Technical paper
Volumetric and Spectrophotometric Determination of Oxcarbazepine in Tablets
Nagaraju Rajendraprasad, Kanakapura Basavaiah* and Kanakapura Basavaiah Vinay
Department of Chemistry, Manasagangothri, University of Mysore, Mysore-570 006, India
* Corresponding author: E-mail: basavaiahk@yahoo.co.in; Mobile: +91 9448939105
Received: 30-10-2010
Abstract
Two cerimetric procedures are described for the assay of oxcarbazepine (OXC) in bulk drug and in tablets. Titrimetry (method A) is based on the reaction of OXC by a measured excess cerium(IV) sulphate in sulphuric acid medium and the determination of the unreacted oxidant by titration with iron(II) solution using ferroin as indicator. Spectrophotometry (method B) is based on oxidation of OXC by cerium(IV) in perchloric acid (HClO4) medium and the determination of the unreacted oxidant using a colour reaction with _p-dimethylaminobenzaldehyde (p-DMAB) having an absorption maximum of 460 nm. The titrimetric method is applicable in the range of 2.0-20.0 mg OXC with a 1:2 reaction stoichiometry [OXC:Ce(IV)]. In the spectrophotometric method a rectilinear relationship is obtained over the concentration range of 0.3-6.0 |g mL-1 OXC. The linear regression equation of the calibration graph is A = 0.9820-0.1477 C with a regression coefficient (r) of -0.9967 (n = 6). The molar absorptivity is calculated to be 3.76 x 104 L mol-1 cm 1 and the Sandell sensitivity is 0.0067 |g cm 2. The limits of detection (LOD) and quantification (LOQ) values are calculated according to ICH guidelines. The methods are successfully applied to the determination of OXC in tablets.
Keywords: oxcarbazepine; assay; titrimetry; spectrophotometry; tablets
1. Introduction
Oxcarbazepine (OXC), (chemically known as 10,11-dihydro-10-oxo-5H-dibenzo[b,f]azepine-5-carbox-amide, (Figure 1) is an antiepileptic agent which belongs to the iminostilbene class and is effective against partial seizures and generalized tonic-clonic seizures1 as well as bipolar affective disorders.2
OXC is not official in any Pharmacopoeia. High performance liquid chromatography,3-6 high performance
O
Figure 1. Chemical structure of OXC
thin layer chromatography,7 gas chromatography,6 microemulsion electrokinetic chromatography,8 capillary electrokinetic chromatography,9 voltammetry,10,11 capillary electrophoresis12 and visible spectrophotometry13-15 were found in the literature for the assay of OXC in pharmaceuticals.
No titrimetric method is reported for OXC. However, few spectrophotometric methods are found. Gandhimathi and Ravi13 have reported two spectrophotometric methods for the determination of OXC. The first method involves addition of Folin-Ciocalteu's (F-C) reagent to OXC in alkaline medium, followed by measurement of absorbance at 760 nm, and the second method involves addition of a fixed volume of 3-methyl-2-ben-zothiazolinone hydrazine hydrochloride (MBTH) after treatment of OXC with iron(III) chloride and measurement of the absorbance at 456 nm. In another report,14 OXC has been determined using iron(III) chloride and potassium hexacyanoferrate(III). The method is based on reduction of iron(III) ions to iron(II) ions by the drug,
Table 1: Comparison of performance characteristics of the proposed spectrophotometric method with reported spectrophotometric methods.
Sl Reagent(s) No	Method	X (nm)	Linear range (^g mL-1) £/LOD/LOQ*	Remarks	Reference
1 a) F-C reagent b) MBTH-iron(III) chloride	Blue chromogen measured Orange coloured product measured	760 456	5-30 8.06 x 103/1.6/5.0 10-50 3.13 x 103/3/10	Narrow linear dynamic range, less sensitive, methanol used as solvent Narrow linear dynamic range, less sensitive	13
2 Iron(III) chloride-hexacyanoferrate(III)	Green chromogen measured	770	4-28 4.63x 103	Narrow linear dynamic range, less sensitive, heating required	14
3 CH3OH-KOH/DMSO	Yellow chromogen measured	430	1.0-7.02 1.21x 104/0.027/0.082	Methanol used, less sensitive	15
4 Cerium(IV)-p-DMAB/HClO4	Orange chromogen measured	460	0.3-6.0 3.76x 104/0.1/0.32	Wide linear dynamic range, Present highly sensitive, no use of work organic solvent, no heatingrequired	
* £ in L mol 1 cm 1; LOD and LOQ are in |g mL 1
which in the presence of hexacyanoferrate(III) produces green-coloured chromogen measured at 770 nm. The yellow chromogen with an absorption maximum at 430 nm formed by the reaction of OXC with methanolic KOH in DMSO medium as the basis for the assay of OXC has been reported by Sathish and Nagendrappa.15 All the reported methods have one or more disadvantages (Table 1) such as low sensitivity,1315 use of a toxic solvent (to dissolve OXC)13 or preparation of reagents15 and require heating on a boiling water bath.14
The present paper describes a titrimetric (method A) and a spectrophotometric (method B) procedure for the assay of OXC in the pure drug and in tablets using ceri-um(IV) as an oxidimetric reagent.
2. Experimental
2. 1. Apparatus
A Systronics model 106 digital spectrophotometer (Systronics Limited, Ahmedabad, India) with 1 cm path length and matched quartz cells was used to record the ab-sorbance values. An Acculab (Sartorious Group, Germany) electronic analytical balance was used for weighing.
2. 2. Reagents and Standards
All chemicals used were of analytical reagent grade. Distilled water was used throughout the investigation.
Acetic acid (7 mol L-1), sulphuric acid (H2SO4) (10 mol L1) and perchloric acid (HClO4) (4 mol L1) were prepared by diluting appropriate volumes of their concentrated acids (99% glacial acetic acid, 98% H2SO4, 70% HClO4 -all from Merck, Mumbai, India) with distilled water, and 10 mol L1 H2SO4 was diluted further to obtain 0.5 mol L1 and
used in the preparation of the cerium(IV) solution. Two brands of tablets, viz. Trioptal-300 (Novartis India Ltd, Mumbai, India) and Oxetol-600 (Sun Pharmaceuticals, Sikkim) were purchased from local commercial sources.
2. 2. 1. Cerium(IV) Sulphate Solution (0.025 mol L-1)
A 0.025 mol L1 solution was prepared by dissolving an accurately weighed quantity of ceric sulphate [Ce(SO4)2.4H2O; assay 99%-from Loba Chemie Ltd, Mumbai, India] in 0.5 mol L1 H2SO4 with the aid of heat. The solution was cooled to room temperature, and filtered using Whatman No. 42 filter paper. The solution was used for the assay in method A after standardization.21 This solution, equivalent to ~3504 ^g mL1 Ce4+, was diluted with 4 mol L1 HClO4 to get a working concentration of 300 mL1 Ce4+.
2. 2. 2. Ferrous Ammonium Sulphate [Fe(II)] Solution (0.025 mol L-1)
An accurately weighed amount of 9.804 g of [NH4]2[Fe][SO4]2 6H2O (Loba Chemie Ltd, Mumbai, India) was dissolved in 10 mL of 0.5 mol L1 H2SO4 in a 1000-mL volumetric flask and the solution was brought up to the mark with water.
2. 2. 3. p-Dimethylaminobenzaldehyde (p-DMAB) (0.5%)
An accurately weighed amount of 1.25 g of p-DMAB (Merck, Mumbai, India) was transferred to a 250mL volumetric flask, dissolved in 4 mol L1 HClO4 and the volume made up to the mark with the same solvent.
2. 2. 4. Stock OXC Solution
A stock standard solution containing 2 mg mL-1 OXC was prepared by dissolving 200 mg of pure OXC (Jubilant Life Sciences Ltd, Nanjangud, Mysore, India, purity 99.5%) in 40 mL of glacial acetic acid; the volume was brought to 100 mL with water in a volumetric flask and used for the assay in method A.
A 100 pg mL-1 OXC standard solution was also prepared by dissolving an accurately weighed amount of 10 mg of pure OXC with 4 mol L-1 HClO4 in a 100-mL calibrated flask. A working solution with a concentration of 10 pg mL-1 OXC was used in method B.
2. 3. General Procedure
2. 3. 1. Titrimetry (Method A)
A 1-10 mL aliquot of pure drug solution (2 mg mL-1) containing 2.0-20.0 mg of OXC was measured accurately and transferred to a 100-mL titration flask; the total volume was brought to 10 mL with 7 mol L-1 acetic acid. The solution was acidified by adding 5 mL of 10 mol L-1 H2SO4. Ten mL of 0.025 mol L-1 Ce(IV) standard solution was added by means of a micro burette and the content was mixed well. After 5 min, the unreacted Ce(IV) was back titrated with 0.025 mol L-1 Fe(II) solution using ferroin as an indicator. A blank titration was also performed in a similar fashion but in the absence of the drug.
The amount of the drug present in the measured aliquot was calculated by using the formula:
where V is the volume of Ce(IV) reacted, M is the molar concentration (mol L-1) of Ce(IV), Mw is the relative molecular mass of OXC and n is the number of moles of Ce(IV) reacting with each mole of OXC.
2. 3. 2. Spectrophotometry (Method B)
Different aliquots (0.3-6.0 mL) of 10 pg mL-1 OXC standard solution were transferred to 10-mL volumetric flasks using a microburette and the total volume in each flask was adjusted to 6 mL by adding 4 mol L-1 HClO4. To each flask, 1 mL of 300 pg mL-1 Ce4+ solution was added, and the content was mixed well and kept aside for 15 min at room temperature. Finally, 1 mL of 0.5% p-DMAB was added to each flask and the volume was made up to mark with 4 mol L-1 HClO4. After 15 min, the absorbance of the coloured product was measured at 460 nm against water.
A calibration graph was prepared by plotting ab-sorbance against concentration and the unknown concentration was read from the graph or computed from the regression equation.
2. 4. Procedure for the Analysis of Tablets
Method A
Twenty tablets were weighed and finely powdered. The tablet powder equivalent to 200 mg OXC was transferred to a 100-mL volumetric flask, and about 40 mL of glacial acetic acid was added. The content of the flask was shaken for 10 min, 30 mL of water was added, and shaking continued for 10 more min before the flask was filled to the mark with water. The content was mixed well and filtered through a Whatman No. 42 filter paper. The first 10-mL portion of the filtrate was discarded and a suitable aliquot (say 5 mL) was then subjected to analysis by following the procedure described earlier.
Method B
A quantity of tablet powder containing 10 mg of OXC was transferred into a 100-mL volumetric flask. The content was shaken well with about 70 mL of 4 mol L-1 HClO4 for 20 min. The mixture was diluted to the mark with the same solvent and filtered using Whatman No 42 filter paper. The first 10-mL portion of the filtrate was discarded and the resulting tablet extract (100 pg mL-1 in OXC) was diluted to 10 pg mL-1 with 4 mol L-1 HClO4. A suitable aliquot was then subjected to analysis by following the general procedure.
2. 5. Procedure for the Analysis of Placebo Blank and Synthetic Mixture
A placebo blank containing starch (10 mg), acacia (15 mg), hydroxyl cellulose (10 mg), sodium citrate (10 mg), talc (20 mg), magnesium stearate (15 mg) and sodium alginate (10 mg) was prepared by combining all components to form a homogeneous mixture. An amount of 5 mg of the placebo blank was accurately weighed and its solution was prepared as described under 'tablets', and then subjected to analysis by following the general procedure.
A synthetic mixture was prepared by adding an accurately weighed amount of 200 mg of OXC to the placebo mentioned above. The extraction procedure for tablets as described for method A and method B were applied separately by taking the required quantity of synthetic mixture to prepare 2 mg mL-1 and 10 pg mL-1 OXC solutions, respectively. Three different volumes of the resulting synthetic mixture solution (equivalent to 5, 10 and 15 mg OXC in method A; 2, 3 and 4 pg mL-1 in method B) were subjected to analysis by following the respective procedure.
3. Results and Discussions
The proposed methods are indirect and are based on the determination of unreacted cerium(IV) after the reaction between OXC and the oxidant is complete according to the following reactions:
OXC + Ce(IV)
(Known excess)-
Unreacted . Ce(IV)
Unreacted + £-DMAB Ce(IV) in HC104 medium
H"1
Oxidation product of OXC
+ Unreacted Ce(lV)
Titrated with standard FAS using ferroin indicator (method A)
Orange coloured product measured at 460 11m (method B)
The titrimetric method (method A) involves oxidation of OXC by a known excess of Ce(IV) sulphate in sulphuric acid medium and the unreacted oxidant was determined by back titrating with FAS. The reaction between OXC and Ce(IV) was found to occur in an 1:2 (drug:oxi-dant) stoichiometric ratio and all calculations are based on this fact. Using 0.025 mol L-1 Ce(IV), 2-20 mg of OXC was conveniently determined. In spectrophotometry (method B), the unreacted Ce4+ was treated with p-DMAB in HClO4 medium to yield formic acid and p-dimethy-laminophenol, which upon further oxidation gave the corresponding quinoimine derivative.22
4. Method Development
4. 1. Absorption Spectra (method B)
The addition of p-DMAB to Ce4+ resulted in the formation of orange coloured product (quinoimine derivative) that was measured at 460 nm. OXC and p-DMAB had no absorption at 460 nm. The decrease in the absorption intensity at 460 nm, caused by the presence of the drug, was directly proportional to the amount of drug reacted. Figure 2 illustrates the absorption spectra of the or-
Figure 2. Absorption spectra of coloured product formed by the reaction between Ce4+ and p-DMAB in the presence of increasing concentrations of OXC and in the absence of OXC.
ange coloured product formed by the reaction between Ce4+ and p-DMAB for various OXC concentrations.
4. 2. Optimization of Reaction Variables
Method A
OXC is not soluble in any of the acids other than acetic acid. To prepare OXC stock solution, different volume ratios of acetic acid and water were tried, and the drug was found to be completely soluble in 7 mol L-1 acetic acid and OXC was found to be stable for more than a day at room temperature. This approach was followed to prepare the OXC solution throughout the investigation.
In order to obtain the optimum conditions necessary for the quantitative determination of OXC, a fixed amount of the drug was titrated under varying experimental conditions. The reaction was found to be quantitative and stoi-chiometric in H2SO4 medium. A constant reaction stoi-chiometry of 1:2 [OXC:Ce(IV)] was obtained when 4.0-6.0 mL of 10 mol L-1 H2SO4 was used in a total volume of 25 mL. Hence, a 5 mL of 10 mol L-1 H2SO4 was used as the optimum for the reaction between OXC and Ce(IV), giving an overall acidity of 2 mol L-1 with respect to H2SO4, and for the latter's titration with iron(II). The reaction time was studied by titrating the unreacted Ce(IV) with iron(II) at different time intervals after addition of oxidant to the acidic solution of OXC. It was found that the reaction yielded a constant stoichiometry in the time range from 5 to 10 min, and at a reaction time less than 5 min and more than 10 min, there was no constant and definite reaction stoichiometry. Hence, it is necessary to terminate the reaction at the end of the fifth min by titrating residual Ce(IV) with iron(II).
Method B
Selection of Reaction Medium
Perchloric acid (4 mol L-1) medium was found necessary for rapid and quantitative reaction between OXC and Ce(IV), and to obtain maximum and constant ab-sorbance values of the Ce4+-p-DMAB reaction product at 460 nm. This may be attributed to the highest oxidation potential of Ce4+ in HClO4 (Eo = 1.75 V) as compared to that of Ce(IV) in H2SO4 (Eo = 1.44 V), HNO3 (Eo = 1.61 V) or HCl (Eo = 1.28 V)23. Therefore, all the solutions [OXC, Ce(IV) and p-DMAB] were prepared in 4 mol L-1
HClO4 throughout the investigation and the same was maintained as reaction medium.
Optimization of Ce4+
To fix the optimum concentration of Ce4+, different concentrations of oxidant were reacted with a fixed concentration of p-DMAB in HClO4 medium and the ab-sorbance measured at 460 nm. A constant and maximum absorbance resulted with 30 |g mL-1 Ce4+; hence, different concentrations of OXC were treated with 1 mL of 300 |g mL-1 Ce4+ in HClO4 medium before determining the residual Ce4+ by reacting with p-DMAB. This facilitated the optimization of the linear dynamic range over which the procedure could be applied for the assay of OXC.
Study of Reaction Time and Stability of the Coloured Species
Under the described experimental conditions, the reaction between OXC and Ce4+ was complete within 15 min (Figure 3) at room temperature (28 ± 2 °C). After the addition of p-DMAB, a reaction time of 15 min was necessary for the formation of the coloured product, and
thereafter, the absorbance of the coloured product (quinoimine derivative) was stable for more than one hour.
Effect of Diluent
In order to select the proper diluent different solvent were tried. The highest absorbance values were obtained when 4 mol L-1 HClO, was used as diluent. Substitution
of 4 mol L-1 HClO and 6 mol L-1
4 with other solvent (methanol, water HClO4) resulted in a decrease in the ab-sorbance values.
Figure 3. Effect of time on the reaction between Ce4+ and OXC (5.0 |g mL-1)
4. 3. Method Validation
4. 3. 1. Linearity and Sensitivity
Over the range investigated (2-20 mg), a fixed stoi-chiometry of 1:2 [OXC : Ce(IV)] was obtained in titrime-try which served as the basis for calculations. A rectilinear calibration graph was obtained for the range 0.3-6.0 l g mL-1 OXC; the measured absorbance values were plotted versus concentration. The least square calibration equation was A = 0.9820-0.1477 C (where the concentration C is measured in |g mL-1) with a regression coefficient of -0.9967 (n = 6). The calculated molar absorptivity and Sandell sensitivity values are 3.76 x 104 L mol-1 cm-1 and 0.0067 |g cm-2, respectively. The limits of detection (LOD) and quantification (LOQ) were calculated according to the ICH guidelines24 using the formulae: LOD = 3.3 S/slope and LOQ = 10 S/slope, where S is the standard deviation of the absorbance of six blank readings. The calculated LOD and LOQ are 0.10 and 0.32 |g mL-1, respectively.
4. 3. 2. Accuracy and Precision
The repeatability of the proposed methods was determined by performing replicate determinations. The in-tra-day and inter-day variations in the analysis of OXC were measured at three different levels by calculating percentage relative standard deviations (%RSD). Accuracy was evaluated as the bias (percentage relative error between the measured and reference value). The results of this study are compiled in Table 2 and show an excellent
Table 2: Intra-day and inter-day accuracy and precision.
Method*	OXC,	Intra-day accuracy and precision			Inter-day accuracy and precision		
	Reference	OXC found	RE %	RSD %	OXC found	RE %	RSD %
A	6.0	5.90	1.67	1.56	5.92	1.33	2.11
	12.0	11.85	1.25	1.11	11.80	1.67	1.89
	18.0	17.50	2.78	1.85	17.42	3.22	1.56
B	2.0	2.04	2.00	3.10	2.05	2.50	3.26
	4.0	4.04	1.00	1.13	4.08	2.00	1.56
	6.0	5.83	2.83	0.50	5.90	1.67	2.13
* In method A, OXC reference/found values are in mg and they are |g mL 1 in method B
intermediate precision (%RSD < 3.26) and accuracy (%RE < 3.22).
4. 3. 3. Selectivity
In the analysis of the placebo blank there was no measurable consumption of Ce(IV) (method A) and the same absorbance value as obtained for the reagent blank was recorded in method B, suggesting that the inactive ingredients added to prepare the placebo are interference-free.
In method A, 5 mL of the resulting solution prepared using the synthetic mixture was assayed titrimetrically (n = 3) yielded a recovery of 102.3 ± 0.62% OXC. In method B, a 3 mL aliquot of 10 ^g mL1 OXC subjected to analysis (n = 5) yielded a recovery of 101.7 ± 0.86% OXC. These results complement the findings of the placebo blank analysis with respect to selectivity.
4. 3. 4. Robustness and Ruggedness
To evaluate the robustness of the methods, reaction time and H2SO4 concentrations were slightly altered with reference to optimum values in titrimetry. However, in spectrophotometry, the reaction time and volume of p-DMAB were altered. To check the ruggedness, analysis was performed by four different analysts and using three different burettes (method A) or cuvettes (method B) by
the same analyst. The robustness and the ruggedness were checked at three different drug levels. The intermediate precision, expressed as percent RSD, is a measure of the robustness and ruggedness and was within acceptable limits (0.72-3.74%, Table 3).
4. 3. 5. Application to Tablet Analysis
Commercial OXC tablets were analyzed by the developed methods and also by a reference published method.13 The published method involves addition of Folin-Ciocalteu's (F-C) reagent to OXC in alkaline medium, followed by measurement of the absorbance at 760 nm. The results obtained were compared statistically by the Student's t-test and the variance-ratio F-test.25 The calculated t- and F- values did not exceed the tabulated values [2.77 (t) and 6.39 (F) at the 95 % confidence level and for four degrees of freedom], indicating a close similarity between the proposed methods and the reference method with respect to accuracy and precision (see Table 4 for a summary).
4. 3. 6. Recovery Study
To further ascertain the accuracy and reliability of the methods, recovery experiments were performed via the method of standard additions. Pre-analyzed tablet powder was spiked with pure OXC at three different levels
Table 3: Robustness and ruggedness.
		Method A					Method B		
	Robustness		Ruggedness			Robustness		Ruggedness	
	(RSD %)		(RSD %)			(RSD %)		(RSD %)	
OXC	Conditions altered*				OXC	Conditions altered*			
studied	Volume	Reaction	Inter-	Inter-	studied	Volume of	Reaction	Inter-	Inter-
mg	of H2SO4	time	analysts	burettes	^g mL1	p-DMAB	time	analysts	instruments
	(n =2 3)	(n=3)	(n = 4)	(n = 4)		(n = 3)	(n = 3)	(n = 4)	(n = 3)
6.0	1.56	2.26	1.65	2.01	2.0	1.58	2.67	1.56	3.74
12.0	1.38	1.84	0.72	1.85	4.0	2.11	1.54	2.38	1.94
18.0	1.74	1.47	1.41	1.56	6.0	1.99	3.14	1.85	2.48
* In method A, volumes of 10 mol L 1 H2SO4 varied were 5 ± 1 mL, and reaction times were 5 ± 0.5 min, In method B, volumes of p-DMAB varied were 1 ± 0.1 mL, and reaction times employed were 15 ± 1 min.
Table 4: Results of analysis of tablets by the proposed methods.
Tablets analysed	Label claim, mg/tablet	Found* (Percent label claim ±SD) Reference method Method A		Method B
Trioptal 300	300	100.3 ± 1.22	98.5 ± 0.89 t = 2.69 F = 1.88	99.6 ± 1.28 t = 0.88 F = 1.10
Oxetol 600	600	99.58 ± 0.85	100.6 ± 1.10 t = 1.65 F = 1.67	101.2±1.56 t = 2.12 F = 3.37
* Mean value of five determinations.
Table 5: Accuracy assessment by recovery experiments.
		Method A				Method B	
Tablets OXC in	Pure OXC	Total	Pure OXC	OXC in	Pure OXC	Total	Pure OXC
studied tablet,	added,	found,	recovered*,	tablet,	added,	found,	recovered*,
mg	mg	mg	Percent ± SD	lg mL1	lg mL1	l^g mL1	Percent ± SD
Oxetol 600 8.05	4.0	12.13	102.0 ± 1.44	2.02	1.0	3.07	105.0 ± 1.56
8.05	8.0	16.15	101.3 ± 0.89	2.02	2.0	4.10	104.0 ± 2.12
8.05	12.0	19.74	97.42 ± 0.97	2.02	3.0	5.07	101.6 ± 1.48
* Mean value of three measurements
and the total was found by the proposed methods. Each determination was repeated three times. The percent recovery of pure OXC added (Table 5) was within the permissible limits indicating the absence of inactive ingredients in the assay.
5. Conclusion
A titrimetric and a spectrophotometry method was developed and validated for the determination of oxcar-bazepine using cerium(IV) sulphate as the oxidimetric reagent. The methods have been demonstrated to be simple, rapid, economical and accurate and precise; they were successfully applied to the determination of OXC in tablets. Especially titrimetry is a simpler and faster technique for determination of oxcarbazepine than all other methods reported so far. It is applicable over a wide range (2-20 mg), requires inexpensive chemicals, and yet provides very accurate and precise results. The proposed spectrophotometric method has the advantages of high sensitivity, which permits the determination of a concentration of oxcarbazepine even down to 0.32 ^g mL-1 with fair accuracy and precision. Compared to many existing instrumental methods for oxcarbazepine, the proposed spectrophotometric method has two additional advantages, viz. simplicity of operation and the use of generic laboratory instruments. Since the method requires easily available reagents [Ce(IV) and p-DMAB], it is certainly the most cost-effective of all the existing spectrophoto-metric methods.
6. Acknowledgements
The authors thank Jubilant Life Sciences Ltd., Nanjangud, Mysore, India, for gifting pure oxcarbazepi-ne. The authors are grateful to the authorities of the University of Mysore, Mysore, for permission and facilities. One of the authors (N.R.P) thanks the University Grants Commission, New Delhi, India, for awarding a Meritorious Research Scholarship.
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Povzetek
Opisana sta cerimetrična postopka za določevanje okskarbazepina (OXC) v farmacevtskih preparatih. Titrimetrična metoda (metoda A) temelji na reakciji OXC s presežkom cerijevega (IV) sulfata v žveplenokislem mediju in določitvijo nezreagiranega oksidanta s titracijo z raztopino Fe(II) z uporabo feroina kot indikatorja. Spektrofotometrična določitev (metoda B) temelji na oksidaciji OXC s Ce(IV) v perkloratnem (HClO4) mediju in določitvijo nezreagiranega oksidanta z barvno reakcijo s p-dimetilaminobenzaldehidom (p-MAB) pri 460 nm. Titrimetrična metoda je primerna za območje od 2,0-20,0 mg OXC. Območje linearnosti je pri spektrofotometrični metodi med 0,3 in 6,0 |g mL-1 OXC s korelacijskim koeficientom (r) 0,9967 (n = 6). Po IHC metodologiji sta bili izračunani meji zaznave in kvantifikacije. Metoda je bila uspešno uporabljena za določevanje OFX v tabletah.