retention time 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 2026-02-20 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
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.
The conservation of genetic material with the intention of conserving a breed. The conservation of genetic material is not limited to non-humans. Many services provide genetic storage or the preservation of stem cells at birth. They may be used to study the generation of cell lines or for stem-cell therapy.
Opioids by themselves put older people at risk of respiratory depression and impaired ability to operate vehicles and other machinery. Combining these two drugs together not only increases a person's risk of the aforementioned adverse effects, but can increase a person's risk of overdose and death. Benzodiazepines are also the second leading cause of teen overdose death after fentanyl. They killed 152 people in 2021, less than a fifth of fentanyl's death toll. Hydrocodone was declared the most widely prescribed opioid between 2007 and 2016, and in 2015 the International Narcotics Control Board reported that greater than 98% of the hydrocodone consumed in the entire world was consumed by Americans.
==== NIH Interagency Pain Research Coordinating Committee ==== On February 13, 2012, the National Institutes of Health (NIH) announced a new group of individuals assigned to research pain. This committee is composed of researchers from different organizations and will focus to "coordinate pain research activities across the federal government with the goals of stimulating pain research collaboration… and providing an important avenue for public involvement" ("Members of new", 2012). With a committee such as this research will not be conducted by each individual organization or person but instead a collaborating group which will increase the information available. With this hopefully more pain management will be available including techniques for those with arthritis. In 2020 Beth Darnall, American scientist and pain psychologist, was appointed as scientific member of the group.
Methoclocinnamox (MCCAM; developmental code name NIH-10420) is a selective pseudo-irreversible partial agonist of the μ-opioid receptor (MOR). It shows a mixture of opioid agonist- and antagonist-like effects. The drug has long-lasting effects and is insurmountable by other MOR ligands. MCCAM was derived from clocinnamox (CCAM), was first described by 1995, and was of interest in the potential treatment of opioid dependence. However, it was not further developed and was never marketed. A close analogue of MCCAM, methocinnamox (MCAM), which in contrast to MCCAM acts as a MOR pseudo-irreversible antagonist, was first described in 2000 and is under development for the treatment of opioid use disorder and opioid overdose as of 2023.
Sources: en.wikipedia.org
The former Trump Plaza hotel in Atlantic City, New Jersey is demolished in a controlled implosion. The U.S. Food and Drug Administration approves the Patient Specific Talus Spacer 3D-printed talus implant for humanitarian use. The Patient Specific Talus Spacer is the first in the world and first-of-its-kind implant to replace the talus—the bone in the ankle joint. February 18 – NASA successfully lands its Perseverance rover on Mars, seven months after launching. February 19 – The U.S. officially rejoins the Paris Agreement, 107 days after leaving. February 22 New York Rangers winger Artemi Panarin takes a personal leave of absence after the Russian tabloid Komsomolskaya Pravda publishes a story in which former Kontinental Hockey League coach Andrei Nazarov accuses him of sexually assaulting an 18-year old Latvian woman in Riga. The team releases a statement calling the allegations against Panarin an "intimidation tactic" against him after speaking out against "recent political events", most notably expressing his support for Russian opposition leader Alexei Navalny, who was detained upon return to Russia from Germany. Enabling legislation for New Jersey Public Question 1 is signed into law by governor Phil Murphy, making New Jersey the 14th state to legalize recreational cannabis. The Supreme Court rejects a last-ditch attempt by Donald Trump to shield his financial records, and issues an order requiring his accountants to turn over his tax and other records to prosecutors in New York.
=== Normal–phase chromatography === Normal–phase chromatography was one of the first kinds of HPLC that chemists developed, but has decreased in use over the last decades. Also known as normal-phase HPLC (NP-HPLC), this method separates analytes based on their affinity for a polar stationary surface such as silica; hence it is based on analyte ability to engage in polar interactions (such as hydrogen-bonding or dipole-dipole type of interactions) with the sorbent surface. NP-HPLC uses a non-polar, non-aqueous mobile phase (e.g., chloroform), and works effectively for separating analytes readily soluble in non-polar solvents. The analyte associates with and is retained by the polar stationary phase. Adsorption strengths increase with increased analyte polarity. The interaction strength depends not only on the functional groups present in the structure of the analyte molecule, but also on steric factors. The effect of steric hindrance on interaction strength allows this method to resolve (separate) structural isomers. The use of more polar solvents in the mobile phase will decrease the retention time of analytes, whereas more hydrophobic solvents tend to induce slower elution (increased retention times). Very polar solvents such as traces of water in the mobile phase tend to adsorb to the solid surface of the stationary phase forming a stationary bound (water) layer which is considered to play an active role in retention.
The capacity to be metabolized by 5α-reductase and the AR activity of the resultant metabolites appears to be one of the major, if not the most important determinant of the androgenic–myotrophic ratio for a given AAS. AAS that are not potentiated by 5α-reductase or that are weakened by 5α-reductase in androgenic tissues have a reduced risk of androgenic side effects such as acne, androgenic alopecia (male-pattern baldness), hirsutism (excessive male-pattern hair growth), benign prostatic hyperplasia (prostate enlargement), and prostate cancer, while incidence and magnitude of other effects such as muscle hypertrophy, bone changes, voice deepening, and changes in sex drive show no difference.
Sources: en.wikipedia.org
HPLC testing measures the presence and amount of one or more compounds in a liquid sample. It separates mixture components and records detector responses as peaks, which are compared with reference standards. Results are usually reported as concentrations or relative percentages.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
System suitability is a set of checks performed before and during a run to confirm that the instrument, column, and method work as expected. Common checks include resolution, tailing factor, theoretical plates, and relative standard deviation of replicate injections. Failure triggers troubleshooting or method adjustment.