Summary

Analytical chemistry explores the principles, methods, and instruments used to separate, identify, and quantify chemical species in complex samples. This collection covers key topics such as chromatographic separation, mass spectrometry, optical and elemental spectrometry, ionization and detection strategies, and hyphenated analytical workflows. It also highlights applications of analytical chemistry in pharmaceuticals, environmental monitoring, clinical diagnostics, food safety, materials characterization, and industrial quality control, showcasing advances in sensitivity, selectivity, throughput, and data reliability that support scientific research and practical decision-making.

Expand All
Entries
Topic Review
Complexation Chromatography
Complexation chromatography obtains selectivity from reversible formation of a coordination or host–guest complex between an analyte and a complexing species located in the stationary phase or mobile phase. Complex formation changes the analyte’s effective affinity, charge, or partition coefficient, and differences in equilibrium constants therefore produce different migration rates. In argentation chromatography, for example, immobilized or dissolved silver(I) forms reversible π-complexes with carbon–carbon multiple bonds, so retention varies with the number, geometry, and accessibility of unsaturated sites [1]. The general mode requires a chemically defined complexing agent, rapid and reversible complexation on the chromatographic timescale, and conditions that preserve the agent while allowing solute release. It differs from ordinary adsorption or partition chromatography because a discrete complexation equilibrium is the intended source of selectivity, and it excludes irreversible derivatization before injection. Ligand-exchange chromatography is a narrower metal-coordination form in which analytes exchange within a metal coordination sphere [2].
  • 7
  • 21 Oct 2026
Topic Review
Chip Mass Spectrometry
Chip mass spectrometry couples a microfabricated fluidic device directly to a mass spectrometer so that sample handling, separation, reaction, and/or ionization occurs in channels and structures formed on the chip. The chip may incorporate capillary electrophoresis, micro-liquid chromatography, preconcentration, digestion, or mixing, but a mass analyzer remains external and measures the mass-to-charge ratios of ions delivered from the device [1]. Coupling commonly uses electrospray from a chip edge, an inserted emitter, or an emitter fabricated as an integral part of the microfluidic substrate; matrix-assisted laser desorption/ionization interfaces form another class [2]. The concept is defined by integration of microfluidics with ion generation or sample introduction, not by a unique mass analyzer. It excludes conventional capillary LC–MS lacking a microfabricated device and excludes genomic or optical chips that do not produce ions for mass analysis. Essential features are a microfabricated flow or sample path, a reproducible chip-to-source interface, and transfer of generated ions into the mass spectrometer [3].
  • 11
  • 21 Oct 2026
Topic Review
Chemical Ionization Mass Spectrometry
Gas-phase ion–molecule reactions between analyte molecules and a reagent-gas plasma constitute chemical ionization (CI) mass spectrometry. In the classical form, a reagent gas such as methane, isobutane, or ammonia is ionized by electrons; the resulting reagent ions transfer a proton, hydride, or charge to the analyte, producing even-electron ions with less fragmentation than electron ionization [1]. Atmospheric-pressure chemical ionization (APCI) and desorption APCI extend the same ion–molecule chemistry to an atmospheric corona or related discharge, so that the ionization step remains chemical rather than purely photonic or electrospray-based [2]. Negative-ion CI uses electron-capture or proton-abstraction reagent ions and is a polarity variant of the same concept [3]. Conceptual boundaries exclude electron ionization, electrospray ionization, and photoionization, each of which generates ions by a different primary process. Essential features are a reagent-ion population, a pressure regime that permits ion–molecule collisions, and a mass analyzer that records the resulting analyte ions, often after chromatographic introduction [4].
  • 16
  • 21 Oct 2026
Topic Review
Capillary Gas Chromatography
Capillary gas chromatography is gas chromatography performed in an open-tubular column of small internal diameter rather than in a column filled throughout with packing. The column wall carries either a thin immobilized liquid film, forming a wall-coated open-tubular column, or a porous adsorbent layer, forming a porous-layer open-tubular column [1]. An inert carrier gas transports vaporized solutes, and differential partitioning or adsorption produces separation according to volatility and stationary-phase selectivity. The absence of a packed bed reduces resistance to mass transfer and permits long columns with high plate numbers, while internal diameter, stationary-phase film thickness, carrier-gas velocity, and temperature program determine efficiency and retention [2]. The concept excludes packed-column gas chromatography, liquid chromatography in fused-silica capillaries, and gas-phase mobility methods without a stationary phase. Its necessary features are a gaseous mobile phase, an open capillary bore with a wall-bound stationary phase, controlled sample vaporization, and chromatographic migration along the column.
  • 9
  • 21 Oct 2026
Topic Review
Capillary Chromatography
Narrow-bore open or packed capillaries, rather than conventional wide-bore packed columns, constitute the geometric defining feature of capillary chromatography. The small inner diameter reduces plate height and solvent consumption and permits electrokinetic as well as pressure-driven flow. Micellar electrokinetic capillary chromatography (MEKC) superimposes a charged micellar pseudostationary phase on capillary electrophoresis, so that neutral and charged solutes acquire differential migration through chromatographic partition into the micelles in addition to electrophoretic mobility [1]. Packed or monolithic capillaries with immobilized ligands, including aptamers, provide a true stationary phase inside the same capillary format [2]. Conceptual boundaries exclude ordinary packed-column HPLC of several millimetres internal diameter, and they exclude free-zone capillary electrophoresis that lacks a chromatographic partition medium. Essential features are a capillary conduit, a defined stationary or pseudostationary phase, and a driving force—pressure, electroosmosis, or both—that transports the mobile phase [3]. Two-dimensional couplings of capillary sieving electrophoresis with MEKC further illustrate that the capillary is the format, while the retention chemistry may vary [4].
  • 6
  • 21 Oct 2026
Topic Review
Anion Exchange Chromatography
Anion-exchange chromatography uses a stationary phase bearing positively charged groups to reversibly retain negatively charged solutes. Strong anion exchangers usually contain permanently charged quaternary-ammonium ligands, whereas weak exchangers such as diethylaminoethyl phases have pH-dependent charge. A solute binds when the mobile-phase pH gives it sufficient net negative charge and when competing-ion concentration is low enough for electrostatic association with the exchanger [1]. Elution is produced by increasing salt concentration, changing counter-ion identity, or shifting pH to decrease solute charge or exchanger ionization [2]. Selectivity reflects charge number and distribution as well as nonideal secondary interactions, while capacity is set by the density and accessibility of cationic ligands. The mode is the anionic counterpart of cation-exchange chromatography and a subclass of ion-exchange chromatography. It is distinct from electrophoresis, reversed-phase chromatography, and affinity chromatography because repeated exchange with immobilized positive sites is its primary retention mechanism.
  • 8
  • 21 Oct 2026
Topic Review
Affinity Chromatography
Biospecific recognition between a target macromolecule and an immobilized ligand is the defining retention principle of affinity chromatography. The ligand—an inhibitor, substrate analog, antibody, lectin, or metal chelate—is covalently attached to an agarose or other hydrophilic bead, often through a spacer, so that the complementary protein is bound from a mixture while unbound species are washed away; the complex is then dissociated by a competing ligand or a change of pH or ionic strength [1]. Cyanogen-bromide and related activations convert hydroxyl groups on the matrix into reactive intermediates that couple primary amines of the ligand [2]. Metal-chelate affinity chromatography is a related subclass in which immobilized metal ions, rather than an organic biospecific ligand, coordinate surface histidine and other residues [3]. Conceptual boundaries exclude ion-exchange and hydrophobic-interaction chromatography that lack a recognition ligand, and they exclude free-solution affinity precipitation. Essential features are a chemically defined immobilized ligand, a reversible binding equilibrium, and a matrix whose nonspecific adsorption is low enough that biospecificity dominates retention [4].
  • 10
  • 21 Oct 2026
Topic Review
Adsorption Chromatography
Differential adsorption of solutes onto a solid surface from a liquid or gaseous mobile phase is the retention mechanism that defines adsorption chromatography. The stationary phase is an adsorbent—silica, alumina, a thiophilic or hydrophobic solid, or a related high-surface-area material—whose sites compete with the eluent for the analyte [1]. Retention is therefore an interfacial phenomenon, not a bulk partition into a liquid film, and it is described by adsorption isotherms and by gradient-elution theory that relates solvent strength to surface coverage [2]. Conceptual boundaries exclude partition chromatography, ion-exchange chromatography whose primary interaction is electrostatic, and affinity chromatography that requires a biospecific ligand, although an adsorbent bed may be operated in an expanded-bed geometry without changing the adsorption definition [3]. Essential features are a reversible adsorption equilibrium, a mobile phase that can modulate surface activity, and a column or bed in which adsorption and desorption occur repeatedly as the solute band migrates. Linear elution adsorption chromatography treats the low-concentration limit in which the isotherm is linear and retention is independent of load.
  • 16
  • 21 Oct 2026
Topic Review
Accelerator Mass Spectrometry
Accelerator mass spectrometry (AMS) counts rare, usually long-lived isotopes after ions have been accelerated to high kinetic energies. A negative-ion source first forms an isotopic beam; mass and charge selection precede acceleration through a tandem or other electrostatic accelerator, and passage through a stripper removes electrons, breaks up molecular ions, and produces positive charge states [1]. Subsequent magnetic and electrostatic analysis separates the desired nuclide, while particle detectors identify individual rare-isotope ions and stable-isotope currents provide ratio normalization [2]. AMS therefore measures atom-number isotope ratios rather than decay rates or molecular fragmentation patterns. Its defining capabilities arise from molecular-isobar destruction, high abundance sensitivity, and single-ion detection at isotope ratios well below those accessible to conventional mass spectrometry [3]. The method is distinct from isotope-ratio mass spectrometry without an accelerator and from radiometric counting. Essential components are an ion source, staged mass filtering, high-energy acceleration and stripping, nuclide-specific interference rejection, and rare-ion detection.
  • 13
  • 21 Oct 2026
Topic Review
Plasma Spectrometry
An ionized gas at several thousand kelvin, most often an inductively coupled argon plasma, forms the atomization and excitation (or ionization) source that defines plasma spectrometry. A liquid or solid sample is introduced as an aerosol or vapor; the plasma desolvates, atomizes, and ionizes the analyte, after which either optical emission from excited atoms and ions or the ions themselves are measured [1]. The same plasma can therefore serve atomic emission spectrometry or mass spectrometry, and the two readouts are distinct plasma-spectrometric techniques rather than a single detector [2]. Conceptual boundaries exclude chemical-flame spectrometry, glow-discharge sources at low pressure, and laser-induced breakdown plasmas that are not a continuous inductively coupled discharge. Essential features are a radiofrequency or related energy coupling that sustains the plasma, a sample-introduction system whose transport efficiency affects the signal, and a spectroscopic or mass-spectrometric observation of species produced in the plasma [3]. Sensitivity differences among oxidation states, as between As(III) and As(V), arise from unequal nebulization and atomization behavior in the plasma rather than from a change in the spectrometric principle [4].
  • 8
  • 21 Oct 2026
  • Page
  • of
  • 6

Other Entry Collections

>>