quality control 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 2025-09-14. Where a claim depends on a specific study, the study is described rather than over-claimed.
Storage and handling conditions affect both peptide stability and the accuracy of later purity tests. Lyophilized powders are commonly kept desiccated at -20 °C or below, while reconstituted solutions require a defined buffer, pH, and temperature range. Repeated freeze-thaw cycles can promote aggregation, oxidation, or hydrolysis over time. Each cycle may alter the chromatogram and complicate comparison with earlier results. Stability data, when available, should guide handling intervals and solvent choice.
Independent verification is used when a supplier result needs confirmation or when a material supports regulated work. A second laboratory can repeat reverse-phase HPLC and mass spectrometry on the same sample. Discrepancies may arise from different columns, gradients, detection wavelengths, or sample preparation. Moisture uptake and counterion content can lower net peptide mass without changing area percent. Documentation of methods and raw data helps distinguish analytical variation from a true quality difference.
Other methods address specific purity concerns. Amino acid analysis gives compositional data after hydrolysis, while capillary electrophoresis separates by charge-to-mass ratio. Karl Fischer titration measures residual water, and gas chromatography can detect residual solvents. Nuclear magnetic resonance can identify organic impurities but is less sensitive for trace levels. No single test covers all possible impurities, so purity testing usually combines orthogonal methods and reports the conditions used. The choice of methods is guided by the impurity classes of interest.
Reverse-phase high-performance liquid chromatography (RP-HPLC) is widely used to estimate peptide purity. It separates components by hydrophobicity on a column with a water-organic mobile phase. Ultraviolet absorbance at 214 nm or 220 nm detects peptide bonds. The main peak area as a percentage of total peak area gives a purity figure. This figure depends on column, gradient, wavelength, and how peaks are integrated, so it is method-specific rather than absolute.
Mass spectrometry provides complementary information by measuring molecular mass. Electrospray ionization or matrix-assisted laser desorption/ionization can confirm the expected peptide mass and reveal related impurities with different masses. It does not directly quantify all species because ionization efficiency varies. When coupled to liquid chromatography, LC-MS can assign masses to chromatographic peaks. This helps distinguish target peptide from truncation, oxidation, or deletion products. Mass accuracy and resolution determine how confidently a mass can be matched to a proposed structure.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | -20 °C or below | For lyophilized powder; keep desiccated. |
| Short-term solution storage | 2-8 °C | For reconstituted peptide; follow stability data. |
| Common research-grade specification | 95% or greater by HPLC area | Widely cited threshold; not a universal standard. |
| Documentation | Certificate of analysis | Lists lot, sequence, method, purity, and storage guidance. |
| Independent verification | Second-laboratory HPLC and mass spectrometry | Repeats tests on submitted sample to confirm supplier result. |
Additional techniques address components that reversed-phase chromatography may not resolve. Ion-exchange chromatography separates by charge, size-exclusion chromatography detects aggregates, and capillary electrophoresis offers high separation efficiency. Water content is measured by Karl Fischer titration, residual solvents by gas chromatography, and elemental impurities by inductively coupled plasma mass spectrometry. Amino acid analysis or nitrogen determination can estimate peptide content on a mass basis. Purity is frequently reported as area percent, yet standardized comparison across laboratories remains an open question because methods and reporting practices differ.
Peptide purity testing measures how much of a sample consists of the intended peptide sequence compared with related substances, water, counterions, and residual solvents. No single analytical method captures all of these components at once. Reversed-phase high-performance liquid chromatography with ultraviolet detection is widely used because it separates peptides by hydrophobicity. The reported purity value therefore depends on the chosen method, column, mobile phase, and detection wavelength. Established practice treats purity as method-dependent rather than an absolute property of the material.
Impurity profiles can include deletion peptides, oxidized forms, truncated sequences, and residual solvents. Some impurities arise during synthesis, cleavage, or purification, while others form during storage. Purity testing often focuses on peptide-related impurities, whereas residual solvents and counterions require separate assays. The significance of a given impurity depends on its amount and properties, which may not be established for a research peptide. Reporting an impurity profile is more informative than reporting a single purity number.
Peptide purity specifications describe the minimum acceptable result from a defined test. A certificate of analysis may list HPLC purity, mass spectrometry identity, appearance, and counterion content. Specifications are method-dependent, so a value obtained with one gradient or wavelength may differ from another. For research use, common thresholds include 95% and 98% by RP-HPLC, but the appropriate limit depends on the application. The specification should always name the analytical method and acceptance criterion.
Quality control includes system suitability, blank injections, and reference standards. System suitability checks column performance and retention time reproducibility, while blank runs detect carryover or mobile-phase contaminants. Reference standards help calibrate retention time and detector response. Without these controls, a purity value is difficult to compare across laboratories or over time. Documentation of instrument settings and integration parameters is also part of quality control, and acceptance criteria should be set before samples are analyzed.
The presentation of amyloidosis is broad and depends on the site of amyloid accumulation. The kidney and heart are the most common organs involved. Amyloid deposition in the kidney often involve the glomerular capillaries and mesangial regions, affecting the organ's ability to filter and excrete waste and retain plasma protein. This can lead to high levels of protein in the urine (proteinuria) and nephrotic syndrome. Several types of amyloidosis, including the AL and AA types, are associated with nephrotic syndrome. Approximately 20% and 40–60% of people with AL and AA amyloidosis respectively progress to end-stage kidney disease requiring dialysis.
Benninghoven graduated from the University of Cologne in 1961 where he worked with Fritz Kirchner (1896–1967) and completed his habilitation in surface physics in Cologne two years later. He first worked as professor in Cologne from 1965 to 1973 until he moved to a full professor position in experimental physics at the University of Münster in 1972. He worked on static secondary ion mass spectrometry (SIMS) and its applications, and developed SIMS instruments. In 1989 he co-founded IonTOF, a company that became a world-leader in TOF-SIMS instrumentation. He has written over 300 scientific articles and several books on the topic of SIMS, many of which have become reference works on SIMS. For his work, he has received the Technology Transfer prize (German Ministry of Education and Research) and the 1984 Gaede-Langmuir Prize (American Vacuum Society) for the development of concepts and instrumentation in static secondary ion mass spectrometry and the demonstration of its usefulness in manifold applications. In 1990 he shared the Fritz-Pregl-Medaille of the Austrian Society of Analytical Chemistry with Wilhelm Simon. From 1977 to 1983, he was president of the German Vacuum Society (part of the German Physical Society).
Some anesthetics and chemotherapy drugs are injected intrathecally into the subarachnoid space, where they spread around CSF, meaning substances that cannot cross the blood–brain barrier can still be active throughout the central nervous system. Baricity refers to the density of a substance compared to the density of human cerebrospinal fluid and is used in regional anesthesia to determine the manner in which a particular drug will spread in the intrathecal space. Liquorpheresis is the process of filtering the CSF in order to clear it from endogen or exogen pathogens. It can be achieved by means of fully implantable or extracorporeal devices, though the technique remains experimental today.
The presentation of amyloidosis is broad and depends on the site of amyloid accumulation. The kidney and heart are the most common organs involved. Amyloid deposition in the kidney often involve the glomerular capillaries and mesangial regions, affecting the organ's ability to filter and excrete waste and retain plasma protein. This can lead to high levels of protein in the urine (proteinuria) and nephrotic syndrome. Several types of amyloidosis, including the AL and AA types, are associated with nephrotic syndrome. Approximately 20% and 40–60% of people with AL and AA amyloidosis respectively progress to end-stage kidney disease requiring dialysis.
Adalimumab, sold under the brand name Humira and others, is a disease-modifying antirheumatic drug and monoclonal antibody used to treat rheumatoid arthritis, juvenile idiopathic arthritis, psoriatic arthritis, ankylosing spondylitis, Crohn's disease, ulcerative colitis, plaque psoriasis, hidradenitis suppurativa, and uveitis. It is administered by subcutaneous injection (injection under the skin). It works by inactivating tumor necrosis factor (TNF). Common side effects include upper respiratory tract infections, pain at the site of injection, rash, and headache. Other side effects may include serious infections, cancer, anaphylaxis, reactivation of hepatitis B, new onset or exacerbation of demyelinating diseases (such as multiple sclerosis), heart failure, liver failure, and aplastic anemia. Use during pregnancy is not recommended, but some sources show use during breastfeeding may be safe. Adalimumab was approved for medical use in the United States in 2002. It is on the World Health Organization's List of Essential Medicines. It is available as a biosimilar medication. In 2023, it was the 244th most commonly prescribed medication in the United States, with more than 3 million prescriptions.
Sources: en.wikipedia.org
The Greek key motif consists of four adjacent antiparallel strands and their linking loops. It consists of three antiparallel strands connected by hairpins, while the fourth is adjacent to the first and linked to the third by a longer loop. This type of structure forms easily during the protein folding process. It was named after a pattern common to Greek ornamental artwork (see meander). Due to the chirality of their component amino acids, all strands exhibit right-handed twist evident in most higher-order β-sheet structures. In particular, the linking loop between two parallel strands almost always has a right-handed crossover chirality, which is strongly favored by the inherent twist of the sheet. This linking loop frequently contains a helical region, in which case it is called a β-α-β motif. A closely related motif called a β-α-β-α motif forms the basic component of the most commonly observed protein tertiary structure, the TIM barrel.
In 2004, development of an antisense therapy for spinal muscular atrophy began. Over the following years, an antisense oligonucleotide later named nusinersen was developed by Ionis Pharmaceuticals under a licensing agreement with Biogen. In December 2016, nusinersen received regulatory approval from FDA and soon after, from other regulatory agencies worldwide. As of 2020, more than 50 antisense oligonucleotides were in clinical trials, including over 25 in advanced clinical trials (phase II or III). A follow-on drug to Inotersen is being developed by Ionis Pharmaceuticals and under license to Akcea Therapeutics for hereditary transthyretin-mediated amyloidosis. In this formulation the ASO is conjugated to N-Acetylgalactosamine enabling hepatocyte-specific delivery, greatly reducing dose requirements and side effect profile while increasing the level of transthyretin reduction in patients.
Antimicrobial peptides have been used as therapeutic agents; their use is generally limited to intravenous administration or topical applications due to their short half-lives. As of January 2018 the following antimicrobial peptides were in clinical use: Bacitracin for pneumonia, topical Boceprevir, Hepatitis C (oral, cyclic peptide) Dalbavancin, bacterial infections, IV Daptomycin, bacterial infections, IV Enfuvirtide, HIV, subcutaneous injection Oritavancin, bacterial infections, IV Teicoplanin, bacterial infections, IV Telaprevir, Hepatitis C, oral cyclic peptide Telavancin, bacterial infection, IV Vancomycin, bacterial infection, IV. AMPs have been observed having functions other than bacterial and fungal killing. These activities include antiviral effects , but also roles in host defence such as anticancer functions and roles in neurology. This has led to a movement for re-branding AMPs as "Host-defence peptides" to encompass the broad scope of activities AMPs can have.
POMC, ACTH and β-lipotropin are secreted from corticotropic cells in the anterior lobe (or adenohypophysis) of the pituitary gland in response to the hormone corticotropin-releasing hormone (CRH) released by the hypothalamus. The pre-pro-opiomelanocortin (Pre-POMC) is the precursor of POMC, its cleavage forms POMC. ACTH, on the other hand, is produced from the cleavage of POMC. The removal of the signal peptide during translation produces the 241-amino acid polypeptide POMC, which undergoes a series of post-translational modifications such as phosphorylation and glycosylation before it is proteolytically cleaved by endopeptidases to yield various polypeptide fragments with varying physiological activity. These fragments include:
These cyclic dipeptides incorporate both donor and acceptor groups for hydrogen bonding. They are conformationally constrained nearly planar scaffolds. Diversity can be introduced at up to six positions and stereochemistry controlled at up to four positions. They are stable to proteolysis. These characteristics underpin theis biologically activity and utility in medicinal chemistry. As a consequence of their predominant biosynthetic origin from L-α-amino acids most naturally occurring 2,5-DKPs are cis configured as the cyclo(L-Xaa-L-Yaa) isomers. 2,5-DKPs epimerize under basic, acidic and thermal conditions. The composition of the cis and trans isomers in the equilibrium state varies widely depending on the bulk of the side chains, if a ring (e.g. proline) is present, or if the nitrogen atoms are alkylated . Although epimerization was historically an issue in the synthesis of 2,5-DKPs, several mild methods have been developed recently that avoid epimerization.
Sources: en.wikipedia.org
Freeze-drying, also known as freeze-casting or ice-templating, offers an alternative to the high temperature and high-pressure requirements of supercritical drying. Additionally, freeze-drying offers more control of the solid structure development by controlling the ice crystal growth during freezing. In this method, a colloidal dispersion of the aerogel precursors is frozen, with the liquid component freezing into different morphologies depending on a variety of factors such as the precursor concentration, type of liquid, temperature of freezing, and freezing container. As this liquid freezes, the solid precursor molecules are forced into the spaces between the growing crystals. Once completely frozen, the frozen liquid is sublimed into a gas through lyophilization, which removes much of the capillary forces, as was observed in supercritical drying. Though typically classified as a "cryogel", aerogels produced through freeze-drying often experience some shrinkage and cracking while also producing a non-homogenous aerogel framework. This often leads to freeze-drying being used for the creation of aerogel powders or as a framework for composite aerogels.
In pharmacology, relative bioavailability measures the bioavailability (estimated as the AUC) of a formulation (A) of a certain drug when compared with another formulation (B) of the same drug, usually an established standard, or through administration via a different route. When the standard consists of intravenously administered drug, this is known as absolute bioavailability (see above). F r e l = 100 ⋅ A U C A ⋅ D B A U C B ⋅ D A {\displaystyle F_{\mathrm {rel} }=100\cdot {\frac {AUC_{\mathrm {A} }\cdot D_{\mathrm {B} }}{AUC_{\mathrm {B} }\cdot D_{\mathrm {A} }}}}
Alpha-synuclein primary structure is usually divided in three distinct domains: Residues 1-60: An amphipathic N-terminal region dominated by four 11-residue repeats including the consensus sequence KTKEGV. This sequence has a structural alpha helix propensity similar to apolipoproteins-binding domains. It is a highly conserved terminal that interacts with acidic lipid membranes, and all the discovered point mutations of the SNCA gene are located within this terminal. Residues 61-95: A central hydrophobic region which includes the non-amyloid-β component (NAC) region, involved in protein aggregation. This domain is unique to alpha-synuclein among the synuclein family. Residues 96-140: a highly acidic and proline-rich region which has no distinct structural propensity. This domain plays an important role in the function, solubility and interaction of alpha-synuclein with other proteins.
Calcitonin gene-related peptide 2 (CGRP2), also called calcitonin related polypeptide beta, is a hormone that in humans is encoded by the CALCB gene (previously CALC2). Like the related hormone, calcitonin gene-related peptide 1 (CGRP1), this hormone induces vasodilation (relaxation of blood vessels) through the activation of the CGRP receptor. This form of calcitonin gene-related peptide is traditionally considered to be the primary form used in the enteric nervous system (nervous system in the gut). The gene that encodes CGRP1, CALCA, also encodes the blood-calcium-reducing hormone calcitonin, but despite its name, this protein is encoded by a distinct gene (CALCB). This hormone activates the CGRP receptor, which is a two protein (heterodimer) complex that is composed of RAMP1 and CALCRL.
Solid-liquid extraction based ambient ionization is based on the use of a charged spray, for example electrospray to create a liquid film on the sample surface. Molecules on the surface are extracted into the solvent. The action of the primary droplets hitting the surface produces secondary droplets that are the source of ions for the mass spectrometer. Desorption electrospray ionization (DESI) is one of the original ambient ionization sources and uses an electrospray source to create charged droplets that are directed at a solid sample. The charged droplets pick up the sample through interaction with the surface and then form highly charged ions that can be sampled into a mass spectrometer. Desorption atmospheric pressure photoionization (DAPPI) is a solid-liquid extraction ambient ionization method that enables the direct analysis of samples deposited on surfaces by means of a jet of hot solvent vapour and ultraviolet light. The hot jet thermally desorbs the sample from a surface and the vaporized sample is ionized by a vacuum ultraviolet light and consequently sampled into a mass spectrometer.
Sources: en.wikipedia.org
Lyophilized powders are typically kept desiccated at -20 °C or below. Reconstituted solutions require a defined buffer, pH, and storage condition based on available stability data.
A certificate commonly lists sequence, lot number, appearance, purity method, purity value, mass confirmation, and storage guidance. It may also note counterion, water content, and test date.
Not always, but independent testing reduces reliance on a supplier's internal result. It is common when a material is used in regulated or repeatable work.
It usually refers to the relative area of the main peak in a chromatographic separation, such as RP-HPLC. It estimates the proportion of UV-absorbing material in that peak, not the absolute mass fraction of the target peptide. Different methods can give different percentages.