This is a working overview of calibration curve, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-01-03. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| 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 |
Regulatory and pharmacopeial texts shape how HPLC testing is performed and documented. The International Council for Harmonisation provides validation guidance, while pharmacopeias publish general chromatography chapters and monographs for specific materials. Accreditation standards such as ISO/IEC 17025 address laboratory competence and traceability. Inspectors may review instrument qualification, analyst training, reference material control, and electronic records. Open questions include how best to validate methods for new complex products and how to handle automated data processing. Laboratories generally resolve these issues through risk assessment, method lifecycle management, and documented scientific justification.
In quality control laboratories, HPLC testing supports batch release, raw material checks, stability studies, and impurity profiling. A validated method defines sample preparation, instrument settings, calibration, and acceptance criteria. Analysts compare results with specifications and investigate out-of-specification outcomes before a batch is approved. Documentation includes chromatograms, integration records, audit trails, and reagent details. Because results influence product decisions, laboratories follow formal quality systems and data integrity rules. The exact tests and limits depend on the material, its intended use, and the applicable regulatory framework.
Method validation examines whether an HPLC procedure is suitable for its intended purpose. Common parameters include accuracy, precision, specificity, linearity, range, detection limit, quantification limit, and robustness. Accuracy describes closeness to a true or accepted value, while precision describes agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from related substances. Robustness tests small deliberate changes in flow, temperature, or solvent composition. Validation is not a one-time event; methods may need partial revalidation after changes to instruments, columns, sample handling, or specification limits. Regulatory guidance provides frameworks, but some details remain method-specific.
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.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. UV detection is widely used because many organic compounds absorb light, but it requires a chromophore. Mass spectrometry provides mass-based identification and high sensitivity for trace analytes. Each detector has trade-offs in selectivity, cost, and compatibility with mobile phases. Quantification typically uses calibration curves prepared from reference standards. Results are reported as concentration, purity, or presence above a limit.
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.
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 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.
== Corneal cross-linking == In 2002, Hafezi's clinical and research interests turned to the cornea. He became a corneal specialist, and his work helped develop the principles of corneal collagen cross-linking (CXL) and translate CXL from a laboratory into a clinical setting, initially for the treatment of keratoconus. Hafezi's combination of basic science knowledge combined with clinical, surgical experience of CXL has led him to become one of the world's leading experts on both keratoconus and cross-linking technology. The impact of CXL on the treatment of keratoconus is hard to underestimate: today, CXL considered to be the treatment of choice for progressive keratoconus and corneal ectasias, reducing the need for corneal transplantation by half. Hafezi continued to work to expand the number of people who could benefit from CXL. Briefly, the original CXL method, termed the Dresden Protocol, involves removing the central 8–10 mm of the corneal epithelium of adult patients with corneas thicker than 400 μm, and applying 0.1% riboflavin solution to the cornea for 30 minutes before, and at 5-minute intervals during 365 nm UV-A irradiation of the corneal surface at an irradiance of 3 mW/cm2. Hafezi has helped push the boundaries, pioneering CXL in children with keratoconus, the use of hypoosmolar riboflavin solutions to treat people with thin (≤400 μm) corneas. and using CXL to treat post-LASIK ectasia. The knowledge Hafezi accrued from this work led to him becoming a leading international expert on corneal ectasia in general and keratoconus in particular.
== Culinary use == In modern times, peach gum is primarily used as a food ingredient, particularly in Asian cuisine. It requires soaking in water for 8-12 hours before use, during which it softens and expands significantly. Common preparations include:
Initially, by analogy with neutron magic number 126, the next proton shell was also expected at element 126, too far beyond the synthesis capabilities of the mid-20th century to get much theoretical attention. In 1966, new values for the potential and spin–orbit interaction in this region of the periodic table contradicted this and predicted that the next proton shell would instead be at element 114, and that nuclei in this region would be relatively stable against spontaneous fission. The expected closed neutron shells in this region were at neutron number 184 or 196, making 298Fl and 310Fl candidates for being doubly magic. 1972 estimates predicted a half-life of around 1 year for 298Fl, which was expected to be near an island of stability centered near 294Ds (with a half-life around 1010 years, comparable to 232Th). After making the first isotopes of elements 112–118 at the turn of the 21st century, it was found that these neutron-deficient isotopes were stabilized against fission. In 2008 it was thus hypothesized that the stabilization against fission of these nuclides was due to their oblate nuclei, and that a region of oblate nuclei was centred on 288Fl. Also, new theoretical models showed that the expected energy gap between the proton orbitals 2f7/2 (filled at element 114) and 2f5/2 (filled at element 120) was smaller than expected, so element 114 no longer appeared to be a stable spherical closed nuclear shell.
Ultralente insulin was a long-acting form of insulin. It has an onset of 4 to 6 hours, a peak of 14 to 24 hours, and a duration of 28 to 36 hours. Due to its slow onset and long duration, daily shots were used to meet basal insulin needs. Ultralente insulin, along with lente insulin, was discontinued in the US by manufacturers in the mid-2000s. One of the reasons for discontinuation was declining use in favor of NPH insulin and other newer insulin products. The FDA withdrew approval for ultralente insulin products by 2011.
Sources: en.wikipedia.org
is the spatial velocity gradient tensor. If only these two original criteria are used to define hypoelasticity, then hyperelasticity would be included as a special case, which prompts some constitutive modelers to append a third criterion that specifically requires a hypoelastic model to not be hyperelastic (i.e., hypoelasticity implies that stress is not derivable from an energy potential). If this third criterion is adopted, it follows that a hypoelastic material might admit nonconservative adiabatic loading paths that start and end with the same deformation gradient but do not start and end at the same internal energy. Note that the second criterion requires only that the function
The effects of growth hormone (GH) deficiency vary depending on the age at which they occur. Alterations in somatomedin can result in growth hormone deficiency with two known mechanisms; failure of tissues to respond to somatomedin, or failure of the liver to produce somatomedin. Major manifestations of GH deficiency in children are growth failure, the development of a short stature, and delayed sexual maturity. In adults, somatomedin alteration contributes to increased osteoclast activity, resulting in weaker bones that are more prone to pathologic fracture and osteoporosis. However, deficiency is rare in adults, with the most common cause being a pituitary adenoma. Other adult causes include a continuation of a childhood problem, other structural lesions or trauma, and very rarely idiopathic GHD. Adults with GHD "tend to have a relative increase in fat mass and a relative decrease in muscle mass and, in many instances, decreased energy and quality of life". Diagnosis of GH deficiency involves a multiple-step diagnostic process, usually culminating in GH stimulation tests to see if the patient's pituitary gland will release a pulse of GH when provoked by various stimuli.
The visionary Swiss painter Peter Birkhäuser was treated by a student of Jung, Marie-Louise von Franz, and corresponded with Jung about the translation of dream symbolism into works of art. American abstract expressionist Jackson Pollock underwent Jungian psychotherapy in 1939 with Joseph Henderson. Henderson engaged Pollock through his art, having him make drawings, which led to the appearance of many Jungian concepts in his paintings. Contrary to some sources, Jung did not visit Liverpool but recorded a dream in which he did, and of which he wrote, "Liverpool is the pool of life, it makes to live." A plaster statue of Jung was erected in Mathew Street in 1987 that was vandalised and replaced by a more durable version in 1993.
=== Moisture control === Desiccants are hygroscopic materials used to reduce water vapour inside sealed packages. They are commonly supplied as sachets, canisters, tablets, closures, labels, or components incorporated into packaging materials. Moisture-control systems are used with foods, pharmaceuticals, electronics, machinery, diagnostic products, and other moisture-sensitive goods. Their performance depends on the initial moisture level, internal package volume, storage humidity, temperature, package permeability, and absorption capacity of the desiccant. Some pharmaceutical containers incorporate desiccants into bottle closures or internal structures. This reduces the risk of consumers accidentally removing or mishandling a loose sachet.
indicate that the four-fold degeneracy (two valley and two spin degrees of freedom) of the Landau energy levels is partially or completely lifted. One hypothesis proposes that magnetic catalysis of symmetry breaking is responsible for this degeneracy lift.
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.
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.