method validation comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-07-11. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Validation parameter | Accuracy | Closeness of measured value to accepted reference value |
| Validation parameter | Precision | Agreement among repeated measurements under specified conditions |
| System suitability check | Resolution ≥ 1.5 | Baseline separation between critical peak pair |
| System suitability check | Tailing factor ≤ 2.0 | Common target for peak symmetry |
| Documentation | Validation report | Summarizes experiments, acceptance criteria, and conclusions |
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.
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 by passing them through a packed column under pressure. A pump delivers a mobile phase at a controlled flow rate, and an injector introduces the sample into the stream. Differences in how analytes partition between the mobile phase and the stationary phase cause them to exit the column at different times. Detection then records a signal proportional to the amount of each separated substance. The resulting chromatogram provides retention times and peak areas for identification and quantification.
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.
Consequently, the players were handed the full minimum suspensions of two years – these were backdated to 31 March 2015, which was the date of the original AFL Tribunal not guilty verdict; and, with credit taken for the periods of provisional suspension already served during the 2014/15 offseason, resulted in most of the suspensions running until November 2016.
Stimulants, also known as "psychostimulants", induce euphoria with improvements in mental and physical function, such as enhanced alertness, wakefulness, and locomotion. Stimulants are also occasionally called "uppers". Depressants or "downers", which decrease mental or physical function, are in stark contrast to stimulants and are considered to be their functional opposites. Stimulants enhance the activity of the central and peripheral nervous systems. Common effects may include increased alertness, awareness, wakefulness, endurance, productivity, and motivation, arousal, locomotion, heart rate, and blood pressure, and a diminished desire for food and sleep. Use of stimulants may cause the body to significantly reduce its production of endogenous compounds that fulfill similar functions. Once the effect of the ingested stimulant has worn off the user may feel depressed, lethargic, confused, and dysphoric. This is colloquially termed a "crash" and may promote reuse of the stimulant. Amphetamines are a significant cause of drug-induced psychosis. Importantly, a 2019 meta-analysis found that 22% of people with amphetamine-induced psychosis transition to a later diagnosis of schizophrenia. Examples of stimulants include:
=== Sonic spray ionization === Sonic spray ionization is method for creating ions from a liquid solution, for example, a mixture of methanol and water. A pneumatic nebulizer is used to turn the solution into a supersonic spray of small droplets. Ions are formed when the solvent evaporates and the statistically unbalanced charge distribution on the droplets leads to a net charge and complete desolvation results in the formation of ions. Sonic spray ionization is used to analyze small organic molecules and drugs and can analyze large molecules when an electric field is applied to the capillary to help increase the charge density and generate multiple charged ions of proteins. Sonic spray ionization has been coupled with high performance liquid chromatography for the analysis of drugs. Oligonucleotides have been studied with this method. SSI has been used in a manner similar to desorption electrospray ionization for ambient ionization and has been coupled with thin-layer chromatography in this manner.
=== Data modelling === Much of Aarons' work focuses on building an understanding of how the effects of drugs or toxic agents are managed in humans. In 2009 he co-authored a paper that aimed to explore an approach to the modelling of effects on people by drugs and toxic agents "based on the underlying physiology and pathology of the biological processes,...[ and to review]...the current status of pharmacodynamic and pharmacokinetic modelling, and outline a conceptual framework that may be helpful in advancing the field." A model was proposed that included the kinetics of the substance as a part of the process. To some extent, this was a challenge to the widely accepted dose/effect concept in pharmacology and toxicology at the time which assumed that the exposure/dose of a drug or a toxin is related to the effects on the patient, beneficial or toxic. The paper explained the purposes of data modelling as being to describe complex data, test hypotheses and make predictions, and noted when a drug interacts with a patient, there is a "chain of events at the molecular level, cellular level, organ/physiological system level, and whole-body level...[and ]... in principle, modelling may be performed at each of these levels." The effect on a patient could be therapeutic or possibly result in adverse outcomes. The authors concluded that including the systems biology model they discussed in the paper into conventional PKPD modelling would require further collaboration to make it robust but able to be clearly defined.
Sources: en.wikipedia.org
In human anatomy, the mesentery is an organ that attaches the intestines to the posterior abdominal wall, consisting of a double fold of the peritoneum. It helps (among other functions) in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestines. The mesocolon (the part of the mesentery that attaches the colon to the abdominal wall) was formerly thought to be a fragmented structure, with all named parts—the ascending, transverse, descending, and sigmoid mesocolons, the mesoappendix, and the mesorectum—separately terminating their insertion into the posterior abdominal wall. However, in 1925, new microscopic and electron microscopic examinations showed the mesocolon to be a single structure derived from the duodenojejunal flexure and extending to the distal mesorectal layer. Thus the mesentery is an internal organ. Now known as a continuous organ the mesentery can be divided into two sections, a mesenteric region or domain containing the abdominal digestive components, and a nonmesenteric region containing the urogenital system, musculoskeletal system, and the great vessels.
=== Aerobic Exercise === Aerobic exercise is also known as cardio because it is a form of cardiovascular conditioning. This includes exercises such as running, cycling, swimming and rowing. Athletes involved in aerobic exercise are typically looking to increase their endurance. These athletes are training their slow twitch muscle fibers to be better at taking in oxygen and getting it to their muscles. This is done by two mechanisms, glycolysis and aerobic respiration. Anaerobic glycolysis is also referred to as the "short term energy system", and is mostly used for high-intensity training, such as sprinting, and any sports which require quick bursts of speed. Slow twitch muscles are smaller in diameter and are slow to contract. These fibers don't store much glycogen, instead they use lipids and amino acids to generate energy. It has been shown that amino acids contributed around 3% of the total energy expenditure during endurance exercise. With a high concentration of myoglobin that stores oxygen, the slow twitch muscle fibers have plenty of oxygen to function properly. These factors help make slow twitch muscle fibers fatigue resistant so athletes can have endurance in their sport. There are many options for supplements that athletes can take to assist with endurance like glycerol and guarana.
The I1 receptor appears to be a G protein-coupled receptor that is localized on the plasma membrane. It may be coupled to PLA2 signalling and thus prostaglandin synthesis. In addition, activation inhibits the sodium-hydrogen antiporter and enzymes of catecholamine synthesis are induced, suggesting that the I1 receptor may belong to the neurocytokine receptor family, since its signaling pathways are similar to those of interleukins. It is found in the neurons of the reticular formation, the dorsomedial medulla oblongata, adrenal medulla, renal epithelium, pancreatic islets, platelets, and the prostate. They are notably not expressed in the cerebral cortex or locus coeruleus. Animal research suggests that much of the antihypertensive action of imidazoline drugs such as clonidine is mediated by the I1 receptor. In addition, I1 receptor activation is used in ophthalmology to reduce intraocular pressure. Other putative functions include promoting Na+ excretion and promoting neural activity during hypoxia.
Sources: en.wikipedia.org
The Battle of Binh Ba, also known as Operation Hammer, was a hard-fought, but one-sided, battle. Troops from the 5th Battalion, Royal Australian Regiment (5RAR) fought a PAVN/VC force in the village of Binh Ba, 5 kilometres (3.1 mi) north of Nui Dat in Phuoc Tuy Province resulting in 107 PAVN/VC killed and eight captured for the loss of one Australian killed.
Due to the concerns of legal risk, few laboratories offer this type of testing anymore, as they deem it unreliable and unsupportable. The Society of Hair Testing also notes the limitations of EtG, stating that this form of testing can determine "chronic excessive alcohol consumption only. This consensus is not applicable for determination of abstinence from alcohol or moderate consumption of alcohol." SoFT also states that "It is not advisable to use the results of the hair testing for alcohol markers in isolation," supporting the belief that additional testing evidence is required to properly identify an individual's alcohol usage. As such, this form of testing is only applicable for scenarios where severe alcohol abuse is present. The U.S. Substance Abuse and Mental Health Services Administration has cautioned that the test is "scientifically unsupportable as the sole basis for legal or disciplinary action" because the highly sensitive tests "are not able to distinguish between alcohol absorbed into the body from exposure to many common commercial and household products containing alcohol or from the actual consumption of alcohol." The U.S. Food and Drug Administration has not granted FDA clearance to the Psychemedics Corporation for their EtG Alcohol test at this time, which brings the accuracy of this test into question.
For example, the development of peptide biosensors—peptides containing incorporated fluorophores improved temporal resolution of in vitro binding assays. One of the most useful techniques to study kinase action is Fluorescence Resonance Energy Transfer (FRET). To utilize FRET for phosphorylation studies, fluorescent proteins are coupled to both a phosphoamino acid binding domain and a peptide that can be phosphorylated. Upon phosphorylation or dephosphorylation of a substrate peptide, a conformational change occurs that results in a change in fluorescence. FRET has also been used in tandem with Fluorescence Lifetime Imaging Microscopy (FLIM) or fluorescently conjugated antibodies and flow cytometry to provide quantitative results with excellent temporal and spatial resolution.
Sources: en.wikipedia.org
It is a set of checks performed before or during an HPLC run to confirm the system works as expected. Parameters may include resolution, tailing factor, theoretical plates, and retention time precision. Failure can trigger maintenance, method adjustment, or repeat analysis.
Validation follows a planned protocol that tests accuracy, precision, specificity, linearity, range, detection limits, quantitation limits, and robustness. Results are compared against predefined acceptance criteria. The validation report supports regulatory filing or routine use.
Revalidation may be needed after changes to column chemistry, mobile phase, detection, sample preparation, or instrument type. It can also follow a pattern of out-of-specification results. The scope depends on whether the change affects method performance.
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.