This is a working overview of precision, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-09-21 and is reviewed periodically as new material appears.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Separation principle | Differential partitioning | Analytes distribute between mobile and stationary phases. |
| Mobile phase | Liquid solvent mixture | Composition controls retention and selectivity. |
| Stationary phase | Packed column particles | Often chemically bonded silica. |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is also common. |
| Common synonym | High-performance liquid chromatography | Abbreviated as HPLC. |
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.
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.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample. A pump moves a liquid mobile phase through a column packed with a solid stationary phase. Compounds interact differently with both phases and travel at different rates, leaving the column at distinct retention times. A detector records these arrivals as peaks on a chromatogram. The resulting pattern supports identification and quantification of substances in mixtures. Modern instruments use high pressure to force solvent through small particles, which improves speed and resolution compared with older low-pressure liquid chromatography methods.
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.
Developing an HPLC method begins with defining the purpose, such as quantifying a main component, measuring impurities, or confirming identity. Analysts select separation mode, column, mobile phase, detection, and sample preparation based on analyte properties and matrix. Experiments vary solvent strength, pH, buffer type, and temperature to achieve resolution between critical peaks. The goal is a robust method that produces reliable results across instruments and operators. Method development often involves trial runs and statistical optimization.
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.
In a flowing plasma afterglow, ions are formed in a flow of inert gas, typically helium or argon. Reagents are added downstream to create ion products and study reaction rates. Flowing-afterglow mass spectrometry is used for trace gas analysis for organic compounds.
== Medical uses == Topical hydrocortisone is indicated for relieving swelling, irritation and redness in a number of skin conditions, including insect bites, heat rash, eczema, psoriasis, contact dermatitis and nappy rash. It could be formulated as a single active ingredient in some medications, e.g. Cortaid, which is applied for anal itchiness. On some occasions, this drug may be used in combination with other types of drugs to alleviate skin problems. For example, it could be used together with antibiotics such as polymyxin, neomycin and bacitracin to improve dermal conditions.
Historically, CAIS has been referred to in the literature under a number of other names, including testicular feminization [syndrome] (deprecated) and Morris syndrome. PAIS has also been referred to as Reifenstein syndrome, which should not be confused with CAIS.
==== Seed-mediated growth ==== Seed-mediated growth is a synthetic method in which small, stable nuclei are grown in a separate chemical environment to a desired size and shape. Seed-mediated methods consist of two different stages: nucleation and growth. Variation of certain factors in the synthesis (e.g. ligand, nucleation time, reducing agent, etc.), can control the final size and shape of nanoparticles, making seed-mediated growth a popular synthetic approach to controlling morphology of nanoparticles. The nucleation stage of seed-mediated growth consists of the reduction of metal ions in a precursor to metal atoms. In order to control the size distribution of the seeds, the period of nucleation should be made short for monodispersity. The LaMer model illustrates this concept. Seeds typically consist small nanoparticles, stabilized by a ligand. Ligands are small, usually organic molecules that bind to the surface of particles, preventing seeds from further growth. Ligands are necessary as they increase the energy barrier of coagulation, preventing agglomeration. The balance between attractive and repulsive forces within colloidal solutions can be modeled by DLVO theory. Ligand binding affinity, and selectivity can be used to control shape and growth. For seed synthesis, a ligand with medium to low binding affinity should be chosen as to allow for exchange during growth phase. The growth of nanoseeds involves placing the seeds into a growth solution.
Sources: en.wikipedia.org
== External links == JPL Develops High-Speed Test to Improve Pathogen Decontamination at the Wayback Machine (archived 2016-03-04) at JPL. Spotting Spores at the Wayback Machine (archived 2016-03-04) at Astrobiology Magazine.
When a growth factor binds to the extracellular domain of an RTK, its dimerization is triggered with other adjacent RTKs. Dimerization leads to a rapid activation of the protein's cytoplasmic kinase domains, the first substrate for these domains being the receptor itself. The activated receptor, as a result, then becomes autophosphorylated on multiple specific intracellular tyrosine residues.
of "Journal J" is the number of citations that all articles published by Journal J in the two previous years received from publications by whatever journal in that given year; normalized by the total number of articles published by Journal J in the two previous years:
Sources: en.wikipedia.org
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.
Pressure drives the liquid mobile phase through a column packed with small particles. Without pressure, flow would be very slow or stop because the packed bed resists liquid movement. Modern pumps maintain a steady flow despite the resistance.
A chromatogram is a plot of detector signal against time after sample injection. Each peak represents a compound or group of compounds eluting from the column. Retention time and peak area are the main measurements read from the plot.
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.