This is a working overview of Reverse-phase HPLC, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-10-14 and is reviewed periodically as new material appears.
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.
Solid-phase peptide synthesis can produce truncated sequences when coupling reactions fail. Deletion peptides lack one or more internal residues, while truncation peptides end prematurely. Side reactions include aspartimide formation, oxidation of methionine, and aggregation during chain assembly. Crude synthetic peptides therefore contain target peptide plus related impurities, counterions, residual solvents, and water. Purification by preparative chromatography reduces these impurities but does not remove every closely related species, including some that differ by a single amino acid.
Handling practices reduce the risk of contamination and degradation. Hygroscopic peptides should be equilibrated to room temperature before opening to prevent condensation on the powder. Weighing and reconstitution in a controlled environment limit exposure to moisture and airborne particles. Aliquotting reconstituted solutions avoids repeated freeze-thaw cycles that can cause aggregation or precipitation. When a purity specification is not met, investigation may consider synthesis byproducts, purification losses, storage conditions, and analytical variability rather than a single cause.
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.
| Property | Value | Notes |
|---|---|---|
| Typical purity specification | ≥95% by RP-HPLC | Common for research-grade material; some assays require 98% or higher. |
| Water content | 5–10% w/w | Lyophilized peptides retain moisture; Karl Fischer titration measures it. |
| Counterion | Trifluoroacetate or acetate | Counterion identity affects mass balance and assay compatibility. |
| Storage temperature | -20 °C or lower | Store desiccated and protected from light; avoid repeated freeze-thaw. |
| Common impurity | Deletion or truncation peptide | Similar sequence complicates chromatographic separation. |
Sampling and sample preparation influence measured purity. Peptides are often hygroscopic, so weighing should occur quickly under controlled humidity to avoid water uptake. Complete dissolution in a suitable solvent is necessary before injection; undissolved material can block columns or distort results. Filtration removes particulates but may also remove aggregates if the filter pore size is too small. Impurities can originate from synthesis, cleavage, purification, or storage, and forced degradation under heat, light, oxidation, or pH extremes can help identify degradation pathways.
Regulatory and accreditation expectations depend on the peptide's intended use. Research reagents may be tested with in-house methods, while pharmaceutical development follows validated procedures and pharmacopeial chapters where applicable. Method validation commonly examines accuracy, precision, specificity, linearity, range, and limits of detection and quantitation. Laboratories accredited to ISO/IEC 17025 must document competence, equipment calibration, and uncertainty. Comparing purity results across laboratories remains difficult because different columns, gradients, detection wavelengths, and integration rules can change reported values; open questions include how best to standardize impurity identification and reporting for diverse peptide products.
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.
Peptide purity testing uses separation methods to estimate the proportion of a sample that corresponds to the target sequence. Reverse-phase high-performance liquid chromatography is the most common technique, separating peptides by hydrophobicity on a nonpolar column. Ultraviolet detection at 214 nm records peptide bonds and aromatic residues. The resulting chromatogram is reported as area percent, which reflects relative absorbance rather than absolute mass. This distinction matters because water, counterions, and residual solvents do not appear in the peptide peak.
Mass spectrometry provides an identity check that complements chromatographic purity. Electrospray ionization or matrix-assisted laser desorption/ionization measures the mass-to-charge ratio of intact peptides. A match to the expected molecular mass supports correct sequence length and terminal groups. Mass accuracy alone does not prove that every peak in a liquid chromatogram is the target peptide. It also does not directly quantify how much water or counterion remains in a lyophilized powder.
Orthogonal methods reduce the chance that a single technique misses an impurity. Capillary electrophoresis separates by charge-to-size ratio and can resolve variants that co-elute under one set of HPLC conditions. Amino acid analysis reports composition after hydrolysis and confirms the presence of expected residues. Karl Fischer titration measures water content, while ion chromatography can quantify counterions. No single number captures all aspects of sample quality, so reports often combine several measurements.
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== History == The sign is named after American physician John Benjamin Murphy (1857–1916), a Chicago surgeon from the 1880s to the early 1900s, who first described the hypersensitivity to deep palpation in the subcostal area when a patient with gallbladder disease takes a deep breath.
Avicenna discouraged opium's use except as a last resort, preferring to address the causes of pain rather than trying to minimize it with analgesics. Many of Avicenna's observations have been supported by modern medical research. Exactly when the world became aware of opium in India and China is uncertain, but opium was mentioned in the Chinese medical work Kaibao Bencao (973 AD) By 1590 AD, opium poppies were a staple spring crop in the Subahs of Agra region. The physician Paracelsus (c. 1493–1541) is often credited with reintroducing opium into medical use in Western Europe, during the German Renaissance. He extolled opium's benefits for medical use. He also claimed to have an "arcanum", a pill which he called laudanum, that was superior to all others, particularly when death was to be cheated. ("Ich hab' ein Arcanum – heiss' ich Laudanum, ist über das Alles, wo es zum Tode reichen will.") Later writers have asserted that Paracelsus' recipe for laudanum contained opium, but its composition remains unknown.
CEEs are a combination of estrogens, or agonists of the estrogen receptors. The major estrogen in CEEs, sodium estrone sulfate, itself is inactive, and rather serves as a prodrug of estrone and then of estradiol. The transformation of estrone sulfate to estrone is catalyzed by steroid sulfatase, and of estrone into estradiol by 17β-hydroxysteroid dehydrogenase. CEEs (as Premarin) and estrone have been found to be equivalent in potency in an animal model of estrogenic activity. On the other hand, the active forms of the equine estrogens in CEEs, such as equilin and 17β-dihydroequilin, have greater potency in the liver relative to bioidentical estradiol, similarly to synthetic estrogens like ethinylestradiol and diethylstilbestrol. This results in disproportionate effects on liver protein production compared to estradiol, although to a lesser extent than ethinylestradiol and diethylstilbestrol. In addition, 17β-dihydroequilenin has shown a selective estrogen receptor modulator (SERM)-like profile of estrogenic activity in studies with monkeys, in which beneficial effects on bone and the cardiovascular system were observed but proliferative responses in breast or endometrium were not seen, although the clinical significance of this is unknown. CEEs consists of the sodium salts of the sulfate esters of equine estrogens in a specific and consistent composition (see the table). The major estrogens in CEEs are sodium estrone sulfate and sodium equilin sulfate, which together account for approximately 71.5–92.0% of the total content of CEEs.
In 2018 Stonewall described UK transgender healthcare as having "significant barriers to accessing treatment, including waiting times that stretch into years, far exceeding the maximums set by law for NHS patients". Patients have the legal right to begin treatment within 18 weeks of referral by their GP, however the average wait for patients to gender identity clinics was 18 months in 2020 with over 13,000 people on the waiting list for appointments at gender identity clinics. As of May 2024, prescription of puberty blockers to new patients under 18 for the treatment of gender dysphoria is banned for both private medical practices (by a law in parliament in May) and the official state healthcare National Health Service (NHS) which stopped their use earlier, in the aftermath of the Cass Review except for use in clinical research trials. Previously, on 30 June 2020, the NHS changed its website, replacing the statement that puberty blockers were "fully reversible" and that "treatment can usually be stopped at any time"; with "little is known about the long-term side effects of hormone or puberty blockers in children with gender dysphoria. The Bell v Tavistock decision by the High Court of Justice for England and Wales ruled children under 16 were not competent to give informed consent to puberty blockers, but this was overturned by the Court of Appeal in September 2021. In 2022, the British Medical Association opposed restrictions on puberty blockers, and the NHS restricted their use for children under 16 years of age to centrally administered clinical research.
Sources: en.wikipedia.org
=== Building of preclinical functional === In the preclinical functional building houses the Department of Secretariat, offices of faculty of Basic Medical Sciences and Clinical Laboratories, the Laboratory and Tutorial Rooms and various auxiliary rooms for students, where take place various events.
=== Cyclic peptides === Extensive research has been performed on nanotubes formed by stacking cyclic peptides with an even number of alternating D and L amino acids. These nanotubes are the narrowest formed by peptides. The stacking occurs through intermolecular hydrogen bonding, and the end product is a cylindrical structure with the amino acid side chains of the peptide defining the properties of the outer surface of the tube and the peptide backbone determining the properties of the inner surface of the tube. Polymers can also be covalently attached to the peptides, in which case a polymer shell around the nanotube can be formed. By applying peptide design, the inner diameter, which is completely uniform, can be specified; the outer surface properties can also be affected by peptide design. Therefore, these cyclic nanotubes can form in a range of different environments.
Complementary to the field of structural genomics, protein structure prediction develops efficient mathematical models of proteins to computationally predict the molecular formations in theory, instead of detecting structures with laboratory observation. The most successful type of structure prediction, known as homology modeling, relies on the existence of a "template" structure with sequence similarity to the protein being modeled; structural genomics' goal is to provide sufficient representation in solved structures to model most of those that remain. Although producing accurate models remains a challenge when only distantly related template structures are available, it has been suggested that sequence alignment is the bottleneck in this process, as quite accurate models can be produced if a "perfect" sequence alignment is known. Many structure prediction methods have served to inform the emerging field of protein engineering, in which novel protein folds have already been designed. Many proteins (in eukaryotes ~33%) contain large unstructured but biologically functional segments and can be classified as intrinsically disordered proteins. Predicting and analysing protein disorder is an important part of protein structure characterisation.
==== Post-traumatic stress disorder and phobias ==== Propranolol is being investigated as a potential treatment for PTSD. Propranolol works to inhibit the actions of norepinephrine (noradrenaline), a neurotransmitter that enhances memory consolidation. In one small study, individuals given propranolol immediately after trauma experienced fewer stress-related symptoms and lower rates of PTSD than respective control groups who did not receive the drug. Due to the fact that memories and their emotional content are reconsolidated in the hours after they are recalled or re-experienced, propranolol can also diminish the emotional impact of already formed memories; for this reason, it is also being studied in the treatment of specific phobias, such as arachnophobia, dental fear, and social phobia. It has also been found to be helpful for some individuals with misophonia. Ethical and legal questions have been raised surrounding the use of propranolol-based medications for use as a "memory damper", including altering memory-recalled evidence during an investigation, modifying the behavioral response to past (albeit traumatic) experiences, the regulation of these drugs, and others. However, Hall and Carter have argued that many such objections are "based on wildly exaggerated and unrealistic scenarios that ignore the limited action of propranolol in affecting memory, underplay the debilitating impact that PTSD has on those who suffer from it, and fail to acknowledge the extent to which drugs like alcohol are already used for this purpose".
Sources: en.wikipedia.org
== External links == Safety MSDS data Mohajer, Fatemeh; Mohammadi Ziarani, Ghodsi (2021). "An Overview of Quantitative and Qualitative Approaches on the Synthesis of Heterocyclic Kojic Acid Scaffolds through the Multi-Component Reactions". Heterocycles. 102 (2). Japan Institute of Heterocyclic Chemistry: 211. doi:10.3987/REV-20-936.
The small intestine is a tubular structure around 6 to 7 m long, that begins at the duodenum, and ends at the ileum. Its mucosal area in an adult human is about 30 m2 (320 sq ft). The combination of the circular folds, the villi, and the microvilli increases the absorptive area of the mucosa about 600-fold, making a total area of about 250 m2 (2,700 sq ft) for the entire small intestine. Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:
The South American bushmaster (Lachesis muta muta) is the longest species of venomous snake in the Western Hemisphere and the longest pit viper in the world. It is native to parts of South America, especially the equatorial forests east of the Andes. They are active at dusk or after dark and they are very secretive and elusive. This species is large, fast and has a reputation for being particularly aggressive when cornered. Some reports suggest that this species produces a large amount of venom that is weak compared to some other vipers. Others, however, suggest that such conclusions may not be accurate. These animals are badly affected by stress and rarely live long in captivity. This makes it difficult to obtain venom in useful quantities and good condition for study purposes. For example, Bolaños (1972) observed that venom yield from his specimens fell from 233 mg to 64 mg while they remained in his care. As the stress of being milked regularly has this effect on venom yield, it is reasoned that it may also affect venom toxicity. This may explain the disparity described by Hardy and Haad (1998) between the low laboratory toxicity of the venom and the high mortality rate of bite victims. However, wild specimens have an average venom yield per bite of 280–450 mg (dry weight) (U.S. Dept. Navy, 1968). According to (Sanchez et al., 1992), who used wild specimens from Pará, Brazil, the average venom yield per bite was 324 mg, with a range of 168–552 mg (dry weight). Brown (1973) gives the following LD50 values for mice: 1.5 mg/kg IV, 1.6–6.2 mg/kg IP, 6.0 mg/kg SC.
Sources: en.wikipedia.org
No. Purity testing measures chemical composition and does not assess biological activity, sterility, or endotoxin levels. Functional performance must be tested in the intended assay.
Water adds mass and can affect concentration calculations. A peptide labeled 95% pure may contain water and counterions that reduce the actual peptide content.
Identity can be checked by mass spectrometry, and purity by RP-HPLC. Store according to supplier instructions and retest if experimental performance changes.
Most lyophilized peptides are stored desiccated at -20 °C or lower, protected from light. Some sequences require -80 °C for long-term stability. Storage recommendations depend on sequence, moisture content, and expected duration.