A new, simple and sensitive spectrophotometric method for the determination of catechol and resorcinol has been developed. The method is based on the reaction of catechol and resorcinol with2,4-di nitrophenyl hydrazine to yield orange-colored products respectively. catechol and resorcinol showed maximum absorbance at385 nm and 404nm with linearity was observed in the concentration range of (1-40 µg/mL) for catechol, and (1-25 µg/mL) for resorcinol with correlation coefficient (0.9982) for both compounds, Sandell's sensitivity 0.0216 (μg cm -2 ) and 0.025 (μg cm -2 ) respectively.

A simple, fast and sensitive spectrophotometric method has been developed for the determination of esomeprazole in its pure form and also in the form of a pharmaceutical preparation. The highest absorption was found at a wavelength of 618 nm and the limits of Beer were (2_24) µg/ml. The molar absorbance (2.1070 ˣ104) L.mol-1 .cm-1, Sandell sensitivity 0.016 µg.cm-2, and limits of detection LOD 0.0153 µg/ml, LOQ 0.0510 µg/ml were determined the method was also applied to pharmaceutical preparations, and the validity of the method was confirmed by standard addition.

An indirect method for the estimation of fluoride ion has been developed.The method is based on the bleaching action of fluoride ion on the color of Ti (IV)with 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthanic acid (HHSNNA) complex with proportional decrease of absorbance. Therefore,the decrease in color intensity is proportionalto the concentration of fluoride ion. Molar absorptivityis 0.1166×10 4 l. mol-1 .cm-1 atwavelength 685 nm. Beer's lawis obeyed over the concentration range of 0.2-4 µg/ml.The proposed method is applied successfullyto determine fluoride ion in different real water samples andpharmaceutical preparations (Tablets). The proposed method is compared favorably with Eriochrome cyanine R-Zirconium method.

In the present research, a spectrophotometric method is suggested as an alternative to the gravimetric method used to find mishraq alum purity. The method is based on the complex formation between aluminium ion and either Chrome Azurol S (CAS) or Eriochrome cyanine R (ECR) to give colored products suitable for the determination of aluminium. The same reaction has been applied to the determination of fluoride in tablet, depending on the bleaching effect of fluoride on the formed aluminium colored complex. Statistical comparison of method has given satisfactory results.

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