Analytical calculations
Analytical calculations: 7 articles from Peptides Info. Handling, storage and laboratory reference.
Peptide Net Charge and pI: A Henderson-Hasselbalch Calculation
The arithmetic that precedes buffer choice: the ionisable groups of a sequence, a stated pKa set, the fractional-charge formulas for acids and bases, a worked summation for an invented dodecapeptide at pH 3, 5, 7 and 9, bisection to the isoelectric point, why calculators disagree, and what the result means for solubility.
Relative Response Factors: Why Area % Is Not Weight %
The correction behind an HPLC purity figure: response factor and relative response factor defined, RRF determination by impurity standard or slope ratio, the 1 ÷ RRF correction applied to a worked four-impurity chromatogram, the 0.8 to 1.2 window in which correction is commonly waived, and the ICH Q3A thresholds the corrected values are judged against.
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.