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1349

ANALYST, OCTOBER 1990, VOL. 115

Simultaneous Determination of Some Active Ingredients in Cough Cold Syrups by Gas - Liquid Chromatography 9

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Oi-Wah Lau and Yiu-Ming Cheung Department of Chemistry, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong

A simple, efficient and accurate gas - liquid chromatography (GLC) method for the simultaneous determination of eight active ingredients in cough - cold syrups has been developed. The active ingredients under study were bromhexine, chlorpheniramine, codeine, dextromethorphan, diphenhydramine, ephedrine/psuedoephedrine, guaiphenesin and papaverine. Before injection, the active ingredients were first separated, from the excipients present in the cough - cold syrups, with chloroform, from alkaline medium. They were then separated by GLC on a glass column (5 ft x 2 m m i.d.) packed with 3% of OV-25 supported on Supelcoport (80-100 mesh). The column temperature was maintained at 170 "C for 1 min, then programmed to 265°C at a rate of 10°C min-1, and maintained at this temperature for 10 and 1 min, respectively, for samples with and without papaverine. The flow-rate of the nitrogen carrier gas was 30 ml min-1. A flame-ionisation detector was used for detection, and clomipramine hydrochloride was used as the internal standard. The recoveries of the drugs ranged from 96.0 to 99.7%, and the relative standard deviations for ten replicate determinations ranged from 0.49 to 4.7%. Results are reported for nine commercially available cough - cold syrups.

Keywords: Simultaneous determination of drugs; cough - cold syrup; gas - liquid chromatography; solvent extraction

Bromhexine, chlorpheniramine, codeine, dextromethorphan, diphenhydramine , ephedrine, guaiphenesin, papaverine and pseudoephedrine are active ingredients commonly found in cough - cold syrups.1.2 High-performance liquid chromatography (HPLC)3-6 is commonly used for the determination of the active ingredients in cough - cold mixtures. Derivative spectrophotometric methods'-9 and gas - liquid chromatography (GLC) meth0ds4~5~10 have also been developed for the analysis of these drugs; however, only two or three components could be determined simultaneously by most of these methods. This paper describes a simple and efficient GLC method for the determination of eight of the active ingredients mentioned above (ephedrine and pseudoephedrine, being stereoisomers, have similar properties and are not found together in cough cold syrups), individually or together, in various cough - cold syrup formulations after extraction of the active ingredients into chloroform. The optimum conditions for carrying out the extraction and for the determinations were established. Nine cough - cold syrups were analysed for the contents of the active ingredients, and the results were compared with those obtained by using HPLC.3

chromatograph and varied in the data processor (8-10, depending on the injection concentration). The chart speed of the data processor was 2.5 mm min-1. The column was kept at 50 "C and at a nitrogen flow-rate of 30 ml min-1 when not in use. When broadening of the peaks was observed, the first few inches of the packing material near the injection port were replaced, and the column could then be used for ca. 6 months. Reagents

All the drugs used were of Pharmacopoeia1 or equivalent purity, and were used without further purification. All other reagents were of analytical-reagent grade. Aqueous internal standard solution Prepared by dissolving exactly 0.0751 g of clomipramine hydrochloride in 50 ml of distilled water in a calibrated flask.

Apparatus The gas chromatograms were recorded with a Varian Model 3700 gas chromatograph , equipped with a flame-ionisation detector and attached to a Hitachi 833A data processor.

Aqueous stock solutions of the drugs A stock solution of bromhexine hydrochloride (2.50 mg ml-1) was prepared by weighing exactly 125.00 mg of the compound into 50 ml of sulphuric acid (0.1 M) in a calibrated flask. Similarly, stock solutions of chlorpheniramine maleate (1.02 mg ml-I), codeine phosphate (5.00 mg ml-I), dextromethorphan hydrobromide (3.12 mg ml-I), diphenhydramine hydrochloride (5.00 mg ml-I), ephedrine hydrochloride (5.00 mg ml-I), guaiphenesin (15.63 mg ml-I), papaverine hydrochloride (1.25 mg ml-1) and pseudoephedrine hydrochloride (6.24 mg ml-1) were prepared by dissolving appropriate amounts of the respective drugs in 50 ml of sulphuric acid (0.1 M) in calibrated flasks.

Chromatographic conditions A glass column (5 ft x 2 mm i.d.) was packed with 3% of OV-25 on Supelcoport (80-100 mesh). The flow-rate of the nitrogen carrier gas was 30 ml min-1. The flow-rates for hydrogen and air were 30 and 300 ml min-1, respectively. The injection port and detector temperatures were both kept at 270 "C. The initial column temperature was kept at 170 "C for 1 min, then programmed to a final temperature of 265 "C at a heating rate of 10°C min-1, and then maintained at this temperature for 10 and 1 min, respectively, for samples with and without papaverine. The attenuation was set at 1in the gas

Aqueous standard solutions Various mixtures of drugs were prepared by mixing appropriate amounts of stock solutions of these drugs to match the active ingredients and their respective label values for each syrup. For example, for sample 4 (in Table 7), containing codeine phosphate (9.0 mg in 5 ml) and ephedrine hydrochloride (7.2 mg in 5 ml), a mixture was prepared by mixing accurately 10 ml each of the codeine phosphate and ephedrine hydrochloride stock solutions and diluting to 25 ml in a calibrated flask with 0.1 M sulphuric acid, the resulting concentrations for both drugs in this mixture being 10.0 mg in

Experimental Instrumentation

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ANALYST, OCTOBER 1990, VOL. 115

5 ml. Other mixtures with different compositions were prepared in a similar manner.

Sample he-treatment

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No sample pre-treatment was necessary, except for samples 7-9 (Table 7) containing high concentrations of the drugs, and they were diluted 5-fold with 0.1 M sulphuric acid.

Extraction Method A 10-ml portion of the cough - cold syrup or aqueous standard solution was pipetted into a 100-ml separating funnel containing 10 ml of 25% v/v ammonia solution (AnalaR grade, Merck). The drugs were then extracted three times with 15-ml aliquots of chloroform. The organic layers were transferred into another separating funnel and washed with 5-6 ml of distilled water. The chloroform layer was then dried with anhydrous sodium sulphate for ca. 5 min, and filtered. The sodium sulphate was washed with small volumes of chloroform, and the washings were added to the filtrate, which was then diluted to 50 ml with chloroform in a calibrated flask.

Preparation of Working Internal Standard Solution An aliquot (10 ml) of the aqueous internal standard solution was treated as for the cough - cold syrups.

Simultaneous Determination of Active Ingredients in Cough Cold Syrup An aliquot (5 ml) of the sample solution and several aliquots (2-10 ml) of the standard solution, after the extraction procedure described above, were evaporated to dryness under a stream of nitrogen on a water-bath at room temperature. Each residue was dissolved in 1 ml of the working internal standard solution, 3 pl of which were injected into the chromatograph with a 10-yl Hamilton syringe under the chromatographic conditions described above. The injections were performed in duplicate. The calibration graph was obtained by plotting the peakarea ratios (drug to internal standard) against the concentrations of the drug. The amount of each drug in the sample was deduced from the respective calibration graph.

Table 1. Peak-area ratios (individual drug to internal standard) after extraction with various solvents*

Peak-area ratios of the drugs in the mixture? Extraction medium 1 2 3 4 5 Chloroform . . . . 3.405 4.332 0.4452 2.777 3.823 Dichloromethane . . 2.787 3.807 0.3307 2.421 3.791 Diethylether . . . . 2.694 1.548 0.2285 2.229 2.870 Hexane . . . . . . 1.005 ND$ 0.3543 2.277 0.7384 3.436 4.724 0.4308 2.850 4.234 10% MeOH in CHC13 * Chromatogaphic conditions as described under Experimental. t The drugs in the mixture, with concentration in the organic solvent in parentheses: (1) ephedrine hydrochloride (1.54 mg ml- l); (2) guaiphenesin (3.04 mg ml-I); (3) chlorpheniramine maleate (0.47 mg ml-1); (4) dextromethorphan hydrobromide (1.32 mg ml-*); and (5) codeine phosphate (2.28 mg ml-I). $ N o guaiphenesin signal was detected.

Results and Discussion In addition to active ingredients, most cough - cold mixtures contain dye(s), preservative(s), flavour(s) and a sweetening agent, making determination of the active ingredients difficult. Hence, HPLC has been commonly used for the analysis of cough - cold mixtures. However, it is worthwhile developing GLC methods as alternatives as gas chromatographs are common items of equipment in most laboratories and the running cost is also cheaper. The key to the success of GLC methods for the analysis of cough - cold mixtures is to develop an efficient extraction procedure capable of separating the active ingredients from the various excipients, and to choose a stationary phase that can resolve a large number of active ingredients in the mixtures.

Choice of Extraction Medium The drugs under study are reported to be extracted by organic solvents from alkaline media. 11,12 Therefore, the aqueous solutions of the drugs were first made alkaline with 25% v/v ammonia solution before extraction. Several common organic solvents, including chloroform, dichloromethane, diethyl ether and hexane, were assessed for their suitability as the extraction medium. A solution (10 ml) containing known amounts of chlorpheniramine maleate, codeine phosphate, dextromethorphan hydrobromide, ephedrine hydrochloride and guaiphenesin was prepared and 2-ml aliquots were extracted once with 20 ml of each solvent, and 10 ml of the organic layer were pipetted out and filtered after being dried with anhydrous sodium sulphate. The filtrate was evaporated to dryness under nitrogen, the residue was dissolved in 1 ml of the working internal standard solution, then 3.0 p1 of the final solution were injected into the chromatograph. The peak-area ratios (drug to internal standard) for various organic solvents are shown in Table 1.

Table 2. Percentage extraction of each drug under study from aqueous solution (10 ml) into chloroform (3 X 15 ml). Each determination was carried out in duplicate

Concentration in aqueous Drug solutiodmg ml-1 Extraction, YO 99.2 Bromhexine hydrochloride .. 0.55 97.4 Chlorpheniraminemaleate . . . . 1.03 1.15 95.3 Codeinephosphate . . . . . . Dextromethorphan hydrobromide 1.03 loo. 1 Diphenhydramine hydrochloride 2.01 97.1 Ephedrine hydrochloride . . . . 3.00 95.1 Guaiphenesin . . . . . . . . 1.35 90.3 0.76 Papaverine hydrochloride . . . . 99.3 3.00 99.0 Pseudoephedrine hydrochloride . . Table 3. Retention times and peak shapes of the drugs under study in a column (5 ft x 2 mm i.d.) packed with 3% of OV-25 on Supelcoport (80-100 mesh) under the optimised conditions

Retention Drug time/min Peak shape Ephedrine hydrochloride* 1.04 Sharp Pseudoephedrine hydrochloride} 3.67 Guaiphenesin . . . . . . . . Sharp with tailing Sharp 4.88 Diphenhydramine hydrochloride 6.22 Sharp Chlorpheniraminemaleate . . . . 7.49 Sharp Dextromethorphan hydrobromide 9.37 Sharp .. Bromhexine hydrochloride 10.84 Sharp Codeinephosphate . . . . . . 19.14 Sharp Papaverine hydrochloride . . . . * Ephedrine hydrochloride and pseudoephedrine hydrochloride had the same retention time.

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ANALYST, OCTOBER 1990, VOL. 115

As the peak-area ratios so obtained were directly proportional to the amounts of drugs extracted from the aqueous into the organic phase, these ratios were used to compare the extraction capability of each solvent. The results shown in Table 1 indicate that chloroform should be the best extraction medium and hexane the poorest. The extraction capability of chloroform was enhanced by the addition of 10% v/v of methanol. Unfortunately, this mixed solvent also extracted the dyes in authentic samples. Hence, chloroform was chosen as the extraction medium for all subsequent determinations. The percentage extraction of each drug under study from an aqueous solution into chloroform by using the procedure described under Experimental was deduced from its concentration in chloroform as determined by ultraviolet spectrophotometry. The results are shown in Table 2.

Choice of Stationary Phase

As it was intended to resolve a large number of drugs by the proposed method, the proper choice of stationary phase was also important. A number of stationary phases on Supelcoport (80-100 mesh) commonly used for the separation of nonvolatile compounds, including OV-1, OV-17, OV-25 and OV-225 (3% of each), were assessed. The flow-rate of nitrogen was set at 30 ml min-1, a flow-rate commonly used for the determination of drugs. The optimum temperature programming conditions for separating the drugs under study were found for each column. In terms of good peak shapes and resolution and over-all running time, the column packed with 3% of OV-25 was found to be the most satisfactory. The retention times and peak shapes of the drugs under the optimised conditions for this column are listed in Table 3, and a typical chromatogram is shown in Fig. 1. Note that ephedrine is shown, but pseudoephedrine is not, as these two compounds are stereoisomers and have the same peak shape and retention time. They have similar properties and are not found together in cough - cold mixtures.

D

t

-

F

c m

.-0

tn

E B

E

I

0

I

8 16 Tirne/rnin

Fig. 1. Gas chromatogram of the drugs under the optimised conditions. A, Solvent; B, ephedrine hydrochloride (0.87 mg ml-1); C. guaiphenesin (1.54 mg ml-1); D, diphenhydramine hydrochloride (1.09 mg ml-I); E, chlorpheniramine maleate (0.90 mg ml-l); F, dextromethorphan hydrobromide (1 .OO mg ml-I); G , bromhexine hydrochloride (0.77 mg ml-1); H, clomipramine hydrochloride (0.30 mg ml-l); I, codeine phosphate (0.91 mg ml-I); and J, papaverine hydrochloride (0.47 mg ml-l)

I

0

I

8 16 Ti rne/rnin

Fig. 2. Chromatogram of sample No. 1. A , Ephedrine hydrochloride; B, diphenhydramine hydrochloride; C, bromhexine hydrochloride; D, clomipramine hydrochloride; E, codeine phosphate; and F, papaverine hydrochloride

Table 4. Data for quantitative gas chromatography of the drugs under study

Detectable Working Correlation amount per range/mg ml- l Regression equation* coefficient injectiont/pg Drug y = 2 . 6 6 ~- 0.03312 ( n = 8) 0.99992 0.18 .. .. .. 0.06-0.90 Bromhexine hydrochloride 0.18 y = 2.654~- 0.1076 ( n = 8) 0.99976 0.06-0.90 Chlorpheniraminemaleate . . .. . . 0.99991 0.30 0.10-1.54 y = 2.810~- 0.1312 ( n = 8) Codeine phosphate . . . . . . . . . . 0.99995 0.60 0.20-1.52 y = 3.474~- 0.3337 ( n = 7) Dextromethorphan hydrobromide .. . . 0.60 y = 4.316~- 0.3963 ( n = 7) 0.99997 Diphenhydramine hydrochloride .. .. 0.20-1.58 1.20 y = 3.098~- 1.172 ( n = 6) 0.99992 Ephedrine hydrochloride . . . . . . , . 0.40-1.54 1.10 y = 2.91 IX - 0.6736 (n = 8) 0.99986 0.35-5.38 Guaiphenesin . . . . . . . . . . . 0.10 y = 3.223~- 0.04843 ( n = 8) 0.99986 Papaverine hydrochloride . . . . . . , . 0.03-0.48 0.99994 1.50 0.50-1.87 y = 2.790~- 0.8799 ( n = 6) Pseudoephedrine hydrochloride . . .. * y = peak-area ratio (drug to internal standard); x = concentration of drug (mg ml-1); n = number of experimentally determined values of X; and each determination was carried out in duplicate. t The lowest possible amount of drug per injection to give a detectable signal.

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Quantitative GLC of the Drugs

Recovery Tests and Precision

Quantitative studies of the drugs were made as described under Experimental. Results were calculated from the linear regression of the standards, relating the peak-area ratios (drug to internal standard) and concentrations. The working ranges, regression equations and correlation coefficients, together with the detectable amount per injection of each drug, are shown in Table 4.

Recovery tests were performed by adding a known amount of each drug to a cough - cold syrup where it was known to be absent. The mean results of four analyses ranged from 96.0 to 99.7% (Table 5 ) , and these can be considered to be good recoveries. The precision of the proposed method was checked by calculating the relative standard deviation (RSD) for ten replicate determinations of the drugs under study, and the results are shown in Table 6. The RSDs ranged from 0.49 to 4.7%.

Table 5. Results of the recovery tests for the drugs under study by using the proposed method. Each result was the mean of four determinations

Drug Bromhexine hydrochloride .. Chlorpheniramine maleate .. Codeinephosphate . . . . . . Dextromethorphan hydrobromide Diphenhydramine hydrochloride Ephedrine hydrochloride . . . . Guaiphenesin . . . . . . . . Papaverine hydrochloride .. Pseudoephedrine hydrochloride * RSD in parentheses.

..

.. ..

.. .. .. ..

.. ..

Amount added/mg per 5 ml 3.02 3.01 5.02 5.08 5.25 5.04 17.9 1.68 6.24

Recovery,* % 96.2 (0.6) 97.9(1.2) 99.7 (1.2) 96.0 (0.5) 98.8(1.1) 97.8 (0.9) 98.1 (1.3) 97.0(1.6) 97.5 (1.7)

Table 6. Precision of the results for the proposed method Drug Bromhexine hydrochloride . . .. Chlorpheniramine maleate .. .. Codeinephosphate . . . . . . . . Dextromethorphan hydrobromide Diphenhydramine hydrochloride Ephedrine hydrochloride . . . . Guaiphenesin . . . . . . . . . . Papaverine hydrochloride .. . . Pseudoephedrine hydrochloride .. * For ten replicate determinations.

Concentration/ mg ml-1 0.77 0.90 0.91 1.oo 1.09 0.87 1.54 0.47 1.25

RSD,* % 0.73 1.3 2.0 0.49 1.3 4.7 3.4 3.3 1.7

-

Determination of Active Ingredients in Cough Cold Syrups The contents of the drugs under study in nine commercially available cough - cold syrups were determined in triplicate by using the proposed method. The samples contained combinations of several active ingredients, which were identified by comparing the retention time of the peaks observed with those obtained from standard solutions, containing the respective active ingredients, examined under the same conditions. The results obtained were compared with those obtained by an established HPLC method3 and with the corresponding label values. The assay results for the samples studied are presented in Table 7. A typical chromatogram (for sample 1) is shown in Fig. 2, where no additional peaks arising from excipients are evident. From Table 7, it can be seen that the results obtained with the proposed method were in good agreement with those obtained by using the counter-check HPLC method and with the respective label values.

Conclusion A simple, efficient and accurate GLC method for the simultaneous determination of bromhexine, chlorpheniramine, codeine, dextromethorphan, diphenhydramine, ephedrine (or pseudoephedrine) , guaiphenesin and papaverine in the cough - cold syrups has been developed. The proposed method involved a preliminary extraction with chloroform, which has been shown to be successful in

Table 7. Assay results for the determination of various active ingredients in cough - cold syrups Percentage of label claim Label value/ Ingredients mg per 5 ml Bromhexine hydrochloride 2.5 Codeine phosphate 4.5 Diphenhydramine hydrochloride 4.5 Ephedrine hydrochloride 4.5 Papaverine hydrochloride 1.25 Chlorpheniramine maleate 2 1.o Dextromethorphan hydrobromide 5.0 Guaiphenesin 25.0 Chlorpheniramine maleate 1.0 3 Dextromethorphan hydrobromide 5.0 Guaiphenesin 25.0 4 Codeine phosphate 9.0 Ephedrine hydrochloride 7.2 Chlorpheniramine maleate 4.0 5 Chlorpheniramine maleate 6 2.0 Codeine phosphate 10.0 Ephedrine hydrochloride 5.0 7 Guaiphenesin 100.0 Guaiphenesin 100.0 8 Pseudoephedrine hydrochloride 30.0 Guaiphenesin 100.0 9 Pseudoephedrine hydrochloride 30.0 Mean of triplicate measurements; relative standard deviation in parentheses. Sample 1

*

Proposed method* 92.5 (0.2) 101.5 (0.1) 104.4 (0.4) 101.4 (1.3) 90.9 (3.8) 93.7 (2.6) 95.3 (0.3) 96.5 (1.5) 88.3 (0.8) 95.1 (0.2) 98.5 (1.3) 99.6 (0.3) 94.8 (1.0) 97.0 (0.9) 84.4 (0.7) 90.6 (3.3) 90.0 (3.3) 103.1 (1.3) 111.4(1.7) 107.8 (2.7) 97.3 (0.5) 102.3 (2.7)

HPLC method 95.2 103.8 96.2 97.1 90.4 93.0 99.4 91.6 93.0 100.6 96.4 102.8 97.9 100.8 85.5 88.5 89.0 102.5 115.3 111.9 99.4 105.6

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ANALYST, OCTOBER 1990. VOL. 115

extracting the basic drugs from the sample matrices so that interference from excipients, such as dyes, flavours and preservatives, could be minimised. The time for running a chromatogram for the syrups was 10 min o r less when papaverine was absent, and ca. 20 min when the latter drug was present. The method has been applied successfully and conveniently to the determination of the drugs mentioned above, individually o r together, in nine commercial cough cold syrups. The method is also suitable as a stabilityindicating assay. The authors thank C. S. Mok of the Government Laboratory for helpful discussions.

References 1. “The Pharmaceutical Codex,” Eleventh Edition, The Pharmaceutical Press. London, 1979, pp. 112, 182, 215, 258, 299, 326. 400. 637 and 761. 2. Reynolds, J. E. F., Editor, “Martindale, The Extra Pharmacopoeia,” Twenty-ninth Edition, The Pharmaceutical Press, London, 1989, pp. 906,448,1298,908,452,1462,910,1598and 1478.

1353 3. Lau, 0. W., Chan, K., Lau, Y. K., and Wong, W. C., J. fharm. Biomed. Anal., 1989, 7 , 725, and references cited therein. 4. Rao, E. V., Rao, G . R., Raghuveer, S . , and Khadgapathi, P., Analyst, 1987, 112, 871. 5. Gibbs, V., and Zaide, Z., J. Pharm. Sci., 1984. 73, 1248. 6. Carnevale, L., J. Pharm. Sci., 1983, 7 2 , 196. 7. Leung, C.-P.. and Law, C.-K., Analyst, 1989, 114.241. 8. Murtha, J. L., Julian, T. N., and Radebaugh, G . W., J . fharm. Sci., 1988, 77, 715. 9. Hoover, J. M., Soltero, R. A., and Bansal, P. C., J. fharm. Sci., 1987, 76, 242. 10. Bambagiotti-Alberti, M., Pinzauti, S . . and Vincieri, F. F., Pharm. Acta Helv., 1987,62,175; Anal. Abstr., 1987,49,8E51. 1 1 . Clarke, E. G. C., Editor, “Isolation and Identification of Drugs,” Volume 1, The Pharmaceutical Press, London, 1974, pp. 255, 268, 289, 315, 327,464 and 525. 12. Clarke, E. G . C., Editor, “Isolation and Identification of Drugs,” Volume 2, The Pharmaceutical Press, London, 1975, p. 1011.

Paper Of014256 Received April 2nd, 1990 Accepted May 30th, 1990

Simultaneous determination of some active ingredients in cough-cold syrups by gas-liquid chromatography.

A simple, efficient and accurate gas-liquid chromatography (GLC) method for the simultaneous determination of eight active ingredients in cough-cold s...
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