The short version of retention time fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2026-01-29 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness to a reference value. |
| Validation parameter | Precision | Repeatability or intermediate precision. |
| Validation parameter | Linearity | Proportional response across a range. |
| System suitability check | Resolution | Separation between adjacent peaks. |
| Quality control tool | Control chart | Tracks results over time for trends. |
Most routine HPLC testing uses reversed-phase columns, where the stationary phase is nonpolar and the mobile phase is a polar mixture such as water with an organic solvent. Analytes partition between the two phases according to polarity, size, and charge. Gradients that change solvent composition over time can separate compounds with broad retention ranges. Isocratic conditions keep solvent composition constant and suit simpler mixtures. The choice of column chemistry, pH, and temperature affects selectivity and peak shape.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. UV detection is widely used because many organic compounds absorb light, but it requires a chromophore. Mass spectrometry provides mass-based identification and high sensitivity for trace analytes. Each detector has trade-offs in selectivity, cost, and compatibility with mobile phases. Quantification typically uses calibration curves prepared from reference standards. Results are reported as concentration, purity, or presence above a limit.
HPLC testing separates dissolved compounds by passing a liquid sample through a column packed with stationary phase. A pump delivers mobile phase at controlled flow, and the sample components interact differently with stationary and mobile phases. Compounds that spend more time in mobile phase elute earlier; those retained by stationary phase elute later. Detectors record elution as peaks, and peak area or height relates to amount. This mechanism underpins quantitative analysis of mixtures.
Arrestins block GPCR coupling to G proteins in two ways. First, arrestin binding to the cytoplasmic face of the receptor occludes the binding site for heterotrimeric G-protein, preventing its activation (desensitization). Second, arrestin links the receptor to elements of the internalization machinery, clathrin and clathrin adaptor AP2, which promotes receptor internalization via coated pits and subsequent transport to internal compartments, called endosomes. Subsequently, the receptor could be either directed to degradation compartments (lysosomes) or recycled back to the plasma membrane where it can again signal. The strength of arrestin-receptor interaction plays a role in this choice: tighter complexes tend to increase the probability of receptor degradation (Class B), whereas more transient complexes favor recycling (Class A), although this rule is far from absolute. More recently direct interactions between Gi/o family G proteins and Arrestin were discovered downstream of multiple receptors, regardless of canonical G protein coupling. These recent findings introduce a GPCR signaling mechanism distinct from canonical G protein activation and β-arrestin desensitization in which GPCRs cause the formation of Gαi:β-arrestin signaling complexes.
Camurus aims to collaborate with biotechnology and pharmaceutical companies worldwide to enable and improve the delivery of a wide range of drug compounds. These compounds including peptides, proteins, and insoluble small molecules make use of delivery solutions ranging from long-acting depots to lipid nanocarriers designed for improved intravenous, transdermal, and oral delivery. Camurus' in-house product portfolio targets healthcare needs in areas of growth-hormone disorders, cancer, oncology supportive care, metabolic disease, and drug addiction. In 2007, British investors evaluated six nominated private companies and chose to Camurus as the best privately owned biotechnology company in the Medicon Valley. The company was awarded the Strictly Financing Award 2007. In 2013, Camurus was awarded CPhI Pharma Award for Best Innovation in Formulation.
F-ATPase gene linkage and gene order are widely conserved across ancient prokaryote lineages, implying that this system already existed at a date before the last universal common ancestor, the LUCA. Nick Lane: The Vital Question: Energy, Evolution, and the Origins of Complex Life, Ww Norton, 2015-07-20, ISBN 978-0393088816 (Link points to Figure 10 showing model of ATP synthase) Boris A. Feniouk: "ATP synthase — a splendid molecular machine" Well illustrated ATP synthase lecture Archived 2008-12-02 at the Wayback Machine by Antony Crofts of the University of Illinois at Urbana–Champaign. Proton and Sodium translocating F-type, V-type and A-type ATPases in OPM database The Nobel Prize in Chemistry 1997 to Paul D. Boyer and John E. Walker for the enzymatic mechanism of synthesis of ATP; and to Jens C. Skou, for discovery of an ion-transporting enzyme, Na+, K+-ATPase. Harvard Multimedia Production Site — Videos – ATP synthesis animation David Goodsell: "ATP Synthase- Molecule of the Month" Archived 2015-09-05 at the Wayback Machine
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula R−C(=O)−NR′R″, where R, R', and R″ represent any group, typically organyl groups or hydrogen atoms. The amide functional group plays an important role in the chemistry of life where, as peptide bonds, they link amino acids together to form proteins. Amides can be viewed as a derivative of a carboxylic acid (R−C(=O)−OH) with the hydroxyl group (−OH) replaced by an amino group (−NR′R″); or, equivalently, an acyl (alkanoyl) group (R−C(=O)−) joined to an amino group. Common amides are formamide (H−C(=O)−NH2), acetamide (H3C−C(=O)−NH2), benzamide (C6H5−C(=O)−NH2), and dimethylformamide (H−C(=O)−N(−CH3)2). Amides are qualified as primary, secondary, and tertiary according to the number of acyl groups bounded to the nitrogen atom.
N-Acetylcysteine amide (abbrev. NACA, AD4 and also known as acetylcysteinamide) is an amide derivative of N-acetylcysteine (NAC) that appears to have better blood–brain barrier permeability and bioavailability possessing potential antioxidant and anti-inflammatory activity When administered, NACA increases glutathione levels. Glutathione neutralizes reactive oxygen species, reduces oxidative stress, and prevents induced cell damage and apoptosis. NACA has increased lipophilicity and membrane permeability compared to NAC. This compound belongs to a class of experimental compounds known as N-acyl-alpha-amino acids and their derivatives. These are compounds containing an alpha-amino acid (or its derivative) with an acyl group on the terminal nitrogen atom.
Sources: en.wikipedia.org
A safety modification to Mark 39 Mod 2 weapons known as Alt 197 had been approved in January 1960, but not yet applied to all deployed weapons prior to the Goldsboro accident, and was not applied to the weapons involved in the accident. Alt 197 replaced the MC-772 Arm/Safe switch with the MC-1288 Arm/Safe switch, with the main change being that the latter would prevent the charging of the low-voltage thermal battery when the Arm/Safe switch was in the "Safe" position, and as such would make sure that no electrical current was available anywhere within the bomb to power additional switches or hardware, legitimately or not. After the accident, all other Mark 39 Mod 2 weapons without the modification were taken off of deployment status ("red-lined") until the modification could be applied to the remaining inventory of the weapons.
Transcriptional gene regulation process depends on many spatial and temporal factors in the nucleus such as global or local chromatin states, nucleosome positioning, TF binding, enhancer/promoter activities. Variant that alter the function of any of these biological processes may alter the gene regulation and cause phenotypic abnormality. Genetic variants that located in distal regulatory region can affect the binding motif of TFs, chromatin regulators and other distal transcriptional factors, which disturb the interaction between enhancer/silencer and its target gene.
In ABO and Rh typing, reagents containing antibodies against the A, B, and RhD antigens are added to suspensions of blood cells. If the relevant antigen is present, the red blood cells will demonstrate visible agglutination (clumping). In addition to identifying the ABO antigens, which is termed forward grouping, routine ABO blood typing also includes identification of the ABO antibodies in the person's plasma. This is called reverse grouping, and it is done to confirm the ABO blood type. In reverse grouping, the person's plasma is added to type A1 and type B red blood cells. The plasma should agglutinate the cells that express antigens that the person lacks, while failing to agglutinate cells that express the same antigens as the patient. For example, the plasma of someone with type A blood should react with type B red cells, but not with A1 cells. If the expected results do not occur, further testing is required. Agglutination is scored from 1+ to 4+ based on the strength of the reaction. In ABO typing, a score of 3+ or 4+ indicates a positive reaction, while a score of 1+ or 2+ is inconclusive and requires further investigation.
There are several national and international bioanalytical organisations active throughout the world. Often they are part of a bigger organisation, e.g. Bioanalytical Focus Group and Ligand Binding Assay Bioanalytical Focus Group, which are both within the American Association of Pharmaceutical Scientists (AAPS) and FABIAN, a working group of the Analytical Chemistry Section of the Royal Netherlands Chemical Society. The European Bioanalysis Forum (EBF), on the other hand, is independent of any larger society or association.
Sources: en.wikipedia.org
Method validation is the documented process of showing that an HPLC procedure produces reliable results for a defined purpose. It examines parameters such as accuracy, precision, specificity, linearity, and robustness. Regulators and quality systems often require validation before routine use.
System suitability is a set of checks run on the chromatographic system before sample analysis. It confirms that resolution, peak shape, retention time, and response meet predefined limits. Failure can invalidate the run and trigger corrective action.
Blank injections reveal peaks or baseline disturbances that come from solvents, reagents, or the instrument rather than the sample. They help distinguish contamination from actual analyte signals. Comparing blanks with sample runs supports accurate interpretation.
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.