Analytical Testing & Quality

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Analytical Testing & Quality

How research peptide identity and purity are verified, and how to read the supporting analytical documentation.

Technical and Biological Replicates Are Not Interchangeable

Three wells from one dilution are three measurements of one thing. Why counting them as the sample size inflates confidence, and what actually counts as independent.

4 min read

Analytical Testing & Quality

Tandem Mass Spectrometry: Reading a Peptide Sequence From Fragment Ions

How MS/MS fragments a selected peptide ion into b and y series, how a sequence is read from the gaps between them, and the three things the spectrum cannot distinguish.

5 min read

Analytical Testing & Quality

Size Exclusion Chromatography and Peptide Aggregate Detection

What size exclusion separates, why apparent molecular weight is not a mass measurement, and which aggregates it detects that a reversed-phase purity trace destroys.

5 min read

Analytical Testing & Quality

Significant Figures, Rounding and How a Result Is Reported

Why 98.7% and 98.70% are different claims, where rounding belongs in a calculation, and how a rounding convention decides whether a borderline lot passes.

4 min read

Analytical Testing & Quality

Protecting Groups: The Mass Signatures of Incomplete Deprotection

Right sequence, wrong mass. The increments that identify which side chain kept its group — and why arginine is the recurring offender.

4 min read

Analytical Testing & Quality

How a Peptide Specification Limit Gets Set

A specification is an attribute, a method and an acceptance criterion. Where the criterion comes from, why the method must be capable of it, and what it leaves unconstrained.

4 min read

Analytical Testing & Quality

Peptide Mapping: Protease Digestion and Sequence Coverage

How a protease digest confirms residue order, what sequence coverage means, and why a peptide map localises a modification that an intact mass cannot.

4 min read

Analytical Testing & Quality

Measuring Concentration by Absorbance at 280 Nanometres

Weighing measures the vial. Absorbance measures the peptide. What the extinction coefficient is built from, a worked example, and the sequences where it simply does not work.

4 min read

Analytical Testing & Quality

Adsorptive Loss: Where the Peptide Goes When It Is Not in the Tube

Peptides bind to glass, plastic, tips and filters. Why the proportion lost depends on concentration, why selective loss changes a measured purity, and what reduces it.

5 min read

Analytical Testing & Quality

What a p-Value Does and Does Not Tell You

A p-value is a statement about data given a hypothesis, not the reverse. The four misreadings, why effect size is the number that matters, and the multiplicity problem.

4 min read

Analytical Testing & Quality

Outliers: When Exclusion Is Legitimate and When It Is Not

An assignable cause independent of the value is the only defensible basis. Why statistical tests do not settle it, and why deciding in advance is the whole discipline.

4 min read

Analytical Testing & Quality

Out-of-Specification Results and What a Retest Can Prove

Why a failing result cannot be replaced by a passing one, what an out-of-specification investigation is for, and the three things a retest is not.

4 min read

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The products offered by ExoLabz are intended solely for research purposes. These products are not for human consumption, are not intended for medical use, and have not been approved by the FDA for any therapeutic or diagnostic purpose. ExoLabz makes no claims regarding the safety, efficacy, or intended use of these products outside of a controlled research environment. By purchasing our products, you agree to use them strictly for scientific research and in compliance with all local laws and regulations.

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