Stationary phase raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-01-09 and is reviewed periodically as new material appears.
HPLC testing is not a single fixed procedure; it is a family of separation modes. Reversed-phase, normal-phase, ion-exchange, size-exclusion, and affinity chromatography each suit different analyte properties. Reversed-phase methods dominate because they handle many neutral and moderately polar compounds. Detection can be optical, electrochemical, or mass spectrometric, and the detector dictates what information is available. Coupling with mass spectrometry increases selectivity and enables identification when standards are unavailable. The technique cannot separate every mixture without adjustment.
HPLC testing is an analytical technique used to separate, identify, and quantify components in a liquid sample. It relies on a pressurized mobile phase that carries the sample through a column packed with stationary phase. Different compounds travel at different rates because of interactions with the stationary and mobile phases. The resulting signal versus time is a chromatogram. Peak position indicates identity under specified conditions, while peak area or height relates to amount.
Laboratories apply HPLC testing across pharmaceutical, food, environmental, and industrial chemistry. The method can measure active ingredients, impurities, additives, preservatives, and degradation products. Sample preparation often includes dilution, filtration, and sometimes extraction or derivatization. The choice of column, mobile phase, pH, temperature, and detector depends on the analytes and matrix. Results are compared with reference standards to assign identity and concentration. Method suitability is judged by resolution, precision, and accuracy.
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.
| Property | Value | Notes |
|---|---|---|
| Abbreviation | HPLC | Also called high-performance liquid chromatography |
| Separation mechanism | Differential partitioning | Compounds distribute between mobile and stationary phases |
| Typical column chemistry | C18 (octadecylsilane) | Used in reversed-phase separations |
| Typical detector | UV-Vis or photodiode array | Mass spectrometry is common for trace and confirmatory work |
| Typical particle size | 1.8–5 µm | Smaller particles require higher pressure and can improve speed |
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 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.
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.
Duke of Modena (Lord 1288, Duke 1452) and Reggio (nell'Emilia) (Lord 1289, Duke 1452) Duke of Ferrara (Lord 1264, Duke 1471–1597) Duke of La Mirandola (1710), Massa (1829) and Guastalla (1847) Prince of the Holy Roman Empire, Prince of Carpi (Count 1530, Prince 1535), Correggio (1635), San Martino in Rio (1752) and of Carrara (1829), Marquis of Montecchio (1597, marquessate in 1569), of Scandiano (1645) and La Concordia (1710) Count palatine of Novellara (1737) and Bagnolo (1737), Count of Jeno ed Avad (Hungary, 1726) Lord of Sassuolo (1373), San Martino in Spino (1710), Campogalliano (1752), Castellarano (1752), Rodeglia (1752), Ieno and San Cassiano
March 7, 2016: Law on the rights of foreigners in France; foreign women victims of violence more easily obtain residence permits. March 14, 2016: Law on child protection. April 13, 2016: Law strengthening the fight against the prostitution system and supporting sex workers; creation of an "exit from prostitution" program. August 8, 2016: Law on labor, modernizing social dialogue, and securing career paths; internal regulations must prohibit sexist behavior; legislative creation of the High Council for Professional Equality. October 7, 2016: Law for a digital republic; creation of the offense of sexual privacy violation (including "revenge porn"). November 18, 2016: Law modernizing justice in the 21st century; divorce by mutual consent no longer requires a judge but must involve lawyers and a notary. December 2, 2016: Social Security Financing Law for 2017, establishing the Agency for the Recovery of Unpaid Child Support. January 27, 2017: Law on equality and citizenship, prioritizing women at risk of forced marriage for social housing. February 27, 2017: Law reforming criminal statute of limitations; extension of limitation periods for offenses such as: moral harassment; death, rape or sexual assault threats; domestic violence; sexual assaults other than rape; further extensions for crimes such as rape, mutilating or permanently disabling domestic violence, murder, abduction, and imprisonment. March 20, 2017: Law extending the offense of obstructing abortion to new online practices (e.g., hindering access to information or the procedure itself).
== Bibliography == K.F. Warner, "Boning Lamb Cuts", Leaflet 74, U.S. Department of Agriculture, Bureau of Animal Industry, June 1931. full text. Bob Kennard, "Much ado about mutton". Ludlow: Merlin Unwin, 2014.
== Definition == Pressure is the amount of force applied perpendicular to the surface of an object per unit area. The symbol for it is p or P. The IUPAC recommendation for pressure is a lower-case p. However, upper-case P is widely used. The usage of P versus p depends upon the field in which one is working, on the nearby presence of other symbols for quantities such as power and momentum, and on writing style.
Druze leaders: The Sheikh al-'Aql, Hikmat al-Hijri, called on Druze fighters to "resist this brutal campaign by all available means", the main sheikh of the Druze in Israel, Muwaffaq Tarif, declared, "The eyes and hearts of the Israeli Druze community are focused on the suffering of the Druze villages around Damascus", although he distanced himself from al-Hijri. Supreme Alawite Islamic Council: The Sheikh Ghazal Ghazal, the leader of the Supreme Alawite Islamic Council, pointed to the attacks against churches and members of the Druze community, emphasizing that "the perpetrator is the same, and the blood is the same". He stated that what the Alawite community has suffered has also affected other sects. Saraya Ansar al-Sunnah: The group threatened on 15 July to expand its sectarian attacks to include the Druze community in Suwayda. Islamic State: Abu Hudhayfa's group, affiliated with ISIS, declared that the Druze "violated the honor of Sunni Muslims," and that the goal of the attack was to kill the "infidel Druze". Minbar Ansar Al-Rasoul: The group celebrated the "victory" of the Internal Security Forces over the Druze protesters in Jaramana.
Sources: en.wikipedia.org
Theranos claimed to have data verifying the accuracy and reliability of its tests that would be published. In February 2016, Theranos announced that it would permit the Cleveland Clinic to complete a validation study of its technology. In March 2016, a study authored by 13 scientists appeared in the Journal of Clinical Investigation, where it was stated that the company's blood test results were flagged "outside their normal range 1.6× more often than other testing services", that 68 percent of lab measurements evaluated "showed significant interservice variability", and that "lipid panel test results between Theranos and other clinical services" were "nonequivalent". In August 2016, the company introduced a new robotic capillary blood testing unit named "miniLab" at the 2016 annual meeting of the American Association for Clinical Chemistry, but did not present any data supporting the claimed abilities of the device. The miniLab was allegedly capable of carrying out a range of tests from a small amount of blood. After Theranos failed to address concerns that it exaggerated the capabilities of the miniLab, Walgreens withdrew from their partnership. It was later revealed that Theranos had voided two years of test results showing inaccuracies with the Edison technology.
== Contraindications == Contraindications of atenolol include sinus bradycardia, heart block greater than first degree, cardiogenic shock, and overt heart failure. There is no basis for use of atenolol in people with heart rate of lower than 50 bpm or systolic blood pressure of less than 100 mm Hg and hence these can be considered contraindications. It is also contraindicated in people with a history of hypersensitivity to atenolol or any of the drug product's other components.
Cooling preserves food by slowing down the growth and reproduction of microorganisms and the action of enzymes that causes the food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the Western world by allowing food such as fresh fruit, salads and dairy products to be stored safely for longer periods, particularly during warm weather. Before the era of mechanical refrigeration, cooling for food storage occurred in the forms of root cellars and iceboxes. Rural people often did their own ice cutting, whereas town and city dwellers often relied on the ice trade. Today, root cellaring remains popular among people who value various goals, including local food, heirloom crops, traditional home cooking techniques, family farming, frugality, self-sufficiency, organic farming, and others.
==== Insurance ==== The transgender population has faced an increased burden of disease due to the lack of gender affirming coverage by insurance. Compared to the cisgender population, the transgender community has a lower insurance rate and faces obstacles with insurance (both private and public) denying coverage for many of their healthcare needs. According to the United States Transgender Survey (USTC), 20% of the transgender community reported insurance coverage for gender affirming care being partially covered or not being covered at all. Without insurance coverage, the transgender community is left with numerous out of pocket costs. The lack of insurance coverage denies these patients their healthcare needs and creates financial insecurity. These challenges with insurance create a decrease in healthcare outreach by the transgender community due to the costs. According to the United States Transgender Survey (USTS), 37.6% of the transgender community reported missing or avoiding preventative screenings and healthcare visits due to the costs This creates an increased burden of disease, and statistics show a higher rate of mental health conditions, poor physical health, and respiratory conditions, such as asthma. Besides the toll on this community's health and financial stability, insurers also refuse to change their records to reflect the true nature of the patient. Many health insurance companies have refused to change the individual's name and gender on their records. This creates another obstacle for this community to receive care while feeling accepted.
Sources: en.wikipedia.org
== History == LAAM was approved in 1993 by the U.S. Food and Drug Administration for use in the treatment of opioid dependence. In 2001, LAAM was removed from the European market due to reports of life-threatening ventricular rhythm disorders. In 2003, Roxane Laboratories, Inc. discontinued Orlaam in the US.
Lemmon, well aware of Quaalude's public image problems, used advertisements in medical journals to urge physicians "not to permit the abuses of illegal users to deprive a legitimate patient of the drug". Lemmon also marketed a small quantity under another name, Mequin, so doctors could prescribe the drug without the negative connotations. The rights to Quaalude were held by the JB Roerig & Company division of Pfizer, before the drug was discontinued in the United States in 1985, mainly due to its psychological addictiveness, widespread abuse, and illegal recreational use. A 2024 Hungarian investigative documentary reported on large-scale production and sales of the drug by the Hungarian People's Republic to the United States in the 1970s and 1980s. It asserts that a Hungarian state-owned company utilized connections to Colombian drug cartels to facilitate the sale of extraordinary amounts to the United States.
The pituitary gland hangs from the base of the brain by the pituitary stalk, and is enclosed by bone. It consists of a hormone-producing glandular portion of the anterior pituitary and a neural portion of the posterior pituitary, which is an extension of the hypothalamus. The hypothalamus regulates the hormonal output of the anterior pituitary and creates two hormones that it exports to the posterior pituitary for storage and later release. Four of the six anterior pituitary hormones are tropic hormones that regulate the function of other endocrine organs. Most anterior pituitary hormones exhibit a diurnal rhythm of release, which is subject to modification by stimuli influencing the hypothalamus. Somatotropic hormone or growth hormone (GH) is an anabolic hormone that stimulates the growth of all body tissues especially skeletal muscle and bone. It may act directly, or indirectly via insulin-like growth factors (IGFs). GH mobilizes fats, stimulates protein synthesis, and inhibits glucose uptake and metabolism. Secretion is regulated by growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH), or somatostatin. Hypersecretion causes gigantism in children and acromegaly in adults; hyposecretion in children causes pituitary dwarfism. Thyroid-stimulating hormone promotes normal development and activity of the thyroid gland. Thyrotropin-releasing hormone stimulates its release; negative feedback of thyroid hormone inhibits it. Adrenocorticotropic hormone stimulates the adrenal cortex to release corticosteroids.
==== Territories of the United States ==== Taco Bell operates several stores in Guam. Taco Bell operates one restaurant in the Northern Mariana Islands, located on the island of Saipan. In 2005 Taco Bell started the permitting process to set up a restaurant in American Samoa in Pago Pago. Taco Bell also operates stores in Puerto Rico.
Allylic, benzylic, and propargylic halides can also be coupled. While commonly employed, allylic halides proceed via an η3 transition state, allowing for coupling with the organostannane at either the α or γ position, occurring predominantly at the least substituted carbon (see example below). Alkenyl epoxides (adjacent epoxides and alkenes) can also undergo this same coupling through an η3 transition state as, opening the epoxide to an alcohol. While allylic and benzylic acetates are commonly used, propargylic acetates are unreactive with organostannanes.
Sources: en.wikipedia.org
It measures the presence and amount of one or more compounds in a liquid sample. Separation occurs in a column, and detection produces a signal proportional to concentration. Identification usually requires comparison with a known reference standard under the same conditions.
In most cases the sample is consumed or altered during analysis, though some detectors are non-destructive. Fractions can be collected after separation for further study. Repeated testing therefore requires additional sample.
Run times range from under a minute for fast methods to over an hour for complex separations. Sample preparation, equilibration, and data review add time. Throughput depends on instrument configuration and method requirements.
System suitability is a set of checks performed before and during a run to confirm that the instrument, column, and method work as expected. Common checks include resolution, tailing factor, theoretical plates, and relative standard deviation of replicate injections. Failure triggers troubleshooting or method adjustment.