mobile phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-06-01. Anything still debated is marked as such rather than presented as settled.
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.
Several separation modes exist, including reversed-phase, normal-phase, ion-exchange, size-exclusion, and hydrophilic interaction liquid chromatography. Reversed-phase uses a nonpolar stationary phase with a polar mobile phase and is widely applied to small organic molecules. Gradient elution changes mobile phase composition during the run, while isocratic elution keeps it constant. Column chemistry, particle size, temperature, flow rate, and mobile phase pH all influence retention and resolution. Method development selects conditions that separate analytes from matrix components and from each other.
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.
| 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 |
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
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.
The analytes are in the vapor phase. This includes breath, odors, VOCs, and other molecules with low volatility that, due to the constant improvements in sensitivity, are detectable in the vapor phase despite their low vapor pressure. Analyte ions are produced via gas-phase chemical reactions, where charging agents collide with the analyte molecules and transfer their charge. In secondary electro-spray ionization (SESI), a nano-electrospray operated at high temperature produces nanodroplets that evaporate very rapidly to produce ions and protonated water clusters that ionize the vapors of interest. SESI is commonly used for the analysis of trace concentrations of vapors being able to detect low volatility species in the gas phase with molecular masses of up to 700 Da.
2,5-DKPs are synthesized by a variety of organisms including humans. In general, they arise by the action of a tRNA-dependent cyclodipeptide synthases, a type of enzyme responsible for creating a cyclic amide linkage between two peptides. The enzymes cyclodipeptide oxidase and S-adenosyl-methionine-dependent O/N methyltransferases act in tandem to chemically modify cyclic dipeptides. 2,5-Diketopiperazines are typically prepared by one of three methods: amide bond formation, N-alkylation and C-acylation.
Acetylcysteine or N-acetylcysteine (NAC) is a mucolytic that is used to treat paracetamol (acetaminophen) overdose and to loosen thick mucus in individuals with chronic bronchopulmonary disorders, such as pneumonia and bronchitis. It has been used to treat lactobezoar in infants. It can be taken intravenously, orally (swallowed by mouth), or by inhalation by use of a nebulizer. It is also sometimes used as a dietary supplement. Common side effects include nausea and vomiting when taken orally. The skin may occasionally become red and itchy with any route of administration. A non-immune type of anaphylaxis may also occur. It appears to be safe in pregnancy. For paracetamol overdose, it works by increasing the level of glutathione, an antioxidant that can neutralize the toxic breakdown products of paracetamol. When inhaled, it acts as a mucolytic by decreasing the thickness of mucus. Acetylcysteine was initially patented in 1960 and came into medical use in 1968. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication.
March 12 – 17: 2018 Youth Pan American Championships (Men) in Guadalajara In the final, Argentina defeated Mexico, 3–2. Canada took third place and Paraguay took fourth place. March 12 – 17: 2018 Youth Pan American Championships (Women) in Guadalajara In the final, Argentina defeated Uruguay, 4–0. Mexico took third place and Paraguay took fourth place. May 13 – 20: 2018 Asian Women's Hockey Champions Trophy in Donghae City South Korea defeated India, 1–0, to win their third Asian Women's Hockey Champions Trophy title. China took third place. October 18 – 28: 2018 Asian Men's Hockey Champions Trophy in Muscat Note: Due to heavy rain, both India and Pakistan took first place here. Malaysia took third place. July 11 – 15: IFA 2018 Fistball U18 World Championships in Roxbury Township July 24 – 28: IFA 2018 Fistball Women's World Championship in Linz
Sources: en.wikipedia.org
In many organisms including Xenopus and Drosophila, the midblastula transition usually occurs after a particular number of cell divisions for a given species, and is defined by the ending of the synchronous cell division cycles of the early blastula development, and the lengthening of the cell cycles by the addition of the G1 and G2 phases. Prior to this transition, cleavage occurs with only the synthesis and mitosis phases of the cell cycle. The addition of the two growth phases into the cell cycle allows for the cells to increase in size, as up to this point the blastomeres undergo reductive divisions in which the overall size of the embryo does not increase, but more cells are created. This transition begins the growth in size of the organism. The mid-blastula transition is also characterized by a marked increase in transcription of new, non-maternal mRNA transcribed from the genome of the organism. Large amounts of the maternal mRNA are destroyed at this point, either by proteins such as SMAUG in Drosophila or by microRNA. These two processes shift the control of the embryo from the maternal mRNA to the nuclei.
APHL works with public health partners to build the foundation for quality testing, comprehensive standards and integrated public health laboratory systems. One of the initiatives, the Laboratory System Improvement Program, provides individual assessments of public health laboratory systems that include engaging stakeholders for system improvement, performance, implementation of strategies and continual evaluation. APHL also collaborates on the National Laboratory System project to build a public-private network of laboratories nationwide. APHL monitors trends in public health laboratory diagnostics, personnel and infrastructure in order to create quality assurance standards. By using these data points to benchmark individual labs against national norms, APHL is able to home in on key issues and help raise the standard of laboratory systems. Member labs have access to research and survey data online, which enables them to leverage new information quickly to identify promising strategies and practices.
It is thought that high glucagon levels and lack of insulin production are the main triggers for the metabolic issues associated with Type I diabetes, in particular maintaining normal blood glucose levels, formation of ketone bodies, and formation of urea. One finding of note is that the glucagon response to hypoglycemia is completely absent in patients with Type I diabetes. Consistently high glucagon concentrations in the blood can lead to diabetic ketoacidosis, which is when ketones from lipid breakdown build up in the blood, which can lead to dangerously low blood glucose levels, low potassium levels, and in extreme cases cerebral edema. It has been proposed that the reason for the high levels of glucagon found in the plasma of patients with Type I diabetes is the absence of beta cells producing insulin and the reciprocal effect this has on delta cells and the secretion of somatostatin.
Adenomatous polyposis coli protein 2 is a protein that in humans is encoded by the APC2 gene. This is a dual-functional protein which is especially prevalant in the developing brain, and involved in cell signaling (specifically Wnt signaling) and stabilizing the cytoskeleton. Frizzled receptors are a type of cell receptor involved in a variety of functions including embryonic development and cell proliferation. These receptors trigger a cascade of reactions called the Wnt signaling pathway that eventually leads to interaction with the DNA via the protein beta-catenin, which affects which proteins get produced by the cell. The APC2 protein promotes the formation of a protein complex which is involved in breaking down the protein beta-catenin. The APC2 protein stabilizes microtubules, which are part of the cell cytoskeleton. It may also be involved in the regulation of actin fibers my means of GTPase activation (specifically the Rho family).
In 1884, Svante Arrhenius attributed the properties of acidity to hydrogen cations (H+), later described as protons or hydrons. An Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in the water. Chemists often write H+(aq) and refer to the hydrogen cation when describing acid–base reactions but the free hydrogen nucleus, a proton, does not exist alone in water, it exists as the hydronium ion (H3O+) or other forms (H5O2+, H9O4+). Thus, an Arrhenius acid can also be described as a substance that increases the concentration of hydronium ions when added to water. Examples include molecular substances such as hydrogen chloride and acetic acid. An Arrhenius base, on the other hand, is a substance that increases the concentration of hydroxide (OH−) ions when dissolved in water. This decreases the concentration of hydronium because the ions react to form H2O molecules:
Sources: en.wikipedia.org
Amylin, or islet amyloid polypeptide (IAPP), is a 37-residue peptide hormone. It is co-secreted with insulin from the pancreatic β-cells in the ratio of approximately 100:1 (insulin:amylin). Amylin plays a role in glycemic regulation by slowing gastric emptying and promoting satiety, thereby preventing spikes in blood glucose levels after a meal. IAPP is processed from an 89-residue coding sequence. Proislet amyloid polypeptide (proIAPP, proamylin, proislet protein) is produced in the pancreatic beta cells (β-cells) as a 67 amino acid, 7404 Dalton pro-peptide and undergoes post-translational modifications including protease cleavage to produce amylin.
Altria, like other tobacco companies, has invested in science and medical companies which develop and produce medical products for conditions caused or aggravated by smoking. As of 2024, Altria's three medical subsidiaries included the following: Cronos group (maker of recreational cannabis), Lexaria Bioscience (Developer of proprietary drug delivery technology, DehydraTECH, to improve active pharmaceutical ingredients entrance into the bloodstream) and Micreos (biotech company focused on discovering and developing recombinant proteins for chronic dermatology and oncology conditions). It has also designed and marketed electronic cigarettes. Altria launched the MarkTen and Green Smoke brands. Both of these were discontinued in December 2018. The company returned to this market through the acquisition of NJOY.
Albumins found in animals can be divided into six subfamilies by phylogeny. The Vitamin-D binding proteins occupy families 1–3. The other albumins are mixed among each other in families 4–6. ECM1 is in family 6. In addition to their medical use, serum albumins are valued in biotechnology. Bovine serum albumin is usually used, although versions from humans and genetically modified rice are also used to reduce animal cruelty. A few other proteins are also sometimes called albumins. They are not in the same family as vertebrate albumins: Ovalbumin is a storage protein in egg white (albumen). It is a serpin. Lactalbumin, or whey protein, is a protein fraction of milk. It is mainly Beta-lactoglobulin, although serum albumin also comprises a small part of it. Some plant seeds, including hemp, encode "2S albumins". These are named for their egg-like coagulation property.
In the anterior pituitary, the term "acidophil" is used to describe two different types of cells which stain well with acidic dyes. Somatotrophs, which secrete growth hormone (a peptide hormone) Lactotrophs, which secrete prolactin (a peptide hormone) When using standard staining techniques, they cannot be distinguished from each other (though they can be distinguished from basophils and chromophobes), and are therefore identified simply as "acidophils". Eosinophilic Acidophile (histology) Basophilic Chromophobe cell Melanotroph Chromophil Basophil cell Oxyphil cell Oxyphil cell (parathyroid) Pituitary gland Neuroendocrine cell
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.
HPLC separates and quantifies compounds in a liquid sample. Detectors produce a response proportional to the amount of a compound passing through the flow cell. Identification by retention time requires comparison with a known standard.