Articles
60 reference articles, each cited to primary literature.
stability study design
Accelerated Stability and Arrhenius Extrapolation: What a Hot Study Can and Cannot Predict
The Arrhenius equation, what the activation energy silently assumes, a worked extrapolation from three temperatures, why lyophilised and solution peptides break the model in different ways, and what ICH allows an accelerated result to support.
Designing a Stability Study: The ICH Q1A Framework Scaled to a Small Lab
How stability is established rather than assumed: storage conditions, pull points, attributes, sample numbers and acceptance criteria, taken from ICH Q1A(R2) and the 2025 consolidated Q1 draft and scaled to a laboratory without a stability department.
Forced Degradation: Stressing a Peptide on Purpose to Learn How It Fails
The deliberate-degradation experiment: how it differs from stress and formal stability testing, the conditions used on peptides, the extent of degradation to aim for, identifying the products, mass balance, and why it has to come before a stability-indicating method.
Photostability Testing: ICH Q1B, Light Sources and Amber Glass
How light sensitivity is established rather than assumed: the Q1B exposure units, the Option 1 and Option 2 sources, dark controls and actinometry, the stepwise container sequence, which residues absorb, and what amber glass does and does not stop.
Stability-Indicating Methods: Why a Purity Assay Alone Does Not Qualify
What a method has to demonstrate before its results can support a stability claim: specificity shown with degraded samples, resolution of degradants, an assay that measures amount, closed mass balance, and the validation elements, with a checklist.
analytical calculations
Assay, Purity and Content: Three Numbers That Are Routinely Confused
Purity is a ratio among related substances. Content is a mass fraction of the whole material on a stated basis. Assay is a measurement against a reference standard that produces a content. Definitions, the mass balance that links them, a worked lot and how each reads on a certificate.
Calibration Curves: Linearity, LOD and LOQ
Building a calibration curve, judging linearity from residuals rather than r², and calculating detection and quantitation limits by the 3.3σ/S and 10σ/S conventions. A worked low-level curve and the rules for reporting results below the limit.
International Units: Why an IU Is Not a Mass and Cannot Always Be Converted
An International Unit is a quantity of biological activity defined by a WHO reference preparation, not a quantity of matter. Where a mass conversion exists, why it exists; where it does not, why no factor can be written. Insulin, vitamins D and A, and heparin as worked cases.
Molar Mass, Moles and Converting a Mass to an Amount of Substance
The conversion is one division. Getting it right depends on which mass goes into the numerator and which molar mass goes into the denominator. Definitions, sequence arithmetic, salt and water corrections, and a worked example on an invented decapeptide.
Significant Figures and Rounding: How a Result Should Be Reported
The number of digits in a result is a claim about the method that produced it. Counting rules, rounding once and at the end, rounding against an uncertainty, comparing with a specification, and why 99.47%, 99.5% and 99% say different things.
transport standards
Chain of Custody for Analytical Samples: The Record ISO/IEC 17025 Expects
What a custody record is, which clauses of ISO/IEC 17025 it satisfies, what each hand-off must capture, how seals bridge the carrier gap, and a field-by-field form with the rules for completing it.
Dry Ice as a Dangerous Good: UN1845, Venting and the Declaration
Why a refrigerant is regulated at all, how its status changes between air, road and post, the marks and air waybill entries that go with it, when a Shipper's Declaration is and is not needed, and how to plan the quantity from a measured loss rate.
Packaging Instruction 650 and UN3373: The Triple-Packaging Standard Explained
What PI 650 requires of each packaging layer, the pressure, drop and marking rules, the quantity limits by route, and the classification step that decides whether it applies at all — which, for dry synthetic peptide, it usually does not.
Qualifying a Shipping Container: Mapping, Hold Time and the Summer and Winter Profiles
A passive shipper is a system with a finite duration, not a storage location. The three qualification stages, the ambient profiles that challenge it, where the probes go, how hold time is determined and written down, and what triggers a repeat.
Sample Receipt: Acceptance Criteria, Rejection and the Receipt Log
What a testing laboratory checks when an item arrives, how temperature on receipt is established and recorded, acceptance criteria written before the item is seen, the consultation and disclaimer ISO/IEC 17025 requires, and a receipt log template.
analytical method design
ESI-LC-MS Versus MALDI-TOF: Which Mass Measurement Proves What
Two ionisation routes, two kinds of spectrum, and different claims each can support. How electrospray and matrix-assisted laser desorption differ, what mass accuracy in ppm actually requires, and how to choose between them for peptide identity.
Peptide Mapping: Confirming Sequence, Not Just Mass
An intact mass confirms composition; the order of residues needs fragments. How a peptide map is designed — enzyme choice, digestion, LC-MS/MS, coverage — when direct fragmentation of the intact peptide is enough, and what a mapping report should contain.
Reversed-Phase HPLC for Peptides: Column, Gradient, Mobile Phase and Detection Wavelength
How a peptide purity method is built rather than read: stationary phase and pore size, trifluoroacetic acid against formic acid, scouting and focused gradients, temperature, injection and wavelength — with a reference method and a development sequence.
Synthesis-Related Impurities: Deletion, Truncation, Incomplete Deprotection and Racemisation
Solid-phase synthesis produces a predictable family of near-copies of the target. The impurity classes, the mass shift and chromatographic behaviour of each, why a single purity figure can hide them, and what an impurity-aware certificate lists.
System Suitability and Reference Standards: Proving the Instrument Before Trusting the Result
Validation shows a method can work; system suitability shows it worked on the day. The parameters and their formulas, how to build a test for a peptide purity method, and how the reference standard behind it is characterised, qualified, stored and recorded.
contamination control
Sterile Filtration and the Bubble Point Test: What a 0.22 Micrometre Rating Claims
A sterilising rating is a bacterial retention claim validated against one organism, not a statement about hole size. Bubble point physics, wetting, adsorption by membrane material, capacity limits, and the contaminant filtration never removes.
Glassware Cleaning and Detergent Residue: Rinse Sequences and the Adsorption Penalty
Detergent residue survives a casual rinse and reappears as ion suppression, ghost peaks and failed assays. Rinse sequences, the final-rinse rule, when acid washing is warranted, and why scrupulously clean glass binds peptide harder than dirty glass did.
Water Grades Type I, II and III: Resistivity, TOC and Bacterial Limits
Laboratory water is specified by measured parameters, not by the process that made it. What each grade guarantees, how distillation, deionisation and reverse osmosis differ, and why water silently moves an analytical result.
Cross-Contamination Between Vials and Tools: Routes, Static and Detection
Carryover moves material between containers on spatulas, needles, gloves and shared surfaces — and, for lyophilised powder, without contact at all. The routes, the controls, the sequencing rule, and what detection can and cannot find afterwards.
Aseptic Technique at the Bench: Cabinets, Surfaces and Movement
Aseptic technique is a sequence of movements and surfaces, not a piece of equipment. Cabinet classes, disinfectant contact times, the errors that break first air, and what an open bench actually costs.
method and records
Method Validation Basics for a Small Laboratory
Specificity, linearity, accuracy, precision, range and robustness defined in plain terms — which of them an identity method needs, which a quantitative method needs, what full validation costs against verification, and a proportionate programme for a laboratory of three.
Out-of-Specification Results and What to Do About Them
The difference between out of specification and out of trend, why retesting is never the first move, how to interrogate the method before the material, the averaging trap, and what to do when a supplier certificate contradicts your own result.
The Laboratory Notebook and Contemporaneous Records
Why recording at the time is not the same as recording accurately later, the attributable-legible-original-accurate vocabulary, how to correct an entry without destroying it, bound versus electronic notebooks, and how long to keep them.
Uncertainty of Measurement in Practice
Why every result is a range rather than a number, how Type A and Type B contributions differ, a worked uncertainty budget for a weighing and a dilution, the coverage factor and reporting convention, and what a purity figure quoted without uncertainty is actually worth.
Writing a Standard Operating Procedure: A Template That Survives Being Followed
Scope, materials, procedure, acceptance, records — the five sections that carry an SOP, how to write steps somebody else can execute, how to version and review them, and a worked goods-in receiving skeleton to copy.
instrumentation
Calibrating a Laboratory Balance: Internal Adjustment, External Weights and the Static Problem
The calibration button is not a calibration. What internal adjustment corrects, what only traceable external weights can measure, and why electrostatic force is the largest invisible error at milligram scale.
Centrifuge Selection and g-Force Calculation: RCF, Rotor Radius and Rotor Geometry
A speed in revolutions per minute describes a motor, not a separation. The conversion to relative centrifugal force, why rotor radius makes the same rpm mean different things, and the vial spin-down that protects a powder before the cap comes off.
Freezer Mapping and Temperature Monitoring: Probes, Excursions and the Record
A freezer holds a temperature field, not a temperature. How to map one, where to place the probes, how door openings distort the trace, and why the display on the front panel is the least useful number available.
pH Meter Calibration and Electrode Care: Brackets, Slope, Offset and Junctions
A pH reading is a millivolt measurement dressed as a number. How to choose calibration brackets, read slope and offset as electrode health, compensate for temperature, and keep a junction working — and why a tenth of a unit changes a peptide's degradation rate.
Pipette Calibration and Gravimetric Verification: Accuracy, Precision and the Z-Factor
A pipette is a balance problem in disguise. The gravimetric check step by step, the density and buoyancy correction that converts mass to volume, acceptance criteria by volume, and the technique faults no calibration can repair.
quantification
Amino Acid Analysis as a Reference Method
The only routine assay that answers how much peptide is in a weighed solid. Hydrolysis and what it destroys, derivatisation and separation, what it costs, and what its absence from a certificate leaves undetermined.
Counter-Ion Content: Trifluoroacetate and Acetate
Synthesised peptides arrive as salts, and the salt is not a trace. How much mass the counter-ion carries, how it is measured, when exchange is worth requesting, and where it sits in the accounting that reconciles gross weight to peptide.
Gravimetric and Volumetric Preparation Error
Balance resolution against pipette tolerance, the volume below which weighing wins, the density and temperature terms that convert between them, and how error behaves as it passes down a dilution series.
Karl Fischer Titration and Residual Moisture
Water is the largest non-peptide term nobody measures. How the titration works, what volumetric and coulometric modes are each good for, where the sub-three-per-cent convention came from, and what a moisture figure on a certificate does and does not describe.
UV Absorbance at 280 nm: Concentration Without a Balance
An optical measurement of peptide concentration that is blind to counterion, water and salt — and that returns nothing at all for a sequence carrying no aromatic residues. Coefficients, path length, interference and the failure cases.
preparation
Weighing and Handling Hygroscopic Solids: Moisture, Static and the Case for Not Weighing
Lyophilised peptide gains water while it sits on the pan, carries charge, and is weighed in quantities where balance error is proportionally large. The control for each, and the route that removes the weighing entirely.
Filtration and Particulate Control: What a Membrane Removes, Including Peptide
Filtration removes particulate and aggregate above the pore rating, and removes peptide by binding it to the membrane. Membrane materials compared, with a procedure for re-measuring what survives the pass.
Stock Solutions and Dilution Series: Concentration Arithmetic
One weighing carried into a whole concentration range by volumetric transfer. Molar and mass concentration, serial versus direct dilution, solvent carry-over, and a worked series.
Solvent Selection and Dissolution: Choosing a Solvent and Getting Peptide Into Solution
Solvent choice is set by the sequence, not by the assay. Charge assessment, a solvent selection table, the dissolve-then-dilute order, and what to record against a batch.
Net Peptide Content and Gross Weight
The mass printed on a vial is total solid, not peptide. This is what makes up the difference, how the peptide fraction is determined, and how to carry it through a concentration calculation.
verification
Endotoxin and Bioburden in Peptide Preparations: What Testing Establishes
Chemical purity, sterility and endotoxin content are three independent properties of a preparation. This is what endotoxin is, why it confounds cell-based assays, and what each test method establishes.
Documentation and Batch Traceability: Minimum Record Sets for Peptide Material
What to record for received batches and for every solution prepared from them. Field-by-field record sets, label content, excursion logging and a receiving-to-first-use procedure.
Mass Spectrometry and Peptide Identity: What a Mass Match Establishes and What It Does Not
A mass measurement establishes composition, not the order of residues. This is where the reported number comes from, why monoisotopic and average masses produce false mismatches, and how to read an offset.
HPLC Purity: What the Figure Measures and What It Omits
A purity percentage is one peak's area as a share of the total integrated area, under one method, at one wavelength. This is what that includes, what it leaves out, and how to tell whether a stated figure is interpretable at all.
Reading a Peptide Certificate of Analysis: Field-by-Field Reference
A certificate of analysis records the results of tests performed on one batch. This is a field-by-field reference to what each entry states, how it is determined, and where it fails.
storage
Cold Chain and Temperature Excursions: Transport, Receipt and Assessment Procedure
What ambient transit costs lyophilised material, and why a solution has no equivalent tolerance. Receipt recording, monitoring devices, cake appearance as thermal evidence, and a procedure for assessing an excursion.
Container Selection and Surface Adsorption: Materials, Closures and Peptide Lost to the Wall
Peptide bound to the container wall is routinely mistaken for low potency. Material comparison, closure selection, mitigation options and a procedure for detecting the loss.
Freeze–Thaw Cycles and Aliquoting: Damage Mechanisms and Sizing Practice
Freeze–thaw damage is applied by the transition, not by the cold. Reference on the physical stresses, the variables under control, and how to size aliquots so the question of cycle count never arises.
Stability of Peptides in Solution: Controlling Variables and Handling Practice
Solution-phase stability is a different problem from the dried solid, governed by different variables. Covers the pH trade-off, adsorptive loss to containers, and a single-use aliquot procedure.
Storage of Lyophilised Peptides: Conditions, Containment and Handling Procedure
Reference conditions for holding freeze-dried peptide material: temperature bands, moisture control, containment and light exclusion. Includes equilibration and receiving procedures.
degradation
pH and Buffer Selection: Competing Dependencies, Buffer Properties and a Recording Procedure
pH is the most influential controllable variable in solution, and the routes it governs pull in opposite directions. Covers the trade-off, isoelectric point estimation, buffer properties and their specific liabilities.
Aggregation and Precipitation: Physical Loss of Peptide from Solution
Aggregation removes peptide from solution without altering its chemistry, so analysis of the dissolved fraction reads normal. Risk factors, detection methods and an investigation procedure.
Deamidation of Asparagine and Glutamine: Mechanism, Sequence Risk and Detection
The succinimide route in detail: how the reaction runs, which motifs are fast, what pH and buffer do to it, and why a +1 Da change costs activity. Includes a sequence-risk assessment procedure.
Oxidation of Susceptible Residues: Vulnerability Order, Mechanism and Control
The detailed treatment of one degradation route. Which residues oxidise and to what, the two mechanistic classes and why they need different controls, and where the oxidant comes from on a laboratory bench.
Peptide Degradation Pathways: Chemistry, Susceptible Residues and Analytical Signatures
The chemical routes by which a peptide preparation loses integrity, the residues each route attacks, and the evidence that identifies it. This is the reference the rest of the stability cluster points back to.