Everything below concerns stationary phase. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2025-12-19. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Abbreviation | HPLC | Also called high-performance liquid chromatography |
| Separation mechanism | Differential partitioning | Compounds distribute between mobile and stationary phases |
| Typical column chemistry | C18 (octadecylsilane) | Used in reversed-phase separations |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is common for trace and confirmatory work |
| Typical particle size | 1.8–5 µm | Smaller particles require higher pressure and can improve speed |
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.
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.
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.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
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.
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.
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 right side of a positive-sensed AAV genome encodes overlapping sequences of three capsid proteins, VP1, VP2 and VP3, and two accessory proteins, MAAP & AAP, which start from one promoter, designated p40. The molecular weights of these proteins are 87, 72 and 62 kiloDaltons, respectively. The AAV capsid is composed of a mixture of VP1, VP2, and VP3 totaling 60 monomers arranged in icosahedral symmetry in a ratio of 1:1:10, with an empty mass of approximately 3.8 MDa. The crystal structure of the VP3 protein was determined by Xie, Bue, et al.
Feoktist I. Bogoyavlenskiy (1933–1935) Vasiliy V. Evlampiev (1935–1939) Faizi F. Faizyllin (1958–1960) Boris A. Arbuzov (1941–1950) Arkadiy N. Pudovik (1950–1958) Faizi F. Faizyllin (1958–1960) Vera F. Toropova (1960–1965) Alexander I. Kostromin (1965–1968) Alexander I. Konovalov (1968–1972) Irina V. Konovalova (1972–1987) Galina A. Chmutova (1987–1992) Nikolai A. Ulakhovich (1992–2000) Vladimir I. Galkin (since 2000– until present) Department of Analytical Chemistry Department of High Molecular and Organoelement Compounds Department of Inorganic Chemistry Department of Organic Chemistry Department of Physical Chemistry Department of Chemical Education Department of Environmental Chemistry Department of Applied Chemistry Department of Stereochemistry Division for Analytical Chemistry Division for Inorganic Chemistry and Coordination chemistry Division for Organic Chemistry Division for Physical Chemistry Division for Organoelement Compounds Division for Stereochemistry Division for Applied Chemistry Division for Environmental Chemistry
In order for a protonated acid to lose a proton, the pH of the system must rise above the pKa of the acid. The decreased concentration of H+ in that basic solution shifts the equilibrium towards the conjugate base form (the deprotonated form of the acid). In lower-pH (more acidic) solutions, there is a high enough H+ concentration in the solution to cause the acid to remain in its protonated form. Solutions of weak acids and salts of their conjugate bases form buffer solutions. To determine the concentration of an acid in an aqueous solution, an acid–base titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of base added. The titration curve of an acid titrated by a base has two axes, with the base volume on the x-axis and the solution's pH value on the y-axis. The pH of the solution always goes up as the base is added to the solution.
Caspases play the central role in the transduction of ER apoptotic signals. Caspases are proteins that are highly conserved, cysteine-dependent aspartate-specific proteases. There are two types of caspases: initiator caspases (caspases 2, 8, 9, 10, 11, and 12) and effector caspases (caspases 3, 6, and 7). The activation of initiator caspases requires binding to specific oligomeric activator protein. These active initiator caspases activate the effector caspases through proteolytic cleavage. The active effector caspases then proteolytically degrade a host of intracellular proteins to carry out the cell death program. There also exists a caspase-independent apoptotic pathway that is mediated by AIF (apoptosis-inducing factor).
Sources: en.wikipedia.org
An interesting feature of these phases is that both polar and nonpolar compounds can be retained over some range of mobile phase composition (organic/aqueous). The retention mechanism of polar compounds has recently been shown to be the result of the formation of a hydroxide layer on the surface of the silica hydride.[3] Thus positively charged analytes are attracted to the negatively charged surface and other polar analytes are likely to be retained through displacement of hydroxide or other charged species on the surface. This property distinguishes it from a pure HILIC (hydrophilic interaction chromatography) columns where separation by polar differences is obtained through partitioning into a water-rich layer on the surface, or a pure RP stationary phase on which separation by nonpolar differences in solutes is obtained with very limited secondary mechanisms operating. Another important feature of the hydride-based phases is that for many analyses it is usually not necessary to use a high pH mobile phase to analyze polar compounds such as bases. The aqueous component of the mobile phase usually contains from 0.1 to 0.5% formic or acetic acid, which is compatible with detector techniques that include mass spectral analysis.
A/B testing (also known as bucket testing, split-run testing or split testing) is a user-experience research method. A/B tests consist of a randomized experiment that usually involves two variants (A and B), although the concept can be also extended to multiple variants of the same variable. It includes application of statistical hypothesis testing or "two-sample hypothesis testing" as used in the field of statistics. A/B testing is employed to compare multiple versions of a single variable, for example by testing a subject's response to variant A against variant B, and to determine which of the variants is more effective. Multivariate testing or multinomial testing is similar to A/B testing but may test more than two versions at the same time or use more controls. Simple A/B tests are not valid for observational, quasi-experimental or other non-experimental situations—commonplace with survey data, offline data, and other, more complex phenomena.
Central obesity can be a feature of lipodystrophies, a group of diseases that is either inherited, or due to secondary causes (often protease inhibitors, a group of medications against AIDS). Central obesity is a symptom of Cushing's syndrome and is also common in patients with polycystic ovary syndrome (PCOS). Central obesity is associated with glucose intolerance and dyslipidemia. Once dyslipidemia becomes a severe problem, an individual's abdominal cavity would generate elevated free fatty acid flux to the liver. The effect of abdominal adiposity occurs not just in those who are obese, but also affects people who are non-obese and it also contributes to insulin sensitivity. Ghroubi et al. (2007) examined whether abdominal circumference is a more reliable indicator than BMI or the presence of knee osteoarthritis in obese patients. They found that it actually appears to be a factor linked with the presence of knee pain as well as osteoarthritis in obese study subjects. Ghroubi et al. (2007) concluded that a high abdominal circumference is associated with great functional repercussion. Research published in The Lancet (2023) found that high levels of visceral fat were related to poorer cognitive performance. The findings suggest that maintaining a healthy weight and metabolic health may be important for preserving cognitive function.
BDNF binds at least two receptors on the surface of cells that are capable of responding to this growth factor, TrkB (pronounced "Track B") and the LNGFR (for low-affinity nerve growth factor receptor, also known as p75). It may also modulate the activity of various neurotransmitter receptors, including the Alpha-7 nicotinic receptor. BDNF has also been shown to interact with the reelin signaling chain. The expression of reelin by Cajal–Retzius cells goes down during development under the influence of BDNF. The latter also decreases reelin expression in neuronal culture. The TrkB receptor is encoded by the NTRK2 gene and is member of a receptor family of tyrosine kinases that includes TrkA and TrkC. TrkB autophosphorylation is dependent upon its ligand-specific association with BDNF, a widely expressed activity-dependent neurotrophic factor that regulates plasticity and is dysregulated following hypoxic injury. The activation of the BDNF-TrkB pathway is important in the development of short-term memory and the growth of neurons.
K a = [ H + ] [ A − ] [ HA ] {\displaystyle K_{a}={\frac {{\ce {[H+] [A^{-}]}}}{{\ce {[HA]}}}}} The stronger of two acids will have a higher Ka than the weaker acid; the ratio of hydrogen cations to acid will be higher for the stronger acid as the stronger acid has a greater tendency to lose its proton. Because the range of possible values for Ka spans many orders of magnitude, a more manageable constant, pKa is more frequently used, where pKa = −log10 Ka. Stronger acids have a smaller pKa than weaker acids. Experimentally determined pKa at 25 °C in aqueous solution are often quoted in textbooks and reference material. Arrhenius acids are named according to their anions. In the classical naming system, the ionic suffix is dropped and replaced with a new suffix, according to the table following. The prefix "hydro-" is used when the acid is made up of just hydrogen and one other element. For example, HCl has chloride as its anion, so the hydro- prefix is used, and the -ide suffix makes the name take the form hydrochloric acid. Classical naming system:
Sources: en.wikipedia.org
ADPRase is a dimer of two identical monomers, each of which contain 209 amino acids. The two monomers are folded into two distinct structural domains and with two equivalent catalytic sites. The C-terminal domain consists of the Nudix sequence mentioned above and the N-terminal domain is primarily involved in dimer stabilization. As noted earlier, the Nudix fold is the catalytic part of the enzyme, but both domains are involved in the active site and they both help with the attachment and coordination of H2O, Mg2+, and the ADP-ribose substrate.
The first class of adenylyl cyclases occur in many bacteria including E. coli (as CyaA P00936 [unrelated to the Class II enzyme]). This was the first class of AC to be characterized. It was observed that E. coli deprived of glucose produce cAMP that serves as an internal signal to activate expression of genes for importing and metabolizing other sugars. cAMP exerts this effect by binding the transcription factor CRP, also known as CAP. Class I AC's are large cytosolic enzymes (~100 kDa) with a large regulatory domain (~50 kDa) that indirectly senses glucose levels. As of 2012, no crystal structure is available for class I AC. Some indirect structural information is available for this class. It is known that the N-terminal half is the catalytic portion, and that it requires two Mg2+ ions. S103, S113, D114, D116 and W118 are the five absolutely essential residues. The class I catalytic domain (Pfam PF12633) belongs to the same superfamily (Pfam CL0260) as the palm domain of DNA polymerase beta (Pfam PF18765). Aligning its sequence onto the structure onto a related archaeal CCA tRNA nucleotidyltransferase (PDB: 1R89) allows for assignment of the residues to specific functions: γ-phosphate binding, structural stabilization, DxD motif for metal ion binding, and finally ribose binding.
Bio-Synthesis, Inc. (BSI) is a biotechnology company headquartered in Lewisville, Texas. It is a provider of custom and catalog peptides, custom oligos, antibodies, organic synthesis, and analytical services. Biomedical researchers worldwide in universities, biotech companies, private clinics, and government agencies use products from Bio-Synthesis, Inc. in studies ranging from PCR diagnostics to cancer research and the Human Genome Project.
The intense research for development of efficient chiral selectors has resulted in the synthesis of over 1400 CSPs and over 200 CSPs have been commercialized and available in the market. The most commonly employed chiral selectors are categorized and presented in the table. It is surprising to note that In 1980, there was no single chiral stationary phase available in the market for performing chiral chromatography. However, In late 1980s the subject of enantioselective chromatography attracted growing interest, particularly under the drive of the institution of Okamoto in Japan, the teams of Pirkle, and Armstrong in the US, Schurig and König in Germany, Lindner in Austria, and Francotte in Switzerland . The Polysaccharides, amylose and cellulose, form the most abundant chiral polymers on earth. These naturally occurring polysaccharides form basis for an important class of chiral selectors.
Originally, seven such proteins were discovered. Of these, six (BMP2 through BMP7) belong to the Transforming growth factor beta superfamily of proteins. BMP1 is a metalloprotease. Since then, thirteen more BMPs, all of which are in the TGF-beta family, have been discovered, bringing the total to twenty. The current nomenclature only recognizes 13, as many others are put under the growth differentiation factor naming instead.
Sources: en.wikipedia.org
It measures the presence and amount of one or more compounds in a liquid sample. Separation occurs in a column, and detection produces a signal proportional to concentration. Identification usually requires comparison with a known reference standard under the same conditions.
In most cases the sample is consumed or altered during analysis, though some detectors are non-destructive. Fractions can be collected after separation for further study. Repeated testing therefore requires additional sample.
Run times range from under a minute for fast methods to over an hour for complex separations. Sample preparation, equilibration, and data review add time. Throughput depends on instrument configuration and method requirements.
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.