Human being use olive oils in their everyday activities. For example, olive oils can be used for chemical industries, food flavoring, cleaning, cooking and cosmetics . Natural olive oils have also been shown to have antioxidant capacities that are important for promoting good human health and may be beneficial for the prevention of many degenerative diseases [2: 4]. The consistency of olive oils in terms of freshness, storability and toxicity can be measured by metal determination. Trace levels metal Trace levels such as Niand Cu are known to increase oil oxidation rates, whereas other elements such as Cd and Pb are very significant due to their toxicity and metabolic role . Atomic absorption spectrometry is the most common technique used for the determination of metals in olive oil . Even then, inductively coupled plasma optical emission (ICP-OES) is an exciting and useful method to provide the trace element profile due to its ability to provide simple multi-element analysis with acceptable detection limits .
1. Analytical Chemistry
Analytical Chemistry is the chemical branch dealing with the qualitative and quantitative study of samples. Different spectroscopic techniques such as Atomic Absorption, Flame Emission, Phosphorescence, X-Ray, Molecular Fluorescence are being used for this purpose. Other analytical techniques that can be used include nuclear magnetic resonance (NMR), high-performance liquid chromatography or gas chromatography (HPLC, GC), differential scanning calorimetry (DSC) or vibrational spectrometry, including Raman and infrared spectrometry. These processes are more effective when quantification is necessary, but they are also more time-consuming, require more complex types of equipment and are typically intended to determine the origin of the EVOO or to carry out anti-fraud tests [8,9].
2. Different methods of analytical technique:
The determination of these metals in olive oil requires specific analytical procedures such as
The potentiometer is a chemical by measurement by calculating the electrochemical cell potential. Measurements can be made with concentration cells or a comparison cell. Concentration cells consist of two half cells that have the same solution, but with different concentrations (concentrated and runny). Both solutions are related to salt bridges containing electrolyte solutions.
Metal electrodes inserted into each solution were analyzed using a potential measurement system . The theory of Le Chatelier in concentration cells applies where the reduction increases with an increase in the concentration of metal. Thus the reduction occurs in more concentrated solutions and the oxidation occurs in dilute solutions . A more concentrated solution acts as a cathode, and a more aqueous solution acts as an anode, such that there is an electron flow from the aqueous solution to the concentrated solution before balance is reached . In addition, the electrical current shifts are calculated using a voltmeter, then the results of the measurements were determined using the Nerst equation. The method has advantages such as good accuracy, low cost, easy-to-use equipment, adequate selectivity, ability to calculate color solutions and low detection limit .
2.2. Flame Atomic Absorption Spectrometry (AAS)
Flame atomic absorption methods are referred to as direct aspiration determinations. They are typically performed as single element analyses and are completely free of inter element spectral interferences. The temperature or type of flame used is important for some of the elements. If flame and analytical conditions are not properly applied, chemical and ionization interferences can occur. Depending on the intended temperature and burning velocity, different flames can be produced using different mixtures of gases. Some elements can only be transformed to atoms at high temperatures. Also at high temperatures, when excess oxygen is present, some metals form oxides that do not dissolve into atoms .
2.3. Atomic Absorption Spectroscopy with graphite furnace (GFAA)
The GFAA and flame AAS measurement principle is the same. The distinction between these two methods is the way the sample is inserted into the instrument. Instead, an electro-thermal graphite furnace is used in the GFAA analysis. The sample is heated to dry stepwise (up to 3000ºC). The advantage of the graphite furnace is that the detection limit is approximately two orders of magnitude greater than that of AAS. The analysis of different species of a given element is important since different oxidation states of the same element can present different toxicity and, as a result, different risks .
2.4. Vibrational spectroscopy (infrared and Raman spectroscopy):
Vibrational spectroscopy is based on the interaction of the vibrational states of the atomic nuclei within their corresponding molecules and electromagnetic radiation. Among analytical techniques, vibrational spectroscopy has many key advantages such as high analytical speed, low operating costs, non-destructive and no or minimal sample preparation prior to the analysis of the sample . Raman and mid-IR (MIR) spectroscopy establish the standard fundamental vibrations used to elucidate the molecular structure of the sample under investigation. Near infrared (NIR) spectroscopy results in substantial overtones and mixture bands of certain fundamental vibrations .
2.5 Inductively-coupled plasma atomic emission spectrometry (ICP-AES)
This is a sensitive analytical technique that can be used to reliably determine the elementary composition of solution. Elemental requirements offered at established and approved concentrations are available from a variety of suppliers and can be used to precisely calculate the concentration of an element at parts per million (ppm) dilutions or below. The elemental analysis is focused on the detection of characteristic atomic spectral bands, which is expressed in the alternative name for this technique, often referred to as inductively coupled plasma optical emission spectrometry (ICP-OES). In order to produce atomic emission spectra, the nebulized sample is injected into an argon-generated, high temperature plasma, that causes the emission of electromagnetic radiation at wavelengths characteristic of the elements present in the sample .
2. 5. a. Principle of ICP-OES:
ICP-OES has been commercially available since 1974 and detects sample elements through the use of plasma (the fourth state of matters, next to solid, liquid & gas) and spectrometers. The instrument consists of a light source, a detector, a spectrometer and a data processing unit. The basic principle is that when plasma energy is supplied to the sample from outside, the components are excited. The emission rays are emitted when the excited atoms return to low energy state and the emission rays corresponding to the photon wavelength are determined by the spectrometer. The element category is calculated by the location of the photon rays and the component of each element is determined by the strength of the rays. Argon gas is supplied to the torch coil to produce plasma, and the high-frequency electrical current is transferred to the work coil at the tip of the torch tube. The torch consists of quartz and three concentric tubes into which argon flows. Argon gas is ionized and plasma is created by the electromagnetic field formed by the high-frequency current in the torch tube. Plasma has a high electron density and a high temperature (6000K- 10000K). In the torch desolvation, atomization and ionization of the sample occur and the samples are administered to the plasma in an atomized state through a narrow tube in the middle of the torch tube [18, 19]
2.5. b. ICP-OES ICAP
The Thermo Scientific iCAP 6200 is a compact, simultaneous dual view ICP emission spectrometer based on the powerful core technologies of the iCAP 6000 Series. The iCAP 6200 provides a cost effective analytical solution for routine analysis of liquids in laboratories with standard sample throughput requirements. Analysis ready sample introduction and method templates form an integral part of the instrument and enable simple ‘out-of-box’ operation for rugged and consistent day to day sample analysis. The iCAP 6200 incorporates future-proofed technology with field-upgradeable hardware and software specifications to allow the instrument’s capabilities to expand with your analytical requirements.