This is a working overview of retention time, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-03-06. Anything still debated is marked as such rather than presented as settled.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Most common for neutral and moderately polar analytes |
| Column particle size | 3–5 µm | Smaller particles improve resolution but raise backpressure |
| Mobile phase pH range | 2–8 | Silica-based columns may degrade outside this range |
| Typical flow rate | 1.0–2.0 mL/min | For analytical columns with 4.6 mm internal diameter |
| Common synonyms | HPLC, LC, high-pressure liquid chromatography | High-performance liquid chromatography is the standard expansion |
Routine quality control uses system suitability, blank injections, check standards, and control samples to detect drift or contamination. System suitability criteria may specify minimum resolution, maximum tailing factor, and a permitted range for repeated injections. Blank injections reveal carryover or solvent contamination, while check standards confirm calibration accuracy over a batch. Control samples with known analyte levels can show whether results remain within statistical limits. When a control result falls outside limits, the analyst investigates the cause and may invalidate affected results before repeating the batch.
Documentation and traceability are central to regulated HPLC testing. Records typically include instrument logs, column history, mobile-phase preparation, sample preparation, injection sequences, raw chromatograms, and audit trails. Electronic systems may require user access controls, time-stamped changes, and backup procedures. Training records show that analysts are qualified for assigned methods. Audits and inspections check whether written procedures match actual practice and whether deviations are documented. These controls support reproducibility and allow results to be reconstructed if questions arise later.
Method validation establishes that an HPLC procedure is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, robustness, and solution stability. Accuracy reflects closeness to a reference value, while precision reflects agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from matrix components. Validation is documented through protocols and reports, and the required extent depends on the method's use and regulatory context.
High-performance liquid chromatography testing separates components of a liquid sample by forcing a mobile phase through a packed column. The stationary phase inside the column interacts with analytes to different degrees, so each compound exits at a characteristic retention time. A pump delivers solvent at controlled flow and pressure, while an injector introduces a precise sample volume. Detectors such as ultraviolet-visible, fluorescence, refractive index, or mass spectrometric instruments record the separated bands. The resulting chromatogram provides qualitative and quantitative information about the mixture.
Separation modes differ by the chemistry of the stationary phase and the composition of the mobile phase. Reversed-phase testing uses a nonpolar column and polar solvents, making it common for pharmaceutical, environmental, and food analytes. Normal-phase testing uses a polar column and nonpolar solvents for compounds that are poorly retained in reversed-phase systems. Ion-exchange and ion-pair methods separate charged species, while size-exclusion methods sort molecules by hydrodynamic volume. Gradient elution changes solvent strength over time to resolve complex mixtures, and isocratic elution holds solvent composition constant for simpler assays.
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.
Several separation modes exist, including reversed-phase, normal-phase, ion-exchange, size-exclusion, and hydrophilic interaction liquid chromatography. Reversed-phase uses a nonpolar stationary phase with a polar mobile phase and is widely applied to small organic molecules. Gradient elution changes mobile phase composition during the run, while isocratic elution keeps it constant. Column chemistry, particle size, temperature, flow rate, and mobile phase pH all influence retention and resolution. Method development selects conditions that separate analytes from matrix components and from each other.
Detection commonly uses ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. Ultraviolet detection depends on molecular chromophores that absorb light at specific wavelengths. Mass spectrometry provides mass information and sensitive quantification, often after electrospray ionization. Before sample batches, performance checks examine resolution, elution time repeatability, peak symmetry, and plate count. Matrix effects and co-elution remain recognized uncertainties; formal validation studies and orthogonal detection help address them. Detector choice depends on analyte properties and required sensitivity.
== Uses == Because of their amphiphilic structures, the polymers have surfactant properties that make them useful in industrial applications. Among other things, they can be used to increase the water solubility of hydrophobic, oily substances or otherwise increase the miscibility of two substances with different hydrophobicities. For this reason, these polymers are commonly used in industrial applications, cosmetics, and pharmaceuticals. They have also been evaluated for various drug delivery applications and were shown to sensitize drug-resistant cancers to chemotherapy. In bioprocess applications, poloxamers are used in cell culture media for their cell cushioning effects because their addition leads to less stressful shear conditions for cells in reactors. There are grades of poloxamers commercially available specifically for cell culture, including Kolliphor P 188 Bio. In materials science, the poloxamer P123 has recently been used in the synthesis of mesoporous materials, including SBA-15. In colloidal science, certain poloxamers such as Pluronic F-108 or Pluronic F-127, are used as steric stabilizers to prevent coalescence and/or reduce aggregation. In the case of hydrophobic colloids, the poloxamer's interior hydrophobic block is absorbed into the colloid while the two hydrophilic tails remain suspended in solution, creating a steric barrier. When mixed with water, concentrated solutions of poloxamers can form hydrogels. These gels can be extruded easily, acting as a carrier for other particles, and used for robocasting.
==== Rebif ==== Rebif is a disease-modifying drug (DMD) used to treat multiple sclerosis in cases of clinically isolated syndromes as well as relapsing forms of multiple sclerosis and is similar to the interferon beta protein produced by the human body. It is co-marketed by Merck Serono and Pfizer in the US under an exception to the Orphan Drug Act. It was approved in the European Union in 1998, and in the US in 2002; it has since been approved in more than 90 countries worldwide including Canada and Australia. EMD Serono has had sole rights to Rebif in the US since January 2016. Rebif is administered via subcutaneous injection.
The US FDA reports 50,000 health problems a year due to dietary supplements and these often involve bodybuilding supplements. For example, the "natural" best-seller Craze, 2012's "New Supplement of the Year" by bodybuilding.com, widely sold in stores such as Walmart and Amazon, was found to contain N,alpha-Diethylphenylethylamine, a methamphetamine analog. Liver damage from herbal and dietary supplements (HDS) accounted for about 16–20% of all drug-induced liver injury, with the proportion growing globally between 2004 and 2014. The total incidence of liver injury caused by HDS throughout the general population was estimated to be 3 per 100,000. The most common liver injuries from weight loss and bodybuilding supplements involve hepatocellular damage and jaundice. The most common supplement ingredients attributed to these injuries are catechins from green tea, anabolic steroids, and the herbal extract, aegeline. Other products by supplement designer and CEO of Driven Sports, Matt Cahill, have contained dangerous substances causing blindness or liver damage, and his pre-workout supplement Craze was found to contain illegal stimulants that resulted in several athletes failing drug tests.
== Bibliography == Greenwood NN, Earnshaw A (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. Holleman AF, Wiberg E, Wiberg N (2007). "Potassium". Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. ISBN 978-3-11-017770-1. Schultz H, Bauer G, Schachl E, Hagedorn F, Schmittinger P (2006). "Potassium compounds". Ullmann's Encyclopedia of Industrial Chemistry. Vol. A22. pp. 39–103. doi:10.1002/14356007.a22_031.pub2. ISBN 978-3-527-30673-2. National Nutrient Database Archived 2014-08-10 at the Wayback Machine at USDA Website
=== Rotation of sites === The infusion set is replaced regularly, usually every 2–3 days. Insulin absorption becomes less effective the longer the set is left in place, leading to poorer control of blood glucose. For this reason, the site of the infusion set is moved when the set is changed. Often a number of favorite sites for the infusion set are used on a rotation basis.
Sources: en.wikipedia.org
== Pulsed SILAC == Pulsed SILAC (pSILAC) is a variation of the SILAC method where the labelled amino acids are added to the growth medium for only a short period of time. This allows monitoring differences in de novo protein production rather than raw concentration.
=== RISC activation and catalysis === Exogenous dsRNA is detected and bound by an effector protein, known as RDE-4 in C. elegans and R2D2 in Drosophila, that stimulates Dicer activity. This protein only binds long dsRNAs, but the mechanism producing this length specificity is unknown. This RNA-binding protein then facilitates the transfer of cleaved siRNAs to the RISC complex. In C. elegans this initiation response is amplified through the synthesis of a population of 'secondary' siRNAs during which the Dicer-produced initiating or 'primary' siRNAs are used as templates. These 'secondary' siRNAs are structurally distinct from Dicer-produced siRNAs and appear to be produced by an RNA-dependent RNA polymerase (RdRP).
Letrozole and anastrozole are aromatase inhibitors which have been shown to be superior to tamoxifen for the first-line treatment of breast cancer in postmenopausal women. Exemestane is an irreversible "aromatase inactivator" which is superior to megestrol acetate for treatment of tamoxifen-refractory metastatic breast cancer, and does not appear to have the osteoporosis-promoting side effects of other drugs in this class. Aminoglutethimide inhibits both aromatase and other enzymes critical for steroid hormone synthesis in the adrenal glands. It was formerly used for breast cancer treatment, but has since been replaced by more selective aromatase inhibitors. It can also be used for the treatment of hyperadrenocortical syndromes, such as Cushing's syndrome and hyperaldosteronism in adrenocortical carcinoma.
== Mechanism == Phosphorylation involves the transfer of phosphate groups from ATP to the enzyme, the energy for which comes from hydrolysing ATP into ADP or AMP. However, dephosphorylation releases phosphates into solution as free ions, because attaching them back to ATP would require energy input. Cysteine-dependent phosphatases (CDPs) catalyse the hydrolysis of a phosphoester bond via a phospho-cysteine intermediate.
Sources: en.wikipedia.org
==== Rate of sickle cell disease in Uganda ==== The data compiled on sickle cell disease in Uganda has not been updated since the early 1970s. The deficiency of data is due to a lack of government research funds, even though Ugandans die daily from sickle cell disease. Data shows that the trait frequency of sickle cell disease is 20% of the population in Uganda. It is also estimated that about 25,000 Ugandans are born each year with sickle cell disease and 80% of those people do not live past five years old. Sickle cell disease also contributes 25% to the child mortality rate in Uganda. The Bamba people of Uganda, located in the southwest of the country, carry 45% of the gene, which is the highest trait frequency recorded in the world. The Sickle Cell Clinic in Mulago is the only sickle cell disease clinic in the country and, on average, sees 200 patients a day.
(1887), banker, prominent figure in Thoroughbred horse racing Richard Stevens (1890), attorney and real estate developer in Hoboken, New Jersey, grandson of inventor John Stevens and son of Stevens Institute of Technology founder Edwin Augustus Stevens Cortlandt F. Bishop (1891), aviator and book collector, grandson of philanthropist Benjamin Hazard Field Howard Gould* (1894), financier, son of railroad tycoon Jay Gould Joseph Peter Grace Sr. (1894), businessman, polo player, heir to W. R. Grace and Company; founder of Pan American-Grace Airways and Grace National Bank Samuel Bloomingdale (1895), businessman, heir to the Bloomingdale's department store fortune Dexter M. Ferry Jr. (1898), director of D.M. Ferry & Co.; member of the Michigan House of Representatives Charles A. Dana (1902), philanthropist who founded the Dana Foundation and Dana Holding Corporation John Knowles Fitch (1902), founder of Fitch Ratings, one of the Big Three rating agencies Marcellus Hartley Dodge Sr. (1903), chairman of the Remington Arms Company, husband of Geraldine Rockefeller Dodge George Earle Warren (1903), vice president of Chase Manhattan Bank Pendleton Dudley (1906), public relations executive, founder of Dudley-Anderson-Yutzy William Gage Brady Jr.
Class 1 – clean wound: a wound that is not infected and without signs of inflammation. This type of wound is typically closed. By definition, this type of wound excludes any wounds of the respiratory, genital, alimentary, or urinary tract. Class 2 – clean-contaminated wound: a wound with a low level of contamination. May involve entry into the respiratory, genital, alimentary, or urinary tract. Class 3 – contaminated wound: an open, accidental wound resulting from trauma outside of a sterile setting is automatically considered a contaminated wound. Additionally, any surgical wound where there is a major break in sterile technique or obvious contamination from the gastrointestinal tract is considered a contaminated wound. Class 4 – dirty/infected: a wound with evidence of an existing clinical infection. Class 4 wounds are usually found in old traumatic wounds which were not adequately treated and will show evidence of devitalized tissue or gross purulence.
Sources: en.wikipedia.org
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.
The pump maintains a steady flow rate and pressure, which keeps retention times reproducible. Pulsation or flow errors can shift peaks and distort quantitation. Modern pumps use feedback control to reduce these variations.
HPLC alone usually separates compounds but does not always identify them. Retention time matching with a known standard provides tentative identification. Coupling HPLC to mass spectrometry adds mass information that supports structural identification.
Method validation is the documented process of confirming that an HPLC procedure is suitable for its intended use. It evaluates accuracy, precision, specificity, linearity, range, detection limits, and robustness. Validation criteria depend on the regulatory context and the sample type.