The short version of stationary phase fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-01-23. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| 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. |
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Method validation establishes that an HPLC procedure is suitable for its intended use. Key parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Accuracy measures agreement with a true or accepted value, while precision describes repeatability and intermediate precision. Specificity confirms that the method measures the analyte without interference from impurities, degradants, or excipients. Validation is documented in a protocol and report, and acceptance criteria are set before experiments begin. Regulatory guidance varies by region, but the general principles are widely harmonized.
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.
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.
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.
Sugar cane accounted for around 21% of the global crop production over the 2000–2021 period. The Americas was the leading region in the production of sugar cane (52% of the world total). Global production of sugarcane in 2022 was 1.9 billion tonnes, with Brazil producing 38% of the world total and India 23% (table). Sugarcane is any of several species, or their hybrids, of giant grasses in the genus Saccharum in the family Poaceae. They have been cultivated in tropical climates in the Indian subcontinent and Southeast Asia over centuries for the sucrose found in their stems.
=== Hunger and satiety hormones === Unlike the surgical sleeve gastrectomy, the ESG does not appear to affect central appetite signaling through the hunger hormone, ghrelin. This is thought to be because the surgical sleeve removes the fundus, the primary site of ghrelin production, and the relatively thinner-walled fundus is avoided in the ESG for safety concerns. Furthermore, in cases where the fundus was sutured in ESG, this did not benefit weight loss outcomes.
He was one of those vigorous, fearless thinkers who seem to be entirely free from the inhibitions which restrain most of us in narrow paths of scientific enquiry. ... His magnificent courage and imagination led him into every aspect of biology which presented problems to his consciousness. ... His originality of mind made him a stimulating colleague, and to his students he was as gracious as he was inspiring. ... Robertson's main service to science was in the realm of ideas. His practical work was of lesser significance, but in almost every direction in which his imagination led him he either contributed new conceptions or reoriented prevailing ideas." Hardolph Wasteneys, Professor of Biochemistry at the University of Toronto, The Biochemical Journal. A memorial collection of 12 Robertson items — comprised of ten of his previously published articles and the text of two of his speeches — with an introduction (SP.3) by his University of Adelaide colleague, Stuart Wortley Pennycuick (1887–1966) D.Sc., B.Sc., and edited by his wife (Jane Winifred Robertson), The Spirit of Research (BR.66), was published in 1931. On 5 September 1931, in the university's Animal Nutrition Building, Sir George Murray, the Chancellor of the University of Adelaide unveiled a bas-relief commemorative plaque (UA.3), designed and executed by Arthur Murch, that was dedicated to Robertson's memory.
=== Nervous system === Microglia are the resident immune cells of the central nervous system (i.e., brain and spinal cord). They are key contributors to the development and maintenance of neural tissues and mediate inflammatory responses to, e.g., bacterial invasion as well as the pathological inflammations which underlie many neurological diseases. Studies have reported that compared to control mice, germ-free mice (which lack SCFAs in their gastrointestinal tracts) have increased levels of immature microglia throughout their brains; SCFA supplementation normalized the microglial cell maturity. Furthermore, Ffar2 gene knockout mice likewise had increased levels of immature microglia throughout their brains. These studies suggest that FFAR2 is required for the maturation, and therefore functionality, of the microglia in mice. Since mouse microglial cells do not express FFAR2, the FFAR2-bearing cells responsible for the maturation and thereby functionality of the mouse's microglia are unclear. Studies have suggested that promoting the intestinal microbiota's production of SCFAs may suppress the development and/or progression of various human neurological diseases, particularly Parkinson's disease, Alzheimer's disease, neuromyelitis optica, and multiple sclerosis. This linkage is thought to involve at least in part SCFA-induced suppression of the inflammation associated with these diseases.
The Fascial Net Plastination Project (FNPP) is an anatomical research initiative led by fascia researcher Robert Schleip. The project aims to enhance the study of fascia through the technique of plastination. Led by an international team of fascia experts and anatomists, the FNPP resulted in the creation of a full-body fascia plastinate known as FR:EIA (Fascia Revealed: Educating Interconnected Anatomy). This plastinate provides a detailed view of the human fascial network, allowing for a better understanding of its structure and function as an interconnected tissue throughout the body. FR:EIA was unveiled at the 2021 Fascia Research Congress and is currently exhibited at the Body Worlds exhibition in Berlin. This project represents a significant contribution to the visualization of fascia and has the potential to influence future research in fields such as medicine, physical therapy, and movement science.
Sources: en.wikipedia.org
=== Magnetophoresis === One application for microfluidic devices is the separation and sorting of different fluids or cell types. Microfluidic devices have been integrated with magnetophoresis: the migration of particles by a magnetic field. This can be accomplished by sending a fluid containing at least one magnetic component through a microfluidic channel that has a magnet positioned along the length of the channel. This creates a magnetic field inside the microfluidic channel which draws magnetically active substances towards it, effectively separating the magnetic and non-magnetic components of the fluid. This technique can be readily utilized in industrial settings where the fluid at hand already contains magnetically active material. For example, a handful of metallic impurities can find their way into certain consumable liquids, namely milk and other dairy products. Conveniently, in the case of milk, many of these metal contaminants exhibit paramagnetism. Therefore, before packaging, milk can be flowed through channels with magnetic gradients as a means of purifying out the metal contaminants. cell separations are of interest in microfluidics. This is accomplished. First, a paramagnetic substance (usually micro/nanoparticles or a paramagnetic fluid) needs to be functionalized to target the cell type of interest. This can be accomplished by identifying a transmembranal protein unique to the cell type of interest and subsequently functionalizing magnetic particles with the complementary antigen or antibody.
In 2015, Xi's administration oversaw the establishment of two circuit courts under the Supreme People's Court, followed by four other circuit courts being established in 2016. Hangzhou Internet Court was established as a court of special jurisdiction in 2017, followed by the establishment of Beijing Internet Court and Guangzhou Internet Court. Shanghai Financial Court was established in 2018 as a specialized financial court. Under Xi, an increasing share of laws passed by the NPC explicitly affirmed the leadership of the CCP, with the share increasing from 4% in 2018 to nearly 70% in 2024.
=== Controversy over formulation === Mirzayanov gives somewhat different structures for Novichok agents in his autobiography than those which have been identified by Western experts. The Western formulations suffered from imperfect information, as can be seen in Fig. 1 of Chai et al in which Mirzayanov describes a family of compounds whereas Western scientists instantiate a particular salt. Mirzyanov makes clear that a large number of compounds were made, and many of the less potent derivatives were reported in the open literature as new organophosphate insecticides, so that the secret chemical weapons program could be disguised as legitimate pesticide research.
Aldosterone is a mineralocorticoid which is synthesized in the adrenal glands. When aldosterone is secreted from the adrenal glands, it binds to the mineralocorticoid receptor in the renal tubule cell and forms a complex. This complex enhances transcription of specific DNA segments in the nucleus, leading to the formation of two protein transporters, Na+/K+ ATPase pump at the basolateral membrane and Na+ channel called ENaC, located at the apical membrane of the renal tubule cell. These protein transporters increase sodium reabsorption and potassium excretion in the distal tubule and the collecting duct of the kidneys. This helps the body to maintain normal volume and electrolyte balance, increasing the blood pressure. Mineralocorticoid receptor antagonists decrease the aldosterone effect by binding to the mineralocorticoid receptor inhibiting aldosterone. This leads to higher levels of potassium in serum and increased sodium excretion, resulting in decreased body fluid and lower blood pressure.
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.
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.