precision comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-06-01. Numbers and descriptions here follow the published literature rather than marketing material.
Routine HPLC testing compares a sample result with a calibration curve prepared from known reference standards. Peak area or peak height is plotted against concentration, and the curve is used to estimate unknown amounts. Retention time supports tentative identification when compared with a standard, though mass spectrometry or another confirmatory method may be needed for definitive identification. Pre-run checks verify repeatability, resolution, and peak symmetry before sample analysis. Limits of detection and quantification describe the smallest amounts that can be reliably observed or measured. Sample preparation, filtration, and degassing help prevent column damage and inconsistent results.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
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.
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.
Validation demonstrates that a method is suitable for its intended use. Typical performance characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulators and standards organizations provide frameworks, but specific requirements depend on the application and jurisdiction. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, retention time repeatability, and sensitivity. A validated method is not permanently fixed; changes may require partial or full revalidation.
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.
A chromogranin A-derived antifungal peptide (CGA 47–66, chromofungin) when embedded on a surface has been shown to have antifungal activity by interacting with the fungal membrane and thereby penetrating the cell. Additionally, in vitro studies have demonstrated that such an antifungal coating can inhibit the growth of yeast Candida albicans by 65% and completely stop the proliferation of filamentous fungus Neurospora crassa. Copper and copper alloy surfaces have demonstrated a die-off of Aspergillus spp., Fusarium spp., Penicillium chrysogenum, Aspergillus niger and Candida albicans fungal spores. Hence, the potential to help prevent the spread of fungi that cause human infections by using copper alloys (instead of non-antifungal metals) in air conditioning systems is worthy of further investigation. The physical topology of a surface will determine the viable environment for bacteria. It may affect a microbe's ability to adhere to its surface. Textile surfaces tend to be very easy for microbes to adhere to due to the abundance of interstitial spacing between fibers.
RCO2H + R'2NH → RCO−2 + R'2NH+2 RCO−2 + R'2NH+2 → RC(O)NR'2 + H2O Esters are far superior substrates relative to carboxylic acids. Further "activating" both acid chlorides (Schotten-Baumann reaction) and anhydrides (Lumière–Barbier method) react with amines to give amides: RCO2R" + R'2NH → RC(O)NR'2 + R"OH RCOCl + 2R'2NH → RC(O)NR'2 + R'2NH+2Cl− (RCO)2O + R'2NH → RC(O)NR'2 + RCO2H Peptide synthesis use coupling agents such as HATU, HOBt, or PyBOP. The hydrolysis of nitriles is conducted on an industrial scale to produce fatty amides. Laboratory procedures are also available. Many specialized methods also yield amides. A variety of reagents, e.g. tris(2,2,2-trifluoroethyl) borate have been developed for specialized applications. Amidogen Amino radical Imidic acid Metal amides IUPAC Compendium of Chemical Terminology
The cytochrome b5 reductase enzyme contains a typical oxidoreductase structure with a diaphorase binding domain complex for NADH and a FAD-binding domain. A three-stranded linker domain is present, as well as water-mediated hydrogen bonds, in order to biochemically connect the complex. Once cytochrome b5 reductase catalyzes electron transfer, the resulting reduced form of cytochrome b5 reduces the oxidized ferric ion of hemoglobin from Fe 3+ to Fe 2+. Mechanism: NADH + H+ + 2 ferricytochrome b5 -> NAD+ + 2 ferrocytochrome b5
Cabergoline was first synthesized by scientists working for the Italian drug company Farmitalia-Carlo Erba in Milan who were experimenting with semisynthetic derivatives of the ergot alkaloids, and a patent application was filed in 1980. The first publication was a scientific abstract at the Society for Neuroscience meeting in 1991. Farmitalia-Carlo Erba was acquired by Pharmacia in 1993, which in turn was acquired by Pfizer in 2003. Cabergoline was first marketed in The Netherlands as Dostinex in 1992. The drug was approved by the FDA on December 23, 1996. It went generic in late 2005 following US patent expiration. Brand names of cabergoline include Cabaser, Dostinex, Galastop (veterinary), and Kelactin (veterinary), among others. Cabergoline was studied in one person with Cushing's disease, to lower adrenocorticotropic hormone (ACTH) levels and cause regression of ACTH-producing pituitary adenomas. Substituted lysergamide Cabergoline – Isomer Design
Sources: en.wikipedia.org
Accelerator mass spectrometry (AMS) is a form of mass spectrometry that accelerates ions to extraordinarily high kinetic energies before mass analysis. The special strength of AMS among the different methods of mass spectrometry is its ability to separate a rare isotope from an abundant neighboring mass ("abundance sensitivity", e.g. 14C from 12C). The method suppresses molecular isobars completely and in many cases can also separate atomic isobars (e.g. 14N from 14C). This makes possible the detection of naturally occurring, long-lived radio-isotopes such as 10Be, 36Cl, 26Al and 14C. (Their typical isotopic abundance ranges from 10−12 to 10−18.) AMS can outperform the competing technique of decay counting for all isotopes where the half-life is long enough. Other advantages of AMS include its short measuring time as well as its ability to detect atoms in extremely small samples.
In order to regulate the secretion of ACTH, many substances secreted within this axis exhibit slow/intermediate and fast feedback-loop activity. Glucocorticoids secreted from the adrenal cortex work to inhibit CRH secretion by the hypothalamus, which in turn decreases anterior pituitary secretion of ACTH. Glucocorticoids may also inhibit the rates of POMC gene transcription and peptide synthesis. The latter is an example of a slow feedback loop, which works on the order of hours to days, whereas the former works on the order of minutes. The half-life of ACTH in human blood is reported to be between ten and 30 minutes. ACTH consists of 39 amino acids, the first 13 of which (counting from the N-terminus) may be cleaved to form α-melanocyte-stimulating hormones (α-MSH) (this common structure is responsible for excessively tanned skin in Addison's disease). After a short period of time, ACTH is cleaved into α-melanocyte-stimulating hormone (α-MSH) and CLIP, a peptide with unknown activity in humans. In the human body, total weight ACTH is 4540 Da.
An automated synthesis is very similar in procedure to performing a manual synthesis. The overseeing chemist decides on a target molecule then formulates the experimental plan, which is a sequential series of steps. Then, they collect the required equipment and execute the plan. The automated synthesis follows the same pathway, except that the computer devises and executes the experimental plan. However, human revision is usually still required to ensure the automated route is practical and there are no implicit steps or conditions missing from the proposed procedure. In organic synthesis, organic synthesis software is used to automate the process of identifying sequences of reactions or routes that can be used to synthesize organic compounds.
In the field of pharmacokinetics, the area under the curve (AUC) is the definite integral of the concentration of a drug in blood plasma as a function of time (this can be done using liquid chromatography–mass spectrometry). In practice, the drug concentration is measured at certain discrete points in time and the trapezoidal rule is used to estimate AUC. In pharmacology, the area under the plot of plasma concentration of a drug versus time after dosage (called "area under the curve" or AUC) gives insight into the extent of exposure to a drug and its clearance rate from the body.
People can also develop CJD because they carry a mutation of the gene that codes for the prion protein (PRNP), located on chromosome 202p12-pter. This occurs in only 10–15% of all CJD cases. In sporadic cases, the misfolding of the prion protein is a process that is hypothesized to occur as a result of the effects of aging on cellular machinery, explaining why the disease often appears later in life. An EU study determined that "87% of cases were sporadic, 8% genetic, 5% iatrogenic and less than 1% variant." Testing for CJD has historically been problematic, due to the nonspecific nature of early symptoms and difficulty in safely obtaining brain tissue for confirmation. The diagnosis may initially be suspected in a person with rapidly progressing dementia, particularly when it is also found with the characteristic medical signs and symptoms such as involuntary muscle jerking, difficulty with coordination/balance and walking, and visual disturbances. Further testing can support the diagnosis and may include:
Sources: en.wikipedia.org
Understanding of the molecular basis of binding to integrins has enabled the development of several drugs for cardiovascular disease and cancer, including eptifibatide, tirofiban and cilengitide. These drugs inhibit integrin binding. PET radiotracers such as fluciclatide utilize RGD-containing peptides to home to tumors, allowing for cancer monitoring. Eptifibatide and tirofiban are anti-clotting drugs indicated to prevent thrombosis in acute ischemic coronary syndromes. Eptifibatide is additionally FDA approved for patients undergoing percutaneous coronary intervention. These drugs block activation of the integrin responsible for aggregation of platelets (αIIbβ3, also known as glycoprotein IIb/IIIa) in response to the blood glycoproteins fibrinogen and von Willebrand factor. Eptifibatide (marketed as Integrilin) is a cyclic (circular) seven amino acid peptide, whereas tirofiban is a small molecule designed to mimic the chemistry and binding affinity of the RGD sequence.
Blood factors (Factor VIII and Factor IX) Thrombolytic agents (tissue plasminogen activator) Hormones (insulin, glucagon, growth hormone, gonadotrophins) Haematopoietic growth factors (Erythropoietin, colony-stimulating factors) Interferons (Interferons-α, -β, -γ) Interleukin-based products (Interleukin-2) Vaccines (Hepatitis B surface antigen) Monoclonal antibodies (Various) Additional products (tumour necrosis factor, therapeutic enzymes) Research and development investment in new medicines by the biopharmaceutical industry stood at $65.2 billion in 2008. A few examples of biologics made with recombinant DNA technology include: Many vaccines are grown in tissue cultures. Viral gene therapy involves artificially manipulating a virus to include a desirable piece of genetic material. Viral gene therapies using engineered plant viruses have been proposed to enhance crop performance and promote sustainable production.
Databases are essential for bioinformatics research and applications. Databases exist for many different information types, including DNA and protein sequences, molecular structures, phenotypes and biodiversity. Databases can contain both empirical data (obtained directly from experiments) and predicted data (obtained from analysis of existing data). They may be specific to a particular organism, pathway or molecule of interest. Alternatively, they can incorporate data compiled from multiple other databases. Databases can have different formats, access mechanisms, and be public or private. Some of the most commonly used databases are listed below: Used in biological sequence analysis: Genbank, UniProt Used in structure analysis: Protein Data Bank (PDB) Used in finding Protein Families and Motif Finding: InterPro, Pfam Used for Next Generation Sequencing: Sequence Read Archive Used in Network Analysis: Metabolic Pathway Databases (KEGG, BioCyc), Interaction Analysis Databases, Functional Networks Used in design of synthetic genetic circuits: GenoCAD
ACC Synthase is 450-516 amino acid long sequence depending on the species of plant from which it is extracted. Though it is comparable in the species in which it is found, its COOH-terminal domain is more variable, leading to differences such as oligomerization. The COOH-terminal domain is responsible for oligomerization. In most ACC Synthase producing cells, ACC Synthase exists as a dimer. However, in some we find a monomer ("which is more active and efficient [than its dimer counterpart"). The structure of ACS has been largely determined via X-ray crystallography. Conservation of the residues in ACS's catalytic domain and sequence homology suggest that ACS catalyzes the synthesis of ACC in a similar fashion as other enzymes that require PLP as a cofactor. However, unlike many other PLP-dependent enzymes, Lys (278) is not the only residue that interacts with the substrate. The proximity of the electronegative oxygen from Tyr (152) to the C-γ-S bond suggests a crucial role in the formation of ACC. X-ray crystallography with aminoethoxyvinylglycine (AVG) a competitive inhibitor confirmed Tyrosine's role in the γ elimination. As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes PDB: 1B8G, PDB: 1IAX, PDB: 1IAY, PDB: 1M4N, PDB: 1M7Y, and PDB: 1YNU.
There are three amino acids with side chains that are cations at neutral pH: arginine (Arg, R), lysine (Lys, K) and histidine (His, H). Arginine has a charged guanidino group and lysine a charged alkyl amino group, and are fully protonated at pH 7. Histidine's imidazole group has a pKa of 6.0, and is only around 10% protonated at neutral pH. Because histidine is easily found in its basic and conjugate acid forms it often participates in catalytic proton transfers in enzyme reactions.
Sources: en.wikipedia.org
HPLC testing measures the presence and amount of one or more compounds in a liquid sample. It separates mixture components and records detector responses as peaks, which are compared with reference standards. Results are usually reported as concentrations or relative percentages.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
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.