This is a working overview of chromatogram, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2025-08-08. Anything still debated is marked as such rather than presented as settled.
Separation modes differ by the chemistry of the stationary phase and the composition of the mobile phase. Reversed-phase testing uses a nonpolar column and polar solvents, making it common for pharmaceutical, environmental, and food analytes. Normal-phase testing uses a polar column and nonpolar solvents for compounds that are poorly retained in reversed-phase systems. Ion-exchange and ion-pair methods separate charged species, while size-exclusion methods sort molecules by hydrodynamic volume. Gradient elution changes solvent strength over time to resolve complex mixtures, and isocratic elution holds solvent composition constant for simpler assays.
Key performance measures include retention time, peak area, peak height, resolution, tailing factor, and plate count. Retention time helps identify a peak under fixed conditions, but confirmation often requires a second method or detector. Peak area and height relate to concentration through calibration curves, which may be linear or nonlinear depending on the detector response. Resolution describes separation between adjacent peaks, while tailing factor and plate count describe peak shape and column efficiency. Performance checks verify these values before and during a run to confirm that the instrument is performing within limits.
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.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Common for polar and moderately polar analytes |
| Typical column length | 100-250 mm | Shorter columns can reduce run time |
| Particle size | 3-5 micrometers | Smaller particles improve efficiency but raise pressure |
| Flow rate | 0.5-2.0 mL/min | Depends on column dimensions and pressure limits |
| Detection | UV-Vis absorbance | Widely used for compounds with chromophores |
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.
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.
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.
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.
Gingival curettage is a surgical procedure designed to remove the soft tissue lining of the periodontal pocket with a curet, leaving only a gingival connective tissue lining. ... Gingival curettage, as originally conceived, was designed to promote new connective tissue attachment to the tooth, by the removal of pocket lining and junctional epithelium. Since there is no evidence that gingival curettage has any therapeutic benefit in the treatment of chronic periodontitis, the American Dental Association has deleted that code from the fourth edition of Current Dental Terminology (CDT-4). In addition, the American Academy of Periodontology, in its Guidelines for Periodontal Therapy, did not include gingival curettage as a method of treatment. This indicates that the dental community as a whole regards gingival curettage as a procedure with no clinical value. Curettage is also a major method used for removing osteoid osteoma and osteoblastoma. Curettage with subsequent culture is more accurate than ulcer base swan culture or aspiration and culture for diabetic foot ulcers. Curettage is also used when excising a chalazion of the eyelid.
An electronic cigarette (e-cigarette) or vape is a device that simulates tobacco smoking. It consists of an atomizer, a power source such as a battery, and a container such as a cartridge or tank. Instead of smoke, the user inhales vapor, often called "vaping". The atomizer is a heating element that vaporizes a liquid solution called e-liquid that cools into an aerosol of tiny droplets, vapor and air. The vapor mainly comprises propylene glycol or glycerin, usually with nicotine and flavoring. Its exact composition varies, and depends on matters such as user behavior. E-cigarettes are activated by taking a puff or pressing a button. Some look like traditional cigarettes, and most kinds are reusable. Vaping is less harmful than smoking, but still has health risks, particularly for those with asthma. Limited evidence indicates that e-cigarettes are less addictive than smoking, with slower nicotine absorption rates. E-cigarettes containing nicotine are more effective than nicotine replacement therapy (NRT) for smoking cessation, but have not been tested as rigorously as nicotine replacement therapy products.
Hundreds of thousands of people took part in the Moratorium to End the War in Vietnam demonstrations across the U.S. on a regular workday. Estimates of turnouts were 250,000 in Washington DC and 100,000 in Boston.
== Laboratory performance == Newborn screening programs participate in quality control programs as in any other laboratory, with some notable exceptions. Much of the success of newborn screening programs is dependent on the filter paper used for the collection of the samples. Initial studies using Robert Guthrie's test for PKU reported high false positive rates that were attributed to a poorly selected type of filter paper. This source of variation has been eliminated in most newborn screening programs through standardization of approved sources of filter paper for use in newborn screening programs. In most regions, the newborn screening card (which contains demographic information as well as attached filter paper for blood collection) is supplied by the organization carrying out the testing, to remove variations from this source.
Gavi's funding for this platform was conditional on the platform meeting vaccine coverage goals. As of the mid-2010s, few in Gavi were working on HSS, most of the former pro-HSS people had left, and some at Gavi dismissed HSS as PR to gain support from pro-HSS donors and counter criticisms that Gavi was harming healthcare systems. Such criticisms were generally not a topic that Gavi engaged with internally; the lack of internal engagement with the issue has been criticized. The disagreements were fairly intense; when Bill Gates came to visit Gavi headquarters, employees would hide the HSS-related posters so that he would not be reminded of this aspect of Gavi's work. Julian Lob-Levitt, who was Gavi's CEO between 2004 and 2010, was rumoured to have left over conflicts around his support for health system strengthening. Seth Berkley has been the CEO of Gavi since 2011, as of 2020. It has been argued that Gavi's HSS spending in the early 2010s went to selective, disease-specific interventions repackaged as HSS. Gavi's HSS support at this time tended to focus on immunisation strengthening support, especially the building of cold chains. Gavi measured HSS using vaccination coverage as the sole indicator. It set the reporting indicators which were required of recipients of its funding; countries were not allowed to use similar indicators they already collected; this has been criticized for conferring a heavy accounting burden and diverting attention from indigenous goals.
Sources: en.wikipedia.org
DiCaprio turned down the role of Anakin Skywalker in Star Wars: Episode II – Attack of the Clones (2002), feeling unprepared to "take that dive" at the time. His first film that year was the biopic Catch Me If You Can, based on the life of Frank Abagnale Jr., who before his 19th birthday committed check fraud to make millions in the 1960s. Directed by Steven Spielberg, the film was shot across 147 different locations in 52 days, making it "the most adventurous, super-charged movie-making" DiCaprio had experienced yet. The film received critical acclaim and grossed $355 million against a budget of $52 million, becoming his second highest-grossing release after Titanic. Roger Ebert praised his departure from dark and troubled characters, and two Entertainment Weekly critics in 2018 called it DiCaprio's best role, labeling him "delightfully persuasive, deceptive, flirtatious, and sometimes tragic—and we dare you to find a better role, if you can". DiCaprio received his third Golden Globe nomination for his performance in the film. Also in 2002, DiCaprio starred in Martin Scorsese's Gangs of New York, a historical drama set in the mid-19th century in the Five Points district of New York City. Scorsese initially struggled selling his idea of realizing the film until DiCaprio became interested in starring in the film, and thus Miramax Films got involved with financing the project. Nonetheless, production on the film was plagued by overshooting of budgets and producer-director disagreements, resulting in an eight-month shoot.
== Signs and symptoms == In one of the few reported cases, the subject presented with muscle weakness and fatigue, muscle twitching, excessive sweating and salivation, small joint pain, itching and weight loss. The subject also developed confusional episodes with spatial and temporal disorientation, visual and auditory hallucinations, complex behavior during sleep and progressive nocturnal insomnia associated with diurnal drowsiness. There was also severe constipation, urinary incontinence, and excessive lacrimation. When left alone, the subject would slowly lapse into a stuporous state with dreamlike episodes characterized by complex and quasi-purposeful gestures and movements (enacted dreams). Marked hyperhidrosis and excessive salivation were evident. Neurological examination disclosed diffuse muscle twitching and spontaneous and reflex myoclonus, slight muscle atrophy in the limbs, absence of tendon reflexes in the lower limbs and diffuse erythema especially on the trunk with scratching lesions of the skin. Compulsive behaviours, stereotypies and reduplicative paramnesias can be part of the CNS spectrum.
An alternative to solvent-based extraction for particulates on filters is the use of thermal extraction (TE)-GC/MS, which utilizes oven interfaced with the GC inlet to vaporize the analyte of the sample and into the GC inlet. This technique is more often used then solvent-based extraction, because of its better sensitivity, eliminates need for solvents, and can be fully automated. To increase the separation of the particles the GC can be coupled with a time of flight (TOF)-MS, which is a mass separation method that separates ions based on their size. Another method that utilizes EI is isotope ratio mass spectrometry (IR-MS) this instrumentation incorporates a magnetic sector analyzer and a faraday-collector detector array and separates ions based on their isotopic abundance. Isotopic abundance of carbon, hydrogen, nitrogen, and oxygen isotopic abundance become locally enriched or depleted through a variety of atmospheric processes. This information helps in determining the source of the aerosols and the interaction it has had. EI is a universal ionization method, but it does cause excessive fragmentation, and thus can be substituted with chemical ionization (CI) which is a much softer ionization method, and is often used to determine the molecular ion. One ionization method the utilizes CI is atmospheric-pressure chemical ionization (APCI).
== Domestic types == Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest is a 4-litre (0.14 cu ft) Peltier refrigerator advertised as being able to hold 6 cans of beer. A large domestic refrigerator stands as tall as a person and may be about 1 metre (3.3 ft) wide with a capacity of 600 litres (21 cu ft). Some models for small households fit under kitchen work surfaces, usually about 86 centimetres (34 in) high. Refrigerators may be combined with freezers, either stacked with refrigerator or freezer above, below, or side by side. A refrigerator without a frozen food storage compartment may have a small section just to make ice cubes. Freezers may have drawers to store food in, or they may have no divisions (chest freezers). Refrigerators and freezers may be free-standing, or built into a kitchen's cabinet. Three distinct classes of refrigerator are common:
Sources: en.wikipedia.org
It measures the amounts and identities of compounds in liquid samples by separation and detection. Depending on the detector and reference standards, results can be qualitative or quantitative. The technique is used in fields such as pharmaceutical analysis, food safety, and environmental monitoring.
Performance checks confirm that the chromatographic system works within preset limits before results are accepted. They examine factors such as peak resolution, tailing, and repeatability. If criteria fail, the run may need correction or repetition.
Retention time alone is not definitive proof because other compounds can elute at similar times. Confirmation usually uses a second method, a different column, or a detector such as mass spectrometry. Authentic standards strengthen identification.
System suitability is a set of checks performed before and during an HPLC run to confirm that the instrument and method are working as expected. It may include retention time repeatability, resolution between peaks, peak symmetry, and signal intensity. Failing suitability criteria usually invalidates the run.