Analytic chemistry

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Gas chromatography laboratory.

Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification, or quantification may constitute the complete analysis or be combined with another method. The separation isolates the analytes. Qualitative analysis identifies the analytes, while quantitative analysis determines the quantity or numerical concentration.

Analytical chemistry consists of classical, wet chemical, and modern instrumental methods. Classical qualitative methods use separations such as precipitation, extraction, and distillation. Identification can be based on differences in color, odor, melting point, boiling point, radioactivity, or reactivity. Classic quantitative analysis uses mass or volume changes to quantify quantity. Instrumental methods can be used to separate samples by chromatography, electrophoresis, or field flow fractionation. Then qualitative and quantitative analysis can be performed, often with the same instrument and can use light interaction, heat interaction, electric fields, or magnetic fields. Often the same instrument can separate, identify and quantify an analyte.

Analytical chemistry also focuses on improvements in experimental design, chemometrics, and the creation of new measurement tools. Analytical chemistry has wide applications for forensics, medicine, science, and engineering.

History

Gustav Kirchhoff (left) and Robert Bunsen (right)

Analytical chemistry has been important since the early days of chemistry, providing methods for determining what elements and chemicals are present in the sample in question. During this period, significant contributions to analytical chemistry include the development of systematic elemental analysis by Justus von Liebig and systematic organic analysis based on specific reactions of functional groups.

The first instrumental analysis was flame emission spectrometry developed by Robert Bunsen and Gustav Kirchhoff, who discovered rubidium (Rb) and cesium (Cs) in 1860.

Most of the major developments in analytical chemistry took place after 1900. During this period, instrumental analysis became increasingly dominant in the field. In particular, many of the basic spectroscopic and spectrometric techniques were discovered early in the 20th century and refined in the late XX.

Separation sciences follow a similar timeline of development and are also becoming increasingly high-throughput instruments. In the 1970s, many of these techniques began to be used together as hybrid techniques to achieve characterization. full of samples.

Starting roughly in the 1970s to the present, analytical chemistry has become increasingly inclusive of biological issues (bioanalytical chemistry), whereas previously it had largely focused on inorganic or small organic molecules. Lasers have been used increasingly in chemistry as probes and even to initiate and influence a wide variety of reactions. The late 20th century also saw an expansion of the application of analytical chemistry from academic chemical questions to forensic questions, environmental, industrial and medical, as in histology.

Modern analytical chemistry is dominated by instrumental analysis. Many analytical chemists focus on only one type of instrument. Academics tend to focus on new applications and discoveries or on new methods of analysis. The discovery of a chemical present in the blood that increases the risk of cancer would be a discovery in which an analytical chemist could be involved. 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 deliberately kept static so that the 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, in addition to quality control, it is used in the discovery of new drug candidates and in clinical applications where understanding drug-patient interactions is critical..

Classical methods

The presence of copper in this qualitative analysis is indicated by the blue 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 stem from traditional techniques, many of which are still in use 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 analyzes do not measure quantity.

Chemical tests

Main article: Chemistry test

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

Flame test

Main article: Rehearsal to the flame

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

Quantitative analysis

Main article: Quantitative analysis (chemical)

Quantitative analysis is the measurement of the amounts of particular chemical constituents present in a substance.

Gravimetric analysis

Main article: 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 in such a way that the difference in weight is due to loss of water.

Volumetric analysis

Main article: Volumetric analysis

Titration involves the addition of a reagent to a solution being tested until some point of equivalence is reached. Often the amount of material in the solution being tested can be determined. Most familiar to those who have taken chemistry through high school is the acid-base titration which involves a color change indicator. There are many other types of titrations, for example potentiometric titrations. These titrations can use different types of indicators to reach some equivalence point.

Instrumental methods

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

Main article: Instrumental chemistry

Spectroscopy

Main article: Spectroscopy

Spectroscopy measures the interaction of 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 polarization interferometry, spectroscopy magnetic polarization spectroscopy, nuclear magnetic resonance, photoemission spectroscopy, photodisposition spectroscopy, Motsensis microscopy spectroscopy.

Mass spectrometry

A throttle mass spectrometer used for radiocarbon dating and other analysis.

Mass spectrometry measures the mass-charge ratio of molecules using electric and magnetic fields. Several methods of ionization exist: electron impact, chemical ionization, electrospray, fast atom bombardment, matrix-assisted laser desorption ionization, and others. Furthermore, mass spectrometry is classified according to the approaches of mass analyzers: magnetic sector, quadrupole mass analyzer, quadrupole ion trap, time of flight, Fourier transform ion cyclotron resonance, etc.

Electrochemical analysis

Electroanalytical methods measure potential (volts) and/or current (amps) in an electrochemical cell containing the analyte. These methods can be classified according to which aspects of the cell are controlled and which are controlled. are measured. The four main categories are potentiometry (the difference in electrode potentials is measured), coulometry (the transferred charge is measured over time), amperimetry (the cell current is measured over time), and voltammetry (the current of the cell is measured while the cell's potential is actively changing).

Thermal analysis

Main articles: Calorimetrics and 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.

Separation processes are used to reduce 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" Several examples are in popular use today and new hybrid techniques are being developed. For example, gas chromatography-mass spectrometry, gas chromatography-infrared spectroscopy, liquid chromatography-mass spectrometry, liquid chromatography-NMR spectroscopy, liquid chromatography, infrared spectroscopy, capillary electrophoresis, and spectrometry of masses.^{[citation needed]}

Hyphenated separation techniques refer to a combination of two (or more) techniques for detecting and separating chemicals from solutions. Very often the other technique is some form of chromatography. Hyphenated techniques are widely used in chemistry and biochemistry. Sometimes a slash is used instead of a hyphen, especially if the name of one of the methods contains a hyphen.^{[citation required]}

Microscopy

Image of fluorescence microscope of two prophase stem cell nuclei (the scale bar is 5 μm)

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

Lab-on-a-chip

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

Mistakes

Error can be defined as a numerical difference between the observed value and the true value.

By mistake, the true value and the observed value in chemical analysis can be related to each other by the equation

{displaystyle varepsilon _{rm {a}}=|x-{bar {x}}|}

where

${displaystyle varepsilon _{rm {a}}}$ It's the absolute mistake.
$x$ is the true value
$bar{x}$ is the observed value.

The error of a measurement is an inverse measure of a precise measurement, that is, the smaller the error, the greater the precision of the measurement.

Mistakes can be expressed relatively. Given the relative error ( ${displaystyle varepsilon _{rm {r}}}$ (c):

{displaystyle varepsilon _{rm {r}}={frac {varepsilon _{rm {a}}}{|x|}}=left|{frac {x-{bar {x}}}{x}}right|}

The percentage error can also be calculated:

{displaystyle varepsilon _{rm {r}}times 100%}

If we want to use these values in a function, we may also want to calculate the function error. Let go $f$ be a function with $N$ variables Therefore, the spread of uncertainty should be calculated to know the error in $f$ :

{displaystyle varepsilon _{rm {a}}(f)approx sum _{i=1}^{N}left|{frac {partial f}{partial x_{i}}}right|varepsilon _{rm {a}}(x_{i})=left|{frac {partial f}{partial x_{1}}}right|varepsilon _{rm {a}}(x_{1})+left|{frac {partial f}{partial x_{2}}}right|varepsilon _{rm {a}}(x_{2})+ldots +left|{frac {partial f}{partial x_{N}}}right|varepsilon _{rm {a}}(x_{N})}

Rules

Standard curve

A calibration curve chart showing the detection limit (LOD), quantification limit (LOQ), dynamic range and linearity limit (LOL)

A general method for concentration analysis involves the creation of a calibration curve. This allows the amount of a chemical in a material to be determined by comparing the results of an unknown sample with 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 the measuring range of an instrument, the addition method can be used. In this method, a known amount of the element or compound under study is added, and the difference between the added concentration and the observed concentration is the amount actually in the sample.

Internal rules

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

Standard addition

The standard addition method is used in instrumental analysis to determine the concentration of a substance (analyte) in an unknown sample compared 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 and minimizing associated noise. 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 fundamental physical processes.

Thermal noise

Thermal noise is the result of the movement of charge carriers (usually electrons) in an electrical circuit generated by their thermal movement. Thermal noise is white noise, which means that the power spectral density is constant throughout the frequency spectrum.

The root mean square value of thermal noise in a resistor is given by

{displaystyle v_{rm {RMS}}={sqrt {4k_{rm {B}}TRDelta f}},}

where k _B It's Boltzmann's constant, T It's the temperature, R is resistance and ${displaystyle Delta f}$ is the frequency bandwidth ${displaystyle f}$ .

Shooting

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) are 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 fluctuation of the root mean square current is given by

{displaystyle i_{rm {RMS}}={sqrt {2eIDelta f}}}

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

Flickering noise

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

Environmental noise

Noise in a thermogravimetric analysis; less noise in the middle of the plot is due to less human activity (and environmental noise) during the night

Ambient noise arises from the environment 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 have limited bandwidth and can therefore be avoided. Temperature and vibration isolation may be required for some instruments.

Noise reduction

Noise reduction can be accomplished 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 averaging, wagon averaging, and correlation methods.

Applications

A scientist from the U.S. Food and Drug Administration. U.S. Uses a portable near-infrared spectroscopy device to detect potentially illegal substances

Analytical chemistry has applications including forensic science, bioanalysis, clinical analysis, environmental analysis, and materials analysis. Analytical chemistry research is largely driven by performance (sensitivity, detection limit, selectivity, robustness, dynamic range, linear range, 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. In direct elemental analysis of solid samples, the new leaders are laser-induced degradation and ablation mass spectrometry. laser ablation and techniques related to the transfer of laser ablation products to inductively coupled plasma. Advances in the design of diode lasers and optical parametric oscillators promote developments in fluorescence and ionization spectrometry and also in absorption techniques where the uses of optical cavities are expected to expand to increase the length of the effective absorption path.. The use of plasma and laser based methods is increasing. Interest in absolute analysis (without norms) has revived, particularly in emissions spectrometry. A lot of effort is being made to reduce analysis techniques to the size of the chip. Although there are few examples of such systems that compete 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. Some examples of rapidly expanding fields in this area are genomics, DNA sequencing, and related genetic identification and DNA microarray research; proteomics the analysis of protein concentrations and modifications, especially in response to various stressors, at various stages of development, or in various parts of the body, metabolomics, which deals with metabolites; transcriptomics, including mRNA and associated fields; lipidomics - lipids and their associated fields; peptidomics - peptides and their associated domains; and metallomics that deals with the concentrations of metals and, especially, with their binding to proteins and other molecules. Analytical chemistry has played a pivotal role in understanding basic science for a variety of practical applications, such as biomedical applications, environmental monitoring, industrial manufacturing quality control, forensic science, etc.

Recent developments in computer automation and information technology have extended analytical chemistry to several new biological fields. For example, automated DNA sequencing machines were the basis for completing the human genome projects that led to the birth of genomics. Protein identification and peptide sequencing by mass spectrometry opened up 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 allow scientists to visualize atomic structures with chemical characterizations.

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