Analytical chemistry is the study of the separation, identification, and quantification of the
chemical components of natural and artificial materials.
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.
Classical 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
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 and caesium in 1860.
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.
The separation sciences follow a similar time line of development and also become increasingly
transformed into high performance instruments.
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, 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.
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, 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
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
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
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
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
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
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
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
Electroanalytical methods measure the potential and/or current in an electrochemical cell
containing the analyte.
These methods can be categorized according to which aspects of the cell are controlled
and which are measured.
The three main categories are potentiometry, coulometry, and voltammetry.
Thermal analysis
Calorimetry and thermogravimetric analysis measure the interaction of a material and
heat.
Separation
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.
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 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
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
Devices that integrate 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 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 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.
The analytical figure of merit is known as the signal-to-noise ratio.
Noise can arise from environmental factors as well as from fundamental physical processes.
Thermal noise
Thermal noise results from the motion of charge carriers 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
where kB is Boltzmann's constant, T is the temperature, R is the resistance, and is the
bandwidth of the frequency . Shot noise
Shot noise is a type of electronic noise that occurs when the finite number of particles
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
where e is the elementary charge and I is the average current.
Shot noise is white noise.
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
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 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.
Applications Analytical chemistry research is largely driven
by performance, and cost.
Among the main branches of contemporary analytical atomic spectrometry, the most widespread and
universal are optical and mass spectrometry.
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 analysis has revived, particularly in emission spectrometry.
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.
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.
See also
List of chemical analysis methods List of materials analysis methods
Important publications in analytical chemistry Sensory analysis - in the field of Food science
Virtual instrumentation Working range
Metrology Measurement uncertainty
Microanalysis Quality of analytical results
References
Further reading Skoog, D.A.; West, D.M.; Holler, F.J.
Fundamentals of Analytical Chemistry New York: Saunders College Publishing, 5th Edition,
1988.
Bard, A.J.; Faulkner, L.R.
Electrochemical Methods: Fundamentals and Applications.
New York: John Wiley & Sons, 2nd Edition, 2000.
Bettencourt da Silva, R; Bulska, E; Godlewska-Zylkiewicz, B; Hedrich, M; Majcen, N; Magnusson, B; Marincic,
S; Papadakis, I; Patriarca, M; Vassileva, E; Taylor, P; Analytical measurement: measurement
uncertainty and statistics, 2012, ISBN 978-92-79-23070-7.
External links Analytical Chemistry at DMOZ