Stationary phase comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2025-08-27. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
Method validation evaluates accuracy, precision, specificity, linearity, range, detection limit, quantitation limit, and robustness. Regulatory guidance for pharmaceuticals, foods, and environmental testing defines expected documentation and acceptance criteria. Verification confirms that a validated method works in a specific laboratory with its own instruments and reagents. Calibration curves use reference standards with known purity and traceability, while measurement uncertainty is estimated from validation data, control charts, and collaborative studies. The scope of validation depends on the method's intended use.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Common for polar and moderately polar analytes |
| Typical column length | 100-250 mm | Shorter columns can reduce run time |
| Particle size | 3-5 micrometers | Smaller particles improve efficiency but raise pressure |
| Flow rate | 0.5-2.0 mL/min | Depends on column dimensions and pressure limits |
| Detection | UV-Vis absorbance | Widely used for compounds with chromophores |
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.
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.
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.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample by passing them through a packed column under pressure. A pump delivers a mobile phase at a controlled flow rate, and an injector introduces the sample into the stream. Differences in how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
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.
Platelets also promote angiogenesis and tissue regeneration to maintain overall vascular integrity by releasing growth factors like vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF). Their multifunctional role displays the challenge of innovating synthetic platelets capable of effectively replicating their physiological functions.
==== Distribution ==== Spironolactone and its metabolite canrenone are highly plasma protein bound, with percentages of 88.0% and 99.2%, respectively. Spironolactone is bound equivalently to albumin and α1-acid glycoprotein, while canrenone is bound only to albumin. Spironolactone and its metabolite 7α-thiospironolactone show very low or negligible affinity for sex hormone-binding globulin (SHBG). In accordance, a study of high-dosage spironolactone treatment found no change in steroid binding capacity related to SHBG or to corticosteroid-binding globulin (CBG), suggesting that spironolactone does not displace steroid hormones from their carrier proteins. This is in contradiction with widespread statements that spironolactone increases free estradiol levels by displacing estradiol from SHBG. Spironolactone appears to cross the blood–brain barrier.
== Structure == ATP consists of three parts: a sugar, an amine base, and a phosphate group. More specifically, ATP consists of an adenine attached by the #9-nitrogen atom to the 1′ carbon atom of a sugar (ribose), which in turn is attached at the 5' carbon atom of the sugar to a triphosphate group. In its many reactions related to metabolism, the adenine and sugar groups remain unchanged, but the triphosphate is converted to di- and monophosphate, giving respectively the derivatives ADP and AMP. The three phosphoryl groups are labeled as alpha (α), beta (β), and, for the terminal phosphate, gamma (γ). In neutral solution, ionized ATP exists mostly as ATP4−, with a small proportion of ATP3−.
Taxodioxylon gysaceum is an extinct species of conifer presently found as fossil wood. Samples of the same wood in various stages of degradation were collected from a forest in Italy, originally existing during the Pliocene period. These samples were milled and filtered into different fractions by coarseness before steam distillation was utilized to extract terpenes. The extraction was then analyzed through GC/MS. The comparative degree of degradation was determined by analysis of holocellulose contents in each sample. Holocellulose refers to the fraction of plant biomass that includes cellulose and hemicellulose but excludes lignin. These carbohydrates are broken down during decomposition, and so their concentrations can be used as a measure of the degree of degradation. A variety of terpenes were detected in the degraded lignite samples, including more than 10% ferruginol, between 5 and 10% podocarpodiol, and less than 5% of sugiol. These compounds were hypothesized to have become more prevalent in the degraded sample due to preferential decomposition of other compounds. The presence of these terpenes in this sample suggest that the organism belongs to the Cupressaceae, Podocarpaceae, or Taxodiaceae families. Given the specific combination of terpenes present, the sample was identified as Taxodioxylon gypsaceum. This combination of terpenes has also been detected in other samples known to be Taxodioxylon gypsaceum, further supporting this identification.
In addition, it extended the mechanistic insight by showing that asprosin bound to Ptprd and inhibited SK3 potassium channels, thereby enhancing AgRP neuron excitability. Altogether, the study reinforced the reproducibility and biological significance of the asprosin-AgRP axis in appetite control. The vertebrate Ptprf study further confirmed this division of function between glucogenic and orexigenic receptors: in zebrafish, asprosin was shown to modulate feeding behavior, manipulations of Ptprf selectively altered glucose metabolism without affecting appetite, and Ptprd paralogs were required for the orexigenic effects of asprosin but not for its glucogenic actions, with Ptprd ligand-binding domains blocking appetite responses to asprosin without affecting hyperglycemia and ptprda/ptprdb knockouts impairing feeding responses while preserving glucogenic responses. PTPRD is highly expressed throughout the brain, with particularly high levels in the cerebellum and cerebellar hemispheres, leading to the discovery of the cerebellum's role in thirst regulation. Researchers demonstrated that asprosin directly activates cerebellar Purkinje neurons to modulate fluid intake in a Ptprd-dependent manner, notably without affecting the well-established role of Purkinje neurons in motor coordination. This finding underscores a remarkable duality in asprosin's function: it regulates both thirst and appetite by acting on the same receptor, PTPRD, while engaging distinct neuronal populations to orchestrate these vital survival behaviors.
Sources: en.wikipedia.org
In April 2008, General Sergio Aponte Polito, the man in charge of the anti-drug campaign in the state of Baja California, made several allegations of corruption against the police forces in the region. Among his claims, Aponte stated that he believed Baja California's anti-kidnapping squad was actually a kidnapping team working in conjunction with organized crime, and that bribed police units were used as bodyguards for drug traffickers. These accusations sent shock waves through the state government. Many of the more than 50 accused officials quit or fled. Four months later, Aponte was relieved of his command. Between 2009 and 2011, Ciudad Juárez, Chihuahua recorded the highest homicide rate in the world, with more than 200 murders per 100,000 inhabitants. Much of the violence was driven by clashes between the Sinaloa Cartel and the Juárez Cartel, and the resulting breakdown of public security produced a climate of pervasive lawlessness. In March 2009, President Calderón called in an additional 5,000 Mexican Army troops to Ciudad Juárez. The U.S. Department of Homeland Security also said that it was considering using state National Guard troops to help the U.S. Border Patrol counter the threat of drug violence in Mexico from spilling over the border into the U.S. The governors of Arizona and Texas encouraged the federal government to use additional National Guard troops from their states to help those already there supporting state law enforcement efforts against drug trafficking.
== Reactivity == Ninhydrin exists in equilibrium with the triketone indane-1,2,3-trione, which reacts readily with nucleophiles (including water). Whereas for most carbonyl compounds, a carbonyl form is more stable than a product of water addition (hydrate), ninhydrin forms a stable hydrate of the central carbon because of the destabilizing effect of the adjacent carbonyl groups. To generate the ninhydrin chromophore [2-(1,3-dioxoindan-2-yl)iminoindane-1,3-dione], the amine must condense to give a Schiff base. The reaction of ninhydrin with secondary amines gives an iminium salt, which is also coloured, generally being yellow–orange.
=== Cultural depictions === Jean-Michel Basquiat depicted two angel dust users in his 1982 painting Dustheads. Tsukasa Hojo's 1985 manga City Hunter features a drug, Angel Dust, presumably a reference to PCP's street name. The related 2023 animated film, City Hunter: Angel Dust, more directly moved the franchise's angel dust into the realm of fantasy, as it is portrayed as a science fiction nanomachine serum developed by a biotech company to create super-soldiers with a tendency to drive them berserk, side-stepping the real-life PCP.
== Research == Mycophenolate mofetil is beginning to be used in the management of auto-immune disorders such as idiopathic thrombocytopenic purpura (ITP), systemic lupus erythematosus (SLE), scleroderma (systemic sclerosis or SSc), and pemphigus vulgaris (PV) with success for some patients. It is also being used as a long-term therapy for maintaining remission of granulomatosis with polyangiitis, though thus far, studies have found it inferior to azathioprine. A combination of mycophenolate and ribavirin has been found to stop infection by and replication of dengue virus in vitro. It has also shown promising antiviral activity against MERS, especially in combination with interferon. Preliminary data suggest that mycophenolate mofetil might have benefits in people with multiple sclerosis. However the evidence is insufficient to determine the effects as an add‐on therapy for interferon beta-1a in people with RRMS.
Sources: en.wikipedia.org
=== Extraction === The recognised metalloids can be obtained by chemical reduction of either their oxides or their sulfides. Simpler or more complex extraction methods may be employed depending on the starting form and economic factors. Boron is routinely obtained by reducing the trioxide with magnesium: B2O3 + 3 Mg → 2 B + 3MgO; after secondary processing the resulting brown powder has a purity of up to 97%. Boron of higher purity (> 99%) is prepared by heating volatile boron compounds, such as BCl3 or BBr3, either in a hydrogen atmosphere (2 BX3 + 3 H2 → 2 B + 6 HX) or to the point of thermal decomposition. Silicon and germanium are obtained from their oxides by heating the oxide with carbon or hydrogen: SiO2 + C → Si + CO2; GeO2 + 2 H2 → Ge + 2 H2O. Arsenic is isolated from its pyrite (FeAsS) or arsenical pyrite (FeAs2) by heating; alternatively, it can be obtained from its oxide by reduction with carbon: 2 As2O3 + 3 C → 2 As + 3 CO2. Antimony is derived from its sulfide by reduction with iron: Sb2S3 → 2 Sb + 3 FeS. Tellurium is prepared from its oxide by dissolving it in aqueous NaOH, yielding tellurite, then by electrolytic reduction: TeO2 + 2 NaOH → Na2TeO3 + H2O; Na2TeO3 + H2O → Te + 2 NaOH + O2. Another option is reduction of the oxide by roasting with carbon: TeO2 + C → Te + CO2. Production methods for the elements less frequently recognised as metalloids involve natural processing, electrolytic or chemical reduction, or irradiation. Carbon (as graphite) occurs naturally and is extracted by crushing the parent rock and floating the lighter graphite to the surface.
Australian Football Hall of Fame (inducted 2011) Essendon Football Club Team of the Century (half-forward flank) Champions of Essendon: no. 3 Essendon captain: 1998–2005 Norm Smith Medal: 2000 Brownlow Medal: 1996 Australian Football Media Association Player of the Year: 1996 5× All-Australian team: 1995, 1996, 2000, 2001, 2003 5× Crichton Medal: 1994, 1995, 1996, 2003, 2007 2× Essendon leading goalkicker: 1995, 1996 Jim Stynes Medal: 2000 2× Australia representative honours in international rules football: 2000 (c), 2004 3× Anzac Medal: 2000, 2003, 2004 Yiooken Award: 2007 AFL Rising Star nominee: 1993
==== Binding site identification ==== Binding site identification is the first step in structure based design. If the structure of the target or a sufficiently similar homolog is determined in the presence of a bound ligand, then the ligand should be observable in the structure in which case location of the binding site is trivial. However, there may be unoccupied allosteric binding sites that may be of interest. Furthermore, it may be that only apoprotein (protein without ligand) structures are available and the reliable identification of unoccupied sites that have the potential to bind ligands with high affinity is non-trivial. In brief, binding site identification usually relies on identification of concave surfaces on the protein that can accommodate drug sized molecules that also possess appropriate "hot spots" (hydrophobic surfaces, hydrogen bonding sites, etc.) that drive ligand binding.
Sources: en.wikipedia.org
It measures the amounts and identities of compounds in liquid samples by separation and detection. Depending on the detector and reference standards, results can be qualitative or quantitative. The technique is used in fields such as pharmaceutical analysis, food safety, and environmental monitoring.
Performance checks confirm that the chromatographic system works within preset limits before results are accepted. They examine factors such as peak resolution, tailing, and repeatability. If criteria fail, the run may need correction or repetition.
Retention time alone is not definitive proof because other compounds can elute at similar times. Confirmation usually uses a second method, a different column, or a detector such as mass spectrometry. Authentic standards strengthen identification.
System suitability is typically performed before each batch or according to the validated method and laboratory procedure. Some long runs include periodic checks during analysis. The required frequency depends on regulatory expectations and method performance.