mobile 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 2026-03-19 and is reviewed periodically as new material appears.
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.
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.
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.
Most routine HPLC testing uses reversed-phase columns, where the stationary phase is nonpolar and the mobile phase is a polar mixture such as water with an organic solvent. Analytes partition between the two phases according to polarity, size, and charge. Gradients that change solvent composition over time can separate compounds with broad retention ranges. Isocratic conditions keep solvent composition constant and suit simpler mixtures. The choice of column chemistry, pH, and temperature affects selectivity and peak shape.
| 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. |
Method validation establishes that an HPLC procedure is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, robustness, and solution stability. Accuracy reflects closeness to a reference value, while precision reflects agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from matrix components. Validation is documented through protocols and reports, and the required extent depends on the method's use and regulatory context.
Routine quality control uses system suitability, blank injections, check standards, and control samples to detect drift or contamination. System suitability criteria may specify minimum resolution, maximum tailing factor, and a permitted range for repeated injections. Blank injections reveal carryover or solvent contamination, while check standards confirm calibration accuracy over a batch. Control samples with known analyte levels can show whether results remain within statistical limits. When a control result falls outside limits, the analyst investigates the cause and may invalidate affected results before repeating the batch.
Developing an HPLC test begins with defining the analytes, matrix, and required reporting limits. Chemists select a separation mode, column chemistry, mobile phase composition, flow rate, and detection wavelength or mass transition. Experiments then adjust these variables to achieve adequate retention, resolution, and peak shape. System suitability tests confirm that the instrument and method perform consistently before sample analysis. Without suitable resolution, quantitative results may be unreliable. Preliminary runs often use scouting gradients to locate retention windows.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
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.
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.
The Institute also fosters the next generation of aging researchers through its NIH-funded Biology of Aging Training Program (T32), which provides postdoctoral and predoctoral trainees with comprehensive research training and opportunities to design, conduct, and present innovative aging research to the broader scientific community.
John Scott Award, created in 1816 as the John Scott Legacy Medal and Premium, is presented to people whose inventions are deemed to have improved the "comfort, welfare, and happiness of human kind" in a significant way. Since 1919 the Board of Directors of City Trusts of Philadelphia provide this award, recommended by an advisory committee.
=== tib-tie === tibalosin (INN) tibeglisene (INN) tibenelast (INN) tibenzate (INN) tibezonium iodide (INN) tibolone (INN) tibric acid (INN) tibrofan (INN) ticabesone (INN) ticagrelor (USAN) ticarbodine (INN) ticarcillin (INN) ticarcillin/clavulanic acid TICE BCG (Organon Teknika Corp) ticlatone (INN) Ticlid ticlopidine (INN) ticolubant (INN) tideglusib (INN) tidembersat (INN) tidiacic (INN) tiemonium iodide (INN) tienilic acid (INN) tienocarbine (INN) tienopramine (INN) tienoxolol (INN)
Sources: en.wikipedia.org
=== High-throughput === Due to the highly time-consuming and work-intensive standard procedure, the method of in-gel digestion was limited to a relatively small number of protein spots to be processed at a time. Therefore, it has been found to be the ideal object for automation ambitions to overcome these limitations for industrial and service laboratories. Today, in laboratories where in-gel digestion is performed in high-throughput quantities, the procedure is usually automated. The degree of automation varies from simple pipetting robots to highly sophisticated all-in-one solutions, offering an automated workflow from gel to mass spectrometry. The systems usually consist of a spot picker, a digestion robot, and a spotter. The advantages of the automation other than the larger number of spots to be processed at a time are the reduced manual work and the improved standardisation. Due to the many handling steps of the method, the results of the manual process could vary depending on the dexterity of the user and the risk of contamination is high. Therefore, the quality of the results is described to be one main advantage of the automated process. Drawbacks of automated solutions are the costs for robots, maintenance and consumables as well as the complicated setup of the process. Since the automated picking needs digitised information of the spot location, the analysis of the gel image for relevant spots has to be done by software requiring standardised imaging methods and special scanners.
Foliate papillae (from Latin foliātus 'leafy') are short vertical folds and are present on each side of the tongue. They are located on the sides at the back of the tongue, just in front of the palatoglossal arch of the fauces. There are four or five vertical folds, and their size and shape is variable. The foliate papillae appear as a series of red colored, leaf–like ridges of mucosa. They are covered with epithelium, lack keratin and so are softer, and bear many taste buds. They are usually bilaterally symmetrical. Sometimes they appear small and inconspicuous, and at other times they are prominent. Because their location is a high risk site for oral cancer, and their tendency to occasionally swell, they may be mistaken as tumors or inflammatory disease. Taste buds, the receptors of the gustatory sense, are scattered over the mucous membrane of their surface. Serous glands drain into the folds and clean the taste buds. Lingual tonsils are found immediately behind the foliate papillae and, when hyperplastic, cause a prominence of the papillae.
=== Medical === Odontostomatology: gingivitis, stomatitis, glossitis, aphthous ulcers, dental surgery and oral ulceration due to radiation therapy. Otorhinolaryngology: glandular fever, pharyngitis, tonsillitis, post-tonsillectomy, radiation or intubation mucositis. It may be used alone or as an adjunct to other therapy giving the possibility of increased therapeutic effect with little risk of interaction. In some markets, the drug is supplied as an over-the-counter cream (Lonol in Mexico from Boehringer Ingelheim) used for topical treatment of musculoskeletal system disorders: sprains, strains, bursitis, tendinitis, synovitis, myalgia, periarthritis.
Sources: en.wikipedia.org
== Precautions == Protactinium is both toxic and highly radioactive; thus, it is handled exclusively in a sealed glove box. Its major isotope 231Pa has a specific activity of 0.048 curies (1.8 GBq) per gram and primarily emits alpha particles, which can be stopped by a thin layer of any material. However, it slowly decays into 227Ac, and then follows the more rapid actinium series, making its total activity (alpha, beta, and gamma) greater than one would calculate from that figure. As protactinium is present in small amounts in most natural products and materials, it is ingested with food or water and inhaled with air. Only about 0.05% of ingested protactinium is absorbed into the blood and the remainder is excreted. From the blood, about 40% of the protactinium deposits in the bones, about 15% goes to the liver, 2% to the kidneys, and the rest leaves the body. The biological half-life of protactinium is about 50 years in the bones, whereas its biological half-life in other organs has a fast and slow component. For example, 70% of the protactinium in the liver has a biological half-life of 10 days, and the remaining 30% for 60 days. The corresponding values for kidneys are 20% (10 days) and 80% (60 days). In each affected organ, protactinium promotes cancer via its radioactivity. The maximum amount of Pa allowed in the human body is 0.03 μCi (1.1 kBq), which corresponds to 0.5 micrograms of 231Pa. The maximum allowed concentrations of 231Pa in the air in Germany is 3×10−4 Bq/m3.
=== Metabolic === One of the primary areas of interest regarding adropin is its role in metabolic regulation. Research indicates that adropin may play a crucial role in glucose and lipid metabolism. It has been associated with insulin sensitivity, suggesting a potential role in the regulation of blood sugar levels. In animal studies, alterations in adropin levels have been linked to changes in energy expenditure and body weight. For example, some studies have shown that mice with elevated adropin levels tend to be more resistant to diet-induced obesity. A study in humans demonstrated that changes in vascular insulin resistance following short-term adverse lifestyle changes were associated with a decrease in plasma adropin in men but not women, perhaps related to adropin's regulation by estrogen.
Most of Poland that was partitioned and annexed to Prussia in the late 18th-century was still part of Greater Germany at the close of World War I, the rest of the Kingdom of Poland being in Austria-Hungary. The portion in Germany included the region of Greater Poland, of which Poznań (Posen) was a major industrial city and its capital. The majority of the population was Polish (more than 60%) and hoped to be within the borders of the new Polish state.
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.
It separates components in a liquid sample and measures their amounts using a detector. Results can indicate concentration, purity, or identity based on retention time and detector response. The technique works for mixtures that can be dissolved and filtered.