Limit of detection raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2025-11-06. Anything still debated is marked as such rather than presented as settled.
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.
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 |
|---|---|---|
| Accuracy | Recovery near 100% | Depends on acceptance criteria and matrix |
| Precision | Relative standard deviation | Often at or below 2% for replicate injections |
| Limit of detection | Signal-to-noise ratio 3:1 | Approximate and method-specific |
| Limit of quantitation | Signal-to-noise ratio 10:1 | Confirmed by precision and accuracy |
| Resolution | 1.5 or greater | Typical system suitability target |
Method validation demonstrates that an HPLC procedure is suitable for its intended purpose. Common validation parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, and robustness. Accuracy reflects agreement with a reference value, while precision describes repeatability under defined conditions. Specificity shows whether the method can measure the analyte in the presence of impurities or matrix components. Validation documents are reviewed before a method is used for routine testing or regulatory submissions.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Typical checks include retention time, peak area precision, resolution between critical pairs, tailing factor, and theoretical plate count. Acceptance criteria are set in the method or pharmacopeial monograph. If a suitability check fails, the run may be rejected and the instrument or sample preparation may need investigation. This practice helps prevent release of data from a system that has drifted out of control.
Validation establishes that a method is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, robustness, and stability of standards and samples. Acceptance criteria are defined in advance, and results are documented in a validation report. Regulatory guidance for pharmaceuticals, foods, and environmental testing differs, so the applicable framework must be identified. Ongoing verification uses control samples and trend charts after validation. Method transfer to another laboratory may require partial revalidation.
Routine quality control includes blanks, duplicates, spiked samples, and certified reference materials. Calibration curves are prepared with standards at several concentrations, and the detector response is checked for linearity. Carryover, column aging, mobile phase evaporation, and temperature drift can shift retention times or peak areas. Maintenance such as replacing seals, filters, and columns helps prevent failures. Records of injections, integration, and deviations support traceability. Audits may request raw data and instrument logs for each batch.
AAA proteins are divided into seven basic clades, based on secondary structure elements included within or near the core AAA fold: clamp loader, initiator, classic, superfamily III helicase, HCLR, H2-insert, and PS-II insert. AAA ATPases assemble into oligomeric assemblies (often homo-hexamers) that form a ring-shaped structure with a central pore. These proteins produce a molecular motor that couples ATP binding and hydrolysis to changes in conformational states that can be propagated through the assembly in order to act upon a target substrate, either translocating or remodelling the substrate. The central pore may be involved in substrate processing. In the hexameric configuration, the ATP-binding site is positioned at the interface between the subunits. Upon ATP binding and hydrolysis, AAA enzymes undergo conformational changes in the AAA-domains as well as in the N-domains. These motions can be transmitted to substrate protein.
The Society recognizes achievements and promotes academic research through four annual awards. The Biemann Medal and the John B. Fenn Award for a Distinguished Contribution in Mass Spectrometry both are awarded in recognition of singular achievements or contributions in fundamental or applied mass spectrometry, with the Biemann Medal being focused on individuals who are early in their careers. The Ronald A. Hites Award is awarded for outstanding original research demonstrated in papers published in the Journal of the American Society for Mass Spectrometry. The Research Awards are given to young scientists in mass spectrometry, based on the evaluation of their proposed research. The Fellows of ASMS are awarded to individuals in recognition for their scientific contribution to mass spectrometry and for their contribution to the ASMS community. Journal of the American Society for Mass Spectrometry Measuring Mass: From Positive Rays to Proteins The past presidents of ASMS are:
Vaginal films are soluble, thin sheets of medication that are inserted into the vagina where they dissolve and release the substances. Typical uses include delivery of contraceptive substances or antibiotics for infections. These films are inserted by simply pushing them into the vagina with one’s fingers. There they dissolve quickly upon interaction with natural vaginal fluids. Bioadhesives are substances that naturally stick to live tissue. Currently, studies are being done on bioadhesives adhering to cervical mucous membranes to allow for an extended release period. The drug would be released with mucus to create a localized treatment with high effectiveness. This is anticipated to be highly useful for treatment of cervical cancer. Bioadhesives can come in multiple forms, such as films, tablets, or gels. The appeal of bioadhesives is that they take advantage of the mucous environment surrounding the cervix and utilize it to benefit the drug delivery mechanism.
Sources: en.wikipedia.org
CSF drug delivery refers to a number of methods designed to administer therapeutic agents directly into the CSF, bypassing the BBB to achieve higher drug concentrations in the CNS. This technique is particularly beneficial for treating neurological disorders such as brain tumors, infections, and neurodegenerative diseases. Intrathecal injection, where drugs are injected directly into the CSF via the lumbar region, and intracerebroventricular injection, targeting the brain's ventricles, are common approaches. These methods ensure that drugs can reach the CNS more effectively than systemic administration, potentially improving therapeutic outcomes and reducing systemic side effects. Advances in this field are driven by ongoing research into novel delivery systems and drug formulations, enhancing the precision and efficacy of treatments. Intrathecal pseudodelivery refers to a particular drug delivery method where the therapeutic agent is introduced into a reservoir connected to the intrathecal space, rather than being released into the CSF and distributed throughout the CNS. In this approach, the drug interacts with its target within the reservoir, allowing for changing the composition of the CSF without systemic release. This method can be advantageous for maximizing efficacy and minimizing systemic side effects.
ASBMB hosts and sponsors numerous meetings each year. The annual meeting is held each April in conjunction with the Experimental Biology meeting. Additionally, themed special symposia are organized throughout the year. The society also produces webinars throughout the year focused on topics related to scientific research, professional development and education. The society offers twenty-five different awards, grants, and scholarships.
The Aviation Safety Reporting System (ASRS) collects voluntarily submitted aviation safety incident/situation reports from pilots, controllers and others. The ASRS uses reports to identify system deficiencies, issue alert messages, and produce two publications, CALLBACK, and ASRS Directline. The collected information is made available to the public, and is used by the FAA, NASA and other organizations working in research and flight safety.
Sources: en.wikipedia.org
One mechanism through which BDNF appears to maintain elevated levels of neuronal excitation is through preventing GABAergic signaling activities. While glutamate is the brain's major excitatory neurotransmitter and phosphorylation normally activates receptors, GABA is the brain's primary inhibitory neurotransmitter and phosphorylation of GABAA receptors tend to reduce their activity. Blockading BDNF signaling with a tyrosine kinase inhibitor or a PKC inhibitor in wild type mice produced significant reductions in spontaneous action potential frequencies that were mediated by an increase in the amplitude of GABAergic inhibitory postsynaptic currents (IPSC). Similar effects could be obtained in BDNF knockout mice, but these effects were reversed by local application of BDNF. This suggests BDNF increases excitatory synaptic signaling partly through the post-synaptic suppression of GABAergic signaling by activating PKC through its association with TrkB. Once activated, PKC can reduce the amplitude of IPSCs through to GABAA receptor phosphorylation and inhibition. In support of this putative mechanism, activation of PKCε leads to phosphorylation of N-ethylmaleimide-sensitive factor (NSF) at serine 460 and threonine 461, increasing its ATPase activity which downregulates GABAA receptor surface expression and subsequently attenuates inhibitory currents.
Lewis acids have been classified in the ECW model and it has been shown that there is no one order of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by C-B plots. It has been shown that to define the order of Lewis acid strength at least two properties must be considered. For Pearson's qualitative HSAB theory the two properties are hardness and strength while for Drago's quantitative ECW model the two properties are electrostatic and covalent. Monoprotic acids, also known as monobasic acids, are those acids that are able to donate one proton per molecule during the process of dissociation (sometimes called ionization) as shown below (symbolized by HA):
The cell membrane can form different types of "supramembrane" structures such as caveolae, postsynaptic densities, podosomes, invadopodia, focal adhesions, and different types of cell junction. These structures are usually responsible for cell adhesion, communication, endocytosis and exocytosis. They are composed of specific proteins, such as integrins and cadherins. They can be visualized by electron microscopy or fluorescence microscopy.
RGD was identified as the minimal recognition sequence within fibronectin required for cell attachment by Ruoslahti and Pierschbacher in the early 1980s. To do this, the authors synthesized various peptides based on the hypothesized cell attachment site of fibronectin. They then coupled those peptides to protein-coated plastic and tested each for cell attachment-promoting activity. Only those that contained the RGD sequence were found to enhance cell attachment. Further, they showed that peptides containing RGD were able to inhibit cell attachment to fibronectin-coated substrates, whereas peptides not containing RGD did not. These foundational studies also identified the cellular receptors that recognize the sequence. These studies utilized a synthetic RGD-containing peptide to isolate the putative receptors, and then demonstrated that liposomes containing the isolated proteins could bind to fibronectin, in much the same way as cells with surface receptors. The discovered receptors were later named integrins. The RGD motif is presented in slightly different ways in different proteins, making it possible for the many RGD-binding integrins to selectively distinguish individual adhesion proteins.
Sources: en.wikipedia.org
Validation establishes suitability for a new method, while verification confirms that a method works in a specific laboratory. Verification is often used when a validated method is adopted with existing equipment and staff. Both rely on documented acceptance criteria.
Quantification usually compares detector response to a standard curve made from reference standards. The curve may be external, internal, or based on standard addition depending on matrix effects. Results are reported with units and, when required, uncertainty.
Carryover occurs when analyte from a previous injection remains in the system and appears in a later chromatogram. It can come from the injector, column, or tubing. Blank injections and needle washes help detect and reduce it.
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.