If you have been reading about Chromatogram and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-07-31. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| 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 |
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.
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.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. UV detection is widely used because many organic compounds absorb light, but it requires a chromophore. Mass spectrometry provides mass-based identification and high sensitivity for trace analytes. Each detector has trade-offs in selectivity, cost, and compatibility with mobile phases. Quantification typically uses calibration curves prepared from reference standards. Results are reported as concentration, purity, or presence above a limit.
HPLC testing separates dissolved compounds by passing a liquid sample through a column packed with stationary phase. A pump delivers mobile phase at controlled flow, and the sample components interact differently with stationary and mobile phases. Compounds that spend more time in mobile phase elute earlier; those retained by stationary phase elute later. Detectors record elution as peaks, and peak area or height relates to amount. This mechanism underpins quantitative analysis of mixtures.
== Background == The value of urine for diagnostic purposes has been recognized since ancient times. Urine examination was practiced in Sumer and Babylonia as early as 4000 BC, and is described in ancient Greek and Sanskrit texts. Contemporary urine testing uses a range of methods to investigate the physical and biochemical properties of the urine. For instance, the results of the routine urinalysis can provide information about the functioning of the kidneys and urinary system; suggest the presence of a urinary tract infection (UTI); and screen for possible diabetes or liver disease, among other conditions. A urine culture can be performed to identify the bacterial species involved in a UTI. Simple point-of-care tests can detect pregnancy by identifying the presence of beta-hCG in the urine and indicate the use of recreational drugs by detecting excreted drugs or their metabolites. Analysis of abnormal cells in urine (urine cytology) can help to diagnose some cancers, and testing for organic acids or amino acids in urine can be used to screen for some genetic disorders.
All adenosine receptor subtypes (A1, A2A, A2B, and A3) are G-protein-coupled receptors. The four receptor subtypes are further classified based on their ability to either stimulate or inhibit adenylate cyclase activity. The A1 receptors couple to Gi/o and decrease cAMP levels, while the A2 adenosine receptors couple to Gs, which stimulates adenylate cyclase activity. In addition, A1 receptors couple to Go, which has been reported to mediate adenosine inhibition of Ca2+ conductance, whereas A2B and A3 receptors also couple to Gq and stimulate phospholipase activity. Researchers at Cornell University have recently shown adenosine receptors to be key in opening the blood-brain barrier (BBB). Mice dosed with adenosine have shown increased transport across the BBB of amyloid plaque antibodies and prodrugs associated with Parkinson's disease, Alzheimer's, multiple sclerosis, and cancers of the central nervous system.
On April 11, 2018, Starbucks began operations in Uruguay, with a location in the Montevideo Shopping mall. The company announced that it planned to open up approximately 12 cafes in the country. In August 2019, a franchised location opened in the Cayman Islands. In October 2019, a franchised location opened in the Turks and Caicos Islands. On April 25, 2023, Starbucks commenced operations in Guyana. On April 29, 2024, Starbucks announced its official entry to Ecuador and Honduras in mid-year and late 2024, respectively. On August 14, 2024, Starbucks commenced operations in Ecuador, with its first location in the country at Scala Shopping Mall in Quito. The company announced the plans of opening four more cafes in the capital city until the end of 2025. In July 2026, Starbucks opened its first location in Guayaquil, and now has 10 stores across the country.
which can be further processed to calculate the enthalpy of metal-ligand interaction. Although this example is between a metal and a ligand, it is applicable to any ITC experiment, regarding binding interactions. As a part of the analysis, a number of protons are required to calculate the solvent-independent thermodynamics. This can be easily done by plotting a graph such as shown below.
=== IPCC findings === Following an investigation, the Independent Police Complaints Commission (IPCC) released a report, dated 3 June 2010, into the actions of the Metropolitan Police Force and their handling of the murder investigation. It described a "catalogue of bad decisions and errors" by the Metropolitan Police which had resulted in Napper being free to kill Nickell. It said that officers missed a series of opportunities to take him off the streets and suggested the lives of Samantha Bisset and her four-year-old daughter, Jazmine, would also have been saved if police had acted on tip-offs, including one by Napper's mother. Rachel Cerfontyne, an IPCC commissioner, said that police failed to investigate the 1989 report that he attacked a woman on Plumstead Common in London and no record of the telephone call can be found. She said, "It is clear that throughout the investigations into the 'Green Chain' rapes and Rachel Nickell's death there was a catalogue of bad decisions and errors made by the Metropolitan Police. The police failed to sufficiently investigate after Napper's mother called police to report that he had confessed to her that he had raped a woman and, inconceivably, they eliminated Napper from inquiries into the Green Chain rapes because he was over 6 feet tall. Without these errors, Robert Napper could have been off the streets before he killed Rachel Nickell and the Bissets, and before numerous women suffered violent sexual attacks at his hands". Detectives had decided to exclude anyone over 6 feet based on the description of a 5' 7" rapist.
Sources: en.wikipedia.org
=== Other === AMH production by the Sertoli cells of the testes remains high throughout childhood in males but declines to low levels during puberty and adult life. AMH has been shown to regulate production of sex hormones, and changing AMH levels (rising in females, falling in males) may be involved in the onset of puberty in both sexes. Functional AMH receptors have also been found to be expressed in neurons in the brains of embryonic mice, and are thought to play a role in sexually dimorphic brain development and consequent development of gender-specific behaviours. In a clade of Sebastes rockfishes in the Northwest Pacific Ocean, a duplicated copy of the AMH gene (called AMHY) is the master sex-determining gene. In vitro experiments demonstrate that the overexpression of AMHY causes female-to-male sex reversal in at least one species, S. schlegelii.
Anti-drug antibodies can cause negative side effects, accelerate the rate of drug clearance, and reduce the therapeutic effects of the biologic. In clinical practice, less than 50% of patients who showed an initial positive response to biological therapy were in remission after one year. The development of anti-drug antibodies can be reduced by limiting any times when there is no biologic present in the body and by taking other immunosuppressants (such as thiopurines or methotrexate) in combination.
human: Cys-Gly-Asn-Leu-Ser-Thr-Cys-Met-Leu-Gly-Thr-Tyr-Thr-Gln-Asp-Phe-Asn-Lys-Phe-His-Thr-Phe-Pro-Gln-Thr-Ala-Ile-Gly-Val-Gly-Ala-Pro Compared to salmon calcitonin, human calcitonin differs at 16 residues.
Jaw joint – The dentary (the lower jaw bone, which carries the teeth) and the squamosal (a small cranial bone) meet to form the joint. In most gnathostomes, including early therapsids, the joint consists of the articular (a small bone at the back of the lower jaw) and quadrate (a small bone at the back of the upper jaw). Middle ear – In crown-group mammals, sound is carried from the eardrum by a chain of three bones, the malleus, the incus and the stapes. Ancestrally, the malleus and the incus are derived from the articular and the quadrate bones that constituted the jaw joint of early therapsids. Tooth replacement – Teeth can be replaced once (diphyodonty) or (as in toothed whales and murid rodents) not at all (monophyodonty). Elephants, manatees, and kangaroos continually grow new teeth throughout their life (polyphyodonty). Prismatic enamel – The enamel coating on the surface of a tooth consists of prisms, solid, rod-like structures extending from the dentin to the tooth's surface. Occipital condyles – Two knobs at the base of the skull fit into the topmost neck vertebra; most other tetrapods, in contrast, have only one such knob. For the most part, these characteristics were not present in the Triassic ancestors of the mammals. Nearly all mammaliaforms possess an epipubic bone, the exception being modern placentals.
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.
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.