Everything below concerns reference standard. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Updated 2026-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Method validation establishes that an HPLC procedure is suitable for its intended use. Key parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Accuracy measures agreement with a true or accepted value, while precision describes repeatability and intermediate precision. Specificity confirms that the method measures the analyte without interference from impurities, degradants, or excipients. Validation is documented in a protocol and report, and acceptance criteria are set before experiments begin. Regulatory guidance varies by region, but the general principles are widely harmonized.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
| Property | Value | Notes |
|---|---|---|
| Abbreviation | HPLC | Also called high-performance liquid chromatography |
| Separation mechanism | Differential partitioning | Compounds distribute between mobile and stationary phases |
| Typical column chemistry | C18 (octadecylsilane) | Used in reversed-phase separations |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is common for trace and confirmatory work |
| Typical particle size | 1.8–5 µm | Smaller particles require higher pressure and can improve speed |
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.
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.
H3O+(aq) + OH−(aq) ⇌ H2O(liq) + H2O(liq) Due to this equilibrium, any increase in the concentration of hydronium is accompanied by a decrease in the concentration of hydroxide. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, while an Arrhenius base increases it. In an acidic solution, the concentration of hydronium ions is greater than 10−7 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidic solutions thus have a pH of less than 7.
Because their backbones are longer than those of normal peptides, β-peptides form disparate secondary structures. The alkyl substituents at both the α and β positions in a β-amino acid favor a gauche conformation about the bond between the α-carbon and β-carbon. This also affects the thermodynamic stability of the structure. Many types of helix structures consisting of β-peptides have been reported. These conformation types are distinguished by the number of atoms in the hydrogen-bonded ring that is formed in solution; 8-helix, 10-helix, 12-helix, 14-helix, and 10/12-helix have been reported. Generally speaking, β-peptides form a more stable helix than α-peptides. β-Peptides are stable against proteolytic degradation in vitro and in vivo, a potential advantage over natural peptides. β-Peptides have been used to mimic natural peptide-based antibiotics such as magainins, which are highly potent but difficult to use as drugs because they are degraded by proteolytic enzymes.
Degradation of an amino acid often begins with transamination, in which its amino group is transferred to α-ketoglutarate, forming glutamate. This process involves transaminases, often the same enzymes used in amino acid synthesis. In many vertebrates, the amino group is subsequently released as ammonia and converted to urea via the urea cycle for excretion. However, amino acid degradation can result in uric acid or ammonia instead, depending on the organism. For example, serine dehydratase converts serine directly to pyruvate and ammonia. After removal of one or more amino groups, the remaining carbon skeleton of an amino acid can serve as a precursor for synthesizing other amino acids, be further metabolized for energy after conversion into intermediates of glycolysis (typically via gluconeogenesis) or of the citric acid cycle, or be used for fatty acid synthesis and storage as triacylglycerol. Amino acids are bidentate ligands, forming transition metal amino acid complexes.
Amitriptyline was developed by the American pharmaceutical company Merck in the late 1950s. In 1958, Merck approached several clinical investigators proposing to conduct clinical trials of amitriptyline for schizophrenia. One of these researchers, Frank Ayd, instead, suggested using amitriptyline for depression. Ayd treated 130 patients and, in 1960, reported that amitriptyline had antidepressant properties similar to another, and the only known at the time, tricyclic antidepressant imipramine. Following this, the US Food and Drug Administration approved amitriptyline for depression in 1961. In Europe, due to a quirk of the patent law at the time allowing patents only on the chemical synthesis but not on the drug itself, Roche and Lundbeck were able to independently develop and market amitriptyline in the early 1960s. According to research by a historian of psychopharmacology David Healy, amitriptyline became a much bigger selling drug than its precursor imipramine because of two factors. First, amitriptyline has a much stronger anxiolytic effect. Second, Merck conducted a marketing campaign raising clinicians' awareness of depression as a clinical entity. Amitriptyline is no longer sold under the brand name Elavil.
The structure of the AG glycans consists of a backbone of β-1,3 linked galactose (Gal), with sidechains of β-1,6 linked Gal and have terminal residues of arabinose (Ara), rhamnose (Rha), Gal, fucose (Fuc), and glucuronic acid (GlcA). These AG glycan moieties are assembled by glycosyltransferases (GTs). O-glycosylation of AGPs is initiated by the action of Hyp-O-galactosyltransferases (Hyp-O-GalTs) that add the first Gal onto the protein. The complex glycan structures are then elaborated by a suite of glycosyltransferases, the majority of which are bio-chemically uncharacterized. The GT31 family is one of the families involved in AGP glycan backbone biosynthesis. Numerous members of the GT31 family have been identified with Hyp-O-GALT activity and the core β-(1,3)-galactan backbone is also likely to be synthesized by the GT31 family. Members of the GT14 family are implicated in adding β-(1,6)- and β-(1,3)-galactans to AGPs. In Arabidopsis, terminal sugars such as fucose are proposed to be added by AtFUT4 (a fucosyl transferase) and AtFUT6 in the GT37 family and the terminal GlcA incorporation can be catalysed by the GT14 family. A number of GTs remain to be identified, for example those responsible for terminal Rha.
Sources: en.wikipedia.org
In physics, atomic spectroscopy is the study of the electromagnetic radiation absorbed and emitted by atoms. Since unique elements have unique emission spectra, atomic spectroscopy is applied for determination of elemental compositions. It can be divided by atomization source or by the type of spectroscopy used. In the latter case, the main division is between optical and mass spectrometry. Mass spectrometry generally provides significantly better analytical performance but is also significantly more complex. This complexity translates into higher purchase costs, higher operational costs, more operator training, and a greater number of components that can potentially fail. Because optical spectroscopy is often less expensive and has performance adequate for many tasks, it is far more common. Atomic absorption spectrometers are one of the most commonly sold and used analytical devices.
3-Aminoacetanilide is a chemical compound which is an amino derivative of acetanilide and meta-isomer of aminoacetanilide. There are two other isomers of aminoacetanilide, 2-aminoacetanilide and 4-aminoacetanilide. Aminoacetanilide derivatives are important synthetic intermediates in heterocyclic and aromatic synthesis. These derivatives have found applications in pharmaceutical industry and dyes and pigment industry. A number of methods are available to synthesize 3'-aminoacetanilide. It could be prepared by reduction of m-nitroacetanilide. m-Chloroacetanilde has been converted into m-aminoacetanilide. 3′-Aminoacetanilide has been used in the preparation of azo compounds, pyrrole, imidazole, thiazole and other heterocycles. It is starting material for Trametinib. It is also used to prepare reactive yellow K-RN and dispersed dye.
4-Chloromethcathinone (also known as 4-CMC and clephedrone) is a stimulant drug of the cathinone class that has been sold online as a designer drug. 4-CMC produces similar effects to mephedrone, and has been sold as an alternative in countries where mephedrone was scheduled. 4-CMC produces similar side effects to mephedrone, including: increased blood pressure, tachycardia, hyperthermia, and anxiety. Its chemical structure closely resembles para-chloromethamphetamine, raising concerns about its potential to readily induce cell death of serotonergic neurons. However, no neurotoxicity of this kind has been found to occur, but studies involving mice do indicate that it is neurotoxic through other mechanisms, similarly to other cathinones. 4-CMC is cytotoxic and induces oxidative stress, more so than 4-MMC. Moreover, β-keto substitution is thought to change cathinone structure activity relationships (SAR) and metabolism compared to amphetamines, leading to differences in pharmacology.
Amyloid beta can be measured semiquantitatively with immunostaining, which also allows one to determine location. Amyloid beta may be primarily vascular, as in cerebral amyloid angiopathy, or in amyloid plaques in white matter. One sensitive method is ELISA which is an immunosorbent assay which utilizes a pair of antibodies that recognize amyloid beta. Atomic force microscopy, which can visualize nanoscale molecular surfaces, can be used to determine the aggregation state of amyloid beta in vitro. Vibrational microspectroscopy is a label-free method that measures the vibration of molecules in tissue samples. Amyloid proteins like Aβ can be detected with this technique because of their high content of β-sheet structures. Dual polarisation interferometry is an optical technique which can measure early stages of aggregation by measuring the molecular size and densities as the fibrils elongate. These aggregate processes can also be studied on lipid bilayer constructs. TPM21 Sylvain Lesné – Aβ*56 Online Mendelian Inheritance in Man (OMIM): 104300
Camurus is a company focused on the development of lipid lyotropic liquid crystal structures for pharmaceutical drug delivery applications. These structures are well-defined three-dimensional formations consisting of lipophilic and hydrophilic domains that can be either interconnected or isolated depending on the environmentally induced phase conditions. The unique crystalline structures offer a unique way of encapsulating and transporting Active pharmaceutical ingredients, such as small molecules, peptides and proteins through the body. The structures also allow for the use of controlled release and prevention of degradation of fragile short half live molecules, a serious issue for amino-acid based drugs.
Sources: en.wikipedia.org
Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for antimicrobial peptides. These peptides are potent, broad spectrum antimicrobials which demonstrate potential as novel therapeutic agents. Antimicrobial peptides have been demonstrated to kill Gram negative and Gram positive bacteria, enveloped viruses, fungi and even transformed or cancerous cells. Unlike the majority of conventional antibiotics it appears that antimicrobial peptides frequently destabilize biological membranes, can form transmembrane channels, and may also have the ability to enhance immunity by functioning as immunomodulators.
Pharmaceutical engineering is an interdisciplinary science that includes drug engineering, novel drug delivery and targeting, pharmaceutical technology, unit operations of chemical engineering, and pharmaceutical analysis. It may be deemed as a part of pharmacy due to its focus on the use of technology on chemical agents in providing better medicinal treatment. This is an extremely broad category—essentially covering all health care products that do not achieve their intended results through predominantly chemical (e.g., pharmaceuticals) or biological (e.g., vaccines) means, and do not involve metabolism. A medical device is intended for use in: the diagnosis of disease or other conditions in the cure, mitigation, treatment, or prevention of disease. Some examples include pacemakers, infusion pumps, the heart-lung machine, dialysis machines, artificial organs, implants, artificial limbs, corrective lenses, cochlear implants, ocular prosthetics, facial prosthetics, somato prosthetics, and dental implants.
The topology of a β-sheet describes the order of hydrogen-bonded β-strands along the backbone. For example, the flavodoxin fold has a five-stranded, parallel β-sheet with topology 21345; thus, the edge strands are β-strand 2 and β-strand 5 along the backbone. Spelled out explicitly, β-strand 2 is H-bonded to β-strand 1, which is H-bonded to β-strand 3, which is H-bonded to β-strand 4, which is H-bonded to β-strand 5, the other edge strand. In the same system, the Greek key motif described above has a 4123 topology. The secondary structure of a β-sheet can be described roughly by giving the number of strands, their topology, and whether their hydrogen bonds are parallel or antiparallel. β-sheets can be open, meaning that they have two edge strands (as in the flavodoxin fold or the immunoglobulin fold) or they can be closed β-barrels (such as the TIM barrel). β-Barrels are often described by their stagger or shear. Some open β-sheets are very curved and fold over on themselves (as in the SH3 domain) or form horseshoe shapes (as in the ribonuclease inhibitor). Open β-sheets can assemble face-to-face (such as the β-propeller domain or immunoglobulin fold) or edge-to-edge, forming one big β-sheet.
In enzymology, 4-aminobutyrate transaminase (EC 2.6.1.19), also called GABA transaminase or 4-aminobutyrate aminotransferase, or GABA-T, is an enzyme that catalyzes the reversible chemical reaction: GABA + α-ketoglutaric acid ⇌ {\displaystyle \rightleftharpoons } succinate semialdehyde + L-glutamic acid The two substrates of this enzyme are GABA and α-ketoglutaric acid. Its products are succinate semialdehyde and L-glutamic acid. Th enzyme is a transferase, specifically a transaminase, which transfer nitrogenous groups. The systematic name of this enzyme class is 4-aminobutanoate:2-oxoglutarate aminotransferase. This enzyme participates in 5 metabolic pathways: alanine and aspartate metabolism, glutamate metabolism, β-alanine metabolism, propanoate metabolism, and butanoate metabolism. It uses pyridoxal phosphate as a cofactor. This enzyme is found in prokaryotes, plants, fungi, and animals (including humans). Pigs have often been used when studying how this protein may work in humans.
Sources: en.wikipedia.org
It measures the presence and amount of one or more compounds in a liquid sample. Separation occurs in a column, and detection produces a signal proportional to concentration. Identification usually requires comparison with a known reference standard under the same conditions.
In most cases the sample is consumed or altered during analysis, though some detectors are non-destructive. Fractions can be collected after separation for further study. Repeated testing therefore requires additional sample.
Run times range from under a minute for fast methods to over an hour for complex separations. Sample preparation, equilibration, and data review add time. Throughput depends on instrument configuration and method requirements.
System suitability is a set of checks that confirm the instrument and method perform within limits before sample analysis. It typically includes resolution, tailing factor, retention time, and peak area reproducibility. If a check fails, the run is invalidated until the cause is resolved.