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 2026-05-12 and is reviewed periodically as new material appears.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it 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 interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
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.
Separation modes differ by the chemistry of the stationary phase and the composition of the mobile phase. Reversed-phase testing uses a nonpolar column and polar solvents, making it common for pharmaceutical, environmental, and food analytes. Normal-phase testing uses a polar column and nonpolar solvents for compounds that are poorly retained in reversed-phase systems. Ion-exchange and ion-pair methods separate charged species, while size-exclusion methods sort molecules by hydrodynamic volume. Gradient elution changes solvent strength over time to resolve complex mixtures, and isocratic elution holds solvent composition constant for simpler assays.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Most common for neutral and moderately polar analytes |
| Column particle size | 3–5 µm | Smaller particles improve resolution but raise backpressure |
| Mobile phase pH range | 2–8 | Silica-based columns may degrade outside this range |
| Typical flow rate | 1.0–2.0 mL/min | For analytical columns with 4.6 mm internal diameter |
| Common synonyms | HPLC, LC, high-pressure liquid chromatography | High-performance liquid chromatography is the standard expansion |
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.
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.
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.
HPLC testing is an analytical technique used to separate, identify, and quantify components in a liquid sample. It relies on a pressurized mobile phase that carries the sample through a column packed with stationary phase. Different compounds travel at different rates because of interactions with the stationary and mobile phases. The resulting signal versus time is a chromatogram. Peak position indicates identity under specified conditions, while peak area or height relates to amount.
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
Biopharmaceuticals may be produced from microbial cells (e.g., recombinant E. coli or yeast cultures), mammalian cell lines (see Cell culture) and plant cell cultures (see Plant tissue culture) and moss plants in bioreactors of various configurations, including photo-bioreactors. Important issues of concern are cost of production (low-volume, high-purity products are desirable) and microbial contamination (by bacteria, viruses, mycoplasma). Alternative platforms of production which are being tested include whole plants (plant-made pharmaceuticals).
While Aβ has been implicated in cancer development, prompting studies on a variety of cancers to elucidate the nature of its possible effects, results are largely inconclusive. Aβ levels have been assessed in relation to a number of cancers, including esophageal, colorectal, lung, and hepatic, in response to observed reductions in risk for developing Alzheimer's disease in survivors of these cancers. All cancers were shown to be associated positively with increased Aβ levels, particularly hepatic cancers. This direction of association however has not yet been established. Studies focusing on human breast cancer cell lines have further demonstrated that these cancerous cells display an increased level of expression of amyloid precursor protein. Adults with Down syndrome had accumulation of amyloid in association with evidence of Alzheimer's disease, including declines in cognitive functioning, memory, fine motor movements, executive functioning, and visuospatial skills.
The enzyme converts adenosine to adenosine monophosphate by transferring a phosphate group. Adenosine diphosphate is produced as a byproduct: The AdK gene/protein is mainly found in eukaryotic organisms and its primary sequence shows a high degree of conservation (>55% aa similarity). However, AdK sequences exhibit low (~ 20-25%), but significant similarity to other PfkB family of proteins such as RK and phosphofructokinases, which are also found in prokaryotic organisms. Although a protein exhibiting AdK activity has been reported in Mycobacterium tuberculosis, sequence and biochemical characteristics of this enzyme reveal it to be an atypical enzyme that is more closely related to ribokinase and fructokinase (35%) than to other ADKs (less than 24%).
The main building of the Institute is located at the intersection of Kremlyovskaya and Lobachevskaya streets. This four-story building built in 1953 in the style of Soviet neoclassicism under the guidance of architect A.G. Bikchentaev. The building of the museum of Kazan chemical school is located in the campus of the main university building, built in the 1830s in a classical style under the guidance of architect M.P. Corinfskiy. In 2015 construction of a large laboratory building in the campus of Alexander Butlerov Institute of Chemistry was finished. The 7-storey building housed classrooms and laboratories of departments of Alexander Butlerov Institute of Chemistry, Institute of Geology and Petroleum Technologies, Institute of Physics. The building was constructed with the support of the President of Tatarstan R.N. Minnikhanov and PSC "TAIF".
Weapon No. 2, which underwent something other than normal release from the aircraft, evidenced by the fact that the parachute did not deploy, also had its arming rods extracted, and those components which were given the opportunity to act, did act in the manner expected. Full operation of this weapon was prevented by several things: Impact occurred so soon after separation of the Bisch rods that the timers were not given an opportunity to run down. The Arm/Safe Switch was in the "Safe" condition as the weapon left the aircraft. Another analysis by Sandia engineers in 1961 concluded that while in both weapons the MC-772 Arm/Safe Switch operated "as it was designed to do," the lanyard-controlled safing-pins "cannot be relied upon to prevent initiation of the fuzing sequence" in this kind of accident, and recommended implementing a modification to the weapons "as rapidly as possible" that would prevent the fuze power supply from activating except when live release was intended. A 1969 analysis by Sandia supervisor Parker F. Jones concluded that the Goldsboro accident illustrated that "the Mk 39 Mod 2 bomb did not possess adequate safety for the airborne alert role in the B-52."
Sources: en.wikipedia.org
Once the substrate is bound and oriented to the active site, catalysis can begin. The residues of the catalytic site are typically very close to the binding site, and some residues can have dual-roles in both binding and catalysis. Catalytic residues of the site interact with the substrate to lower the activation energy of a reaction and thereby make it proceed faster. They do this by a number of different mechanisms including the approximation of the reactants, nucleophilic/electrophilic catalysis and acid/base catalysis. These mechanisms will be explained below.
Therefore, Akt promotes G1 phase progression in a positive feedback loop. Akt promotes cyclin D1 translation via indirect activation of mTOR. mTOR increases translation of cyclin D1 by activating ribosomal protein S6K, and inhibiting eukaryotic translation initiation factor 4E-binding protein (4E-BP), thus increasing eIF4e activity. Akt both indirectly and directly regulates cyclin-dependent kinase (CDK) inhibitors p21Cip1 and p27Kip1, allowing cell cycle progression. Akt phosphorylates p27Kip1 at Thr157, preventing its nuclear import. In addition, Akt phosphorylates Thr145 and Ser146 of p21Cip1, preventing PCNA binding and decreasing stability. Akt phosphorylation of Foxo transcription factors also affects the cell cycle, as inhibitory phosphorylation of FoxO4 (also named AFX) prevents p27 gene expression. Akt phosphorylates many proteins involved in polymerisation and stabilisation of the actin cytoskeleton. In normal cells, this can either increase the stability of cytoskeleton components or promote migration via remodelling. Examples are listed below:
Developing standards-based messaging, to allow for automated data exchange Creating an exchange network, to ensure specific laboratories receive the information most pertinent to their work Improving reporting capabilities Selection and implementation of the best information management system for the laboratory's needs Strengthening the information network by sharing technical resources across public health laboratories One effort by the Informatics program is PHLIP, the Public Health Laboratory Interoperability Project. PHLIP aims to establish reliable laboratory data exchange between state public health laboratories and the CDC by fostering collaboration in IT and laboratory science.
Glycogenolysis and gluconeogenesis in liver. Glycogenolysis and lactate release in skeletal muscle. Contract sphincters of Gastrointestinal tract. Thickened secretions from salivary glands. Insulin and glucagon secretion from pancreas. Inhibit histamine-release from mast cells. Increase protein content of secretions from lacrimal glands. Receptor also present in cerebellum. Bronchiole dilation (targeted while treating asthma attacks) Involved in brain - immune - communication Short-acting β2 agonists (SABA) bitolterol fenoterol hexoprenaline isoprenaline (INN) or isoproterenol (USAN) levosalbutamol (INN) or levalbuterol (USAN) orciprenaline (INN) or metaproterenol (USAN) pirbuterol procaterol salbutamol (INN) or albuterol (USAN) terbutaline Long-acting β2 agonists (LABA) arformoterol (some consider it to be an ultra-LABA) bambuterol clenbuterol formoterol salmeterol Ultra-long-acting β2 agonists (ultra-LABA) carmoterol indacaterol milveterol (GSK 159797) olodaterol vilanterol (GSK 642444)
Sources: en.wikipedia.org
Lab Matters: Each issue of APHL's quarterly magazine, Lab Matters, considers a pressing health issue of importance to public health laboratories. Bridges: Connecting the nation's environmental laboratories, Bridges is APHL's semi-annual newsletter for environmental health professionals. Social Media: APHL is active on Twitter, Facebook and LinkedIn, and has video channels on both YouTube and Vimeo. Blog: APHL's Public Health LabLog features recent and interesting stories about the work of APHL and public health laboratories. 1899: American Public Health Association formed the Committee of Laboratories 1921: Southern Public Health Laboratory Association (SPHLA) formed 1927: SPHLA became State Laboratory Directors Conference and opened membership to other states 1939: SPHLA changed its name to Conference of State and Provincial Laboratory Directors 1951: Association of State and Territorial Public Health Laboratory Directors founded 1998: Renamed the Association of Public Health Laboratories (APHL) and became a more inclusive organization with new membership categories
The United States Food and Drug Administration and the European Medicines Agency have approved weight loss medications for adults with either a body-mass index (BMI) of at least 30, or a body-mass index of at least 27 with at least one weight-related comorbidity. This patient population is considered to have sufficiently high baseline health risks to justify the use of anti-obesity medication. The American Academy of Pediatrics had not previously supported the use of weight loss medication in adolescents but issued new guidelines in 2023, which recommend considering the use of weight loss medication in some overweight children aged 12 or older. The European Medicines Agency has approved semaglutide for children aged 12 or older who have a BMI in the 95 percentile for their age and a weight of at least 60 kilograms (130 lb). However, GLP-1 agonists may not be cost effective in this population.
detailed family history conducting a detailed physical examination to document morphological features testing for genetic defect in FGDY1 x-rays can identify skeletal abnormalities echo cardiogram can screen for heart abnormalities CT scan of the brain for cystic development X-ray of the teeth Ultrasound of abdomen to identify undescended testis Similar to all genetic diseases Aarskog–Scott syndrome cannot be cured, although numerous treatments exist to increase the quality of life. Surgery may be required to correct some of the anomalies, and orthodontic treatment may be used to correct some of the facial abnormalities. Trials of growth hormone have been effective to treat short stature in this disorder. Some people may have some mental slowness, but children with this condition often have good social skills. Some males may have problems with fertility. The syndrome is named for Dagfinn Aarskog, a Norwegian pediatrician and human geneticist who first described it in 1970, and for Charles I. Scott, Jr., an American medical geneticist who independently described the syndrome in 1971.
Although an estimated 43,000 species of bacteria have been named, most of them have never been studied. In fact, just 10 bacterial species account for half of all publications, whereas nearly 75% of all named bacteria have no academic research devoted to them. The best-studied species, Escherichia coli, has more than 300,000 studies published on it, but many of these papers likely use it only as a cloning vehicle to study other species, without providing any insight into its own biology. 90% of scientific studies on bacteria focus on less than 1% of species, mostly pathogenic bacteria relevant to human health. While E. coli is probably the best-studied bacterium, a quarter of its 4000 genes are poorly studied or remain uncharacterized. Some bacteria with minimal genomes (< 600 genes, e.g. Mycoplasma) usually have a large fraction of their genes functionally characterized, given that most of them are essential and conserved in many other species.
Aerospace 9100 (AS9100) is an international standard for aerospace management systems that is a widely adopted and standardized quality management system for the aerospace sector. It was developed in March 1999 by Society of Automotive Engineers. The goal of the standard is to provide for continual improvement, emphasizing defect prevention and the reduction of variation and waste in the aerospace industry supply chain and assembly process. The standard was designed to fit into an integrated management system. AS9100 replaces the earlier AS9000 and fully incorporates the entirety of the current version of ISO 9001, while adding requirements relating to quality and safety. Major aerospace manufacturers and suppliers worldwide require compliance with AS9100 as a condition of doing business with them.
Sources: en.wikipedia.org
HPLC testing separates and quantifies components in a liquid sample. It is used to check identity, purity, concentration, or stability. The technique works best for compounds that dissolve and are not easily vaporized.
The pump maintains a steady flow rate and pressure, which keeps retention times reproducible. Pulsation or flow errors can shift peaks and distort quantitation. Modern pumps use feedback control to reduce these variations.
HPLC alone usually separates compounds but does not always identify them. Retention time matching with a known standard provides tentative identification. Coupling HPLC to mass spectrometry adds mass information that supports structural identification.
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.