Stationary phase is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-01-20. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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 |
|---|---|---|
| Accuracy | Recovery near 100% | Depends on acceptance criteria and matrix |
| Precision | Relative standard deviation | Often at or below 2% for replicate injections |
| Limit of detection | Signal-to-noise ratio 3:1 | Approximate and method-specific |
| Limit of quantitation | Signal-to-noise ratio 10:1 | Confirmed by precision and accuracy |
| Resolution | 1.5 or greater | Typical system suitability target |
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.
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.
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.
Quality control laboratories use HPLC to check identity, purity, concentration, and stability of raw materials and finished products. A validated method specifies the column, mobile phase, flow rate, detection wavelength, injection volume, and run time. Samples are prepared and compared against reference standards of known concentration. The resulting chromatogram provides quantitative data, such as assay values and impurity levels. This approach is common in pharmaceutical, food, environmental, and industrial testing where consistent measurements are required.
=== Surgery === Bariatric surgery has also been proposed as another approach to treat BED, and a recent meta-analysis showed that approximately two-thirds of individuals who seek this type of surgery for weight loss purposes have BED. Bariatric surgery recipients who had BED before receiving the surgery tend to have poorer weight-loss outcomes and are more likely to continue to exhibit eating behaviors characteristic of BED.
==== Dopamine ==== Dopamine is the principal prolactin-inhibiting factor. It acts on D2 receptors (D2R) on the lactotroph membrane. Two D2R isoforms (D2L and D2S) couple to Gi/Go proteins and produce inhibition through multiple time-dependent mechanisms:
== Etymology == BmK is the abbreviation for Buthus martensi Karsch, an old name for the scorpion that is the source of BmKAEP; AEP is an abbreviation for anti-epilepsy peptide. At the NCBI Protein Database, the full name of this peptide is listed as "Toxin BmKAEP".
Sources: en.wikipedia.org
C-value The total amount of DNA contained within a haploid nucleus (e.g. a gamete) of a particular organism or species, expressed in number of base pairs or in units of mass (typically picograms); or, equivalently, one-half the amount in a diploid somatic cell. For simple diploid eukaryotes the term is often used interchangeably with genome size, but in certain cases, e.g. in hybrid polyploids descended from parents of different species, the C-value may actually represent two or more distinct genomes contained within the same nucleus. C-values apply only to genomic DNA, and notably exclude extranuclear DNA.
=== Oceania === Since the end of Australia’s Whitlam government, the Australian Labour Party (ALP) has moved towards centrist policies and Third Way ideals which are supported by the ALP's Right Faction members while the supporters of democratic socialism and social democracy lie within the ALP's Left Faction. There has been an increase in interest for socialism in recent years, especially among young adults. Interest is strongest in Victoria, where the Victorian Socialists party was founded. 2017-23 Prime Minister Jacinda Ardern of the democratic socialist New Zealand Labour Party, who has called capitalism a "blatant failure" due to the extent of homelessness in New Zealand, has been described and identified herself as democratic socialist. In Melanesia, Melanesian socialism was inspired by African socialism and developed in the 1980s. It aims to achieve full independence from Britain and France in Melanesian territories and creation of a Melanesian federal union. It is very popular with the New Caledonia independence movement.
== Mythological origins == In Greek mythology, the centaur Chiron was a "Wounded Healer", after being poisoned with an incurable wound by one of Hercules's arrows. Jung mentioned the Chiron myth "wounding by one's own arrow means, first of all, the state of introversion"; For Jung, "a good half of every treatment that probes at all deeply consists in the doctor's examining himself... it is his own hurt that gives a measure of his power to heal. This, and nothing else, is the meaning of the Greek myth of the wounded physician." Jung felt that depth psychology can be potentially dangerous, because the analyst is vulnerable to being infected by his analysis by having his own wounds reopened. To avoid this, the analyst must have an ongoing relationship with the unconscious, otherwise he or she could identify with the "healer archetype", and create an inflated ego. Withdrawal of both projections may however ultimately activate the powers of the inner healer in the patients themselves. Jung’s closest colleague, Marie Louise Von Franz, said “the wounded healer IS the archetype of the Self [our wholeness, the God within] and is at the bottom of all genuine healing procedures.” Jungians warn of the dangers of inflation and splitting in the helping professions, involving projection of the 'wounded' pole of the archetype onto the patient alone, with the analyst safely separated off as 'healer'.
The United States, having become the only global superpower, used that ideological victory to reinforce its leadership position in the new world order, proclaiming that "the United States and its allies are on the right side of history." This new world order is referred to as "liberal hegemony" in international relations theory. Using the peace dividend, the United States Armed Forces were able to cut much of its expenditure, but the level rose again to comparable heights after the September 11 attacks and the initiation of the war on terror in 2001. Accompanying NATO expansion, Ballistic Missile Defense (BMD) systems were installed in Eastern Europe. However, from a relatively-weak developing country, China appeared as a fledgling emerging superpower that would challenge the U.S. and liberal democracy, creating new potential for worldwide conflict. In response to the rise of China, the U.S. has strategically "rebalanced" to the Asia-Pacific region, but also began to retreat from international commitments in favor of its own interests. Starting from the 2020s onward, the perceived threat of global terrorism in the post-9/11 era has expanded beyond Middle Eastern jihadist groups, culminating in the United States and Canada designating several drug cartels and transnational criminal organizations as terrorist organizations in the context of narcoterrorism and the war on drugs. The 2020s also found the Monroe Doctrine once again playing a central role in US foreign policy.
Sources: en.wikipedia.org
Validation establishes suitability for a new method, while verification confirms that a method works in a specific laboratory. Verification is often used when a validated method is adopted with existing equipment and staff. Both rely on documented acceptance criteria.
Quantification usually compares detector response to a standard curve made from reference standards. The curve may be external, internal, or based on standard addition depending on matrix effects. Results are reported with units and, when required, uncertainty.
Carryover occurs when analyte from a previous injection remains in the system and appears in a later chromatogram. It can come from the injector, column, or tubing. Blank injections and needle washes help detect and reduce it.
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.