precision raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2025-11-15. Anything still debated is marked as such rather than presented as settled.
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.
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.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it 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 interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
| 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 |
Detection commonly uses ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. Ultraviolet detection depends on molecular chromophores that absorb light at specific wavelengths. Mass spectrometry provides mass information and sensitive quantification, often after electrospray ionization. Before sample batches, performance checks examine resolution, elution time repeatability, peak symmetry, and plate count. Matrix effects and co-elution remain recognized uncertainties; formal validation studies and orthogonal detection help address them. Detector choice depends on analyte properties and required sensitivity.
High-performance liquid chromatography, or HPLC, separates dissolved compounds by passing a liquid mobile phase through a packed column. Components distribute differently between the stationary phase and the moving liquid, so they travel at different speeds and exit at different times. A detector records these eluting bands as peaks, and peak area or height relates to amount. The technique supports testing in pharmaceuticals, foods, environmental samples, and industrial chemicals. Quantification usually depends on calibration with known standards.
=== 1950–2000 === In the 1950s, thiazide diuretics were developed by Merck scientists Karl H. Beyer, James M. Sprague, John E. Baer, and Frederick C. Novello and led to the marketing of the first drug of this class, chlorothiazide, under the trade name Diuril in 1958. The research leading to the discovery of chlorothiazide, leading to "the saving of untold thousands of lives and the alleviation of the suffering of millions of victims of hypertension" was recognized by a special Public Health Award from the Lasker Foundation in 1975. In 1953, Merck & Co. merged with Philadelphia-based Sharp & Dohme, Inc., becoming the largest U.S. drugmaker. Sharp and Dohme had acquired H. K. Mulford Company in 1929, adding smallpox vaccines to its portfolio. The combined company kept the trade name Merck in the United States and Canada, and as Merck Sharp & Dohme (MSD) outside these two countries. In 1965, Merck & Co. acquired Charles Frosst Ltd. of Montreal (founded 1899), creating Merck-Frosst Canada, Inc., as its Canadian subsidiary and pharmaceutical research facility. Merck & Co. closed this facility in July 2010 but reemerged in 2011 as Merck Canada. Maurice Hilleman, a scientist at Merck, developed the first mumps vaccine in 1967, the first rubella vaccine in 1969, and the first trivalent measles, mumps, rubella (MMR vaccine) in 1971. The incidence of rubella-associated birth defects fell from up to 10,000 per year in the U.S. to zero in the aftermath of the rubella vaccine's development.
== Chemistry == In terms of chemical structure, tianeptine is similar to tricyclic antidepressants (TCAs), but it has significantly different pharmacology and important structural differences, so it is not usually grouped with them.
Differences in gene expression are especially clear within multicellular organisms, where cells all contain the same genome but have very different structures and behaviors due to the expression of different sets of genes. All the cells in a multicellular organism derive from a single cell, differentiating into variant cell types in response to external and intercellular signals and gradually establishing different patterns of gene expression to create different behaviors. Within eukaryotes, there exist structural features of chromatin that influence the transcription of genes, often in the form of modifications to DNA and chromatin that are stably inherited by daughter cells. These features are called "epigenetic" because they exist "on top" of the DNA sequence and retain inheritance from one cell generation to the next. Because of epigenetic features, different cell types grown within the same medium can retain very different properties. Although epigenetic features are generally dynamic over the course of development, some, like the phenomenon of paramutation, have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as the basis for inheritance.
=== Automatic Fraction Collector === The Automatic Fraction Collector (AFC) is a programmable, automation technology designed to enhance the reproducibility and scalability of sample collection from qEV columns. The AFC manages the collection of fractions from the qEV column by differentiating between the buffer volume, and the volume of fractions containing extracellular vesicles. It has an in-built rotational carousel for holding collection tubes, and precisely measures the volume of each fraction by weight as the sample elutes from the column. Together, qEV columns and the AFC are known as the qEV isolation platform. Multiple AFCs can be used in parallel to increase the throughput of extracellular vesicle isolation.
Sources: en.wikipedia.org
Although Mexican authorities often distinguish between homicides linked to organized crime and those that are not, the conflict has strained state resources and created an environment of impunity that has worsened crime overall. In 2009, the Mexican attorney general's office claimed that 9 of 10 victims of the Mexican drug war are members of organized crime groups, although other sources have questioned this figure. Deaths among military and police personnel are an estimated 7% of the total. The states that suffer from the conflict the most are Baja California, Guerrero, Chihuahua, Michoacán, Tamaulipas, Nuevo León, and Sinaloa.
Member of the State Committee on Vocational Education (1948–1951) Member of numerous committees for the foundation of new industries in postwar Greece (throughout the 1950s) First Vice-President of the National Hellenic Research Foundation (1958–1968), of which he was a key founder Minister of Industry in the Paraskevopoulos technocratic caretaker government (1963–1964) President of the Greek Atomic Energy Commission (1964–1965) The democratic ideals of Zervas made him a target of the military junta established in 1967, which removed him from his position in the University of Athens in 1968 after almost three decades of dedicated research and teaching. In response, the Academy of Athens of which Zervas had been a member since 1956 elected him as its president in 1970. After his term as President of the Academy, Zervas retired in 1971.
Epidermolysis bullosa simplex (EBS) is a form of EB that causes blisters at the site of rubbing. It typically affects the hands and feet, and is typically inherited in an autosomal dominant manner, affecting the keratin genes KRT5 and KRT14. Therefore, there is a failure in keratinization, which affects the integrity and the ability of the skin to resist mechanical stresses.
Alprazolam is a GABAA receptor positive allosteric modulator. When it binds to the receptor, effects of GABA are enhanced, leading to inhibition of neurons in the brain. This results in effects including reduced anxiety, muscle relaxant, and anticonvulsant activity. The activity of alprazolam in the central nervous system is dose-dependent.
==== Energy and climate ==== The Duterte administration initially adopted a "technology neutral" policy in energy generation. Earlier in his term, Duterte stressed that coal remains the most viable source of energy if the Philippines is to accelerate industrialization, and questioned the sanctions imposed by the United States and European Union on smaller countries including the Philippines when the country's carbon footprint is not significant compared to the superpowers. The administration shifted its energy policy to prefer renewable sources of energy later in Duterte's term. At his fourth State of the Nation address in July 2019, Duterte issued an order to cut coal dependence and hasten a transition to renewable energy. In October 2020, the energy department issued a moratorium on the construction of new coal power plants and favored renewable energy sources. On February 28, 2022, Duterte issued an executive order approving the inclusion of nuclear power in the country's energy mix. To hasten the expansion of the nation's power capacity, Duterte established the inter-agency Energy Investment Coordinating Council tasked with simplifying and streamlining the approval process of big-ticket projects. On January 21, 2022, he signed a law promoting the use of microgrid systems in unserved and underserved areas to accelerate total electrification of the country. The administration made initiatives to liberalize the energy sector, allowing 100% foreign ownership in large-scale geothermal projects starting October 2020.
Sources: en.wikipedia.org
Stolen Focus: Why You Can't Pay Attention was published in the UK on January 6th, 2022, followed by the US on January 25th the same month. In Stolen Focus, Hari argues that elements of modern lifestyles, including smart phones and social media, are "destroying our ability to concentrate." The book also discusses opinions on chronic stress, a decrease in outdoor play among children, and the potential effect of ultra-processed foods on brain functions. Stolen Focus debuted at number seven on the New York Times nonfiction best-seller list for the week ending 12 February 2022. The original UK and US releases of Stolen Focus have different subtitles. The full title of the UK edition reads: Stolen Focus: Why You Can't Pay Attention, while the US edition continues this subtitle: Stolen Focus: Why You Can't Pay Attention—and How to Think Deeply Again.
Erbium(III) oxide (also known as erbia) is the only known oxide of erbium, first isolated by Carl Gustaf Mosander in 1843, and first obtained in pure form in 1905 by Georges Urbain and Charles James. It has a cubic structure resembling the bixbyite motif. The Er3+ centers are octahedral. The formation of erbium oxide is accomplished by burning erbium metal, erbium oxalate or other oxyacid salts of erbium. Erbium oxide is insoluble in water and slightly soluble in heated mineral acids. The pink-colored compound is used as a phosphor activator and to produce infrared-absorbing glass.
== Deaths == January 6 – Alex Felipe, 32, futsal player (Sporting CP, Norilsk Nickel, national team) January 10 – Isabel Veloso, 19, social media influencer January 24 – Constantino de Oliveira Júnior, 57, founder and CEO (2004–2012) of Gol Linhas Aéreas February 4 – Ricardo Schnetzer, 72, voice actor February 13 – José Álvaro Moisés, 81, political scientist. April 17 – Oscar Schmidt, 68, Hall of Fame basketball player (JuveCaserta, Corinthians, national team). April 18 – Oscar Andrade, 68, deputy (1996–2003). April 19 – Gerardo Renault, 96, Minas Gerais MLA (1968–1978), deputy (1978–1986). April 27 – Luciana Novaes, 42, social worker, politician, and Rio de Janeiro city councilwoman. May 4 – Hermano da Silva Ramos, 100, French-Brazilian racing driver (Formula One). May 2 – Raimundo Rodrigues Pereira, 85, journalist. May 5 – Guto Graça Mello, 78, composer and music producer. May 23 – Gabriel Ganley, 22, bodybuilder and social media influencer. June 9 – Orlando Senna, 86, film director (Iracema: Uma Transa Amazônica). June 11 – Brito, 86, football player. June 14 – Oliver Tree, 32, American singer-songwriter. Lucas Frota, 27, record producer, musician, and DJ. June 19 – Brasão, 44, footballer (Athletico Paranaense, Santa Cruz, Salgaocar). July 3 – Lydia Möcklinghoff, 45, German ecologist and zoologist. July 7 – Benedito Ruy Barbosa, 95, telenovela writer (Pantanal, O Rei do Gado, Terra Nostra). July 16 – Renato Machado, 83, newscaster and journalist (TV Globo). July 26 – Octavio Gallotti, 95, minister (1984–2000) and president (1991, 1993–1995) of the Supreme Federal Court.
=== Aging === Tissue homeostasis generally declines with age, in part because stem/progenitor cells fail to self-renew or differentiate. Skin aging is caused in part by TGF-β by blocking the conversion of dermal fibroblasts into fat cells which provide support. Common changes in the skin as a result of aging range from wrinkles, discoloration, and skin laxity, but can manifest in more severe forms such as skin malignancies. Moreover, these factors may be worsened by sun exposure in a process known as photoaging.
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 separates and quantifies components in a liquid sample. It is used to check identity, purity, concentration, or stability. The technique works best for compounds that dissolve and are not easily vaporized.