This is a working overview of precision, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-03-05. Anything still debated is marked as such rather than presented as settled.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Method validation establishes that an HPLC procedure is suitable for its intended use. Key parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Accuracy measures agreement with a true or accepted value, while precision describes repeatability and intermediate precision. Specificity confirms that the method measures the analyte without interference from impurities, degradants, or excipients. Validation is documented in a protocol and report, and acceptance criteria are set before experiments begin. Regulatory guidance varies by region, but the general principles are widely harmonized.
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.
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 | Measured value compared with true or accepted value |
| Precision type | Repeatability | Same analyst, instrument, and short time interval |
| Linearity range | 50–150% of target concentration | Common for assay methods; method-dependent |
| Limit of quantitation | Signal-to-noise ratio of 10:1 | Lowest concentration with acceptable precision |
| Common synonyms | Method validation, analytical validation | Documented confirmation that a method is suitable |
HPLC testing is an analytical technique used to separate, identify, and quantify components in a liquid sample. It relies on a pressurized mobile phase that carries the sample through a column packed with stationary phase. Different compounds travel at different rates because of interactions with the stationary and mobile phases. The resulting signal versus time is a chromatogram. Peak position indicates identity under specified conditions, while peak area or height relates to amount.
Laboratories apply HPLC testing across pharmaceutical, food, environmental, and industrial chemistry. The method can measure active ingredients, impurities, additives, preservatives, and degradation products. Sample preparation often includes dilution, filtration, and sometimes extraction or derivatization. The choice of column, mobile phase, pH, temperature, and detector depends on the analytes and matrix. Results are compared with reference standards to assign identity and concentration. Method suitability is judged by resolution, precision, and accuracy.
HPLC testing is not a single fixed procedure; it is a family of separation modes. Reversed-phase, normal-phase, ion-exchange, size-exclusion, and affinity chromatography each suit different analyte properties. Reversed-phase methods dominate because they handle many neutral and moderately polar compounds. Detection can be optical, electrochemical, or mass spectrometric, and the detector dictates what information is available. Coupling with mass spectrometry increases selectivity and enables identification when standards are unavailable. The technique cannot separate every mixture without adjustment.
== History == Unintentional use of nickel can be traced back as far as 3500 BCE. Bronzes from what is now Syria have been found to contain as much as 2% nickel. Some ancient Chinese manuscripts suggest that "white copper" (cupronickel, known as baitong) was used there in 1700–1400 BCE. This Paktong white copper was exported to Britain as early as the 17th century, but the nickel content of this alloy was not discovered until 1822. Coins of nickel-copper alloy were minted by Bactrian kings Agathocles, Euthydemus II, and Pantaleon in the 2nd century BCE, possibly out of the Chinese cupronickel.
== Gameplay == We Happy Few is an action game played from the first-person perspective that includes elements of stealth and survival games. Players control one of three characters in the game's three different acts, each having their own skills and abilities, and their own reasons for escaping the village of Wellington Wells. Arthur Hastings is a well-balanced character adept at running and blending in; Sally Boyle is adept at sneaking and crafting chemical concoctions; and Ollie Starkey is adept at combat and crafting powerful explosives. The game uses procedural generation to create the layouts of some parts of the game world at the start of each playthrough. Each act presents the player with a main story goal, with a series of main quests to follow, with several optional side quests that can be completed to gain additional rewards. Completing objectives can earn the player character rewards as well as skill points which the player can allocate among a skill tree to improve the character's attributes or give them new abilities, with each character having a special "Super-Duper" branch that improves their weaknesses and faults by strengthening them. Throughout the game, the player can collect melee weapons, items, food, and wealth. Items are used to craft various tools to help progress in the world, like lockpicks, or medication, like healing balms, and can usually be found through simple scavenging or foraging.
Shawn voiced his support for the Palestinian people during the 2014 Gaza War. He has been on the advisory board of Jewish Voice for Peace. On October 16, 2023, Shawn spoke at a Washington, D.C., rally organized by Jewish Voice for Peace and IfNotNow. The rally called for a ceasefire in the Gaza war and for President Joe Biden to support a ceasefire. Also that month, Shawn was among the artists to sign the Artists4Ceasefire campaign's open letter urging Biden to push for a ceasefire. In April 2024, Shawn narrated a political ad by a group of organizations opposing the American Israel Public Affairs Committee's influence in Democratic Party primaries. In a January 2025 interview, Shawn compared Israel to Nazi Germany, saying the Israelis were "doing evil that is just as great as what the Nazis did. And in some ways, it's worse, because they kind of boast about it. Hitler had the decency to try to keep it secret... the Israelis are almost proud of it, and it's demonically evil."
Sources: en.wikipedia.org
== Early life and education == Born in Shawinigan, Quebec. He is the brother of Jean Chrétien, who was Prime Minister of Canada from 1993 to 2003. He received a Bachelor of Arts degree from the Séminaire de Joliette in 1955, a M.D. from the Université de Montréal in 1960, and a Master of Science in Experimental Medicine from McGill University in 1962. He did post-graduate studies from 1962 to 1964 at Harvard University and from 1964 to 1967 at the University of California, Berkeley and University of California, San Francisco.
By 15 January 1919, Poles had taken control of most of the province, and they engaged in heavy fighting with the regular German army and irregular units such as the Grenzschutz Ost. Fighting continued until the renewal of the truce between the Entente and Germany on 16 February. The truce also affected the front line in Greater Poland, but despite the ceasefire, skirmishes continued until the final signing of the Treaty of Versailles on 28 June 1919. The uprising is one of the two most successful Polish uprisings, the other being the Great Poland uprising of 1806, which ended with the entry of Napoleon's army on the side of the Poles fighting against Prussia. Many of the Greater Poland insurrectionists later took part in the Silesian Uprisings against German rule, which started in late 1919 and ended in 1921.
== Preparation and reactions == DNCB is produced commercially by the nitration of p-nitrochlorobenzene with a mixture of nitric and sulfuric acids. Other methods afford the compound less efficiently include the chlorination of 1,3-dinitrobenzene, nitration of o-nitrochlorobenzene and the dinitration of chlorobenzene. By virtue of the two nitro substituents, the chloride in DNCB is particularly susceptible to nucleophilic substitution, at least relative to simple chlorobenzene. In this way, the compound is a precursor to many other compounds. For example, the chloride can be replaced by iodide easily. Reaction of DNCB with ammonia gives 2,4-dinitrochloroaniline, again a versatile precursor. DNCB is as a substrate in glutathione S-transferase, relevant to activity assays.
Sources: en.wikipedia.org
System suitability is a set of checks that confirm the instrument and method perform within limits before sample analysis. It typically includes resolution, tailing factor, retention time, and peak area reproducibility. If a check fails, the run is invalidated until the cause is resolved.
QC samples are usually injected at the beginning, at intervals during the run, and at the end. The exact frequency depends on the method, sample count, and regulatory requirements. Results outside acceptance limits can require rejection of the affected samples and investigation.
Method validation demonstrates that an HPLC procedure produces reliable results for its intended purpose. It provides documented evidence for accuracy, precision, specificity, and other performance characteristics. Regulators and quality systems require validation before a method is used for release or stability testing.
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.