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.
Updated 2026-04-13. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Quality control for peptides begins with a documented specification that states the required purity, identity, and appearance. Suppliers often release research-grade material at 95% or greater by HPLC area, but this threshold is not universal. A certificate of analysis typically records the lot number, sequence, test methods, and measured values. The document allows a user to compare batches and to trace deviations. Specifications should match the intended use rather than a generic label.
Chromatographic separation resolves truncated, oxidized, deamidated, and epimerized peptide variants when their retention times differ from the target. Mass spectrometry confirms molecular mass and can reveal modifications that UV detection misses. Liquid chromatography coupled to mass spectrometry combines separation with identity information, which helps distinguish a pure target from a co-eluting impurity. UV-based area percent can overestimate purity if an impurity lacks a chromophore or if the target and impurity have similar response factors. Researchers often report both chromatographic purity and mass confirmation to give a fuller picture.
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.
| 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. |
Peptide purity can change during storage, handling, and reconstitution, and lyophilized peptides are generally more stable than solutions because water promotes hydrolysis and aggregation. Residual moisture, oxygen, and trace metals can accelerate degradation even in solid form. Temperature fluctuations during shipping may cause condensation and local moisture uptake. Quality control therefore includes appearance, water content, and analytical testing before and after storage challenges. Peptides containing cysteine, methionine, or tryptophan are especially susceptible to oxidation, while asparagine and glutamine residues can deamidate under neutral or alkaline conditions.
Analytical quality control compares a stored sample against a baseline profile. Reverse-phase chromatography remains common, but stability studies may also use mass spectrometry to detect oxidation, deamidation, or truncation products. Accelerated aging at elevated temperature can reveal degradation pathways, although extrapolation to room temperature is uncertain. Forced degradation studies expose peptides to heat, light, acid, base, and oxidants to identify likely breakdown products. Documentation should record lot number, storage history, and the exact method used for each measurement.
Mass spectrometry provides complementary information about molecular identity and certain impurities. Electrospray ionization and matrix-assisted laser desorption/ionization are common ionization techniques for peptides. A measured mass close to the expected value supports correct sequence length and modifications, while extra mass signals can reveal truncations, adducts, or incomplete deprotection. Mass spectrometry alone is not a quantitative purity assay, because ionization efficiency varies between compounds. Coupling liquid chromatography to mass spectrometry links retention time with mass and helps assign peaks that ultraviolet detection records.
Orthogonal separation methods address impurities that RP-HPLC may not resolve. Size-exclusion chromatography detects aggregates and higher-order species, while ion-exchange chromatography separates charge variants. Capillary electrophoresis can assess charge-to-mass ratios and, in some formats, size-based impurities. Amino acid analysis and nitrogen determination estimate peptide content rather than chromatographic purity. Because each technique has a different selectivity, a complete purity profile usually combines results from more than one method. The choice of method depends on the impurity classes of concern.
Reversed-phase high-performance liquid chromatography (RP-HPLC) is widely used to estimate peptide purity. Separation depends on interactions between peptide residues and a hydrophobic stationary phase, with gradients of water and organic solvent. Ultraviolet detection near 214 nm responds to the peptide backbone and to many related impurities. The resulting chromatogram is often expressed as area percent, which reports the proportion of peak area assigned to the main component. Different columns, gradients, and wavelengths can produce different purity values for the same material.
National teams April 29 – May 1: 2018 FIBA 3x3 Asia Cup in Shenzhen Men: Australia defeated Mongolia, 17–16, in the final. Japan took third place. Women: New Zealand defeated China, 14–11, in the final. Australia took third place. August 5 – 11: 2018 FIBA Under-18 Asian Championship in Thailand In the final, Australia defeated New Zealand, 73–62, to win their 1st title. China took third place. Note: All teams mentioned here, plus Philippines, have qualified to compete at the 2019 FIBA Under-19 Basketball World Cup. October 28 – November 3: 2018 FIBA Under-18 Women's Asian Championship in Bangalore China defeated Japan, 89–76, to win their fifth consecutive and 16th overall FIBA Under-18 Women's Asian Championship title. Australia took third place. Note: All teams mentioned here, plus South Korea, have qualified to compete at the 2019 FIBA Under-19 Women's Basketball World Cup. Clubs teams November 17, 2017 – May 2: 2017–18 ABL season San Miguel Alab Pilipinas defeated Mono Vampire, 3–2 in games played in a 5-legged final, to win their first ABL title. July 17 – 22: Summer Super 8 in Macau Guangzhou Long-Lions defeated Seoul Samsung Thunders, 78–72, to win their first title. Incheon Electroland Elephants took third place.
== The Human Growth Hormone, Creutzfeld Jakob Disease Controversy == Wilhelmi was an important researcher involved in harnessing human grown hormone from cadavers in the 1960s and 1970s. Early studies conducted in 1958 by Maurice Raben at Tufts University School of Medicine showed it was possible to cause children with pituitary dwarfism to grow by injecting them with human growth hormone. In 1961, the National Institutes of Health (NIH) formed the National Pituitary Agency to organize collection and redistribution of human endocrine glands to three universities for processing into growth hormone: Emory University, Tufts University and Cornell University. For the first 14 of these years, Wilhelmi supervised the Emory laboratory, which was the largest seat of hormone production. In 1985, however, two patients who previously had received the exogenous hormone treatment died in the United States. That caused the NIH to suspend the human growth hormone program and launch an investigation. The deaths were attributed to Creutzfeldt–Jakob disease (CJD) transmitted by impurities in the hormone injected into the patients years earlier using the Wilhelmi protocol. As of 2000, there had been 22 CJD deaths among American recipients of unfiltered hormone prior to 1977.
Carlos Outeiral, CASP14: what Google DeepMind's AlphaFold 2 really achieved, and what it means for protein folding, biology and bioinformatics, Oxford Protein Informatics Group. (3 December) Mohammed AlQuraishi, AlphaFold2 @ CASP14: "It feels like one's child has left home." (blog), 8 December 2020 Mohammed AlQuraishi, The AlphaFold2 Method Paper: A Fount of Good Ideas (blog), 25 July 2021 AlphaFold-3 web server AlphaFold v2.1 code and links to model on GitHub Open access to protein structure predictions for the human proteome and 20 other key organisms at European Bioinformatics Institute (AlphaFold Protein Structure Database) CASP 14 website AlphaFold: The making of a scientific breakthrough, DeepMind, via YouTube. ColabFold, version for homooligomeric prediction and complexes
The AToFMS allows for the determination of mixing state, or distribution of chemical species, within individual particles. These mixing states are important in the determination of climate and health impact of aerosols. The schematic of a typical AToFMS is shown to the right. The overall structure of ATOF instruments is; sampling, sizing, and the mass analyzer region. The inlet system is similar to the AMS by using the same aerodynamic focusing lens, but it has smaller orifices because of its analysis of single particles. In the sizing region particle passes through the first continuous solid state laser that generates an initial pulse of scattered light. Then the particle passes through the second laser that is orthogonal to the first and produces a pulse of scattered light. The light is detected by a photomultiplier (PMT) that is matched up to each laser. Using the transit times between the two detected pulses and the fixed distance the velocity and size of each particle is calculated. Next the particles travel through to the mass analyzer region where it is ionized by a pulsed LDI laser, which is timed to hit the particle as it reaches the center of the ion extraction region. Once ionized, the positive ions are accelerated towards the positive ToF section and the negative ions are accelerated towards the negative ToF section where they are detected.
Sources: en.wikipedia.org
The American Society for Biochemistry and Molecular Biology publishes three research journals and a monthly magazine covering society news and activity updates. ASBMB journals are peer-reviewed and cover research in the fields of microbiology, molecular genetics, RNA-related research, proteomics, genomics, transcription, peptides, cell signaling, lipidomics, and systems biology. All articles are published online as "Papers in Press" upon acceptance. As of January 2021, all three ASBMB journals are fully open access.
Aside from the 22 proteinogenic amino acids, many non-proteinogenic amino acids are known. These either are not found in proteins (for example carnitine, GABA, ornithine) or are not produced directly and in isolation by standard cellular machinery. For example, hydroxyproline is synthesized from proline, and selenomethionine is produced by metabolic modification of methionine. Non-proteinogenic amino acids that are found in proteins are formed by post-translational modification. Such modifications can also determine the localization of the protein, e.g., the addition of long hydrophobic groups can cause a protein to bind to a phospholipid membrane. Examples:
Afucosylated antibodies are intensely used in the field of advanced medicine, also due to their high ADCC (antibody-dependent cellular cytotoxicity). This makes them effective in binding to specific targets while minimizing damage to surrounding tissue. Some of the fields in which afucosylated antibodies are used or considered for application are: cancer immunotherapy autoimmune diseases Infectious diseases Furthermore, afucosylated antibodies are used as diagnostic tools and play a role in the development of personalized medications.
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 peak area of the target peptide in a chromatogram, not the mass fraction of the entire sample. Different analytical methods can yield different purity values. Water, counterions, and residual solvents are excluded unless the calculation specifies otherwise.