A practical reference on calibration curve: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-11-06. 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.
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.
Routine quality control monitors retention time shifts, baseline noise, system pressure, and peak shape. Trends can reveal column aging, mobile phase preparation errors, detector drift, or sample degradation. Corrective actions may include replacing the column, preparing fresh mobile phase, or recalibrating the detector. Stability testing often uses HPLC to measure parent compound loss and degradation product formation. Open questions remain about how accelerated stability results extrapolate to long-term storage under varied conditions.
| 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 |
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.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample by passing them 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 how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
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.
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.
TNF is a cytokine produced mainly by activated macrophages, and is the major extrinsic mediator of apoptosis. Most cells in the human body have two receptors for TNF: TNFR1 and TNFR2. The binding of TNF to TNFR1 has been shown to initiate the pathway that leads to caspase activation via the intermediate membrane proteins TNF receptor-associated death domain (TRADD) and Fas-associated death domain protein (FADD). cIAP1/2 can inhibit TNF signaling by binding to TRAF2. FLIP inhibits the activation of caspase-8. Binding of this receptor can also indirectly lead to the activation of transcription factors involved in cell survival and inflammatory responses. However, signalling through TNFR1 might also induce apoptosis in a caspase-independent manner. The link between TNF and apoptosis shows why an abnormal production of TNF plays a fundamental role in several human diseases, especially in autoimmune diseases. The TNF receptor superfamily also includes death receptors (DRs), such as DR4 and DR5. These receptors bind to the protein TRAIL and mediate apoptosis. Apoptosis is known to be one of the primary mechanisms of targeted cancer therapy. Luminescent iridium complex-peptide hybrids (IPHs) have recently been designed, which mimic TRAIL and bind to death receptors on cancer cells, thereby inducing their apoptosis.
DNA binding site prediction on protein DNA the Double Helix Game From the official Nobel Prize web site DNA under electron microscope Dolan DNA Learning Center Double Helix: 50 years of DNA, Nature Proteopedia DNA Proteopedia Forms_of_DNA ENCODE threads explorer ENCODE home page at Nature Double Helix 1953–2003 National Centre for Biotechnology Education Genetic Education Modules for Teachers – DNA from the Beginning Study Guide PDB Molecule of the Month DNA "Clue to chemistry of heredity found". The New York Times, June 1953. First American newspaper coverage of the discovery of the DNA structure DNA from the Beginning Another DNA Learning Center site on DNA, genes, and heredity from Mendel to the human genome project. The Register of Francis Crick Personal Papers 1938 – 2007 at Mandeville Special Collections Library, University of California, San Diego Seven-page, handwritten letter that Crick sent to his 12-year-old son Michael in 1953 describing the structure of DNA. See Crick's medal goes under the hammer, Nature, 5 April 2013.
The most commonly used dye in agarose gel gel electrophoresis of DNA and RNA, dating as far back as the 1970s, is ethidium bromide (2,7-diamino-10-ethyl-9-phenylphenanthridiniumbromide). Ethidium Bromide (EtBr) is an orange-colored fluorescent intercalating dye. The dye inserts itself between the double helical structure of nucleic acids, allowing for visualization of the molecules under UV light. EtBr has absorbance maxima at 300-360 nm and fluorescent emission maxima at 500-590 nm, with the detection limit of 0.5-5.0 ng/band. The dye, however, has reduced sensitivity in the detection of single-stranded nucleic acid samples. EtBr should be handled with care, as it is a potent mutagen. A more sensitive alternative for nucleic acid staining in gel electrophoresis is SYBR™ Green I. The dye is 25 times more sensitive than EtBr in the staining of dsDNA, and is especially useful in staining assays containing single-stranded nucleic acids. SYBR Green is, however, more expensive when compared to EtBr.
Diphtheria toxin is produced by virulent Corynebacterium diphtheriae that infect the mucosal membranes of the throat and nasal cavity causing a gray, thickened lining of the throat, sore throat, weakness, mild fever, swollen glands of the neck, and difficulty breathing. Diphtheria toxin is an ADP-ribosyltransferase that inhibits protein synthesis which causes the symptoms associated with the disease. Diphtheria used to be a leading cause of childhood death until the creation of a vaccine. The diphtheria vaccine contains a diphtheria toxoid, antigenically identical yet inactivated and non-toxic. When the toxoid is introduced to the body in a vaccine, an immune response is mounted without sequelae associated with the toxigenicity.
Sources: en.wikipedia.org
79. Glipizide. Correa R(1), Patel P, Nappe TM(2). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. 2025 Nov 28. Author information: (1)University of Arizona (2)University of South Florida/Tampa General Hospital Glipizide is a second-generation sulfonylurea widely used in the management of type 2 diabetes. It remains an important therapeutic option for improving glycemic control in adults requiring pharmacologic therapy in addition to diet and exercise. As an insulin secretagogue, glipizide enhances pancreatic beta-cell insulin release and may modestly reduce hepatic glucose output, contributing to adequate glucose lowering. Although generally well tolerated, glipizide carries clinically relevant risks, including hypoglycemia, weight gain, and drug-drug interactions that may potentiate or diminish its therapeutic effect. These considerations underscore the need for careful patient selection, ongoing monitoring, and interprofessional coordination. Copyright © 2025, StatPearls Publishing LLC.
failure mode and effects analysis (FMEA) manual statistical process control (SPC) manual measurement systems analysis (MSA) manual production part approval process (PPAP) manual APQP serves as a guide in the development process and also a standard way to share results between suppliers and automotive companies. APQP specifies three phases: Development, Industrialization, and Product Launch. Through these phases, 23 main topics will be monitored. These topics must be completed before the production is started. They include the following aspects: design robustness, design testing, and specification compliance, production process design, quality inspection standards, process capability, production capacity, product packaging, product testing, and operator training plan. These activities are sometimes carried out by third-party inspection and quality control companies such as SGS, Bureau Veritas, or QCADvisor, which provide on-site inspections, audits, and testing services to support APQP compliance. APQP focuses on:
There are numerous theories as to the exact cause and mechanism in type 2 diabetes. Central obesity is known to predispose individuals for insulin resistance. Abdominal fat is especially active hormonally, secreting a group of hormones called adipokines that may possibly impair glucose tolerance. But adiponectin, an anti-inflammatory adipokine, which is found in lower concentration in obese and diabetic individuals has shown to be beneficial and protective in type 2 diabetes mellitus (T2DM). Insulin resistance is a major feature of diabetes mellitus type 2, and central obesity is correlated with both insulin resistance and T2DM itself. Increased adiposity (obesity) raises serum resistin levels, which in turn directly correlate to insulin resistance. Studies have also confirmed a direct correlation between resistin levels and T2DM. And it is waistline adipose tissue (central obesity) which seems to be the foremost type of fat deposits contributing to rising levels of serum resistin. Conversely, serum resistin levels have been found to decline with decreased adiposity following medical treatment.
The magnetic mass separators are able to separate isobars by mass number, however they are unable to sort isotopes of the same mass. If an experiment requires a higher degree of chemical purity, it will need the beam to have an additional separation, by proton number. RILIS provides this separation by using step-wise resonance photo-ionisation, involving precisely tuned laser wavelengths matched exactly to a specific element's successive electron transition energies. Ionisation will only occur of the desired element, and the other elements within the ion-source will remain unchanged. This process of laser ionisation takes place in a hot metal cavity to provide the spatial confinement needed for the atomic vapour to be illuminated. A high frequency laser system is needed to ionise the atom before it leaves the cavity. All in all, the ISOLDE facility provides 1300 isotopes from 75 elements in the periodic table.
Site-specific recombination makes use of phage integrases instead of restriction enzymes, eliminating the need for having restriction sites in the DNA fragments. Instead, integrases make use of unique attachment (att) sites, and catalyse DNA rearrangement between the target fragment and the destination vector. The Invitrogen Gateway cloning system was invented in the late 1990s and uses two proprietary enzyme mixtures, BP clonase and LR clonase. The BP clonase mix catalyses the recombination between attB and attP sites, generating hybrid attL and attR sites, while the LR clonase mix catalyse the recombination of attL and attR sites to give attB and attP sites. As each enzyme mix recognises only specific att sites, recombination is highly specific and the fragments can be assembled in the desired sequence. Vector design and assembly Because Gateway cloning is a proprietary technology, all Gateway reactions must be carried out with the Gateway kit that is provided by the manufacturer. The reaction can be summarised into two steps. The first step involves assembling the entry clones containing the DNA fragment of interest, while the second step involves inserting this fragment of interest into the destination clone.
Sources: pubmed.ncbi.nlm.nih.gov
ASBMB Award for Exemplary Contributions to Education ASBMB Leadership Awards ASBMB–Merck Award ASBMB Young Investigator Award Avanti Award in Lipids Bert and Natalie Vallee Award in Biomedical Science DeLano Award for Computational Biosciences Earl and Thressa Stadtman Distinguished Scientist Award Earl and Thressa Stadtman Young Scholar Award Herbert Tabor Research Award Mildred Cohn Award in Biological Chemistry - The Mildred Cohn Award in Biological Chemistry was established in 2013 to honor the scientific achievements of Mildred Cohn. Cohn was the first female president of the society, in 1978. The award of $5,000 is presented annually to a scientist who has made substantial advances in understanding biological chemistry using innovative physical approaches. The recipient is expected to deliver the Mildred Cohn Award lecture at the annual meeting. Ruth Kirschstein Diversity in Science Award The Alice and C. C. Wang Award in Molecular Parasitology Walter A. Shaw Young Investigator Award in Lipid Research William C. Rose Award
The amino acids in an α-helix are arranged in a right-handed helical structure where each amino acid residue corresponds to a 100° turn in the helix (i.e., the helix has 3.6 residues per turn), and a translation of 1.5 Å (0.15 nm) along the helical axis. Dunitz describes how Pauling's first article on the theme in fact shows a left-handed helix, the enantiomer of the true structure. Short pieces of left-handed helix sometimes occur with a large content of achiral glycine amino acids, but are unfavorable for the other normal, biological L-amino acids. The pitch of the alpha-helix (the vertical distance between consecutive turns of the helix) is 5.4 Å (0.54 nm), which is the product of 1.5 and 3.6. The most important thing is that the N-H group of one amino acid forms a hydrogen bond with the C=O group of the amino acid four residues earlier; this repeated i + 4 → i hydrogen bonding is the most prominent characteristic of an α-helix. Official international nomenclature specifies two ways of defining α-helices, rule 6.2 in terms of repeating φ, ψ torsion angles (see below) and rule 6.3 in terms of the combined pattern of pitch and hydrogen bonding. The α-helices can be identified in protein structure using several computational methods, such as DSSP (Define Secondary Structure of Protein).
AlphaFold's predicted structures are widely used in biological research, though the precise scale of that use is difficult to measure. More than 40% of protein-structure papers published in 2023 in Cell, Nature, and Science cited AlphaFold 2. A 2024 bibliometric analysis of the Web of Science database identified 1,680 peer-reviewed papers referencing AlphaFold published between January 2019 and May 2024. Measures of this kind rely on authors citing the AlphaFold papers when they use the tool, a convention encouraged but not enforced by the maintainers of the AlphaFold Protein Structure Database. Attempts to validate these counts against the full text of papers suggest that citations to foundational AlphaFold papers can both overstate and understate how widely the tool is used. In an analysis of about 8,900 papers in the PubMed Central Open Access corpus that mentioned AlphaFold, roughly 30% cited none of three foundational AlphaFold papers, while only about half of the papers citing at least one of those three mentioned AlphaFold anywhere in their text. A smaller manual check of 100 papers from a curated protein-literature database found a similar shortfall, with fewer than half of those mentioning AlphaFold including a formal citation.
RGD-based peptides have found many applications in biological research and medical devices. Culture plates coated with peptides mimicking ECM proteins' adhesion motifs, which promote prolonged culture of human embryonic stem cells, are on the market. RGD is also a universally used tool in the construction of multifunctional "smart" materials, such as tumor-targeted nanoparticles. Further, RGD is widely used in tissue engineering to promote tissue regeneration.
Leucine-rich repeat protein SHOC-2 is a protein that in humans is encoded by the SHOC2 gene. This protein was initially identified in Caenorhabditis elegans as SUR-8/SOC2 and was found to be a critical positive regulator of the ERK1/2 signaling pathway that integrates the Ras and RAF components of the ERK1/2 pathway into a multiprotein complex. Specifically, SHOC2 tethers RAS and PP1C proteins and in close proximity to RAF to dephosphorylate “S259” to enable MAPK signaling. The best-studied role of SHOC2 is in modulating signals of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway by forming a holophosphatase complex that activates RAF proteins.
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.
System suitability is typically performed before each batch or according to the validated method and laboratory procedure. Some long runs include periodic checks during analysis. The required frequency depends on regulatory expectations and method performance.