reversed-phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-07-13 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.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it 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 interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
| 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. |
Routine quality control includes blanks, duplicates, spiked samples, and certified reference materials. Calibration curves are prepared with standards at several concentrations, and the detector response is checked for linearity. Carryover, column aging, mobile phase evaporation, and temperature drift can shift retention times or peak areas. Maintenance such as replacing seals, filters, and columns helps prevent failures. Records of injections, integration, and deviations support traceability. Audits may request raw data and instrument logs for each batch.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
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.
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.
[RO−P(O)2−O−P(O)2−O−PO3]4− + H2O → [RO−P(O)2−O−PO3]3− + [HPO4]2− + H+ [RO−P(O)2−O−P(O)2−O−PO3]4− + H2O → [RO−PO3]2− + [HO3P−O−PO3]3− + H+ For ATP hydrolysis that takes place with the physiological concentrations of ATP, ADP, and inorganic phosphate (Pi) within the living cell, the change in Gibbs free energy is given by:
Following the invasion and annexation of Kuwait by Iraq, on September 25, 1990, the Italian Government sent eight multirole fighter bombers Tornado IDS (plus two spare) in the Persian Gulf, belonging to the 6º, 36º and 50º Stormo, which were deployed at the Al Dhafra Air Base, near Abu Dhabi, in the United Arab Emirates. During the 42 days of war, Italian fighters made 226 sorties for a total of 589 flight hours. The Italian Air Force lost one aircraft in the Gulf War. The use of Italian aircraft as part of the Desert Storm operation represented the first operational employment in combat missions of Italian Air Force aircraft since the end of World War II.
=== Mating === When ready to mate, cabbage loopers display by elevating their abdomen and fanning their wings. Males also fan out their abdominal hairs, open their genital claspers, and partially stick out their spermatophores. Males gradually expose more of their spermatophores as they wait for a mate. Upon interest, a potential mate examines the other's abdomen with antennae, and mating occurs if both agree. Mating on average occurs at 2am, but has been observed occurring between 12 and 4am. Mating generally occurs 3–4 days after emergence, but can occur up to 16 days afterwards. Usually, mating does not occur before the third day, as eggs are not fully developed upon emergence and require a few days to reach maturity. Multiple matings is a mating strategy where individuals have multiple mates in their lifetime. This is in contrast to monogamy, where individuals have one mate for life. Mating multiply can be advantageous to both sexes, which is why this strategy has evolved in many species, including the cabbage looper. For female cabbage loopers, rate of oviposition increases with the number of matings, and ultimately lay more eggs total. While it was once believed that multiple matings were necessary to fertilize all eggs, evidence shows that only one mating is needed to fertilize almost all eggs. Instead, it is more likely that the spermatophore provides nutrients to the female that confers reproductive benefits. This may explain why males produce female-attracting pheromones, as females may be seeking nutrient-rich spermatophores.
== Definition == In scientific literature, porous glass is a porous material containing approximately 96% silica, which is produced by an acidic extraction or a combined acidic and alkaline extraction respectively, of phase separated alkali borosilicate glasses, and features a three-dimensional interconnected porous microstructure. For commercially available porous glasses, the terms porous VYCOR-Glass (PVG) and Controlled Pore Glass (CPG) are used. The pore structure is formed by a syndetic channel system and has a specific surface from 10 to 300 m2/g. Porous glasses can be generated by an acidic extraction of phase separated alkaliborosilica glasses, or by a sol-gel-process. By regulating the manufacturing parameters, it is possible to produce a porous glass with a pore size of between 0.4 and 1000 nm in a very narrow pore size distribution. You can generate various moulds, for example, irregular particles (powder, granulate), spheres, plates, sticks, fibers, ultra thin membranes, tubes and rings.
Sources: en.wikipedia.org
== External links == A Conversation with Fred W. McLafferty 2006, 90 minute video, for Cornell University. Center for Oral History. "Fred W. McLafferty". Science History Institute. Grayson, Michael A. (23 January 2007). Fred W. McLafferty, Transcript of Interviews Conducted by Michael A. Grayson at Cornell University Ithaca, New York on 22 and 23 January 2007 (PDF). Philadelphia, PA: Chemical Heritage Foundation.
== Natural occurrence == Myristicin can be found in the essential oil of nutmeg, black pepper, kawakawa, and many members of the Umbelliferae family, including anise, carrots, parsley, celery, dill, and parsnip. Trace amounts have also been isolated from a variety of plant species including Ridolfia segetum (harvest fennel), species of the Oenanthe genus (water dropworts), some species of the Lamiaceae family (mint family), Cinnamomum glanduliferum (Nepal camphor tree), and Piper mullesua ("Hill Pepper"). Depending on the conditions of growth and storage of the plant, a high quality nutmeg (Myristica fragrans) seed can contain up to 13 mg of myristicin per 1 gram.
Historically, an association between the color of blood and rust occurs in the association of the planet Mars, with the Roman god of war, since the planet is an orange-red, which reminded the ancients of blood. Although the color of the planet is due to iron compounds in combination with oxygen in the Martian soil, it is a common misconception that the iron in hemoglobin and its oxides gives blood its red color. The color is actually due to the porphyrin moiety of hemoglobin to which the iron is bound, not the iron itself, although the ligation and redox state of the iron can influence the pi to pi* or n to pi* electronic transitions of the porphyrin and hence its optical characteristics. Artist Julian Voss-Andreae created a sculpture called Heart of Steel (Hemoglobin) in 2005, based on the protein's backbone. The sculpture was made from glass and weathering steel. The intentional rusting of the initially shiny work of art mirrors hemoglobin's fundamental chemical reaction of oxygen binding to iron. Montreal artist Nicolas Baier created Lustre (Hémoglobine), a sculpture in stainless steel that shows the structure of the hemoglobin molecule. It is displayed in the atrium of McGill University Health Centre's research centre in Montreal. The sculpture measures about 10 metres × 10 metres × 10 metres.
=== Side-effects === Although patients at high risk of bleeding were excluded from the phase III clinical study (PROWESS), 25% of patients treated with drotrecogin and 18% of those receiving placebo experienced at least one bleeding event (principally ecchymoses or GI bleeding) during the 28-day study period. During treatment, serious bleeding events (e.g., intracranial hemorrhage, any life-threatening bleeding event, any bleeding event requiring administration of at least 3 units of packed red blood cells daily for 2 consecutive days) occurred in 2.4% of patients treated with drotrecogin and in 1% of those receiving placebo. No significant differences between geriatric patients and younger patients regarding bleeding events in the drotrecogin group were found. No non-bleeding side-effects were observed. A second study, encompassing approximately 1700 adult patients, was completed in 2011 and showed a comparable side-effect profile.
Homoarginine is an nonproteinogenic alpha-amino acid. It is structurally equivalent to a one-methylene group-higher homolog of arginine and to the guanidino derivative of lysine. L-Homoarginine is the naturally occurring enantiomer. Physiologically, homoarginine increases nitric oxide (NO) supply and betters endothelial functions in the body, with a particular correlation and effect towards cardiovascular outcome and mortality. At physiological pH, homoarginine is cationic: the guanidino group is protonated.
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.
HPLC testing separates and quantifies components in a liquid sample. It is used to check identity, purity, concentration, or stability. The technique works best for compounds that dissolve and are not easily vaporized.