reversed-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 2026-06-13 and is reviewed periodically as new material appears.
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.
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.
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.
Several separation modes exist, including reversed-phase, normal-phase, ion-exchange, size-exclusion, and hydrophilic interaction liquid chromatography. Reversed-phase uses a nonpolar stationary phase with a polar mobile phase and is widely applied to small organic molecules. Gradient elution changes mobile phase composition during the run, while isocratic elution keeps it constant. Column chemistry, particle size, temperature, flow rate, and mobile phase pH all influence retention and resolution. Method development selects conditions that separate analytes from matrix components and from each other.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Most common for neutral and moderately polar analytes |
| Column particle size | 3–5 µm | Smaller particles improve resolution but raise backpressure |
| Mobile phase pH range | 2–8 | Silica-based columns may degrade outside this range |
| Typical flow rate | 1.0–2.0 mL/min | For analytical columns with 4.6 mm internal diameter |
| Common synonyms | HPLC, LC, high-pressure liquid chromatography | High-performance liquid chromatography is the standard expansion |
Routine HPLC testing depends on controlled reagents, calibrated instruments, and documented procedures. Columns degrade over time, so retention times and peak shapes are monitored for drift. Mobile phases are filtered and degassed to prevent pump damage and detector noise. Reference standards must be traceable and stored under suitable conditions. Data handling systems record injections, calculations, and audit trails. Quality control samples interspersed with unknowns help detect errors during a run.
Developing an HPLC method begins with defining the purpose, such as quantifying a main component, measuring impurities, or confirming identity. Analysts select separation mode, column, mobile phase, detection, and sample preparation based on analyte properties and matrix. Experiments vary solvent strength, pH, buffer type, and temperature to achieve resolution between critical peaks. The goal is a robust method that produces reliable results across instruments and operators. Method development often involves trial runs and statistical optimization.
=== Construction === The main use of calcium carbonate is in the construction industry, either as a building material, as limestone aggregate for road building, as an ingredient of cement, or as the starting material for the preparation of builders' lime by heating in a kiln. However, because of weathering mainly caused by acid rain, calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw primary substance for building materials. Calcium carbonate is also used in the purification of iron from iron ore in a blast furnace. The carbonate is calcined in situ to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron. In the oil industry, calcium carbonate is added to drilling fluids as a formation-bridging and filtercake-sealing agent; it is also a weighting material which increases the density of drilling fluids to control the downhole pressure. Calcium carbonate is added to swimming pools, as a pH corrector for maintaining alkalinity and offsetting the acidic properties of the disinfectant agent. It is also used as a raw material in the refining of sugar from sugar beet; it is calcined in a kiln with anthracite to produce calcium oxide and carbon dioxide. This burnt lime is then slaked in fresh water to produce a calcium hydroxide suspension for the precipitation of impurities in raw juice during carbonatation. Calcium carbonate in the form of chalk has traditionally been a major component of blackboard chalk.
=== SIMBAS === In March 2011, a team of researchers from UC Berkeley, DCU and University of Valparaíso have developed lab-on-a-chip that can diagnose diseases within 10 minutes without the use of external tubing and extra components. It is called Self-powered Integrated Microfluidic Blood Analysis System (SIMBAS). It uses tiny trenches to separate blood cells from plasma (99 percent of blood cells were captured during experiments). Researchers used plastic components, to reduce manufacturing costs.
Fast atom bombardment (FAB) is an ionization technique used in mass spectrometry in which a beam of high energy atoms strikes a surface to create ions. It was developed by Michael Barber at the University of Manchester in 1980. When a beam of high energy ions is used instead of atoms (as in secondary ion mass spectrometry), the method is known as liquid secondary ion mass spectrometry (LSIMS). In FAB and LSIMS, the material to be analyzed is mixed with a non-volatile chemical protection environment, called a matrix, and is bombarded under vacuum with a high energy (4000 to 10,000 electron volts) atomic beam. The atoms are typically from an inert gas such as argon or xenon. Common matrices include glycerol, thioglycerol, 3-nitrobenzyl alcohol (3-NBA), 18-crown-6 ether, 2-nitrophenyloctyl ether, sulfolane, diethanolamine, and triethanolamine. This technique is similar to secondary ion mass spectrometry and plasma desorption mass spectrometry.
== Medical uses == Rivastigmine is indicated for the treatment of mild to moderate Alzheimer's dementia, and for mild to moderate Parkinson's disease dementia. Rivastigmine is available in capsules, liquid solution, and patches. Rivastigmine has demonstrated treatment effects on the cognitive (thinking and memory), functional (activities of daily living) and behavioural problems commonly associated with Alzheimer's.
In August 2022, the Inflation Reduction Act passed, requiring companies to cap the price of insulin at US$35 per month for Medicare. On November 10, a Twitter account impersonating the pharmaceutical company Eli Lilly and Company—one of the three largest manufacturers of insulin—posted a tweet stating that insulin would be made free. According to The Washington Post, Twitter failed to respond to the company for several hours. The incident resulted in Eli Lilly pulling advertisements from Twitter. United States senator Bernie Sanders used the tweet to highlight the price of insulin as other users began creating satirical accounts jovially apologizing for making insulin free, with one such account writing, "Humalog is now $400. We can do this whenever we want and there's nothing you can do about it". The identity of the user who posted the tweet remained unknown until November 22, when Sean Morrow, a 34-year-old writer for the media organization More Perfect Union, admitted to operating the account and writing the tweet. In a video, Morrow stated that he used the account of the Mothman running for the United States Senate for West Virginia, and put that the account was a parody in its biography. Morrow took the video to detail the history of insulin manufacturing and the monopolization of the insulin industry. Eli Lilly further lowered the price of insulin in March 2023.
Sources: en.wikipedia.org
3-Dimensional images of choroid plexus (marked red) "Anatomy diagram: 13048.000-3". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2012-07-22. MedPix Images of Choroid Plexus More info at BrainInfo
== Plant interactions == Post-harvest decays are a main source of fruit loss, with the most common source of Citrus fruit decay being infections caused by P. digitatum and P. italicum. Penicillium digitatum is responsible for 90% of citrus fruits lost to infection after harvesting, and is considered the largest cause of post-harvest diseases occurring in California citrus fruits. Its widespread impact derives from the post-harvest disease it causes in citrus fruits known as green rot or mould. As a wound pathogen, the disease cycle begins when P. digitatum conidia germinate with release of water and nutrients from the site of injury on the fruit surface. For example, after infection at 24 °C, rapid growth ensues, with active infection taking place within 48 hours, and initial symptom onset occurring within 3 days. As temperature at time of infection decreases, the delay of initial symptom onset increases. Initial symptoms include a moist depression on the surface, which expands as white mycelium colonizes much of the surface. The centre of the mycelial mass eventually turns olive as conidial production begins. Near the end of the disease cycle, the fruit eventually decreases in size, and develops into an empty, dry shell. This end result is commonly used to distinguish P. digitatum infections from those of P. italicum, which produce a blue-green mould and ultimately render the fruit slimy. Infection with green mould at 25 °C (77 °F) can last 3 to 5 days, with the rate of conidial production per infected fruit being as high as 1–2 billion conidia.
=== Afghanistan === Prior to the takeover of the Islamic Emirate of Afghanistan in August 2021, a member of parliament (MP) was a member of the lower house of the bicameral National Assembly of Afghanistan: a member of the Wolesi Jirga (House of People) held one of the in total 250 seats in the lower house. The 102 members of the upper house Meshrano Jirga (House of Elders) were called Senators.
Higher temperatures accelerate germination, with 23 °C (73 °F) promoting faster colony formation than 19 °C (66 °F). Light exposure is unnecessary for early fungal growth—cultures in darkness develop healthier, more extensive mycelial networks. Developing mycobiont morphology provides insights into early symbiosis. In vitro, X. parietina forms septate, branched hyphae, which later develop into lobed structures, resembling early lichen thalli. Scanning electron microscopy reveals a dense, interwoven hyphal network, potentially facilitating photobiont interactions during natural lichenization. These adaptations support X. parietina's regenerative ability and symbiotic establishment across varied environments. Although X. parietina lacks specialized vegetative propagules, it has a regenerative capacity that enhances its ecological success. Older, apothecia-covered thalli detach along drought-induced cracks, while younger margins remain attached. When fragments land on suitable substrates, they regenerate new lobes along wound margins, acting as natural propagules. Field studies show a 150% laminal size increase in just 13 months in regenerating thalli. In a five-year experiment, X. parietina maintained 50% substrate coverage, despite losing 90% of its initial thallus area, as regrowth compensated for these losses. Total turnover (growth + loss) exceeded 170%, highlighting its dynamic life cycle.
== Chemistry == Pseudoephedrine, also known structurally as (1S,2S)-α,N-dimethyl-β-hydroxyphenethylamine or as (1S,2S)-N-methyl-β-hydroxyamphetamine, is a substituted phenethylamine, amphetamine, and β-hydroxyamphetamine derivative. It is a diastereomer of ephedrine. Pseudoephedrine is a small-molecule compound with the molecular formula C10H15NO and a molecular weight of 165.23 g/mol. It has an experimental log P of 0.89, while its predicted log P values range from 0.9 to 1.32. The compound is relatively lipophilic, but is also more hydrophilic than other amphetamines. The lipophilicity of amphetamines is closely related to their brain permeability. For comparison to pseudoephedrine, the experimental log P of methamphetamine is 2.1, of amphetamine is 1.8, of ephedrine is 1.1, of phenylpropanolamine is 0.7, of phenylephrine is -0.3, and of norepinephrine is -1.2. Methamphetamine has high brain permeability, whereas phenylephrine and norepinephrine are peripherally selective drugs. The optimal log P for brain permeation and central activity is about 2.1 (range 1.5–2.7). Pseudoephedrine is readily reduced into methamphetamine or oxidized into methcathinone.
Sources: en.wikipedia.org
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.
The pump maintains a steady flow rate and pressure, which keeps retention times reproducible. Pulsation or flow errors can shift peaks and distort quantitation. Modern pumps use feedback control to reduce these variations.
HPLC alone usually separates compounds but does not always identify them. Retention time matching with a known standard provides tentative identification. Coupling HPLC to mass spectrometry adds mass information that supports structural 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.