If you have been reading about robustness and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-07-06. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Separation in HPLC depends on the chemistry of the stationary phase, the composition of the mobile phase, and the physical properties of the column. Reverse-phase separations use a nonpolar stationary phase and a polar mobile phase, and they are common for many organic compounds. Ion-exchange, size-exclusion, and normal-phase modes serve other classes of analytes. Gradient elution changes solvent strength over time, while isocratic elution holds it constant. Flow rate, temperature, particle size, and column length all influence peak shape and resolution. Detection may use ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry, depending on the analyte and the required sensitivity.
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.
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.
| 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 |
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.
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.
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.
Christian René Marie Joseph, Viscount de Duve (2 October 1917 – 4 May 2013) was a Nobel Prize-winning Belgian cytologist and biochemist. He made serendipitous discoveries of two cell organelles, peroxisomes and lysosomes, for which he shared the Nobel Prize in Physiology or Medicine in 1974 with Albert Claude and George E. Palade ("for their discoveries concerning the structural and functional organization of the cell"). In addition to peroxisome and lysosome, he invented scientific names such as autophagy, endocytosis, and exocytosis on a single occasion. The son of Belgian refugees during the First World War, de Duve was born in Thames Ditton, Surrey, England. His family returned to Belgium in 1920. He was educated by the Jesuits at Our Lady College, Antwerp, and studied medicine at the Catholic University of Louvain. Upon earning his MD in 1941, he joined research in chemistry, working on insulin and its role in diabetes mellitus. His thesis earned him the highest university degree agrégation de l'enseignement supérieur (equivalent to PhD) in 1945. With his work on the purification of penicillin, he obtained an MSc degree in 1946. He went for further training under later Nobel Prize winners Hugo Theorell at the Karolinska Institutet in Stockholm, and Carl and Gerti Cori at the Washington University in St. Louis. He joined the faculty of medicine at Leuven in 1947. In 1960 he was invited to the Rockfeller Institute (now Rockefeller University).
=== EC 1.1.98 With other, known, acceptors === EC 1.1.98.1: Now EC 1.1.9.1, alcohol dehydrogenase (azurin) EC 1.1.98.2: glucose-6-phosphate dehydrogenase (coenzyme-F420) EC 1.1.98.3: decaprenylphospho-β-D-ribofuranose 2-oxidase EC 1.1.98.3: decaprenylphospho-β-D-ribofuranose 2-dehydrogenase EC 1.1.98.4: F420H2:quinone oxidoreductase EC 1.1.98.5: secondary-alcohol dehydrogenase (coenzyme-F420) EC 1.1.98.6: ribonucleoside-triphosphate reductase (formate) EC 1.1.98.7: serine-type anaerobic sulfatase-maturating enzyme
Escherichia coli: 0.12–128 μg/mL Klebsiella pneumoniae: 0.25–128 μg/mL Pseudomonas aeruginosa: ≤0.06–16 μg/mL For example, colistin in combination with other drugs is used to attack P. aeruginosa biofilm infection in lungs of patients with cystic fibrosis. Biofilms have a low-oxygen environment below the surface where bacteria are metabolically inactive, and colistin is highly effective in this environment. However, P. aeruginosa reside in the top layers of the biofilm, where they remain metabolically active. This is because surviving tolerant cells migrate to the top of the biofilm via pili and form new aggregates via quorum sensing.
== Products == Its primary products are based on Morpholino oligomers (PMOs), synthetic nucleic acid analogs that were conceived of by James Summerton and invented by Summerton with Dwight Weller, originally developed under the name NeuGene Antisense. Since morpholino oligomers can form sequence-specific double-stranded complexes with RNA they are suitable use in antisense therapy. In one application, translation blocking, a morpholino oligomer binds to messenger RNA produced by a known disease-causing gene to prevent it from being translated into protein. Morpholinos can also work as splice-switching oligos, targeting pre-mRNA to alter splicing and so causing changes in the structure of the mature mRNA (the mechanism of the approved drug eteplirsen). Morpholinos have been tested for a wide range of applications including prevention of cardiac restenosis after angioplasty, treatment of coronary artery bypass grafts, treatment of polycystic kidney disease, redirection of drug metabolism, treatment of some mutations causing Duchenne muscular dystrophy (DMD), and inhibition of infectious diseases. Their greatest clinical and commercial success thus far has been in the treatment of DMD. A new class of Morpholino oligos, the peptide-linked Morpholinos or PPMO, are linked to an arginine-rich cell-penetrating peptide to enhance their delivery into cells and have entered clinical trials.
Sources: en.wikipedia.org
The α-helix is the most abundant type of secondary structure in proteins. The α-helix has 3.6 amino acids per turn with an H-bond formed between every fourth residue; the average length is 10 amino acids (3 turns) or 10 Å but varies from 5 to 40 (1.5 to 11 turns). The alignment of the H-bonds creates a dipole moment for the helix with a resulting partial positive charge at the amino end of the helix. Because this region has free NH2 groups, it will interact with negatively charged groups such as phosphates. The most common location of α-helices is at the surface of protein cores, where they provide an interface with the aqueous environment. The inner-facing side of the helix tends to have hydrophobic amino acids and the outer-facing side hydrophilic amino acids. Thus, every third of four amino acids along the chain will tend to be hydrophobic, a pattern that can be quite readily detected. In the leucine zipper motif, a repeating pattern of leucines on the facing sides of two adjacent helices is highly predictive of the motif. A helical-wheel plot can be used to show this repeated pattern. Other α-helices buried in the protein core or in cellular membranes have a higher and more regular distribution of hydrophobic amino acids, and are highly predictive of such structures. Helices exposed on the surface have a lower proportion of hydrophobic amino acids. Amino acid content can be predictive of an α-helical region.
The park was closed for renovations on July 11, 1988. The four-year project to rebuild Bryant Park entailed new entrances, repairs to paths and lighting, and a redesign of the park's garden by Lynden Miller. Biederman worked with William H. Whyte, a sociologist whose influence led them to implement two decisions. One was the placement of 2,000 movable chairs in the park. The other was to lower the park itself, because Bryant Park had been elevated from the street and isolated by tall hedges prior to the 1988 redesign. The 1988 renovation lowered the park to nearly street level and tore out the hedges, though much of the park was still slightly elevated. The park's restrooms, which had been closed for 35 years, were renovated as well. The BPRC also found that several of the sculptures would need to be repaired, and called on William Cullen Bryant's descendants and other entities to provide funding for the restoration of these sculptures. Landscape architect Laurie Olin of Hanna/Olin recalls that the design process focused on "the different abilities of people [who] use these spaces...as well as making spaces that people are comfortable being with each other in." The restoration cost $8.9 million, which included $5.7 million of city funding and $3.2 million of private funding. The renovation took place at the same time as the NYPL's expansion of the main branch's stacks underneath Bryant Park.
== Equations == The Beer–Lambert law states that there is a logarithmic dependence between the transmission (or transmissivity), T, of light through a substance and the product of the absorption coefficient of the substance, α, and the distance the light travels through the material (i.e. the path length), ℓ. The absorption coefficient can, in turn, be written as a product of either a molar absorptivity of the absorber, ε, and the concentration c of absorbing species in the material, or an absorption cross section, σ, and the (number) density N of absorbers. (see Beer Lambert Law link for full derivation)
The beta blocker pindolol has been found to robustly potentiate the effects of DMT. This is thought to be due to pindolol's serotonin 5-HT1A receptor antagonism, which is thought to disinhibit the effects of DMT. The serotonin receptor agonist methysergide (UML-491) has been reported to greatly intensify the effects of DMT.
Radical SAM enzymes belong to a superfamily of enzymes that use an iron-sulfur cluster (4Fe-4S) to reductively cleave S-adenosyl-L-methionine (SAM) to generate a radical, usually a 5′-deoxyadenosyl radical (5'-dAdo), as a critical intermediate. These enzymes utilize this radical intermediate to perform diverse transformations, often to functionalize unactivated C-H bonds. Radical SAM enzymes are involved in cofactor biosynthesis, enzyme activation, peptide modification, post-transcriptional and post-translational modifications, metalloprotein cluster formation, tRNA modification, lipid metabolism, biosynthesis of antibiotics and natural products etc. The vast majority of known radical SAM enzymes belong to the radical SAM superfamily, and have a cysteine-rich motif that matches or resembles CxxxCxxC. Radical SAM enzymes comprise the largest superfamily of metal-containing enzymes.
Sources: en.wikipedia.org
By the beginning of 2008, his final year in office, Bush's approval rating had dropped to a low of just 19 percent, largely from the loss of support among Republicans. Commenting on his low poll numbers and accusations of being "the worst president", Bush would say, "I make decisions on what I think is right for the United States based upon principles. I frankly don't give a damn about the polls." There were calls for Bush's impeachment, though most polls showed a plurality of Americans would not support such an action. The arguments offered for impeachment usually centered on the NSA warrantless surveillance controversy, the Bush administration's justification for the war in Iraq, and alleged violations of the Geneva Conventions. Representative Dennis Kucinich (D-OH), who had run against Bush during the 2004 presidential campaign, introduced 35 articles of impeachment on the floor of the House of Representatives against Bush on June 9, 2008, but Speaker Nancy Pelosi (D-CA) declared that impeachment was "off the table". In April 2008, Bush's disapproval ratings reached the highest ever recorded for any president in the 70-year history of the Gallup poll, with 69 percent of those polled disapproving of the job Bush was doing as president and 28 percent approving – although the majority (66 percent) of Republicans still approved of his job performance. In polls conducted in the fall, just before the 2008 election, his approval ratings remained at record lows of 19 to 20 percent, while his disapproval ratings ranged from 67 percent to as high as 75 percent.
=== Enzyme production === A significant milestone in the use of K. phaffii in food technology was its GRAS classification by the US Food and Drug Administration, alongside their approval of recombinant proteins. It is now used to produce various enzymes that serve as processing aids and food additives. In bakery production, enzymes produced by genetically modified Komagataella can maintain bread freshness and compensate for variations in flour and malt quality. In brewing, they can reduce beer's alcohol content or modify the flavour and filtration properties of wine. Recombinant expressed phospholipase C is used to degum high-phosphorus vegetable oils by hydrolysing phospholipids. In animal feed, phytase produced by K. phaffii breaks down phytic acid, an antinutrient. Recently, K. phaffii has been used increasingly to produce soy leghemoglobin, a plant heme protein that gives plant-based meat analogues their colour and flavour. This expands the industrial application of K. phaffii from technical enzymes towards functional food ingredients. For this purpose, the yeast utilises its strong methanol-inducible promoters and efficient secretion to produce functional leghemoglobin for use as a food ingredient. Through strain engineering, including optimisation of heme biosynthesis and signal peptides, and controlled fed-batch fermentation, gram-per-litre titres of secreted leghemoglobin have been achieved. This makes large-scale production for meat analogues economically viable.
=== Measures of success === Success of liquid–liquid extraction is measured through separation factors and decontamination factors. The best way to understand the success of an extraction column is through the liquid–liquid equilibrium (LLE) data set. The data set can then be converted into a curve to determine the steady state partitioning behavior of the solute between the two phases. The y-axis is the concentration of solute in the extract (solvent) phase, and the x-axis is the concentration of the solute in the raffinate phase. From here, one can determine steps for optimization of the process.
== Clinical significance == Altered PREP activity may be associated with autism spectrum disorders and various psychological diseases such as schizophrenia, mania and clinical depression. However, there is conflicting information as to the exact role that prolyl endopeptidase plays in the pathophysiology of depression, with earlier studies documenting a decreased activity of the enzyme in depressed patients, but more recent studies demonstrating that inhibition of the same enzyme actually results in alleviation of depressive symptoms. Some types of prolyl endopeptidase have been used in studies to decrease the propensity of gluten-containing wheat products to aggravate coeliac disease. However, orally administered enzymes are potentially subject to inactivation in the gastrointestinal tract.
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.
It is a set of checks performed before or during an HPLC run to confirm the system works as expected. Parameters may include resolution, tailing factor, theoretical plates, and retention time precision. Failure can trigger maintenance, method adjustment, or repeat analysis.