Saturday, 1 March 2014

OCH 213. ADVANCED INORGANIC CHEMISTRY----- BY. MWL. JAPHET MASATU.

F. Albert Cotton

Frank Albert Cotton
Born	April 9, 1930 Philadelphia, PA
Died	February 20, 2007 (aged 76) College Station, TX
Institutions	Texas A&M University
Doctoral advisor	Geoffrey Wilkinson
Notable awards	National Medal of Science, Wolf Prize, Priestley Medal, FRS

Frank Albert Cotton (April 9, 1930 – February 20, 2007)^[1] was an American chemist. He was the W.T. Doherty-Welch Foundation Chair and Distinguished Professor of Chemistry at Texas A&M University. He authored over 1700 scientific articles.^[2] Cotton was recognized for his research on the chemistry of the transition metals.

Education

Frank Albert Cotton (known as "Al" Cotton, or "F Albert" on publications) was born on April 9, 1930 in Philadelphia, Pennsylvania. He attended local public schools before Drexel University and then Temple University.^[3] After earning his BA degree from Temple in 1951, Cotton pursued a Ph.D. thesis under the guidance of Sir Geoffrey Wilkinson at Harvard where he worked on metallocenes.^[4] He received his Ph.D in 1955.^[5]

Independent career

Following his graduation from Harvard, Cotton began teaching at MIT. In 1961, at thirty-one years of age, he became the youngest person to have received a full professorship at MIT.^[3] His work emphasized both electronic structure and chemical synthesis. He pioneered the study of multiple bonding between transition metal atoms, starting with research on rhenium halides,^[6] and in 1964 identified the quadruple bond in the Re
2Cl2−
8 ion. His work soon focused on other metal-metal bonded species,^[7] elucidating the structure of chromium(II) acetate.
He was an early proponent of single crystal X-ray diffraction as a tool for elucidating the extensive chemistry of metal complexes. Through his studies on clusters, he demonstrated that many exhibited "fluxionality", whereby ligands interchange coordination sites on spectroscopically observable time-scales. He coined the term "hapticity" and the nomenclature that derives from it.
In 1962 he undertook the crystal structure of the Staphylococcal nuclease enzyme,^[8] solved to 2Å resolution in 1969, published in 1971,^[9] and deposited in the Protein Data Bank (PDB code 1SNS) as one of the first dozen protein crystal structures.^[10]
In 1972 Cotton moved to Texas A&M University as the Robert A. Welch Professor of Chemistry. The following year he was named the Doherty-Welch Distinguished Professor of Chemistry. He also served as the director of the university's Laboratory for Molecular Structure and Bonding.^[3]^[11]

Pedagogical influence

In addition to his research, Cotton taught inorganic chemistry. He authored Chemical Applications of Group Theory.^[12] This text focuses on group theoretical analysis of bonding and spectroscopy.
Among college students, Cotton is perhaps best known as the coauthor of the textbook Advanced Inorganic Chemistry, now in its sixth English edition.^[13]^[14] Coauthored with his thesis advisor, Sir Geoffrey Wilkinson, and now with coauthors Carlos Murillo and Manfred Bochmann, the textbook is colloquially known as "Cotton and Wilkinson." The text surveys coordination chemistry, cluster chemistry, homogeneous catalysis, and organometallic chemistry.^[3]^[15]
Cotton served on various editorial boards of scientific journals, including those of the Journal of the American Chemical Society, Inorganic Chemistry, and Organometallics. He chaired the Division of Inorganic Chemistry of the ACS and was an ACS Councillor for five years. He served on the U.S. National Science Board (1986–1998), which oversees the National Science Foundation, and the Scientific and Technical Advisory Committee of Argonne National Laboratory, and the National Research Laboratory Commission of Texas.
Cotton supervised the thesis research of 116 doctoral students^[11] as well as more than 150 postdoctoral associates.^[5]

Recognition

Among the awards Cotton received included the U.S. National Medal of Science in 1982,^[16] the Wolf Prize in 2000; and the Priestley Medal, the American Chemical Society's highest recognition, in 1998.^[11]
In 1995, the Department of Chemistry at Texas A&M along with the local section of the American Chemical Society, inaugurated the annual F.A. Cotton Medal for excellence in chemical research. A second award named in his honor, the F. Albert Cotton Award for Synthetic Inorganic Chemistry,^[17] is presented at the National Meeting of the American Chemical Society each year.^[11]
Cotton was a member of the National Academy of Sciences in the United States, and the corresponding academies in Russia, China, the United Kingdom, France, and Denmark, as well as the American Philosophical Society. He received twenty-nine honorary doctorates.^[11]

Run for ACS presidency

Cotton caused a controversy in his run for President of the American Chemical Society for 1984, wherein he mailed a letter to selected members describing his opponent as “a mediocre industrial chemist”.^[18] Cotton ultimately lost the bid to his opponent Dr. Warren D. Niederhauser of Rohm & Haas.^[19]

F.A. Cotton Medal for Excellence in Chemical Research

The F.A. Cotton Medal is awarded annually by the American Chemical Society, and sponsored by the The F. Albert Cotton Endowment Fund. Previous winners have included :
2012 R. Graham Cooks, Purdue University;^[20] 2011 George M. Whitesides, Harvard University; 2010 Peter J. Stang, University of Utah; 2009 Richard N. Zare, Stanford University; 2008 Chi-Huey Wong, The Scripps Research Institute, and National Taiwan University; 2007 Jacqueline K. Barton, California Institute of Technology; 2006 Robin M. Hochstrasser, University of Pennsylvania; 2005 Richard H. Holm, Harvard University; 2004 Albert Eschenmoser, Swiss Federal Institute of Technology, Zurich, and Scripps Research Institute; 2003 Gabor A. Somorjai, University of California, Berkeley; 2002 Ada Yonath, Weizman Institute of Science; 2001 Samuel J. Danishefsky, Department of Chemistry, Columbia University; 2000 Tobin J. Marks, Department of Chemistry, Northwestern University; 1999 Alexander Pines, Department of Chemistry, University of California, Berkeley; 1998 JoAnne Stubbe, Department of Chemistry, Massachusetts Institute of Technology; 1997 Pierre-Gilles de Gennes, École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, Collège de France; 1996 George A. Olah, Department of Chemistry, University of Southern California; 1995 F. Albert Cotton, Department of Chemistry, Texas A&M University ^[21]

Death

Cotton died on February 20, 2007 in College Station, Texas from complications of a head injury he suffered in a fall in October 2006.^[22] He was survived by his wife, the former Diane Dornacher, whom he married in 1959, and their two daughters, Jennifer and Jane.^[3] The Brazos County Sheriff's Department opened an investigation into his death, describing his death as "suspicious

Geoffrey Wilkinson

Sir Geoffrey Wilkinson

Born	14 July 1921 Springside, England
Died	26 September 1996 (aged 75) London, England
Nationality	United Kingdom
Fields	Inorganic chemistry
Institutions	University of California, Berkeley Harvard University Imperial College
Alma mater	Imperial College
Doctoral advisor	Henry Vincent Aird Briscoe
Known for	Homogeneous transition metal catalysis
Notable awards	Nobel Prize in Chemistry (1973) Fellow of the Royal Society^[1]

Sir Geoffrey Wilkinson FRS^[1] (14 July 1921 – 26 September 1996) was a Nobel laureate English chemist who pioneered inorganic chemistry and homogeneous transition metal catalysis.^[2]

Biography

Wilkinson was born at Springside, Todmorden, in Yorkshire. His father,Henry Wilkinson,^[3] was a master house painter and decorator; his mother,Ruth,^[3] worked in a local cotton mill. One of his uncles, an organist and choirmaster, had married into a family that owned a small chemical company making Epsom and Glauber's salts for the pharmaceutical industry; this is where he first developed an interest in chemistry.
He was educated at the local council primary school and, after winning a County Scholarship in 1932, went to Todmorden Grammar School. His physics teacher there, Luke Sutcliffe, had also taught Sir John Cockcroft, who received a Nobel Prize for "splitting the atom".

Wilkinson's catalyst RhCl(PPh₃)₃

In 1939 he obtained a Royal Scholarship for study at Imperial College London, from where he graduated in 1941. In 1942 Professor Friedrich Paneth was recruiting young chemists for the nuclear energy project. Wilkinson joined and was sent out to Canada, where he stayed in Montreal and later Chalk River Laboratories until he could leave in 1946. For the next four years he worked with Professor Glenn T. Seaborg at University of California, Berkeley, mostly on nuclear taxonomy.^[4] He then became a Research Associate at the Massachusetts Institute of Technology and began to return to his first interest as a student - transition metal complexes of ligands such as carbon monoxide and olefins.
He was then at the Harvard University from September 1951 until he returned to England in December 1955, with a sabbatical break of nine months in Copenhagen. At Harvard, he still did some nuclear work on excitation functions for protons in cobalt, but had already begun to work on olefin complexes.
In June 1955 he was appointed to the chair of Inorganic Chemistry at Imperial College London, and from then on worked almost entirely on the complexes of transition metals.
In 1980 he was awarded an honorary doctorate of science from the University of Bath. Imperial College London named a new hall of residence after him, which opened in October 2009.
He was married, with two daughters.

Work

Structure of ferrocene Fe(C₅H₅)₂

He is well known for his development of Wilkinson's catalyst RhCl(PPh₃)₃, and for the discovery of the structure of ferrocene. Wilkinson's catalyst is used industrially in the hydrogenation of alkenes to alkanes.^[5]
He received many awards, including the Nobel Prize for Chemistry in 1973 for his work on “organometallic compounds” (with Ernst Otto Fischer). He is also well known for writing, with his former doctoral student F. Albert Cotton, "Advanced Inorganic Chemistry", often referred to simply as "Cotton and Wilkinson", one of the standard inorganic chemistry textbooks.[

OCH 212. BASIC ORGANIC SPECTROSCOPY ----- BY. MWL. JAPHET MASATU.

BASIC ORGANIC SPECTROSCOPY.

Analysis of white light by dispersing it with a prism is an example of spectroscopy.

Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and radiated energy.^[1]^[2] Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism. Later the concept was expanded greatly to comprise any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is often represented by a spectrum, a plot of the response of interest as a function of wavelength or frequency.

Introduction

Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are often used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers.
Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies (colors). Neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors and hues. A commonly encountered molecular spectrum is that of nitrogen dioxide. Gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky.
Spectroscopic studies were central to the development of quantum mechanics and included Max Planck's explanation of blackbody radiation, Albert Einstein's explanation of the photoelectric effect and Niels Bohr's explanation of atomic structure and spectra. Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy is also used in astronomy and remote sensing on earth. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature and velocity).

Theory

One of the central concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency. This plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance.
In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy $(E)$ of a photon is related to its frequency $(\nu)$ by $E = h\nu$ where $h$ is Planck's constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.
Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford-Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough.

Classification of methods

Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques. The various implementations and techniques can be classified in several ways.

Type of radiative energy

Types of spectroscopy are distinguished by the type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy. The types of radiative energy studied include:

Electromagnetic radiation was the first source of energy used for spectroscopic studies. Techniques that employ electromagnetic radiation are typically classified by the wavelength region of the spectrum and include microwave, terahertz, infrared, near infrared, visible and ultraviolet, x-ray and gamma spectroscopy.
Particles, due to their de Broglie wavelength, can also be a source of radiative energy and both electrons and neutrons are commonly used. For a particle, its kinetic energy determines its wavelength.
Acoustic spectroscopy involves radiated pressure waves.
Mechanical methods can be employed to impart radiating energy, similar to acoustic waves, to solid materials.

Nature of the interaction

Types of spectroscopy can also be distinguished by the nature of the interaction between the energy and the material. These interactions include:^[1]

Absorption occurs when energy from the radiative source is absorbed by the material. Absorption is often determined by measuring the fraction of energy transmitted through the material; absorption will decrease the transmitted portion.
Emission indicates that radiative energy is released by the material. A material's blackbody spectrum is a spontaneous emission spectrum determined by its temperature. Emission can also be induced by other sources of energy such as flames or sparks or electromagnetic radiation in the case of fluorescence.
Elastic scattering and reflection spectroscopy determine how incident radiation is reflected or scattered by a material. Crystallography employs the scattering of high energy radiation, such as x-rays and electrons, to examine the arrangement of atoms in proteins and solid crystals.
Impedance spectroscopy studies the ability of a medium to impede or slow the transmittance of energy. For optical applications, this is characterized by the index of refraction.
Inelastic scattering phenomena involve an exchange of energy between the radiation and the matter that shifts the wavelength of the scattered radiation. These include Raman and Compton scattering.
Coherent or resonance spectroscopy are techniques where the radiative energy couples two quantum states of the material in a coherent interaction that is sustained by the radiating field. The coherence can be disrupted by other interactions, such as particle collisions and energy transfer, and so often require high intensity radiation to be sustained. Nuclear magnetic resonance (NMR) spectroscopy is a widely used resonance method and ultrafast laser methods are also now possible in the infrared and visible spectral regions.

Type of material

Spectroscopic studies are designed so that the radiant energy interacts with specific types of matter.

Atoms

Atomic spectroscopy was the first application of spectroscopy developed. Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due to electronic transitions of outer shell electrons as they rise and fall from one electron orbit to another. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states.
Atoms of different elements have distinct spectra and therefore atomic spectroscopy allows for the identification and quantitation of a sample's elemental composition. Robert Bunsen and Gustav Kirchhoff discovered new elements by observing their emission spectra. Atomic absorption lines are observed in the solar spectrum and referred to as Fraunhofer lines after their discoverer. A comprehensive explanation of the hydrogen spectrum was an early success of quantum mechanics and explained the Lamb shift observed in the hydrogen spectrum led to the development of quantum electrodynamics.
Modern implementations of atomic spectroscopy for studying visible and ultraviolet transitions include flame emission spectroscopy, inductively coupled plasma atomic emission spectroscopy, glow discharge spectroscopy, microwave induced plasma spectroscopy, and spark or arc emission spectroscopy. Techniques for studying x-ray spectra include X-ray spectroscopy and X-ray fluorescence (XRF).

Molecules

The combination of atoms into molecules leads to the creation of unique types of energetic states and therefore unique spectra of the transitions between these states. Molecular spectra can be obtained due to electron spin states (electron paramagnetic resonance), molecular rotations, molecular vibration and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimeter-wave spectral regions; rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of the atomic nuclei and are studied by both infrared and Raman spectroscopy. Electronic excitations are studied using visible and ultraviolet spectroscopy as well as fluorescence spectroscopy.
Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser.

Crystals and extended materials

The combination of atoms or molecules into crystals or other extended forms leads to the creation of additional energetic states. These states are numerous and therefore have a high density of states. This high density often makes the spectra weaker and less distinct, i.e., broader. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material. Acoustic and mechanical responses are due to collective motions as well.
Pure crystals, though, can have distinct spectral transitions and the crystal arrangement also has an effect on the observed molecular spectra. The regular lattice structure of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies.

Nuclei

Nuclei also have distinct energy states that are widely separated and lead to gamma ray spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows for NMR spectroscopy.

Organic Chemistry/Spectroscopy

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There are several spectroscopic techniques which can be used to identify organic molecules: infrared (IR), mass spectroscopy (MS) UV/visible spectroscopy (UV/Vis) and nuclear magnetic resonance (NMR).
IR, NMR and UV/vis spectroscopy are based on observing the frequencies of electromagnetic radiation absorbed and emitted by molecules. MS is based on measuring the mass of the molecule and any fragments of the molecule which may be produced in the MS instrument.

UV/Visible Spectroscopy

UV/Vis Spectroscopy uses ultraviolet and/or visible light to examine the electronic properties of molecules. Irradiating a molecule with UV or Visible light of a specific wavelength can cause the electrons in a molecule to transition to an excited state. This technique is most useful for analyzing molecules with conjugated systems or carbonyl bonds.

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) Spectroscopy is one of the most useful analytical techniques for determining the structure of an organic compound. There are two main types of NMR, ¹H-NMR (Proton NMR) and ¹³C-NMR (Carbon NMR). NMR is based on the fact that the nuclei of atoms have a quantized property called spin. When a magnetic field is applied to a ¹H or ¹³C nucleus, the nucleus can align either with (spin +1/2) or against (spin -1/2) the applied magnetic field.
These two states have different potential energies and the energy difference depends on the strength of the magnetic field. The strength of the magnetic field about a nucleus, however, depends on the chemical environment around the nucleus. For example, the negatively charged electrons around and near the nucleus can shield the nucleus from the magnetic field, lowering the strength of the effective magnetic field felt by the nucleus. This, in turn, will lower the energy needed to transition between the +1/2 and -1/2 states. Therefore, the transition energy will be lower for nuclei attached to electron donating groups (such as alkyl groups) and higher for nuclei attached to electron withdrawing groups (such as a hydroxyl group).
In an NMR machine, the compound being analyzed is placed in a strong magnetic field and irradiated with radio waves to cause all the ¹H and ¹³C nuclei to occupy the higher energy -1/2 state. As the nuclei relax back to the +1/2 state, they release radio waves corresponding to the energy of the difference between the two spin states. The radio waves are recorded and analyzed by computer to give an intensity versus frequency plot of the sample. This information can then be used to determine the structure of the compound.

Aromatics in H-NMR Electron Donating Groups vs. Electron Withdrawing Groups
On monosubstituted rings, electron donating groups resonate at high chemical shifts. Electron donating groups increase the electron density by releasing electrons into a reaction center, thus stabilizing the carbocation. An example of an electron donating group is methyl (-CH3).
Accordingly, electron withdrawing groups are represented at low chemical shifts. Electron withdrawing groups pull electrons away from a reacting center. This can stabilize an electron rich carbanion. Some examples of electron withdrawing groups are halogens (-Cl, -F) and carboxylic acid (-COOH).
Looking at the H NMR spectrum of ethyl benzene, we see that the methyl group is the most electron withdrawing, so it appears at the lowest chemical shift. The aromatic phenyl group is the most electron donating, so it has the highest chemical shift.

Disubstituted Rings
The sum of integrated intensity values for the entire aromatic region shows how many substituents are attached to the ring, so a total value of 4 indicates that the ring has 2 substituents. When a benzene ring has two substituent groups, each exerts an influence on following substitution reactions. The site at which a new substituent is introduced depends on the orientation of the existing groups and their individual directing effects. For a disubstituted benzene ring, there are three possible NMR patterns.

Note that para-substituted rings usually show two symmetric sets of peaks that look like doublets.
The order of these peaks is dependent on the nature of the two substituents. For example, the three NMR spectra of chloronitrobenzene isomers are below:

Mass Spectroscopy

A mass spectroscope measures the exact mass of ions, relative to the charge. Many times, some form of seperation is done beforehand, enabling a spectrum to be collected on a relatively pure sample. An organic sample can be introduced into a mass spectroscope and ionised. This also breaks some molecules into smaller fragments.
The resulting mass spectrum shows:
1) The heaviest ion is simply the ionised molecule itself. We can simply record its mass.
2) Other ions are fragments of the molecule and give information about its structure. Common fragments are:

species	formula	mass
methyl	CH₃⁺	15
ethyl	C₂H₅⁺	29
phenyl	C₆H₅⁺	77

Infrared spectroscopy.

Absorbing infrared radiation makes covalent bonds vibrate. Different types of bond absorb different wavelengths of infrared:
Instead of wavelength, infrared spectroscopists record the wavenumber; the number of waves that fit into 1 cm. (This is easily converted to the energy of the wave.)
For some reason the spectra are recorded backwards (from 4000 to 500 cm^-1 is typical), often with a different scale below 1000 cm^-1 (to see the fingerprint region more clearly) and upside-down (% radiation transmitted is recorded instead of the absorbance of radiation).
The wavenumbers of the absorbed IR radiation are characteristic of many bonds, so IR spectroscopy can determine which functional groups are contained in the sample. For example, the carbonyl (C=O) bond will absorb at 1650-1760cm^-1.

Summary of absorptions of bonds in organic molecules

w:Infrared Spectroscopy Correlation Table

Bond	Minimum wavenumber (cm^-1)	Maximum wavenumber (cm^-1)	Functional group (and other notes)
C-O	1000	1300	Alcohols and esters
N-H	1580	1650	Amine or amide
C=C	1610	1680	Alkenes
C=O	1650	1760	Aldehydes, ketones, acids, esters, amides
O-H	2500	3300	Carboxylic acids (very broad band)
C-H	2850	3000	Alkane
C-H	3050	3150	Alkene (Compare intensity to alkane for rough idea of relative number of H atoms involved.)
O-H	3230	3550	H-bonded in alcohols
N-H	3300	3500	Amine or amide
O-H	3580	3670	Free –OH in alcohols (only in samples diluted with non-polar solvent)

Absorptions listed in cm^-1.

Typical method

^[1]

Typical apparatus

A beam of infra-red light is produced and split into two separate beams. One is passed through the sample, the other passed through a reference which is often the substance the sample is dissolved in. The beams are both reflected back towards a detector, however first they pass through a splitter which quickly alternates which of the two beams enters the detector. The two signals are then compared and a printout is obtained.
A reference is used for two reasons:

This prevents fluctuations in the output of the source affecting the data

This allows the effects of the solvent to be cancelled out (the reference is usually a pure form of the solvent the sample is in).

OCH 116. BASIC ANALYTICAL CHEMISTRY ----- BY. MWL. JAPHET MASATU.

ANALYTICAL CHEMISTRY.

Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials.^[1] Qualitative analysis gives an indication of the identity of the chemical species in the sample, and quantitative analysis determines the amount of certain components in the substance. The separation of components is often performed prior to analysis.
Analytical methods can be separated into classical and instrumental.^[2] Classical methods (also known as wet chemistry methods) use separations such as precipitation, extraction, and distillation and qualitative analysis by color, odor, or melting point. Classical quantitative analysis is achieved by measurement of weight or volume. Instrumental methods use an apparatus to measure physical quantities of the analyte such as light absorption, fluorescence, or conductivity. The separation of materials is accomplished using chromatography, electrophoresis or Field Flow Fractionation methods.
Analytical chemistry is also focused on improvements in experimental design, chemometrics, and the creation of new measurement tools to provide better chemical information. Analytical chemistry has applications in forensics, bioanalysis, clinical analysis, environmental analysis, and materials analysis.

History

Gustav Kirchhoff (left) and Robert Bunsen (right)

Analytical chemistry has been important since the early days of chemistry, providing methods for determining which elements and chemicals are present in the object in question. During this period significant analytical contributions to chemistry include the development of systematic elemental analysis by Justus von Liebig and systematized organic analysis based on the specific reactions of functional groups.
The first instrumental analysis was flame emissive spectrometry developed by Robert Bunsen and Gustav Kirchhoff who discovered rubidium (Rb) and caesium (Cs) in 1860.^[3]
Most of the major developments in analytical chemistry take place after 1900. During this period instrumental analysis becomes progressively dominant in the field. In particular many of the basic spectroscopic and spectrometric techniques were discovered in the early 20th century and refined in the late 20th century.^[4]
The separation sciences follow a similar time line of development and also become increasingly transformed into high performance instruments.^[5] In the 1970s many of these techniques began to be used together to achieve a complete characterization of samples.
Starting in approximately the 1970s into the present day analytical chemistry has progressively become more inclusive of biological questions (bioanalytical chemistry), whereas it had previously been largely focused on inorganic or small organic molecules. Lasers have been increasingly used in chemistry as probes and even to start and influence a wide variety of reactions. The late 20th century also saw an expansion of the application of analytical chemistry from somewhat academic chemical questions to forensic, environmental, industrial and medical questions, such as in histology.^[6]
Modern analytical chemistry is dominated by instrumental analysis. Many analytical chemists focus on a single type of instrument. Academics tend to either focus on new applications and discoveries or on new methods of analysis. The discovery of a chemical present in blood that increases the risk of cancer would be a discovery that an analytical chemist might be involved in. An effort to develop a new method might involve the use of a tunable laser to increase the specificity and sensitivity of a spectrometric method. Many methods, once developed, are kept purposely static so that data can be compared over long periods of time. This is particularly true in industrial quality assurance (QA), forensic and environmental applications. Analytical chemistry plays an increasingly important role in the pharmaceutical industry where, aside from QA, it is used in discovery of new drug candidates and in clinical applications where understanding the interactions between the drug and the patient are critical.

Classical methods

The presence of copper in this qualitative analysis is indicated by the bluish-green color of the flame.

Although modern analytical chemistry is dominated by sophisticated instrumentation, the roots of analytical chemistry and some of the principles used in modern instruments are from traditional techniques many of which are still used today. These techniques also tend to form the backbone of most undergraduate analytical chemistry educational labs.

Qualitative analysis

A qualitative analysis determines the presence or absence of a particular compound, but not the mass or concentration. By definition, qualitative analyses do not measure quantity.

Chemical tests

For more details on this topic, see Chemical test.

There are numerous qualitative chemical tests, for example, the acid test for gold and the Kastle-Meyer test for the presence of blood.

Flame test

For more details on this topic, see Flame test.

Inorganic qualitative analysis generally refers to a systematic scheme to confirm the presence of certain, usually aqueous, ions or elements by performing a series of reactions that eliminate ranges of possibilities and then confirms suspected ions with a confirming test. Sometimes small carbon containing ions are included in such schemes. With modern instrumentation these tests are rarely used but can be useful for educational purposes and in field work or other situations where access to state-of-the-art instruments are not available or expedient.

Quantitative analysis

Gravimetric analysis

For more details on this topic, see Gravimetric analysis.

Gravimetric analysis involves determining the amount of material present by weighing the sample before and/or after some transformation. A common example used in undergraduate education is the determination of the amount of water in a hydrate by heating the sample to remove the water such that the difference in weight is due to the loss of water.

Volumetric analysis

For more details on this topic, see Titration.

Titration involves the addition of a reactant to a solution being analyzed until some equivalence point is reached. Often the amount of material in the solution being analyzed may be determined. Most familiar to those who have taken chemistry during secondary education is the acid-base titration involving a color changing indicator. There are many other types of titrations, for example potentiometric titrations. These titrations may use different types of indicators to reach some equivalence point.

Instrumental methods

Main article: Instrumental analysis

Block diagram of an analytical instrument showing the stimulus and measurement of response

Spectroscopy

For more details on this topic, see Spectroscopy.

Spectroscopy measures the interaction of the molecules with electromagnetic radiation. Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, x-ray fluorescence spectroscopy, infrared spectroscopy, Raman spectroscopy, dual polarisation interferometry, nuclear magnetic resonance spectroscopy, photoemission spectroscopy, Mössbauer spectroscopy and so on.

Mass spectrometry

For more details on this topic, see Mass spectrometry.

An accelerator mass spectrometer used for radiocarbon dating and other analysis.

Mass spectrometry measures mass-to-charge ratio of molecules using electric and magnetic fields. There are several ionization methods: electron impact, chemical ionization, electrospray, fast atom bombardment, matrix assisted laser desorption ionization, and others. Also, mass spectrometry is categorized by approaches of mass analyzers: magnetic-sector, quadrupole mass analyzer, quadrupole ion trap, time-of-flight, Fourier transform ion cyclotron resonance, and so on.

Electrochemical analysis

For more details on this topic, see Electroanalytical method.

Electroanalytical methods measure the potential (volts) and/or current (amps) in an electrochemical cell containing the analyte.^[7]^[8] These methods can be categorized according to which aspects of the cell are controlled and which are measured. The three main categories are potentiometry (the difference in electrode potentials is measured), coulometry (the cell's current is measured over time), and voltammetry (the cell's current is measured while actively altering the cell's potential).

Thermal analysis

Further information: Calorimetry, thermal analysis

Calorimetry and thermogravimetric analysis measure the interaction of a material and heat.

Separation

Separation of black ink on a thin layer chromatography plate.

Further information: Separation process, Chromatography, electrophoresis

Separation processes are used to decrease the complexity of material mixtures. Chromatography, electrophoresis and Field Flow Fractionation are representative of this field.

Hybrid techniques

Combinations of the above techniques produce a "hybrid" or "hyphenated" technique.^[9]^[10]^[11]^[12]^[13] Several examples are in popular use today and new hybrid techniques are under development. For example, gas chromatography-mass spectrometry, gas chromatography-infrared spectroscopy, liquid chromatography-mass spectrometry, liquid chromatography-NMR spectroscopy. liquid chromagraphy-infrared spectroscopy and capillary electrophoresis-mass spectrometry.
Hyphenated separation techniques refers to a combination of two (or more) techniques to detect and separate chemicals from solutions. Most often the other technique is some form of chromatography. Hyphenated techniques are widely used in chemistry and biochemistry. A slash is sometimes used instead of hyphen, especially if the name of one of the methods contains a hyphen itself.

Microscopy

Fluorescence microscope image of two mouse cell nuclei in prophase (scale bar is 5 µm).^[14]

For more details on this topic, see Microscopy.

The visualization of single molecules, single cells, biological tissues and nanomaterials is an important and attractive approach in analytical science. Also, hybridization with other traditional analytical tools is revolutionizing analytical science. Microscopy can be categorized into three different fields: optical microscopy, electron microscopy, and scanning probe microscopy. Recently, this field is rapidly progressing because of the rapid development of the computer and camera industries.

Lab-on-a-chip

A glass microreactor

Further information: microfluidics, lab-on-a-chip

Devices that integrate (multiple) laboratory functions on a single chip of only millimeters to a few square centimeters in size and that are capable of handling extremely small fluid volumes down to less than picoliters.

Standards

Standard curve

A calibration curve plot showing limit of detection (LOD), limit of quantification (LOQ), dynamic range, and limit of linearity (LOL).

A general method for analysis of concentration involves the creation of a calibration curve. This allows for determination of the amount of a chemical in a material by comparing the results of unknown sample to those of a series of known standards. If the concentration of element or compound in a sample is too high for the detection range of the technique, it can simply be diluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition can be used. In this method a known quantity of the element or compound under study is added, and the difference between the concentration added, and the concentration observed is the amount actually in the sample.

Internal standards

Sometimes an internal standard is added at a known concentration directly to an analytical sample to aid in quantitation. The amount of analyte present is then determined relative to the internal standard as a calibrant. An ideal internal standard is isotopically-enriched analyte which gives rise to the method of isotope dilution.

Standard addition

The method of standard addition is used in instrumental analysis to determine concentration of a substance (analyte) in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve. Standard addition can be applied to most analytical techniques and is used instead of a calibration curve to solve the matrix effect problem.

Signals and noise

One of the most important components of analytical chemistry is maximizing the desired signal while minimizing the associated noise.^[15] The analytical figure of merit is known as the signal-to-noise ratio (S/N or SNR).
Noise can arise from environmental factors as well as from fundamental physical processes.

Thermal noise

Main article: Johnson–Nyquist noise

Thermal noise results from the motion of charge carriers (usually electrons) in an electrical circuit generated by their thermal motion. Thermal noise is white noise meaning that the power spectral density is constant throughout the frequency spectrum.
The root mean square value of the thermal noise in a resistor is given by^[15]

$v_{{RMS}} = \sqrt { 4 k_B T R \Delta f },$

where k_B is Boltzmann's constant, T is the temperature, R is the resistance, and $\Delta f$ is the bandwidth of the frequency $f$ .

Shot noise

Main article: Shot noise

Shot noise is a type of electronic noise that occurs when the finite number of particles (such as electrons in an electronic circuit or photons in an optical device) is small enough to give rise to statistical fluctuations in a signal.
Shot noise is a Poisson process and the charge carriers that make up the current follow a Poisson distribution. The root mean square current fluctuation is given by^[15]

$i_{{RMS}}=\sqrt{2\,e\,I\,\Delta f}$

where e is the elementary charge and I is the average current. Shot noise is white noise.

Flicker noise

Main article: flicker noise

Flicker noise is electronic noise with a 1/ƒ frequency spectrum; as f increases, the noise decreases. Flicker noise arises from a variety of sources, such as impurities in a conductive channel, generation and recombination noise in a transistor due to base current, and so on. This noise can be avoided by modulation of the signal at a higher frequency, for example through the use of a lock-in amplifier.

Environmental noise

Noise in a thermogravimetric analysis; lower noise in the middle of the plot results from less human activity (and environmental noise) at night.

Environmental noise arises from the surroundings of the analytical instrument. Sources of electromagnetic noise are power lines, radio and television stations, wireless devices, Compact fluorescent lamps^[16] and electric motors. Many of these noise sources are narrow bandwidth and therefore can be avoided. Temperature and vibration isolation may be required for some instruments.

Noise reduction

Noise reduction can be accomplished either in computer hardware or software. Examples of hardware noise reduction are the use of shielded cable, analog filtering, and signal modulation. Examples of software noise reduction are digital filtering, ensemble average, boxcar average, and correlation methods.^[15]

Applications

Analytical chemistry research is largely driven by performance (sensitivity, selectivity, robustness, linear range, accuracy, precision, and speed), and cost (purchase, operation, training, time, and space). Among the main branches of contemporary analytical atomic spectrometry, the most widespread and universal are optical and mass spectrometry.^[17] In the direct elemental analysis of solid samples, the new leaders are laser-induced breakdown and laser ablation mass spectrometry, and the related techniques with transfer of the laser ablation products into inductively coupled plasma. Advances in design of diode lasers and optical parametric oscillators promote developments in fluorescence and ionization spectrometry and also in absorption techniques where uses of optical cavities for increased effective absorption pathlength are expected to expand. The use of plasma- and laser-based methods is increasing. An interest towards absolute (standardless) analysis has revived, particularly in emission spectrometry.^{[citation needed]}
great effort is put in shrinking the analysis techniques to chip size. Although there are few examples of such systems competitive with traditional analysis techniques, potential advantages include size/portability, speed, and cost. (micro Total Analysis System (µTAS) or Lab-on-a-chip). Microscale chemistry reduces the amounts of chemicals used.
Many developments improve the analysis of biological systems. Examples of rapidly expanding fields in this area are:

Genomics - DNA sequencing and its related research. Genetic fingerprinting and DNA microarray are important tools and research fields.
Proteomics - the analysis of protein concentrations and modifications, especially in response to various stressors, at various developmental stages, or in various parts of the body.
Metabolomics - similar to proteomics, but dealing with metabolites.
Transcriptomics - mRNA and its associated field
Lipidomics - lipids and its associated field
Peptidomics - peptides and its associated field
Metalomics - similar to proteomics and metabolomics, but dealing with metal concentrations and especially with their binding to proteins and other molecules.

Analytical chemistry has played critical roles in the understanding of basic science to a variety of practical applications, such as biomedical applications, environmental monitoring, quality control of industrial manufacturing, forensic science and so on.
The recent developments of computer automation and information technologies have extended analytical chemistry into a number of new biological fields. For example, automated DNA sequencing machines were the basis to complete human genome projects leading to the birth of genomics. Protein identification and peptide sequencing by mass spectrometry opened a new field of proteomics.
Analytical chemistry has been an indispensable area in the development of nanotechnology. Surface characterization instruments, electron microscopes and scanning probe microscopes enables scientists to visualize atomic structures with chemical characterizations.