الفهرس 
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Abstract
The present thesis includes a systematic study on the spectrophotometric
determination of the drug sildenafil citrate by forming ion-associate or ion-pair
complexes between the drug and some chromotropic acid azo dyes.
The present thesis comprises four chapters:
1- Chapter 1: It includes an introduction concerning the important rules of
analytical chemistry in the analysis of the pharmaceutical products. Also
this chapter includes the spectrophotometric methods used for
pharmaceutical analysis.
2- Chapter 2: It comprises the literature survey on the different analytical
methods used for determination of sildenafil citrate. Also it includes a
literature data on the spectrophotometric determination of some
pharmaceutical compounds by using chromotropic acid azo dyes.
3- Chapter 3: It includes the experimental part, where the materials and
reagents, preparation of various compounds and solutions and the
instruments used are presented. Also this chapter includes the optimum
experimental conditions for formation of the ion-associate/pair
complexes between the investigated drug and the mono- and bi-azo dyes
of chromotropic acid.
4- Chapter 4: It includes the results and discussion.
a- Using of some chromotropic acid mono-and bi-azo dyes for quantitative
spectrophotometric determination of the investigated drug, where in slightly
acidic solutions, the nitrogenous drugs are present in positively charged
protonated forms, so ion-associates complexes are formed between the drug
and anionic dyes of chromotropic acid. These ion-associates are extracted in
organic solvent followed by spectrophotometric determination at their λmax.
b- The stoichiometric composition of the formed complexes was carried out
using continuous variation method. The results indicated that the complexes
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were formed having a ratio 1: 2 or 1: 1 (reagent:drug) in case of mono- or –
bi-azo dyes, respectively.
c- Study on the influence of acidity, effect of extraction solvents, reagent
concentration, time and foreign ions are carried out to establish the optimum
experimental conditions for formation of the ion-associates. Also the
association constants of the formed ion-associates were calculated.
d- The ion-association reactions were used for quantitative determination of
the drug in pure form and in their pharmaceutical formulation (vigoran).
e- The results obtained were treated statistically for estimation of the
precision and accuracy. Also the present methods were validated, through
calculation of the molar absorptivity, Sandell’s sensitivity, detection limit,
quantification limit, application range and comparison of the results with one
of the published methods which based on direct measurement of the
absorbance of the formed charge-transfer complex with σ acceptors like
iodine.
f- The solid complexes of SC with the cited reagents were prepared, and
then subjected to the elemental analysis, IR and UV/Vis measurements to
elucidate the structure of these complexes. The results showed that, the
elemental analysis values of C, H, N and S are in good agreement with the
calculated values according to the proposed molecular formulae of the
complexes. The small shift in the absorption maxima (λmax) in the UV/Vis
spectra and the change in the molar absorptivity values of the solid
complexes relative to those of pure azo dyes is an indication for formation of
new ion-pair complexes. This was confirmed by the changes occuring in the
position of the IR spectral bands of the prepared solid complexes.
The thesis ends with a list of references that was of great help to the author.