A practical reference on stationary phase: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2025-08-31 and is reviewed periodically as new material appears.
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.
Quality control laboratories use HPLC to check identity, purity, concentration, and stability of raw materials and finished products. A validated method specifies the column, mobile phase, flow rate, detection wavelength, injection volume, and run time. Samples are prepared and compared against reference standards of known concentration. The resulting chromatogram provides quantitative data, such as assay values and impurity levels. This approach is common in pharmaceutical, food, environmental, and industrial testing where consistent measurements are required.
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.
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.
| Parameter | Typical acceptance criterion | Notes |
|---|---|---|
| Resolution | ≥ 1.5 | Baseline separation of adjacent peaks |
| Tailing factor | ≤ 2.0 | Peak symmetry measure |
| Theoretical plates | > 2000 | Column efficiency indicator |
| Injection repeatability | ≤ 2% RSD | Relative standard deviation for replicate injections |
| Linearity | r² ≥ 0.995 | Calibration curve over the working range |
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.
Quality control for HPLC testing combines scheduled checks, documented procedures, and review of results. Before sample analysis, system suitability testing confirms that the instrument, column, and method meet predefined criteria. Common criteria include resolution between critical peaks, retention time precision, peak tailing, and theoretical plate count. Failure triggers investigation before results are reported. Records link raw data, calculations, instrument logs, and analyst identity to each batch, supporting audits and repeat analysis.
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.
== Partitioning methods == The most common method of measuring amino acid hydrophobicity is partitioning between two immiscible liquid phases. Different organic solvents are most widely used to mimic the protein interior. However, organic solvents are slightly miscible with water and the characteristics of both phases change making it difficult to obtain pure hydrophobicity scale. Nozaki and Tanford proposed the first major hydrophobicity scale for nine amino acids. Ethanol and dioxane are used as the organic solvents and the free energy of transfer of each amino acid was calculated. Non liquid phases can also be used with partitioning methods such as micellar phases and vapor phases. Two scales have been developed using micellar phases. Fendler et al. measured the partitioning of 14 radiolabeled amino acids using sodium dodecyl sulfate (SDS) micelles. Also, amino acid side chain affinity for water was measured using vapor phases. Vapor phases represent the simplest non polar phases, because it has no interaction with the solute. The hydration potential and its correlation to the appearance of amino acids on the surface of proteins was studied by Wolfenden. Aqueous and polymer phases were used in the development of a novel partitioning scale. Partitioning methods have many drawbacks. First, it is difficult to mimic the protein interior. In addition, the role of self solvation makes using free amino acids very difficult. Moreover, hydrogen bonds that are lost in the transfer to organic solvents are not reformed but often in the interior of protein.
People convicted of murder, drug trafficking, corruption or human rights violations will not qualify under the amnesty law. The measure was long requested by the US-backed Venezuelan opposition. Opposition leader María Corina Machado said that the bill was not taken "voluntarily, but rather in response to pressure from the US government". Rodríguez also announced the shutdown of El Helicoide prison, which she said would be transformed into a cultural and sport center. Independent organizations have documented many cases of torture and human rights violation in El Helicoide. Family of some of the prisoners gathered outside El Helicoide chanting "Freedom!". Venezuelan opposition politician and ally of Machado, Juan Pablo Guanipa, was released from prison on 8 February but taken by unknown armed groups hours later; by 10 February, his family confirmed he was under house arrest in Maracaibo, calling the measure unjust detention. On 19 February, the amnesty law was approved by the National Assembly of Venezuela. Jorge Rodríguez said that over 1557 request liberty a day after. Juan Pablo Guanipa was also released from house arrest. During the 2026 State of the Union Address, Trump invited Venezuelan politician Enrique Márquez, who was imprisoned in 2025 and was released in early January. Trump said "Since the raid we have worked with the new leadership and they have ordered the closure of that vile prison and released hundreds of political prisoners already, with more to come."
Creation-science means origin through abrupt appearance in complex form, and includes biological creation, biochemical creation (or chemical creation), and cosmic creation. (...) Creation-science does not include as essential parts the concepts of catastrophism, a world-wide flood, a recent inception of the earth or life, from nothingness (ex nihilo), the concept of kinds, or any concepts from Genesis or other religious texts.
Not only paints and inks, but other industries such as pharmaceutical, construction, and cosmetics, especially hair styling aids and facial detoxifying masks increasingly favor bentonite and attapulgite clays over other rheology modifiers, dispersion aids, opacifying fillers, antifoam, and numerous niche uses which exploit the numerous inherent qualities which have drawn artisans to this material. Clays are sustainably sourced and do not involve any egregious environmental damage, which were among the cheapest bulk materials until recently, when the pricing went up steadily, following the upsurge in its use pattern. Cellulosics - CMC, HMC, HPMC, and others, are chemically substituted cellulose macromolecules. The hydroxyl groups are substituted by other functional groups, such as methyl or propyl. The amount of substitution and molecular weight determine viscosity of the solution, assuming concentration stays the same; adding more also increases viscosity. Sulfonates - Sodium or calcium salts, good water retention, versatile, and highly efficient. Gums - guar, xanthan, cellulose, locust bean, and acacia are the main ones. Saccharides - carrageenan, pullulan, konjac, and alginate, sometimes called hydrocolloids, these thickeners are extremely versatile and specific in function—each has a series of grades or types which behave differently, for example kappa carrageenan will form strong gels (potassium activated) but iota carrageenan will not form gels and only thickens. Proteins - Casein, collagen, and sometimes albumin.
Sources: en.wikipedia.org
The International Criminal Court (ICC) opened a preliminary investigation into Duterte's drug war in 2018, prompting Duterte to withdraw the Philippines from that body in response. Duterte was arrested on March 11, 2025 and transferred to ICC custody in The Hague the next day, making him the first Philippine president to face an international tribunal and the first Asian leader to face a trial before the ICC. Despite this, he was re-elected as the mayor of Davao City in 2025; as he remains in The Hague, his son Baste is serving in his place as the acting mayor. As he failed to take his oath within the prescribed six-month period, he was disqualified from assuming office under the provisions of the Local Government Code. Duterte is scheduled to face trial for crimes against humanity on November 30, 2026.
==== Federal level ==== On 6 August 2020, US President Donald Trump signed an order which would ban TikTok transactions in 45 days if it was not sold by ByteDance. On 14 August 2020, Trump issued another order giving ByteDance 90 days to sell or spin off its US TikTok business. In the order, Trump said that there is "credible evidence" that leads him to believe that ByteDance "might take action that threatens to impair the national security of the United States". In June 2021, US President Joe Biden signed an executive order revoking the Trump administration ban on TikTok, and instead ordered the Secretary of Commerce to investigate the app to determine if it poses a threat to US national security. On 27 December 2022, the Chief Administrative Officer of the United States House of Representatives banned TikTok from all devices managed by the House of Representatives. On 30 December 2022, President Joe Biden signed the No TikTok on Government Devices Act, prohibiting the use of the app on devices owned by the federal government, with some exceptions. On 13 March 2024, the United States House of Representatives passed H.R. 7521, which would ban TikTok entirely unless it was divested from its Chinese parent company, ByteDance. In April, the House of Representatives included a revised version of the bill in a foreign aid package, which was passed by the Senate on 23 April 2024, and signed into law by President Joe Biden the following day. The law was challenged in TikTok, Inc. v. Garland but was upheld as constitutional.
A large number of synthetic progestogens, or progestins, have been derived from progesterone and are used as medications as well. Examples include medroxyprogesterone acetate and norethisterone. In 2023, it was the 117th most commonly prescribed medication in the United States, with more than 5 million prescriptions.
Sources: en.wikipedia.org
Method validation is the documented process of confirming that an HPLC procedure is suitable for its intended use. It evaluates accuracy, precision, specificity, linearity, range, detection limits, and robustness. Validation criteria depend on the regulatory context and the sample type.
System suitability tests are short checks performed before or during an HPLC run to verify instrument and method performance. They often include resolution, tailing factor, theoretical plates, and injection precision. Results must meet predefined limits for sample data to be accepted.
HPLC retention time alone cannot definitively identify an unknown substance. A match with a reference standard under identical conditions provides supporting evidence. Confirmation typically requires mass spectrometry, nuclear magnetic resonance, or another orthogonal technique.
HPLC separates and detects individual compounds in a liquid sample, producing peaks at characteristic retention times. Peak area or height can be used to estimate concentration when calibrated with known standards. It does not identify unknown compounds with certainty unless additional detectors or reference materials are used.