ANALYTICAL SCIENCES NOVEMBER 2000, VOL. 16 1127 2000 © The Japan Society for Analytical Chemistry A Simple Spectrophotometric Determination of Some Phenothiazine Drugs in Pharmaceutical Samples Padmarajaiah NAGARAJA,* Nandipura D. DINESH,* Netkal M. MADE GOWDA,** and Kanchugarakoppal S. RANGAPPA*† *Department of Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, India **Department of Chemistry, Western Illinois University, Macomb, IL 61455, USA A new, simple and sensitive spectrophotometric method for the determination of some phenothiazine drugs has been developed. The proposed method is based on the reaction of promethazine hydrochloride (PH), chlorpromazine hydrochloride (CPH), triflupromazine hydrochloride (TPH), fluphenazine hydrochloride (FPH), trifluoperazine hydrochloride (TFPH), perazine dimaleate (PDM) and prochlorperazine maleate (PCPM) with iron(III) and a subsequent reaction with ferricyanide in an acetic acid medium to yield Prussian blue colored product with a maximum absorption at 700 – 720 nm. The common excipients used as additives in pharmaceuticals do not interfere with the proposed method. Analytical data for determination of the pure compound are presented together with the applications of the proposed method to the analysis of some pharmaceutical formulations. The results compare favorably with those of the official method. (Received July 13, 2000; Accepted September 13, 2000) Phenothiazines are an important group of neuroleptics used in drug on heating for 10 min and have low sensitivity.28 the treatment of moderate and severe mental and emotional However, no method has been found for dealing with the use of conditions. They are also known for their antiemetic effects, the combinations of these two reagents for the spectrophotometric potency of the effects of anaesthetics, analgesics and sedatives determination of phenothiazine derivatives. This method offers and also as antihistamines.1 More than 100 compounds derived the advantages of simplicity, specificity without the need of from the fundamental phenothiazine skeleton have been extraction or heating, besides having higher sensitivity range synthesized and pharmacologically tested in the past four than most of the existing spectrophotometric methods. decades.2 The vast number of phenothiazine derivatives and the Moreover, this method is totally free from the twin continued introduction of these drugs have instigated many disadvantages of critical acid or reagent concentration and workers to explore new methods for their determination. Many instability of the colored species; such disadvantages are typical phenothiazine derivatives and their formulations are official in of most spectrophotometric methods. British Pharmacopoeia3 and Indian Pharmacopoeia.4 The methods used for their determination include spctrofluorometry,5 conductometry,6 fluoroimmunoassay,7 Experimental HPLC,8 GLC,9 adsorptive voltametry10 and chemiluminescence measurements.11 Many spectrophotometric methods have been Apparatus already proposed, but some of them either lack sensitivity or A JASCO Model UVIDEC-610 UV-VIS spectrophotometer specificity12–19 or require long heating times20–23 or involve non- with a 1.0-cm matched cell was used for electronic spectral aqueous media.24,25 Almost all spectrophotometric methods are measurements. based on the formation of colored radical cation, which suffer from two disadvantages: critical acid or oxidant concentration Reagents and instability of colored species ranging from 10 – 30 min. All the reagents used were of AR grade where otherwise not Some other spectrophotometric methods have very narrow mentioned. Deionized water was used to prepare all solutions. limits of detection.25,26 Freshly prepared solutions were always employed. Standard The present communication reports on the investigations for solutions of phenothiazines (1000 µg ml–1) were prepared by the use of iron(III) salts in the presence of ferricyanide as dissolving 100 mg each of phenothiazine salts in distilled water reagent for the spectrophotometric determination of and diluting to the mark in a 100-ml calibrated flask. A phenothiazines listed in Table 1. working standard solution of phenothiazines containing 50 µg Ferricyanide has been used as an oxidizing agent for the ml–1 was prepared by further dilution. A potassium ferricyanide determination of phenothiazines by titrimetry.27 Iron(III) salts solution (0.002 M), ferric chloride solution (0.005 M) and a 1:1 are also used as a reagent for the analysis of chlorpromazine acetic acid solution were prepared in water. hydrochloride in hydrochloric acid medium. It reacts with the Recommended procedure † To whom correspondence should be addressed. Aliquots of standard phenothiazine solutions such as PH (2.5 – 1128 ANALYTICAL SCIENCES NOVEMBER 2000, VOL. 16 Table 1 Phenothiazines studied Sl. Derivative Abbrev. Structure No. studied 1. promethazine PH (hydrochloride) 2. chlorpromazine CPH (hydrochloride) 3. triflupromazine TPH (hydrochloride) Fig. 1 Absorption spectra of PH product (1) with reagent blank, (2) PH taken 5 mg ml–1. 4. fluphenazine FPH (hydrochloride) Results and Discussion The spectrophotometric method for the determination of 5. trifluoperazine TFPH (hydrochloride) phenothiazine derivative is based on the oxidation reaction of the drug with iron(III) and subsequent chelation with ferricyanide to form a Prussian blue colored product.29 The factors affecting the color development, reproducibility, 6. perazine PDM sensitivity and adherence to Beer’s law were investigated with dimaleate PH as the model compound, since the other phenothiazine derivatives behaved similarly to it. Spectral characteristics 7. prochlorperazine PCPM A blue complex is formed when PH was allowed to react with maleate iron(III) salts in the presence of ferricyanide in acetic acid medium with maximum absorption as shown in Fig. 1. The colorless reagent blank has practically negligible absorbance at this wavelength. Optimum conditions for complex formation 175 µg), CPH (5 – 200 µg), TPH (6.25 – 200 µg), FPH (6.25 – In order to establish the optimum conditions necessary for a 200 µg), PDM (5 – 200 µg), PCPM (10 – 200 µg) or TFPH (12.5 rapid and quantitative formation of the colored product with – 200 µg) were transferred into 25 ml calibrated flasks maximum stability and sensitivity, the investigators measured separately, to each flask, 4 ml of ferricyanide and 2 ml of ferric the absorbance of a series of solutions by varying one and fixing chloride were added. Each mixture was set aside for 10 min. the other parameters at 700 nm. After 3.5 ml of 1:1 acetic acid was added, the contents were It was found that a 0.005 M solution of ferric chloride in the diluted to the mark with water and mixed thoroughly; after 20 range 1.0 – 3.0 ml and a 0.002 M solution of potassium min, the absorbance values at λmax 700 – 720 were measured ferricyanide in the range 2.0 – 6.0 ml were necessary to achieve against a reagent blank and a calibration graph was constructed. the maximum color intensity of the product. The color intensity decreased below the lower limit and above the upper limit. Procedure for tablets Therefore, 2.0 ml of ferric chloride and 4.0 ml of ferricyanide Twenty tablets were weighed and finely powdered. An were recommended for all measurements. accurately weighed portion of the powder equivalent to 50 mg Dilution of the blue product with different solvents like water, of the phenothiazine salt was transferred into a 100-ml methanol, ethanol, hydrochloric acid, sulfuric acid, phosphoric calibrated flask and diluted to volume with water. Using a acid and acetic acid were tested. Nitric acid was not used mechanical stirrer, the powder was completely disintegrated and because of its strong oxidizing power. In methanol or ethanol the solution was filtered. A suitable aliquot of this solution in medium, the blue color product precipitates out. Results the individual phenothiazine working range was treated as showed that 1:1 acetic acid gives clear blue color with described in the recommended procedure. maximum intensity and stability compared to hydrochloric, sulfuric or phosphoric acids. It was found that 1:1 solution of Procedure for injections acetic acid in the range of 2.5 – 15.0 ml was necessary to get An accurately measured volume was appropriately diluted to clear, sensitive and stable color. Therefore, a 3.5 ml volume of get 500 µg ml–1 of phenothiazine salt solution. A suitable acetic acid was recommended for all subsequent measurements. aliquot of solution was taken and the recommended procedure was followed for the analysis of drug content. ANALYTICAL SCIENCES NOVEMBER 2000, VOL. 16 1129 Table 2 Parameters for the spectrophotometric determination of phenothiazine derivatives Parameter PH CPH TFPH FPH PDM PCPM TFPH Color blue blue blue blue blue blue blue λmax (nm) 700 700 700 720 720 720 720 Stability (h) 48 48 48 48 48 48 48 Beer’s law range (µg ml–1) 0.1 – 7 0.2 – 8 0.25 – 8 0.25 – 8 0.2 – 8 0.4 – 8 0.5 – 8 Molar absorptivitiy (L mol–1 cm–1) 3.66 × 104 2.14 × 104 2.72× 104 2.87 × 104 2.86 × 104 2.46 × 104 2.43 × 104 Sandell’s sensitivity (µg cm–2) 0.0087 0.0166 0.0176 0.0177 0.0199 0.0246 0.0160 Photometric range (µg ml–1) 0.5 – 6 0.8 – 7.2 1 – 6.5 0.9 – 7 0.8 – 7.0 1 – 6 1.2 – 6.4 Regression equation (ya) Slope (a) 0.026 0.020 0.111 0.039 0.110 0.020 0.038 Intercept (b) 0.010 –0.050 0.037 –0.032 0.037 –0.050 0.011 Correlation coefficient (r) 0.998 0.998 0.997 1.010 0.998 0.998 0.990 R.S.D. (%)b 1.12 1.40 1.22 0.80 1.13 1.14 1.02 a. y = ax + b where x is the concentration (µg ml–1) of phenothiazines. b. Calculated from five determinations. Table 3 Determination of PHa in the presence of excipients seriously. Material Amount/mg % Recovery of PH ± % RSDb Application of the method The applicability of the method for the assay of Lactose 40 98.9 ± 1.41 Dextrose 40 98.6 ± 1.10 pharmaceutical formulations was examined.