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Analytical Techniques
Spectroscopy
Spectroscopy is the use of the absorption, emission, or scattering of electromagnetic radiation by matter to qualitatively or quantitatively analyze or study the matter or to study physical processes. The matter can be atoms, molecules, atomic or molecular ions, or solids. The interaction of radiation with matter can cause redirection of the radiation and/or transitions between the energy levels of the atoms or molecules.
Beer-Lambert Law: Beer-Lambert law or simply Beer’s law is the heart of spectrometry.
Experimental measurements are usually made in terms of transmittance (T), which is defined as: where P is the power of light after it passes through the sample and Po is the initial light power. The relation between A and T is:
The figure shows the case of absorption of light through a sample cell and includes other processes that decreases the transmittance such as surface reflectance and scattering.
Instrumentation
General aspects of UV-Vis spectrophotometers are given in the introductory document on UV- Vis spectroscopy. Single-beam spectrophotometers can utilize a fixed wavelength light source or a continuous source. The simplest instruments use a single-wavelength light source, such as a light-emitting diode (LED), a sample container, and a photodiode detector. Instruments with a continuous source have a dispersing element and aperture or slit to select a single wavelength before the light passes through the sample cell. (see schematic below).
Five known concentrations of KMnO 4 : 1ppm, 20ppm, 40ppm, 60ppm, 80ppm were prepared and absorbance readings were taken at 520 nm. The absorbance readings are shown in the table.
Te calibration curve is in accordance with Beer’s law from which the concentration of the unknown solution is determined.
analytical quantity of interest, generally the concentration of some component of the analyte solution. The potential that develops in the electrochemical cell is the result of the free energy change that would occur if the chemical phenomena were to proceed until the equilibrium condition has been satisfied. This concept is typically introduced in quantitative analysis courses in relation to electrochemical cells that contain an anode and a cathode. For these electrochemical cells, the potential difference between the cathode electrode potential and the anode electrode potential is the potential of the electrochemical cell. If the reaction is conducted under standard state conditions, this equation allows the calculation of the standard cell potential. When the reaction conditions are not standard state, however, one must utilize the Nernst equation to determine the cell potential. In the following equations Ox stands for oxidized species and Red for its reduced form. For example Cu2+^ is oxidized form and Cu is reduced form.
pH Meters
pH meter measures the pH of a solution using an ion-selective electrode (ISE) that responds to the H+^ concentration of the solution. The pH electrode produces a voltage that is proportional to the concentration of the H+^ concentration, and making measurements with a pH meter is therefore a form of potentiometry. The pH electrode is attached to control electronics which convert the voltage to a pH reading and displays it on a meter.
Instrumentation
A pH meter consists of a H+-selective membrane, an internal reference electrode, an external reference electrode, and a meter with control electronics and display. Commercial pH electrodes usually combine all electrodes into one unit that are then attached to the pH meter. Picture of a pH meter
As the components elute from the column they can be quantified by a detector and/or collected for further analysis. An analytical instrument can be combined with a separation method for on- line analysis. Examples of such "hyphenated techniques" include gas and liquid chromatography with mass spectrometry (GC-MS and LC-MS). GC: It is applied to volatile organic compounds. The mobile phase is a gas and the stationary phase is usually a liquid on a solid support or sometimes a solid adsorbent.
