If you have been reading about stationary phase 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.
Updated 2025-11-14. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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 is an analytical technique that separates components in a liquid sample. A pump moves a liquid mobile phase through a column packed with a solid stationary phase. Compounds interact differently with both phases and travel at different rates, leaving the column at distinct retention times. A detector records these arrivals as peaks on a chromatogram. The resulting pattern supports identification and quantification of substances in mixtures. Modern instruments use high pressure to force solvent through small particles, which improves speed and resolution compared with older low-pressure liquid chromatography methods.
Separation in HPLC depends on the chemistry of the stationary phase, the composition of the mobile phase, and the physical properties of the column. Reverse-phase separations use a nonpolar stationary phase and a polar mobile phase, and they are common for many organic compounds. Ion-exchange, size-exclusion, and normal-phase modes serve other classes of analytes. Gradient elution changes solvent strength over time, while isocratic elution holds it constant. Flow rate, temperature, particle size, and column length all influence peak shape and resolution. Detection may use ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry, depending on the analyte and the required sensitivity.
Routine HPLC testing compares a sample result with a calibration curve prepared from known reference standards. Peak area or peak height is plotted against concentration, and the curve is used to estimate unknown amounts. Retention time supports tentative identification when compared with a standard, though mass spectrometry or another confirmatory method may be needed for definitive identification. Pre-run checks verify repeatability, resolution, and peak symmetry before sample analysis. Limits of detection and quantification describe the smallest amounts that can be reliably observed or measured. Sample preparation, filtration, and degassing help prevent column damage and inconsistent results.
| Property | Value | Notes |
|---|---|---|
| Column particle size | 3–5 µm for conventional HPLC; sub-2 µm for UHPLC | Smaller particles increase backpressure and efficiency. |
| Typical flow rate | 0.5–2.0 mL/min for a 4.6 mm internal diameter column | Flow scales with column diameter and particle size. |
| UV detection wavelength | 190–400 nm | Selection depends on analyte chromophore. |
| Column temperature | 25–40 °C | Temperature affects retention, selectivity, and pressure. |
| Injection volume | 1–20 µL | Larger volumes may distort early-eluting peaks. |
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.
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.
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Method validation establishes that an HPLC procedure is suitable for its intended use. Key parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Accuracy measures agreement with a true or accepted value, while precision describes repeatability and intermediate precision. Specificity confirms that the method measures the analyte without interference from impurities, degradants, or excipients. Validation is documented in a protocol and report, and acceptance criteria are set before experiments begin. Regulatory guidance varies by region, but the general principles are widely harmonized.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
== Further reading == Allen, Jeannie (6 September 2001). Ultraviolet Radiation: How it Affects Life on Earth. Earth Observatory. NASA, USA. Hockberger, Philip E. (2002). "A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms". Photochemistry and Photobiology. 76 (6): 561–569. doi:10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2. PMID 12511035. S2CID 222100404. Hu, S; Ma, F; Collado-Mesa, F; Kirsner, R. S. (July 2004). "UV radiation, latitude, and melanoma in US Hispanics and blacks". Arch. Dermatol. 140 (7): 819–824. doi:10.1001/archderm.140.7.819. PMID 15262692. Strauss, CEM; Funk, DJ (1991). "Broadly tunable difference-frequency generation of VUV using two-photon resonances in H2 and Kr". Optics Letters. 16 (15): 1192–4. Bibcode:1991OptL...16.1192S. doi:10.1364/ol.16.001192. PMID 19776917.
=== Investors === In January 2024, TEG announced that it had secured a multi-million-dollar investment round from venture capitalists, including Thiel, Angermayer and Balaji Srinivasan. In February 2025, businessman Donald Trump Jr. said that his venture fund 1789 Capital would be involved in an investment round, saying "The Enhanced Games represent the future – real competition, real freedom, and real records being smashed. This is about excellence, innovation, and American dominance on the world stage – something the MAGA movement is all about." Others include Saudi prince Khaled bin Alwaleed Al Saud, and cryptocurrency investors Cameron and Tyler Winklevoss.
=== Core layer === The core of an aquasome can be made from either ceramic or polymeric materials. Examples of such polymers include acrylates and gelatin. However, because ceramic materials are more ordered due to their naturally occurring crystalline structure, they are more often preferred as the material type for the core. Some of the most common ceramic materials used in the formation of an aquasome core include tin oxide, calcium phosphate, and even diamond. Another characteristic that ceramic materials provide is enhanced binding of the carbohydrate layer due to the high surface energy present on the orderly surface. The binding affinity of the carbohydrate layer also reduces surface tension for its bond to the ceramic core. The first aquasomes fabricated with a nanocrystalline core using ceramic material are detailed in Kossovsky et al. in 1996. Calcium phosphate ceramic nanoparticles (brushite) were first prepared via the method of solution precipitation and sonication. Precipitation methods are the most common techniques employed when synthesizing the core of an aquasome as they offer control over the homogeneity and purity of the precipitated products, which are important design features in the core structure. Once the cores are prepared, they are separated by centrifugation and then washed to remove any salt byproducts from the solution precipitation process. Finally, the washed cores are passed through a Millipore filter to selectively isolate core particles of a certain size.
Sources: en.wikipedia.org
=== Space age swimsuit === Langley Research Center's wind tunnel testing facilities and fluid flow analysis software supported Speedo's design of a space age-enriched swimsuit. The resulting LZR Racer reduced skin friction drag 24% more than the previous Speedo swimsuit. In March 2008, athletes wearing the LZR Racer broke 13 swimming world records.
Local border traffic is the flow of travellers residing within the area surrounding a controlled international or internal border. In many cases, local border traffic is subject to special regulations to expedite it. Depending on the particular border in question, these measures may be restricted to residents, implemented as a blanket regional visa waiver by one jurisdiction for nationals of the other, restricted to frequent cross-border travellers, or available to individuals lawfully present in one jurisdiction seeking to visit the other. Schengen Area: Schengen states which share an external land border with a non-Schengen state are authorised by EU Regulation 1931/2006 to conclude bilateral agreements with neighbouring countries implementing a simplified local border traffic regime. Such agreements define a border area and provide for the issuance of local border traffic permits to residents of the border area that may be used to cross the EU external border within the border area.
polymerase chain reaction (PCR) Any of a wide variety of molecular biology methods involving the rapid production of millions or billions of copies of a specific DNA sequence, allowing scientists to selectively amplify fragments of a very small sample to a quantity large enough to study in detail. In its simplest form, PCR generally involves the incubation of a target DNA sample of known or unknown sequence with a reaction mixture consisting of oligonucleotide primers, a heat-stable DNA polymerase, and free deoxyribonucleotide triphosphates (dNTPs), all of which are supplied in excess. This mixture is then alternately heated and cooled to pre-determined temperatures for pre-determined lengths of time according to a specified pattern which is repeated for many cycles, typically in a thermal cycler which automatically controls the required temperature variations. In each cycle, the most basic of which includes a denaturation phase, annealing phase, and elongation phase, the copies synthesized in the previous cycle are used as templates for synthesis in the next cycle, causing a chain reaction that results in the exponential growth of the total number of copies in the reaction mixture. Amplification by PCR has become a standard technique in virtually all molecular biology laboratories.
is the elementary charge. The most important difference is that, in the absence of field line-breaking, the magnetic field is tied to the electrons rather than to the bulk fluid. Electron MHD Electron magnetohydrodynamics (EMHD) describes small-scale plasmas in which electron motion is much faster than the ion motion. The main effects are changes in conservation laws, additional resistivity, and the importance of electron inertia. Many effects of Electron MHD are similar to those of two-fluid MHD and Hall MHD. EMHD is especially important for z-pinches, magnetic reconnection, ion thrusters, neutron stars, and plasma switches. Collisionless MHD is also used for collisionless plasmas. In that case, the MHD equations are derived from the Vlasov equation. Reduced By using a multiscale analysis, the (resistive) MHD equations can be reduced to a set of four closed scalar equations. This allows for, among other things, more efficient numerical calculations.
Sources: en.wikipedia.org
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.
UHPLC uses columns with smaller particles and operates at higher pressures than conventional HPLC. These conditions can improve speed, resolution, and sensitivity. Both techniques use the same fundamental separation principles.
Validation shows that a method performs reliably for its intended purpose across a defined range. It assesses accuracy, precision, specificity, linearity, and robustness. Regulated testing often requires documented validation before routine use.
HPLC testing measures the presence and amount of one or more compounds in a liquid sample. It separates mixture components and records detector responses as peaks, which are compared with reference standards. Results are usually reported as concentrations or relative percentages.