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Ritodrine hydrochloride (RTH), chemically 1-(4hydroxy phenyl)-2-[2-(4-hydroxy phenyl) ethyl amino] propanol, is a potent tocolytic drug. Amoxicillin (AMX), 6-(p-hydroxy-α-aminophenyl acetamido) penicillanic acid, is the only phenolic penicillin, and it is used as an antibacterial drug. Many analytical procedures have been adopted for the determination of AMX, whereas very few methods have been used for RTH. The methods used for the determination of these drugs include titrimetry 1,2 , HPLC 3-7 , spectrophotometry for AMX 8-14 and for RTH. 15 Recently, 2-iodoxybenzoate was employed for the titrimetric determination of AMX. 16 Other methods, such as polarography 17,18 and fluorometry 19 , have been reported in the literature for the determination of AMX. The present paper describes the application of 3-methylbenzothiazolin-2one hydrazone (MBTH) for the determination of RTH and AMX in both pure and dosage forms. Reaction mechanism of the method Ritodrine and amoxicillin form a pink-colored product (λ max of 520 nm for RTH or 490 nm for AMX) with MBTH in the presence of ammonium cerium(IV) sulfate in acidic media. The absorption spectra of the colored products are given in Fig. 1. Under the reaction conditions, MBTH(I), upon oxidation with Ce(IV) ions, loses two electrons and one proton, forming an electrophilic intermediate(II), which is an active coupling species. 20,21 The intermediate of MBTH(II) undergoes electrophilic substitution with the phenolic moieties of RTH and AMX to form a colored product [III(a) and III(b)] according to Scheme 1. Experimental Apparatus Jasco (Model UVIDEC-610) and Elico (Model CL-27) spectrophotometers with 1 cm matched quartz cells were used for all absorbance measurements.

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A method for the spectrophotometric determination of four phenothiazines (promazine hydrochloride, mepazine hydrochloride, chlorpromazine hydrochloride and prochlorperazine maleate), based on the coloured compounds formed between the phenothiazines and molybdoarsenic acid, is described. The infrared and electron spin resonance spectra of these coloured compounds showed that the molybdoarsenic acid oxidises phenothiazines to a radical cation with which it subsequently forms the coloured compound. The method is simple and rapid. The influence of the substrates commonly employed as excipients with phenothiazine drugs was studied. The proposed method has been applied to the analysis of commercial phenothiazinecontaining preparations, the results of which are in good agreement with those obtained by the official method of the British Pharmacopoeia.During the past 25 years, interest in mental health and the continued introduction of new phenothiazine drugs have resulted in an extensive literature on the analysis of phenothiazines. The methods available for the determination of phenothiazines are all in some way unsatisf a~t o r y , l -~ and there is at present a great demand for a rapid, simple and accurate method for the routine quality control of phenothiazines. We therefore investigated the colour reaction between molybdoarsenic acid and four phenothiazines [promazine hydrochloride (PMH), mepazine hydrochloride (MH) , chlorpromazine hydrochloride (CPH) and prochlorperazine maleate (PCPM)]. The proposed method offers the advantages of simplicity, rapidity, reasonable sensitivity and a wide range of concentrations. Further, the reaction occurs at room temperature and without the need for extraction. Experimental ApparatusA Beckman, Model DB, spectrophotometer with matched 10-mm silica cells was used for absorbance measurements. A Perkin-Elmer, Model 257, infrared spectrophotometer and a Varian E-4 X-band electron spin resonance spectrometer were used for spectral analyses of the coloured compounds. ReagentsMolybdoarsenic acid was obtained from Doxa Laboratory, India. A 4% m/V aqueous solution was prepared.Stock solutions of PMH, MH, CPH and PCPM were prepared by dissolving the appropriate amount of sample in water, and were then standardised gra~imetrically.~ Working solutions were prepared as required by dilution. All other reagents were of analytical-reagent grade. Doubly distilled water was used throughout. Molybdoarsenic acid.Phenothiazines. ProcedureProcedure and preparation of calibration graph CPH or 155-1 180 pg of PCPM were transferred into a series of 25-ml calibrated flasks.Various aliquots containing 100-890 pg of PMH, 100-930 pg of MH, 140-1 115 pg of A

Summaw. Penicillins are determined by means of ion-pair formation with azure B and extraction into chloroform:the absorbance of the extract is stable for several days. The apparent molar absorptivities for sodium penicillin G and potassium penicillin V at 634 nm are 3.91 x 10' and 1.25 x 10' 1 mol-' cm-', respectively_ Calibration graphs are linear over the range 60-950 pg of sodium penicillin G and 40-600 pg of potassium penicillk V in 10 ml. The method is successfully applied to pharmaceutical preparations.