- Email: [email protected]
The determination of glutethimide by n.m.r. spectrometry
Anulytica Chimica Acta. 73 ( 1974) 399-401 0 Elscvier Scientific Publishing Company.
SHORT
399 Amsterdam
- Printed
in The Netherlands
COMMUNICATION .
TXe determination
HASSAN
of glutethimide
spectrometry
Y. ABOUL-ENEIN
The Toxicology Cetr ter, Departrrtertt City, Iowa 52242 (U.S.A.) (Received
by n.m.r.
of Phatwtacology,
College
qf Metikirte.
Utriversity
of Iowa,
Iowa
14th May 1974)
Glutethimide (2-ethyl-2-phenylglutarimide) is a sedative hypnotic agent chemically related to the barbiturates. Several analytical approaches have been successfully applied to the isolation and determination of glutethimide in biological fluids, such as serum and cerebrospinal fluidls3. The U.V. spectrophotometric method described in NF XIII4 for determination of glutethimide in tablet dosage form requires separation by column chromatography which renders the method lengthy. The acid-base titration method adopted by the British Pharmacopaeia5 involves ether extraction of the drug from tablets, which &so .make.s the method time-consuming. This paper describes a method based on n.m.r. ,spectrometry to determine glutethimide in tablet formulations. The method utilizes carbon tetrachloride as the solvent, and hexamethylcyclotrisiloxane is used as an internal standard. Known mixtures and commercial tablets were analyzed by this procedure, which proved to be simple, rapid (40 min) and accurate; the method provides a spdctrum of the drug as conlirmatory identification. Experimert tal A Varian T-60 n.m.r. spectrometer was used. Glutethimide standard (USV Pharmaceutical Corp., Tuckahoe, N.Y.) and glutethimide tablets (Doriden 500-mg, tablets, USV Pharmaceutical Corp., Tuckahoe, N.Y.). Procedure. Dry the tablets at 45” C over phosphorus pentoxide overnight in a desiccator. Place a tablet into a 50 ml stoppered flask. Carefully crack the tablet with the end of a spatula. Use a measured amount of carbon tetrachloride so that the linal concentration of glutethimide will be about 20 mg ml-‘. Wash down the end of the spatula to ensure quantitative removal of the sample. Add an accurately weighed amount of hexamethylcyclotrisiloxane (K&K Laboratories) as internal standard, to the sample solution so that its final concentration is about 7 mg ml -I, then add the remainder of the solvent to the flask. Stopper the flask and place it in a shaker for 10 min to effect dissolution. Filter through a cotton wad, and transfer about 0.4 ml of the clear solution to an analytical n.m.r. tube. Place the tube in the spectrometer, adjust the spin rate to eliminate spinning side band, and obtain a spectrum. All .
400
SHORT
COMMUNICATION
peak field pgsitions are referenced to hexamethylcyclotrisiloxane at 0.00 p.p.m. Ic’.egrate the peaks of interest (phenyl group at 7.3 S and hexamethylcyclotrisiloxane at 0.00 61 at least live times. The amount of glutethimide may be then calculated as follows: L&E!% EW x (mg of hexamethylcyclotrisiloxane) = A 11 11
mg of glutethimide
where A, is the integral value of the signal representing glutethimide; A,, the integral value of the signal representing the internal standard; EW, the molecular weight of glutethimide (5 = 43.45) ; and E W, the molecular weight of internal standard (18= 12.35).
Results
aid discussiort “” “’ _ The n.m.r. of pure glutethimide shows a singlet at 7.3 6 for the phenyl protons, when hexamethylcyclotrisiloxane is used as a reference. This is an ideal peak for precise integration. The utility of this internal standard has been demonstrated previouslye-*. It appears as a single signal at an extreme uplield position. The n.m.r. spectrum of glutethimide (Fig. 1) under the described analytical conditions is free of excipient peaks and provides identification of the active ingredient in addition to quantitative results. The results of the determination of a series of glutethimide standards (Table I) demonstrate good precision ( + 0.70%). Table II summarizes the analysis of commercial tablets; good agreement with the declared value was found. Measurements shown in both -tables are within the NF monograph limits of 95.0-105.0 %, for glutethimide and glutethimide tablets. The use of n.m.r. for quantitative analysis is attractive’ because it is a simnle and rapid procedure. _
a C
I
i 11.
.I. I.0
Fig. 1. N.m.r.
1.. 1.0
spectrum
.I 6.0
of glutethimide(1)
,.. ..a
“”
. I * 3
..a
I..
. 2.D
and hcxame:hylcyclotrisiloxane(II)
I..
1.0
.
I
1.0
in carbon
tetrachloride.
SHORT
CdMMUNICATION
TABLE
I
ANALYSIS
401
OF GLUTETHIMIDE
Sample
Internal (WI)
STANDARDS
standurd
BY N.M.R.
Glrttethirnide Added
39.57 103.73 114.46 65.33 30.12 19.26 17.64 17.24 14.59 15.65
1 2 3 4 5 6 7 8 9 10
(nag)
50.58 45.10 76.50 52.39 45.53 49.49 70.50 72.80 71.98 70.92
Found (mg)
Recovereri (%)
50.32 44.89 75.98 52.33 45.76 48.99 70.02 73.67 71.62 70.13
99.48 99.53 99.32 99.88 100.50 98.99 99.32 101.20 99.50 98.89
.
Menu 99.66 s, 0.70
TABLE
II
ASSAY
OF
GLUTETHIMIDE
Sample
111tenial stamiurtl
1 2 3 4 5 6 7
75.5 108.45 120.24 84.84 54.47 42.96 45.94
IN PHARMACEUTICAL
(my)
Percent
PREPARATIONS
of declareda
BY N.M.R.
aniouti t
98.70 101.06 99.60 91f.97 99.22 97.89 98.97
99.20 Mean sr & 0.97 It Declared
amount
is 500 mg per tablet.
The author acknowledges Dr. L. J. Fischer and Dr. A. R. Hansen valuable suggestions. This work was supported by U.S.P.H.S. Grant GM REFERENCES 1 A. R. Hansen and L. J. Fischer, Clirt. Chem, 20 (1974) 236. 2 I. Sunshine, R. Maes and R. Faracci, Clin. CIWIIL, 14 (1968) 595. 3 J. J. Ambre and L. J. Fischer, Res. Cornnttrn. Chem. Pathol. Pltarmacol., 4 (1972) 4 The National Formulary, Ma&, Easton, Pa., 13th edn., 1970, p. 329. 5 The British Pharmacopoeia, Pharmaceutical Press, London, 1968, p. 443. 6 S. Barcza, J. Org. Cltent., 28 (1963) 1941. 7 J. W. Truczan and B. A. Goldwitz, J. Pltarm. Sci., 61 (1972) 1309. 8 J. W. Truczan and B. A. Goldwitz, J. Pharm. Sci., 62 (1973) 1705.
307.
for their 12675.
SHORT
399 Amsterdam
- Printed
in The Netherlands
COMMUNICATION .
TXe determination
HASSAN
of glutethimide
spectrometry
Y. ABOUL-ENEIN
The Toxicology Cetr ter, Departrrtertt City, Iowa 52242 (U.S.A.) (Received
by n.m.r.
of Phatwtacology,
College
qf Metikirte.
Utriversity
of Iowa,
Iowa
14th May 1974)
Glutethimide (2-ethyl-2-phenylglutarimide) is a sedative hypnotic agent chemically related to the barbiturates. Several analytical approaches have been successfully applied to the isolation and determination of glutethimide in biological fluids, such as serum and cerebrospinal fluidls3. The U.V. spectrophotometric method described in NF XIII4 for determination of glutethimide in tablet dosage form requires separation by column chromatography which renders the method lengthy. The acid-base titration method adopted by the British Pharmacopaeia5 involves ether extraction of the drug from tablets, which &so .make.s the method time-consuming. This paper describes a method based on n.m.r. ,spectrometry to determine glutethimide in tablet formulations. The method utilizes carbon tetrachloride as the solvent, and hexamethylcyclotrisiloxane is used as an internal standard. Known mixtures and commercial tablets were analyzed by this procedure, which proved to be simple, rapid (40 min) and accurate; the method provides a spdctrum of the drug as conlirmatory identification. Experimert tal A Varian T-60 n.m.r. spectrometer was used. Glutethimide standard (USV Pharmaceutical Corp., Tuckahoe, N.Y.) and glutethimide tablets (Doriden 500-mg, tablets, USV Pharmaceutical Corp., Tuckahoe, N.Y.). Procedure. Dry the tablets at 45” C over phosphorus pentoxide overnight in a desiccator. Place a tablet into a 50 ml stoppered flask. Carefully crack the tablet with the end of a spatula. Use a measured amount of carbon tetrachloride so that the linal concentration of glutethimide will be about 20 mg ml-‘. Wash down the end of the spatula to ensure quantitative removal of the sample. Add an accurately weighed amount of hexamethylcyclotrisiloxane (K&K Laboratories) as internal standard, to the sample solution so that its final concentration is about 7 mg ml -I, then add the remainder of the solvent to the flask. Stopper the flask and place it in a shaker for 10 min to effect dissolution. Filter through a cotton wad, and transfer about 0.4 ml of the clear solution to an analytical n.m.r. tube. Place the tube in the spectrometer, adjust the spin rate to eliminate spinning side band, and obtain a spectrum. All .
400
SHORT
COMMUNICATION
peak field pgsitions are referenced to hexamethylcyclotrisiloxane at 0.00 p.p.m. Ic’.egrate the peaks of interest (phenyl group at 7.3 S and hexamethylcyclotrisiloxane at 0.00 61 at least live times. The amount of glutethimide may be then calculated as follows: L&E!% EW x (mg of hexamethylcyclotrisiloxane) = A 11 11
mg of glutethimide
where A, is the integral value of the signal representing glutethimide; A,, the integral value of the signal representing the internal standard; EW, the molecular weight of glutethimide (5 = 43.45) ; and E W, the molecular weight of internal standard (18= 12.35).
Results
aid discussiort “” “’ _ The n.m.r. of pure glutethimide shows a singlet at 7.3 6 for the phenyl protons, when hexamethylcyclotrisiloxane is used as a reference. This is an ideal peak for precise integration. The utility of this internal standard has been demonstrated previouslye-*. It appears as a single signal at an extreme uplield position. The n.m.r. spectrum of glutethimide (Fig. 1) under the described analytical conditions is free of excipient peaks and provides identification of the active ingredient in addition to quantitative results. The results of the determination of a series of glutethimide standards (Table I) demonstrate good precision ( + 0.70%). Table II summarizes the analysis of commercial tablets; good agreement with the declared value was found. Measurements shown in both -tables are within the NF monograph limits of 95.0-105.0 %, for glutethimide and glutethimide tablets. The use of n.m.r. for quantitative analysis is attractive’ because it is a simnle and rapid procedure. _
a C
I
i 11.
.I. I.0
Fig. 1. N.m.r.
1.. 1.0
spectrum
.I 6.0
of glutethimide(1)
,.. ..a
“”
. I * 3
..a
I..
. 2.D
and hcxame:hylcyclotrisiloxane(II)
I..
1.0
.
I
1.0
in carbon
tetrachloride.
SHORT
CdMMUNICATION
TABLE
I
ANALYSIS
401
OF GLUTETHIMIDE
Sample
Internal (WI)
STANDARDS
standurd
BY N.M.R.
Glrttethirnide Added
39.57 103.73 114.46 65.33 30.12 19.26 17.64 17.24 14.59 15.65
1 2 3 4 5 6 7 8 9 10
(nag)
50.58 45.10 76.50 52.39 45.53 49.49 70.50 72.80 71.98 70.92
Found (mg)
Recovereri (%)
50.32 44.89 75.98 52.33 45.76 48.99 70.02 73.67 71.62 70.13
99.48 99.53 99.32 99.88 100.50 98.99 99.32 101.20 99.50 98.89
.
Menu 99.66 s, 0.70
TABLE
II
ASSAY
OF
GLUTETHIMIDE
Sample
111tenial stamiurtl
1 2 3 4 5 6 7
75.5 108.45 120.24 84.84 54.47 42.96 45.94
IN PHARMACEUTICAL
(my)
Percent
PREPARATIONS
of declareda
BY N.M.R.
aniouti t
98.70 101.06 99.60 91f.97 99.22 97.89 98.97
99.20 Mean sr & 0.97 It Declared
amount
is 500 mg per tablet.
The author acknowledges Dr. L. J. Fischer and Dr. A. R. Hansen valuable suggestions. This work was supported by U.S.P.H.S. Grant GM REFERENCES 1 A. R. Hansen and L. J. Fischer, Clirt. Chem, 20 (1974) 236. 2 I. Sunshine, R. Maes and R. Faracci, Clin. CIWIIL, 14 (1968) 595. 3 J. J. Ambre and L. J. Fischer, Res. Cornnttrn. Chem. Pathol. Pltarmacol., 4 (1972) 4 The National Formulary, Ma&, Easton, Pa., 13th edn., 1970, p. 329. 5 The British Pharmacopoeia, Pharmaceutical Press, London, 1968, p. 443. 6 S. Barcza, J. Org. Cltent., 28 (1963) 1941. 7 J. W. Truczan and B. A. Goldwitz, J. Pltarm. Sci., 61 (1972) 1309. 8 J. W. Truczan and B. A. Goldwitz, J. Pharm. Sci., 62 (1973) 1705.
307.
for their 12675.