The short version of reversed-phase fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-11-30. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Nonpolar stationary phase with polar mobile phase |
| Typical column particle size | 3–5 µm | Smaller particles improve resolution but raise pressure |
| Typical flow rate | 0.5–2.0 mL/min | Depends on column dimensions and pressure limits |
| Common detection | UV-Vis absorbance | Requires analytes with chromophores |
| Typical run time | 5–30 min | Varies with method, gradient, and sample complexity |
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.
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.
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.
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.
Total production from fishing in North and Baltic Seas was 40 780 tonnes in 2019, ca. 1/3 German production. In the Baltic Sea total production amounted to 10377 tonnes (2019), of which 5432 tonnes of sprat, 2568 tonnes of flatfish and 1190 tonnes of cod. In the North Sea the numbers were 19,487 tonnes of mussels, 3560 tonnes of North Sea shrimp, 1166 tonnes of herring and 7062 other fishes. One important aquaculture product is mussels, 16864 tonnes. Inland fishing and aquaculture are not significant, with 221 and 250 tonnes in 2019, respectively.
=== Mathematics === Simplicial link, a set of simplices "surrounding" a given vertex in a simplicial complex Link (knot theory), a collection of knots entangled with one another Link function in statistics
== Activism == Ly is active in advocacy within the Cambodian diaspora. He focuses on post-conflict recovery, civil liberties, and educational access in Southeast Asia, and participates in outreach programs linking Cambodian students with academic institutions abroad.
Sources: en.wikipedia.org
==== External tissue expansion ==== The successful outcome of fat-graft breast augmentation is enhanced by achieving a pre-expanded recipient site to create the breast-tissue matrix that will receive grafts of autologous adipocyte fat. The recipient site is expanded with an external vacuum tissue-expander applied upon each breast. The biological effect of negative pressure (vacuum) expansion upon soft tissues derives from the ability of soft tissues to grow when subjected to controlled, distractive, mechanical forces. (see distraction osteogenesis) The study reported the technical effectiveness of recipient-site pre-expansion. In a single-group study, 17 healthy women (aged 18–40 years) wore a brassiere-like vacuum system that applied a 20-mmHg vacuum (controlled, mechanical, distraction force) to each breast for 10–12 hours daily for 10 weeks. Pre- and post-procedure, the breast volume (size) was periodically measured; likewise, a magnetic resonance image (MRI) of the breast-tissue architecture and water density was taken during the same phase of the patient's menstrual cycle; of the 17-woman study group, 12 completed the study, and 5 withdrew, because of non-compliance with the clinical trial protocol. The breast volume (size) of all 17 women increased throughout the 10-week treatment period, the greatest increment was at week 10 (final treatment) – the average volume increase was 98+/–67 percent over the initial breast-size measures.
Three-quarters of sickle cell cases occur in Africa. A World Health Organization report dated 2006 estimated that around 2% of newborns in Nigeria are affected by sickle cell anaemia, giving a total of 150,000 affected children born every year in Nigeria alone. The carrier frequency ranges between 10 and 40% across equatorial Africa, decreasing to 1–2% on the North African coast and <1% in South Africa. In the West African countries of Ghana and Nigeria, the frequencies can vary from 15 to 30%. In Nigeria, 24% of the population carries the gene, and 20 per 1,000 newborns are born with the disease, or 150,000 annually. Uganda has the fifth-highest sickle cell disease burden in Africa. One study indicates that 20,000 babies per year, or 0.7% of the total, are born with sickle cell disease, and 13.3% carry the trait. In Uganda, carrier frequency of the trait varies strongly across tribal lines: among the Baamba, it reaches 45%.
Earle (1990), dean of Roger Hadfield Ogden Honors College at Louisiana State University Melissa Michelson (1990), dean of arts and sciences at Menlo College Melanie Jacobs (1991), dean of the University of Louisville School of Law and Michigan State University College of Law Ashish Jha (1992), dean of the Brown University School of Public Health and former professor of the Harvard T.H. Chan School of Public Health Sarah Bunin Benor (1997), vice provost of Hebrew Union College – Jewish Institute of Religion, recipient of 2019 Sami Rohr Choice Award for Jewish Literature
where wt = Density of the wound area at time t ct = Density of the cell area at time t The above are basic metrics that can be measured with this assay. However efforts are still being made to improve the interpretation of this assay. Three different measurements: direct rate average, regression rate average and average distance regression rate have been evaluated. Direct rate average and average distance regression rate were more resistant to outliers, whereas regression rate average were more sensitive to outliers.
Sources: en.wikipedia.org
Laurus nobilis is a widespread relict of the laurel forests that originally covered much of the Mediterranean Basin when the climate of the region was more humid. With the drying of the Mediterranean during the Pliocene era, the laurel forests gradually retreated, and were replaced by the more drought-tolerant sclerophyll plant communities familiar today. Most of the last remaining laurel forests around the Mediterranean are believed to have disappeared approximately ten thousand years ago, although some remnants still persist in the mountains of southern Turkey, northern Syria, southern Spain, north-central Portugal, northern Morocco, the Canary Islands and in Madeira.
Although the Soviet Union had nuclear weapon capabilities at the beginning of the Cold War, the United States still had an advantage in terms of bombers and weapons. In any exchange of hostilities, the United States would have been capable of bombing the Soviet Union, whereas the Soviet Union would have more difficulty carrying out the reverse mission. The widespread introduction of jet-powered interceptor aircraft upset this imbalance somewhat by reducing the effectiveness of the American bomber fleet. In 1949 Curtis LeMay was placed in command of the Strategic Air Command and instituted a program to update the bomber fleet to one that was all-jet. During the early 1950s the B-47 Stratojet and B-52 Stratofortress were introduced, providing the ability to bomb the Soviet Union more easily. Before the development of a capable strategic missile force in the Soviet Union, much of the war-fighting doctrine held by western nations revolved around using a large number of smaller nuclear weapons in a tactical role. It is debatable whether such use could be considered "limited" however because it was believed that the United States would use its own strategic weapons (mainly bombers at the time) should the Soviet Union deploy any kind of nuclear weapon against civilian targets. Douglas MacArthur, an American general, was fired by President Harry Truman, partially because he persistently requested permission to use his own discretion in deciding whether to utilize atomic weapons on the People's Republic of China in 1951 during the Korean War.
=== Major neuroendocrine axes === Oxytocin and vasopressin (also called anti-diuretic hormone), the two neurohypophysial hormones of the posterior pituitary gland (the neurohypophysis), are secreted from the nerve endings of magnocellular neurosecretory cells into the systemic circulation. The cell bodies of the oxytocin and vasopressin neurons are in the paraventricular nucleus and supraoptic nucleus of the hypothalamus, respectively, and the electrical activity of these neurons is regulated by afferent synaptic inputs from other brain regions. By contrast, the hormones of the anterior pituitary gland (the adenohypophysis) are secreted from endocrine cells that, in mammals, are not directly innervated, yet the secretion of these hormones (adrenocorticotrophic hormone, luteinizing hormone, follicle-stimulating hormone, thyroid-stimulating hormone, prolactin, and growth hormone) remains under the control of the hypothalamus. The hypothalamus controls the anterior pituitary gland via releasing factors and release-inhibiting factors; these are substances released by hypothalamic neurons into blood vessels at the base of the brain, at the median eminence. These vessels, the hypothalamo-hypophysial portal vessels, carry the hypothalamic factors to the anterior pituitary, where they bind to specific receptors on the surface of the hormone-producing cells. For example, the secretion of growth hormone is controlled by two neuroendocrine systems: the growth hormone-releasing hormone (GHRH) neurons and the somatostatin neurons, which stimulate and inhibit GH secretion, respectively.
==== High resolution melting analysis (HRM) ==== A further method to differentiate converted from unconverted bisulfite-treated DNA is using high-resolution melting analysis (HRM), a quantitative PCR-based technique initially designed to distinguish SNPs. The PCR amplicons are analyzed directly by temperature ramping and resulting liberation of an intercalating fluorescent dye during melting. The degree of methylation, as represented by the C-to-T content in the amplicon, determines the rapidity of melting and consequent release of the dye. This method allows direct quantitation in a single-tube assay, but assesses methylation in the amplified region as a whole rather than at specific CpG sites.
== Avoiding categorical diagnosis == Current nosological approach does not provide a framework for internal (sub-threshold symptoms) or external (comorbidity) heterogeneity of the different diagnostic categories. The prevailing "Neo-Kraepelinian" diagnostic system solely accounts for a categorical diagnosis, therefore not allowing for the possibility of dual diagnosis. There has been substantial criticism to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), due to problems of diagnostic overlap, lack of clear boundaries between normality and disease, a failure to take into account findings from novel research and the lack of diagnostic stability over time.
Sources: en.wikipedia.org
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.
It offers high resolution, reproducibility, and compatibility with many sample types. A single run can separate and quantify multiple analytes. It is common in pharmaceutical, food, environmental, and industrial laboratories.
Samples must be soluble in a suitable mobile phase and free of particles that can block the column. Detector response depends on analyte structure, so some compounds need derivatization or alternative detection. Complex matrices may require extensive sample preparation.
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.