A practical reference on stationary phase: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-06-11. Anything still debated is marked as such rather than presented as settled.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample by passing them 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 how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
Instrumentation includes a solvent delivery system, an autosampler, a column oven, and one or more detectors. Reversed-phase columns with chemically modified silica are widely used, but normal-phase, ion-exchange, size-exclusion, and affinity modes exist for specific separations. Detectors may rely on ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry. Column temperature, mobile phase composition, and flow rate are adjusted to improve resolution. System pressure is monitored because rising pressure can indicate column blockage or deteriorating packing.
Separation performance depends on particle size, pore size, column length, and the chemistry of the stationary phase. Smaller particles generally improve efficiency but require higher pressure and suitable instrumentation. The mobile phase often contains buffers and organic solvents that influence retention and selectivity. Testing labs select conditions based on the analytes, sample matrix, and required sensitivity. Method development frequently involves screening several columns and solvent mixtures before a final set of conditions is chosen.
Method validation demonstrates that an analytical procedure is suitable for its intended purpose. Typical validation characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulatory guidance from bodies such as the International Council for Harmonisation and the United States Pharmacopeia outlines expectations, though specific criteria depend on the product and method. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, column efficiency, and injection repeatability. Failure of these checks can invalidate a batch of measurements.
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.
| Property | Value | Notes |
|---|---|---|
| Separation principle | Differential partitioning | Analytes distribute between mobile and stationary phases. |
| Mobile phase | Liquid solvent mixture | Composition controls retention and selectivity. |
| Stationary phase | Packed column particles | Often chemically bonded silica. |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is also common. |
| Common synonym | High-performance liquid chromatography | Abbreviated as HPLC. |
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.
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.
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.
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.
Burmese tofu (to hpu in Burmese) is a legume product made from besan (chana dal) flour; the Shan variety uses yellow split pea flour instead. Both types are yellow in color and generally found only in Myanmar, and Yunnan province of China, though the Burman variety is also available in some overseas restaurants serving Burmese cuisine. The term is believed to be derived from Dou Fen (bean Jelly) from Chinese and it was adopted to Burmese cuisine through Shan people (Dai people of Yunnan) . Burmese tofu may be fried as fritters cut into rectangular or triangular shapes. A variety called hsan to hpu (or hsan ta hpo in Shan regions) is made from rice flour (called hsan hmont or mont hmont) and is white in color with the same consistency as yellow Burmese tofu when set. It is eaten as a salad in the same manner as yellow tofu.
== Finnigan Instrument Corporation == In 1967, Finnigan formed Finnigan Instrument Corporation with venture capital from Roger Sant and T. Z. Chu. He was joined by Michael Story from EAI, and William Fies from SRI. In early 1968, Finnigan Instrument Corporation delivered its first prototype quadrupole GC/MS instruments. One was sent to Nobel Prize winner Joshua Lederberg at Stanford University. The other was sent to Purdue University. The first commercial model for a computerized GC/MS, Finnigan's Model 1015/System 150, was introduced soon after for a price of $100,000. The first delivery went to Evan Charles Horning and Marjorie G. Horning at Baylor Medical College. For three years, Finnigan was the only company producing a computerized GC/MS. The next one to be introduced came from the Hewlett-Packard Company in 1971. Quadrupole mass spectrometry offered advantages in terms of size, cost, speed and sensitivity compared to the magnetic-sector mass spectrometry equipment most commonly used at that time. Quadrupoles offered high sensitivity and high-pressure tolerance. They could operate with a low voltage ion source. Rapid scanning became feasible because computers could be used to step the spectrometer from one ion peak to the next. This allowed acquisition and display of data in real-time, and gave operators the potential to interact with the system and modify what was being monitored. A major strength of the instrument was precise quantitation.
Phenylacetic acid was added to switch it to producing the highly potent penicillin G. This strain could produce up to 550 milligrams of penicillin per litre. Pfizer was a small New York company that specialised in making citric acid, for which it had developed deep submergence techniques. This involved converting molasses to citric acid by fermenting it in a large tank in which it was stirred and the pH was carefully controlled. Pfizer's vice president, John L. Smith, whose daughter had died from an infection, put all of Pfizer's resources into the development of a practical deep submergence technique. The company invested $2.98 million in penicillin in 1943 and 1944 (equivalent to $55 million in 2025). Pfizer scientists Jasper H. Kane, G. M. Shull, E. M. Weber, A. C. Finlay and E. J. Ratajak worked on the fermentation process while R. Pasternak, W. J. Smith, V. Bogert and P. Regna developed extraction techniques.
A keystone species is a singular species within an ecosystem that others within the same ecosystem, or the entire ecosystem itself, rely upon. Keystone species' are so vital for an ecosystem that without their presence, an ecosystem could transform or stop existing entirely. One way keystone species impact an ecosystem is through their presence in an ecosystem's food web and, by extension, a food chain within said ecosystem. Sea otters, a keystone species in Pacific coastal regions, prey on sea urchins. Without the presence of sea otters, sea urchins practice destructive grazing on kelp populations which contributes to declines in coastal ecosystems within the northern pacific regions. The presence of sea otters controls sea urchin populations and helps maintain kelp forests, which are vital for other species within the ecosystem.
Sources: en.wikipedia.org
This is problematic long-term and can lead to ACTH-receptor pathway-related side effects including: Cushing's syndrome, fluid retention, glaucoma, and cardiovascular disorders. Mutations in this receptor cause familial glucocorticoid deficiency (FGD) type 1, in which patients have high levels of serum ACTH and low levels of cortisol. Mutation of the receptor gene causes 25% of FGD, and mutation on the MRAP gene causes 20% of FGD. Mutations of ACTH can also contribute to this pathology: mutation of the "message sequence" inhibits cAMP production when bound to the ACTH receptor, and mutation of the "address sequence" inhibits binding to the receptor altogether.
resigned as corporation chairman, and was replaced by childhood friend, Roger Harvin. In March 1996, Hala Moddelmog was appointed president of Church's Chicken, making her the first female president of a fast food restaurant chain.
Lactinex is a brand name for a probiotic supplement used to replace microorganisms (gut flora) in the human intestines and colon. The brand is a registered trademark of Becton, Dickinson and Company. It may be used to treat diarrhea resulting from infection or when an antibiotic regimen destroys harmful bacteria and beneficial gut flora alike. The principal ingredient is one or more bacteria from the genus Lactobacillus regularly found in unpasteurized milk products (a blend of Lactobacillus acidophilus and Lactobacillus helveticus (bulgaricus)). It is considered a dietary supplement and is not a prescription. The brand Lactinex requires refrigeration because it contains live microorganisms. Similar ingredients are also found in freeze dried varieties that do not require refrigeration.
== Cause == PMOS's root cause is unknown. Risk factors include a family history of PMOS, early development of pubic hair and sweat gland development (adrenarche), and obesity. Low birth weight, exposure to androgens in the womb, and exposure to hormone disruptors may also predispose people to PMOS.
== External links == Official website of the Essendon Football Club Official website of the Australian Football League Archived 22 February 2011 at the Wayback Machine 2012 Season scores and results at AFL Tables 2012 Essendon player statistics at AFL Tables
Sources: en.wikipedia.org
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.
Pressure drives the liquid mobile phase through a column packed with small particles. Without pressure, flow would be very slow or stop because the packed bed resists liquid movement. Modern pumps maintain a steady flow despite the resistance.
A chromatogram is a plot of detector signal against time after sample injection. Each peak represents a compound or group of compounds eluting from the column. Retention time and peak area are the main measurements read from the plot.
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.