UV/Vis spectroscopy is routinely used in analytical chemistry for the quantitative determination of different analytes, such as transition metal ions, highly conjugated organic compounds, and biological macromolecules.

There are two regions in UV.

(i) Vacuum UV region: Below \(200\mathrm{nm}\)

(ii) Ordinary UV region: \(200 - 400\mathrm{nm}\)

IR spectroscopy (which is short for infrared spectroscopy) deals with the infrared region of the electromagnetic spectrum, i.e. light having a longer wavelength and a lower frequency than visible light. Infrared Spectroscopy generally refers to the analysis of the interaction of a molecule with infrared light.

1. UV/Electronic spectroscopy:

Promotion of e- from the ground state to the higher energy state

Vacuum UV region \(< 200\mathrm{nm}\)

UV region \(200\sim 400\mathrm{nm}\)

VIS region \(400\sim 800\mathrm{nm}\)

2. IR spectroscopy:

Near IR region \(800\sim 2500\mathrm{nm}\)

Mid IR/IR region \(2500\sim 15000\mathrm{nm}\) \(4000\mathrm{cm}^{-1}\sim 667\mathrm{cm}^{-1}\) (wave number)

Far IR region \(15000\sim 25000\mathrm{nm}\)

Finger print region \(>6666.7\mathrm{nm}\) less than \(1500\mathrm{cm}^{-1}\) (wave number) Absorption at higher wavelength in the IR region

3. NMR spectroscopy:

Radiation of the longest wavelength range --- radio waves --- 60-300 MHz

Ionic bonds result from the mutual attraction between oppositely charged ions while a covalent bond is a bond that results from a sharing of electrons between nuclei. They tend to be stronger than covalent bonds due to the columbic attraction between ions of opposite charges.

The functional group is defined as an atom or a group of atoms joined in a specific manner, which gives the chemical properties of the organic compound and are the centers for chemical reactivity. Compounds having a similar functional group have undergone similar reactions.

Bond dissociation energy is the minimum amount energy required to break a single bond. The greater is the bond dissociation energy, the more stable is the compound.

In methane, a carbon atom is bonded to 4 hydrogen atoms and has no lone pairs. With 4 bonding sites, it will have a hybridization of \(\mathrm{SP}^3\) with a tetrahedral shape.

We know carbon is tetravalent and hydrogen is monovalent. Thus, after formation of \(\mathrm{CH}_4\) molecule it have 4 sigma or bond pairs \((bp)\) and 0 lone pair \((lp)\) or pi bond. Thus its hybridization is sp3 and its bond angle is 109.5 degrees.

A water molecule consists of two hydrogen atoms bonded to an oxygen atom, and its overall structure is bent. This is because the oxygen atom, in addition to forming bonds with the hydrogen atoms, also carries two pairs of unshared \((lp)\) electrons.

Water has 8 electrons around the central oxygen atom. This means there are four electron pairs arranged in a tetrahedral shape. There are two bonding pairs and two lone pairs. The resulting shape is bent with an H-O-H angle of \(104.5^{\circ}\).

Water has hydrogen bonds, dipole-induced dipole forces, and London dispersion forces.

Actually, water has all three types of intermolecular forces, with the strongest being hydrogen bonding.

All things have London dispersion forces - the weakest interactions being temporary dipoles that form by shifting of electrons within a molecule.

Water, having hydrogen bound to an oxygen atom (which is much more electronegative than hydrogen, thus not sharing those bonded electrons very nicely) form dipoles of a special type called hydrogen bonds.

[The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction. London forces are the attractive forces that cause nonpolar substances to condense to liquids and to freeze into solids when the temperature is lowered sufficiently.]

Van der Waals forces include attractions and repulsions between atoms, molecules, and surfaces, as well as other intermolecular forces. They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles (a consequence of quantum dynamics).

Lewis Acid: a species that accepts an electron pair (i.e., an electrophile) and will have vacant orbitals.

Lewis Base: a species that donates an electron pair (i.e., a nucleophile) and will have lone-pair electrons.

pH is a measure of hydrogen ion concentration, a measure of the acidity or alkalinity of a solution. The pH scale usually ranges from 0 to 14. Aqueous solutions at \(25^{\circ}C\) with a pH less than 7 are acidic, while those with a pH greater than 7 are basic or alkaline.

A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it.

The Arrhenius acid-base concept classifies a substance as an acid if it produces hydrogen ions \(\mathrm{(H^{+})}\) or hydronium ions in water. A substance is classified as a base if it produces hydroxide ions \(\mathrm{(OH^{-})}\) in water.

A Bronsted-Lowry acid is a chemical species that donates one or more hydrogen ions in a reaction. In contrast, a Bronsted-Lowry base accepts hydrogen ions. When an acid donates its proton, the acid becomes its conjugate base and when a base accepts proton, the base becomes its conjugate acid.

A more general look at the theory is as an acid as a proton donor and a base as a proton acceptor.

118 elements have been identified: the first 94 occur naturally on Earth, and the remaining 24 are synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radionuclides, which decay over time into other elements. Iron is the most abundant element (by mass) making up Earth, while oxygen is the most common element in the Earth's crust.

S-block elements are the elements found in Group 1 and Group 2 on the periodic table. Group 1 is the alkali metals which have one valence electron. They have low ionization energies which makes them very reactive. Group 2 is the alkali earth metals which have two valence electrons, filling their s sublevel.

Oxidation occurs when there is addition of oxygen or removal of hydrogen or removal of electrons. The substance which oxidizes other substance is called oxidizing agent.

Reduction occurs when there is addition of hydrogen or removal of oxygen or addition of electrons. The substance which reduces other substance is called reducing agent.

When reduction and oxidation occurs simultaneously it is called redox reaction.

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first or initial ionization energy or Ei of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions.

Ionization energy exhibits periodicity on the periodic table. The general trend is for ionization energy to increase moving from left to right across an element period. Moving left to right across a period, atomic radius decreases, so electrons are more attracted to the (closer) nucleus.

The shielding effect is when the electron and the nucleus in an atom have a decrease in attraction which changes the nuclear charge. An example of shielding effect is in nuclear fission when electrons furthest from the center of the atom are pulled away.

Shielding effect is the reduction in the effective nuclear charge on the electron cloud, due to differences in the attraction forces between electrons and the nucleus. Shielding effect is also known as the Screening Effect.

Atomic radius patterns are observed throughout the periodic table. Atomic size gradually decreases from left to right across a period of elements. This is because, within a period or family of elements, all electrons are added to the same shell.

In chemistry, a radical is an atom, molecule, or ion that has an unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes.

The s-block of elements is the alkali metals and the alkaline earth metals. The d-block of elements is the transition metals. The f-block of elements is the lanthanides (first row) and the actinides (second row).

The p-block elements are unified by the fact that their valence electrons (outermost electrons) are in the p orbital.

The elements which have partially filled d-orbitals either ground state or in one or more of their ions, are called d-block elements or outer transition elements. Their properties are intermediate between s-block elements and p-block elements.

The f block elements are the lanthanides and actinides and are called the inner transition elements because of their placement in the periodic table due to their electron configurations. The f orbitals of the electron shell are filled with "n-2." Total 28 atoms are.

In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

Electron affinity increases upward for the groups and from left to right across periods of a periodic table because the electrons added to energy levels become closer to the nucleus, thus a stronger attraction between the nucleus and its electrons.

A titration is a technique where a solution of known concentration (titrant) is used to determine the concentration of an unknown solution (titrand). Typically, the titrant is added from a burette to a known quantity of the analyte (the unknown solution) until the reaction is complete.

A primary standard is a reagent that is extremely pure, stable, it not a hydrate/has no water of hydration, and has a high molecular weight.

Example: \(\mathrm{CaCO_3}\), \(\mathrm{Na_2CO_3}\), \(\mathrm{Na_2SO_4}\), \(\mathrm{Na_2C_2O_4}\), \(\mathrm{NaCl}\), \(\mathrm{AgNO_3}\), \(\mathrm{K_2Cr_2O_7}\), \(\mathrm{As_2O_3}\), Oxalic acid, Benzoic acid, KBr, Potassium hydrogen phthalate, Sulfanilic acid, Zn, Mg, Ni etc.

A secondary standard is a standard that is prepared in the laboratory for a specific analysis. It is usually standardized against a primary standard.

Example: \(\mathrm{KMnO_4}\), \(\mathrm{NaOH}\), \(\mathrm{KOH}\), \(\mathrm{HCl}\), \(\mathrm{H_2SO_4}\) etc.

Thin-layer chromatography (TLC) is a chromatography technique used to separate nonvolatile mixtures. Thin-layer chromatography is performed on a sheet of glass, plastic, or aluminium foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide (alumina), or cellulose. This layer of adsorbent is known as the stationary phase.

Chromatography is a technique to separate mixtures of substances into their components on the basis of their molecular structure and molecular composition.

This involves a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas). The mobile phase flows through the stationary phase and carries the components of the mixture with it. Sample components that display stronger interactions with the stationary phase will move more slowly through the column than components with weaker interactions. This difference in rates causes the separation of various components.

High Performance Liquid Chromatography (HPLC) is a form of column chromatography that pumps a sample mixture or analyte in a solvent (known as the mobile phase) at high pressure through a column with chromatographic packing material (stationary phase).

Mobile phase is the liquid or gas that flows through a chromatography system, moving the materials to be separated at different rates over the stationary phase.

Stationary phase is the solid or liquid phase of a chromatography system on which the materials are to be separated or selectively adsorbed.

Column is the stationary phase in HPLC.

Chromatography works on the principle that different compounds will have different solubility and adsorption to the two phases between which they are to be partitioned. Thin Layer Chromatography (TLC) is a solid-liquid technique in which the two phases are a solid (stationary phase) and a liquid (moving phase).

Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume.

Types of potentiometric titrations for the determination of analytes in photo processing solutions include acid-base, redox, precipitation, and complexometric.

Isomers are molecules with the same chemical formula but different chemical structures. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms in space.

Two molecules are described as stereoisomers if they are made of the same atoms connected in the same sequence, but differ in the three-dimensional orientations of their atoms in space.

In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other but non-superposable (not identical), much as one's left and right hands are mirror images of each other that cannot appear identical simply by reorientation.

D-alanine and L-alanine are examples of enantiomers or mirror images. Only the L-forms of amino acids are used to make proteins.

An asymmetric carbon atom (chiral carbon) is a carbon atom that is attached to four different types of atoms or groups of atoms.

Enantiomers have identical chemical and physical properties in an achiral environment. Enantiomers rotate the direction of plane polarized light to equal, but to opposite angles and interact with other chiral molecules differently.

Diastereomers are stereoisomers that are not mirror images of one another and are non-superimposable on one another.

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electrically, such a solution is neutral.

A solvent is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. The quantity of a solute that can be dissolved in a specific volume of solvent varies with temperature.

Organic solvent: Chloroform, Acetone, Ethanol, Methanol, etc.

Inorganic solvent: Water, Ammonia, Carbon dioxide, Carbon tetrachloride, Hydrogen fluoride, Molten salt, Sulfuric acid, etc.

Hard water contains a noticeable amount of dissolved minerals, namely calcium and magnesium, but also chalk and lime.

Soft water is treated water that only contains sodium.

For many solids dissolved in liquid water, the solubility increases with temperature. The increase in kinetic energy that comes with higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.

Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent.

Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as paint thinners (e.g. toluene, turpentine), as nail polish removers and glue solvents (acetone, methyl acetate, ethyl acetate), in spot removers (e.g. hexane, petrol ether), in detergents (citrus terpenes) and in perfumes (ethanol).

Polar solvents have large dipole moments (aka "partial charges"); they contain bonds between atoms with very different electronegativity, such as oxygen and hydrogen.

Non polar solvents contain bonds between atoms with similar electronegativity, such as carbon and hydrogen (think hydrocarbons, such as gasoline).

Non-polar solvents are lipophilic as they dissolve non-polar substances such as oils, fats, greases.

Examples: carbon tetrachloride \((\mathrm{CCl}_4)\), pentane, toluene, benzene \((\mathrm{C}_6\mathrm{H}_6)\), and diethyl ether \((\mathrm{CH}_3\mathrm{CH}_2\mathrm{OCH}_2\mathrm{CH}_3)\), hexane \((\mathrm{CH}_3(\mathrm{CH}_2)_4\mathrm{CH}_3)\), methylene chloride \((\mathrm{CH}_2\mathrm{Cl}_2)\).

A polar solvent is a liquid with molecules that have a slight electrical charge due to its shape.

Example: water, deuterium oxide (heavy water for NMR), ethanol, methanol, acetone, methyl ethyl ketone, isopropanol, n-propanol, acetonitrile, DMSO (dimethyl sulfoxide) or deuterated DMSO (heavy DMSO for NMR), DMF (dimethyl formamide);

HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with adsorbent, leading to the separation of the sample components. The active component of the column, the adsorbent, is typically a granular material made of solid particles (e.g., silica, polymers, etc.), 2-50μm in size.

There are following variants of HPLC, depending upon the phase system (stationary) in the process:

1. Normal Phase HPLC

This method separates analytes on the basis of polarity. NP-HPLC uses polar stationary phase and non-polar mobile phase. Therefore, the stationary phase is usually silica and typical mobile phases are hexane, methylene chloride, chloroform, diethyl ether, and mixtures of these. Polar samples are thus retained on the polar surface of the column packing longer than less polar materials.

2. Reverse Phase HPLC

The stationary phase is nonpolar (hydrophobic) in nature, while the mobile phase is a polar liquid, such as mixtures of water and methanol or acetonitrile. It works on the principle of hydrophobic interactions hence the more nonpolar the material is, the longer it will be retained.

3. Size-exclusion HPLC

The column is filled with material having precisely controlled pore sizes, and the particles are separated according to it's their molecular size. Larger molecules are rapidly washed through the column; smaller molecules penetrate inside the porous of the packing particles and elute later.

4. Ion-Exchange HPLC

The stationary phase has an ionically charged surface of opposite charge to the sample ions. This technique is used almost exclusively with ionic or ionizable samples. The stronger the charge on the sample, the stronger it will be attracted to the ionic surface and thus, the longer it will take to elute. The mobile phase is an aqueous buffer, where both pH and ionic strength are used to control elution time.

HPLC instrumentation includes a pump, injector, column, detector and integrator or acquisition and display system. The heart of the system is the column where separation occurs.

1. Solvent Reservoir

Mobile phase contents are contained in a glass reservoir. The mobile phase, or solvent, in HPLC is usually a mixture of polar and non-polar liquid components whose respective concentrations are varied depending on the composition of the sample.

2. Pump

A pump aspirates the mobile phase from the solvent reservoir and forces it through the system's column and detector. Depending on a number of factors including column dimensions, particle size of the stationary phase, the flow rate and composition of the mobile phase, operating pressures of up to 42000 kPa (about 6000 psi) can be generated.

3. Sample Injector

The injector can be a single injection or an automated injection system. An injector for an HPLC system should provide injection of the liquid sample within the range of 0.1-100 mL of volume with high reproducibility and under high pressure (up to 4000 psi).

4. Columns

Columns are usually made of polished stainless steel, are between 50 and \(300~\mathrm{mm}\) long and have an internal diameter of between 2 and \(5\mathrm{mm}\). They are commonly filled with a stationary phase with a particle size of \(3 - 10\mu \mathrm{m}\).

Columns with internal diameters of less than \(2\mathrm{mm}\) are often referred to as microbore columns. Ideally the temperature of the mobile phase and the column should be kept constant during an analysis.

5. Detector

The HPLC detector, located at the end of the column detects the analytes as they elute from the chromatographic column. Commonly used detectors are UV-spectroscopy, fluorescence, mass-spectrometric and electrochemical detectors.

6. Data Collection Devices

Signals from the detector may be collected on chart recorders or electronic integrators that vary in complexity and in their ability to process, store and reprocess chromatographic data. The computer integrates the response of the detector to each component and places it into a chromatograph that is easy to read and interpret.

They are of three types, i.e. fixed wavelength detectors, variable wavelength detectors and the diode array detectors.

1. UV, VIS, and PDA Detectors
2. Refractive-Index Detector (RID)
3. Evaporative Light Scattering Detector
4. Multi-Angle Light Scattering Detector
5. Mass Spectrometer
6. Conductivity Detector
7. Fluorescence Detector
8. Chemiluminescence Detector
9. Optical Rotation Detector
10. Electro Chemical Detector

When molecules in the mixture are very similar, direct quantification becomes difficult. HPLC is a form of column chromatography used frequently to separate, identify and quantify compounds. It consists of a stationary phase that absorbs the analytes and holds them for a particular time.

Isocratic means that the mixture of your mobile phase is consistent over the complete testing time.

Using a gradient implies that the compounding of the eluent mixture is changed during measurement and so influences the retention of analytes.

Speed, efficiency and accuracy.

Compared to other chromatographic techniques, such as TLC, HPLC is extremely quick and efficient. It uses a pump, rather than gravity, to force a liquid solvent through a solid adsorbent material, with different chemical components separating out as they move at different speeds.

Retention time (RT) is a measure of the time taken for a solute to pass through a chromatography column. It is calculated as the time from injection to detection. The RT for a compound is not fixed as many factors can influence it even if the same GC and column are used.

The refractive index (RI) detector is the only universal detector in HPLC. The detection principle involves measuring of the change in refractive index of the column effluent passing through the flow-cell. The greater the RI difference between sample and mobile phase, the larger the imbalance will become.

System suitability is defined by ICH as "the checking of a system, before or during analysis of unknowns, to ensure system performance." System suitability criteria may include such factors as plate count, tailing, retention, and/or resolution.

The resolution of an elution is a quantitative measure of how well two elution peaks can be differentiated in a chromatographic separation. It is defined as the difference in retention times between the two peaks, divided by the combined widths of the elution peaks.

Theoretical plate number (N) is an index that indicates column efficiency. It describes the number of plates as defined according to plate theory, and can be used to determine column efficiency based on calculation in which the larger the theoretical plate number the sharper the peaks.

The noise is measured between two lines bracketing the baseline and the signal is measured from the middle of the baseline to the top of the peak. S/N is merely the signal divided by the noise.

The tailing factor is a measure of peak tailing. It is defined as the distance from the front slope of the peak to the back slope divided by twice the distance from the center line of the peak to the front slope, with all measurements made at \(5\%\) of the maximum peak height.

Limit of detection (LoD) (also called detection limit) - the smallest amount or concentration of analyte in the test sample that can be reliably distinguished from zero.

Limit of quantitation (LoQ) - the lowest concentration of analyte that can be determined with an acceptable repeatability and trueness.

C18 is has 18 carbon atoms while C8 has 8 carbons in the column packing that are bonded to the silica (Si). From what I have seen practically, generally, C18 retains more than C8 such that for a similar compound eluted on the two columns, it will elute later on the C18.

The accuracy of an analytical method is the degree of agreement of test results generated by the method to the true value. Accuracy is measured by spiking the sample matrix of interest with a known concentration of analyte standard and analyzing the sample using the "method being validated.

Precision of an analytical method is the degree of agreement among individual test results when the method is applied repeatedly to multiple samplings of a homogenous sample.

The linearity of an analytical method is its ability to elicit test results that are directly proportional to the concentration of the analyte in samples within a given range.

Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.

For example, carbon-12, carbon-13, and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7, and 8 respectively.

Chemical indicator is any substance that gives a visible sign, usually by a color change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution. An example is the substance called methyl yellow, which imparts a yellow color to an alkaline solution.

The most common indicators are Litmus, Phenolphthalein and Methyl Orange.

Litmus is a weak acid. Methyl orange is a weak base. Phenolphthalein is a weak acid.

pH indicators detect the presence of \(\mathrm{H+}\) and \(\mathrm{OH-}\). They do this by reacting with \(\mathrm{H+}\) and \(\mathrm{OH-}\): they are themselves weak acids and bases. If an indicator is a weak acid and is coloured and its conjugate base has a different color, deprotonation causes a color change.

First of all the color of KMnO4 is dark purple due to \(+7\) oxidation state of Mn (manganese). Usually KMnO4 is used in titrations against solutions like oxalic acid, FAS (ferrous ammonium sulfate, etc.). KMnO4 oxidizes these standard solutions. As we do the titration we would reach the end point. The end point indicates that the standard solution was completely oxidized. So once all the permanganate ions are used up in the reaction, the solution loses its pink color. This indicates the end of the reaction and hence potassium permanganate is called a self-indicator as it acts as an indicator apart from being one of the reactants.

A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth color changes over a wide range pH values to indicate the acidity or alkalinity of solutions.

A universal indicator is typically composed of thymol blue (1.2 - 2.8) & (8.0 - 9.6), methyl orange (3.1 - 4.4), methyl red (4.4 - 5.8), bromothymol blue (6.0 - 7.6) and phenolphthalein (8.3 - 10.0).

When universal indicator is added to a solution, the color change can indicate the approximate pH of the solution. Acids cause universal indicator solution to change from green toward red. Bases cause universal indicator to change from green toward purple.

A catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction. A catalyst will appear in the steps of a reaction mechanism, but it will not appear in the overall chemical reaction (as it is not a reactant or product).

Catalysts called enzymes are important in biology. A catalyst works by providing an alternative reaction pathway to the reaction product. The rate of the reaction is increased as this alternative route has lower activation energy than the reaction route not mediated by the catalyst.

Activation energy, in chemistry, the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport.

In chemistry and physics, activation energy is the energy which must be provided to a chemical or nuclear system with potential reactants to result in: a chemical reaction, nuclear reaction, or various other physical phenomena.

The activation energy (Ea) of a reaction is measured in joules (J) and or kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).

Chromatographic separations can be carried out using a variety of stationary phases, including immobilized silica on glass plates (thin-layer chromatography), volatile gases (gas chromatography), paper (paper chromatography), and liquids (liquid chromatography).

Plane polarized light is a light wave in which all photons have the same polarization i.e. the waves oscillate in only one direction.

Any substance capable of rotating the plane of vibration of polarized light to the right or left: Dextrorotatory or levorotatory — used of compounds, molecules, or atoms.

The force of attraction between the molecules affects the melting point of a compound. Stronger intermolecular interactions result in higher melting points. Ionic compounds usually have high melting points because the electrostatic forces holding the ions (ion-ion interaction) are much stronger.

Monomer, a molecule of any of a class of compounds, mostly organic, that can react with other molecules to form very large molecules, or polymers. The essential feature of a monomer is polyfunctionality, the capacity to form chemical bonds to at least two other monomer molecules.

Polymer, any of a class of natural or synthetic substances composed of very large molecules, called macromolecules that are multiples of simpler chemical units called monomers. Polymers make up many of the materials in living organisms, including, for example, proteins, cellulose, and nucleic acids.

Molarity, molality, and normality are all units of concentration in chemistry.

Molarity (M) is defined as the number of moles of solute per liter of solution.

Molality (m) is defined as the number of moles of solute per kilogram of solvent.

Normality (N) is defined as the number of equivalents per liter of solution.

A mole corresponds to the mass of a substance that contains \(6.023 \times 10^{23}\) particles of the substance. The mole is the SI unit for the amount of a substance. Its symbol is mol. By definition: 1 mol of carbon-12 has a mass of 12 grams and contains \(6.022140857 \times 10^{23}\) of carbon atoms (to 10 significant figures).

Avogadro's number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance. It is equal to \(6.022 \times 10^{23}\) mol\(^{-1}\) and is expressed as the symbol \(\mathrm{NA}\).

Avogadro's law states that "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules."

Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many systems that use buffering for pH regulation. For example, the bicarbonate buffering system is used to regulate the pH of blood.

The term "spectroscopy" defines a large number of techniques that use electromagnetic radiation to obtain information on the structure and properties of matter.

The basic principle shared by all spectroscopic techniques is to shine a beam of electromagnetic radiation onto a sample, and observe how it responds to such a stimulus.

Ultraviolet and visible (UV-Vis) absorption spectroscopy is the measurement of the intensity of a beam of light after it passes through a sample or after reflection from a sample surface. Absorption measurements can be at a single wavelength or over an extended spectral range.

Molecules containing bonding and non-bonding electrons (n-electrons) can absorb energy in the form of ultraviolet or visible light to excite these electrons to higher anti-bonding molecular orbitals. The more easily excited the electrons (i.e. lower energy gap between the HOMO and the LUMO), the longer the wavelength of light it can absorb. There are four possible types of transitions \((\pi - \pi^{*}, \mathrm{n} - \pi^{*}, \sigma - \sigma^{*},\) and \(\mathrm{n} - \sigma^{*})\), and they can be ordered as follows: \(\sigma - \sigma^{*} > \mathrm{n} - \sigma^{*} > \pi - \pi^{*} > \mathrm{n} - \pi^{*}\).

The term vacuum UV (below \(\approx 200 \mathrm{nm}\)) refers to the wavelength range where a vacuum apparatus is often used, because the light is strongly absorbed in air. The vacuum UV includes the far and extreme UV.

UV/VIS/NIR spectroscopy is a powerful analytical technique to determine the optical properties (transmittance, reflectance and absorbance) of liquids and solids. It can be applied to characterize semiconductor materials, coatings, glass and many other research and manufacturing materials.

Electronegativity is the property of an atom which increases with its tendency to attract the electrons of a bond. If two bonded atoms have the same electronegativity values as each other, they share electrons equally in a covalent bond.

Moving down a group on the periodic table, the electronegativity of an element decreases because the increased number of energy levels puts the outer electrons very far away from the pull of the nucleus. Electronegativity increases as you move from left to right across a period on the periodic table.

pH stands for Potential of Hydrogen. It refers to the hydrogen ion concentration in a solution. It is the measure of the acidity or alkalinity of a solution. The pH value ranges from 0 to 14 on a pH scale.

A buffer is a chemical substance that helps maintain a relatively constant pH in a solution, even in the face of addition of acids or bases. Buffering is important in living systems as a means of maintaining a fairly constant internal environment, also known as homeostasis.

There are several buffer systems in the body. The most important include: (1) bicarbonate buffer \((\mathrm{HCO}_{3}^{-} / \mathrm{CO}_{2})\), (2) haemoglobin buffer (in erythrocytes), (3) phosphate buffer, (4) proteins, and (5) ammonium buffer.

Sodium, calcium, potassium, chloride, phosphate, and magnesium are all electrolytes.

Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.