Everything below concerns stationary phase. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2025-12-14. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Typical checks include retention time, peak area precision, resolution between critical pairs, tailing factor, and theoretical plate count. Acceptance criteria are set in the method or pharmacopeial monograph. If a suitability check fails, the run may be rejected and the instrument or sample preparation may need investigation. This practice helps prevent release of data from a system that has drifted out of control.
Quality control samples are inserted at intervals to monitor accuracy and precision throughout a batch. Blank samples detect contamination, while spiked samples assess recovery from the sample matrix. Calibration standards establish the relationship between detector response and concentration, and control samples are prepared independently from them whenever possible. Laboratories also participate in proficiency testing and maintain audit trails, instrument logs, and reagent records. Ongoing review of control charts can reveal trends before they cause out-of-specification results.
Method validation demonstrates that an HPLC procedure is suitable for its intended purpose. Common validation parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, and robustness. Accuracy reflects agreement with a reference value, while precision describes repeatability under defined conditions. Specificity shows whether the method can measure the analyte in the presence of impurities or matrix components. Validation documents are reviewed before a method is used for routine testing or regulatory submissions.
| 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 |
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Method validation establishes that an HPLC procedure is suitable for its intended use. Key parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Accuracy measures agreement with a true or accepted value, while precision describes repeatability and intermediate precision. Specificity confirms that the method measures the analyte without interference from impurities, degradants, or excipients. Validation is documented in a protocol and report, and acceptance criteria are set before experiments begin. Regulatory guidance varies by region, but the general principles are widely harmonized.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
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.
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 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.
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.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
Routine quality control includes blanks, duplicates, spiked samples, and certified reference materials. Calibration curves are prepared with standards at several concentrations, and the detector response is checked for linearity. Carryover, column aging, mobile phase evaporation, and temperature drift can shift retention times or peak areas. Maintenance such as replacing seals, filters, and columns helps prevent failures. Records of injections, integration, and deviations support traceability. Audits may request raw data and instrument logs for each batch.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
== Further reading == Lin, Y.; Zou, J.; Yang, W.; Li, C. Q. (2018). "A Review of Recent Advances in Research on PM2.5 in China". International Journal of Environmental Research and Public Health. 15 (3): 438. Bibcode:2018IJERP..15..438L. doi:10.3390/ijerph15030438. PMC 5876983. PMID 29498704. Abdel Hameed, A. A.; Yasser, I. H.; Khoder, I. M. (2004). "Indoor air quality during renovation actions: a case study". Journal of Environmental Monitoring. 6 (9): 740–744. Bibcode:2004JEnMo...6..740A. doi:10.1039/b402995j. PMID 15346177.
=== Olympics === There were concerns dairy products consumed during the 2008 Summer Olympics may have been contaminated. Li Changjiang, the then Director of AQSIQ reassured the international community that all the food, including dairy products, was indeed safe. "We took special quality management measures aimed at food supply for the Games."
in the bond orders within the rings, in the number of methyl groups attached to the ring (and, when present, on the prominent side chain at C17), in the functional groups attached to the rings and side chain, and in the configuration of groups attached to the rings and chain. For instance, sterols such as cholesterol and lanosterol have a hydroxyl group attached at position C-3, while testosterone and progesterone have a carbonyl (oxo substituent) at C-3. Among these compounds, only lanosterol has two methyl groups at C-4. Cholesterol which has a C-5 to C-6 double bond, differs from testosterone and progesterone which have a C-4 to C-5 double bond.
==== Fat ==== Until approximately one year of age, kittens are in a growth phase during which energy requirements can be up to 2.5 times higher than maintenance. Pet nutritionists often suggest offering a commercial cat food designed specifically for kittens starting at four weeks of age. Fat has a higher caloric value than carbohydrates and protein, supplying 9 kcal/g. The growing kitten requires arachidonic and linoleic acid, which can be provided in omega−3 fatty acids. Docosahexaenoic acid (DHA) is another vital nutrient that can be supplied through omega−3 fatty acids. Addition of DHA to the diet benefits the cognition, brain, and visual development of kittens.
Sources: en.wikipedia.org
=== 2016: Court of Arbitration for Sport verdict === On 12 January 2016, CAS handed down a guilty verdict on the thirty-four Essendon players, overturning the AFL Anti-Doping Tribunal's not-guilty verdict, after finding it was comfortably satisfied that the players were injected with Thymosin beta-4. Key to the appeal's success was the treatment of evidence: the CAS rejected the AFL Tribunal's approach, known as "links in the chain", where any individual chain of evidence is dismissed if any one link within it cannot be proven, and endorsed WADA's approach, known as "strands in the cable", where individual evidence chains with missing links may still be accepted if the combination of all such chains forms a sufficiently strong case. A complete account of the verdict and the arguments made by each side was released publicly. Vital to the case was determining whether or not the unspecified Thymosin used in the program was the banned Thymosin Beta-4 or a different, legal variety of Thymosin. A paper trail had confirmed that Dank had been dispensed Thymosin Beta-4 by the Como Compounding Pharmacy; however, no direct evidence was found that it was this Thymosin rather than a different legal Thymosin which had been administered to players, and this missing evidence link had been key to the AFL Tribunal's not guilty verdict under the 'links in the chain' method.
== Further reading == Martin, Christopher S.; Chung, Tammy; Langenbucher, James W. (2017). "Part 1: Defining and Characterizing the Nature and Extent of Substance Use Disorders – Historical and Cultural Perspectives on Substance Use and Substance Use Disorders". In Sher, Kenneth J. (ed.). The Oxford Handbook of Substance Use and Substance Use Disorders: Volume 1. Oxford Library of Psychology. Oxford and New York: Oxford University Press. pp. 27–59. doi:10.1093/oxfordhb/9780199381678.013.001. ISBN 978-0-19-938167-8. LCCN 2016020729. Anthony, James; Barondess, David A.; Radovanovic, Mirjana; Lopez-Quintero, Catalina (2017). "Part 1: Psychiatric Comorbidity – Polydrug Use: Research Topics and Issues". In Sher, Kenneth J. (ed.). The Oxford Handbook of Substance Use and Substance Use Disorders: Volume 2. Oxford Library of Psychology. Oxford and New York: Oxford University Press. pp. 27–59. doi:10.1093/oxfordhb/9780199381708.013.006. ISBN 978-0-19-938170-8. LCCN 2016020729. Hernández-Serrano, Olga; Gras, Maria E.; Font-Mayolas, Sílvia; Sullman, Mark J. M. (2016). "Part VI: Dual and Polydrug Abuse – Chapter 83: Types of Polydrug Usage". In Preedy, Victor R. (ed.). Neuropathology of Drug Addictions and Substance Misuse, Volume 3: General Processes and Mechanisms, Prescription Medications, Caffeine and Areca, Polydrug Misuse, Emerging Addictions and Non-Drug Addictions. Cambridge, Massachusetts: Academic Press, imprint of Elsevier. pp. 839–849. doi:10.1016/B978-0-12-800634-4.00083-4. ISBN 978-0-12-800634-4.
=== Fire hazards === Like other organic compounds, polystyrene is flammable. Polystyrene is classified according to DIN4102 as a "B3" product, meaning highly flammable or "Easily Ignited". As a consequence, although it is an efficient insulator at low temperatures, its use is prohibited in any exposed installations in building construction. It must be concealed behind drywall, sheet metal, or concrete. Foamed polystyrene plastic materials have been accidentally ignited and caused huge fires and losses of life, for example at the Düsseldorf International Airport and in the Channel Tunnel (where polystyrene was inside a railway carriage that caught fire).
== Genetics == In terms of the genetics of UCMD1, there are mutations in the genes COL6A1, COL6A2, and COL6A3. This sub-type of muscular dystrophy is both autosomal recessive and autosomal dominant in nature. COL6A1 plays an important part in maintaining the human body's integrity of various tissues. Alpha 1 subunit of type VI collagen is the encoded protein. In terms of the genetics of UCMD2, there are mutations in the gene COL12A1, and is autosomal recessive. Collagen VI is a principal structural component of the extracellular matrix (ECM), where it self-assembles into a distinct microfibrillar network that links the muscle fiber's basal lamina to the surrounding interstitial matrix, thereby anchoring muscle cells to the ECM. Mutations in COL6A1, COL6A2, and COL6A3 impair the proper assembly, secretion, or incorporation of collagen VI microfibrils into the ECM, disrupting its structural integrity and contributing to the muscle-fiber degeneration observed in UCMD.
In contrast to mirtazapine, the selective serotonin reuptake inhibitors, serotonin–norepinephrine reuptake inhibitors, monoamine oxidase inhibitors, and some tricyclic antidepressants acutely increase the general activity of the 5-HT2A, 5-HT2C, and 5-HT3 receptors, leading to a number of negative changes and side effects, the most prominent of which include anorexia, insomnia, nausea, and diarrhea, among others. However, most of these adverse effects are temporary, since down regulation of 5-HT2A receptors eventually occurs following chronic SSRI treatment, and desensitization of 5-HT3 receptors often occurs within a week or less. This is precisely why SSRIs have a delayed antidepressant and anxiolytic effect, and occasionally, an acute anxiogenic effect before down regulation occurs. Mirtazapine, on the other hand, is an antagonist of the 5-HT2A receptor, and antagonists at this receptor typically induce reverse tolerance. Thus, the antidepressant and anxiolytic effects of mirtazapine occur more rapidly than with SSRIs. Furthermore, its reduced incidence of sexual dysfunction (such as loss of libido and anorgasmia) could be a product of negligible binding to the serotonin transporter and antagonism of the 5-HT2A receptors; however, Mirtazapine's high affinity towards and inverse agonism of the 5-HT2C receptors may greatly attenuate those pro-sexual factors (as evidenced by the pro-sexual effects of drugs like m-CPP and lorcaserin which agonize 5-HT2C receptors in a reasonably selective manner).
Sources: en.wikipedia.org
=== Pasteurized donkey milk === Donkey milk is pasteurized in a closed circuit of pasteurization and bottling (aseptic) at least 72 °C for 15 seconds or equivalent times and temperatures. In the case of pasteurization in discontinuous systems, the temperature must be higher depending on the method used and the type of plant and destination.
"In the period 1821–1822, the liberator José de San Martín and Bernardo Monteagudo, his trusted minister, expropriated and squandered the mercantile and economic elite of Lima, without achieving the definitive independence of Peru. Monteagudo had little regard for the level of civilization and the democratic possibilities of Peruvians. His main objective was to eradicate the Spanish threat in independent La Plata and Chile at any cost, including the economic ruin of Peru. He confiscated wealth and other resources to organize local spy networks and covert operations, clearly damaging to gaining the confidence of the local population and their support for the cause of independence. (…) The kidnapping policy inaugurated by Monteagudo further undermined a weak tradition of the right to property and laid the foundations for politically motivated expropriations. The agricultural and urban properties confiscated from royalist Spaniards and Creoles, mainly in the central coast region, were valued at approximately two million pesos. This policy caused greater economic problems and a drop in investment. (...) Eventually, most of the expropriated assets were awarded to military officers who sought compensation and rewards for their patriotic exploits. Among the high-ranking officers who received these rewards we have Antonio José de Sucre, Bernardo O'Higgins, and José Rufino Echenique. Juan Francisco Ryes, Blas Sardeña and José María Plaza, among others. In the provinces, local officials repeated the abuses of power and the plundering committed in the name of the patriot cause.
Venous ulcer is defined by the American Venous Forum as "a full-thickness defect of skin, most frequently in the ankle region, that fails to heal spontaneously and is sustained by chronic venous disease, based on venous duplex ultrasound testing." Venous ulcers are wounds that are thought to occur due to improper functioning of venous valves, usually of the legs (hence leg ulcers). They are an important cause of chronic wounds, affecting 1% of the population. Venous ulcers develop mostly along the medial distal leg, and can be painful with negative effects on quality of life. Exercise, together with compression stockings, increases healing. The NICE guideline recommends that everyone with a venous leg ulcer, even if healed, should be referred to a vascular specialist for venous duplex ultrasound and assessment for endovenous surgery.
TDL Group recorded $1.48 billion in sales in 2005. Tim Hortons also operates locations on Canadian and American university campuses, including Brock University, Durham College, Georgian College, Algonquin College, Canisius College, York University, Toronto Metropolitan University, University at Buffalo, SUNY Plattsburgh, University of British Columbia, Memorial University of Newfoundland, University of Western Ontario, and Simon Fraser University. In March 2010, Tim Hortons announced further expansion on both sides of the Canada–US border to be completed by 2013. The plan called for 600 new stores in Canada (primarily in Quebec and Western Canada but also including smaller communities) and 300 new stores in the U.S. (primarily in its existing markets of Michigan, New York, and Ohio). It also called for expansion into such non-standard store locations as hospitals, universities, and airports, as well as extending its co-branding initiative with U.S. ice cream chain Cold Stone Creamery, which began in 2009, to cover 60 Canadian stores and 25 to 35 new and existing U.S. stores. It also included testing a new café/bake shop concept in at least 10 existing U.S. locations, including "enhanced finishes, fixtures, and seating areas" as well as an expansion of menu offerings. In 2010, Tim Hortons opened what were then its northernmost locations: three kiosks at NorthMart stores in Iqaluit, Nunavut. This expanded Tim Hortons' presence in every province and territory of Canada.
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 showing that an HPLC procedure produces reliable results for a defined purpose. It examines parameters such as accuracy, precision, specificity, linearity, and robustness. Regulators and quality systems often require validation before routine use.