stationary phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-12-17 and is reviewed periodically as new material appears.
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.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Nonpolar stationary phase with polar mobile phase |
| Typical column particle size | 3–5 µm | Smaller particles improve resolution but raise pressure |
| Typical flow rate | 0.5–2.0 mL/min | Depends on column dimensions and pressure limits |
| Common detection | UV-Vis absorbance | Requires analytes with chromophores |
| Typical run time | 5–30 min | Varies with method, gradient, and sample complexity |
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.
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.
In a typical MS procedure, a sample, which may be solid, liquid, or gaseous, is ionized, for example by bombarding it with a beam of electrons. This may cause some of the sample's molecules to break up into positively charged fragments or simply become positively charged without fragmenting. These ions (fragments) are then separated according to their mass-to-charge ratio, for example by accelerating them and subjecting them to an electric or magnetic field: ions of the same mass-to-charge ratio will undergo the same amount of deflection. The ions are detected by a mechanism capable of detecting charged particles, such as an electron multiplier. Results are displayed as spectra of the signal intensity of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses (e.g. an entire molecule) to the identified masses or through a characteristic fragmentation pattern.
Christianity does not require male circumcision, with covenant theology teaching that the Christian sacrament of baptism fulfills the Israelite practice of circumcision, both being signs and seals of the covenant of grace. Most mainstream Christian denominations currently maintain a neutral position on the practice of non-religious circumcision. Male circumcision is commonly practiced in many predominantly Christian countries and many Christian communities. In the Coptic Orthodox Church, the Ethiopian Orthodox Church and the Eritrean Orthodox Tewahedo Church male circumcision is an established practice, and require that their male members undergo circumcision, and it is seen as a rite of passage. While male circumcision is widely practiced by the Druze, the procedure is practiced as a cultural tradition, and has no religious significance in the Druze faith. There is no special date for this act in the Druze faith: male Druze infants are usually circumcised shortly after birth, however some remain uncircumcised until the age of ten or older. Some Druzes do not circumcise their male children, and refuse to observe this "common Muslim practice".
The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, and in the uptake of external materials by a cell. The cytoskeleton is composed of microtubules, intermediate filaments and microfilaments. There are a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments. The outermost part of the cytoskeleton is the cell cortex, or actin cortex, a thin layer of cross-linked actomyosins. Its thickness varies with cell type and physiology. It directs the transport through the ER and the Golgi apparatus. The cytoskeleton in the animal cell also plays a part in cytokinesis, in the formation of the spindle apparatus during cell division, the separation of daughter cells.
Sources: en.wikipedia.org
In those with prediabetes, alpha-glucosidase inhibitors such as acarbose may delay or reduce the risk of type 2 diabetes when compared to placebo, however there was no conclusive evidence that acarbose improved cardiovascular mortality or cardiovascular events, according to a 2018 Cochrane review. In those with prediabetes, pioglitazone may delay or reduce the risk of developing type 2 diabetes compared to placebo or no intervention, but no difference was seen compared to metformin, and data were missing on mortality and complications and quality of life, according to a 2020 Cochrane review. In those with prediabetes, there was insufficient data to draw any conclusions on whether SGLT2 inhibitors may delay or reduce the risk of developing type 2 diabetes, according to a 2016 Cochrane review.
=== Associated conditions === Researchers have implicated estrogens in various estrogen-dependent conditions, such as ER-positive breast cancer, as well as a number of genetic conditions involving estrogen signaling or metabolism, such as estrogen insensitivity syndrome, aromatase deficiency, and aromatase excess syndrome. Estrogens promote salt and water retention, which can lead to facial swelling and edema. High estrogen can amplify stress-hormone responses in stressful situations.
== Pharmacology == As with other nonsteroidal anti-inflammatory drugs, the primary mechanism responsible for its anti-inflammatory, antipyretic and analgesic action is thought to be inhibition of prostaglandin synthesis through COX-inhibition. The main target in the inhibition of prostaglandin synthesis appears to be the transiently expressed prostaglandin-endoperoxide synthase-2 (PGES-2), also known as cycloxygenase-2 (COX-2). That is, diclofenac is partially selective for COX-2. The reported selectivity for COX-2 varies from 1.5 to 30 depending on the source. The drug may be bacteriostatic via inhibiting bacterial DNA synthesis. Diclofenac has a relatively high lipid solubility, making it one of the few nonsteroidal anti-inflammatory drugs that are able to enter the brain by crossing the blood-brain barrier. As in the rest of the body, it is thought to exert its effect in the brain through inhibition of COX-2. In addition, it may have effects inside the spinal cord. Diclofenac may be a unique member of the nonsteroidal anti-inflammatory drugs in other aspects. Some evidence indicates it inhibits the lipoxygenase pathways, thus reducing the formation of leukotrienes (also pro-inflammatory autacoids). It also may inhibit phospholipase A2, which may be relevant to its mechanism of action. These additional actions may explain its high potency –it is the most potent NSAID on a broad basis. Marked differences exist among nonsteroidal anti-inflammatory drugs in their selective inhibition of the two subtypes of cyclooxygenase, COX-1, and COX-2.
Sources: en.wikipedia.org
===== MeSH D08.811.682.608 – nadh, nadph oxidoreductases ===== MeSH D08.811.682.608.047 – apoptosis inducing factor MeSH D08.811.682.608.191 – cytochrome reductases MeSH D08.811.682.608.191.237 – cytochrome-b(5) reductase MeSH D08.811.682.608.191.500 – nadph-ferrihemoprotein reductase MeSH D08.811.682.608.504 – electron transport complex i MeSH D08.811.682.608.504.500 – nadh dehydrogenase MeSH D08.811.682.608.530 – nadh tetrazolium reductase MeSH D08.811.682.608.540 – nadp transhydrogenase MeSH D08.811.682.608.550 – nadph dehydrogenase MeSH D08.811.682.608.575 – nadph oxidase MeSH D08.811.682.608.800 – quinone reductases MeSH D08.811.682.608.800.500 – nad(p)h dehydrogenase (quinone) MeSH D08.811.682.608.800.500.500 – zeta-crystallins
=== Jonah Atterbury === Jonah Atterbury (Kal Penn) is the co-founder and CEO of Tender, which he started with his college friend Whitney Halberstram. Once an ambitious business school graduate, Jonah has since devolved into an irresponsible and inattentive CEO, addicted to partying, drugs, and pornography, and frequently showing up intoxicated to the office. He clashes with Whitney over the latter's desire to pivot Tender away from lucrative "alternative merchants" like porn and gambling and towards banking. Whitney and the Tender board soon use behavioral clauses in Jonah's contract to remove him as CEO, citing his inappropriate behavior, poor hygiene, and misuse of company funds; Whitney takes over in the interim. Jonah is later contacted by Sweetpea Golightly, who is investigating Tender's shady finances as part of a short; a vengeful Jonah, who is suing Whitney for defamation, emails Sweetpea a trove of subpoenaed internal Tender emails that she uses to uncover a connection to Accra. After Tender's stock plummets following revelations of its fraud, Whitney attempts to contact Jonah, who rebuffs him.
Bukele's relationship with the FMLN began to deteriorate after he became mayor of San Salvador. He clashed with other party members on Twitter, and frequently resisted FMLN party leadership. Bukele became a strong critic of Salvador Sánchez Cerén, the FMLN president of El Salvador who was elected in 2014. He threatened to leave the party in 2015 if the FMLN-led government reappointed Luis Martínez as the country's attorney general, describing Martínez as "a gangster, very corrupt, [and] the worst of the worst". The FMLN relented and replaced Martínez, and Bukele later admitted that his threat to leave the party "was a bluff". In September 2017, San Salvador FMLN member Xóchitl Marchelli alleged that Bukele had thrown an apple at her, calling her a "damn traitor" ("maldita traidora") and a "witch" ("bruja"). Bukele did not attend an FMLN ethics tribunal on 7 October 2017, saying that the tribunal was biased in favor of Marchelli. On 10 October 2017, he was expelled from the party after the tribunal determined that he had engaged in "defamatory acts" ("actos difamatorios") against the party, showed "disrespect" ("irrespeto") for women's rights and the party's statutes, and made "disqualifying comments" ("comentarios descalificadores") to party members. Marchelli sued Bukele through the Specialized Investigative Court, but sent a letter to the court in October 2018 saying that she would no longer pursue the matter for health reasons. Despite Marchelli's withdrawal, the FGR proceeded with the case. On 29 March 2019, the Specialized Sentencing Court acquitted Bukele.
Sources: en.wikipedia.org
It separates components in a liquid sample and measures their amounts using a detector. Results can indicate concentration, purity, or identity based on retention time and detector response. The technique works for mixtures that can be dissolved and filtered.
It offers high resolution, reproducibility, and compatibility with many sample types. A single run can separate and quantify multiple analytes. It is common in pharmaceutical, food, environmental, and industrial laboratories.
Samples must be soluble in a suitable mobile phase and free of particles that can block the column. Detector response depends on analyte structure, so some compounds need derivatization or alternative detection. Complex matrices may require extensive sample preparation.
System suitability is a set of checks performed before and during a run to confirm that the instrument, column, and method work as expected. Common checks include resolution, tailing factor, theoretical plates, and relative standard deviation of replicate injections. Failure triggers troubleshooting or method adjustment.