A practical reference on HPLC: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-06-19. Anything still debated is marked as such rather than presented as settled.
Quality control for HPLC testing combines scheduled checks, documented procedures, and review of results. Before sample analysis, system suitability testing confirms that the instrument, column, and method meet predefined criteria. Common criteria include resolution between critical peaks, retention time precision, peak tailing, and theoretical plate count. Failure triggers investigation before results are reported. Records link raw data, calculations, instrument logs, and analyst identity to each batch, supporting audits and repeat analysis.
Method validation evaluates accuracy, precision, specificity, linearity, range, detection limit, quantitation limit, and robustness. Regulatory guidance for pharmaceuticals, foods, and environmental testing defines expected documentation and acceptance criteria. Verification confirms that a validated method works in a specific laboratory with its own instruments and reagents. Calibration curves use reference standards with known purity and traceability, while measurement uncertainty is estimated from validation data, control charts, and collaborative studies. The scope of validation depends on the method's intended use.
Routine quality control monitors retention time shifts, baseline noise, system pressure, and peak shape. Trends can reveal column aging, mobile phase preparation errors, detector drift, or sample degradation. Corrective actions may include replacing the column, preparing fresh mobile phase, or recalibrating the detector. Stability testing often uses HPLC to measure parent compound loss and degradation product formation. Open questions remain about how accelerated stability results extrapolate to long-term storage under varied conditions.
Validation demonstrates that a method is suitable for its intended use. Typical performance characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulators and standards organizations provide frameworks, but specific requirements depend on the application and jurisdiction. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, retention time repeatability, and sensitivity. A validated method is not permanently fixed; changes may require partial or full revalidation.
Routine HPLC testing depends on controlled reagents, calibrated instruments, and documented procedures. Columns degrade over time, so retention times and peak shapes are monitored for drift. Mobile phases are filtered and degassed to prevent pump damage and detector noise. Reference standards must be traceable and stored under suitable conditions. Data handling systems record injections, calculations, and audit trails. Quality control samples interspersed with unknowns help detect errors during a run.
| Property | Value | Notes |
|---|---|---|
| Retention time RSD | ≤1% for five replicate injections | Typical criterion; method-specific limits apply. |
| Resolution | ≥1.5 between critical pair | Baseline separation is generally desired. |
| Tailing factor | ≤2.0 | Measures peak symmetry. |
| Theoretical plates | ≥2000 per column | Method-dependent; higher values indicate greater efficiency. |
| Peak area RSD | ≤2% for replicate injections | Reflects autosampler and detector precision. |
Quality control laboratories use HPLC to check identity, purity, concentration, and stability of raw materials and finished products. A validated method specifies the column, mobile phase, flow rate, detection wavelength, injection volume, and run time. Samples are prepared and compared against reference standards of known concentration. The resulting chromatogram provides quantitative data, such as assay values and impurity levels. This approach is common in pharmaceutical, food, environmental, and industrial testing where consistent measurements are required.
Method validation demonstrates that an analytical procedure is suitable for its intended purpose. Typical validation characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulatory guidance from bodies such as the International Council for Harmonisation and the United States Pharmacopeia outlines expectations, though specific criteria depend on the product and method. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, column efficiency, and injection repeatability. Failure of these checks can invalidate a batch of measurements.
Practical HPLC testing depends on careful sample preparation and instrument maintenance. Samples may require filtration, dilution, pH adjustment, or extraction to avoid column damage and matrix interference. Mobile phases are degassed and filtered, and columns are equilibrated before injection. Common problems include peak tailing, baseline drift, ghost peaks, carryover, and co-elution of analytes. Documentation of instrument logs, calibration records, and electronic audit trails supports data integrity and traceability. Ongoing training and routine maintenance help reduce variability between analysts and laboratories.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample by passing them through a packed column under pressure. A pump delivers a mobile phase at a controlled flow rate, and an injector introduces the sample into the stream. Differences in how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
Instrumentation includes a solvent delivery system, an autosampler, a column oven, and one or more detectors. Reversed-phase columns with chemically modified silica are widely used, but normal-phase, ion-exchange, size-exclusion, and affinity modes exist for specific separations. Detectors may rely on ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry. Column temperature, mobile phase composition, and flow rate are adjusted to improve resolution. System pressure is monitored because rising pressure can indicate column blockage or deteriorating packing.
Separation performance depends on particle size, pore size, column length, and the chemistry of the stationary phase. Smaller particles generally improve efficiency but require higher pressure and suitable instrumentation. The mobile phase often contains buffers and organic solvents that influence retention and selectivity. Testing labs select conditions based on the analytes, sample matrix, and required sensitivity. Method development frequently involves screening several columns and solvent mixtures before a final set of conditions is chosen.
Separation in HPLC depends on the chemistry of the stationary phase, the composition of the mobile phase, and the physical properties of the column. Reverse-phase separations use a nonpolar stationary phase and a polar mobile phase, and they are common for many organic compounds. Ion-exchange, size-exclusion, and normal-phase modes serve other classes of analytes. Gradient elution changes solvent strength over time, while isocratic elution holds it constant. Flow rate, temperature, particle size, and column length all influence peak shape and resolution. Detection may use ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry, depending on the analyte and the required sensitivity.
Routine HPLC testing compares a sample result with a calibration curve prepared from known reference standards. Peak area or peak height is plotted against concentration, and the curve is used to estimate unknown amounts. Retention time supports tentative identification when compared with a standard, though mass spectrometry or another confirmatory method may be needed for definitive identification. Pre-run checks verify repeatability, resolution, and peak symmetry before sample analysis. Limits of detection and quantification describe the smallest amounts that can be reliably observed or measured. Sample preparation, filtration, and degassing help prevent column damage and inconsistent results.
While Vietnam was affected by the Cold War, the country's factions also affected the Cold War, especially through the remarkable and calculated efforts of Vietnamese leaders to leverage superpower rivalry to their own advantage.
Titulaire – gold palm sewn on white silk; Officier l'Université – silver palm sewn on white silk; Officier d'Académie – blue palm sewn on white silk. The Titulaires were limited to the grand masters of the university, chancellors, treasurers, and councilors for life. The Officiers de l'Université were ordinary councilors, university inspectors, rectors, academy inspectors, deans and faculty professors. The Officiers d'Académie were headmasters, censors, teachers of the two most distinguished classes of high schools, principals of colleges, and, in exceptional cases, high school teachers or college regents. Those working in primary education were ineligible. On 9 October 1850, the number of classes was reduced to two:
== See also == Abigail Alliance for Better Access to Developmental Drugs Animal drug Biologics license application Drug discovery FDA Fast Track Development Program Good Manufacturing Practice Inverse benefit law Lists of investigational drugs Orphan drug TOL101
Re2O7 + 17 CO → Re2(CO)10 + 7 CO2 If metal oxides are used carbon dioxide is formed as a reaction product. In the reduction of metal chlorides with carbon monoxide phosgene is formed, as in the preparation of osmium carbonyl chloride from the chloride salts. Carbon monoxide is also suitable for the reduction of sulfides, where carbonyl sulfide is the byproduct.
Sources: en.wikipedia.org
=== Chemical === Copernicium is the tenth and last member of the 6d series and is the heaviest group 12 element in the periodic table, below zinc, cadmium and mercury. It is predicted to differ significantly from the lighter group 12 elements. The valence s-subshells of the group 12 elements and period 7 elements are expected to be relativistically contracted most strongly at copernicium. This and the closed-shell configuration of copernicium result in it probably being a very noble metal. A standard reduction potential of +2.1 V is predicted for the Cn2+/Cn couple. Copernicium's predicted first ionization energy of 1155 kJ/mol almost matches that of the noble gas xenon at 1170.4 kJ/mol. Copernicium's metallic bonds should also be very weak, possibly making it extremely volatile like the noble gases, and potentially making it gaseous at room temperature. However, it should be able to form metal–metal bonds with copper, palladium, platinum, silver, and gold; these bonds are predicted to be only about 15–20 kJ/mol weaker than the analogous bonds with mercury. In opposition to the earlier suggestion, ab initio calculations at the high level of accuracy predicted that the chemistry of singly-valent copernicium resembles that of mercury rather than that of the noble gases. The latter result can be explained by the huge spin–orbit interaction which significantly lowers the energy of the vacant 7p1/2 state of copernicium. Once copernicium is ionized, its chemistry may present several differences from those of zinc, cadmium, and mercury.
Mast cells use a variety of cell surface receptors to detect pathogens. The best known pathway involves FcεRI, a high-affinity receptor for the Fc region of IgE antibodies, involved in allergies. As a molecular target, FcεRI initiates various outcomes in mast cells (MCs) in response to antigens (Ags). Ags bind to immunoglobulin E (IgE) that is bound to FcεRI to cause the crosslinking of IgE–FcεRI complexes and trigger mast cell activation. Activation leads within minutes to degranulation of mast cells and the release of mediators such as histamine, serotonin, and leukotrienes, followed over a period of hours by the secretion of cytokines, chemokines, and growth factors. FcεRI regulates the Ag–IgE interaction, driving allergic responses. FcεRI clustering controls signal transduction and the quality of MC responses. Under resting conditions in the cell membrane, the IgE–FcεRI complex diffuses freely. Multivalent Ag binding to IgE reorganizes FcεRI within seconds to minutes, forming large aggregates on the cell surface, and causing a transition in the receptor from a diffuse to an immobile state. Small aggregates remain mobile on the cell surface, whereas large aggregates abruptly become immobile. Changes in the mobility, kinetics, and size of FcεRI clusters may govern signal initiation and termination. In addition to IgE-dependent MC activation, forms of IgE-independent MC activation have been studied. One of these involves MRGPRX2, a G protein-coupled receptor (GPCR).
=== Physics === Candlepower (cp), a measure of luminous intensity Centipoise (cP), a unit of viscosity CP symmetry, in particle physics, the product of charge conjugation and parity Cp, the specific heat capacity at constant pressure Pressure coefficient (Cp), a parameter for studying the flow of fluids Center of pressure (fluid mechanics), the point where the total sum of a pressure field acts on a body
Sources: en.wikipedia.org
== Biochemistry and functional relevance == Kinases mediate the transfer of a phosphate moiety from a high energy molecule (such as ATP) to their substrate molecule, as seen in the figure below. Kinases are needed to stabilize this reaction because the phosphoanhydride bond contains a high level of energy. Kinases properly orient their substrate and the phosphoryl group within their active sites, which increases the rate of the reaction. Additionally, they commonly use positively charged amino acid residues, which electrostatically stabilize the transition state by interacting with the negatively charged phosphate groups. Alternatively, some kinases utilize bound metal cofactors in their active sites to coordinate the phosphate groups. Protein kinases can be classed as catalytically active (canonical) or as pseudokinases, reflecting the evolutionary loss of one or more of the catalytic amino acids that position or hydrolyse ATP. However, in terms of signalling outputs and disease relevance, both kinases and pseudokinases are important signalling modulators in human cells, making kinases important drug targets. Kinases are used extensively to transmit signals and regulate complex processes in cells. Phosphorylation of molecules can enhance or inhibit their activity and modulate their ability to interact with other molecules. The addition and removal of phosphoryl groups provides the cell with a means of control because various kinases can respond to different conditions or signals.
The word "aptamer" is a neologism coined by Andrew D. Ellington and Jack Szostak in their first publication on the topic. They did not provide a precise definition, stating "We have termed these individual RNA sequences 'aptamers', from the Latin aptus, to fit." The word itself, however, derives from the Greek word ἅπτω, to connect or fit (as used by Homer (c. 8th century BC)) and μέρος, a component of something larger. A typical aptamer is a synthetically generated ligand exploiting the combinatorial diversity of DNA, RNA, XNA, or peptide to achieve strong, specific binding for a particular target molecule or family of target molecules. Aptamers are occasionally classified as "chemical antibodies" or "antibody mimics". However, most aptamers are small, with a molecular weight of 6-30 kDa, in contrast to the 150 kDa size of antibodies, and contain one binding site rather than the two matching antigen binding regions of a typical antibody.
Hypoprolactinemia, or serum prolactin deficiency, is associated with ovarian dysfunction in women, and arteriogenic erectile dysfunction, premature ejaculation, oligozoospermia, asthenospermia, hypofunction of seminal vesicles and hypoandrogenism in men. In one study, normal sperm characteristics were restored when prolactin levels were raised to normal values in hypoprolactinemic men. Hypoprolactinemia can result from hypopituitarism, excessive dopaminergic action in the tuberoinfundibular pathway and ingestion of D2 receptor agonists such as bromocriptine. Dextroamphetamine has been shown to reduce serum prolactin, presumably due to its dopaminergic effects, indirectly increasing activation of dopamine D2 receptors with data showing intravenous dextroamphetamine at doses between 7.5 mg to 15 mg reducing serum prolactin by 27-32% and 30-37%, respectively, while an oral dose of 20 mg led to a sustained 40% reduction of serum prolactin in postpartum women.
Sources: en.wikipedia.org
System suitability is typically performed before each batch or according to the validated method and laboratory procedure. Some long runs include periodic checks during analysis. The required frequency depends on regulatory expectations and method performance.
Retention time drift can result from changes in mobile phase composition, column temperature, pump flow, or column age. A gradual shift often points to column degradation. A sudden shift may indicate a leak, mixing error, or incorrect mobile phase.
Retention time alone cannot confirm identity because different compounds may elute at similar times. Coupling HPLC with mass spectrometry or comparing against authenticated standards increases confidence. Confirmation usually requires orthogonal data.
It is a set of checks performed before or during an HPLC run to confirm the system works as expected. Parameters may include resolution, tailing factor, theoretical plates, and retention time precision. Failure can trigger maintenance, method adjustment, or repeat analysis.