A practical reference on quality control: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-07-18. Anything still debated is marked as such rather than presented as settled.
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 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.
Documentation and traceability are central to regulated HPLC testing. Records typically include instrument logs, column history, mobile-phase preparation, sample preparation, injection sequences, raw chromatograms, and audit trails. Electronic systems may require user access controls, time-stamped changes, and backup procedures. Training records show that analysts are qualified for assigned methods. Audits and inspections check whether written procedures match actual practice and whether deviations are documented. These controls support reproducibility and allow results to be reconstructed if questions arise later.
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.
| Property | Value | Notes |
|---|---|---|
| Retention time RSD | ≤1% for five replicate injections | Typical criterion; method-specific limits apply. |
| Resolution | ≥1.5 between critical pair | Baseline separation is generally desired. |
| Tailing factor | ≤2.0 | Measures peak symmetry. |
| Theoretical plates | ≥2000 per column | Method-dependent; higher values indicate greater efficiency. |
| Peak area RSD | ≤2% for replicate injections | Reflects autosampler and detector precision. |
High-performance liquid chromatography is an analytical technique that separates components of a liquid sample by passing it 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 interaction with the stationary phase cause analytes to migrate at different rates. Detectors record elution as peaks, and a data system converts signals into a chromatogram. The method is suited to compounds that dissolve in a liquid and are not volatile enough for gas chromatography.
Reversed-phase chromatography dominates modern HPLC testing, using a nonpolar stationary phase such as chemically bonded octadecyl groups and a polar mobile phase of water mixed with organic solvent. Analytes partition between the mobile and stationary phases according to hydrophobicity. Gradient elution changes the mobile phase composition over time to separate compounds with a wide range of retention. Isocratic elution keeps the composition constant and is simpler for routine assays. Column temperature, pH, and flow rate influence selectivity, peak shape, and retention time, so these parameters are controlled during a validated method.
Detection in HPLC testing commonly relies on ultraviolet-visible absorbance, fluorescence, refractive index, or mass spectrometry. A diode array detector records full spectra across a wavelength range, which helps identify co-eluting peaks. Mass spectrometry provides mass-to-charge ratios and can confirm molecular identity at low concentrations. The choice of detector depends on analyte structure, required sensitivity, and whether quantitation or identification is the goal. No single detector works for every compound, and method development often compares responses before selecting one.
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. 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.
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.
Most routine HPLC testing uses reversed-phase columns, where the stationary phase is nonpolar and the mobile phase is a polar mixture such as water with an organic solvent. Analytes partition between the two phases according to polarity, size, and charge. Gradients that change solvent composition over time can separate compounds with broad retention ranges. Isocratic conditions keep solvent composition constant and suit simpler mixtures. The choice of column chemistry, pH, and temperature affects selectivity and peak shape.
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 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.
=== 2006: The first deaths are reported === Several of the deaths are notable due either to the publicity that followed or unusual circumstances of the case. One of the earliest published instances of a death attributed to cheese heroin was that of Karen Becerra, an 18-year-old high school senior found dead by her father in their West Dallas home on April 24, 2006. Police attributed her death to snorting cheese and drinking alcohol. On November 1, 2006, 17-year-old Keith Witherspoon died in nearby Mesquite; a story the following month in The Dallas Morning News profiled Witherspoon as "the first Dallas-area youth publicly known to have died of a heroin overdose since the 'cheese' concerns were raised." The death was also notable because Mesquite is located northeast of Dallas, indicating the problem had moved beyond its origins in the northwest quadrant of the city.
== Research == The research name of emapalumab was NI-0501. A phase II/III trial began in 2013 and is ongoing as of August 2018. The trial targets patients under the age of 18 who have failed to improve on conventional treatments. This study was realised in the context of an EU-funded FP7 project, named FIGHT-HLH (306124).
President Biden signs his first executive orders reversing several Trump administration actions, including rejoining the Paris Agreement and the World Health Organization, repealing the 2017 travel bans, ending funding for the Mexico–United States border wall, and revoking the permit for the Keystone XL pipeline. January 21 – The Food and Drug Administration (FDA) approves Cabenuva as a complete regimen for the treatment of HIV/AIDS. January 22 – Recreational cannabis sales begin in Arizona. January 24 COVID-19 pandemic: Nationwide confirmed COVID-19 cases surpass 25 million. The Tampa Bay Buccaneers advance to Super Bowl LV after a 31–26 victory against the Green Bay Packers, the first time an NFL team will play the Super Bowl on their home field. January 25 President Biden repeals the Trump administration's ban on transgender personnel in the military. COVID-19 pandemic: Minnesota reports the first national case of the Lineage P.1 variant of SARS-CoV-2. Dominion Voting Systems sues former New York City mayor Rudy Giuliani, accusing him of defamation during the 2020 presidential election. January 26 COVID-19 pandemic: The Biden administration announces it will purchase 200 million COVID-19 vaccine doses from Pfizer/BioNTech and Moderna, in addition to the prior order of 400 million. January 27 The U.S. Army announces new personal grooming and appearance standards, relaxing rules regarding makeup and jewelry and allowing for more diverse hairstyles.
HPLC is distinguished from traditional ("low pressure") liquid chromatography because operational pressures are significantly higher (around 50–1400 bar), while ordinary liquid chromatography typically relies on the force of gravity to pass the mobile phase through the packed column. Due to the small sample amount separated in analytical HPLC, typical column dimensions are 2.1–4.6 mm diameter, and 30–250 mm length. Also HPLC columns are made with smaller adsorbent particles (1.5–50 μm in average particle size). This gives HPLC superior resolving power (the ability to distinguish between compounds) when separating mixtures in a shorter period of time, which makes it a popular chromatographic technique. The schematic of an HPLC instrument typically includes solvents' reservoirs, one or more pumps, a solvent-degasser, a sampler, a column, and a detector. The solvents are prepared in advance according to the needs of the separation, they pass through the degasser to remove dissolved gasses, mixed to become the mobile phase, then flow through the sampler, which brings the sample mixture into the mobile phase stream, which then carries it into the column. The pumps deliver the desired flow and composition of the mobile phase through the stationary phase inside the column, then directly into a flow-cell inside the detector. The detector generates a signal proportional to the amount of sample component emerging from the column, hence allowing for quantitative analysis of the sample components.
Sources: en.wikipedia.org
In transcription, RNA polymerase reads a DNA strand and produces an mRNA strand that can be further translated. In order to initiate transcription, the DNA segment that is to be transcribed must be accessible (i.e. it cannot be tightly packed). Once the DNA segment is accessible, the RNA polymerase can begin to transcribe the coding DNA strand by pairing RNA nucleotides to the template DNA strand. During the initial transcription phase, the RNA polymerase searches for a promoter region on the DNA template strand. Once the RNA polymerase binds to this region, it begins to “read” the template DNA strand in the 3’ to 5’ direction. RNA polymerase attaches RNA bases complementary to the template DNA strand (Uracil will be used instead of Thymine). The new nucleotide bases are bonded to each other covalently. The new bases eventually dissociate from the DNA bases but stay linked to each other, forming a new mRNA strand. This mRNA strand is synthesized in the 5’ to 3’ direction. Once the RNA reaches a terminator sequence, it dissociates from the DNA template strand and terminates the mRNA sequence as well. Transcription is regulated in the cell via transcription factors. Transcription factors are proteins that bind to regulatory sequences in the DNA strand such as promoter regions or operator regions. Proteins bound to these regions can either directly halt or allow RNA polymerase to read the DNA strand or can signal other proteins to halt or allow RNA polymerase reading.
=== Immune response === Cortisol prevents the release of substances in the body that cause inflammation. Cortisol is used to treat conditions resulting from overactivity of the B-cell-mediated antibody response. Examples include inflammatory and rheumatoid diseases, as well as allergies. Low-dose topical hydrocortisone, available as a nonprescription medicine in some countries, is used to treat skin problems such as rashes and eczema. Cortisol inhibits production of interleukin 12 (IL-12), interferon gamma (IFN-gamma), IFN-alpha, and tumor necrosis factor alpha (TNF-alpha) by antigen-presenting cells (APCs) and T helper cells (Th1 cells), but upregulates interleukin 4, interleukin 10, and interleukin 13 by Th2 cells. This change results in a shift toward a Th2 immune response rather than general immunosuppression. The activation of the stress system (and resulting increase in cortisol and Th2 shift) seen during an infection is believed to be a protective mechanism which prevents an over-activation of the inflammatory response. Cortisol can weaken the activity of the immune system. Cortisol prevents proliferation of T-cells by rendering the interleukin-2 producer T-cells unresponsive to interleukin-1, and unable to produce the T-cell growth factor IL-2. Cortisol downregulates the expression of the IL2 receptor IL-2R on the surface of the helper T-cell which is necessary to induce a Th1 'cellular' immune response.
A suture is a type of fibrous joint that is only found in the skull (cranial suture). The bones are bound together by Sharpey's fibres. A tiny amount of movement is permitted at sutures, which contributes to the compliance and elasticity of the skull. These joints are synarthroses. It is normal for many of the bones of the skull to remain unfused at birth. The fusion of the skull's bones before birth is known as craniosynostosis. The term "fontanelle" is used to describe the resulting "soft spots". The relative positions of the bones continue to change during the life of the adult (though less rapidly), which can provide useful information in forensics and archaeology. In old age, cranial sutures may ossify (turn to bone) completely. The joints between the teeth and jaws (gomphoses) and the joint between the mandible and the cranium, the temporomandibular joint, form the only non-sutured joints in the skull.
Sources: en.wikipedia.org
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.
Retention time drift can result from changes in mobile phase composition, column temperature, pump flow, or column age. A gradual shift often points to column degradation. A sudden shift may indicate a leak, mixing error, or incorrect mobile phase.
Retention time alone cannot confirm identity because different compounds may elute at similar times. Coupling HPLC with mass spectrometry or comparing against authenticated standards increases confidence. Confirmation usually requires orthogonal data.
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.