Optimization and analysis of some oxinate metal complex system as introduction test for HPLC analysis

Heavy metals are metals that have a mass of more than 5 g / cm3 in the lower right corner of the periodic system. Heavy metals rarely form atoms themselves in water, but are usually bound by other compounds to form molecules. Heavy metal is a chemical compound that has the potential to cause environmental pollution problems. Methods of heavy metal content analysis in the aquatic environment developed simultaneously are still being developed. The simultaneous analysis provides an advantage in terms of time and cost efficiency. In this study is being developed heavy metal analysis based on the formation of complexes with oxin compounds. It is known that the oxide can form a yellow complex with several metal ions. The use of oxine as a complex is selected based on the color and pH of the complexes formed. By performing optimization and analysis of the complex system formed it is expected to produce an excellent method for the analysis of several heavy metals simultaneously using High Performance Liquid Chromatography (HPLC).


Introduction
The presence of heavy metals in the environment comes from mining, household, agricultural, industrial waste and others. Of the four types of waste, the most commonly heavy metal waste is industrial waste [1]. Uncontrolled heavy metals give an opportunity for accumulation of heavy metals in the environment. Heavy metals can enter into the plant tissue through the roots and stomata leaves, then will enter into the food chain cycle [2].
Heavy metals, although in small amounts, can have a considerable effect on the food chain. This is caused by the buildup of heavy metals in each biota. Some heavy metals can contaminate the environment and are toxic, including Cr, Ag, Cd, Pb, Zn, Hg, Cu, Fe Mo, Ni, Sn, Co and elements included in light metals such as As, Al and Se [3]. Although some heavy metals in small concentrations are essential for living things as necessary for the body's metabolism. However, the presence of heavy metals in rivers that exceed the threshold value can cause harmful effects to living things [4]. This is due to the nature of heavy metals that can not decompose through biodegradation such as organic pollutants. Heavy metals can also accumulate mainly in river sediments as they can be bound to organic and inorganic compounds through the process of adsorption and the formation of complex compounds [5].
Methods of heavy metal analysis can be done qualitatively and quantitatively. Qualitative analysis is usually based on metal precipitation reactions using certain reagents such as hydrochloric acid, hydrogen  [6,7,8]. So in this study used a more practical chromatographic technique for the analysis of heavy metal content.
The science of separation and analysis plays a very important role in the application of analytical chemistry, the latest techniques and substances associated with such analysis techniques continue to grow [9]. Since its introduction in 1975, ion chromatography has been the dominant method of analysis in the determination of organic and inorganic ions [10]. The determination of inorganic ions has been carried out not using ion exchange columns [11,12] but also by using other stationary phases [13,14,15,16]. Chromatography technique is an analytical technique that has many advantages such as can determine the content of organic compounds, inorganic, metal, amino acids either in solid, liquid or gas samples in a single measurement.
In addition to the determination of ions directly, it can also be determined the ions are indirectly by reacting the ion first with a ligand so as to form a complex. Quantitative metal ion analysis can be done by changing the metal ion into a complex compound. High Performance Liquid Chromatography (HPLC) can be used as a tool for determining complex compounds and will increase the sensitivity and selectivity of metal ion separation [17]. Metal ions can be transformed into compounds of neutral complexes using organic compounds such as oxine to form compounds of metal-oxinate complexes [18]. Most such complexing reagents are weak acids that react with most metals to form uncharged complexes dissolved in organic solvents such as ether, hydrocarbons, ketones, chloroform and carbon [19]. Among them are oxides (8-hydroxyquinoline) which form a stable chelate complex with several types of metal ions [20, 21,22].
Oxygen is given a HOx notation, a bidentate ligand which has two donor atoms on oxygen atoms in phenolic hydroxy group and nitrogen on its cyclic chain so as to form a neutral chelate complex with metal. This complex is formed by replacing the hydrogen atoms in the hydroxyl group by the metal and the coordination bond of the nitrogen atom with the metal forming an uncharged chelate ring compound. The metal complex is insoluble in water but soluble in organic solvents such as chloroform [18]. The metal-oxinic complex is a color complex so that the metal concentration can be detected using UV-Vis detector on HPLC instrument.
In this research, we have investigated the condition of the formation of metal oxinate complexes of some heavy metal ions such as Fe (III), Pb (II), Ni (II), Co (II), Cu (II) and Zn (II) maximum waves, pH, complex stability, stirring time, ligand concentration. The results of this study will be used for the separation of the metal ions in complex form with oxine using HPLC.

Apparatus
Determination of wavelength using Spectronic Genesys 20 D, pH of the solution was determined using a pH meter Hanna Instrument HI2211, weighing chemicals to make reagents using analytical balance, separating funnel used for organic phase separation, glassware and reagent bottle.

Determine Optimum Oxine Concentration in Complex Formation.
The absorbance for the metaloxinate complex of each metal ion solution was measured after oxine added with a concentration of 0.01; 0.05; 0.1; 0.15 and 0.2 M of 3.5 mL into each of the metal ion solutions, the optimum oxine concentration will be obtained when the absorbance of the metal-oxinate complex is flat.

Determine Complex Wavelength
The maximum wavelength of each metal oxinate complex is determined to obtain the optimum wavelength of the entire complex for simultaneous determination. 1 ml of 10 ppm metal ion was added with 3.5 ml oxine 0.1 M. In this study all the complexes formed were yellow. In this procedure, oxine is dissolved in ethanol, so the advantage is that the complex compounds formed do not need to be separated. This causes faster analysis time. Furthermore, the complex was analyzed using spectronic at a wavelength of 400 to 600 nm. The wavelength for each metal oxinate complex can be seen in Figure 1 below.

Determine Optimum Oxine Concentration in Complex Formation
Determination of optimum oxine concentration aims to obtain the correct oxine concentration reacts with metal ions so that the oxine is used optimally and not excessively in the reaction. In general, an increase in the oxide concentration will increase the amount of metal ions which are transacted to the organic phase until they reach a point called the optimum point. Having reached the optimum point of increase the oxine concentration only slightly affects the extraction of metal ions. The following curve relation influence the variation of oxine concentration to absorbance value of metal oxinate complex compound can be seen in Figure 2.

Determine effect of pH in Complex Formation
Determination of the effect of pH on the formation of oxinate metal complex compounds aims to obtain a suitable pH range of the metal ion extraction process. The stability of complex formation is strongly influenced by the pH of metal ion solution. At low pH, the abundance of H + ions causes the reaction equilibrium to tends toward the formation of metal ions and oxides rather than the formation of oxinate metal complex compounds, so that the compound of the metal oxinate complex is formed very little. At high pH, decreasing H + ions and increasing OHions in solution metallic ions tend to react with OHions forming Fe(OH) 3 or Pb(OH) 2 [23]. Reduced metal ions reacting with the oxine cause the compound of the oxinate complexes formed slightly. The determination of pH optimum is based on the high absorbance value in the uptake of oxinate metal complex compounds.

Determine Shaking Time in Complex Formation
Determination of the effect of shaking time on the formation of metal oxinate complex compounds aimed to obtain optimum time so that all metal ions extracted into the organic phase form oxinate complex compounds. If the time for shaking is less, it will be a little complex that is formed. Optimum conditions will be obtained when the addition of time does not provide additional value of absorbance.

Determine Complex Stability Time
The timing of the formation stability of the complex is determined to determine how long the formed complex remains stable and is good for analyzing. This is because the possibility of re-decomposition of complex compounds that have been formed or the formation of colloids that will interfere with measurements [23]. From the curve above can be seen that the longer time complexing the higher the absorbance value. This suggests that more and more complex nickel metals as time goes by. The optimum period of time is 20 minutes for all metal oxinates complex, which means that at this time the formation of nickel metal complex with the most stable oxine.

Conclusion
Conclusions that can be taken based on research data are as follows: •