reversed-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 2026-08-01 and is reviewed periodically as new material appears.
Quality control laboratories use HPLC to check identity, purity, concentration, and stability of raw materials and finished products. A validated method specifies the column, mobile phase, flow rate, detection wavelength, injection volume, and run time. Samples are prepared and compared against reference standards of known concentration. The resulting chromatogram provides quantitative data, such as assay values and impurity levels. This approach is common in pharmaceutical, food, environmental, and industrial testing where consistent measurements are required.
Method validation demonstrates that an analytical procedure is suitable for its intended purpose. Typical validation characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulatory guidance from bodies such as the International Council for Harmonisation and the United States Pharmacopeia outlines expectations, though specific criteria depend on the product and method. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, column efficiency, and injection repeatability. Failure of these checks can invalidate a batch of measurements.
Practical HPLC testing depends on careful sample preparation and instrument maintenance. Samples may require filtration, dilution, pH adjustment, or extraction to avoid column damage and matrix interference. Mobile phases are degassed and filtered, and columns are equilibrated before injection. Common problems include peak tailing, baseline drift, ghost peaks, carryover, and co-elution of analytes. Documentation of instrument logs, calibration records, and electronic audit trails supports data integrity and traceability. Ongoing training and routine maintenance help reduce variability between analysts and laboratories.
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.
| Parameter | Typical acceptance criterion | Notes |
|---|---|---|
| Resolution | ≥ 1.5 | Baseline separation of adjacent peaks |
| Tailing factor | ≤ 2.0 | Peak symmetry measure |
| Theoretical plates | > 2000 | Column efficiency indicator |
| Injection repeatability | ≤ 2% RSD | Relative standard deviation for replicate injections |
| Linearity | r² ≥ 0.995 | Calibration curve over the working range |
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.
Laboratories apply HPLC testing across pharmaceutical, food, environmental, and industrial chemistry. The method can measure active ingredients, impurities, additives, preservatives, and degradation products. Sample preparation often includes dilution, filtration, and sometimes extraction or derivatization. The choice of column, mobile phase, pH, temperature, and detector depends on the analytes and matrix. Results are compared with reference standards to assign identity and concentration. Method suitability is judged by resolution, precision, and accuracy.
Separation in HPLC depends on the chemistry of the stationary phase, the composition of the mobile phase, and the physical properties of the column. Reverse-phase separations use a nonpolar stationary phase and a polar mobile phase, and they are common for many organic compounds. Ion-exchange, size-exclusion, and normal-phase modes serve other classes of analytes. Gradient elution changes solvent strength over time, while isocratic elution holds it constant. Flow rate, temperature, particle size, and column length all influence peak shape and resolution. Detection may use ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry, depending on the analyte and the required sensitivity.
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.
Lung disease: Lung cancer Interstitial lung disease most commonly idiopathic pulmonary fibrosis Complicated tuberculosis Suppurative lung disease: lung abscess, empyema, bronchiectasis, cystic fibrosis Mesothelioma of the pleura Sarcoidosis Heart disease: Any disease featuring chronic hypoxia Cyanotic heart defect (most common cardiac cause) Infective endocarditis Atrial myxoma (benign tumor) Arteriovenous fistula or malformation Gastrointestinal and hepatobiliary: Malabsorption Crohn's disease and ulcerative colitis Cirrhosis, especially in primary biliary cholangitis Hepatopulmonary syndrome, a complication of cirrhosis Others: Graves' disease (autoimmune hyperthyroidism) – in this case, it is known as thyroid acropachy Familial and hereditary clubbing and "pseudoclubbing" (people of African descent often have what appears to be clubbing) Vascular anomalies of the affected arm such as an axillary artery aneurysm (in unilateral clubbing) Primary hypertrophic osteoarthropathy Nail clubbing is not specific to chronic obstructive pulmonary disease (COPD). Therefore, in patients with COPD and significant degrees of clubbing, a search for signs of bronchogenic carcinoma (or other causes of clubbing) might still be indicated.
Without the fully functional sar1B protein, the COPll coatomer proteins engulf pre-chylomicrons exiting the ER but are unable to disassemble upon arrival at the cis-Golgi, preventing membrane fusion with this organelle.
=== Hu-SRC-scid model === The humanized severe combined immunodeficiency (SCID) mouse model, also known as the hu-SRC-scid model, has been extensively utilized in various research areas, including immunology, infectious diseases, cancer, and drug development. This model has been instrumental in studying the human immune response to xenogeneic and allogeneic decellularized biomaterials, providing valuable insights into the biocompatibility and gene expression regulation of these materials. Hu-SRC-scid mice are developed by engrafting CD34+ human hematopoietic stem cells into immunodeficient mice. The cells are obtained from human fetal liver, bone marrow or from blood derived from the umbilical cord, and engrafted via intravenous injection. The advantages of this model are that it offers multilineage development of hematopoietic cells, generation of a naïve immune system, and if engraftment is carried out by intrahepatic injection of newborn mice within 72 hours of birth, it can lead to enhanced human cell reconstitution. Nevertheless, limitations associated with the model are that it takes a minimum of 10 weeks for cell differentiation to occur, it harbors low levels of human RBCs, polymorphonuclear leukocytes, and megakaryocytes.
Within any crystal, there will usually be some defects. To maintain electroneutrality of the crystals, defects that involve loss of a cation will be associated with loss of an anion, i.e. these defects come in pairs. Frenkel defects consist of a cation vacancy paired with a cation interstitial and can be generated anywhere in the bulk of the crystal, occurring most commonly in compounds with a low coordination number and cations that are much smaller than the anions. Schottky defects consist of one vacancy of each type, and are generated at the surfaces of a crystal, occurring most commonly in compounds with a high coordination number and when the anions and cations are of similar size. If the cations have multiple possible oxidation states, then it is possible for cation vacancies to compensate for electron deficiencies on cation sites with higher oxidation numbers, resulting in a non-stoichiometric compound. Another non-stoichiometric possibility is the formation of an F-center, a free electron occupying an anion vacancy. When the compound has three or more ionic components, even more defect types are possible. All of these point defects can be generated via thermal vibrations and have an equilibrium concentration. Because they are energetically costly but entropically beneficial, they occur in greater concentration at higher temperatures. Once generated, these pairs of defects can diffuse mostly independently of one another, by hopping between lattice sites.
Sources: en.wikipedia.org
The use of bioorthogonal chemistry typically proceeds in two steps. First, a cellular substrate is modified with a bioorthogonal functional group (chemical reporter) and introduced to the cell; substrates include metabolites, enzyme inhibitors, etc. The chemical reporter must not alter the structure of the substrate dramatically to avoid affecting its bioactivity. Secondly, a probe containing the complementary functional group is introduced to react and label the substrate. Although effective bioorthogonal reactions such as copper-free click chemistry have been developed, development of new reactions continues to generate orthogonal methods for labeling to allow multiple methods of labeling to be used in the same biosystems. Carolyn R. Bertozzi was awarded the Nobel Prize in Chemistry in 2022 for her development of click chemistry and bioorthogonal chemistry.
Kiwis and shorebirds with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches. Divers, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion, while aerial predators such as sulids, kingfishers and terns plunge dive after their prey. Flamingos, three species of prion, and some ducks are filter feeders. Geese and dabbling ducks are primarily grazers. Some species, including frigatebirds, gulls, and skuas, engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of great frigatebirds stealing from masked boobies estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%. Other birds are scavengers; some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists.
== Gene structure and evolution == The CSP structure is highly flexible. CSPs are characterized by RNA editing and/or post-translational modifications as discovered in the silkworm moth, B. mori [9-14]. The addition of glycine near cysteine at specific location, amino acid inversion and motif insertion in protein sequence strongly argues for the existence of recoding at the level of protein synthesis in the CSP family [9-14]. In addition, they are capable of breathing or specific conformational changes upon ligand binding, which may represent another key feature of the ancestral primitive multifunctional soluble binding protein [15]. The number of CSP genes is usually very low in insects as found in Drosophila flies, Anopheles mosquitoes, Pediculus lice, honeybees and jewel wasps (4-8) [4, 24, 40-41]. A significantly higher number of CSP genes exist in butterfly, moth and beetle genomes (nb CSPs=19-20) [32, 42-43]. Culex mosquito species have between 27 and 83 CSP genes [44]. More than hundreds of protein variants can be produced from CSP genes through or mediated via post-translational modifications and/or RNA-peptide editing as in the case of Dscam and cochlear sensory genes [9-14]. CSP genes evolved via duplication, intron loss and gain, and retrotransposition events [4, 14, 32, 40-41, 45]. A single unified hypothesis of RNA editing and retrotransposition-driven evolution of CSPs, i.e. initial production of new CSP protein motifs via DNA and RNA -dependent RNA polymerization before retro- transposition of edited CSP-RNA variants, has been proposed in moths [11].
terpene A class of naturally occurring unsaturated hydrocarbons with carbon skeletons derived from one or more units of isoprene (C5H8). Terpenes are often subclassified according to the total number of carbon atoms they contain, e.g. the C5 hemiterpenes, C10 monoterpenes, C20 diterpenes, etc.
In two tandem Letters to the Editor (1936), Wrinch and Frank addressed the question of whether the cyclol form of the peptide group was indeed more stable than the amide form. A relatively simple calculation showed that the cyclol form is significantly less stable than the amide form. Therefore, the cyclol model would have to be abandoned unless a compensating source of energy could be identified. Initially, Frank proposed that the cyclol form might be stabilized by better interactions with the surrounding solvent; later, Wrinch and Irving Langmuir hypothesized that hydrophobic association of nonpolar sidechains provides stabilizing energy to overcome the energetic cost of the cyclol reactions. The lability of the cyclol bond was seen as an advantage of the model, since it provided a natural explanation for the properties of denaturation; reversion of cyclol bonds to their more stable amide form would open up the structure and allows those bonds to be attacked by proteases, consistent with experiment. Early studies showed that proteins denatured by pressure are often in a different state than the same proteins denatured by high temperature, which was interpreted as possibly supporting the cyclol model of denaturation. The Langmuir-Wrinch hypothesis of hydrophobic stabilization shared in the downfall of the cyclol model, owing mainly to the influence of Linus Pauling, who favored the hypothesis that protein structure was stabilized by hydrogen bonds.
Sources: en.wikipedia.org
IUPAC is involved today with many processes relating to the periodic table: the recognition and naming of new elements, recommending group numbers and collective names, and the updating of atomic weights.
In 1972, eight remarkably preserved mummies were discovered at an abandoned Inuit settlement called Qilakitsoq, in Greenland. The "Greenland Mummies" consisted of a six-month-old baby, a four-year-old boy, and six women of various ages, who died around 500 years ago. Their bodies were naturally mummified by the sub-zero temperatures and dry winds in the cave in which they were found.
== Future research == The National Institute of Diabetes and Digestive Kidney Diseases sponsored a phase 2 clinical study in 2001 that would look at the effectiveness of leptin to treat severe insulin resistance. In the study, two children with severe insulin resistance of ages 11 and 13 with known a known defect in the insulin receptor. The goal for the study was to see if leptin could overcome insulin receptor defects by initiating molecules in the insulin-signal cascade. While no outcomes have yet been reported to date, the direction in which this clinical trial is heading is promising.
His recommendations were acted upon; the War Office established a training course for pathologists and clinicians at the Royal Herbert Hospital, which made use of film that Florey shot in North Africa. Although he intended that penicillin be used to treat the seriously wounded, there were large numbers of bacterial sexually transmitted infection cases, against which penicillin was particularly effective, and from a military point of view being able to cure gonorrhea in 48 hours was a breakthrough. The supply situation improved, and 20 million units per day were made available for Allied invasion of Italy in September. During the campaign in Western Europe in 1944–1945, penicillin was widely used both to treat infected wounds and as a prophylactic to prevent wounds from becoming infected. Gas gangrene had killed 150 out of every 1,000 casualties in the First World War, but the instance of this disease now disappeared almost completely. Open fractures now had a recovery rate of better than 94 per cent, and recovery from burns of one-fifth of the body or less was 100 per cent.
Sources: en.wikipedia.org
Method validation is the documented process of confirming that an HPLC procedure is suitable for its intended use. It evaluates accuracy, precision, specificity, linearity, range, detection limits, and robustness. Validation criteria depend on the regulatory context and the sample type.
System suitability tests are short checks performed before or during an HPLC run to verify instrument and method performance. They often include resolution, tailing factor, theoretical plates, and injection precision. Results must meet predefined limits for sample data to be accepted.
HPLC retention time alone cannot definitively identify an unknown substance. A match with a reference standard under identical conditions provides supporting evidence. Confirmation typically requires mass spectrometry, nuclear magnetic resonance, or another orthogonal technique.
HPLC separates and quantifies compounds in a liquid sample. Detectors produce a response proportional to the amount of a compound passing through the flow cell. Identification by retention time requires comparison with a known standard.