This is a working overview of reversed-phase, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2025-11-21. Anything still debated is marked as such rather than presented as settled.
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.
High-performance liquid chromatography, or HPLC, separates dissolved compounds by passing a liquid mobile phase through a packed column. Components distribute differently between the stationary phase and the moving liquid, so they travel at different speeds and exit at different times. A detector records these eluting bands as peaks, and peak area or height relates to amount. The technique supports testing in pharmaceuticals, foods, environmental samples, and industrial chemicals. Quantification usually depends on calibration with known standards.
HPLC testing is an analytical technique used to separate, identify, and quantify components in a liquid sample. It relies on a pressurized mobile phase that carries the sample through a column packed with stationary phase. Different compounds travel at different rates because of interactions with the stationary and mobile phases. The resulting signal versus time is a chromatogram. Peak position indicates identity under specified conditions, while peak area or height relates to amount.
Laboratories apply HPLC testing across pharmaceutical, food, environmental, and industrial chemistry. The method can measure active ingredients, impurities, additives, preservatives, and degradation products. Sample preparation often includes dilution, filtration, and sometimes extraction or derivatization. The choice of column, mobile phase, pH, temperature, and detector depends on the analytes and matrix. Results are compared with reference standards to assign identity and concentration. Method suitability is judged by resolution, precision, and accuracy.
HPLC testing is not a single fixed procedure; it is a family of separation modes. Reversed-phase, normal-phase, ion-exchange, size-exclusion, and affinity chromatography each suit different analyte properties. Reversed-phase methods dominate because they handle many neutral and moderately polar compounds. Detection can be optical, electrochemical, or mass spectrometric, and the detector dictates what information is available. Coupling with mass spectrometry increases selectivity and enables identification when standards are unavailable. The technique cannot separate every mixture without adjustment.
| Property | Value | Notes |
|---|---|---|
| Column particle size | 3–5 µm for conventional HPLC; sub-2 µm for UHPLC | Smaller particles increase backpressure and efficiency. |
| Typical flow rate | 0.5–2.0 mL/min for a 4.6 mm internal diameter column | Flow scales with column diameter and particle size. |
| UV detection wavelength | 190–400 nm | Selection depends on analyte chromophore. |
| Column temperature | 25–40 °C | Temperature affects retention, selectivity, and pressure. |
| Injection volume | 1–20 µL | Larger volumes may distort early-eluting peaks. |
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.
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.
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.
Quality control samples are inserted at intervals to monitor accuracy and precision throughout a batch. Blank samples detect contamination, while spiked samples assess recovery from the sample matrix. Calibration standards establish the relationship between detector response and concentration, and control samples are prepared independently from them whenever possible. Laboratories also participate in proficiency testing and maintain audit trails, instrument logs, and reagent records. Ongoing review of control charts can reveal trends before they cause out-of-specification results.
Method validation demonstrates that an HPLC procedure is suitable for its intended purpose. Common validation parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, and robustness. Accuracy reflects agreement with a reference value, while precision describes repeatability under defined conditions. Specificity shows whether the method can measure the analyte in the presence of impurities or matrix components. Validation documents are reviewed before a method is used for routine testing or regulatory submissions.
=== As NCCIH (2014–present) === In 2014, while Josephine Briggs was the director, the NCCAM was renamed the National Center for Complementary and Integrative Health (NCCIH). Briggs retired in October 2017. On August 29, 2018, the NCCIH announced Helene Langevin as the new director. She was previously the director of the Osher Center and professor-in-residence of medicine at Harvard Medical School. Her medical interests involve connective tissue. Langevin "believes that the stretching of connective tissue is how several CAM modalities 'work,' such as chiropractic, massage, and ... acupuncture". Langevin has been studying acupuncture since the 1990s. At the time of her appointment, Gorski expressed concern that the balance of power at NCCIH would "shift back towards pseudoscience" with a massive budget to fund the shift. Under Langevin, NCCIH adopted a "whole person health" research framework, investigating how different domains of health—physiology, psychology, and environment—interconnect across the continuum between health and illness. She co-led several trans-NIH initiatives, including the NIH HEAL Initiative on opioid addiction and pain management, and the funding of a Whole Person Reference Physiome and Coordination Center co-funded by 20 NIH Institutes, Centers, and Offices. The NCCIH budget grew to approximately $170 million annually under her leadership. Langevin retired from NCCIH on November 30, 2025, returning to the University of Vermont as director of research at the Osher Center for Integrative Health.
The 227AcBe neutron sources can be applied in a neutron probe – a standard device for measuring the quantity of water present in soil, as well as moisture/density for quality control in highway construction. Such probes are also used in well logging applications, in neutron radiography, tomography and other radiochemical investigations. The medium half-life of 227Ac makes it a very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of the concentration depth-profiles for different isotopes allows estimating the mixing rates. The physics behind this method is as follows: oceanic waters contain homogeneously dispersed 235U. Its decay product, 231Pa, gradually precipitates to the bottom, so that its concentration first increases with depth and then stays nearly constant. 231Pa decays to 227Ac; however, the concentration of the latter isotope does not follow the 231Pa depth profile, but instead increases toward the sea bottom. This occurs because of the mixing processes which raise some additional 227Ac from the sea bottom. Thus analysis of both 231Pa and 227Ac depth profiles allows researchers to model the mixing behavior.
== History == Occurrence of iron-containing red protein in bovine milk was reported as early as in 1939; however, the protein could not be properly characterized because it could not be extracted with sufficient purity. Its first detailed studies were reported around 1960. They documented the molecular weight, isoelectric point, optical absorption spectra and presence of two iron atoms per protein molecule. The protein was extracted from milk, contained iron and was structurally and chemically similar to serum transferrin. Therefore, it was named lactoferrin in 1961, though the name lactotransferrin was used in some earlier publications, and later studies demonstrated that the protein is not restricted to milk. The antibacterial action of lactoferrin was also documented in 1961, and was associated with its ability to bind iron. Recombinant lactoferrin production began in the 1990s with the expression of human lactoferrin (hLF) in microbial hosts, notably filamentous fungi such as Aspergillus oryzae, achieving yields exceeding 2 g/L in some cases. Yeast expression systems, particularly Pichia pastoris, were subsequently developed for scalable and cost-effective production. In a landmark development, Sydney-based biotechnology company All G became the first in the world to gain regulatory approval to sell recombinant bovine lactoferrin in China, achieved in November 2024 through precision fermentation (animal-free, microbe-based production).
Sources: en.wikipedia.org
== Current Research and Future Implications == Currently, studies and experiments are being done to test for dedifferentiation-like abilities in mammalian cells, with hopes that this information can provide more insight into possible regenerative abilities in mammals. Dedifferentiation could spark innovation in regenerative medicine because it suggests that one's own cells can change cell fates, which would remove immunological response risks from treatment with allogeneic cells, or cells that are not genetically matched with the patient. A concept that has been explored for mammals is that of inducible dedifferentiation, which would make cells that do not naturally dedifferentiate be able to revert to a pluripotent or progenitor-like state. This is achieved by expressing the appropriate transcription factors in the cell and suppressing others. More information about this as well as the possible risks can be found here [1] .
Former Labour MP Jared O'Mara, who submitted fake expense claims to fund his cocaine habit, is convicted of fraud. The following day, he is sentenced to four years in prison. Royal Mail unveils a new stamp design that will be available from 4 April, featuring an image of the unadorned head of King Charles III. 9 February The UK commits additional funding to help the victims of the earthquake in Turkey and Syria. 2023 West Lancashire by-election: Labour hold the seat with a large vote share of 62.3%, an increase of 10.3%. Ashley Dalton is the new MP. In a radio interview before his appointment as Deputy Chairman of the Conservative Party, Lee Anderson says he will support the return of capital punishment where the perpetrators are clearly identifiable. Prime Minister Rishi Sunak says neither he nor the government shares Anderson's stance. 10 February Chancellor Jeremy Hunt tells the BBC households are unlikely to receive extra help with their energy bills from April 2023, as he does not think the government has the "headroom to make a major new initiative to help people". Data released by the Office for National Statistics indicates the UK narrowly avoided a recession at the end of 2022 following zero per cent growth during October to December. This is also despite a fall in output of 0.5% during December due to strike action being staged prior to Christmas. Coronation of Charles III and Camilla Buckingham Palace unveils the official Coronation logo, designed by Sir Jony Ive. A ballot offering 10,000 free tickets to the Coronation concert at Windsor Castle on 7 May opens.
A memorial collection of scientific papers contributed by former pupils and colleagues of Robertson, edited by Sir Charles James Martin and Hedley R. Marston, was published in January 1932 as a special issue of The Australian Journal of Experimental Biology and Medical Science. A memorial window, commissioned by his wife — designed and produced by Edith Lungley, a member of the British Society of Master Glass Painters — was presented to the University of Adelaide, and was unveiled in the Mitchell Building at a ceremony on 18 March 1932 by Sir George Murray, the university's Chancellor. The Medical Sciences Club of South Australia sponsored the annual Brailsford Robertson Memorial Lecture in Robertson's memory. Notable lecturers have been: Sir Howard Florey (1944), Edward Slater (1957)[9], Frank G. Young (1960)[10], Derek Denny-Brown (1964)[11], M.F.A. Woodruff (1965)[12], Stephen Boyden (1968)[13], Geoffrey Burnstock (1971), Frank Macfarlane Burnet (1976)[14], and John B. West (1978). In 2001, the Brailsford Robertson Award was jointly created by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of Adelaide specifically to encourage collaborative research in areas of health identified as strategic priorities by the CSIRO Food and Nutritional Sciences division and the University of Adelaide. In 2001, the former CSIRO Division of Animal Nutrition Building on the University of Adelaide's campus was re-named the Brailsford Robertson Building.
The OSA frequency increase with age for the women, and is in particular linked to the onset of menopause and associated hormonal changes. The mortality is higher for women. If studied carefully in a sleep lab by polysomnography (formal "sleep study"), it is believed that approximately 1 in 5 American adults would have at least mild OSA. In the US, some studies report that it is more frequent among the Hispanic and African American population than among the white population.
Sources: en.wikipedia.org
HPLC separates and quantifies compounds in a liquid sample. Detectors produce a response proportional to the amount of a compound passing through the flow cell. Identification by retention time requires comparison with a known standard.
UHPLC uses columns with smaller particles and operates at higher pressures than conventional HPLC. These conditions can improve speed, resolution, and sensitivity. Both techniques use the same fundamental separation principles.
Validation shows that a method performs reliably for its intended purpose across a defined range. It assesses accuracy, precision, specificity, linearity, and robustness. Regulated testing often requires documented validation before routine use.
It measures the presence and amount of one or more compounds in a liquid sample. Separation occurs in a column, and detection produces a signal proportional to concentration. Identification usually requires comparison with a known reference standard under the same conditions.