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Flow injection spectrophotometric determination of tenoxicam
Analytica Chimica Acta 375 (1998) 277±283
Flow injection spectrophotometric determination of tenoxicam S.A. Al-Tamrah* Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh-11451, Saudi Arabia Received 25 November 1997; received in revised form 29 May 1998; accepted 14 June 1998
Abstract A new spectrophotometric ¯ow injection method has been established for the determination of tenoxicam [4-hydroxy2,methyl-N-2-pyridyl-2H-thieno(2,3-e)-1,2-thiazine-3-carboxamide-1,1-dioxide]. The method is based on the reaction of tenoxicam with iron(III) nitrate. The produced iron(II) reacts with potassium hexacyanoferrate(III) forming Prussian blue measurable at 724 nm. Maximum colour formation was obtained through heating. The blue complex that gradually adhered to the ¯ow lines and the ¯ow cell walls was removed by employing an alkaline oxalate solution. Linearity was in the range 0.5± 100 mg mlÿ1 tenoxicam with a limit of detection (signal:noise3) of 0.4 mg mlÿ1. The method was successfully applied to the determination of tenoxicam in pharmaceutical preparations. The correlation coef®cient was 0.99943 (n8) with a relative standard deviation of 1.04%, for ®ve determinations of 5 mg mlÿ1 drug. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Spectrophotometric; Tenoxicam; Hexacyanoferrate
1. Introduction Tenoxicam [4-hydroxy-2,methyl-N-2-pyridyl-2Hthieno(2,3-e)-1,2-thiazine-3-carboxamide-1,1-dioxide], is a new non-steroidal drug which has antiin¯ammatory, analgetic and antipyretic effects. The drug is widely used in the treatment of rheumatic diseases [1,2]. It is a derivative of oxicam with a thiophene ring replacing the benzene ring in piroxicam. Tenoxicam inhibits cyclooxygenase which catalyses the formation of cyclic endoperoxides [3,4]. Liquid chromatography (LC) is predominantly used for the determination of the drug in biological ¯uids. Dixon et al. [5] reported an LC method for the determination of tenoxicam in plasma. The limit of *Fax: +966-467-4253. 0003-2670/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0003-2670(98)00410-3
detection was 0.1 mg mlÿ1 tenoxicam. LC has also been used for the determination of tenoxicam in urine samples [6]. A very recent LC method was applied to estimate the drug in plasma using piroxicam as an internal marker. The calibration graph was linear from 5±2000 ng mlÿ1 [7]. The electrochemical behaviour of tenoxicam has been investigated by adsorptive stripping voltammetry and square-wave voltammetry [8]. The method was applied for the quanti®cation of the drug in aqueous solution and urine samples. The polarographic behaviour and the optimum conditions for the determination of tenoxicam are based on the reduction of the enol group of the molecule at a dropping mercury electrode [9]. The method was applied to the determination of the drug in pharmaceutical preparations. The utility of electroanalytical methods has recently been reviewed [10].
278
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
Apart from the direct UV spectrophotometric detection at 371 nm [4], only one spectrophotometric method is available for the analysis of tenoxicam. The method is based on the reaction of tenoxicam with copper(II) sulphate in ammoniacal solution. The absorbance was measured at 370 nm. Beer's law was valid from 1±10 mg mlÿ1 and the method was applied to the determination of tenoxicam in tablets [11]. The lack of spectrophotometric methods encouraged this work to establish a new spectrophotometric ¯ow-injection method based on the reduction properties of the drug. 2. Experimental 2.1. Apparatus An LKB 4050 UV±VIS Ultraspect II spectrophotometer was used equipped with an LKB 80 ml ¯ow cell attached to a chart recorder (Chessell, Type BD 40). A Perkin Elmer Lambda 2S was used for the max determination. 2.2. Manifold The ¯ow manifold is shown in Fig. 1. A four channel peristaltic pump (Gilson Minipuls 3 MP4) was used to deliver the solutions. The sample was injected into the nitric acid stream through a PTFE rotary valve (Rheodyne RH 5020). Solutions were propelled by the Gilson pump with individual ¯owrates of 1.5 ml minÿ1. A GFL type 1D23 water bath was used to attain complete reaction. The absorbance was measured at 724 nm, with a 1 cm path length.
2.3. Reagents Tenoxicam was supplied by Hoffmann La Roche. A 1000 mg mlÿ1 solution was prepared by dissolving 0.10 g of tenoxicam in 100 ml of 510ÿ3 M sodium hydroxide. Working solutions were prepared in distilled water. Nitric acid (Riedel de Haen) stock solution (0.5 M) was prepared by transferring 31.5 ml of conc. HNO3 into a 100 ml volumetric ¯ask and completing to volume with distilled water. Iron(III) nitrate (BDH AnalaR), 0.1 M solution, was prepared by dissolving 4.04 g of Fe(NO3)3.9H2O in 100 ml of 0.01 M nitric acid; working solutions were also diluted with 0.01 M nitric acid. Potassium hexacyanoferrate(III) (BDH), 0.1 M stock solution, was prepared by dissolving 3.29 g of K3Fe(CN)6 in 100 ml of distilled water. Oxalic acid (Merck) in alkaline solution, 5% (w/v), was prepared by dissolving 5 g of C2H2O4 in 100 ml of 0.1 M sodium hydroxide. Working solutions were likewise diluted with 0.1 M sodium hydroxide. 3. General procedure Tenoxicam sample (250 ml) is injected into a stream of 110ÿ2 M nitric acid and allowed to react with a stream of 110ÿ2 M iron(III) nitrate at a PTFE Tpiece. The reaction is done by passing the solution through a 150 cm reaction coil submerged in a water bath at 508C. The produced iron(II) is reacted with a stream of 110ÿ2 M potassium hexacyanoferrate(III) in the second coil (200 cm). The absorbance of the resulting blue solution is measured at 724 nm. All streams are pumped at an individual ¯ow-rate of
Fig. 1. Flow system: Ppump; IVinjection valve; SXSample; RCreaction coil; Ddetector; Rrecorder; Wwaste.
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
1.5 ml minÿ1. PTFE tubing of 0.8 mm i.d. is used throughout. 4. Calibration data Under the optimized conditions, a linear calibration graph was obtained over the range 0.5±100 mg mlÿ1 tenoxicam. The limit of detection (signal-to-noise ratio3) is 0.4 mg mlÿ1. The correlation coef®cient was 0.99943 based on the equation Amcb, where m0.0169; b0.0284; Aabsorbance and cconcentration in mg mlÿ1; n8.The relative standard deviation was 1.04% for 5 mg mlÿ1 tenoxicam based on 10 replicate determinations. 5. Results and discussion Tenoxicam reacts with iron(III) in the presence of potassium hexa-cyanoferrate(III) to form a blue compound (Prussian blue) measurable at 724 nm Fig. 2.
279
The absorbance is directly related to the concentration of tenoxicam and can be used for its spectrophotometric determination. The development of the colour depends very much on the reaction conditions. Therefore, it is very important to optimize the reaction conditions. Oxidation of the drug was found to take place in acidic media. Various acids including acetic, sulphuric, perchloric, nitric, hydrochloric and phosphoric acids were tested. Nitric acid was found to give the highest sensitivity by enhancing the absorbance. In this regard different concentrations of nitric acid were investigated. 110ÿ2 M was found to be adequate, as shown in Table 1. Higher acid concentrations increase the blank readings. 5.1. Effect of iron(III) nitrate Iron(III) is reduced to iron(II) by tenoxicam, which reacts with K3Fe(CN)6 to form a blue colour. The effect of different concentrations of iron(III) nitrate was investigated. A concentration of 110ÿ2 M gave the highest absorbance and thus was chosen for further use. Results obtained are summarized in Table 2. 5.2. Effect of potassium hexacyanoferrate(III)
F i g . 2 . S p e c t r a o f d i ff e r e n t r e a c t i n g s o l u t i o n s : ( 1 ) Fe( NO 3 ) 3 tenoxicam; (2) K 3 Fe(CN) 6 tenoxica m (3) Fe(NO3)3K3Fe(CN)6; (4) Fe(NO3)3K3Fe(CN)6tenoxicam.
The effect of potassium hexacyanoferrate(III) concentration was similarly studied 110ÿ2 M gave the best results. Higher concentrations gave high blank readings because of the adherence of the insoluble blue compound to the walls of the tubes.The results obtained are shown in Table 3. The blue compound gradually accumulated on the walls of the ¯ow-lines and the ¯ow cell, thus increasing the baseline readings. It should therefore be removed; 0.5% (w/v) alkaline oxalic acid solution was found to be suitable for this purpose by dissolving the blue product. Temperature greatly enhances the reaction. Different temperatures were tested, from 25±808C, using the water bath. It must be noted that boiling the solutions was omitted to avoid possible disintegration of the product. 508C gave the best results as shown in Fig. 3. Temperatures higher than 508C gave noticeable noisy baseline readings. Flow-rate is an essential parameter and can be controlled by the peristaltic pump. The effect of total
280
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
Table 1 Effect of nitric acid concentration on the reaction of 10 mg mlÿ1 tenoxicam using 0.01 M Fe(NO3)3; 0.01 M K3Fe(CN)6; temp. 508C and flowrate 6 ml minÿ1 HNO3 concentration (M)
110ÿ3
510ÿ3
110ÿ2
510ÿ2
0.1
0.5
Absorbance
0.203
0.203
0.222
0.199
0.195
0.168
Table 2 Effect of iron(III) nitrate concentration on the reaction of 10 mg mlÿ1 tenoxicam under the same conditions as in Table 1 Iron(III) nitrate concentration (M)
110ÿ4
510ÿ4
110ÿ3
510ÿ3
110ÿ2
510ÿ2
0.1
Absorbance
0.016
0.048
0.062
0.191
0.244
0.216
0.211
Table 3 Effect of K3Fe(CN6) concentration on the reaction of 10 mg mlÿ1 tenoxicam using the same condition as in Table 1 K3Fe(CN)6 concentration (M)
110ÿ3
510ÿ3
110ÿ2
510ÿ2
0.1
Absorbance
0.038
0.184
0.211
0.214
0.181
¯ow-rate was studied keeping other conditions constant, over the range 3.2±10.4 ml minÿ1, with equal ¯ow in each channel. No signi®cant effect was observed on the absorbance. A 6.0 mg mlÿ1 ¯ow-rate was adapted for tenoxicam determination because it allows enough time for the reaction to complete with reasonable sample throughput rate. The effect of sample volume was investigated by injecting different volumes using different lengths of
the sample loop. It was found that the absorbance increases while increasing the sample volume. 250 ml gave the highest absorbance, as shown in Fig. 4. Coil length is also another important parameter for the reaction to be complete. Two coils have been used in the manifold as shown in Fig. 1. The ®rst coil (RC1) is for the reduction of iron(III) to iron(II) by tenoxicam and the second coil (RC2) is for the reaction of the resulting iron(II) with hexacyanoferrate(III) to form
Fig. 3. Effect of temperature on 5 mg mlÿ1 tenoxicam response: HNO30.01 M; Fe(NO3)30.01 M; Fe(CN)]60.01 M.
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
281
Fig. 4. Effect of sample volume on 5 mg mlÿ1 tenoxicam response; (HNO30.01 M; Fe(NO3)30.01 M; Fe(CN)6-40.01 M.
the blue compound. Both coils were submerged in a 508C water bath. Different coil lengths were investigated. A remarkable increase in the absorbance was obtained when 150 cm and 200 cm lengths were used for the ®rst and second coil respectively, as shown in Fig. 5. The calibration plot obtained under the optimised condition is shown in Fig. 6. 5.3. Interferences The effects of some common excipients usually present in pharmaceutical preparations and some
amino acids which are normally found in biological samples were investigated. Up to 100 mg mlÿ1 of arabinose, fructose, glucose, sucrose, alanine, histidine, methionine, carbowax, nicotinamide, ribo¯avin, starch, and glucosamine gave no signi®cant interfering effect on the absorbance of 5 mg mlÿ1 tenoxicam. 6. Pharmaceutical applications The method was applied to the determination of tenoxicam in Tilcotil tablets (20 mg, Roche, Switzerland). Sample preparation was done by individually
Fig. 5. Effect of length of reaction coils on 5 mg mlÿ1 tenoxicam response: (HNO30.01 M; Fe(NO3)30.01 M; Fe(CN)60.01 M.
282
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
Fig. 6. Typical calibration group for peak absorbance concentrations of tenoxicam.
weighing three tablets. The tablets were crushed and pulverized and a representative weight equivalent to 20 mg of drug as labelled was taken and then dissolved in 510ÿ3 M sodium hydroxide. The sample was ®ltered to achieve a clear solution. Working solutions were prepared from the original ®ltrate by diluting with distilled water. Very good results with excellent recovery (100.6%) were obtained for three samples of tenoxicam based on three determinations of each sample. The results are summarized in Table 4.
Table 4 Determination of tenoxicam in Tilcotil tablets using the new procedure Tenoxicam sample (Tilcotil Tablet)
Sample (1) Sample (2) Sample (3) a
Amount of tenoxicam (mg) Claimed
Founda
20 20 20
20.12a 20.11 20.10
Each result is the average of three determinations.
Recovery (%)
100.6 100.6 100.5
7. Conclusions The new method provides a rapid, simple and sensitive means of determining tenoxicam in pharmaceutical preparations. It has the advantage of being accurate and does not require the removal of excipients. The manipulation and intervention of the operator is minimal. Acknowledgements The author thanks Mr. E.A. Basco for his excellent technical assistance. References [1] J.F. Gonzales, P.A. Todd, Drugs 34 (1987) 298. [2] The Merck Index, 11th ed., Merck, Rahway, NJ, USA, 1989, p. 1441. [3] T.F. Woolf, L.L. Radulovic, Drug Metab. Rev. 21(2) (1989) 255. [4] P. Heizmann, J. Korner, K. Kinapold, J. Chromatogr. Biomed. App. 374 (1986) 95.
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283 [5] J.S. Dixon, J.R. Lowe, D.B. Galloway, J. Chromatogr. 310 (1984) 455. [6] D. Dell, R. Joly, W. Meiester, W. Arnold, C. Patros, B. Guldimann, J. Chromatogr. 317 (1984) 483. [7] M.I. Munera-Jaramillo, S. Boter-Garces, J. Chromatogr. 616 (1993) 349.
283
[8] N. Abo El-Maali, J.C. Vire, G.J. Patriarche, M.A. Ghandour, G.D. Christian, Anal. Sci. 6 (1990) 245. [9] Z. Atkopur, M. Tuncell, Anal. Lett. 29 (1996) 2383. [10] A.I. Al-Amoud, M.Sc. Dissertation, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia, 1995. [11] G. Yener, Y. Topaloglu, Sci. Pharmacy 60 (1992) 247.
Flow injection spectrophotometric determination of tenoxicam S.A. Al-Tamrah* Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh-11451, Saudi Arabia Received 25 November 1997; received in revised form 29 May 1998; accepted 14 June 1998
Abstract A new spectrophotometric ¯ow injection method has been established for the determination of tenoxicam [4-hydroxy2,methyl-N-2-pyridyl-2H-thieno(2,3-e)-1,2-thiazine-3-carboxamide-1,1-dioxide]. The method is based on the reaction of tenoxicam with iron(III) nitrate. The produced iron(II) reacts with potassium hexacyanoferrate(III) forming Prussian blue measurable at 724 nm. Maximum colour formation was obtained through heating. The blue complex that gradually adhered to the ¯ow lines and the ¯ow cell walls was removed by employing an alkaline oxalate solution. Linearity was in the range 0.5± 100 mg mlÿ1 tenoxicam with a limit of detection (signal:noise3) of 0.4 mg mlÿ1. The method was successfully applied to the determination of tenoxicam in pharmaceutical preparations. The correlation coef®cient was 0.99943 (n8) with a relative standard deviation of 1.04%, for ®ve determinations of 5 mg mlÿ1 drug. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Spectrophotometric; Tenoxicam; Hexacyanoferrate
1. Introduction Tenoxicam [4-hydroxy-2,methyl-N-2-pyridyl-2Hthieno(2,3-e)-1,2-thiazine-3-carboxamide-1,1-dioxide], is a new non-steroidal drug which has antiin¯ammatory, analgetic and antipyretic effects. The drug is widely used in the treatment of rheumatic diseases [1,2]. It is a derivative of oxicam with a thiophene ring replacing the benzene ring in piroxicam. Tenoxicam inhibits cyclooxygenase which catalyses the formation of cyclic endoperoxides [3,4]. Liquid chromatography (LC) is predominantly used for the determination of the drug in biological ¯uids. Dixon et al. [5] reported an LC method for the determination of tenoxicam in plasma. The limit of *Fax: +966-467-4253. 0003-2670/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0003-2670(98)00410-3
detection was 0.1 mg mlÿ1 tenoxicam. LC has also been used for the determination of tenoxicam in urine samples [6]. A very recent LC method was applied to estimate the drug in plasma using piroxicam as an internal marker. The calibration graph was linear from 5±2000 ng mlÿ1 [7]. The electrochemical behaviour of tenoxicam has been investigated by adsorptive stripping voltammetry and square-wave voltammetry [8]. The method was applied for the quanti®cation of the drug in aqueous solution and urine samples. The polarographic behaviour and the optimum conditions for the determination of tenoxicam are based on the reduction of the enol group of the molecule at a dropping mercury electrode [9]. The method was applied to the determination of the drug in pharmaceutical preparations. The utility of electroanalytical methods has recently been reviewed [10].
278
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
Apart from the direct UV spectrophotometric detection at 371 nm [4], only one spectrophotometric method is available for the analysis of tenoxicam. The method is based on the reaction of tenoxicam with copper(II) sulphate in ammoniacal solution. The absorbance was measured at 370 nm. Beer's law was valid from 1±10 mg mlÿ1 and the method was applied to the determination of tenoxicam in tablets [11]. The lack of spectrophotometric methods encouraged this work to establish a new spectrophotometric ¯ow-injection method based on the reduction properties of the drug. 2. Experimental 2.1. Apparatus An LKB 4050 UV±VIS Ultraspect II spectrophotometer was used equipped with an LKB 80 ml ¯ow cell attached to a chart recorder (Chessell, Type BD 40). A Perkin Elmer Lambda 2S was used for the max determination. 2.2. Manifold The ¯ow manifold is shown in Fig. 1. A four channel peristaltic pump (Gilson Minipuls 3 MP4) was used to deliver the solutions. The sample was injected into the nitric acid stream through a PTFE rotary valve (Rheodyne RH 5020). Solutions were propelled by the Gilson pump with individual ¯owrates of 1.5 ml minÿ1. A GFL type 1D23 water bath was used to attain complete reaction. The absorbance was measured at 724 nm, with a 1 cm path length.
2.3. Reagents Tenoxicam was supplied by Hoffmann La Roche. A 1000 mg mlÿ1 solution was prepared by dissolving 0.10 g of tenoxicam in 100 ml of 510ÿ3 M sodium hydroxide. Working solutions were prepared in distilled water. Nitric acid (Riedel de Haen) stock solution (0.5 M) was prepared by transferring 31.5 ml of conc. HNO3 into a 100 ml volumetric ¯ask and completing to volume with distilled water. Iron(III) nitrate (BDH AnalaR), 0.1 M solution, was prepared by dissolving 4.04 g of Fe(NO3)3.9H2O in 100 ml of 0.01 M nitric acid; working solutions were also diluted with 0.01 M nitric acid. Potassium hexacyanoferrate(III) (BDH), 0.1 M stock solution, was prepared by dissolving 3.29 g of K3Fe(CN)6 in 100 ml of distilled water. Oxalic acid (Merck) in alkaline solution, 5% (w/v), was prepared by dissolving 5 g of C2H2O4 in 100 ml of 0.1 M sodium hydroxide. Working solutions were likewise diluted with 0.1 M sodium hydroxide. 3. General procedure Tenoxicam sample (250 ml) is injected into a stream of 110ÿ2 M nitric acid and allowed to react with a stream of 110ÿ2 M iron(III) nitrate at a PTFE Tpiece. The reaction is done by passing the solution through a 150 cm reaction coil submerged in a water bath at 508C. The produced iron(II) is reacted with a stream of 110ÿ2 M potassium hexacyanoferrate(III) in the second coil (200 cm). The absorbance of the resulting blue solution is measured at 724 nm. All streams are pumped at an individual ¯ow-rate of
Fig. 1. Flow system: Ppump; IVinjection valve; SXSample; RCreaction coil; Ddetector; Rrecorder; Wwaste.
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
1.5 ml minÿ1. PTFE tubing of 0.8 mm i.d. is used throughout. 4. Calibration data Under the optimized conditions, a linear calibration graph was obtained over the range 0.5±100 mg mlÿ1 tenoxicam. The limit of detection (signal-to-noise ratio3) is 0.4 mg mlÿ1. The correlation coef®cient was 0.99943 based on the equation Amcb, where m0.0169; b0.0284; Aabsorbance and cconcentration in mg mlÿ1; n8.The relative standard deviation was 1.04% for 5 mg mlÿ1 tenoxicam based on 10 replicate determinations. 5. Results and discussion Tenoxicam reacts with iron(III) in the presence of potassium hexa-cyanoferrate(III) to form a blue compound (Prussian blue) measurable at 724 nm Fig. 2.
279
The absorbance is directly related to the concentration of tenoxicam and can be used for its spectrophotometric determination. The development of the colour depends very much on the reaction conditions. Therefore, it is very important to optimize the reaction conditions. Oxidation of the drug was found to take place in acidic media. Various acids including acetic, sulphuric, perchloric, nitric, hydrochloric and phosphoric acids were tested. Nitric acid was found to give the highest sensitivity by enhancing the absorbance. In this regard different concentrations of nitric acid were investigated. 110ÿ2 M was found to be adequate, as shown in Table 1. Higher acid concentrations increase the blank readings. 5.1. Effect of iron(III) nitrate Iron(III) is reduced to iron(II) by tenoxicam, which reacts with K3Fe(CN)6 to form a blue colour. The effect of different concentrations of iron(III) nitrate was investigated. A concentration of 110ÿ2 M gave the highest absorbance and thus was chosen for further use. Results obtained are summarized in Table 2. 5.2. Effect of potassium hexacyanoferrate(III)
F i g . 2 . S p e c t r a o f d i ff e r e n t r e a c t i n g s o l u t i o n s : ( 1 ) Fe( NO 3 ) 3 tenoxicam; (2) K 3 Fe(CN) 6 tenoxica m (3) Fe(NO3)3K3Fe(CN)6; (4) Fe(NO3)3K3Fe(CN)6tenoxicam.
The effect of potassium hexacyanoferrate(III) concentration was similarly studied 110ÿ2 M gave the best results. Higher concentrations gave high blank readings because of the adherence of the insoluble blue compound to the walls of the tubes.The results obtained are shown in Table 3. The blue compound gradually accumulated on the walls of the ¯ow-lines and the ¯ow cell, thus increasing the baseline readings. It should therefore be removed; 0.5% (w/v) alkaline oxalic acid solution was found to be suitable for this purpose by dissolving the blue product. Temperature greatly enhances the reaction. Different temperatures were tested, from 25±808C, using the water bath. It must be noted that boiling the solutions was omitted to avoid possible disintegration of the product. 508C gave the best results as shown in Fig. 3. Temperatures higher than 508C gave noticeable noisy baseline readings. Flow-rate is an essential parameter and can be controlled by the peristaltic pump. The effect of total
280
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
Table 1 Effect of nitric acid concentration on the reaction of 10 mg mlÿ1 tenoxicam using 0.01 M Fe(NO3)3; 0.01 M K3Fe(CN)6; temp. 508C and flowrate 6 ml minÿ1 HNO3 concentration (M)
110ÿ3
510ÿ3
110ÿ2
510ÿ2
0.1
0.5
Absorbance
0.203
0.203
0.222
0.199
0.195
0.168
Table 2 Effect of iron(III) nitrate concentration on the reaction of 10 mg mlÿ1 tenoxicam under the same conditions as in Table 1 Iron(III) nitrate concentration (M)
110ÿ4
510ÿ4
110ÿ3
510ÿ3
110ÿ2
510ÿ2
0.1
Absorbance
0.016
0.048
0.062
0.191
0.244
0.216
0.211
Table 3 Effect of K3Fe(CN6) concentration on the reaction of 10 mg mlÿ1 tenoxicam using the same condition as in Table 1 K3Fe(CN)6 concentration (M)
110ÿ3
510ÿ3
110ÿ2
510ÿ2
0.1
Absorbance
0.038
0.184
0.211
0.214
0.181
¯ow-rate was studied keeping other conditions constant, over the range 3.2±10.4 ml minÿ1, with equal ¯ow in each channel. No signi®cant effect was observed on the absorbance. A 6.0 mg mlÿ1 ¯ow-rate was adapted for tenoxicam determination because it allows enough time for the reaction to complete with reasonable sample throughput rate. The effect of sample volume was investigated by injecting different volumes using different lengths of
the sample loop. It was found that the absorbance increases while increasing the sample volume. 250 ml gave the highest absorbance, as shown in Fig. 4. Coil length is also another important parameter for the reaction to be complete. Two coils have been used in the manifold as shown in Fig. 1. The ®rst coil (RC1) is for the reduction of iron(III) to iron(II) by tenoxicam and the second coil (RC2) is for the reaction of the resulting iron(II) with hexacyanoferrate(III) to form
Fig. 3. Effect of temperature on 5 mg mlÿ1 tenoxicam response: HNO30.01 M; Fe(NO3)30.01 M; Fe(CN)]60.01 M.
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
281
Fig. 4. Effect of sample volume on 5 mg mlÿ1 tenoxicam response; (HNO30.01 M; Fe(NO3)30.01 M; Fe(CN)6-40.01 M.
the blue compound. Both coils were submerged in a 508C water bath. Different coil lengths were investigated. A remarkable increase in the absorbance was obtained when 150 cm and 200 cm lengths were used for the ®rst and second coil respectively, as shown in Fig. 5. The calibration plot obtained under the optimised condition is shown in Fig. 6. 5.3. Interferences The effects of some common excipients usually present in pharmaceutical preparations and some
amino acids which are normally found in biological samples were investigated. Up to 100 mg mlÿ1 of arabinose, fructose, glucose, sucrose, alanine, histidine, methionine, carbowax, nicotinamide, ribo¯avin, starch, and glucosamine gave no signi®cant interfering effect on the absorbance of 5 mg mlÿ1 tenoxicam. 6. Pharmaceutical applications The method was applied to the determination of tenoxicam in Tilcotil tablets (20 mg, Roche, Switzerland). Sample preparation was done by individually
Fig. 5. Effect of length of reaction coils on 5 mg mlÿ1 tenoxicam response: (HNO30.01 M; Fe(NO3)30.01 M; Fe(CN)60.01 M.
282
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283
Fig. 6. Typical calibration group for peak absorbance concentrations of tenoxicam.
weighing three tablets. The tablets were crushed and pulverized and a representative weight equivalent to 20 mg of drug as labelled was taken and then dissolved in 510ÿ3 M sodium hydroxide. The sample was ®ltered to achieve a clear solution. Working solutions were prepared from the original ®ltrate by diluting with distilled water. Very good results with excellent recovery (100.6%) were obtained for three samples of tenoxicam based on three determinations of each sample. The results are summarized in Table 4.
Table 4 Determination of tenoxicam in Tilcotil tablets using the new procedure Tenoxicam sample (Tilcotil Tablet)
Sample (1) Sample (2) Sample (3) a
Amount of tenoxicam (mg) Claimed
Founda
20 20 20
20.12a 20.11 20.10
Each result is the average of three determinations.
Recovery (%)
100.6 100.6 100.5
7. Conclusions The new method provides a rapid, simple and sensitive means of determining tenoxicam in pharmaceutical preparations. It has the advantage of being accurate and does not require the removal of excipients. The manipulation and intervention of the operator is minimal. Acknowledgements The author thanks Mr. E.A. Basco for his excellent technical assistance. References [1] J.F. Gonzales, P.A. Todd, Drugs 34 (1987) 298. [2] The Merck Index, 11th ed., Merck, Rahway, NJ, USA, 1989, p. 1441. [3] T.F. Woolf, L.L. Radulovic, Drug Metab. Rev. 21(2) (1989) 255. [4] P. Heizmann, J. Korner, K. Kinapold, J. Chromatogr. Biomed. App. 374 (1986) 95.
S.A. Al-Tamrah / Analytica Chimica Acta 375 (1998) 277±283 [5] J.S. Dixon, J.R. Lowe, D.B. Galloway, J. Chromatogr. 310 (1984) 455. [6] D. Dell, R. Joly, W. Meiester, W. Arnold, C. Patros, B. Guldimann, J. Chromatogr. 317 (1984) 483. [7] M.I. Munera-Jaramillo, S. Boter-Garces, J. Chromatogr. 616 (1993) 349.
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[8] N. Abo El-Maali, J.C. Vire, G.J. Patriarche, M.A. Ghandour, G.D. Christian, Anal. Sci. 6 (1990) 245. [9] Z. Atkopur, M. Tuncell, Anal. Lett. 29 (1996) 2383. [10] A.I. Al-Amoud, M.Sc. Dissertation, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia, 1995. [11] G. Yener, Y. Topaloglu, Sci. Pharmacy 60 (1992) 247.