This is a working overview of Stationary phase, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-05-20 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness of measured value to accepted reference value |
| Validation parameter | Precision | Agreement among repeated measurements under specified conditions |
| System suitability check | Resolution ≥ 1.5 | Baseline separation between critical peak pair |
| System suitability check | Tailing factor ≤ 2.0 | Common target for peak symmetry |
| Documentation | Validation report | Summarizes experiments, acceptance criteria, and conclusions |
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.
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.
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.
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.
==== Mesoporous aerogel – selective oxidation of benzene ==== Silver nanoparticles supported on aerogel are advantageous due to the higher number of active sites. The highest selectivity for oxidation of benzene to phenol was observed at low weight percent of silver in the aerogel matrix (1% Ag). This better selectivity is believed to be a result of the higher monodispersity within the aerogel matrix of the 1% Ag sample. Each weight percent solution formed different sized particles with a different width of size range.
=== February === 1 February A ban on owning an American XL Bully dog comes into force in England and Wales. It is now a criminal offence to own one of the dogs unless the owner has successfully applied for the dog to be exempt. The Bank of England holds interest rates at 5.25%. Climate activist Greta Thunberg appears at Westminster Magistrates' Court, charged with breaching section 14 of the Public Order Act 1986. Her case, and that of four co-defendants, is thrown out the following day. COVID-19 vaccination in the United Kingdom: The first private service for COVID-19 vaccination begins rolling out to pharmacies around the UK, allowing those who are under 65 to receive the latest booster. 2 February Senior Labour MP Darren Jones confirms that the party has ditched its commitment to spend £28bn a year on green investment schemes if it wins the next general election. The killers of 16-year-old transgender girl Brianna Ghey are named as Scarlett Jenkinson and Eddie Ratcliffe, both aged 15 at the time of the murder in February 2023. They are sentenced at Manchester Crown Court to minimum terms of 22 and 20 years, respectively. Water UK, the umbrella trade organisation for the UK's water companies, says that the average annual water bill is expected to increase by 6% in England and Wales from April, an average rise of £27 to £473. 3 February 2024 Northern Ireland Executive formation: The Northern Ireland Assembly meets to elect a new Speaker. Edwin Poots, a former leader of the DUP, is chosen to be the Assembly's 7th Speaker.
Carbohydrates are the main source of energy in organisms for metabolism. They are an important source of fuel in exercise. A study conducted by the Institute of Food, Nutrition, and Human Health at Massey University investigated the effect of consuming a carbohydrate and electrolyte solution on muscle glycogen use and running capacity on subjects that were on a high carbohydrate diet. The group that consumed the carbohydrate and electrolyte solution before and during exercise experienced greater endurance capacity. This could not be explained by the varying levels of muscle glycogen; however, higher plasma glucose concentration may have led to this result. Dr. Stephen Bailey posits that the central nervous system can sense the influx of carbohydrates and reduces the perceived effort of the exercise, allowing for greater endurance capacity.
== Discovery of Y-chromosomal markers for languages == The next development was the discovery of specific Y-chromosomal markers linked to a language. These Y-chromosomal variants do not cause language change, but happened to be carried by the historic or prehistoric male speakers spreading the language. These language-specific Y-chromosomal markers create correlations such as those observed by Poloni et al. 1997, and furthermore allow the geographic extent, the time depth and the male immigration level underlying an unrecorded (prehistoric) language change to be determined.
Sources: en.wikipedia.org
The European Commission is the main executive body of the European Union. Article 17(1) of the Treaty on European Union states the commission should "promote the general interest of the Union" while Article 17(3) adds that Commissioners should be "completely independent" and not "take instructions from any Government". Under Article 17(2), "Union legislative acts may only be adopted on the basis of a Commission proposal, except where the Treaties provide otherwise". This means that the commission has a monopoly on initiating the legislative procedure, although the council or Parliament are the "de facto catalysts of many legislative initiatives".
Glycocyamine kinase (EC 2.7.3.1), which catalyses the transfer of phosphate from ATP to guanidoacetate. Arginine kinase (EC 2.7.3.3), which catalyses the transfer of phosphate from ATP to arginine. Taurocyamine kinase (EC 2.7.3.4), an annelid-specific enzyme that catalyses the transfer of phosphate from ATP to taurocyamine. Lombricine kinase (EC 2.7.3.5), an annelid-specific enzyme that catalyses the transfer of phosphate from ATP to lombricine. Smc74, a cercaria-specific enzyme from Schistosoma mansoni. Creatine kinase (EC 2.7.3.2) (CK), which catalyses the reversible transfer of high energy phosphate from ATP to creatine, generating phosphocreatine and ADP. Creatine kinase plays an important role in energy metabolism of vertebrates. There are at least four different, but very closely related, forms of CK. Two isozymes, M (muscle) and B (brain), are cytosolic, while the other two are mitochondrial. In sea urchins there is a flagellar isozyme, which consists of the triplication of a CK-domain. A cysteine residue is implicated in the catalytic activity of these enzymes and the region around this active site residue is highly conserved. ATP:guanido phosphotransferases contain a C-terminal catalytic domain which consists of a duplication where the common core consists of two beta-alpha-beta2-alpha repeats. The substrate binding site is located in the cleft between N and C-terminal domains, but most of the catalytic residues are found in the larger C-terminal domain.
Palmitoyl pentapeptide-4 (Matrixyl, called palmitoyl pentapeptide-3 before 2006) is a matrikine used in anti-wrinkle cosmetics. It was launched in 2000 as an active ingredient for the personal care industry under the trade name Matrixyl by the French cosmetic active ingredient manufacturer Sederma SAS.
== Reconstitution of the tablets == The cuneiform tablets confirming Amat-Mamu's inheritance were stored in the home of her uncle, Ikun-pī-Sîn. They were kept separate from the family archive so as not to suggest that the inheritance was part of the family estate. It is unknown why they were kept in her uncle's house, though such storage arrangements with family members were not uncommon. When they were lost, her father Sîn-ilî had a deposition taken from the uncle admitting to their loss. Amat-Mamu was forced to go to the court so the judges could authorize the creation of new tablets. The tablets that Belessunu received as a girl during her own adoption were not reconstituted, for her and her witnesses to that contract had already died. The court also ruled that should the previous tablets be found, they were still the sole property of Amat-Mamu. The sequence of events describing both the legal dispute and the tablets' loss was documented on the reconstituted tablet. The reconstitution meant that some details were lost and inconsistencies were introduced, primarily in the description of the fields. The tablet is dated to the 14th year of Samsu-iluna's rule, placing its creation around 1736 BC. It has been preserved and is designated by archeologists as CT 47.63. Amat-Mamu's story is listed on the tablet alongside that of Belessunu, including Belessunu's dedication as a nadītu and her adoption by her aunt. The tablet is used in the modern era as a reference to understand Babylonian property and inheritance law.
Belarus Governorate (Belorussian Gubernya, 1802) divided into Vitebsk and Mogilev Gubernya Bratslav Governorate (or Bratslav uyezd, see Podolia Governorate) Chernigov Governorate Izyaslav Governorate Yekaterinoslav Governorate/Novorossiya Governorate (1764) Kiev Governorate (1708) Lithuania Governorate (1795), later split into Lithuania-Grodno Governorate and Lithuania-Vilna Governorate, the last one later split into Vilna and Kovno Governorates Minsk Governorate (1793) Mogilev Governorate (1772) Podolia Governorate (1773) Polotsk Governorate Pskov Governorate Slonim Governorate (1795) (several months after creation connected to Lithuania Governorate in and split off from it in 1801 as Lithuania-Grodno Governorate) Volhynia Governorate (1793) After the Congress of Vienna in 1815, the Russian Empire created a separate entity called Congress Poland out of some of the above governorates. See administrative division of Congress Poland for details. Territories in the Russian partition which were not incorporated into Congress Poland were officially known as the Western Krai, and in Poland as the taken lands (Polish: ziemie zabrane). The Western Krai comprised the following lands of the Commonwealth:
Sources: en.wikipedia.org
Once the plume is neutrally buoyant, it can no longer continue to rise through the water column and instead begins to spread laterally throughout the ocean, potentially over several thousands of kilometers. Chemical reactions occur concurrently with the physical evolution of hydrothermal plumes. While seawater is a relatively oxidizing fluid, hydrothermal vent fluids are typically reducing in nature. Consequently, reduced chemicals such as hydrogen gas, hydrogen sulfide, methane, Fe2+, and Mn2+ that are common in many vent fluids will react upon mixing with seawater. In fluids with high concentrations of H2S, dissolved metal ions such as Fe2+ and Mn2+ readily precipitate as dark-colored metal sulfide minerals (see "black smokers"). Furthermore, Fe2+ and Mn2+ entrained within the hydrothermal plume will eventually oxidize to form insoluble Fe and Mn (oxy)hydroxide minerals. For this reason, the hydrothermal "near field" has been proposed to refer to the hydrothermal plume region undergoing active oxidation of metals while the term "far field" refers to the plume region within which complete metal oxidation has occurred.
==== Charter schools ==== The State of North Carolina provides for a legislated number of charter schools. These schools are administered independently of the Wake County Public School System. Raleigh is currently home to 11 such charter schools:
==== Amyloid beta (Aβ) ==== Alzheimer's disease has been identified as a protein misfolding disease, a proteopathy, caused by the accumulation of abnormally folded Aβ protein into amyloid plaques, and tau protein into neurofibrillary tangles in the brain. Plaques are made up of small peptides, 39–43 amino acids in length, called Aβ. Aβ is a fragment derived from the larger Aβ precursor protein (APP), a transmembrane protein that penetrates the cell's membrane. APP is critical to neuronal growth, survival, and post-injury repair. In Alzheimer's disease, the enzymes gamma secretase and beta secretase act together in a proteolytic process that divides APP into smaller fragments. One of these fragments is Aβ, which misfolds and self-assembles into fibrils; these fibrils form clumps that deposit outside neurons in dense formations known as Aβ plaques. Excitatory neurons are known to be major producers of Aβ that contribute to extracellular plaque deposition.
Another phenotype, Muscle-eye-brain disease (MEB) is the dystroglycanopathy most prevalent in Finland, and is caused by mutations in the POMGnT1, FKRP, FKTN, ISPD, and TMEM5 genes. The POMGnT1 gene is expressed in the same tissues as FKTN, and MEB appears to have a similar severity as FCMD. However, symptoms unique to MEB include glaucoma, atrophy of the optic nerves, and retinal generation. The least severe phenotype of dystroglycanopathies is CMD type 1c (MDC1C), caused by mutations in the FKRP and the LARGE gene, with a phenotype similar to MEB and WWS. MDC1C also includes Limb-Girdle muscular dystrophy.
Terrorism Act 2000 Anti-terrorism, Crime and Security Act 2001 Proceeds of Crime Act 2002 Serious Organised Crime and Police Act 2005 Criminal Finances Act 2017 Sanctions and Anti-Money Laundering Act 2018 Money Laundering Regulations are designed to protect the UK financial system, as well as preventing and detecting crime. If a business is covered by these regulations then controls are put in place to prevent it being used for money laundering. The Proceeds of Crime Act 2002 contains the primary UK anti–money laundering legislation, including provisions requiring businesses within the "regulated sector" (banking, investment, money transmission, certain professions, etc.) to report to the authorities suspicions of money laundering by customers or others. Money laundering is broadly defined in the UK. In effect any handling or involvement with any proceeds of any crime (or monies or assets representing the proceeds of crime) can be a money laundering offence. An offender's possession of the proceeds of his own crime falls within the UK definition of money laundering. The definition also covers activities within the traditional definition of money laundering, as a process that conceals or disguises the proceeds of crime to make them appear legitimate. Unlike certain other jurisdictions (notably the US and much of Europe), UK money laundering offences are not limited to the proceeds of serious crimes, nor are there any monetary limits. Financial transactions need no money laundering design or purpose for UK laws to consider them a money laundering offence.
Sources: en.wikipedia.org
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.
Validation follows a planned protocol that tests accuracy, precision, specificity, linearity, range, detection limits, quantitation limits, and robustness. Results are compared against predefined acceptance criteria. The validation report supports regulatory filing or routine use.
Revalidation may be needed after changes to column chemistry, mobile phase, detection, sample preparation, or instrument type. It can also follow a pattern of out-of-specification results. The scope depends on whether the change affects method performance.
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.