A practical reference on precision: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-01-31 and is reviewed periodically as new material appears.
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.
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.
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 |
Routine HPLC testing compares a sample result with a calibration curve prepared from known reference standards. Peak area or peak height is plotted against concentration, and the curve is used to estimate unknown amounts. Retention time supports tentative identification when compared with a standard, though mass spectrometry or another confirmatory method may be needed for definitive identification. Pre-run checks verify repeatability, resolution, and peak symmetry before sample analysis. Limits of detection and quantification describe the smallest amounts that can be reliably observed or measured. Sample preparation, filtration, and degassing help prevent column damage and inconsistent results.
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.
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.
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.
Monocytes respond to bacterial pathogen-associated molecular patterns (PAMPs), or damage-associated molecular patterns (DAMPs) by activating the extrinsic pathway of coagulation. Neutrophils facilitate the blood coagulation by NETosis, while platelets facilitate neutrophils' NETosis. NETs bind tissue factor, binding the coagulation centers to the location of infection. They also activate the intrinsic coagulation pathway by providing a negatively charged surface for factor XII. Other neutrophil secretions, such as proteolytic enzymes which cleave coagulation inhibitors, also bolster the process. In case of imbalance in the regulation of immunothrombosis, this process can become aberrant. Regulatory defects in immunothrombosis are suspected to be a major factor in pathological thrombosis in forms such as disseminated intravascular coagulation (DIC) or deep vein thrombosis. DIC in sepsis is a prime example of both the dysregulated coagulation process and an undue systemic inflammatory response. It results in a multitude of microthrombi. These are similar in composition to the thrombi produced in native immunothrombosis — they are made up of fibrin, platelets, neutrophils and NETs.
A herbarium is a collection of preserved plant specimens and associated data used for scientific study. Originally, the word "herbarium" referred to books about medicinal plants. In 1700, French botanist Joseph Pitton de Tournefort used the word to describe a collection of dried plants and Carl Linnaeus continued to use this term in his work which is where the term caught on. Initially, herbarium collections were bound in volumes instead of on individual sheets as it is done today. It is not exactly known how long dry plant specimens last in storage, but with proper conservation, they have been able to last many centuries. Specimens collected by Linnaeus in the eighteenth century and by Banks and Solander on the Endeavour voyage in 1788 are still excellently preserved. The specimens may be whole plants or plant parts. These will usually be dried and pressed and mounted on a sheet of paper but, depending upon the material, may also be stored in boxes or kept in alcohol or other preservatives.
In particular, the Osedax worm lacks specific gene families involved in bone lipid and carbohydrate metabolism. This function is complemented by the Oceanospirillales symbionts, which utilize the glyoxylate cycle to catabolize nutrients from whale bones and convert fatty acids into carbohydrates. The Osedax are then able to take up and store the end products as glycogen. Bacteriocytes are present in the Osedax lower trunk subepidermal connective tissue, and there are additional genes in the bacteriocytes that encode amino acids and glucose and aid in digestion and absorption of proteins into the roots.
== Pathophysiology == Hemoglobin H disease is a genetic disorder resulting in absent or impaired production of the α-globin protein, a normal component of the hemoglobin. The disease occurs when the α-globin gene expression is reduced to less than 30% of the normal expression. In a healthy individual there are four copies of the gene which encode the α-globin protein. α-globin is encoded by the HBA1 (2 copies) and HBA2 (2 copies) genes. The genotype of healthy individuals with four normal copies of α-globin is annotated as αα/αα. In individuals with deletional HbH disease, there is deletion of three of the four α-globin alleles, which is annotated as --/-α. Non-deletional HbH disease refers to a decreased α-globin that has not occurred as a result of the complete deletion of the DNA sequences encoding HBA1 and HBA2, and this is more rare than the deletional type. The most common hemoglobin found within adult red blood cells is hemoglobin A. The structure of HbA consists of two α-globin chains bound to two β-globin chains to form a tetramer (a protein made up four protein chains). When there is lower than normal production of α-globin, as in HbH disease, the excess β-globin form β4-tetramers, termed hemoglobin H. These β4-tetramers accumulate in red blood cells and precipitate to form HbH inclusion bodies. The inclusion bodies in the mature red blood cells are removed by the spleen and this results in an early destruction of these red blood cells. This destruction of red blood cells by the spleen is termed extravascular hemolysis.
Sources: en.wikipedia.org
=== Phosphorylation and sulfation === Some of the tyrosine residues can be tagged (at the hydroxyl group) with a phosphate group (phosphorylated) by protein kinases. In its phosphorylated form, tyrosine is called phosphotyrosine. Tyrosine phosphorylation is considered to be one of the key steps in signal transduction and regulation of enzymatic activity. Phosphotyrosine can be detected through specific antibodies. Tyrosine residues may also be modified by the addition of a sulfate group, a process known as tyrosine sulfation. Tyrosine sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.
It was like a cloudy day all day long, in fact, we didn’t realize it was smoke at first. The smoke was about 500 feet above us, so we couldn’t see the sky. However, we could see horizontally for long distances with no problem. We knew it was smoke when the mucous from our nostrils started to look black..." A paper published in 2000 analyzed the degree of exposure by troops to particulate matter, including soot. However, the paper focused more-so on silica sand, which can produce silicosis. The paper included troop medical records, and in its conclusion: "A literature review indicated negligible to nonexistent health risk from other inhaled particulate material (other than silica) during the Gulf War".
Theo Wallimann (born 13 October 1946 in Alpnach, Obwalden, Switzerland) is a Swiss biologist who was research group leader and Adjunct-Professor at the Institute of Cell Biology ETH Zurich and later at the Institute of Molecular Health Science https://mhs.biol.ethz.ch/about-us/emeriti-formermembers/wallimann.html at the ETH Zurich at the Biology Department https://biol.ethz.ch/en/, of the ETH Zurich, Switzerland.
The same cannot be said for human bone collagen, as δ18O values in collagen seem to be impacted by drinking water, food water, and a combination of metabolic and physiological processes. δ18O values from bone minerals are essentially an averaged isotopic signature throughout the entire life of the individual. While carbon and nitrogen are used primarily to investigate the diets of ancient humans, oxygen isotopes offer insight into body water at different life stages. δ18O values are used to understand drinking behaviors, animal husbandry, and track mobility. 97 burials from the ancient Maya citadel of Tikal were studied using oxygen isotopes. Results from tooth enamel identified statistically different individuals, interpreted to be individuals from Maya lowlands, Guatemala, and potentially Mexico. Historical context combined with isotopic data from burials were used to argue that migrant individuals were a part of lower and higher social classes within Tikal. Female migrants who arrived in Tikal during Early Classic period could have been the brides of Maya elite.
Three prime untranslated regions (3′UTRs) of mRNAs often contain regulatory sequences that post-transcriptionally cause RNAi. Such 3′-UTRs often contain both binding sites for miRNAs as well as for regulatory proteins. By binding to specific sites within the 3′-UTR, miRNAs can decrease gene expression of various mRNAs by either inhibiting translation or directly causing degradation of the transcript. The 3′-UTR also may have silencer regions that bind repressor proteins that inhibit the expression of a mRNA. The 3′-UTR often contains microRNA response elements (MREs). MREs are sequences to which miRNAs bind, primarily through evolutionarily conserved seed sequences six to eight nucleobases in length. These are prevalent motifs within 3′-UTRs. Among all regulatory motifs within the 3′-UTRs (e.g. including silencer regions), MREs make up about half of the motifs. As of 2023, the miRBase web site, an archive of miRNA sequences and annotations, listed 28,645 entries in 271 biologic species. Of these, 1,917 miRNAs were in annotated human miRNA loci. miRNAs were predicted to have an average of about four hundred target mRNAs (affecting expression of several hundred genes). Friedman et al. estimate that >45,000 miRNA target sites within human mRNA 3′UTRs are conserved above background levels, and >60% of human protein-coding genes have been under selective pressure to maintain pairing to miRNAs. Direct experiments show that a single miRNA can reduce the stability of hundreds of unique mRNAs.
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.