stationary 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 2026-05-26 and is reviewed periodically as new material appears.
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.
Validation demonstrates that a method is suitable for its intended use. Typical performance characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulators and standards organizations provide frameworks, but specific requirements depend on the application and jurisdiction. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, retention time repeatability, and sensitivity. A validated method is not permanently fixed; changes may require partial or full 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.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness of measured value to accepted reference value |
| Validation parameter | Precision | Agreement among repeated measurements under specified conditions |
| System suitability check | Resolution ≥ 1.5 | Baseline separation between critical peak pair |
| System suitability check | Tailing factor ≤ 2.0 | Common target for peak symmetry |
| Documentation | Validation report | Summarizes experiments, acceptance criteria, and conclusions |
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.
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 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.
Instrumentation includes a solvent delivery system, an autosampler, a column oven, and one or more detectors. Reversed-phase columns with chemically modified silica are widely used, but normal-phase, ion-exchange, size-exclusion, and affinity modes exist for specific separations. Detectors may rely on ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry. Column temperature, mobile phase composition, and flow rate are adjusted to improve resolution. System pressure is monitored because rising pressure can indicate column blockage or deteriorating packing.
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.
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.
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.
== Examples == The unique interaction between the oligosaccharide chains have different applications. First, it aids in quality control by identifying misfolded proteins. The oligosaccharide chains also change the solubility and polarity of the proteins that they are bonded to. For example, if the oligosaccharide chains are negatively charged, with enough density around the protein, they can repulse proteolytic enzymes away from the bonded protein. The diversity in interactions lends itself to different types of glycoproteins with different structures and functions. One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes. Glycoproteins are important for white blood cell recognition. Examples of glycoproteins in the immune system are:
=== 2011–2017: The Only Way Is Essex, I'm a Celebrity...Get Me Out of Here! and Celebrity Big Brother === In January 2011, Julie Childs, mother of Collins' friend Amy, suggested to producers of the ITV2 reality series The Only Way Is Essex that Collins would be an appropriate subject. They visited Collins' house and subsequently filmed her and her friends for two weeks. After returning to work as a car sales executive for a week, she was cast in the programme and began appearing in The Only Way Is Essex from its second series beginning in March 2011. Her first scene saw her attempting to sell a car to Kirk Norcross and taking him for a test drive. Collins ultimately quit her job to appear on the programme full time, and was paid £50 a day for her early appearances on the show, which she described as a "massive risk". Her mother Joan joined the programme during the fifth series in April 2012. From September 2011 until March 2013, Collins wrote a regular column in the tabloid magazine Closer. In April 2013, she released her debut autobiography Basically...: My Life as a Real Essex Girl, which became a bestseller in its first week of release. In January 2014, Collins took part in the second series of the ITV diving competition Splash!. During training, Collins suffered severe bruising and admitted she had to overcome a fear of water. She became the third celebrity to be eliminated after losing the splash-off to Michaela Strachan in the first heat. In November 2014, she took part in the fourteenth series of I'm a Celebrity...Get Me Out of Here! on ITV.
==== Photorejuvenation ==== Laser resurfacing is an FDA-cleared skin resurfacing procedure in which lasers are used to improve the condition of the skin. Two types of lasers are used to reduce the appearance of fine lines and wrinkles on the face; laser ablation, which removes thin layers of skin, and nonablative lasers that stimulate collagen production. Nonablative lasers are less effective than ablative ones, but they are less invasive, and recovery time is short. After the procedure people experience temporary redness, itching and swelling.
=== Burnup === "Burnup" is a measure of how much energy has been extracted from a given mass of heavy metal in fuel, often expressed (for power reactors) in terms of gigawatt-days per ton of heavy metal. Burnup is an important factor in determining the types and abundances of isotopes produced by a fission reactor. Burnup is distinct from the conversion or breeding ratio. A 2003 study of reduced-moderation water reactor fuel assemblies reported a configuration with an average core burnup of 38.2 GWd/t and a conversion ratio of 1.0, and another with 45 GWd/t and a conversion ratio of 0.97. In the past, breeder-reactor development focused on reactors with low breeding ratios, from 1.01 for the Shippingport Reactor running on thorium fuel and cooled by conventional light water to over 1.2 for the Soviet BN-350 liquid-metal-cooled reactor. Theoretical models of breeders with liquid sodium coolant flowing through tubes inside fuel elements ("tube-in-shell" construction) suggest breeding ratios of at least 1.8 are possible on an industrial scale. The Soviet BR-1 test reactor achieved a breeding ratio of 2.5 under non-commercial conditions.
Sources: en.wikipedia.org
=== The molecular clock and the units of time === Typically, a branch length of a phylogenetic tree is expressed as the expected number of substitutions per site; if the evolutionary model indicates that each site within an ancestral sequence will typically experience x substitutions by the time it evolves to a particular descendant's sequence then the ancestor and descendant are considered to be separated by branch length x. Sometimes a branch length is measured in terms of geological years. For example, a fossil record may make it possible to determine the number of years between an ancestral species and a descendant species. Because some species evolve at faster rates than others, these two measures of branch length are not always in direct proportion. The expected number of substitutions per site per year is often indicated with the Greek letter mu (μ). A model is said to have a strict molecular clock if the expected number of substitutions per year μ is constant regardless of which species' evolution is being examined. An important implication of a strict molecular clock is that the number of expected substitutions between an ancestral species and any of its present-day descendants must be independent of which descendant species is examined. Note that the assumption of a strict molecular clock is often unrealistic, especially across long periods of evolution. For example, even though rodents are genetically very similar to primates, they have undergone a much higher number of substitutions in the estimated time since divergence in some regions of the genome.
2nd Lieutenant Tanimoto Kikuo an intelligence officer who was originally supposed to remain behind in Indonesia, but linked up with the 34th Brigade to try to get home, only to end up as an instructor at the Quảng Ngãi Military Academy until 1954. 2nd Lieutenant Nakahara Mitsunobu – an intelligence officer of the 34th Independent Mixed Brigade; became a decorated soldier in the Việt Minh forces, and later an instructor at the Quảng Ngãi Military Academy.
Alternative splicing of intron 9 creates the β and γ isoforms with altered C-termini. An internal promoter in intron 4 produces the ∆133 and ∆160 isoforms, which lack part of the TAD and DBD. Alternative translation initiation at codons 40 or 160 results in ∆40p53 and ∆160p53 isoforms, respectively.
Sources: en.wikipedia.org
After a Spanish reconquest, Colombian independence was secured and the Gran Colombia period began in 1819. The new polity experimented with federalism as the Granadine Confederation (1858) and then the United States of Colombia (1863), before becoming a centralised republic in 1886. With the backing of the US and France, Panama seceded from Colombia in 1903, resulting in Colombia's present borders. Beginning in the 1960s, the country has suffered from an asymmetric low-intensity armed conflict and political violence, both of which escalated in the 1990s. Since 2000, there has been improvement in security, stability, and rule of law, as well as economic growth and development. Colombia is recognized for its healthcare system, being the best healthcare in the Americas according to the World Health Organization and 22nd in the world. Its diversified economy is the third-largest in South America, with macroeconomic stability and favorable long-term growth prospects. The country has one of the widest recognitions of LGBT rights, gender equality, animal rights, and human rights, permitting same-sex adoption, same-sex marriage, legality of abortion, legality of euthanasia, and animal rights protections. Colombia is one of the world's seventeen megadiverse countries; it has the highest level of biodiversity per square mile in the world, and second-highest level overall. Its territory encompasses the Amazon rainforest, highlands, grasslands and deserts.
If it's a legitimate rape, the female body has ways to try to shut the whole thing down." In 2017, Shaw had a supporting role as Gail Hurley in the feature film Stronger, which was directed by David Gordon Green, and starred Jake Gyllenhaal as 2013 Boston Marathon bombing survivor Jeff Bauman. In 2019, it was reported that Shaw is attached to direct an adaption of the Katherine Faw Morris novel Ultraluminous, produced by Steven Soderbergh. In 2020, numerous announcements were made regarding projects Shaw is attached to: she is reported to be writer and executive producer of an HBO series adapting the 1978 Judy Blume novel Wifey, and will direct the first episode; she is reportedly to star in Kill Switch, a film to be directed by Soderbergh; and she is attached to direct an adaption of T Kira Madden's memoir Long Live the Tribe of Fatherless Girls. She is also set to direct a film adaptation of the comic 4 Kids Walk Into a Bank.
Josh Allen became the first player to score a rushing touchdown, a receiving touchdown and multiple passing touchdowns in a single game. Bobby Wagner extended his streak of recording 100 tackles in a season to 13 years. He is the second player to record the feat, joining London Fletcher. Jayden Daniels became the first rookie to complete 80 percent of his passes, throw three touchdowns, and run for a touchdown in a single game. Jameis Winston became the first player in the Super Bowl era to have at least 400 passing yards, four passing touchdowns and two interceptions returned for touchdowns in a game. Justin Herbert became the third player to have at least 10 consecutive games without interception (minimum 15 attempts per game), joining Tom Brady and Derek Carr. The Pittsburgh Steelers tied the record for most consecutive seasons finishing with a winning percentage of .500 or better, with 21. They share the record with the Dallas Cowboys, who did so from 1965 to 1985. The Cincinnati Bengals tied the single-season record for most games lost while scoring at least 30 points, with four. They share the record with the 2002 Kansas City Chiefs. Week 14
Sources: en.wikipedia.org
It is a set of checks performed before or during an HPLC run to confirm the system works as expected. Parameters may include resolution, tailing factor, theoretical plates, and retention time precision. Failure can trigger maintenance, method adjustment, or repeat analysis.
Validation follows a planned protocol that tests accuracy, precision, specificity, linearity, range, detection limits, quantitation limits, and robustness. Results are compared against predefined acceptance criteria. The validation report supports regulatory filing or routine use.
Revalidation may be needed after changes to column chemistry, mobile phase, detection, sample preparation, or instrument type. It can also follow a pattern of out-of-specification results. The scope depends on whether the change affects method performance.
System suitability is a set of checks that confirm the instrument and method perform within limits before sample analysis. It typically includes resolution, tailing factor, retention time, and peak area reproducibility. If a check fails, the run is invalidated until the cause is resolved.