an based ISEs (with an internal solution) have been reported Ag/AgCl reference electrode (Azar electrode company, for potentiometric determination of codeine.29 30 However, Urmia, Iran) in a beaker containing a desired concentrathe short lifetime and the difficulty of miniaturization are tion of codeine phosphate solution. During the measuretheir main drawbacks.6 Elimination of the internal fillments, the solutions were stirred with a mechanical stirrer ing solution from conventional ISEs results in solid-state if needed. The following electrochemical assembly was ISEs, which are more durable and easier to miniaturize.27 used for all potential measurements: Many kinds of these solid-state ISEs such as coated-wire CuAgAgCl(s)sat’d KClcodeine phosphate solution electrodes (CWE) and coated graphite electrodes in which (cM ISECu polymer membranes are cast on a solid surface (withThe calibration curve of the codeine ion selective elecout internal reference solution) has been introduced for trode was obtained using the codeine phosphate solutions other anti-inflammatory narcotic drugs in pharmaceutical in the concentration range of 1 × 10−7 –1 × 10−1 mol L−1 . 31–41 preparations. They offer the advantages of simplicity The pH of solutions were adjusted at pH 5 by the addition of preparation and operation, capability of miniaturization of NaOH or HCl solution (0.5 mol L−1 just before the 1342

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2.3. Preparation of Codeinium-Tetraphenylborate Ion-Pair The ion-pair complex of codeinium-tetraphenylborate (CoTPB) was prepared by adding 10 mL of 0.01 mol L−1 codeine phosphate solution into 10 mL of 0.01 mol L−1 of sodium tetraphenylborate solution. The white precipitate formed was filtered off, washed thoroughly with deionized water, dried at room temperature and ground to fine powders. The ion-pair was used as the active substance to prepare the PVC membrane ion selective electrodes of codeine. 2.4. Preparation of the Electrodes 2.4.1. Preparation of the Membrane Solution The membrane solution was prepared by thoroughly dissolving the proper amounts of the membrane ingredients (under optimal conditions: 52.5 mg of PVC, 43.2 mg of o-NPOE, and 4.3 mg of the ion pair) in 2 mL of THF. The resulting mixture was slowly evaporated, until an oily concentrated mixture obtained.

of the strip-shaped pencil lead (2 cm length) in the membrane solution for three times. The resulting thin film was air-dried for 24 h. The electrode was finally conditioned by soaking it in a 1.0 × 10−3 mol L−1 codeine phosphate solution 24 h before use. 2.5. Determination of Codeine in Pharmaceutical Preparations The pharmaceutical tablets containing codeine phosphate (codeine containing paracetamol tablets, 10 mg/tablet; Jalinus pharmaceutical company) were purchased from a local pharmacy. Eight tablets were dissolved in deionized water, transferred to a 200 mL volumetric flask and diluted to the mark. Then, 50 mL portions of this solution were transferred to a beaker and subjected to potentiometric analysis by standard addition method.

3. RESULTS AND DISCUSSION

Polymeric membrane-based ISEs are fabricated by doping a polymer membrane with sensing ingredients which selectively binds a target ion.41 A conventional ion-selective electrode usually consists of a membrane in the form of a disc attached to the stem of a plastic or glass tube42 and is in electrical contact with the inner reference electrode through the inner reference solution. The for miniaturization and mass fabrication of sensors 2.4.2. Construction of Conventional Delivered by Publishingdesire Technology to: ? requires electrode shapes which has been led Membrane Electrodes IP: 126.120.22.239 On: Sun, 08 Febalternative 2015 03:51:07 to the development of potentiometric solid-state sensors. Copyright: American Scientific Publishers A polyethylene micropipet tip was dipped into the memCoated-wire electrodes refer to a type of ISE in which brane solution for about 2 s, so that a transparent meman electroactive species is incorporated into a thin polybrane was formed. Then, the membrane was air dried for meric support film coated directly on a solid conductor. 24 h and the tube was then filled with internal solution −3 −1 This leads to the total elimination of the internal filling (1.0×10 mol L codeine phosphate solution). Then, the solution and enables to moves towards miniaturization. tip of a saturated Ag/AgCl reference electrode was placed Here, three different designs have been used to construct in this internal solution and fitted to the opening of the the ISEs which include conventional polymeric membrane micropipette tip. The electrode was finally conditioned by −3 −1 electrodes, stainless steel wire coated electrodes, and stripsoaking the membrane in a 1.0 × 10 mol L codeine shaped pencil graphite coated electrodes. The operating phosphate solution 24 h before use. conditions have been optimized for all three types of ISEs. 2.4.3. Construction of Stainless Steel Wire 3.1. Effect of the Membrane Composition Coated Electrodes (SSWCE) The response of ISEs is usually dominated by the phase The metal wire is a 20 gauge and 9.0 cm length stainless boundary potential at the membrane/sample interface. steel spinal needle (Dr. Japan Co., Tokyo, Japan). CoatInternal construction of the electrode and its composition ing process of the stainless steel electrode was performed are the most important factors which controls the perforby dipping the tip of the metal wire (2 cm length) three mance of the electrode;25 i.e., its sensitivity and selectivity. times into the membrane mixture. Then, the membrane was air dried for 24 h until a thin film was formed. The In order to achieve optimum electrode performance, sevelectrode was finally conditioned by soaking it in a 1.0 × eral influencing parameters such as electrode design and 10−3 mol L−1 codeine phosphate solution for 24 h. membrane ingredients have been evaluated for their characteristic parameters and the results provided in Table I. Codeine forms a water-insoluble ion pair with NaTPB 2.4.4. Construction of Strip-Shaped Pencil Lead Coated Electrodes (SPLCE) (Co-TPB) which can be used as an active material for codeine sensor. To show its effectiveness, membranes with Calligraphic pencil leads (0.8 mm × 18 mm × 59 mm) and without this ion pair were prepared. The responses of from Tip Top™ Company were purchased from the local the latter membranes were not reliable and it was found markets. The electrodes were prepared by dipping the tip Sensor Letters 12, 1341–1346, 2014

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measurements. The potential readings were recorded when the potential became stable within the range of ± 1 mV. The calibration curve was constructed by plotting the measured potentials as a function of –log[codeine phosphate].


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Table I. Composition of membranes and performance characteristics of the electrodes.

RESEARCH ARTICLE

Composition (%) No.

PVC

Ionophore

1 2 3 4 5 6 7 8 9

50.5 50.5 50.5 52.5 52.5 54.5 56.5 48.5 56.8

6.3 6.3 6.3 4.3 4.3 2.3 4.3 4.3 0

10 11 12 13 14

50.5 50.5 50.5 50.5 56.8

6.3 6.3 6.3 4.3 0

15 16 17 18 19 20

52.5 52.5 52.5 50.5 54.5 56.8

4.3 4.3 4.3 6.3 2.3 0

Plasticizer

Working concentration range (M)

Slope (mV decade−1 )

Correlation coefficient

450 ± 10 545 ± 30 545 ± 05 591 ± 05 520 ± 25 517 ± 05 531 ± 17 511 ± 18 –

09841 09970 09981 09972 09989 09989 09984 09957 –

382 ± 04 578 ± 38 360 ± 42 458 ± 12 –

09694 09989 09821 09966 –

487 ± 33 477 ± 04 548 ± 16 336 ± 51 324 ± 67 05 ± 41

09924 09884 09989 09975 09714 07506

Strip-shaped solid state electrodes 43.2 DBP (10 × 10−3 –10 × 10−5 ) 43.2 DOP (10 × 10−3 –10 × 10−5 ) 43.2 NPOE (10 × 10−2 –10 × 10−4 43.2 NPOE (10 × 10−1 –10 × 10−4 43.2 DOP (10 × 10−2 –10 × 10−4 43.2 NPOE (10 × 10−2 –10 × 10−5 39.2 NPOE (10 × 10−1 –10 × 10−4 47.2 NPOE (10 × 10−1 –10 × 10−4 43.2 NPOE – Stainless steel wire coated electrodes 43.2 DBP (10 × 10−4 –10 × 10−6 43.2 DOP (10 × 10−3 –10 × 10−5 43.2 NPOE (10 × 10−3 –10 × 10−5 43.2 DOP (10 × 10−3 –10 × 10−5 43.2 DOP – Conventional membrane electrodes with internal solution 43.2 43.2 43.2 43.2 43.2 43.2

DBP NPOE DOP DOP DOP DOP

(10 × 10−2 –10 × 10−5 (10 × 10−2 –10 × 10−5 (10 × 10−2 –10 × 10−5 (10 × 10−2 –10 × 10−5 (10 × 10−2 –10 × 10−5 (10 × 10−2 –10 × 10−5

that the presence of ion pair greatly enhances the potentioof the codeinium ion with the ion pair at the surface of the Delivered by Publishingelectrode. Technology to: ? metric response of the membrane in the terms of sensitivity IP: 126.120.22.239 On: Sun, 08 Feb 2015 and reproducibility. Therefore, the quantities of the memBased on the03:51:07 results in Table I, the electrode #4 with Copyright: American Scientific Publishers brane ingredients have been varied in order to achieve an the membrane composition of 52.5% of PVC, 43.2% of optimized (Nernstian) response for the ISE. It is obvious o-NPOE, and 4.3% of the ion pair coated on the surface that the membrane composition plays an important role in of a pencil lead proves to show the closest value to the the response of a given ISE. Nernstian slope. This composition has been selected as the Choice of an appropriate plasticizer is an important facoptimum and used throughout the entire work. tor in obtaining a suitable response. The nature of the plasticizer influences the selectivity and the detection lim3.2. Effect of pH its of ISEs. Insufficient plasticizer lipophilicity may cause In order to study the effect of pH on the performance its leaching during the measurements which is undesirof the electrode, the potentials were measured as a funcable. O-nitrophenyloctylether (o-NPOE) with = 239, tion of pH at the concentration of 1.0 × 10−3 mol L−1 of dioctylphthalate (DOP) with = 54, and dibutylphthacodeine phosphate. The pH of solutions was adjusted by late (DBP) with = 64 are traditionally used as senthe addition of NaOH or HCl solutions. The results shown sor membrane plasticizers. It is obvious from Table I that in Figure 2 indicate that the potential remains approxiwhen strip-shaped pencil lead has been used as the elecmately constant over the pH values ranged from 5 to 9. trode substrate, the o-NPOE represents the best Nernstian Variations at pH values higher than 9 can be attributed to −1 response (with the slope of 591 ± 05 mV decade . This the formation of the free codeine base in the test solution can be related to the nature of the substrate which is while at the pH values lower than 5 the membrane may highly lipophilic; thus, a polar plasticizer causes the surrespond to H+ which is present in the solution. face to have a good wetting property and a more effective electrode–electrolyte interface. However, with the other 3.3. Response Time types of the electrode substrates, i.e., conventional memResponse time is one of the most important factors for anabrane and stainless steel wire coated electrodes, the DOP lytical applications of selective electrodes. The response shows to be the best plasticizer. The polar nature of the time depends on the dynamics of all processes involved internal solution in conventional membrane electrode and in the analyte-membrane interaction and it is defined as the stainless steel in the coated electrode eliminates the the time lapse between the moment of a sudden change in need for a highly polar plasticizer. Thus, DOP with a modanalyte concentration and the instant at which the response erate polarity is suitable since it facilitates the interaction 1344

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RESEARCH ARTICLE

Fig. 2.

Fig. 3. Titration curve of 5 mL of 10 × 10−3 mol L−1 of codeine solution with a 10 × 10−2 mol L−1 solution of Na-TPB as titrant.

Effect of pH on sensor response.

change reaches its steady-state value within 1 mV or has reached 90% of the final value.46 In order to evaluate the practical static response time of the electrode, the average time required to achieve a potential within ± 1 mV of the final steady-state potential was measured to be 15 s.

Table III. Potentiometric determination of codeine contents in codeine containing paracetamol tablets.

Procedure Standard addition Titration

Added value (mg)

Founded value (mg)

Recovery*

RSD*

0 10 2

86 189 20

– 103 100

4.9 6 0

3.4. Selectivity of the Electrode Note: ∗ Mean recovery and relative standard deviations of three determinations in %. One of the most important characteristics to evaluate the electrode performance is selectivity toward other species; Delivered by Publishing3.5. Technology ? Analyticalto:Application specially, those with similar structure and properties On: withSun, 08 Feb 2015 03:51:07 IP: 126.120.22.239 The practical applicability of the proposed electrodes was the analyte. Two solution method (TSM) has beenAmerican recom- Scientific Publishers Copyright: tested by using it as indicator electrode in titration of 5 mL mended by IUPAC to determine the selectivity of the elecof 1.0 × 10−3 mol L−1 of codeine solution with a 1.0 × trode. This method involves measuring potentials of a pure 10−2 mol L−1 solution of NaTPB as titrant. As shown in solution of the primary ion, EA , and a mixed solution conFigure 3, the break point is relatively sharp. The amount taining the primary and interfering ions, EA+B . The potenof codeine can be accurately obtained from the titration tiometric selectivity coefficient is calculated by inserting curve (Table III). the value of the potential difference, E = EA+B –EA , into the following equation:47 3.6. Real Sample Analysis In order to evaluate the applicability of the proposed selecpot KAB = aA eEzA F /RT − 1/aB zA /zB tive electrodes, the method was applied for determination of codeine phosphate in its pharmaceutical preparations. The resulting values presented in Table II, display selecThe standard additions method has been applied to detertivity of the electrode towards some amino acids and carmine the codeine phosphate content in tablets (Table III). bohydrates, and also urea. In all cases, the electrode shows The average recovery of 103% was obtained for codeine a relatively high selectivity for codeine. phosphate which shows the reliability of the results obtained by the proposed electrode. Table II.

Selectivity coefficient values for codeine selective electrode.

Interferent Urea Sucrose Dextrose Arginine Phenyl alanine Paracetamol Na+ Cl

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Selectivity coefficient 17 × 10−3 59 × 10−3 17 × 10−3 27 × 10−3 55 × 10−3 0 21 × 10−3 13 × 10−2

4. CONCLUSIONS The present study shows that the solid state electrode based on Co-TPB as an active electrode material in a PVC membrane plasticized with o-NPOE can be applied to the detection of codeine in the pharmaceutical tablets. The new substrates (strip shaped pencil lead) used for coating of the PVC membrane enables the fabrication of low cost, miniaturized, and disposable ion selective electrode which require low sample volumes. 1345

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Acknowledgments: The authors would like to thank Ferdowsi University of Mashhad for financial supports of this work under the Grant No. 18058 dated at 1390/03/24.

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