The short version of mobile phase fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-01-08. Anything still debated is marked as such rather than presented as settled.
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.
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.
| 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 |
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.
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.
The first β-sheet structure was proposed by William Astbury in the 1930s. He proposed the idea of hydrogen bonding between the peptide bonds of parallel or antiparallel extended β-strands. However, Astbury did not have the necessary data on the bond geometry of the amino acids in order to build accurate models, especially since he did not then know that the peptide bond was planar. A refined version was proposed by Linus Pauling and Robert Corey in 1951. Their model incorporated the planarity of the peptide bond which they previously explained as resulting from keto-enol tautomerization.
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.
The word "aptamer" is a neologism coined by Andrew D. Ellington and Jack Szostak in their first publication on the topic. They did not provide a precise definition, stating "We have termed these individual RNA sequences 'aptamers', from the Latin aptus, to fit." The word itself, however, derives from the Greek word ἅπτω, to connect or fit (as used by Homer (c. 8th century BC)) and μέρος, a component of something larger. A typical aptamer is a synthetically generated ligand exploiting the combinatorial diversity of DNA, RNA, XNA, or peptide to achieve strong, specific binding for a particular target molecule or family of target molecules. Aptamers are occasionally classified as "chemical antibodies" or "antibody mimics". However, most aptamers are small, with a molecular weight of 6-30 kDa, in contrast to the 150 kDa size of antibodies, and contain one binding site rather than the two matching antigen binding regions of a typical antibody.
The Bailey peptide synthesis is a name reaction in organic chemistry developed 1949 by J. L. Bailey. It is a method for the synthesis of a peptide from α-amino acid-N-carboxylic acid anhydrides (NCAs) and amino acids or peptide esters. The reaction is characterized by short reaction times and a high yield of the target peptide. The reaction can be carried out at low temperatures in organic solvents. The residues R1 and R2 can be organic groups or hydrogen atoms, R3 is the used amino acid or peptide ester: The reaction mechanism is not known in detail. Supposedly, the reaction begins with a nucleophilic attack of the amino group on the carbonyl carbon of the anhydride group of the N-carboxylic acid anhydride (1). After an intramolecular proton migration, a 1,4-proton shift and the cleavage of carbon dioxide follows, resulting in the peptide bond in the final product (2):
Sources: en.wikipedia.org
In 80–85% of cases, the ALK detected in ALK-positive ALCL is a NPM1-ALK fusion protein. It is made by a fusion of NPM1 gene, which makes nucleophosmin 1, located on the long or "q" arm of chromosome 5 at position 35 (notated as 5q35) with the ALK gene located on the short or "p" arm of chromosome 2 at position 23 (notated as 2p23) to form a chimeric gene notated as (2;5)(p23;q35). In 13% of cases ALK fuses with the TPM3 gene or in <1% of cases for each of the following genes: TFG, ATIC, CLTC, TPM4, MSN, RNF213 (also termed ALO17), MYH9, or TRAF1. All of these fusion proteins are considered to act like NPMI-ALK in possessing high ALK activity that promotes the development and progression ALK-positive ALCL by activating the cell signaling pathways cited in the Introduction. 15% Of individuals with ALK-positive ALCL also have point mutations in the NOTCH1 gene. While most of these abnormalities are thought to be detrimental not all are. For example, DUSP22 gene rearrangements are associated with favorable outcomes in ALK-positive (as well as ALK-negative) ALCL.
Isoforms I, III, and VIII are also stimulated by Ca2+/calmodulin. Isoforms V and VI are inhibited by Ca2+ in a calmodulin-independent manner. Isoforms II, IV and IX are stimulated by alpha subunit of the G protein. Isoforms I, V and VI are most clearly inhibited by Gi, while other isoforms show less dual regulation by the inhibitory G protein. Soluble AC (sAC) is not a transmembrane form and is not regulated by G proteins or forskolin, instead acts as a bicarbonate/pH sensor. It is anchored at various locations within the cell and, with phosphodiesterases, forms local cAMP signalling domains. In neurons, calcium-sensitive adenylyl cyclases are located next to calcium ion channels for faster reaction to Ca2+ influx; they are suspected of playing an important role in learning processes. This is supported by the fact that adenylyl cyclases are coincidence detectors, meaning that they are activated only by several different signals occurring together. In peripheral cells and tissues adenylyl cyclases appear to form molecular complexes with specific receptors and other signaling proteins in an isoform-specific manner.
ProIAPP consists of 67 amino acids, which follow a 22 amino acid signal peptide which is rapidly cleaved after translation of the 89 amino acid coding sequence. The human sequence (from N-terminus to C-terminus) is: (MGILKLQVFLIVLSVALNHLKA) TPIESHQVEKR^ KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTYG^ KR^ NAVEVLKREPLNYLPL. The signal peptide is removed during translation of the protein and transport into the endoplasmic reticulum. Once inside the endoplasmic reticulum, a disulfide bond is formed between cysteine residues numbers 2 and 7. Later in the secretory pathway, the precursor undergoes additional proteolysis and posttranslational modification (indicated by ^). 11 amino acids are removed from the N-terminus by the enzyme proprotein convertase 2 (PC2) while 16 are removed from the C-terminus of the proIAPP molecule by proprotein convertase 1/3 (PC1/3). At the C-terminus Carboxypeptidase E then removes the terminal lysine and arginine residues. The terminal glycine amino acid that results from this cleavage allows the enzyme peptidylglycine alpha-amidating monooxygenase (PAM) to convert the terminal glycine to an amine group (releasing glycolate). After this step, the transformation from the precursor protein proIAPP to the biologically active IAPP (amylin) is complete (IAPP sequence: KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTY-NH2).
Sources: en.wikipedia.org
ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) is a laboratory technique used in molecular biology to assess genome-wide chromatin accessibility. The technique was introduced in 2013 by the labs of Will Greenleaf and Howard Chang at Stanford University as an alternative to MNase-seq, FAIRE-Seq and DNase-Seq with faster turnaround time, simpler protocol, and lower DNA input requirements.
ASQ provides its members with certification, training, publications, conferences, and other services. ASQ is a founding partner of the American Customer Satisfaction Index (ACSI), a quarterly economic indicator. Since 1989, ASQ has administered the annual Malcolm Baldrige National Quality Award. The ASQ also gives the Dorian Shainin Medal, which is awarded annually for the "Development and Application of Creative or Unique Statistical Approaches in the Solving of Problems Relative to the Quality of Product or Service".
Large AGE proteins unable to enter the Bowman's capsule are capable of binding to receptors on endothelial and mesangial cells and to the mesangial matrix. Activation of RAGE induces production of a variety of cytokines, including TNFβ, which mediates an inhibition of metalloproteinase and increases production of mesangial matrix, leading to glomerulosclerosis and decreasing kidney function in patients with unusually high AGE levels. Peptides and free adducts, the only breakdown products of AGE that are suitable for urinary excretion, are more aggressive than the AGE proteins from which they are derived, and they can perpetuate related pathology in people with diabetes, even after hyperglycemia has been brought under control.
White was married to his wife Edna for more than 40 years. He died unexpectedly on February 14, 1980, in Santa Barbara, California, where he had gone that day from his home in Palo Alto to deliver a lecture at the University of California. Several awards in the field of biochemistry have been named for White, including at Oakland University in Michigan, Wayne State University, George Washington University School of Medicine and the Gladstone Institutes. 1935 – Traveling Fellowship, American Physiological Society, for the XVth International Congress of Physiology (Leningrad and Moscow) 1938 – Eli Lilly Prize in Biochemistry 1960 – Distinguished Alumni Award, University of Denver 1967 – Sesquicentennial Alumni Award, University of Michigan 1969 – Borden Award, Association of American Medical Colleges 1959 – Doctor of Humane Letters, Yeshiva University 1975 – Doctor of Science, University of Denver
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.
It separates components in a liquid sample and measures their amounts using a detector. Results can indicate concentration, purity, or identity based on retention time and detector response. The technique works for mixtures that can be dissolved and filtered.