A practical reference on calibration curve: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-05-01 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.
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.
| 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. |
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.
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.
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.
==== Lieutenant of the Royal Victorian Order (LVO) ==== Hamish Blair, Senior Executive Officer, Scottish Office. Captain Robert Neil Blair, Royal Navy, Private Secretary to The Duke of York and to Princess Alexandra, the Honourable Lady Ogilvy. Laurence Albert Brown. For services to the Royal Collection. Donald Reeve Buttress, Surveyor of the Fabric, Westminster Abbey. Bernard Joseph Frahm, . For services to the Crown on Royal Visits to New Zealand. Commander Thomas Dixon Laidlaw, , Metropolitan Police. Leonora Mary, The Countess of Lichfield, Extra Lady in Waiting to The Princess Royal. Allan Arthur Percival, lately Press Secretary to The Prince of Wales. Alexander Hay Sutherland, Chief Publicity Officer, Scottish Office.
=== Anxiety disorders === Recent studies have linked smoking to anxiety disorders, suggesting the correlation (and possibly mechanism) may be related to the broad class of anxiety disorders, and not limited to just depression. Current and ongoing research attempts to explore the addiction-anxiety relationship. Data from multiple studies suggest that anxiety disorders and depression play a role in cigarette smoking. A history of regular smoking was observed more frequently among individuals who had experienced a major depressive disorder at some time in their lives than among individuals who had never experienced major depression or among individuals with no psychiatric diagnosis. People with major depression are also much less likely to quit due to the increased risk of experiencing mild to severe states of depression, including a major depressive episode. Depressed smokers appear to experience more withdrawal symptoms on quitting, are less likely to be successful at quitting, and are more likely to relapse.
By 1951, Alec Todd and collaborators at the University of Cambridge had determined by biochemical methods how the backbone of DNA is structured via the successive linking of carbon atoms 3 and 5 of the sugar to phosphates. This would help to corroborate Watson and Crick's later X-ray structural work. Todd would later be awarded the 1957 Nobel Prize in Chemistry for this and other discoveries related to DNA. Late in 1951, Francis Crick started working with James Watson at the Cavendish Laboratory within the University of Cambridge. DNA's role in heredity was confirmed in 1952 when Alfred Hershey and Martha Chase in the Hershey–Chase experiment showed that DNA is the genetic material of the enterobacteria phage T2.
Sources: en.wikipedia.org
On July 13, 2024, Trump survived an assassination attempt while addressing a campaign rally near Butler, Pennsylvania. Trump was shot and wounded on his right ear by 20-year-old Thomas Crooks, who fired eight rounds with an AR-15–style rifle from the roof of a building approximately 400 feet (120 metres) from the stage; the shots killed one audience member and critically injured two others. Seconds later, Crooks was shot and killed by the U.S. Secret Service's counter-sniper team. On September 11, 2024, a bipartisan Senate report identified technical issues and other preventable mistakes by the Secret Service during the event. On September 15, 2024, Trump survived a second assassination attempt at Trump International Golf Club in West Palm Beach, Florida. The perpetrator, 58-year-old Ryan Wesley Routh, took position in nearby shrubbery holding an SKS-style rifle just outside the fence of the golf course. After hiding there for nearly 12 hours, Routh pointed his weapon through the fence line, approximately 400 yards (370 m) away from Trump. A Secret Service agent noticed this and fired four rounds towards Routh, who fled the scene and was later captured in Martin County. No injuries were reported. Routh was later indicted on five federal charges and three state charges, all of which Routh pleaded not guilty to. His trial began on September 8, 2025. Two weeks later on September 23, Routh was found guilty on all federal counts, where he then grabbed a pen and attempted to stab himself in the neck, before being tackled by U.S. marshals.
Examples of China's increasing global presence as an arms supplier in 2010–14 included deals with Venezuela for armoured vehicles and transport and trainer aircraft, with Algeria for three frigates, with Indonesia for the supply of hundreds of anti-ship missiles and with Nigeria for the supply of several unmanned combat aerial vehicles. Following rapid advances in its arms industry, China has become less dependent on arms imports, which decreased by 42 percent between 2005–09 and 2010–14. Russia accounted for 61 percent of Chinese arms imports, followed by France with 16 percent and Ukraine with 13 per cent. Helicopters formed a major part of Russian and French deliveries, with the French designs produced under licence in China. From 2021 to 2026, China's arms imports fell by 72 percent; Russia accounted for 66 percent of China's arms imports. Over the years, China has struggled to design and produce effective engines for combat and transport vehicles. It continued to import large numbers of engines from Russia and Ukraine in 2010–14 for indigenously designed combat, advanced trainer and transport aircraft, and naval ships. It also produced British-, French- and German-designed engines for combat aircraft, naval ships and armoured vehicles, mostly as part of agreements that have been in place for decades. In August 2021, China tested a nuclear-capable hypersonic missile that circled the globe before speeding towards its target.
Leukotriene C4 synthase is an enzyme that in humans is encoded by the LTC4S gene. The protein encoded by this gene, LTC4S (or glutathione S-transferase II) is an enzyme that converts leukotriene A4 and glutathione to create leukotriene C4. This is a member of MAPEG family of transmembrane proteins. A trimer of Leukotriene C4 synthase is localized on the outer nuclear membrane and endoplasmic reticulum, where it forms a complex with 5-Lipoxygenase-activating protein. This protein is remotely related to microsomal glutathione S-transferase.
Sources: en.wikipedia.org
Because of its position at the mouth of the Guadalquivir, Sanlúcar is a convenient home base for exploring the nearby Doñana National Park (Parque Nacional de Doñana) and its natural features. Within the park lies the Marisma de Hinojos (Salt Marsh of Fennel Plants); also within its precincts is the possible site of the legendary lost city of Tartessos, the capital of an ancient civilization that predated the Phoenicians in Iberia.
The colour-fast (non-fading) dye was an item of luxury trade, prized by Romans, who used it to colour ceremonial robes. Used as a dye, the colour shifts from blue (peak absorption at 590 nm, which is yellow-orange) to reddish-purple (peak absorption at 520 nm, which is green). It is believed that the intensity of the purple hue improved rather than faded as the dyed cloth aged. Vitruvius mentions the production of Tyrian purple from shellfish. In his History of Animals, Aristotle described the shellfish from which Tyrian purple was obtained and the process of extracting the tissue that produced the dye. Pliny the Elder described the production of Tyrian purple in his Natural History:
=== Industrial origin === Perchlorates are used mostly in rocket propellants but also in disinfectants, bleaching agents, and herbicides. Perchlorate contamination is caused during both the manufacture and ignition of rockets and fireworks. Fireworks are also a source of perchlorate in lakes. Removal and recovery methods of these compounds from explosives and rocket propellants include high-pressure water washout, which generates aqueous ammonium perchlorate.
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.
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.