A practical reference on stationary phase: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-09-13. Anything still debated is marked as such rather than presented as settled.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
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.
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.
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.
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.
This single-exon gene was then duplicated in the stem amniote into the three subclasses of interferons, Ia (alpha, beta, delta, epsilon, sigma, nu, omega) Ib (kappa), and Ic (subsequently lost in mammals). The evolution of the Type I IFNs was characterized by extensive gene duplication and non-allelic homologous recombination (NAHR) between the many copies. The NAHR causes further duplication and also homogenizes the blocks by gene conversion. In catarrhine primates (including humans), the region between IFNA14 and IFNA21 remains a recombination hotspot. The evolution of types II and III in amniotes had been a lot less eventful as they generally stayed in the same location from shark to amniotes (between DYRK2 and IL22 for type II, near SYCN, SUPT5H, or TIMM50 for type III), with the exception of the birds and reptiles having duplicated their type II to the so-called IFNLB loci. The loss of introns in type III IFNs happened independently in a few tetrapod groups. Type IV (upsilon) stayed in the same location between the zebrafish and the chicken (between ADARB2 and PFKP) but was lost in humans. The nomenclature of interferons is inconsistent between species, growing in chaoticness as the distance from humans increase. For example, among reptiles, "IFN I" refers to interferon Type Ic and "IFN III" and "IFN IV" are sibling branches of type Ia. Due to the many gene conversion events, using the sequence alone does not always show the correct gene-to-gene correspondence (orthology) and colinearity is needed.
== Roles in disease == Diseases related to lysine are a result of the downstream processing of lysine, i.e., the incorporation into proteins or modification into alternative biomolecules. The role of lysine in collagen has been outlined above, however, a lack of lysine and hydroxylysine involved in the crosslinking of collagen peptides has been linked to a disease state of the connective tissue. As carnitine is a key lysine-derived metabolite involved in fatty acid metabolism, a substandard diet lacking sufficient carnitine and lysine can lead to decreased carnitine levels, which can have significant cascading effects on an individual's health. Lysine has also been shown to play a role in anaemia, as lysine is suspected to have an effect on the uptake of iron and, subsequently, the concentration of ferritin in blood plasma. However, the exact mechanism of action is yet to be elucidated. Most commonly, lysine deficiency is seen in non-western societies and manifests as protein-energy malnutrition, which has profound and systemic effects on the health of the individual. There is also a hereditary genetic disease that involves mutations in the enzymes responsible for lysine catabolism, namely the bifunctional AASS enzyme of the saccharopine pathway. Due to a lack of lysine catabolism, the amino acid accumulates in plasma and patients develop hyperlysinaemia, which can present as asymptomatic to severe neurological disabilities, including epilepsy, ataxia, spasticity, and psychomotor impairment.
=== Depression === A comparative meta-analysis of 21 major antidepressants found that venlafaxine, agomelatine, amitriptyline, escitalopram, mirtazapine, paroxetine, and vortioxetine were more effective than other antidepressants, although the quality of many comparisons was assessed as low or very low. Open-label evidence also suggests potential benefit in treatment-resistant cases: in a multicenter Canadian study of adults with inadequate response to prior antidepressants (n=159), 58% achieved response and 28% remission after 8 weeks of venlafaxine (mean 260 mg/day); tolerability was generally acceptable. Venlafaxine was similar in efficacy to the atypical antidepressant bupropion; however, the remission rate was lower for venlafaxine. In a double-blind study, patients who did not respond to an SSRI were switched to either venlafaxine or another SSRI (citalopram); similar improvement was observed in both groups. Studies have not established its efficacy for use in pediatric populations. In children and adolescents with depression, venlafaxine increases the risk of suicidal thoughts or attempts. Higher doses (e.g., 225 mg and 375 mg per day) of venlafaxine are more effective than lower doses (e.g., 75 mg per day) but also cause more side effects. Studies have shown that the extended-release is superior to the immediate-release form of venlafaxine. A 2017 meta-analysis has shown that the efficacy of venlafaxine is not correlated with baseline severity of depression.
US and Canada: Pentacarinat 300 injection powder 300 mg vial (Avantis Pharma Inc - Canada) Pentam 300 (APP Pharmaceuticals LLC - US) Pentamidine isethionate 300 mg for injection (David Bull Laboratories LTD - Canada, Hospira Healthcare Corporation - Canada) International Brands: Pentamidine isethionate (Abbott) Pentacarinat (Sanofi-Aventis) Pentacrinat (Abbott) Pentam (Abbott) Pneumopent
Sources: en.wikipedia.org
In fluid dynamics, the continuity equation states that the rate at which mass enters a system is equal to the rate at which mass leaves the system plus the accumulation of mass within the system. The differential form of the continuity equation is:
In the present day, Quechuas continue to be victims of political conflicts and ethnic persecution. In the internal conflict in Peru in the 1980s between the government and Sendero Luminoso about three-quarters of the estimated 70,000 death toll were Quechuas, whereas the war parties were without exception whites and mestizos (people with mixed descent from both Natives and Spaniards).
=== IRAP catalytic site inhibitors === Peptidomimetics The first reported IRAP inhibitors were designed as angiotensin IV (AngIV) analogs. In 2006, Axén et al published a macrocyclized version of an AngIV derivative (Compound 1) which confers metabolic stability together with high affinity for IRAP (Ki = 25.8 nM). Under a similar scope Lukaszuk et al produced compound AL-11, which was able to inhibit IRAP (Ki = 27.5 nM) and displayed around 200-fold selectivity over APN. Further structural modifications on the AngIV-based inhibitors from Anderson et al led to optimized macrocycle HA08 (available crystal structure within IRAP, Figure 2) with excellent IRAP potency (Ki = 3.3 nM) and selectivity over APN, but poor metabolic stability.
==== Pregnancy ==== During pregnancy, DHEA-S is metabolized into the sulfates of 16α-hydroxy-DHEA and 15α-hydroxy-DHEA in the fetal liver as intermediates in the production of the estrogens estriol and estetrol, respectively.
It is on the World Health Organization's List of Essential Medicines for its obstetric uses. Lubiprostone is a PGE1 derivative used to treat chronic constipation. It is taken orally. Common side effects include diarrhea, vomiting, and abdominal pain.
Sources: en.wikipedia.org
=== Non-canonical/alternate pathway === A select set of cell-differentiating or developmental stimuli, such as lymphotoxin β-receptor (LTβR), BAFF or RANKL, activate the non-canonical NF-κB pathway to induce NF-κB/RelB:p52 dimer in the nucleus. In this pathway, activation of the NF-κB inducing kinase (NIK) upon receptor ligation led to the phosphorylation and subsequent proteasomal processing of the NF-κB2 precursor protein p100 into mature p52 subunit in an IKK1/IKKa dependent manner. Then p52 dimerizes with RelB to appear as a nuclear RelB:p52 DNA binding activity. RelB:p52 regulates the expression of homeostatic lymphokines, which instructs lymphoid organogenesis and lymphocyte trafficking in the secondary lymphoid organs. In contrast to the canonical signaling that relies on NEMO-IKK2 mediated degradation of IκBα, -β, -ε, non-canonical signaling depends on NIK mediated processing of p100 into p52. Given their distinct regulations, these two pathways were thought to be independent of each other. However, it was found that syntheses of the constituents of the non-canonical pathway, viz RelB and p52, are controlled by canonical IKK2-IκB-RelA:p50 signaling. Moreover, generation of the canonical and non-canonical dimers, viz RelA:p50 and RelB:p52, within the cellular milieu are mechanistically interlinked. These analyses suggest that an integrated NF-κB system network underlies activation of both RelA and RelB containing dimer and that a malfunctioning canonical pathway will lead to an aberrant cellular response also through the non-canonical pathway.
== Sponsorship == In April 2022, the team announced their sponsorship with car retailer Cazoo starting in July 2022. The Cazoo brand is visible on the front of the new jerseys as the team's main sponsor. In addition to the Bundesliga professionals, Cazoo appeared as shirt sponsor and advertising partner of the second team of SC Freiburg in the third division and as co-sponsor of the Freiburg Football School, and became visible at all matches of the SC junior teams. Cazoo also became a co-sponsor and sleeve sponsor of SC Freiburg's Bundesliga women.
The dye substance is a mucous secretion from the hypobranchial gland of one of several species of medium-sized predatory sea snails that are found in the eastern Mediterranean Sea, and off the Atlantic coast of Morocco. David Jacoby remarks that "twelve thousand snails of Murex brandaris yield no more than 1.4 grams (22 grains) of pure dye, enough to colour only the trim of a single garment." These are the marine gastropods Bolinus brandaris the spiny dye-murex (originally known as Murex brandaris Linnaeus, 1758), the banded dye-murex Hexaplex trunculus, the rock-shell Stramonita haemastoma, and less commonly a number of other species such as Bolinus cornutus. The dye is an organic compound of bromine (i.e., an organobromine compound), a class of compounds often found in algae and in some other sea life, but much more rarely found in the biology of land animals. This dye is in contrast to the imitation purple that was commonly produced using cheaper materials than the dyes from the sea snail. In nature, the snails use the secretion as part of their predatory behaviour to sedate prey and as an antimicrobial lining on egg masses. The snail also secretes this substance when it is attacked by predators, or physically antagonized by humans (e.g., poked). Therefore, the dye can be collected either by "milking" the snails, which is more labor-intensive but is a renewable resource, or by collecting and destructively crushing the snails. The dye is collected via the snail-harvesting process, involving the extraction of the hypobranchial gland (located under the mollusk's mantle).
=== From minerals and other natural occurrences === In some places, there is no clear source of perchlorate, and it may be naturally occurring. Natural perchlorate on Earth was first identified in terrestrial nitrate deposits /fertilizers of the Atacama Desert in Chile as early as the 1880s and for a long time considered a unique perchlorate source. The perchlorate released from historic use of Chilean nitrate based fertilizer which the U.S.imported by the hundreds of tons in the early 19th century can still be found in some groundwater sources of the United States, for example Long Island, New York. Recent improvements in analytical sensitivity using ion chromatography based techniques have revealed a more widespread presence of natural perchlorate, particularly in subsoils of Southwest USA, salt evaporites in California and Nevada, Pleistocene groundwater in New Mexico, and even present in extremely remote places such as Antarctica. The data from these studies and others indicate that natural perchlorate is globally deposited on Earth with the subsequent accumulation and transport governed by the local hydrologic conditions. Despite its importance to environmental contamination, the specific source and processes involved in natural perchlorate production remain poorly understood. Laboratory experiments in conjunction with isotopic studies have implied that perchlorate may be produced on earth by oxidation of chlorine species through pathways involving ozone or its photochemical products.
Once a nucleic acid sequence has been obtained from an organism, it is stored in silico in digital format. Digital genetic sequences may be stored in sequence databases, be analyzed (see Sequence analysis below), be digitally altered and be used as templates for creating new actual DNA using artificial gene synthesis.
Sources: en.wikipedia.org
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.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
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.