Method validation 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 2026-05-31 and is reviewed periodically as new material appears.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness to a reference value. |
| Validation parameter | Precision | Repeatability or intermediate precision. |
| Validation parameter | Linearity | Proportional response across a range. |
| System suitability check | Resolution | Separation between adjacent peaks. |
| Quality control tool | Control chart | Tracks results over time for trends. |
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.
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.
High-performance liquid chromatography testing separates components of a liquid sample by forcing a mobile phase through a packed column. The stationary phase inside the column interacts with analytes to different degrees, so each compound exits at a characteristic retention time. A pump delivers solvent at controlled flow and pressure, while an injector introduces a precise sample volume. Detectors such as ultraviolet-visible, fluorescence, refractive index, or mass spectrometric instruments record the separated bands. The resulting chromatogram provides qualitative and quantitative information about the mixture.
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.
MDMA has become widely known as ecstasy (shortened "E", "X", or "XTC"), usually referring to its tablet form, although this term may also include the presence of possible adulterants or diluents. The UK term "mandy" and the US term "molly" colloquially refer to MDMA in a crystalline powder form that is thought to be free of adulterants. MDMA is also sold in the form of the hydrochloride salt, either as loose crystals or in gelcaps. MDMA tablets can sometimes be found in a shaped form that may depict characters from popular culture. These are sometimes collectively referred to as "fun tablets". Partly due to the global supply shortage of sassafras oil—a problem largely assuaged by use of improved or alternative modern methods of synthesis—the purity of substances sold as molly have been found to vary widely. Some of these substances contain methylone, ethylone, MDPV, mephedrone, or any other of the group of compounds commonly known as bath salts, in addition to, or in place of, MDMA. Powdered MDMA ranges from pure MDMA to crushed tablets with 30–40% purity. MDMA tablets typically have low purity due to bulking agents that are added to dilute the drug and increase profits (notably lactose) and binding agents. Tablets sold as ecstasy sometimes contain 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxyethylamphetamine (MDEA), other amphetamine derivatives, caffeine, opiates, or painkillers. Some tablets contain little or no MDMA. The proportion of seized ecstasy tablets with MDMA-like impurities has varied annually and by country.
=== Das Buch der von Neil Young Getöteten (2002) === Kermani's first literary text appeared in 2002: „Das Buch der von Neil Young Getöteten“ [The Book of Those Killed by Neil Young] which combines three themes: first, the music of Neil Young, to whose songs numerous song interpretations are dedicated; second, the astonishing therapeutic effect of Neil Young’s music on the first-person narrator's daughter while suffering from three-month colic and during her first year of life; and third, the narrator's biography, which has been significantly influenced by Neil Young (whose importance to the narrator is as obvious as the narrator’s tendency toward ironic exaggeration). Omnipresent (self-)irony as the book’s foremost narrative principle allows the narrator to integrate the major literary themes, ranging from God to love to death, into the flow of his narration without making the text seem overloaded. Whereas the first half of the text is shaped by philosophical and literary reminiscences where Neil Young's lyrics undergo exacting philological analysis, the second half focuses on the mystical dimensions that the narrator regards as constituting the core of Neil Young's music and of his own listening experience. The enigmatic title of the book refers to „The Book of Those Killed by the Koran“, an historic manuscript that tells of mystics who heard the Koran and died as a result. For the narrator, this calls to mind the existential significance of Neil Young's music for his own life, giving him the impulse to write the Neil Young book in the first place.
=== Displacement by electrostatic actuation === Three-dimensional droplet actuation has been made possible by implementing a closed system; this system contains a μL sized droplet in immiscible fluid medium. The droplet and medium are then sandwiched between two electromagnetic plates, creating an EM field between the two plates. The purpose of this method is to transfer the droplet from a lower planar surface to an upper parallel planar surface and back down via electrostatic forces. The physics behind such particle actuation and perpendicular movement can be understood from early works of N. N. Lebedev and I. P. Skal'skaya. In their research, they attempted to model the Maxwell electrical charge acquired by a perfectly round conducting particle in the presence of a uniform magnetic field caused by a perfectly-conducting and infinitely-stretching surface. Their model helps to predict the Z-direction motion of the microdroplets within the device as it points to the magnitude and direction of forces acting upon a micro droplet. This can be used to help accurately predict and correct for unwanted and uncontrollable particle movement. The model explains why failing to employ dielectric coating on one of the two surfaces causes reversal of charge within the droplet upon contact with each electrode and in turn causes the droplets to uncontrollably bounce of between electrodes. Digital microfluidics (DMF), has already been readily adapted in many biological fields.
ago. A more correct treatment would require the use of delay differential equations. Latent period is the transition time between contagion event and disease manifestation. In cases of diseases with varying latent periods, the basic reproduction number can be calculated as the sum of the reproduction numbers for each transition time into the disease. An example of this is tuberculosis (TB). Blower and coauthors calculated from a simple model of TB the following reproduction number:
The Alexander von Humboldt Fellowship to Germany (2003–2005) Visiting Scientist to the University of Pittsburgh, (2007–2008) The ANDI Bright Contest Award for the Best African Innovative Researcher, South Africa (2009) Young Scientist (representing Nigeria) at the "Summer Davos" Annual Meeting of New Champions, Tianjin, China (2010) CV Raman Senior Fellowship, India (2013) Fellow of the Nigerian Academy of Science (2017) Pioneer national president of the Nanomedicine Society of Nigeria Recipient of various national and international grants and a reviewer to several national and international journals.
Sources: en.wikipedia.org
Mala is a numbing and pungent seasoning derived from Sichuan peppercorn and chili. Most commonly, mala is made into a sauce (麻辣醬 málàjiàng) by simmering it in oil and other spices. Characteristic of Sichuan cuisine, particularly Chongqing cuisine, it has become one of the most popular and synthesized ingredients in Chinese cuisine.
Carole Ann Bewley is an American chemist. She is a senior investigator and Chief of the Laboratory of Bioorganic Chemistry at the United States National Institute of Diabetes and Digestive and Kidney Diseases. Bewley researches secondary metabolites and basic principles involved in protein-carbohydrate interactions and how these can be exploited to engineer therapeutics.
In organic chemistry, a nitrile is any organic compound that has a −C≡N functional group. The name of the compound is composed of a base, which includes the carbon of the −C≡N, suffixed with "nitrile", so for example CH3CH2C≡N is called "propionitrile" (or propanenitrile). The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons. For the organic compounds of the form R−N+≡C− instead of R−C≡N, they are referred to as isonitriles, or isocyanides. Inorganic compounds containing the −C≡N group are not called nitriles, but cyanides instead. Though both nitriles and cyanides can be derived from cyanide salts, most nitriles are not nearly as toxic.
In dermatology, the base of a topical medication is often as important as the medication itself. It is extremely important to receive a medication in the correct base, before applying to the skin. A pharmacist should not substitute an ointment for a cream, or vice versa, as the potency of the medication can change. Some physicians use a thick ointment to replace the waterproof barrier of the inflamed skin in the treatment of eczema, and a cream might not accomplish the same clinical intention.
External (interface) pressure applied over an area of the body, especially over the bony prominences can result in obstruction of the blood capillaries, which deprives tissues of oxygen and nutrients, causing ischemia (deficiency of blood in a particular area), hypoxia (inadequate amount of oxygen available to the cells), edema, inflammation, and, finally, necrosis and ulcer formation. Ulcers due to external pressure occur over the sacrum and coccyx, followed by the trochanter and the calcaneus (heel). In healthy individuals, ulcers caused by external pressure do not occur when the body is stationary, such as during sleep, as involuntary movements of the body frequently occur, allowing for repositioning and the relief of pressure. Friction is damaging to the superficial blood vessels directly under the skin. It occurs when two surfaces rub against each other. The skin over the elbows can be injured due to friction. The back can also be injured when patients are pulled or slid over bed sheets while being moved up in bed or transferred onto a stretcher. Shearing is a separation of the skin from underlying tissues. When a patient is partially sitting up in bed, skin may stick to the sheet, making the skin susceptible to shearing in case underlying tissues move downward with the body toward the foot of the bed. This may also be possible on a patient who slides down while sitting in a chair. Moisture is also a common pressure ulcer culprit. Sweat, urine, feces, or excessive wound drainage can further exacerbate the damage done by pressure, friction, and shear.
Sources: en.wikipedia.org
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.
System suitability is a set of checks run on the chromatographic system before sample analysis. It confirms that resolution, peak shape, retention time, and response meet predefined limits. Failure can invalidate the run and trigger corrective action.
Blank injections reveal peaks or baseline disturbances that come from solvents, reagents, or the instrument rather than the sample. They help distinguish contamination from actual analyte signals. Comparing blanks with sample runs supports accurate interpretation.
HPLC testing separates and quantifies components in a liquid sample. It is used to check identity, purity, concentration, or stability. The technique works best for compounds that dissolve and are not easily vaporized.