This is a working overview of retention time, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-03-21. Anything still debated is marked as such rather than presented as settled.
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.
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.
Method validation evaluates accuracy, precision, specificity, linearity, range, detection limit, quantitation limit, and robustness. Regulatory guidance for pharmaceuticals, foods, and environmental testing defines expected documentation and acceptance criteria. Verification confirms that a validated method works in a specific laboratory with its own instruments and reagents. Calibration curves use reference standards with known purity and traceability, while measurement uncertainty is estimated from validation data, control charts, and collaborative studies. The scope of validation depends on the method's intended use.
Routine quality control monitors retention time shifts, baseline noise, system pressure, and peak shape. Trends can reveal column aging, mobile phase preparation errors, detector drift, or sample degradation. Corrective actions may include replacing the column, preparing fresh mobile phase, or recalibrating the detector. Stability testing often uses HPLC to measure parent compound loss and degradation product formation. Open questions remain about how accelerated stability results extrapolate to long-term storage under varied conditions.
| Property | Value | Notes |
|---|---|---|
| Common abbreviation | HPLC | High-performance liquid chromatography |
| Separation basis | Differential partitioning | Between liquid mobile phase and solid stationary phase |
| Common mode | Reverse phase | Nonpolar column, polar mobile phase |
| Typical detector | UV-Vis absorbance | Widely used for compounds with chromophores |
| Typical column particle size | 2–5 µm | Smaller particles can improve resolution |
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.
Method validation demonstrates that an analytical procedure is suitable for its intended purpose. Typical validation characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulatory guidance from bodies such as the International Council for Harmonisation and the United States Pharmacopeia outlines expectations, though specific criteria depend on the product and method. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, column efficiency, and injection repeatability. Failure of these checks can invalidate a batch of measurements.
Practical HPLC testing depends on careful sample preparation and instrument maintenance. Samples may require filtration, dilution, pH adjustment, or extraction to avoid column damage and matrix interference. Mobile phases are degassed and filtered, and columns are equilibrated before injection. Common problems include peak tailing, baseline drift, ghost peaks, carryover, and co-elution of analytes. Documentation of instrument logs, calibration records, and electronic audit trails supports data integrity and traceability. Ongoing training and routine maintenance help reduce variability between analysts and laboratories.
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.
High-performance liquid chromatography is an analytical technique that separates components in a liquid sample by passing them 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 how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
Stage one: Enterprises operate as isolated islands. Stage two: Corporate-level interactions with little operational-level liaison. Stage three: Agile organizations form virtual enterprises, cooperating at both corporate and operational levels. Agile teams work across company partners. A virtual partnerships enables harnessing and coordination of resources and diverse skills for manufacturing products quickly and facilitates customer involvement in the web of firms. But there are challenges in achieving the 3rd stage. Some key business processes are still poorly understood and ill defined, despite the availability of technology. Furthermore there is a need for techniques to manage companies promoting workforce initiative and performance measures for self-directed, inter-enterprise project teams. The method to operationalize virtual enterprise is different for each scale of company. Big corporations can reorganize business units and refocus on core competences to operate as a virtual enterprise. Small companies can collaborate to deliver quality, scope and scale collectively. SMEs can potentially exploit agile principles thru rapid partnership formation. But this is easier said than done. There is still a lack of clarity on how to become agile, with insufficiently developed mindset, underdeveloped business practices, processes, methods and tools.
In May 2023, the FDA approved the iLet Bionic Pancreas system for people with Type 1 diabetes of six years and older. The device uses a closed-loop system to deliver both insulin and glucagon in response to sensed blood glucose levels. The 4th generation iLet prototype, presented in 2017, is around the size of an iPhone, with a touchscreen interface. It contains two chambers for both insulin and glucagon, and the device is configurable for use with only one hormone, or both. A 440-patient study of type I diabetes ran in 2020 and 2021 using a device configuration that delivered only insulin in comparison to standard of care; device use led to better circulating glucose control (measured by continuous monitoring) and a reduction in glycated hemoglobin (versus no change for the standard of care group). However, the incidence of severe hypoglycemic events was more than 1.5 times higher among device users versus standard care patients. There are several non-commercial, non-FDA approved DIY options, using open source code, including OpenAPS, Loop, and/or AndroidAPS.
Once active, Akt translocates from the plasma membrane to the cytosol and nucleus, where many of its substrates reside. Akt regulates a wide range of proteins by phosphorylation. Akt target substrates contain a minimum consensus sequence R-X-R-X-X-[Ser/Thr]-Hyd, where Hyd is a hydrophobic amino acid, although other factors such as sub-cellular localisation and 3-dimensional structure are important. Phosphorylation by Akt can be inhibitory or stimulatory, either suppressing or enhancing the activity of target proteins.
In 1974, GM offered driver and passenger airbags as optional equipment on large Cadillacs, Buicks, and Oldsmobiles. In 1976, the crash test dummy Hybrid III was introduced to assess the impacts of car collisions. It represented the 50th percentile male standing at approximately 5' 9" tall and weighing 78 kg (171 lbs). In 1979, NHTSA began crash-testing popular cars and publishing the results, to inform consumers and encourage manufacturers to improve the safety of their vehicles. Initially, the US NCAP (New Car Assessment Program) crash tests examined compliance with the occupant-protection provisions of FMVSS 208. Over the subsequent years, this NHTSA program was gradually expanded in scope.
Sources: en.wikipedia.org
The carbohydrate-insulin model (CIM) posits that obesity is caused by excess consumption of carbohydrate, which then disrupts normal insulin metabolism leading to weight gain and weight-related illnesses. It is contrasted with the mainstream energy balance model (EBM), which holds that obesity is caused by an excess in calorie consumption compared to calorie expenditure. According to the carbohydrate–insulin model, low-carbohydrate diets would be the most effective in causing long-term weight loss. Notable proponents of the carbohydrate–insulin model include Gary Taubes and David Ludwig. The CIM has been tested in mice and humans. Although some experts consider that these studies falsified the CIM, proponents disagree. Available evidence does not support the existence of a long-term advantage in weight loss for low-carbohydrate diets.
Hydrophilic/cytosolic – are soluble in water and are localized at the cytosol, including cAMP, cGMP, IP3, Ca2+, cADPR and S1P. Their main targets are protein kinases as PKA and PKG, being then involved in phosphorylation mediated responses. Hydrophobic/membrane-associated – are insoluble in water and membrane-associated, being localized at intermembrane spaces, where they can bind to membrane-associated effector proteins. Examples: PIP3, DAG, phosphatidic acid, arachidonic acid and ceramide. They are involved in regulation of kinases and phosphatases, G protein associated factors and transcriptional factors. Gaseous – can be widespread through cell membrane and cytosol, including nitric oxide and carbon monoxide. Both of them can activate cGMP and, besides of being capable of mediating independent activities, they also can operate in a coordinated mode.
APHL monitors trends in public health laboratory diagnostics, personnel and infrastructure. It uses this data to benchmark against national norms and to define issues of importance to lab practice and policy. APHL also disseminates research findings via issue briefs and communications with federal decision makers, health partners and the laboratory community. Members have access to survey data online, enabling them to leverage this information quickly to identify promising strategies and practices. In an effort to improve laboratory practice, APHL provides free resources, such as tools kits that explain how to: Write a laboratory quality manual Conduct an internal audit Recruit students in STEM fields Deal with laboratory floods In addition to on-demand research and reports, APHL provides continuing education courses to help laboratory scientists keep up with emerging trends, and innovative testing techniques. Training sessions are conducted through conferences, seminars, workshops and online courses.
The first automated insulin delivery system was known as the Biostator. Currently available AID systems fall into three broad classes based on their capabilities. The first systems released can only halt insulin delivery (predictive low glucose suspend) in response to already low or predicted low glucose. Hybrid Closed Loop systems can modulate delivery both up and down, although users still initiate insulin doses (boluses) for meals and typically "announce" or enter meal information. Fully Closed Loops require no manual insulin delivery actions or announcement for meals. A step forward from threshold suspend systems, predictive low glucose suspend (PLGS) systems use a mathematical model to extrapolate predicted future blood sugar levels based on recent past readings from a CGM. This allows the system to reduce or halt insulin delivery prior to a predicted hypoglycemic event.
No chromosome translocations, chimeric genes, or fusion proteins have been described in BIA-ALCL although the neoplastic cells in the disease have been described to have gene copy number variations involving gains in gene copies on the p arm of chromosome 19 and losses of gene copies in the p arms of chromosome 10 and 1. The neoplastic cells in BIA-ALCL show mutations of the STAT3 gene in 64% of cases and reports of mutations in JAK1, JAK3, DNMT3A, and TP53 genes. The development of BIA-ALCL, it has often been suggested, may be at least in part a T-cell-induced, inflammation-driven cancer response to the implant.
Sources: en.wikipedia.org
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.
Retention time is the interval between sample injection and the detector response for a given compound. It depends on the compound's interactions with the stationary and mobile phases under set conditions. Matching a retention time to a standard supports tentative identification but is not always unique.
HPLC alone can separate unknown compounds and provide retention times, but it often cannot identify them with certainty. Coupling HPLC to mass spectrometry gives mass information that improves identification. Confirmation usually requires comparison with reference standards or complementary techniques.
System suitability is typically performed before each batch or according to the validated method and laboratory procedure. Some long runs include periodic checks during analysis. The required frequency depends on regulatory expectations and method performance.