الفهرس 
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Abstract
Spectrophotometric analysis is one of the most important methods that used in chemical analysis due to its simplicity, rapidity, availability and accuracy in the analysis of several elements as well as holmium and erbium.
In the present work, a detailed study for the determination of holmium and erbium in lanthanide concentrates (monazite and xenotime) using spectrophotometric analysis by forming a complex of holmium and erbium with kojic acid (Koj) dye in presence of cetylpyridinium chloride (CPC) cationic surfactant.
The Thesis consists of three main chapters:
Chapter I include
• Over view of holmium and erbium ( history, occurrence, chemical properties, importance and health hazardous)
• Different determination methods of holmium and erbium with focusing on spectrophotometric methods.
Chapter II include
• Editing of all chemical materials that used during measuring process with referring to its preparations.
• Also include information about the used apparatus (spectrophotometer and pH meter)
• Editing all the experimental that concerned the determination method
Chapter III
This chapter includes three parts
Part I
This part describes the determination method of holmium and erbium with Koj and CPC using spectrophotometer by measuring the yellow color of Ho-Koj-CPC & Er-Koj-CPC complexes. This part include also the optimization of the relevant factors affecting holmium and erbium determinations as determination of wavelength (it was found 450nm and 520nm for Ho and Er respectively), media (pH 9.3), concentration of dye (2X10-3 M was the optimum), complex composition, that determined by using two different methods, the first is the continuous variation method and the second is the molar ratio method. It was found that the molar ratio of the complex Ho-Koj-CPC & Er-Koj-CPC complexes is 2:8:1 respectively. Effect of duration time, it was found that the complexes of Ho-Koj-CPC & Er-Koj-CPC were formed instantly and be stable for four hours. The effect of interfering elements on the measuring of holmium and erbium complexes was also studied. It was found that there is a strong effect of the foreign ions even at very low concentrations on the measuring of holmium and erbium causing a large systematic error.
Part II
This part includes the study of elimination of the effect of the interfering elements on holmium and erbium determination. Accordingly, we apply separation of cerium element and also heavy rare earth elements (HREEs) in the samples that contain high light rare earth (LREEs) contents and also study the ability to apply the derivative spectrophotometer (DS) where; it is consider the best among different analytical methods. The method depends on the measuring of the yellow color of the complexes of Ho and Er with Koj in presence of CPC using third-derivative spectrophotometer. Optimization of the relevant factors (that mentioned previously) affecting the measuring of holmium and erbium using third-derivative spectrophotometer were studied.
Part III
This part includes the application of the investigated method for the determination of holmium and erbium. In this trend the investigated method applied on two synthetic samples (were prepared according to the composition of monazite concentrate) and two measured geological concentrate samples. from the results it was found that the method is available for measuring holmium and erbium in good accuracy in presence of other interfering elements.