Everything below concerns stationary phase. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2025-12-17. Where a claim depends on a specific study, the study is described rather than over-claimed.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Typical checks include retention time, peak area precision, resolution between critical pairs, tailing factor, and theoretical plate count. Acceptance criteria are set in the method or pharmacopeial monograph. If a suitability check fails, the run may be rejected and the instrument or sample preparation may need investigation. This practice helps prevent release of data from a system that has drifted out of control.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness to a reference value. |
| Validation parameter | Precision | Repeatability or intermediate precision. |
| Validation parameter | Linearity | Proportional response across a range. |
| System suitability check | Resolution | Separation between adjacent peaks. |
| Quality control tool | Control chart | Tracks results over time for trends. |
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.
Quality control for HPLC testing combines scheduled checks, documented procedures, and review of results. Before sample analysis, system suitability testing confirms that the instrument, column, and method meet predefined criteria. Common criteria include resolution between critical peaks, retention time precision, peak tailing, and theoretical plate count. Failure triggers investigation before results are reported. Records link raw data, calculations, instrument logs, and analyst identity to each batch, supporting audits and repeat analysis.
Key performance measures include retention time, peak area, peak height, resolution, tailing factor, and plate count. Retention time helps identify a peak under fixed conditions, but confirmation often requires a second method or detector. Peak area and height relate to concentration through calibration curves, which may be linear or nonlinear depending on the detector response. Resolution describes separation between adjacent peaks, while tailing factor and plate count describe peak shape and column efficiency. Performance checks verify these values before and during a run to confirm that the instrument is performing within limits.
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.
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.
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.
The lower the barrier and the masses of the fragments, the greater the probability per unit time of a split. Protons in a nucleus are bound together by the strong force, which counterbalances the Coulomb repulsion between positively charged protons. In heavier nuclei, larger numbers of uncharged neutrons are needed to reduce repulsion and confer additional stability. Even so, as physicists started to synthesize elements that are not found in nature, they found the stability decreased as the nuclei became heavier. Thus, they speculated that the periodic table might come to an end. The discoverers of plutonium (element 94) considered naming it "ultimium", thinking it was the last. Following the discoveries of heavier elements, of which some decayed in microseconds, it then seemed that instability with respect to spontaneous fission would limit the existence of heavier elements. In 1939, an upper limit of potential element synthesis was estimated around element 104, and following the first discoveries of transactinide elements in the early 1960s, this upper limit prediction was extended to element 108.
He stated STURP lacked expertise in medieval art techniques, and their findings need reassessment due to 35 years of development in microscopy. Andrea Nicolotti declared "We have known for four centuries that the image on the Shroud is flat, like a rectangular projection, and could not have been created by contact with a three-dimensional body."
biloba leaves and sarcotesta contain ginkgolic acids – which are highly allergenic – long-chain alkylphenols, such as bilobol or adipostatin A (bilobol is a substance related to anacardic acid from cashew nut shells and urushiols present in poison ivy and other Toxicodendron spp.) Individuals with a history of strong allergic reactions to poison ivy, mangoes, cashews and other alkylphenol-producing plants are more likely to experience an allergic reaction when consuming non-standardized ginkgo-containing preparations. The level of these allergens in standardized pharmaceutical preparations from Ginkgo biloba was restricted to 5 ppm by the Commission E of the former Federal German Health Authority. Overconsumption of seeds from Ginkgo biloba can deplete vitamin B6.
== External links == "The Cheminformatics and QSAR Society". Retrieved 2009-05-11. "The 3D QSAR Server". Retrieved 2011-06-18. Verma, Rajeshwar P.; Hansch, Corwin (2007). "Nature Protocols: Development of QSAR models using C-QSAR program". Protocol Exchange. doi:10.1038/nprot.2007.125. Archived from the original on 2007-05-01. Retrieved 2009-05-11. A regression program that has dual databases of over 21,000 QSAR models "QSAR World". Archived from the original on 2009-04-25. Retrieved 2009-05-11. A comprehensive web resource for QSAR modelers Chemoinformatics Tools Archived 2017-07-04 at the Wayback Machine, Drug Theoretics and Cheminformatics Laboratory Multiscale Conceptual Model Figures for QSARs in Biological and Environmental Science
=== Dietary sources === Aspartic acid is not an essential amino acid, which means that it can be synthesized from central metabolic pathway intermediates in humans, and does not need to be present in the diet. In eukaryotic cells, roughly 1 in 20 amino acids incorporated into a protein is an aspartic acid, and accordingly almost any source of dietary protein will include aspartic acid. Additionally, aspartic acid is found in:
Sources: en.wikipedia.org
2026 United States federal budget – $6.8 trillion (submitted 2025 by President Trump) 2025 United States federal budget – $7 trillion (submitted 2024 by President Biden) 2024 United States federal budget – $6.8 trillion (submitted 2023 by President Biden) 2023 United States federal budget – $6.1 trillion (submitted 2022 by President Biden) 2022 United States federal budget – $6.3 trillion (submitted 2021 by President Biden) 2021 United States federal budget – $6.8 trillion (submitted 2020 by President Trump) 2020 United States federal budget – $6.5 trillion (submitted 2019 by President Trump) 2019 United States federal budget – $4.4 trillion (submitted 2018 by President Trump) 2018 United States federal budget – $4.1 trillion (submitted 2017 by President Trump) 2017 United States federal budget – $4.2 trillion (submitted 2016 by President Obama) 2016 United States federal budget – $4 trillion (submitted 2015 by President Obama) 2015 United States federal budget – $3.9 trillion (submitted 2014 by President Obama) 2014 United States federal budget – $3.5 trillion (submitted 2013 by President Obama) 2013 United States federal budget – $3.8 trillion (submitted 2012 by President Obama) 2012 United States federal budget – $3.7 trillion (submitted 2011 by President Obama) 2011 United States federal budget – $3.8 trillion (submitted 2010 by President Obama) 2010 United States federal budget – $3.6 trillion (submitted 2009 by President Obama) 2009 United States federal budget – $3.5 trillion (submitted 2008 by President Bush) 2008 United States federal budget – $2.9 trillion (submitted 2007 by President Bush) 2007 United States federal budget – $2.8 trillion (submitted 2006 by President Bush) 2006 United States federal budget – $2.7 trillion (submitted 2005 by President Bush) 2005 United States federal budget – $2.4 trillion (submitted 2004 by President Bush) 2004 United States federal budget – $2.3 trillion (submitted 2003 by President Bush) 2003 United States federal budget – $2.2 trillion (submitted 2002 by President Bush) 2002 United States federal budget – $2 trillion (submitted 2001 by President Bush) 2001 United States federal budget – $1.9 trillion (submitted 2000 by President Clinton) 2000 United States federal budget – $1.8 trillion (submitted 1999 by President Clinton) 1999 United States federal budget – $1.7 trillion (submitted 1998 by President Clinton) 1998 United States federal budget – $1.7 trillion (submitted 1997 by President Clinton) 1997 United States federal budget – $1.6 trillion (submitted 1996 by President Clinton) 1996 United States federal budget – $1.6 trillion (submitted 1995 by President Clinton) The budget year runs from October 1 to September 30 the following year and is submitted by the President to Congress prior to October for the following year. In this way the budget of 2013 is submitted before the end of September 2012. This means that the budget of 2001 was submitted by Bill Clinton and was in force during most of George W. Bush's first year in office. The budget submitted by George W. Bush in his last year in office was the budget of 2009, which was in force through most of Barack Obama's first year in office. The President's budget also contains revenue and spending projections for the current fiscal year, the coming fiscal years, as well as several future fiscal years. In recent years, the President's budget contained projections five years into the future. The Congressional Budget Office (CBO) issues a "Budget and Economic Outlook" each January and an analysis of the President's budget each March. CBO also issues an updated budget and economic outlook in August. Actual budget data for prior years is available from the Congressional Budget Office; see the "Historical Budget Data" links on the main page of "The Budget and Economic Outlook". and from the Office of Management and Budget (OMB).
In Japan, Mochida Healthcare, a subsidiary of Mochida Pharmaceutical, produces a line of body soaps and shampoo under the brand name Collage (コラージュ) that contain miconazole nitrate as their main ingredient.
==== Medical conditions ==== Undiagnosed maternal celiac disease may cause a short duration of the breastfeeding period. Treatment with the gluten-free diet can increase its duration and restore it to the average value of the healthy women. Mothers with all types of diabetes mellitus normally use insulin to control their blood sugar, as the safety of other antidiabetic drugs while breastfeeding is unknown. Women with polycystic ovary syndrome, which is associated with some hormonal differences and obesity, may have greater difficulty with producing a sufficient supply to support exclusive breastfeeding, especially during the first weeks.
=== Parasitology === MALDI-TOF spectra have been used for the detection and identification of various parasites such as trypanosomatids, Leishmania and Plasmodium. In addition to these unicellular parasites, MALDI/TOF can be used for the identification of parasitic insects such as lice or cercariae, the free-swimming stage of trematodes.
As a result of his later work he proved that wide differences exist between different food proteins; and he was the first to direct attention to this fact, and to discuss its probable bearing on their relative value in nutrition. Osborne then joined forces with Lafayette Mendel at the Connecticut Agricultural Experiment Station to determine the essential amino acids. In the 1950s and 1960s, Nevin S. Scrimshaw took this knowledge to India and Guatemala. He designed meals using local vegetables to fight against the scourge of kwashiorkor. In Guatemala he used the combination of cottonseed flour with maize, while in India he combined peanut flour with wheat.
Sources: en.wikipedia.org
So pressure increases with depth below the surface of a liquid, as z denotes the distance from the surface of the liquid into it. Any object with a non-zero vertical depth will have different pressures on its top and bottom, with the pressure on the bottom being greater. This difference in pressure causes the upward buoyancy force. The buoyancy force exerted on a body can now be calculated easily, since the internal pressure of the fluid is known. The force exerted on the body can be calculated by integrating the stress tensor over the surface of the body which is in contact with the fluid:
Worldwide weather conditions during the flight were extremely favorable with most of the regions of the Earth the spacecraft passed over dominated by high pressure zones—in the three previous flights, only the Western Sahara and Southwestern United States were reliably cloudless. Nonetheless, haze and air pollution impeded visibility for Cooper—despite passing over Los Angeles and Calcutta, he could see neither city due to smog. At the start of the 17th orbit while crossing Cape Canaveral, Florida, Cooper transmitted slow scan black and white television pictures to Mercury Control. The picture showed a ghostly image of the astronaut. In the murky picture, a helmet and hoses could be seen. It was the first time an American astronaut had sent back television images from space. On the 17th and 18th orbits, Cooper took infrared weather photos and moonset Earth-limb pictures. He also resumed Geiger counter measurements of radiation. He sang during orbits 18 and 19, and marveled at the greenery of Earth. It was nearing 30 hours since liftoff.
Tazarotene, sold under the brand name Tazorac, among others, is a third-generation prescription topical retinoid. It is primarily used for the treatment of plaque psoriasis and acne. Tazarotene is also used as a therapeutic for photoaged and photodamaged skin. It is a member of the acetylenic class of retinoids. Tazarotene was approved for medical use in 1997 and is available as a generic medication.
Protein DHX8 is part of a protein complex called spliceosome, which is in charge of pre-mRNA splicing. The spliceosome has eight major functional states, each with distinct composition and structure; five of the eight states have been structurally characterized. DHX8 have different domains: a S1 RNA binding domain (DEAD/DEAH box), an helicase conserved C-terminal domain, helicase associated domain (HA2), and an oligonucleotide/oligosaccharide-binding (OB)-fold, each joined by intrinsically disordered regions. There are some regions of the protein which are very important for its activity, like R620 and the hook-loop and hook-turn regions. Also, DHX8Δ547 is the catalytically active core of the protein DHX8. It is made of two RecA domains and the C-terminal WH, ratchet-like and OB-fold domains and the N-terminal region. The total weight of the DHX8 structure is 156580.13 Da. Secondary structure:
boiling Also ebullition. A more rapid, highly energetic form of vaporization, in which a substance undergoes a phase transition from liquid to gas, as contrasted with the much slower process of vaporization. Boiling occurs when a liquid is heated to its boiling point, above which the liquid's internal vapor pressure exceeds the pressure exerted upon it by the surrounding atmosphere, causing the gaseous phase to rapidly and often violently separate from the liquid phase.
Sources: en.wikipedia.org
Method validation is the documented process of showing that an HPLC procedure produces reliable results for a defined purpose. It examines parameters such as accuracy, precision, specificity, linearity, and robustness. Regulators and quality systems often require validation before routine use.
System suitability is a set of checks run on the chromatographic system before sample analysis. It confirms that resolution, peak shape, retention time, and response meet predefined limits. Failure can invalidate the run and trigger corrective action.
Blank injections reveal peaks or baseline disturbances that come from solvents, reagents, or the instrument rather than the sample. They help distinguish contamination from actual analyte signals. Comparing blanks with sample runs supports accurate interpretation.
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.