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ABSTRACT:One titrimetric and two spectrophotometric methods are described for the determination of ciprofloxacin in bulk drug and in formulations using cerium (IV) sulphate as the oxidimetric agent and methyl orange and indigo carmine as chromogenic agents. In titrimetry (method A), ciprofloxacin is treated with a measured excess of cerium (IV) sulphate in acid medium and the unreacted oxidant is back titrated with standard ammonium ferrous sulphate using ferroin indicator. In spectrophotometric methods, ciprofloxacin is treated with a known excess of cerium (IV) sulphate and the residual oxidant is determined by treating with a fixed amount of either methyl orange, and measuring the absorbance at 520 nm (Method B) or indigo carmine, and measuring the absorbance at 610 nm (Method C). In all the three methods, the amount of cerium (IV) sulphate reacted corresponds to the amount of ciprofloxacin. Titrimetry is applicable over 2-12 mg range and in the spectrophotometric methods, calibration curves are linear over the concentration ranges of 0.5-3.5 µg ml -1 (method B) and 1.0-7.0 µg ml -1 (method C). The methods were satisfactorily applied to the determination of ciprofloxacin in tablet and injection formulations and no interferences from excipients were noticed.

One titrimetric and two spectrophotometric methods which are simple, sensitive and rapid are described for the assay of salbutamol sulphate (SBS) in bulk drug and in tablet dosage forms using N-bromosuccinimide (NBS) and two dyes, rhodamine-B and methylene blue, as reagents. In titrimetry, aqueous solution of salbutamol sulphate is treated with a measured excess of NBS in acetic acid medium and after the oxidation of SBS is complete, the unreacted oxidant is determined iodometrically. Spectrophotometric methods entail addition of a known excess of NBS in acid medium followed by the determination of residual oxidant by reacting with a fixed amount of either rhodamine B and measuring the absorbance at 555 nm (method A) or methylene blue and measuring the absorbance at 665 nm (method B). In all methods, the amount of NBS reacting corresponds to the amount of SBS content. Titrimetric method is applicable over 1.74 x 10(-4) - 8.68 x 10(-4) mol L(-1) range and the reaction stoichiometry is found to be 1:6 (SBS:NBS). In spectrophotometric methods, the absorbance is found to increase linearly with the concentration of SBS, which is corroborated by the correlation of coefficients of 0.9993 and 0.9988 for method A and method B, respectively. The systems obey Beer's law for 0.25-1.75 microg mL(-1) (method A) and 0.5-5.0 microg mL(-1) (method B). The calculated apparent molar absorptivity values were found to be 2.10 x 10(5) and 6.16 x 10(4) L mol(-1) cm(-1), for method A and method B, respectively. The limits of detection and quantification are also reported for both spectrophotometric methods. Intra-day and inter-day precision and accuracy for the developed methods were evaluated. The methods were successfully applied to the assay of SBS in tablet and capsule formulations and the results were statistically compared with those of a reference method. No interference was observed from common tablet adjuvants. The accuracy and reliability of the methods were further ascertained by recovery experiments via the standard-addition technique.

Two spectrophotometric methods are proposed for the assay of lansoprazole (LPZ) in bulk drug and in dosage forms using ceric ammonium sulphate (CAS) and two dyes, methyl orange and indigo carmine, as reagents. The methods involve addition of a known excess of CAS to LPZ in acid medium, followed by determination of residual CAS by reacting with a fixed amount of either methyl orange, measuring the absorbance at 520 nm (method A), or indigo carmine, measuring the absorbance at 610 nm (method B). In both methods, the amount of CAS reacted corresponds to the amount of LPZ and the measured absorbance was found to increase linearly with the concentration of LPZ, which is corroborated by the correlation coefficients of 0.9979 and 0.9954 for methods A and B, respectively. The systems obey Beer's law for 0.5-7.0 mg mL -1 and 0.25-3.0 mg mL -1 for methods A and B, respectively. The apparent molar absorptivities were calculated to be 3.0 x 10 4 and 4.4 x 10 4 L mol -1 cm -1 for methods A and B, respectively. The limits of detection (LOD) and quantification (LOQ) were calculated to be 0.08 and 0.25 mg mL -1 for method A, and 0.09 and 0.27 mg mL -1 for method B, respectively. The intra-day and inter-day precision and accuracy of the methods were evaluated according to the current ICH guidelines. Both methods were of comparable accuracy (e r £ 2 %). Also, both methods are equally precise as shown by the relative standard deviation values < 1.5%. No interference was observed from common pharmaceutical adjuvants. The accuracy of the methods was further ascertained by performing recovery studies using the standard addition method. The methods were successfully applied to the assay of LPZ in capsule preparations and the results were statistically compared with those of the literature UV-spectrophotometric method by applying Student's t-test and F-test.

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