Polarographic analysis for corticosteroids

Analytica Chimica Acta, 108 (1979) 389-393 o EIsevier Scientific Publishing Company, Amsterdam -

Printed in The Netherlands

Short Communication POL~O~~~HIC ANALYSIS FOR CORTICOSTEROIDS Part 2. Determination of Corticosteroids in Single-component Solutions, Suspensions, Ointments and Creams H . S, de BOER, P. H. LANSAAT

and W. J. van OORT*

Deportment of Analytical Pharmacy, Faculty of Pharmacy, State University of Utrecht. Catharijnesingel 60. 3511 GH Utrecht (The Netherlands)

(Received 1 lth December 1978)

Summary. Differential pulse polarographic methods are presented for corticosteroids in singlecomponent pharmaceutical preparations. Adaptation of the supporting electrolyte to the lipopbiicity of the preparation and standard addition methods give fast and reliable procedures_ Standard deviations are about 1% for aqueous and alcoholic for creams, suspensions and ointments.

solutions and about 2%

The electro-analyticalproperties of corticosteroids were described in Part 1 of this series [ 11. This Part deals with the differential pulse polarographic (d.p.p.) determination of corticosteroids in single-component preparationsof different lipophilieity. Direct current and d.p.p. methods have been reported for severalcorticosteroids in ointments and creams [ 2-51. Chatten et al. [ 61 mentioned the determination of certain A4-3 ketosteroids in some parenteral formulations by d-p-p., and h.p.1.c. has been applied 171 to the determination of triamcinolone acetonide in creams and suspensions. All these polarographic methods made use of calibration curves and supporting electrolytes which were mainly aqueous. Therefore, time-consuming clean-up procedures were needed or the excipients of the pharmaceuticalpreparationhad to be added to the calibration solutions; the latter procedure cannot be applied to formuIations of unknown content. Most h.p.1.c. methods also need an extended cleanup procedure. The h.p.1.c. method of Upton et al. [S] for steroid phosphates does not need a preliminaryclean-up, but is applicable only to water-soluble phosphate esters. In order to avoid these difficulties standardaddition methods were applied here and the lipophilicity of the polarographicsolvents was adapted to the lipophilicity of the formulations. D.p.p. offers the sensitivity required for this procedure. Experimental Apparatus. Three polarographswere used: a PAR model 174 polarograph

and a Brucker E310 modular electrochemical system, both of which were equipped with a drop timer and a Houston model 2200-3-3 X-Y recorder, and

a Metrohm Polarecord EF06 equipped with a polarographic stand E505. A water-jacketed lo-ml pal-dographic cell (Metrohm EA880-T-5) was empioyed with a dropping mercury electrode, a Metrohm EA432 Ag/AgCl reference electrode and a platinum wire auxiliary electrode. The cell was maintained at 20 f 0.2”C. The “salt bridge” of the reference electrode was filled with the supporting electrolyte. A piston microburette (Metrohm E457) was used for standard additions. Chemicals. The steroid preparations used are listed, with their sources in Table 1. The solvents and mater%& for the supporting electrolytes were: methanol (Nanograde, Mallinckrodt); methanol (zur Analyse), dimethylformamide (DMF; Uvasol), tetramethylammonium hydroxide (TMAH; 10% zur Polarographie), acetic acid (99% reinst), phosphoric acid (99% rein&) (Merck); boric acid (Baker) and Dowex l-X2 strongly basic anion exchanger (50-100 mesh, chloride; Fluka) All reagents were used without further purification. Procedures. Because of the variety of dosage forms of corticosteroids, three solvents were used with different lipophilic properties: a (1 + 1) mixture of Britton-Robinson buffer pH 10 and methanol, 0.03 M TMAH in methanol, and 0.02 M TMAH in (87 f 13) DMF-water. A d-p-p. curve of 10 ml of the supporting electrolyte (solvent) was recorded after deaeration with oxygen-free nitrogen [ 9 J for 15 min. Then, a suitable amount of the sample was added, to obtain a concentration between 10m3 and lo-’ M steroid in the polarographic cell. After deaeration for 1 min the polarogram was recorded. A small volume of the standard solution containing about the same amount of steroid was then added and the polarogram was recorded again. Deaeration for 1 min was sufficient. Dilution by addition of the standard should not exceed 1%. Standard solutions of the steroids were prepared in methanol or DMF depending on the supporting electrolyte used. The normal scan parameters +vere: drop time 2 s, scan rate 2 mV s-l, modulation amplitude 100 mV. Results and discussion Aqueous solutions. In general, the sample containing ionic steroid esters was added directly to the blank solution consisting of Britton-Robinson buffer pH 10 in 50% (v/v) methanol. The results are listed in Table 1. When 0.03 M TMAH in methanol was used as solvent, the average values were similar, but the standard deviation increased about five times. Some injections contain nonionic compounds which increase t% base line, such as non-ionic polar viscosityincreasing compounds (e.g., to improve the solubility of the corticosteroidalcohol which appears after slow hydrolysis of the corticosteroid ester) or decomposition products of preservatives (e.g., benzaldehyde from oxidation of benzyl alcohol)_ The results then obtained are too high when the normal base line is used for calculation. A base line corrected for this interference can he obtained by addition of some anion exchanger (500 mg of Dowex 1) to the supporting electrolyte after addition of sample and standard solution: the ionic

391 TABLE

1

ResuIts of assay of the dosage forms and standard deviations based on 5 determinations with separate sampling Name

Source

Active constituent

Glaxo

Betamethasone disodium phosphate= Dexamethasone-21phosphate= (as disodium phosphate) Dexamethasone disodium phosphate= Dexamethasone disodium phosphate= Betamethasone (as disodium phosphate)

Aqueous solutions Betnesol drops for eye, ear or nose Decadron-4 injection

MSD

Oradexon

Organon

injection

Dexamethasone disodium Organon phosphate Schering Celestone injection Alcoholic solution Celestoderm-V akohol Solution in wegetable oil Neo-Hombreol Solution in oleic acid Testosterone undecanoate in oleic acid Suspensions Albicort-10 Hydro-Adreson Cream Betnelan-V Ointments Betnelan-V

ointment

Celestoderm-V

ointment

Content (mg ml-’ )

Found (mg ml-’ )

R.s.d. (%)

1

1.00

0.5

4

4.04

0.8

5

5.02

1.1

20

20.2

1.3

4

4.03

1.2

lb

1.09b

1.4

Schering

Betamethasone (as l7-valerate) d

Organon

Testosterone

propionate=

Organon

Testosterone

undecanoatea167

Labaz Organon

Triamcinolone acetonidea Hydrocortisone acetateC

Glaxo

Betamethasone (as 17-valerate)=

lb

l.OOb

2.2

Glaxo

Betamethasone (as 17-valerate)a Betametbasone (as 17-valerate)d

lb

1.03u

2.5

lb

0.94b

3.2

Schering

=Obtained in pure form from the manufacturer bContent in mg g-r _ =Obtained in pure form from Nogepha. dObtaiued in pure form from Glaxo

50

50.49 175

10 25

10.1 24.9

1.0 1.3

2.1 2.7

cited.

corticosteroid ester is bound completely during the lo-min mixing time. Line (d) in Fig. 1A represents the “base line” obtained, which was used for calculation of the content. Addition of anion exchanger to a normal blank solution did not influence the normal base line (a), whereas addition to a standard solution gave a “base line” (d) which coincided with base line (a). Alcoholic solutions. The samples were added directly to the blank solution consisting of 0.03 M TMAH in methanol.

392

8

1

I , 16011~

d I - 1.4

Q

I -1.6

I -l.%V

I

I

i

-L.4

-1.6

-1.8

-210

v

Fig. 1. Differential pulse poiarograms for (A) Oradexon injection with methanolic BrittonRobinson buffer pH 10 and (B) Aibicort 10 suspension with methanolic 0.03 M TMAH. (a) Blank solution; (b) blank solution + sample addition; (c) blank solution + sample f standard addition; (d) bIank solution + sample + standard addition + Dowex. The final wave of triamcinolone (broken line in B) is overlapped by a sodium peak from NaCi and/or buffer in the sample.

Solution in vegetable oil A suitable amount of the sample, diluted to 5.00 ml with toluene, was added to the blank solution consisting of 0.02 M TMAH in DMF (87% v/v), The oil was only partly miscible with the blank solution, but the steroid remained dissolved, obviously because of the large partition coefficient and the favourable phase-volume ratio (actually testosterone is a A4 -3 ketosteroid, not a corticosteroid). Suspensions_ The suspensions consisted of a dispersed system of lipophilic steroid esters in water After the suspension had been shaken thoroughly, a suitable amount was added directly to the blank solution consisting of O-03 M TMAH in methanol_ The active compounds dissolved in this medium quickly and completely (Fig. lB)_ The standard deviations were relatively high, probably because of the less reproducible sampling from the suspension_ Cream. The cream analyzed is an oil-in-water emulsion in which the steroid ester is dispersed. A suitable amount of the cream disintegrated on adding 5.0 mf of methanol and the active compound dissolved completely. An aliquot was pipetted into the blank solution consisting of 0.03 M TMAH in methanol_ The emulsifying agent lost its properties in this non-aqueous medium, and there was no interference. A standard quantity of pure betamethasone-l7valerate was added to an amount of cream to determine the yield of the cleanup procedure. The recovery was 100%.

393

I -1.6

I -I .0

I -2.ov

Fig. 2. Differential pulse polarogram of Betnelan-V ointment with O-02 M TMAH in DMF (87% v/v). (a) Blank solution; (b) blank solution + sample addition; (c) blank solution + sample + standard addition.

Ointments. A suitable amount of ointment was dissolved completely in 5.00 ml of toluene. An aliquot was added to the blank solution, consisting of 0.02 M TMAH in DMF (87% v/v). The fatty constituents did not dissolve in the blank solution whereas the active compound remained dissolved (Fig. 2). Testosterone undecanoate in oleic acid. In this preparation the steroid is dissolved in oleic acid, not in a vegetable oil. It appeared to be better to use 0.03 M TMAH in methanol as supporting electrolyte rather than the 0.02 M TMAH in DMF (87% v/v) preferred for the vegetable oil preparation. A suitable amount of the sample was added directly to the blank solution_ Oleic acid is miscible with methanol. The authors thank Organon International B-V., Oss, The Netherlands, for kindly supplying some of the examined preparations, Dr. H. Hindriks and Mr. J. van Gorp (Organon) for helpful discussions, and Mr. K. R. Kooistra for experimental assistance. REFERENCES 1 H. S. de Boer, J. den Hartigh, H.H.J.L. Ploegmakers and W. J. van Oort, Anal. Chim. Acta, 102 (1978) 141_ 2 P. Gantes and J. P. Juhasz, Ann. Pharm. Fr., 24 (1966) 687. 3 M. J. Haesman and A. J. Wood, J. Pharm. Pharmacol., 23 (1971) 1765. 4 D. Cantin, J. Alar-y and A_ Coeur, J. Pharm. Belg., 32 (1977) 255. 5 E. Jacobsen and B. Korvald, Anal. Chim. Acta, 99 (1978) 255. 6 L. G. Chatten, R. N. Yadav and D. K_ Madan, Pharm. Acta Helv., 51 (1976) 381. 7 G. Gordon and P. R. Wood, Analyst, 101 (1976) 876. 8 L. N. Upton, E. R. Townley and F. D. Sancilio, J. Pharm. Sci., 67 (1978) 913. 9 L. Meites,Polarographic Techniques,2nd edn., Interscience, New York, 1964, p. 87.