quality control raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2025-12-03. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Separation mode | Reversed-phase | Nonpolar stationary phase with polar mobile phase |
| Typical column particle size | 3–5 µm | Smaller particles improve resolution but raise pressure |
| Typical flow rate | 0.5–2.0 mL/min | Depends on column dimensions and pressure limits |
| Common detection | UV-Vis absorbance | Requires analytes with chromophores |
| Typical run time | 5–30 min | Varies with method, gradient, and sample complexity |
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.
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.
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.
In 2021, FAO released the first definition of agrifood systems and agrifood systems' resilience in The State of Food and Agriculture 2021 – Making agrifood systems more resilient to shocks and stresses. The definition of agrifood systems' resilience is adapted from Tendall et al.'s definition of food system resilience, which is "capacity over time of a food system and its units at multiple levels, to provide sufficient, appropriate and accessible food to all, in the face of various and even unforeseen disturbances". Agrifood systems are broader than food systems, as these encompass the entire range of actors and their interlinked value-adding activities in the primary production of food and non-food agricultural products, as well as in food storage, aggregation, post-harvest handling, transportation, processing, distribution, marketing, disposal and consumption.
The SeV genome is non-segmented, negative-sense RNA, of about 15.384 n. in length, and contains the noncoding 3′ leader and 5′ trailer regions, which are about 50 nucleotides in length. As in other respiroviruses from family Paramyxoviridae, in SeV they work as cis-acting elements essential for replication. A 3′ leader sequence acts as a transcriptional promoter. Between these non-coding regions are located six genes, which encode the nucleocapsid (NP) protein, phosphoprotein (P), matrix protein (M), fusion protein (F), hemagglutinin-neuraminidase (HN) and large (L) protein in this order from the 3′ terminus. The RNA-dependent RNA polymerase of the SeV consists of the large protein (L) and the phosphoprotein (P). The structural gene sequence of SeV is as follows: 3′-NP-P-M-F-HN-L-5′. Intergenomic regions between these genes are three nucleotides long as in other respiroviruses. Additional proteins, which are frequently called non structural or accessory proteins can be produced from the P gene, using alternative reading frames. The Sendai virus P/C mRNA contains five ribosomal initiation sites between positions 81 and 201 from the 5' end. One of these sites initiates in the P open reading frame, whereas four others initiate a nested set of C proteins (C', C, Y1, Y2). These C proteins are initiated in the + 1 reading frame to that of P at different translation starting sites. Sendai virus uses ribosome shunting to express Y1 and Y2 proteins that initiate at the fourth and fifth start sites on the P/C mRNA (respectively).
The study of pathology, including the detailed examination of the body, dissection and inquiry into specific maladies, dates back to antiquity. Rudimentary understanding of many conditions was present in most early societies and is attested to in the records of the earliest historical societies, including those of the Middle East, India, and China. By the Hellenic period of ancient Greece, a concerted causal study of disease was underway (see Medicine in ancient Greece), with many notable early physicians (such as Hippocrates, for whom the modern Hippocratic Oath is named) having developed methods of diagnosis and prognosis for a number of diseases. The medical practices of the Romans and those of the Byzantines continued from these Greek roots, but, as with many areas of scientific inquiry, growth in understanding of medicine stagnated somewhat after the Classical Era, but continued to slowly develop throughout numerous cultures. Notably, many advances were made in the medieval era of Islam (see Medicine in medieval Islam), during which numerous texts of complex pathologies were developed, also based on the Greek tradition. Even so, growth in complex understanding of disease mostly languished until knowledge and experimentation again began to proliferate in the Renaissance, Enlightenment, and Baroque eras, following the resurgence of the empirical method at new centers of scholarship.
Sources: en.wikipedia.org
A powdered egg is a fully dehydrated egg. Most powdered eggs are made using spray drying in the same way that powdered milk is made. First the eggs are cracked and separated from the shell. The egg yolk and white are beaten together and atomized into fine droplets by a spray nozzle that emits the droplets into a column of hot air to rapidly evaporate the moisture without cooking the egg. The use of a cyclone flow of air allows solid particles to be ejected from the drying column, falling to the sides and base of the drying tower to be collected. The major advantages of powdered eggs over fresh eggs are the increased weight per volume of whole egg equivalent—reducing storage space required—the much longer shelf life, and not needing refrigeration. Powdered eggs can be used without rehydration when baking, and can be rehydrated to make dishes such as scrambled eggs and omelettes.
The concept of border controls has its origins in antiquity. In Asia, the existence of border controls is evidenced in classical texts. The Arthashastra (c. 3rd century BCE) makes mention of passes issued at the rate of one masha per pass to enter and exit the country. Chapter 34 of the Second Book of Arthashastra is concerned with the duties of the Mudrādhyakṣa (lit. 'Superintendent of Seals') who must issue sealed passes before a person could enter or leave the countryside. Passports resembling those issued today were an important part of the Chinese bureaucracy as early as the Western Han (202 BCE-220 CE), if not in the Qin dynasty. They required details such as age, height, and physical features. The passports (zhuan) determined a person's ability to move throughout imperial counties and through points of control. Even children needed passports, but those of one year or less who were in their mother's care may not have needed them.
oligo dT A short, single-stranded DNA oligonucleotide consisting of a sequence of repeating deoxythymidine (dT) nucleotides. Oligo dTs are commonly synthesized de novo to be used as primers for in vitro reverse transcription reactions during rtPCR techniques, where short chains of 12 to 18 thymine bases readily complement the poly(A) tails of mature messenger RNAs, allowing the selective amplification and preparation of a cDNA library from a pool of coding transcripts.
=== Addition to alkenes and alkynes === The Hg2+ center binds to alkenes, inducing the addition of hydroxide and alkoxide. For example, treatment of methyl acrylate with mercuric acetate in methanol gives an α-mercuri ester:
Sources: en.wikipedia.org
In the United States, a medical laboratory scientist (MLS), medical technologist (MT), or a clinical laboratory scientist (CLS) typically earns a bachelor's degree in medical laboratory science, clinical laboratory science, or medical technology. Other routes include attaining a degree in biomedical science or in a life / biological science (biology, biochemistry, microbiology, etc.). Both routes typically requires the MLS/MT/CLS to obtain certification from a national certifying board (AAB, AMT, or ASCP) as most laboratories exceed the federal minimum requirements established by the Clinical Laboratory Improvement Amendments (CLIA). Common comprehensive medical laboratory scientist degree programs are set up in a few different ways.
=== On resin cyclization === Peptides can be cyclized on a solid support. A variety of cyclization reagents can be used such as HBTU/HOBt/DIEA, PyBop/DIEA, PyClock/DIEA. Head-to-tail peptides can be made on the solid support. The deprotection of the C-terminus at some suitable point allows on-resin cyclization by amide bond formation with the deprotected N-terminus. Once cyclization has taken place, the peptide is cleaved from resin by acidolysis and purified. The strategy for the solid phase synthesis of cyclic peptides is not limited to attachment through Asp, Glu or Lys side chains. Cysteine has a very reactive sulfhydryl group on its side chain. A disulfide bridge is created when a sulfur atom from one cysteine forms a single covalent bond with another sulfur atom from a second cysteine in a different part of the protein. These bridges help to stabilize proteins, especially those secreted from cells. Some researchers use modified cysteines using S-acetamidomethyl (Acm) to block the formation of the disulfide bond but preserve the cysteine and the protein's original primary structure.
SSRIs can also induce apoptosis, programmed cell death, in T-cells. The full mechanism of action for the anti-inflammatory effects of SSRIs is not fully known. However, there is evidence for various pathways to have a hand in the mechanism. One such possible mechanism is the increased levels of cyclic adenosine monophosphate (cAMP) as a result of interference with activation of protein kinase A (PKA), a cAMP-dependent protein. Other possible pathways include interference with calcium ion channels, or inducing cell death pathways like MAPK and Notch signaling pathway. The anti-inflammatory effects of SSRIs have prompted studies of the efficacy of SSRIs in the treatment of autoimmune diseases such as multiple sclerosis, RA, inflammatory bowel diseases, and septic shock. These studies have been performed in animal models but have shown consistent immune regulatory effects. Fluoxetine, an SSRI, has also shown efficacy in animal models of graft vs. host disease. SSRIs have also been used successfully as pain relievers in patients undergoing oncology treatment. The effectiveness of this has been hypothesized to be at least in part due to the anti-inflammatory effects of SSRIs.
Sources: en.wikipedia.org
It separates components in a liquid sample and measures their amounts using a detector. Results can indicate concentration, purity, or identity based on retention time and detector response. The technique works for mixtures that can be dissolved and filtered.
It offers high resolution, reproducibility, and compatibility with many sample types. A single run can separate and quantify multiple analytes. It is common in pharmaceutical, food, environmental, and industrial laboratories.
Samples must be soluble in a suitable mobile phase and free of particles that can block the column. Detector response depends on analyte structure, so some compounds need derivatization or alternative detection. Complex matrices may require extensive sample preparation.
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.