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High‐performance Liquid Chromatographic Analysis of Docusate Sodium in Soft Gelatin Capsules
High-Performance Liquid Chromatographic Analysis of Docusate Sodium in Soft Gelatin Capsules DAVIDR. HOGUE,JOSEPH A. ZIMMARDI, AND KIRIT A.
SHAH'
Received March 14, 1990, from Product Develo. ment, R. P. Scherer North America, 2725 Scherer Drive North, St. Petersburg, FL 33716.
Accepted for pubfcatlon June 20, 1991.
Abatrncl 0 A rapid and simple high-performance liquid chromatographic (HPLC) method for the analysis of docusate sodium in soft gelatin capsules was developed with progesterone as the internal standard. The method requires a reversed-phase column and a pairedion technique to separate docusate sodium from other components. A CZ column was used with a mobile phase of acetonitri1e:water (70:30) contaming 0.005 M tetrabutylammoniumphosphate. The flow rate was 1.8 mUmin, and the effluent was monitored at 214 nm. Docusate sodlum and progesterone had retention times of 4.5 and 6.8 min, respectively. The proposed HPLC method is linear, accurate, and precise. A mean assay value of 99.6% was obtained by the proposed method when five samples, each containing a composite of 10 capsules, were analyzed. The results obtained by the proposed HPLC, tetra-mbutylammonium iodide titration, and USP XXll HPLC methods are compared.
Docusate sodium [sodium 1,I-bis(2-ethylhexyl) sulfosuccinate; see structure] is a wetting agent that is uaed mainly as a stool softener. The agent is available in soft gelatin capsule formulation for internal use. Docusate sodium capsules can be assayed by titration with tetra-n-butylammonium iodide, with bromophenol blue as an indicator, in the presence of chloroform; this method was the official method in United States Pharmacopeia (USP) XX.1 Recently, USP XXIP updated the assay procedure to a high-performance liquid chromatographic (HPLC) method. Unfortunately, the methods of standard preparation and assay preparation in the official method are somewhat tedious in that they involve chloroform extraction and drying. Docusate sodium can also be analyzed by colorimetric,g-8 turbidimetric,S and polarographic analysis.10 The objective of this investigation was to devise a simpler and more expedient procedure by applying a reversed-phase, paired-ion HPLC analysis of docusate sodium to soft gelatin capsule formulations. The results obtained from this HPLC procedure were compared with those obtained from the official USP procedure and the tetra-n-butylammonium iodide titration method.
received. Docusate sodium reference standard (USP) was used after the water content was determined by Karl Fiacher titration. Instrumentation-A liquid chromatograph (model 344; Beckman Instruments, Berkeley, CAI equipped with single piston pump (model 112; Beckman Instruments) waa operated in the isocratic mode. A 2 0 4 , loop injector (model 210; Beckman Instruments), variable wavelength detector (model 165; Beckman Instruments), electronic data printer-plotter (model 3353; Hewlett-Packard, Palo Alto, CA), and a microparticulate reversed-phase column (4.6 mm x 30 cm) consisting of 10-pmparticles with a pore diameter of 100 A (Chromegabond C-22, ES Industries, Marlton, NJ)were used throughout. The HPLC detector was operated at a wavelength of 214 nm. Mobile Phase-The mobile phase was prepared by adding tetrabutylammonium phosphate (Pic Reagent A: Waters Associates, Milford, MA) to a mixture of 300 mL of water and 700 mL of acetonitrile to yield a final salt concentration of 0.005 M. Internal Standard Solution-A stock solution of progesterone (2 mg/mL) was prepared in methanol. Standard Solution-Docusate sodium (100 mg) was placed in a
a
b
P
6
Experimental Section Chemicals and Reagents-Acetonitrile, water, and methanol (Fisher Scientific Company, Fair Lawn, NJ) were WLC quality. Progesterone (Sigma Chemical Company, St. Louis, MO)was used as
C2Hs
I
CH~-COOCH~-CH-(CH,),-CH, I
NaO,S-CH-COO CH2-CH-(CH2),-CH,
3
I C2Hs
Docusate Sodium
OO22-3S9/9YO4OOa59$02.50/0 0 1992, American Pharmaceutical Association
6
9
Mmns Figure 1-Typical chromatogram of a standard solution of docusate sodium (1 mg/mL): (a) docusate sodium; (b) progesterone (internal
standard).
JOUm8l of Ph8maceutical SciencesI 359 Vol. 81, No. 4, April 1992
A
B
C
a a
a
P
B
3
6
1 111 111 11 3 3 6
u 3
0
6
Mll(rrrs
Figure 2-Typical chromatograms of a docusate sodium soft gelatin capsule containing 100 mg of docusate sodium (A), docusate sodium capsules with casanthranol, containing 100 mg of docusate sodium (B), and docusate sodium capsules With ferrous fumarate, containing 100 mg of docusate sodium (C). Key: (a) docusate sodium; (b) progesterone (internal standard). Table Mecoverler by Proposed HPLC Method Formula A.
0b
CC
Amount of Fill Material, mg 276.0 275.0 263.4 269.2 312.2 328.4 327.9 321.7 694.6 707.6 687.6 700.6
Docusate Sodium, mg
Amount of Docusate Sodium in Fill Material, mg
Added
Theory
95.5 91.5 93.5
10.80 21.60 32.40
106.3 113.1 125.9
104.3 104.1 102.1
10.80 21.60 32.40
115.1 125.7 134.5
103.2 100.3 102.2
10.80 21.60 32.40
114.0 121.9 134.6
Found 95.8 108.7 115.8 128.3 99.1 114.1 123.9 135.7 101.3 111.9 121.0 134.1
Recovery, %
102.3 102.4 101.9 99.1 98.6 100.9 101.9 99.3 99.6
a Docusate sodium (label claim: 100 mg). Docusate sodium with casanthranol (label claim: docusate sodium, 100 mg, and casanthranol, 30 mg). Docusate sodium with ferrous fumarate (label claim: docusate sodium, 100 mg, and ferrous fumarate, 150 mg).
100-mL volumetric flask. Internal standard solution (2 mL) was added to this flask and diluted to 100 mL with methanol to produce a docusate sodium concentration of 1 mg/mL and a progesterone concentration of 0.04 mg/mL. Sample Preparation-For capsules containing 100 mg of docusate sodium, 100 mg of docusate sodium and casanthranol, or 100 mg of docusate sodium and ferrous fumarate, one capeule was placed in a
360 I Journal of Pharmaceutical Sciences Vol. 81, NO. 4, April 1992
100-mL volumetric flask.Water (10 mL) was added, and the flask was heated to dissolve the gelatin. Finally, 2.0 mL of internal standard solution was added, and the mixture was diluted to 100 mL with methanol. The methanol precipitated the gelatin. The precipitates were allowed to settle, and an aliquot was filtered through a 25-mm, 0.46-pm nylon syringe filter. The same procedure was used for capsules containing 250 mg of docusate sodium, except that a 260-mL
Tabla ICAnalyslo of Docuaate Sodlum Soft Gelatln Capsules by Propored HPLC Method
Sample Number
Percentage of Labela
SD
100.4 100.6 98.4 99.3 99.5
0.82 1.03 1.75 1.16 1.56
RSD,b %
0.82 1.02 1.78 1.16 1.57
Each value represents the average of five replicate analyses of each sample containing the composite of 10 capsules; label claim, 100 mg. RSD is relative standard deviation.
Table IlCComparatlve Analysls of Docuaate Sodium by Three Assay Methods
Formulaa A
B
a
volumetric flask was used and 25 mL of water and 5 mL of internal standard solution were added. Additionally, because of possible interaction between the ferrous ion and docuaate, these samples should be injected as won as possible after preparation. The standard solution (20 FL) and prepared sample were injected into the chromatograph. Chromatographic C o n d i t i o n s T h e volumetric flow rate was 1.8 mumin, and the column was at ambient temperature. Ten replicate injections of standard solution produced a relative standard deviation of 0.72%. The resolution between the docusate sodium peak and the internal standard peak was 1.96. Calculations-Because linearity experiments indicated that the peak areas (peak heights also) were related to the concentrations of docusate sodium (range, 0.61.4mg/mL), the results were calculated by using the following relationship: R x C x D = drug concentration (mg/capsule), where R is the area ratio of sample or standard to internal standard, C is the concentration of standard solution Cmg/ mL), and D is the dilution factor (mL).
Results and Discussion Figure 1shows a typical chromatogram for docusate sodium standard. The chromatograms shown in Figures 2A-2C were obtained for docusate sodium capsules, docusate sodium with casanthranol capsules, and docusate sodium with ferrous fumarate capsules, respectively. When injected into the chromatograph, docusate sodium was eluted first, followed by progesterone (internal standard), at retention times of 4.5 and 6.8 min, respectively. The calibration curve for docusate sodium was linear (r = 0.9998) over the concentration range 0.61.4 mg/mL. The recovery data were determined by adding different amounts of reference standard to three different formulation mixes (Table I). The proposed method produced satisfactory values for recovery of docusate sodium from the placebo matrix. The system precision of the proposed method was determined by using 20 pL of each of a series of 10 standard solutions containing docusate sodium at a concentration of 1.021 mg/mL. The relative standard deviation was 0.72%. The data indicate that the precision of the described chromatographic system is satisfactory.
C
Lot 1 2 3 1 2 3 1 2 3
Percentage of Label Claimb Proposed Titration
USP MethodC
Methodd
Methodd
103.2 100.2 99.7 97.5 97.3 103.0 101.1 100.1 101.2
101.8 100.7 101.3 98.8 100.0 101.4 99.0 105.1 103.4
103.0 101.5 103.2 99.2 99.5 98.3 101 .8 104.8 103.8
a See Table I for compositions. Label claim of 100 mg. Value represents composite of 10 capsules. Value represents average of three determinations.
Application of the proposed assay to docusate sodium soft gelatin capsules provided the results given in Table 11. These data were obtained from five replicate analyses of each sample containing a composite of 10 capsules. A placebo was made for each of the three formulations of docusate sodium capsules. No interfering peaks were found when these placebos were chromatographed with the proposed procedure. Three different lots of soil gelatin capsules from each of the three formulations were assayed by the titration procedure, the recent USP HPLC procedure, and the proposed HPLC procedure (Table 111). All three methods show good correlation. However, the USP method incorporates an ion-exchange technique that involves lengthy extraction, and the titration method has an end point that is difficult to read. The HPLC procedure described is simple, rapid, and precise for the quantitation of the docusate sodium in several docusate sodium-containing products.
References and Notes 1. U.S.Pharmacopeia, 20th rev., U.S.Pharmacopeial Convention: Rockville, MD, 1980;p 262. 2. US.Pharmacopeia, 22th rev., U.S.Pharmacopeial Convention: Rockville, MD, 1990;pp 471472. 3. Fairing, J. D.; Short, F. R.Anal. Chem. 1956.28.11827. 4. Wallin, G.R.Anal. Chem. 1950,22,616. 5. Motomizu, S.;Fu’iwara, S.; Fqjiwara, A.; Toei, K. Anal. Chem. 1982,54,392-39+ 6. Tarmchi. S.: Goto.’K.Talnntu 1980.27.289-291. 7. Hikchi; K:;Shimoishi, Y.;MiyaG, H.; Toei, K.; Hayarmi, T. Analvst 1980. 106. 768-763. 8. Ta “chi, S.;K d a r a , Y.; Fukushima, Y.; Goto, K. Talantu 1 9 K 28,616418. 9. Tavernier, S . M. F.; Gubels, R. Tulantu 1981,28,221-224. 10. Shinozuka, N.;Suzuki, H.; Hayano, S. Bunseki Kagaku 1972,21, 517321.
Journal of Pharmaceutical Sciences / 361 Vol. 81, No. 4, April 1992
SHAH'
Received March 14, 1990, from Product Develo. ment, R. P. Scherer North America, 2725 Scherer Drive North, St. Petersburg, FL 33716.
Accepted for pubfcatlon June 20, 1991.
Abatrncl 0 A rapid and simple high-performance liquid chromatographic (HPLC) method for the analysis of docusate sodium in soft gelatin capsules was developed with progesterone as the internal standard. The method requires a reversed-phase column and a pairedion technique to separate docusate sodium from other components. A CZ column was used with a mobile phase of acetonitri1e:water (70:30) contaming 0.005 M tetrabutylammoniumphosphate. The flow rate was 1.8 mUmin, and the effluent was monitored at 214 nm. Docusate sodlum and progesterone had retention times of 4.5 and 6.8 min, respectively. The proposed HPLC method is linear, accurate, and precise. A mean assay value of 99.6% was obtained by the proposed method when five samples, each containing a composite of 10 capsules, were analyzed. The results obtained by the proposed HPLC, tetra-mbutylammonium iodide titration, and USP XXll HPLC methods are compared.
Docusate sodium [sodium 1,I-bis(2-ethylhexyl) sulfosuccinate; see structure] is a wetting agent that is uaed mainly as a stool softener. The agent is available in soft gelatin capsule formulation for internal use. Docusate sodium capsules can be assayed by titration with tetra-n-butylammonium iodide, with bromophenol blue as an indicator, in the presence of chloroform; this method was the official method in United States Pharmacopeia (USP) XX.1 Recently, USP XXIP updated the assay procedure to a high-performance liquid chromatographic (HPLC) method. Unfortunately, the methods of standard preparation and assay preparation in the official method are somewhat tedious in that they involve chloroform extraction and drying. Docusate sodium can also be analyzed by colorimetric,g-8 turbidimetric,S and polarographic analysis.10 The objective of this investigation was to devise a simpler and more expedient procedure by applying a reversed-phase, paired-ion HPLC analysis of docusate sodium to soft gelatin capsule formulations. The results obtained from this HPLC procedure were compared with those obtained from the official USP procedure and the tetra-n-butylammonium iodide titration method.
received. Docusate sodium reference standard (USP) was used after the water content was determined by Karl Fiacher titration. Instrumentation-A liquid chromatograph (model 344; Beckman Instruments, Berkeley, CAI equipped with single piston pump (model 112; Beckman Instruments) waa operated in the isocratic mode. A 2 0 4 , loop injector (model 210; Beckman Instruments), variable wavelength detector (model 165; Beckman Instruments), electronic data printer-plotter (model 3353; Hewlett-Packard, Palo Alto, CA), and a microparticulate reversed-phase column (4.6 mm x 30 cm) consisting of 10-pmparticles with a pore diameter of 100 A (Chromegabond C-22, ES Industries, Marlton, NJ)were used throughout. The HPLC detector was operated at a wavelength of 214 nm. Mobile Phase-The mobile phase was prepared by adding tetrabutylammonium phosphate (Pic Reagent A: Waters Associates, Milford, MA) to a mixture of 300 mL of water and 700 mL of acetonitrile to yield a final salt concentration of 0.005 M. Internal Standard Solution-A stock solution of progesterone (2 mg/mL) was prepared in methanol. Standard Solution-Docusate sodium (100 mg) was placed in a
a
b
P
6
Experimental Section Chemicals and Reagents-Acetonitrile, water, and methanol (Fisher Scientific Company, Fair Lawn, NJ) were WLC quality. Progesterone (Sigma Chemical Company, St. Louis, MO)was used as
C2Hs
I
CH~-COOCH~-CH-(CH,),-CH, I
NaO,S-CH-COO CH2-CH-(CH2),-CH,
3
I C2Hs
Docusate Sodium
OO22-3S9/9YO4OOa59$02.50/0 0 1992, American Pharmaceutical Association
6
9
Mmns Figure 1-Typical chromatogram of a standard solution of docusate sodium (1 mg/mL): (a) docusate sodium; (b) progesterone (internal
standard).
JOUm8l of Ph8maceutical SciencesI 359 Vol. 81, No. 4, April 1992
A
B
C
a a
a
P
B
3
6
1 111 111 11 3 3 6
u 3
0
6
Mll(rrrs
Figure 2-Typical chromatograms of a docusate sodium soft gelatin capsule containing 100 mg of docusate sodium (A), docusate sodium capsules with casanthranol, containing 100 mg of docusate sodium (B), and docusate sodium capsules With ferrous fumarate, containing 100 mg of docusate sodium (C). Key: (a) docusate sodium; (b) progesterone (internal standard). Table Mecoverler by Proposed HPLC Method Formula A.
0b
CC
Amount of Fill Material, mg 276.0 275.0 263.4 269.2 312.2 328.4 327.9 321.7 694.6 707.6 687.6 700.6
Docusate Sodium, mg
Amount of Docusate Sodium in Fill Material, mg
Added
Theory
95.5 91.5 93.5
10.80 21.60 32.40
106.3 113.1 125.9
104.3 104.1 102.1
10.80 21.60 32.40
115.1 125.7 134.5
103.2 100.3 102.2
10.80 21.60 32.40
114.0 121.9 134.6
Found 95.8 108.7 115.8 128.3 99.1 114.1 123.9 135.7 101.3 111.9 121.0 134.1
Recovery, %
102.3 102.4 101.9 99.1 98.6 100.9 101.9 99.3 99.6
a Docusate sodium (label claim: 100 mg). Docusate sodium with casanthranol (label claim: docusate sodium, 100 mg, and casanthranol, 30 mg). Docusate sodium with ferrous fumarate (label claim: docusate sodium, 100 mg, and ferrous fumarate, 150 mg).
100-mL volumetric flask. Internal standard solution (2 mL) was added to this flask and diluted to 100 mL with methanol to produce a docusate sodium concentration of 1 mg/mL and a progesterone concentration of 0.04 mg/mL. Sample Preparation-For capsules containing 100 mg of docusate sodium, 100 mg of docusate sodium and casanthranol, or 100 mg of docusate sodium and ferrous fumarate, one capeule was placed in a
360 I Journal of Pharmaceutical Sciences Vol. 81, NO. 4, April 1992
100-mL volumetric flask.Water (10 mL) was added, and the flask was heated to dissolve the gelatin. Finally, 2.0 mL of internal standard solution was added, and the mixture was diluted to 100 mL with methanol. The methanol precipitated the gelatin. The precipitates were allowed to settle, and an aliquot was filtered through a 25-mm, 0.46-pm nylon syringe filter. The same procedure was used for capsules containing 250 mg of docusate sodium, except that a 260-mL
Tabla ICAnalyslo of Docuaate Sodlum Soft Gelatln Capsules by Propored HPLC Method
Sample Number
Percentage of Labela
SD
100.4 100.6 98.4 99.3 99.5
0.82 1.03 1.75 1.16 1.56
RSD,b %
0.82 1.02 1.78 1.16 1.57
Each value represents the average of five replicate analyses of each sample containing the composite of 10 capsules; label claim, 100 mg. RSD is relative standard deviation.
Table IlCComparatlve Analysls of Docuaate Sodium by Three Assay Methods
Formulaa A
B
a
volumetric flask was used and 25 mL of water and 5 mL of internal standard solution were added. Additionally, because of possible interaction between the ferrous ion and docuaate, these samples should be injected as won as possible after preparation. The standard solution (20 FL) and prepared sample were injected into the chromatograph. Chromatographic C o n d i t i o n s T h e volumetric flow rate was 1.8 mumin, and the column was at ambient temperature. Ten replicate injections of standard solution produced a relative standard deviation of 0.72%. The resolution between the docusate sodium peak and the internal standard peak was 1.96. Calculations-Because linearity experiments indicated that the peak areas (peak heights also) were related to the concentrations of docusate sodium (range, 0.61.4mg/mL), the results were calculated by using the following relationship: R x C x D = drug concentration (mg/capsule), where R is the area ratio of sample or standard to internal standard, C is the concentration of standard solution Cmg/ mL), and D is the dilution factor (mL).
Results and Discussion Figure 1shows a typical chromatogram for docusate sodium standard. The chromatograms shown in Figures 2A-2C were obtained for docusate sodium capsules, docusate sodium with casanthranol capsules, and docusate sodium with ferrous fumarate capsules, respectively. When injected into the chromatograph, docusate sodium was eluted first, followed by progesterone (internal standard), at retention times of 4.5 and 6.8 min, respectively. The calibration curve for docusate sodium was linear (r = 0.9998) over the concentration range 0.61.4 mg/mL. The recovery data were determined by adding different amounts of reference standard to three different formulation mixes (Table I). The proposed method produced satisfactory values for recovery of docusate sodium from the placebo matrix. The system precision of the proposed method was determined by using 20 pL of each of a series of 10 standard solutions containing docusate sodium at a concentration of 1.021 mg/mL. The relative standard deviation was 0.72%. The data indicate that the precision of the described chromatographic system is satisfactory.
C
Lot 1 2 3 1 2 3 1 2 3
Percentage of Label Claimb Proposed Titration
USP MethodC
Methodd
Methodd
103.2 100.2 99.7 97.5 97.3 103.0 101.1 100.1 101.2
101.8 100.7 101.3 98.8 100.0 101.4 99.0 105.1 103.4
103.0 101.5 103.2 99.2 99.5 98.3 101 .8 104.8 103.8
a See Table I for compositions. Label claim of 100 mg. Value represents composite of 10 capsules. Value represents average of three determinations.
Application of the proposed assay to docusate sodium soft gelatin capsules provided the results given in Table 11. These data were obtained from five replicate analyses of each sample containing a composite of 10 capsules. A placebo was made for each of the three formulations of docusate sodium capsules. No interfering peaks were found when these placebos were chromatographed with the proposed procedure. Three different lots of soil gelatin capsules from each of the three formulations were assayed by the titration procedure, the recent USP HPLC procedure, and the proposed HPLC procedure (Table 111). All three methods show good correlation. However, the USP method incorporates an ion-exchange technique that involves lengthy extraction, and the titration method has an end point that is difficult to read. The HPLC procedure described is simple, rapid, and precise for the quantitation of the docusate sodium in several docusate sodium-containing products.
References and Notes 1. U.S.Pharmacopeia, 20th rev., U.S.Pharmacopeial Convention: Rockville, MD, 1980;p 262. 2. US.Pharmacopeia, 22th rev., U.S.Pharmacopeial Convention: Rockville, MD, 1990;pp 471472. 3. Fairing, J. D.; Short, F. R.Anal. Chem. 1956.28.11827. 4. Wallin, G.R.Anal. Chem. 1950,22,616. 5. Motomizu, S.;Fu’iwara, S.; Fqjiwara, A.; Toei, K. Anal. Chem. 1982,54,392-39+ 6. Tarmchi. S.: Goto.’K.Talnntu 1980.27.289-291. 7. Hikchi; K:;Shimoishi, Y.;MiyaG, H.; Toei, K.; Hayarmi, T. Analvst 1980. 106. 768-763. 8. Ta “chi, S.;K d a r a , Y.; Fukushima, Y.; Goto, K. Talantu 1 9 K 28,616418. 9. Tavernier, S . M. F.; Gubels, R. Tulantu 1981,28,221-224. 10. Shinozuka, N.;Suzuki, H.; Hayano, S. Bunseki Kagaku 1972,21, 517321.
Journal of Pharmaceutical Sciences / 361 Vol. 81, No. 4, April 1992