Potentiometric Flow Injection Analysis of Bromhexine Hydrochloride and its Pharmaceutical Preparation Using Conventional and Coated Wire Ion-Selective Electrodes

Bromhexine hydrochloride ion-selective electrodes (conventional type) based on bromhexinium tetraphenyl borate (I) and bromhexinium-phosphotungstate (II) were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 59.8 mV per decade of bromhexine concentration at 25 C for electrode (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16x10-1.00x10 M bromhexine within the pH range 2.0-4.5. The standard electrodes potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00065 and 0.00050 V C for (I) and (II), respectively. The electrodes showed a very good selectivity for bromhexine with respect to a number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of bromhexine hydrochloride and its pharmaceutical preparation under batch and flow injection conditions. Graphite, copper and silver coated wires were prepared, characterized and successfully applied as sensors for the drug under investigation.

In the presentw ork, plasticm embrane electrodes, selective for bromhexine hydrochloride are constructed, their performancec haracteristics studied and then used to determine the drug both in batch and with af low injection technique, which is considered av ery efficient way of improving the performancec haracteristics of ISEs.The electrodesa re based on the incorporation of bromhexinium tetraphenylborate(Brom-TPB) and bromhexinium phosphotungstate (Brom-PT)ionexchangers in poly (vinylc hloride) (PVC) membranes plasticizedw ith dibutylphthalate (DBP).The selectivity of the electrodes was also tested in batch and FIA techniques.Fine-graphite, copper and silver wiresc oated with as olution mixture of liquid ion-exchangers and poly (vinyl chloride) in THF were used as an ion-selectiveelectrodesfor bromhexinium cation.
Potentiometric measurements as well as thec onstruction of an FIA system and the methods used for recording the peaks as af unction of the potential were performedasmentioned in ourpreviouslystudies [17,18].
The Several membrane composition electrodes as well as graphite, copper, and silver wires (3 mm in diameter and 12 cm in length) were constructed and used as previously described [19].
Conductimetric measurements and determination of the solubility product of the Brom-TPB and Brom-PT ion-exchangers were carried out as in previously described method [20].The solubility (s) and the solubility product (Ksp) of the precipitates, Brom-TPB and Brom-PT were calculated using the following equations: s=Ksx1000/( Brom-TPB) and Ksp =s 2 s=Ksx1000/( Brom-PT) and Ksp =27s 4   where Ks is the specific conductivity of as aturated solution of the ion-associate, determined at 25 Ca nd corrected for the effect of the solvent and is the equivalent conductancea ti nfinite dilution and it is obtained from the ionic conductanceo ft he constituents ions using Kohlrausch's law of independent migration.

Effect of soaking
Freshlyp repared electrodesc an be useda fter presoakingi n1 0 -3 M bromhexine hydrochloride where the mean slopes are 59.Fort he coated wire electrodes, it was found that the plastic membrane coat must be reformed prior to every use by immersing the bared terminal of the electrode in the solution mixture containing the ion-exchanger for af ew seconds and left it to dry in air.For Brom-TPB coatedwires electrodes,the calibrationgraph slopes for the fresh graphite, copper and silver were 61.9, 58.7 and 60.0 mV/decade, respectively.After daily use of the graphite, copper and silver electrodes for 14, 7a nd 11 days the slopes decreasedt o4 8.6,4 2.4 and 44.8 mV/decade, respectively.While for Brom-PTc oated wires, the calibrationg raph slopes were 63.3,6 2.0a nd 60.7 mV/decadef or theg raphite, copper ands ilver coated electrodes,r espectively, anda fter dailyu se of theg raphite, copper and silver electrodes for16, 8and 16 days theslopesdecreased to 47.5,45.6and46.5 mV/decade, respectively.The usable concentration range of the electrodes was 1.77x10 -5 -1.00x10 -2 M. Also the wire electrodes do not need conditioning before each use.Fig. 1s hows representative calibrationg raphs for Brom-PT graphite coated electrode.

Effect of temperature of the test solution
To study the thermal stability of the electrodes, calibration graphs (cell potential, E cell sp Brom) were constructed at different test solution temperatures covering the range 25-65 C. The isothermal coefficients (dEº/dt) of the electrodes were calculated with the help of theseg raphs [21] and foundt ob e0 .00065and

Optimization of FIA response
The flow injection measurements were carried out in at wo-line configuration as shown in Fig. 2.T he dispersion coefficientr angedb etween 1.45 and 1.49, i.e., limited dispersion coefficients that aid optimum sensitivitya nd fast response of the electrodes [22].

Optimization of flow rate and sample volume.
Several flow rates( 4.15-27.00ml min -1 )w ere checked.Af low rate of 9.7 ml min -1 was adopted, providing about 99% of the maximum peak height obtained by higher flowrates, withashortertimetor each the baseline and lessconsumption of

Optimization of pH
The effect of the pH of the test solution on the electrodep otentialw as studied in batch and FIA measurements as previously described [17].It was found that the (I) and (II) electrodes do not respond to pH changes in the range 2.0-4.5 in both batch and FIA conditions.A tap Hl ess than 2.0, the drop in potential of both electrodes (I) and (II) may be due to penetrationofchloride ions into the membrane network at the interface between the test solution and the matrixo fm embrane.

Electrode response in FIA
The slopeo ft he calibration plotsi nF IA was high compared with batch measurements,w herep otentiali sm easured underc onditions very closet ot he equilibrium at the membrane-solution interface [23].The slopes of the calibration graphs were7 2.9a nd 68.6i nF IA compared to the batch 59.4a nd 59.8m Vp er concentration decadef or Brom-TPB and Brom-PT electrodes,r espectively.The usable concentrationranges of the electrodes in FIA are 5.62x10 -5 -1.00x10 -2 which is nearly thesameasinbatch mode.

Conclusion
The investigated electrodes were shown to be useful as potentiometric sensors for the determination of bromhexine hydrochloride and its pharmaceutical preparation, the proposed methods are characterized by high degree of precision and accuracy whenc ompared witht he official method (potentiometric titration), within wide concentration, temperatureand pH ranges as shown by F-and t-values.
Comparingt he results obtained from potentiometric determinationo ft he drug in conductivities were measured with the aid of an Engineered Systems & Designs [ESD] conductometer model 72 (Conductance/TDS) (USA) provided with conductivity cell of 1.000cell constant.
4 and 59.8 mV/decade of concentrationa t2 5 Cf or electrodes (I) and (II), respectively.In the present work, thes lopesr emaineds tableo ver1 0a nd 17 days andt hen, they sharplyd ecreased reaching 44.5 and 46.2 mV/decadeo fc oncentrationf or electrodes (I) and (II), respectively.T he electrodes respondedc orrectly within thec oncentration range 3.16x10 -5 -1.00x10 -2 Mand their response has not been affected by soaking.On the other hand, the electrode that has been kept dry in ac losed vessel and stored in a refrigerator showedn earlyc onstant slope value and the same response properties extendingtoabout 45 and30daysfor electrodes (I)and (II),respectively.
3 x10 -4 under batch and FIA conditions, respectively, for both electrodes,w hich reflect very high selectivities of the investigated electrodes for the bromhexinium cation.The selectivity mechanism is mainly based on the sterospecificity and electrostatic environment, and is dependent on how much fitting is present between the locations of the lipophilicity sites in the two competing species on the bathing solution side and those present in the receptor of Nour T. Abdel-Ghani et al.: cation,t he greateri st he response of them embrane.Thee lectrodese xhibit good tolerancet owards aminoa cids ands ugars, wherei tw as foundt hatt he Brom-TPB electrodec ould be safely used withouti nterferences in thep resenceo fg lucose, fructose,m altose,l actose,a scorbica cid, vitamine B 1 ,l eucine, alanine and glycine up to 320, 482, 233, 165, 210, 133, 96, 202 and 1166 folds of the investigated drug and 400, 385, 200, 145, 167, 154, 112, 198 and 960 folds in the case of the Brom- The valuesgiven inTable1, show that the present methods are of comparable Nour T. Abdel-Ghani et al.: precisiont oe acho ther andt here is no significantd ifferenceb etween them ean values obtained by thethree methods.
Potentiometric Flow Injection Analysis of Bromhexine Hydrochloride and its... batch( usings tandarda dditions method)a nd FIAc onditionsa nd thoseo btained from the conductimetric titrations with ther esults obtained from the official method, it is cleart hate itherB rom-TPBo rB rom-PT electrodei sr ecommended usingF IA conditions sincep otentiometrica nd conductimetric titrations aret imec onsuming (20m in in each run),i na dditiont he applicationo ft he electrodes in FIAs hortened thet imer equiredf or thed etermination of thed rugi ni ts pure stateo ri ni ts pharmaceutical preparation.Regardingc oatedw iree lectrodes, either Brom-TPB or Brom-PTgraphiteorsilvercoatedwireelectrodesisrecommended foruse because of its high life time compared to the copper coated electrode.