If you have been reading about retention time and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-02-09. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
Most routine HPLC testing uses reversed-phase columns, where the stationary phase is nonpolar and the mobile phase is a polar mixture such as water with an organic solvent. Analytes partition between the two phases according to polarity, size, and charge. Gradients that change solvent composition over time can separate compounds with broad retention ranges. Isocratic conditions keep solvent composition constant and suit simpler mixtures. The choice of column chemistry, pH, and temperature affects selectivity and peak shape.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. UV detection is widely used because many organic compounds absorb light, but it requires a chromophore. Mass spectrometry provides mass-based identification and high sensitivity for trace analytes. Each detector has trade-offs in selectivity, cost, and compatibility with mobile phases. Quantification typically uses calibration curves prepared from reference standards. Results are reported as concentration, purity, or presence above a limit.
HPLC testing separates dissolved compounds by passing a liquid sample through a column packed with stationary phase. A pump delivers mobile phase at controlled flow, and the sample components interact differently with stationary and mobile phases. Compounds that spend more time in mobile phase elute earlier; those retained by stationary phase elute later. Detectors record elution as peaks, and peak area or height relates to amount. This mechanism underpins quantitative analysis of mixtures.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness of measured value to accepted reference value |
| Validation parameter | Precision | Agreement among repeated measurements under specified conditions |
| System suitability check | Resolution ≥ 1.5 | Baseline separation between critical peak pair |
| System suitability check | Tailing factor ≤ 2.0 | Common target for peak symmetry |
| Documentation | Validation report | Summarizes experiments, acceptance criteria, and conclusions |
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
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.
=== Dental use === Dentin adhesives were first designed and produced in the 1950s based on a co-monomer chelate with calcium on the surface of the tooth and generated very weak water-resistant chemical bonding (2–3 MPa).
Mérimée illustrated these color relationships with a simple diagram located between pages 244 and 245: Chromatic Scale (Echelle Chromatique).De la peinture à l’huile : ou, Des procédés matériels employés dans ce genre de peinture, depuis Hubert et Jean Van-Eyck jusqu’à nos jours was published in 1830 and an English translation by W. B. Sarsfield Taylor was published in London in 1839. Similar ideas about the creation of color using red, yellow, and blue were discussed in Theory of Colours (1810) by the German poet, color theorist and government minister Johann Wolfgang von Goethe. In The Law of Simultaneous Color Contrast (1839) by the French industrial chemist Michel Eugène Chevreul discussed the creation of numerous color nuances and his color theories were underpinned by the RYB color model. Separate to the RYB color model, cyan, magenta, and yellow primary colors are associated with CMYK commonly used in the printing industry. Cyan, magenta, and yellow are often referred to as "process blue", "process red", and "process yellow".
=== Role in cancer === Some of the laminin isoforms have been implicated in cancer pathophysiology. The majority of transcripts that harbor an internal ribosome entry site (IRES) are involved in cancer development via corresponding proteins. A crucial event in tumor progression, referred to as the epithelial-to-mesenchymal transition (EMT) allows carcinoma cells to acquire invasive properties. The translational activation of the extracellular matrix component laminin B1 (LAMB1) during EMT has been recently reported, suggesting an IRES-mediated mechanism. The IRES activity of LamB1 was determined by independent bicistronic reporter assays. Strong evidence excludes an impact of cryptic promoter or splice sites on IRES-driven translation of LamB1. Furthermore, no other LamB1 mRNA species arising from alternative transcription start sites or polyadenylation signals were detected that account for its translational control. Mapping of the LamB1 5'-untranslated region (UTR) revealed the minimal LamB1 IRES motif between -293 and -1 upstream of the start codon. RNA affinity purification demonstrated that the La protein interacts with the LamB1 IRES. This interaction and its regulation during EMT were confirmed by ribonucleoprotein immunoprecipitation. La is able to positively modulate LamB1 IRES translation, so LamB1 IRES is activated by binding to La which leads to translational upregulation during hepatocellular EMT.
ideal gas A hypothetical gas composed of many randomly moving point particles that do not participate in any interparticle interactions, thereby making it mathematically convenient to describe and predict their behavior as state variables change. The ideal gas concept is useful because it obeys the ideal gas law and can be analyzed within the framework of statistical mechanics.
Sources: en.wikipedia.org
== Career == After graduation, Baker did post-doctoral research in Richard D. Smiths' laboratory at Pacific Northwest National Laboratory (PNNL), and was later promoted to senior research scientist. In 2018, she began her academic career at North Carolina State University as associate professor, and moved to University of North Carolina at Chapel Hill in 2022. The scope of Baker's research involves both developing high throughput ion mobility–mass spectrometry (IMS–MS) systems and using these hybrid instruments to study biological and environmental systems. She was one of five researchers from the PNNL Interactive Omics Group who worked on the Structures for lossless ion manipulations (SLIM). The group received the R&D 100 Award for their effort on SLIM in 2017. She was also part of the PNNL team who helped with the commercialization of the Agilent 6560 Ion Mobility Quadrupole Time-of-Flight (IM–QTOF) Liquid Chromatography–Mass Spectrometer system. She is an expert in the research of perfluoroalkyl and polyfluoroalkyl substances (PFAS) analysis. She is the director of the Core of Advanced Platform Technologies Used for Remediation and Exploration (CAPTURE), the analytical branch of the PFAS Superfund Research Centre. She is named one of the "Worldwide Water Warriors" in 2017. Baker served as a member-at-large for education for the American Society for Mass Spectrometry from 2019 to 2020. She serves on the editorial board of Journal of the American Society for Mass Spectrometry, Journal of Proteome Research, International Journal of Mass Spectrometry, and Scientific Reports.
In one study in aged men with prostate cancer, testosterone levels were initially suppressed by 70%, but increased to 50% of baseline levels between 6 and 12 months, remaining stable thereafter up to 24 months of therapy. The combination of progestogens like CPA with an estrogen is synergistic in terms of antigonadotropic effect, and is able to fully suppress gonadal testosterone production even with very small doses of the estrogen. One study found that 100 to 300 mg/day CPA combined with an "extremely low" dosage of diethylstilbestrol (0.1 mg/day), a nonsteroidal estrogen, suppressed testosterone levels into the castrate range (to 30 ng/dL) in men with prostate cancer. Discontinuation of diethylstilbestrol at 5 months resulted in a rapid 6-fold increase in testosterone levels (to 135 ng/dL) and then further (to almost 200 ng/dL) by 12 months. Another study likewise found that the combination of 160 mg/day oral megestrol acetate, a progestin closely related to CPA, with 0.5 to 1.5 mg/day oral estradiol suppressed testosterone levels into the castrate range in men with prostate cancer. A study by Fung and colleagues (2017) found no difference in suppression of circulating testosterone levels (~95% suppression) in transgender women by the combination of either 25 mg/day oral CPA or 50 mg/day oral CPA with a moderate dosage of oral or transdermal estradiol (mean 3.3 mg/day oral, 3.4 g/day gel, or 95.6 μg/day patches).
Speaker of the House – Gerry Brownlee Prime Minister – Christopher Luxon Deputy Prime Minister – Winston Peters until 31 May, and then David Seymour Leader of the House – Chris Bishop Minister of Finance – Nicola Willis Minister of Foreign Affairs – Winston Peters
=== Brush type columns (Pirkle Type) === The brush type, or Pirkle type chiral stationary phases are also called π-π Donnor-Acceptor columns. According to some theoretical models separation on these CSPs are based on a three-point attachment between the solute and the bonded chiral ligand on the surface of the stationary phase. These interactions may be attractive or repulsive in nature, depending on the mutual properties. Pirkle columns discriminate enantiomers by binding of one enantiomer with the chiral stationary phase, thereby forming a diastereomeric complex through π-π bonding, hydrogen bonding, steric interactions, and/or dipole stacking. Pirkle CSP can be categorized into three classes: (i) π-electron acceptor (ii) π-electron donor (iii) π-electron donor-π-electron acceptor.
Nuclear medicine is the use of open radionuclides for diagnostic and therapeutic purposes (radionuclide therapy). It also includes the use of other radioactive substances and nuclear physics techniques for functional and localization diagnostics. George de Hevesy (1885-1966) lived as a lodger and in 1923 suspected that his landlady was offering him pudding that he had not eaten the following week. He mixed a small amount of a radioactive isotope into the leftovers. When she served him the pudding a week later, he was able to detect radioactivity in a sample of the casserole. When he showed this to his landlady, she immediately gave him notice. The method he used made him the father of nuclear medicine. It became known as the tracer method, which is still used today in nuclear medicine diagnostics. A small amount of a radioactive substance, its distribution in the organism, and its path through the human body can be tracked externally. This provides information about various metabolic functions of the body. The continuous development of radionuclides has improved radiation protection. For example, the mercury compounds 203chloro-merodrin and 197chloro-merodrin were abandoned in the 1960s as substances were developed that allowed a higher photon yield with less radiation exposure. Beta emitters such as 131I and 90Y are used in radionuclide therapy. In nuclear medicine diagnostics, the beta+ emitters 18F, 11C, 13N, and 15O are used as radioactive markers for tracers in positron emission tomography (PET).
Sources: en.wikipedia.org
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.
Validation follows a planned protocol that tests accuracy, precision, specificity, linearity, range, detection limits, quantitation limits, and robustness. Results are compared against predefined acceptance criteria. The validation report supports regulatory filing or routine use.
Revalidation may be needed after changes to column chemistry, mobile phase, detection, sample preparation, or instrument type. It can also follow a pattern of out-of-specification results. The scope depends on whether the change affects method performance.
It separates components in a liquid sample and measures their amounts using a detector. Results can indicate concentration, purity, or identity based on retention time and detector response. The technique works for mixtures that can be dissolved and filtered.