Kinon Bileşiklerine Dayalı Suyun Voltametrik Yöntemle Tayini

Abstract

Birçok araştırma ve endüstriyel proseslerde en rutin prosedürlerden biri olan su miktarının tayin edilmesi endüstriyel ve çevre yönünden büyük bir önem taşımaktadır. Başta gıda, ilaç ve kozmetik sanayi olmak üzere pek çok endüstri ürünün içeriğindeki suyu, ürünü bozan bir kirletici olarak değerlendirmektedir. Zira eser miktardaki su varlığının dahi ürünler üzerinde yıkıcı ve bozucu etkisi olabildiği gibi kimyasal reaksiyonlarda verim düşüşü, madde karakteristiğinin değişmesi, ürün akışkanlığının değişmesi ve korozyona yol açma gibi olumsuz etkileri olabilmektedir. Sözgelimi ilaç endüstrisinde ürün içeriğindeki nem miktarı ürünün dayanıklılığını, etkinliğini ve son kullanma tarihini değiştirmektedir. Bu yüzden gıda, ilaç, kozmetik, petrokimya, boya ve plastik sektörlerinde; kimyasallarda, su ve nem miktarının mutlak surette tespit edilmesi gerekmektedir. Bugün başta gıda ve ilaç sanayi olmak üzere, kozmetik, petrokimya, boya, plastik vb. gibi sektörler üretimleri aşamasında ve ürünlerinde nem tayini yapmak durumundadır.To determine the amount of water which is one of the routine processes in research and industry, has a great importance from the point of industry and environment. A great number of industries, such as food, pharmaceutical and cosmetics , evaluate water in the product as a pollutant which spoils it. Even small amounts of water has a damaging and spoiling effect on the product and it causes a decrease in efficiency in chemical reactions, a change in the fluency of the product and corrosion. These are negative effects of water. For example, in pharmaceutical industry, a small amount of humidity affects the durability (strength), efficiency and its expiration date. For that reason, in food, pharmaceutical, cosmetics, petrochemistry, dye and plastic industries and sectors; it is vital to determine the amount of water and humidity in chemicals. Today industries mentined before have to determine the humidity amount in products during the production stage. In order to perform their goals and aims, these sectors used the Karl Fischer technique developed by Karl Fischer (German) in 1935. The technique has been improved a lot so far and has an active use. This titration method means the oxidation of the element iodine, in the medium by Sulphur dioxide in the presence of water. The emergence of determination of water analytically in organic solvents and determination of water by using Karl Fischer titration technique overlap at the same time. Even if Karl Fischer technique is preferred in industrial applications, different techniques has used in academic studies to determine small amount of water and humidity. The most featured ones are gravimetric, spectrophotometric, conductometric, isotropic dilution and voltammetric methods. Determination of small amount of water by spectrophotometric methods: the spectrophotometric techniques developed to determine small amounts of water in organic solvents are spectrophotometric, UV-vis and NIR (near –infrared). The determination of water by using spectroflourometric techniques: flourometric methods used in literature are based on fluorescence quenching of a molecule having fluorescence property in presence of water. We made use of voltammetric techniques in our experiments. Voltammetry is based on the measurement of the current in an electrochemical cell under conditions of polarization in which the rate of oxidation and reduction of the analyte are limited by the rate of mass transfer of the analyte to the electrode surface. Cyclic voltammetry and square-wave voltammetry are two types of voltammetric methods. We used cyclic voltammetry in this study. The current in voltammetry is formed by the reduction or the oxidation of materials on the working electrode. Electrochemistry is an eclectic science that draws on and has applications in many disciplines ranging from solid state physics, molecular biology, electrical engineering, synthetic organic chemistry to others. A review of quinone electrochemistry, consequently, touches on recent developments in many areas, as well as current thinking in fundamental electrochemistry. The thread of quinonoid redox chemistry in the recent literature outlines and underscores the chemistry in electrochemical science. Quinone compounds are one of the most important and widely-studied examples of organic redox systems, because they often play very important roles in biological reactions. In addition, Q couples have been extensively studied because they display fundamentally interesting chemically reversible redox properties in a solution. In our experiments, we preferred p-benzokinon, 1,4- naphtakinon, antrakinon for water determination. We obtained these from Merk Company. The aprotic solvent is acetonitrile (ACN) it is also from Merk Company. The supporting electrolyte TBAP (tetrabutylammonium perchloride) has been obtained from Fluka Company. For voltammetric analysis PARSTAT 2263 model potansiyostat, for Karl Fischer measurements, Metter Toledo C20 model Karl Fischer titrator have been used. We preferred cyclic voltammetric analysis for our experiments and used 0.2 M TBAB. We kept TBAP in 400C for two days in vacuum. Before measurements, we kept under argon gas for nearly 30 minutes in order to remove the oxygen in solvent medium. As working electrode, we used glassy carbon and Ag/AgNO3 without water as reference electrode. The quinone concentration for measurements is 5.0 ×10-3 M. We dried ACN in an activated molecular sieve (3Å size) (Alfa Aesar) for three days to use in measurements before experiments and we dyried the water in it. The sieve has also been processed before using. For these process, we kept the molecular sieve in a 573 K oven for one day. We took it out directly from the oven then and put it in a glass reservoir and cooled it in a vacuum desiccator. We added the solvent after cooling it and waited for 3 days. We measured the dried solvent by Karl Fischer instrument before experiment and determined the water amount in it. Then we put the quinone solution having 0.2 M TBAP by dissolving it in ACN, into electrochemical cell medium (environment) and passed Argon gas for 30 minutes in order to remove the medium oxygen . After that, we started cyclic voltammetry measurements. We determined the amount of water in a solvent medium by Karl Fischer tool before adding water. We added 10 µL water by a micro pipet into the electrochemical cell medium and mixed for a minute by magnet and measured again. We added water by 10 µL intervals and continued till E1 and E2 cathodic peaks are merged. We determined the amount of water in the solvent again by Karl Fischer after the experiment. Karl Fischer (KF) titration is a classic titration method in analytical chemistry that uses coulometric or volumetric titration to determine the trace amounts of water in a sample. The KF titration is the standard method for obtaining the water content of various substances. The great advantage of the KF titration is that it does not need calibration, since the charge can be directly correlated with the amount of water present. However, some limitations exist. In particular, there is a minimum charge that can be accurately measured by the coulometer, meaning that low concentrations of water requires higher masses of the analyte to achieve the greatest accuracy. With care, the KF titration can accurately give measurements down to 1 ppm water. We also know from literatures with quinones hydrogen bonding is formed and the peak potentials move towards positive and even a small amount of water bonds with mono-anion and di-anion. We know that di-anion is affected more by the water in medium and it moves right. If we name di-anion peak potential E2, and mono-anion peak potential E1, these two peaks join after a certain water concentration. H-bonding is necessary in our topic that H-bonds, being one of the strongest intermolecular interactions, are used extensively in the supramolecular chemistry of both man and nature. Their high electrostatic character makes it straightforward to perturb their strength electrochemically. There are two main ways to do this. Reduction can be used to make a H-acceptor a better acceptor by increasing the negative charge on a H-accepting atom, or oxidation can be used to make a H-donor a better donor by increasing the positive charge on a H-donating atom. We calculated the water amount bonded to mono-anion radical and equilibrium constant, the water amount bonded to di-anion and its equilibrium constant, water concentration linear range and correlation constant and we applied this to all the quinones we worked on. Also, we determined the most sensible quinone, benzokinon because of its reversibility properties and having the best linear range. By increasing the cycle amount of quinone, amount of water molecules also increased. Especially, di- anion is more sensible than the mono- anion according to water attaching. As a result, we determined that the water concentration linear range is between 0.13M< CH2O