Microdetermination of cinchona alkaloids by atomic absorption spectroscopy

Specrrochimica Acm. Vol. Printed in Great Bntain

40B.No.9.

pp. 1205-1209.

1985. 6

0X+8547/85 53.00 + .OO 1985. Pergsmon PITSLtd.

Microdetermieation of cinchona alkaloids by atomic absorption spectroscopy MAGDAM. AYAD,S. E. KHAYYAL’and N. M. FARRAG Faculty of Pharmacy, Zagazig University, Egypt (Received 30 August 1984; infinal form 1 March 1985) Abstract-A sensitive and rapid microdetermination method has been developed for the determination ofcinchona alkaloids via their mercury complex. Different parameters of the procedure have been thoroughly studied. The percentage recoveries for quinine, quinidine, cinchonine and cinchonidine were found to be 98.97kO.62, 99.06 f 0.62,98.90 f 0.74, respectively. The results obtained are favourably compared to the official ones. The method is characterised by its specificity, accuracy and good precision.

of which quinine is perhaps the most important, occur in the bark of trees or shrubs of various species of two Rubiaceous genera, Cinchona and Remijia. The cinchona alkaloids of known structure are quinoline derivatives and constitute four pairs of stereoisomerides. The major alkaloids fall into two configurational and polarimetric groups. The dextrorotatory species constitute cinchonine, quinidine and their dihydroderivatives while cinchonidine and quinine are levorotatory in nature [ 11. Therapeutically the most important are quinine and quinidine, the first having had popular usage in the relief of myalgia, neuralgia, headache and as an antipyretic [2]. Several methods have been described for the determination of these alkaloids either in crude drug composites, in body fluids or in pharmaceutical formulations. Chromatographic and electrochromatographic techniques have played an important role in facilitating the detection and quantitation of these compounds. Techniques have included TLC [3,4], GLC [5], HPLC [6-8-J, ca t ion exchange paper chromatography [9] and reversed phase ion pair chromatography [lo]. The alkaloids have been determined by gravimetry [ll, 123, spectrophotometry [13-l 51, spectrofluorimetry [ 163 and differential pulse polarography THE ALKALOIDS,

PA.

This paper reports a new approach for the application of Atomic Absorption Spectroscopy (A.A.S.) in drug analysis, however this technique is successfully used for microdetermination *National Organisation for Drug Research and Control, Cairo, Egypt.

[ 1] R. H. R. MANSKE and H. L. HOLMES, The Alkaloids Chemistry and Physiology, Vol. III, Academic Press, New York (1953). [2] K. C. JOHNand C. JELLEFF, The Pharmacologic Principles of Medical Practice, 5th Edn, Williams BrWilkins, Baltimore (1961). [3] U. HEZEL,GIT Fachz. Lab. 21, 694, 699 and 704 (1977). [4] C. BEAUBAT, B. RESIBOIS, C. LESENNE and I. BERTAND, Sci. Techn. Pharm. 6.93 (1977). [5] I. G. LEFERINK, R. A. A. MOES,I. SUNSHINE and R. B. BORNEY,J. Anal. Toxicol. 1.62 (1977). [6] P. K. NARANG and G. W. GROUTHAMEL, J. Pharm. Sci. 68, 917 (1979). [7] E. R. KATES,W. D. MCKENNON and J. T. CONSTOCK, J. Pharm. Sci. 67, 269 (1978). [8] A. F. HOBSONand W. T. E. EDWARDS, J. Chromologr. 249, 369 (1982). [9] H. SYBRISKA, Acta Pol. Phorm. 34, 187 (1977). [lo] I. H. JEURING, W. VAN DENHOWVEN,P. VANDooRNlCKand R. TENBROCKE, Z. Lebensm-Unrers.Forsch. 169, 281 (1979). [ 111 T. QUANGand J. GRUCU,loan Rev. Chim. 28, 585 (1977). [12] F. J. RODRIGUEZ GARCIA,F. R. MAYORand J. G. RIBAS BERNAT,An. Quim. 73, 1296 (1977). [13] M. MALAT,AM!. Chim. Acta 109, 191 (1979). [14] M. S. KARAWYA and M. A. DIAB,J. Phorm. Sci. 66, 1317 (1977). [15] M. A. EL SAYEDand P. S. AGARWAL, Talanta 29, 353 (1982). [16] A. OSINGAand F. A. DE WOLFF, C/in. Chim. Acta 73, 505 (1976). [17] G. SONTAGand G. KAINZ, Microchim. Acta 11, 425 (1977). 1205

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of inorganic medicinals, e.g. calcium in pharmaceutical preparations [18]. The proposed procedure is based upon the measurements of the mercury content of the precipitated mercury complex after treatment with Mayer’s reagent. EXPERIMENTAL Materials, reagents and standards

All reagents are of analytical grade. Water used is doubly distilled deionized water. Cinchona alkaloids: Quinine (Arabic-Laboratory Equipment Co., Egypt), Quinidine (pure and crystallized obtained from Prolabo, Rhone-Poulenc, France); Cinchonine (Hopkins, Williams-Chadwell Health, England); Cinchonidine (B.D.H. Chemical Ltd, Poole, England). Alkaloid solutions

1 x lo- 2 M solution of each alkaloid is prepared by dissolving the equivalent amount of the base in the least volume of dilute hydrochloric acid and diluted with water successively to contain 3.24 mg ml- 1 for quinine or quinidine and 2.94 mg ml- ’ for cinchonine or cinchonidine. Mayer’s reagent [ 191

This reagent is prepared by dissolving 1.36 g of HgC12 in 60 ml of distilled H2 0, dissolving 5 g of KI in 20 ml of distilled H20, mixing the two solutions and making up to 100 ml with distilled water. Standard solutions are prepared to contain 1-10p.p.m. of Hg’+. Also a 1 x 10e2 M solution is prepared. Apparatus

The AAS measurements were made with an atomic absorption Instrumentation Laboratory Inc., Lexington, MA 02173. Instrumental parameters for mercury were: hollow cathode. Light source: Lamp current: 3 mA. 253.7 nm. Wavelength: Slit width: 320 pm. 1 nm. Bandpass: single slot. Burner head Air-acetylene, oxidizing, blue. Flame:

spectrophotometer,

Model 457,

Procedure

The calibration graph for Hg2+ was constructed by plotting the absorbance, A, vs concentration, C. Solutions containing l-10 ppm of Hg were aspirated. For the alkaloids, transfer a l-4 ml aliquot of the alkaloid solution to a 20-ml centrifuge tube, add 6 ml of Mayer’s reagent (1 x 10e2 M). Leave to stand for 30 min, centrifuge, then decant the supernatant layer. Wash the precipitate several times with water, till free from Hg’+. Dissolve the residue in ethanol, transfer quantitatively to a lOO-ml volumetric flask and fill to volume with ethanol. Aspirate these solutions and measure the absorbance of the mercury content of the complex. From the calibration graph, deduce the mercury content and calculate the equivalent of the alkaloid, where 1 mg of Hg 2+ is equivalent to 3.42 mg of quinine or quinidine and 2.94 mg of cinchonine or cinchonidine. RESULTS ANDDISCUSSION

In this work attempts were made to use more recent and precise techniques. The alkaloids discussed here form a stable mercury complex with Mayer’s reagent. Optimum conditions for obtaining quantitative precipitation were studied. The complex formation was complete after 30 min. The equivalent mercury was determined in the resulting complex. The stoichiometry of the chelate was achieved by taking several volumes of a solution (1 x lo- ’ M) of each alkaloid and reacting it with a known slight excess of the metal solution of the same molarity. The equivalent Hg2 + was then determined. A.A.S. determination of the metal in the complex revealed that the complex had the structure ML2 where M = metal, L = alkaloid. It was [18] [19]

B. A. DALRYMPLE and C. T. KENNER, J. Pharm. Sci. 58, 604-606 (1969). B. I. SHAFIK, Medicinal Plant Constituents, 3rd Edn. Central Agency for University

Books, Cairo

(1981).

AAS microdetermination

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of cinchona alkaloids

Table 1. Stoichiometry of quinidine-mercury

complex

Quinidine taken @g ml-‘)

Equivalent Hg* + obtained olg)

Molar ratio Hgr+ quinidine

30 40 50 60 70 80 90 100 120

9.1 12.1 15.4 18.1 21.3 24.4 27.5 30.3 36.4

1 : 2.035 1 : 2.035 1:2.ooo 1: 2.046 1 : 2.030 1 : 2.020 1 : 2.020 1 : 2.037 1 : 2.030 1 : 2.028

Mol. wt of Hg = 200.61. Mol. wt of quinidine = 324.4.

shown that the molar ratios were 1: 2.02, 1: 2.03, 1 : 1.97 and 1: 2 for quinine, quinidine, cinchonine and cinchonidine respectively. Table 1 and Fig. 1 show the stoichiometry of quinidine_Hg complex, as an example. The complexes obtained were also subjected to elemental analysis. Using the quinidine mercury complex as an example (Fig. l), the following data were obtained: N = 4.8 %, Cl = 2.49 % and I = 45.4 %. The relative atomic ratios for Cl and I were Cl = $$

= 0.07 and I = g

= 0.36,

giving an atomic ratio for Cl of 1 and for I of 5. Thus the suggested formula of the quinidine-Mayer’s complex is B,.4 HI.HgICl with a molecular weight of 1424.5. The i.r. spectrum of the quinidine-Hg complex, as a model, was obtained on a Pye-Unicam SP 1100 Infra-red spectrophotometer, using the KBr disc technique. Figures 2 and 3 and

\

I

\

/

I

\

I

\ \

\

\

I I/

/

/

/’

/’ 2HI

Cl-Hg-I

Fig. 1. Suggested structure of the quinidine_Hg complex. SUB)

40:9-D

MAZDA M. AYADet al.

1208

Wavelength

loo?

3 I

4 I

5 I

(pm)

6 I

7 I

8 I

9 I

IO I

15 I

20 !

25

90-

IO0 4wx

I

I

I 35co

3000

I

2500

I

2000

I

I800 1600 Wavenumber km-‘1

I

I

I

1400

1200

1000

I

I

800

600

400

Fig. 2. The i.r. absorption spectrum of the quinidine_Hg complex.

Wavelength 6 I

1002

(pm) 7

8 I

9 1

IO I

15 I

9080-

I

I

I

4”ooo

3500

3cQO

I

t

2500

zoo0

I

I

I

ISo0

1600

1400

I cm-‘)

Wavenumber

Fig. 3. The i.r. absorption spectrum of quinidine.

Table 2. Comparative i.r. (v, cm- ‘) of quinidine and quinidine_Mayer’s complex

Group 4H Aromatic N Aliphatic N

Quinidine base (cm’)

Complex (cm-‘)

3600 sharp

3500 broad

1360-1310 very prominent 1110-1080 prominent

disappeared

Explanation

disappeared

Change of the vibration due to complexation Change of the vibration due to complexation Change of the vibration due to complexation

Table 3. Recovery of cinchona alkaloids by the proposed method and the official method [20, 213 Recovery (%)* Compound

AAS method

Quinine Quinidine Cinchonine Cinchonidine

99.97 f 99.06 f 98.90 f 99.00 f

0.63 0.62 0.64 0.14

Official method 100.85 f 99.45 f 98.82 f 98.95 f

0.88 1.Ol 0.73 0.76

*Each value is the mean of six different experiments f SD. [20] The United States Pharmacopoeia, 9th Revision, p. 433. U.S.P. XIX P, Rockville, Maryland (1975). [21] British Pharmacopoeia, A 18. Her Majesty’s Stationary Office, London (1973).

20 I

25

AAS microdetermination of cinchona alkaloids

1209

Table 2 reveal the stretching vibration of an OH group at 3600 cm- ’ becoming broad and slightly shifted to 3500 cm-‘. The aromatic N exhibits very prominent bending vibration at 1360-1310 cm-’ in the quinidine spectrum. In the spectrum of the complex this peak disappeared. Moreover the aliphatic N peak at 1110 cm - ’ also disappeared. From these observations, it is obvious that the complex spectrum is different from the quinidine spectrum, confirming the complexation reaction. The percentage recoveries of the alkaloid in Table 3 are satisfactory, ranging from 98.9 to 100.0 with S.D. & 0.6 and f 0.7. The results when compared with the official method are in good agreement. In conclusion, the proposed procedure offers a novel opportunity for pharmaceutical analysis. It is characterized by adequate sensitivity and good precision. These alkaloids can be determined in complex biological fluids since the selectivity of the AAS method provides little interference. This application will be further explored.