mass spectrometry 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.
Updated 2026-07-06. Numbers and descriptions here follow the published literature rather than marketing material.
Other chromatographic modes provide complementary information that reverse-phase separation may not capture. Ion-exchange chromatography separates peptides by net charge and can resolve deamidated, oxidized, or truncated variants that co-elute under hydrophobic conditions. Size-exclusion chromatography detects aggregates and higher-order oligomers, which are often invisible in reverse-phase assays. Chiral chromatography can quantify D-amino acid epimers when stereochemical purity matters. Because each mode uses a different separation principle, a single purity number from one method cannot describe all possible impurities.
Interpreting chromatographic purity requires attention to detection limits and response factors. Peptides without aromatic residues may absorb weakly at 280 nm, so 214 nm is often preferred, but mobile-phase additives and solvents also absorb at low wavelengths. Co-eluting impurities with different molar absorptivities can produce area percentages that differ from mass percentages. Integration parameters, peak tailing, and baseline choice further affect reported values. For these reasons, method details belong alongside any purity figure, and orthogonal methods are needed to confirm identity and impurity profiles.
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 primary method | Reverse-phase HPLC | Separates mainly by hydrophobicity |
| Typical detection wavelength | 214 nm | Peptide bond absorbance; low UV |
| Common ion-pairing agent | Trifluoroacetic acid | Improves peak shape in acidic mobile phase |
| Typical purity metric | Area percent of main peak | Depends on detection and integration |
| Complementary method | Ion-exchange chromatography | Resolves charge variants |
Quality control specifications for peptides typically include appearance, identity, purity by RP-HPLC, water content, counterion content, and residual trifluoroacetic acid. Karl Fischer titration measures water, while ion chromatography or elemental analysis can quantify counterions. Purity specifications may be set at 95% or 98% area percent, but the appropriate threshold depends on the application. For research reagents, a lower purity may be acceptable if identity is confirmed. For assays sensitive to impurities, higher purity and orthogonal testing are often required.
Handling and storage influence measured purity, and peptides can oxidize, deamidate, aggregate, or adsorb to surfaces over time. Lyophilized powders stored at -20 °C or lower are generally more stable than solutions, though some sequences require different conditions. Repeated freeze-thaw cycles can promote aggregation and loss, so testing after storage checks whether purity has changed. Stability-indicating methods compare stressed and unstressed samples to detect degradation pathways. Light exposure and pH can also accelerate modification.
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.
Vaginal films are soluble, thin sheets of medication that are inserted into the vagina where they dissolve and release the substances. Typical uses include delivery of contraceptive substances or antibiotics for infections. These films are inserted by simply pushing them into the vagina with one’s fingers. There they dissolve quickly upon interaction with natural vaginal fluids. Bioadhesives are substances that naturally stick to live tissue. Currently, studies are being done on bioadhesives adhering to cervical mucous membranes to allow for an extended release period. The drug would be released with mucus to create a localized treatment with high effectiveness. This is anticipated to be highly useful for treatment of cervical cancer. Bioadhesives can come in multiple forms, such as films, tablets, or gels. The appeal of bioadhesives is that they take advantage of the mucous environment surrounding the cervix and utilize it to benefit the drug delivery mechanism.
The modern era of CCC began with the development of the planetary centrifuge by Dr. Yoichiro Ito which was first introduced in 1966 as a closed helical tube which was rotated on a "planetary" axis as is turned on a "sun" axis. A flow-through model was subsequently developed and the new technique was called countercurrent chromatography in 1970. The technique was further developed by employing test mixtures of DNP amino acids in a chloroform:glacial acetic acid:0.1 M aqueous hydrochloric acid (2:2:1 v/v) solvent system. Much development was needed to engineer the instrument so that required planetary motion could be sustained while the phases were being pumped through the coil(s). Parameters such as the relative rotation of the two axes (synchronous or non-synchronous), the direction of flow through the coil, and the rotor angles were investigated.
5β-Pregnane, also known as 17β-ethyletiocholane or as 10β,13β-dimethyl-17β-ethyl-5β-gonane, is a steroid and a parent compound of a variety of steroid derivatives. It is one of the epimers of pregnane, the other being 5α-pregnane. Derivatives of 5β-pregnane include the naturally occurring steroids 5β-dihydroprogesterone, pregnanolone, epipregnanolone, pregnanediol, and pregnanetriol, and the synthetic steroids hydroxydione, renanolone, ORG-20599, and SAGE-217. These derivatives include metabolites of progesterone and endogenous and synthetic neurosteroids. Etiocholane Gonane
Vaccine therapies are a type of specific active immunotherapy. Vaccine therapies deliver various agents that will lead to a specific immune response e.g. antibody development or CTL response. Tumor antigens have been a main target in specific active immunotherapy by way of vaccination. Tumor antigens are antigens produced by tumor cells and can be common among patients with the same cancer-type, or unique to a particular patient. Their specificity to malignant tumor cells makes tumor antigens ideal candidates for vaccination. Cancer vaccine C-Met#Active immunotherapy, Mantle cell lymphoma Immunotherapy,
In addition, cysteine, tyrosine, and arginine are considered semiessential amino acids, and taurine a semi-essential aminosulfonic acid in children. Some amino acids are conditionally essential for certain ages or medical conditions. Essential amino acids may also vary from species to species. The metabolic pathways that synthesize these monomers are not fully developed. Amino acids are sometimes added to animal feed because some of the components of these feeds, such as soybeans, have low levels of some of the essential amino acids, especially of lysine, methionine, threonine, and tryptophan. Likewise amino acids are used to chelate metal cations in order to improve the absorption of minerals from feed supplements.
Sources: en.wikipedia.org
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.
ADAM (A Database of Anti-Microbial peptides) Archived 2015-06-17 at the Wayback Machine at ntou.edu.tw AntiFP Prediction of antifungal peptides AntiMPmod Prediction of antimicrobial potential of modified peptides Antimicrobial+Cationic+Peptides at the U.S. National Library of Medicine Medical Subject Headings (MeSH) AntiTbPred Prediction of anti-tuberculosis peptides Antimicrobial Peptide Database Archived 2011-07-20 at the Wayback Machine at University of Nebraska Medical Center Antimicrobial Peptide Scanner Deep Learning based AMP prediction server AntiTbPdb Anti Tubercular Peptide Database BioPD[link removed] at Peking University Health Science Center CAMP:Collection of Anti-Microbial Peptides at National Institute for Research in Reproductive Health (NIRRH) DBAASP - Database of Antimicrobial Activity and Structure of Peptides] LAMP at Fudan University PeptideLocator Prediction of functional peptides, including antimicrobial peptides, in a protein sequence PeptideRanker Bioactive peptide, including antimicrobial peptide, prediction modlAMP Python package for computational work with antimicrobial peptides, including sequence handling, -design, -prediction, descriptor calculation and plotting
The following table illustrates variability in reference ranges of serum prolactin between some commonly used assay methods (as of 2008), using a control group of healthy health care professionals (53 males, age 20–64 years, median 28 years; 97 females, age 19–59 years, median 29 years) in Essex, England: An example of the use of the above table is, if using the Centaur assay to estimate prolactin values in μg/L for females, the mean is 168 mIU/L (7.92 μg/L) and the reference range is 71–348 mIU/L (3.35–16.4 μg/L). Hyperprolactinaemia, or excess serum prolactin, is associated with hypoestrogenism, anovulatory infertility, oligomenorrhoea, amenorrhoea, unexpected lactation and loss of libido in women and erectile dysfunction and loss of libido in men. Causes of Elevated Prolactin Levels
The American Society for Biochemistry and Molecular Biology (ASBMB) is a learned society that was founded on December 26, 1906, at a meeting organized by John Jacob Abel (Johns Hopkins University). The roots of the society were in the American Physiological Society, which had been formed some 20 years earlier. ASBMB is the US member of the International Union of Biochemistry and Molecular Biology. The ASBMB was originally called the American Society of Biological Chemists, before obtaining its current name in 1987. The society is based in Rockville, Maryland. ASBMB's mission is to advance the science of biochemistry and molecular biology through publication of scientific and educational journals, the organization of scientific meetings, advocacy for funding of basic research and education, support of science education at all levels, and by promoting the diversity of individuals entering the scientific workforce. The organization currently has over 12,000 members.
Sources: en.wikipedia.org
HPLC purity measures the relative area of the main peptide peak compared with all detected peaks under one set of separation and detection conditions. It is an operational value rather than an absolute mass fraction. Compounds that do not absorb at the detection wavelength or that co-elute with the main peak are not counted.
The peptide bond absorbs ultraviolet light near 214 nm, so this wavelength detects the backbone of most peptides regardless of aromatic content. It is more universal than 280 nm, which mainly detects tryptophan, tyrosine, and phenylalanine. Mobile-phase components can also absorb at 214 nm, so blank subtraction and method controls are important.
No single chromatographic method resolves all possible peptide impurities, because variants may differ in charge, size, hydrophobicity, or stereochemistry. Deamidated and oxidized forms may co-elute in reverse-phase systems, while aggregates require size-exclusion separation. Orthogonal methods and mass spectrometry are therefore used together for a fuller impurity profile.
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.