- Email: [email protected]
Spectrophotometric determination of nitrazepam in tablets
Talmra, Vol. 33, No. 9, pp. 143-144, Printed in Great Britain
1986
0039-9140/86
$3.00 + 0.00
Pergamon Journals Ltd
SHORT COMMUNICATIONS SPECTROPHOTOMETRIC NITRAZEPAM
DETERMINATION IN TABLETS
OF
SALWA &ZK EL-SIIABOURI Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Assiut, Assiut, Egypt
(Received 11 November 1985. Revised 16 March 1986. Accepted 15 May 1986)
Summary-A sensitive spectrophotometric method is reported for the determination of nitrazepam either in pure form or in tablets. The method is based on reduction with zinc dust and calcium chloride followed by reaction with sodium pentacyanoaminoferrate(I1) to give a violet product having an absorbance maximum at 560 nm. Beer’s law is obeyed over the concentration range l-20 pg/ml in the final solution.
The common excipients in tablets do not interfere. The recovery and precision are similar to those of the official B.P. method.
Methods for the determination of nitrazepam include spectrophotometric,’ colorimetric,2,4 gas chromatographic,‘s6 TLC,’ HPLC8 fluorimetric,’ and differential pulse polarographiciO*” procedures. The B.P. recommends a non-aqueous titration for the bulk drug and a spectrophotometric method for tablets.i2 Sodium pentacyanoaminoferrate(I1) (SCAF) has been used to detect aromatic nitro compounds.‘3*‘4 This report describes its use for determining nitrazepam.
RESULTS
AND DISCUSSION
Nitrazepam, when reduced with zinc and calcium chloride solution and subsequently reacted with SCAF in aqueous ethanol, produces a violet product having a broad absorption peak with its maximum at 560 mn (Fig. 1) and molar absorptivity 1.15 x IO4 1 .mole-’ .cm-i. Beer’s law is obeyed over the range l-20 pg/ml in the final solution. The absorbance is stable for 10 hr at room temperature. Reaction
EXPERIMENTAL
Reagents Sodium pentacyanoaminoferrate(II) Nu,[Fe(CN)sNH,I @CAP). Prepared according to Vogel,” and used as a 0.1%
solution, made fresh daily. Calcium chloride solution, 10%. Zinc dust. Standard nitrazepam solution. Prepared by dissolving 50
mg of nitrazepam (accurately weighed) in 25.0 ml of ethanol. This solution must be freshly prepared daily, and is further diluted with ethanol as required. All chemicals used were of analytical grade. Precedures Calibration graph. Pipette 0.500 ml of the nitrazepam standards (in the range 50-1000 pg/ml) into SO-ml conical flasks, containing 100 mg of zinc dust and 5 ml of calcium chloride solution. Let stand for 5 min at room temperature (25”) with occasional shaking. Filter (7-cm Whatman No. 1 papers) into 25-ml standard flasks, washing each residue thoroughlv with three 2-ml portions of ethanol. Add 5 ml of SCAF solution to each combined filtrate and washings, mix well, let stand for 10 min at room temperature, and dilute to volume with water. Measure the absorbance at 560 nm against a blank prepared at the same time. Analvsis of tablets. Weigh and uowder 20 tablets. Transfer an accurately weighed quantity of the powder, equivalent to about 50 mg of nitrazepam, to a 25-ml standard flask, and dissolve and dilute it to volume with ethanol. Filter (dry paper etc.), and discard the first portion of the filtrate. Dilute an aliquot of the filtrate as required, and determine the nitrazepam content by the procedure above.
conditions
Any amount of zinc dust in the range 50-300 mg gives the same final absorbance for a fixed amount of nitrazepam, but larger quantities give slightly lower absorbance. The volume of 10% calcium chloride solution used along with 100 mg of zinc dust can be varied from 1 to 10 ml without altering the completeness of reduction of nitrazepam in the concentration range l-20 pg/ml. Maximum colour intensity is achieved by reduction for 2 min at room temperature. Further reduction time (up to 20 min) gives no change in the absorbance.
743
I
400
I1
I
I 500
II
I
I
I 600
Wavelength
I
I,
I
I 700
(nm)
Fig. 1. Absorption spectrum for the coloured reaction product of reduced nitrazepam with SCAF.
744
SHORT
Table 1. Determination
COMbKINlCATIONS
of nitrazepam in tablets by the proposed method and the B.P. method Proposed method Nitrazepam added, w
Recovery, *% f SD
B.P. method Found, *% f SD
5.00
99.1 f 0.6
99.3 f 0.6
99.5 f 1.2 t = 1.36 F = 2.69
10.00
98.7 + 0.7
99.0 f 0.8
99.2 f 1.O t = 1.36 F = 2.89
15.00
99.9 f 0.8
99.6 f 0.6
Sample
Found, *% f SD
A
98.9 f 1.1 t = 1.69 F = 2.96
B
C
*Average of 10 determinations, calculated on nominal content of 5 mg of nitrazepam. Theoretical values at the 95% confidence level: t = 2.26, F = 3.18.
Varying the volume of SCAF solution used (from 1 to 10 ml) shows that 3 ml will suffice to give full colour intensity. The colour takes 10 min to reach full intensity. The final solution can be diluted to volume with water, ethanol, methanol or dioxan with no change in the wavelength of maximum absorption or the molar absorptivity, but use of isopropyl alcohol gives a 25% decrease in the absorbance. Water is preferred. The colour is stable for at least 10 hr. The method has been successfully applied to the analysis of nitrazepam tablets. Commonly encountered excipients such as starch, talc, lactose, and magnesium stearate do not interfere. The results obtained compare favourably with those of the official method (Table 1). The chemistry of the colour reaction may be suggested on the basis of a previously reported mechanism.14 The nitro compound (nitrazepam in this case) is first reduced under the proposed conditions to the corresponding nitroso derivative. Addition of SCAF then causes further reduction to the corresponding hydroxylamine derivative. Subsequent substitution of ammonia in the reagent by the hydroxylamine derivative results in the violet colour.
ArNO + 2Na,[Fe(CN),NH,]
+ 2H20
+ ArNHOH + 2Na,[Fe(CN),NH,]
+ 2NaOH
ArNHOH + NaJFe(CN,)NH,] + Na,[Fe(CN)&NHOH]
+ NH,
where ArNO = nitroso derivative of nitrazepam and ArNHOH = hydroxylamine derivative of nitrazepam. REFERENCES
1. 0. L. Grom, N. S. Komar and N. S. Ladyzhinshaya, Farm. Zh. (Kiev), 1976, 31, 82. 2. H. Raber and J. Gruber, Sci. Pharm., 1972,40, 35. 3. N. M. Sanghavi and N. G. Jivani, Tafanta, 1979,X, 63. 4. Y. A. Beltagy, A. S. Issa and M. S. Mahrous, Egypt. J. Pharm. Sci., 1978, 19, 115. 5. K. M. Jensen, J. Chromatog., 1975, 111, 389. 6. H. Ehrsson and A. Tilly, Anal. Lett., 1973, 6, 197. 7. P. Haefelfinger, J. High Resol. Chromarog., Chromatog. Commun., 1979, 1, 39. 8. H. B. Hanekamp, W. H. Voogt, P. Bos and R. W. Frei, J. Liq. Chromatog., 1980, 3, 1205. 9. J. Reider, Arzneimittel-Forsch., 1973, 23, 207. 10. P. Van Doorne, Pharm. Weekblad, 1975, 110, 149. 11. S. Halvorsen and E. Jacobson, Anal. Chim. Acta, 1972, 59, 127. 12. British Pharmacopoeia, 1980, pp. 305, 793. HMSO, London. 13. C. 0. Baudisch, Ber., 1921, 54, 413. 14. F. Feigl, Spar Tests in Organic Analysis, 7th Ed., pp. 290, 297-299. Elsevier, Amsterdam, 1966. 15. A. I. Vogel, A Text Book of Quantitative Inorganic Analysis, 3rd Ed., p. 727. Longmans, London, 1975.
1986
0039-9140/86
$3.00 + 0.00
Pergamon Journals Ltd
SHORT COMMUNICATIONS SPECTROPHOTOMETRIC NITRAZEPAM
DETERMINATION IN TABLETS
OF
SALWA &ZK EL-SIIABOURI Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Assiut, Assiut, Egypt
(Received 11 November 1985. Revised 16 March 1986. Accepted 15 May 1986)
Summary-A sensitive spectrophotometric method is reported for the determination of nitrazepam either in pure form or in tablets. The method is based on reduction with zinc dust and calcium chloride followed by reaction with sodium pentacyanoaminoferrate(I1) to give a violet product having an absorbance maximum at 560 nm. Beer’s law is obeyed over the concentration range l-20 pg/ml in the final solution.
The common excipients in tablets do not interfere. The recovery and precision are similar to those of the official B.P. method.
Methods for the determination of nitrazepam include spectrophotometric,’ colorimetric,2,4 gas chromatographic,‘s6 TLC,’ HPLC8 fluorimetric,’ and differential pulse polarographiciO*” procedures. The B.P. recommends a non-aqueous titration for the bulk drug and a spectrophotometric method for tablets.i2 Sodium pentacyanoaminoferrate(I1) (SCAF) has been used to detect aromatic nitro compounds.‘3*‘4 This report describes its use for determining nitrazepam.
RESULTS
AND DISCUSSION
Nitrazepam, when reduced with zinc and calcium chloride solution and subsequently reacted with SCAF in aqueous ethanol, produces a violet product having a broad absorption peak with its maximum at 560 mn (Fig. 1) and molar absorptivity 1.15 x IO4 1 .mole-’ .cm-i. Beer’s law is obeyed over the range l-20 pg/ml in the final solution. The absorbance is stable for 10 hr at room temperature. Reaction
EXPERIMENTAL
Reagents Sodium pentacyanoaminoferrate(II) Nu,[Fe(CN)sNH,I @CAP). Prepared according to Vogel,” and used as a 0.1%
solution, made fresh daily. Calcium chloride solution, 10%. Zinc dust. Standard nitrazepam solution. Prepared by dissolving 50
mg of nitrazepam (accurately weighed) in 25.0 ml of ethanol. This solution must be freshly prepared daily, and is further diluted with ethanol as required. All chemicals used were of analytical grade. Precedures Calibration graph. Pipette 0.500 ml of the nitrazepam standards (in the range 50-1000 pg/ml) into SO-ml conical flasks, containing 100 mg of zinc dust and 5 ml of calcium chloride solution. Let stand for 5 min at room temperature (25”) with occasional shaking. Filter (7-cm Whatman No. 1 papers) into 25-ml standard flasks, washing each residue thoroughlv with three 2-ml portions of ethanol. Add 5 ml of SCAF solution to each combined filtrate and washings, mix well, let stand for 10 min at room temperature, and dilute to volume with water. Measure the absorbance at 560 nm against a blank prepared at the same time. Analvsis of tablets. Weigh and uowder 20 tablets. Transfer an accurately weighed quantity of the powder, equivalent to about 50 mg of nitrazepam, to a 25-ml standard flask, and dissolve and dilute it to volume with ethanol. Filter (dry paper etc.), and discard the first portion of the filtrate. Dilute an aliquot of the filtrate as required, and determine the nitrazepam content by the procedure above.
conditions
Any amount of zinc dust in the range 50-300 mg gives the same final absorbance for a fixed amount of nitrazepam, but larger quantities give slightly lower absorbance. The volume of 10% calcium chloride solution used along with 100 mg of zinc dust can be varied from 1 to 10 ml without altering the completeness of reduction of nitrazepam in the concentration range l-20 pg/ml. Maximum colour intensity is achieved by reduction for 2 min at room temperature. Further reduction time (up to 20 min) gives no change in the absorbance.
743
I
400
I1
I
I 500
II
I
I
I 600
Wavelength
I
I,
I
I 700
(nm)
Fig. 1. Absorption spectrum for the coloured reaction product of reduced nitrazepam with SCAF.
744
SHORT
Table 1. Determination
COMbKINlCATIONS
of nitrazepam in tablets by the proposed method and the B.P. method Proposed method Nitrazepam added, w
Recovery, *% f SD
B.P. method Found, *% f SD
5.00
99.1 f 0.6
99.3 f 0.6
99.5 f 1.2 t = 1.36 F = 2.69
10.00
98.7 + 0.7
99.0 f 0.8
99.2 f 1.O t = 1.36 F = 2.89
15.00
99.9 f 0.8
99.6 f 0.6
Sample
Found, *% f SD
A
98.9 f 1.1 t = 1.69 F = 2.96
B
C
*Average of 10 determinations, calculated on nominal content of 5 mg of nitrazepam. Theoretical values at the 95% confidence level: t = 2.26, F = 3.18.
Varying the volume of SCAF solution used (from 1 to 10 ml) shows that 3 ml will suffice to give full colour intensity. The colour takes 10 min to reach full intensity. The final solution can be diluted to volume with water, ethanol, methanol or dioxan with no change in the wavelength of maximum absorption or the molar absorptivity, but use of isopropyl alcohol gives a 25% decrease in the absorbance. Water is preferred. The colour is stable for at least 10 hr. The method has been successfully applied to the analysis of nitrazepam tablets. Commonly encountered excipients such as starch, talc, lactose, and magnesium stearate do not interfere. The results obtained compare favourably with those of the official method (Table 1). The chemistry of the colour reaction may be suggested on the basis of a previously reported mechanism.14 The nitro compound (nitrazepam in this case) is first reduced under the proposed conditions to the corresponding nitroso derivative. Addition of SCAF then causes further reduction to the corresponding hydroxylamine derivative. Subsequent substitution of ammonia in the reagent by the hydroxylamine derivative results in the violet colour.
ArNO + 2Na,[Fe(CN),NH,]
+ 2H20
+ ArNHOH + 2Na,[Fe(CN),NH,]
+ 2NaOH
ArNHOH + NaJFe(CN,)NH,] + Na,[Fe(CN)&NHOH]
+ NH,
where ArNO = nitroso derivative of nitrazepam and ArNHOH = hydroxylamine derivative of nitrazepam. REFERENCES
1. 0. L. Grom, N. S. Komar and N. S. Ladyzhinshaya, Farm. Zh. (Kiev), 1976, 31, 82. 2. H. Raber and J. Gruber, Sci. Pharm., 1972,40, 35. 3. N. M. Sanghavi and N. G. Jivani, Tafanta, 1979,X, 63. 4. Y. A. Beltagy, A. S. Issa and M. S. Mahrous, Egypt. J. Pharm. Sci., 1978, 19, 115. 5. K. M. Jensen, J. Chromatog., 1975, 111, 389. 6. H. Ehrsson and A. Tilly, Anal. Lett., 1973, 6, 197. 7. P. Haefelfinger, J. High Resol. Chromarog., Chromatog. Commun., 1979, 1, 39. 8. H. B. Hanekamp, W. H. Voogt, P. Bos and R. W. Frei, J. Liq. Chromatog., 1980, 3, 1205. 9. J. Reider, Arzneimittel-Forsch., 1973, 23, 207. 10. P. Van Doorne, Pharm. Weekblad, 1975, 110, 149. 11. S. Halvorsen and E. Jacobson, Anal. Chim. Acta, 1972, 59, 127. 12. British Pharmacopoeia, 1980, pp. 305, 793. HMSO, London. 13. C. 0. Baudisch, Ber., 1921, 54, 413. 14. F. Feigl, Spar Tests in Organic Analysis, 7th Ed., pp. 290, 297-299. Elsevier, Amsterdam, 1966. 15. A. I. Vogel, A Text Book of Quantitative Inorganic Analysis, 3rd Ed., p. 727. Longmans, London, 1975.