If you have been reading about retention time and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2025-05-30. Numbers and descriptions here follow the published literature rather than marketing material.
Routine HPLC testing depends on controlled reagents, calibrated instruments, and documented procedures. Columns degrade over time, so retention times and peak shapes are monitored for drift. Mobile phases are filtered and degassed to prevent pump damage and detector noise. Reference standards must be traceable and stored under suitable conditions. Data handling systems record injections, calculations, and audit trails. Quality control samples interspersed with unknowns help detect errors during a run.
Developing an HPLC method begins with defining the purpose, such as quantifying a main component, measuring impurities, or confirming identity. Analysts select separation mode, column, mobile phase, detection, and sample preparation based on analyte properties and matrix. Experiments vary solvent strength, pH, buffer type, and temperature to achieve resolution between critical peaks. The goal is a robust method that produces reliable results across instruments and operators. Method development often involves trial runs and statistical optimization.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness of measured value to accepted reference value |
| Validation parameter | Precision | Agreement among repeated measurements under specified conditions |
| System suitability check | Resolution ≥ 1.5 | Baseline separation between critical peak pair |
| System suitability check | Tailing factor ≤ 2.0 | Common target for peak symmetry |
| Documentation | Validation report | Summarizes experiments, acceptance criteria, and conclusions |
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.
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.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample. A pump moves a liquid mobile phase through a column packed with a solid stationary phase. Compounds interact differently with both phases and travel at different rates, leaving the column at distinct retention times. A detector records these arrivals as peaks on a chromatogram. The resulting pattern supports identification and quantification of substances in mixtures. Modern instruments use high pressure to force solvent through small particles, which improves speed and resolution compared with older low-pressure liquid chromatography methods.
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.
Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Professor Marshall Urist and Professor Hari Reddi discovered their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of pivotal morphogenetic signals, orchestrating tissue architecture throughout the body. The important functioning of BMP signals in physiology is emphasized by the multitude of roles for dysregulated BMP signalling in pathological processes. Cancerous disease often involves misregulation of the BMP signalling system. Absence of BMP signalling is, for instance, an important factor in the progression of colon cancer, and conversely, overactivation of BMP signalling following reflux-induced esophagitis provokes Barrett's esophagus and is thus instrumental in the development of esophageal adenocarcinoma. Recombinant human BMPs (rhBMPs) are used in orthopedic applications such as spinal fusions, nonunions, and oral surgery. rhBMP-2 and rhBMP-7 are Food and Drug Administration (FDA)-approved for some uses. rhBMP-2 causes more overgrown bone than any other BMPs and is widely used off-label.
As of 2026, there is no cure or effective treatment for CJD. Some of the symptoms, like twitching, can be managed, but otherwise treatment is palliative care. Psychiatric symptoms like anxiety and depression can be treated with sedatives and antidepressants. Myoclonic jerks can be handled with clonazepam or sodium valproate. Opiates can help with pain. Seizures are very uncommon but can nevertheless be treated with antiepileptic drugs. In 2022, results of an early-stage trial of PRN100, a monoclonal antibody against PrP, were reported: the drug appeared safe and reached the brain, but treated patients did not show clearly improved survival compared to historical controls. While not curative, this trial demonstrated the feasibility of immunotherapy for prion disease. In 2025, preclinical research demonstrated that oral, low-dose treatment with the antiretroviral medication efavirenz extended survival and slowed disease progression in a humanized mouse model of sporadic CJD (sCJD). The drug acts as an allosteric activator of the brain-specific cholesterol-metabolizing enzyme CYP46A1. This mechanism promotes brain cholesterol turnover, reduces the neurotoxic accumulation of pathological prion proteins (PrPSc), and alleviates metabolic lipid alterations in the brain.
This term has become very popular and commonly used in practice. But the appropriate expression is "enantioselective chromatography". Chiral chromatography has advanced to turn into the most preferred technique for the determination of enantiomeric purity as well as separation of pure enantiomers both on analytical and preparative scale. Chiral chromatographic assay is the first step in any study pertaining to enantioselective synthesis or separation. This includes the use of techniques viz. gas chromatography (GC), high performance liquid chromatography (HPLC), chiral supercritical fluid chromatography (SFC), capillary electrophoresis (CE) and thin-layer chromatography (TLC). The result of a literature survey done identifies HPLC-based chiral assays as the most dominating technology in use. An overview of various analytical methods engaged for chiral separation and analysis are listed in the table.
Aspartate has many other biochemical roles. It is a metabolite in the urea cycle and participates in gluconeogenesis. It carries reducing equivalents in the malate-aspartate shuttle, which utilizes the ready interconversion of aspartate and oxaloacetate, which is the oxidized (dehydrogenated) derivative of malic acid. Aspartate donates one nitrogen atom in the biosynthesis of inosine, the precursor to the purine bases. In addition, aspartic acid acts as a hydrogen acceptor in a chain of ATP synthase. Dietary L-aspartic acid has been shown to act as an inhibitor of Beta-glucuronidase, which serves to regulate enterohepatic circulation of bilirubin and bile acids. Click on genes, proteins and metabolites below to link to respective articles. Aspartate (the conjugate base of aspartic acid) stimulates NMDA receptors, though not as strongly as the amino acid neurotransmitter L-glutamate does. Aspartate is the "A" in NMDA (N-methyl-D-aspartate receptor).
Sources: en.wikipedia.org
June 13 – 23: 2019 Men's Softball World Championship in Prague-Havlíčkův Brod Argentina defeated Japan, 3–2, to win their first Men's Softball World Championship title. Canada took third place. July 23 – 27: Europe/Africa Softball 2020 Olympic Qualifier in Utrecht Italy defeated Great Britain, 5–0, to book their team and compete at the 2020 Summer Olympics. July 26 – 30: 2019 Women's U12 Softball World Cup in Tainan (debut event) Chinese Taipei defeated Peru, 3–2, to win the inaugural Women's U12 Softball World Cup title. The Czech Republic took third place. Indonesia took fourth place. August 10 – 17: 2019 Women's U19 Softball World Cup in Irvine The United States defeated Japan, 4–3, to win their third consecutive and seventh overall Women's U19 Softball World Cup title. Canada took third place. August 25 – September 1: Americas Softball 2020 Olympic Qualifier in Surrey Champions: Mexico; Second: Canada; Third: Puerto Rico Note: Both Mexico and Canada have qualified to compete at the 2020 Summer Olympics. September 24 –28: Asia/Oceania Softball 2020 Olympic Qualifier in Shanghai Champions: Australia; Second: Chinese Taipei; Third: China Note: Australia has qualified to compete at the 2020 Summer Olympics.
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.
5-Oxo-ETE and 5-oxo-15(S)-hydroxy-ETE but not 5-hydroxy members of the 5-HETE family such as 5-(S)-HETE activate peroxisome proliferator-activated receptor gamma (PPARγ). This activation does not proceed through OXER1; rather, it involves the direct binding of the oxo analog to PPARγ with 5-oxo-15-(S)-hydroxy-ETE being more potent than 5-oxo-ETE in binding and activating PPARγ. The Activation of OXER1 receptor and PPARγ by the oxo analogs can have opposing effects on cell function. For example, 5-oxo-ETE-bound OXER1 stimulates whereas 5-oxo-ETE-bound PPARγ inhibits the proliferation of various types of human cancer cell lines; this results in 5-oxo-ETE and 5-oxo-15-(S)-HETE having considerably less potency than anticipated in stimulating these cancer cells to proliferate relative to the potency of 5-(S)-HETE, a relationship not closely following the potencies of these three compounds in activating OXER1. 5-Oxo-ETE relaxes pre-contracted human bronchi by a mechanism that does not appear to involve OXER1 but is otherwise undefined.
Sources: en.wikipedia.org
It is a set of checks performed before or during an HPLC run to confirm the system works as expected. Parameters may include resolution, tailing factor, theoretical plates, and retention time precision. Failure can trigger maintenance, method adjustment, or repeat analysis.
Validation follows a planned protocol that tests accuracy, precision, specificity, linearity, range, detection limits, quantitation limits, and robustness. Results are compared against predefined acceptance criteria. The validation report supports regulatory filing or routine use.
Revalidation may be needed after changes to column chemistry, mobile phase, detection, sample preparation, or instrument type. It can also follow a pattern of out-of-specification results. The scope depends on whether the change affects method performance.
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.