Quantitative Chemical Analysis

Proof required

Submit your analyte specification (the chemical species being quantified and the sample matrix it is in), your chosen technique (titration, gravimetric, spectrophotometric, colorimetric, or equivalent) with a justification for why that technique is appropriate, your protocol for calibration (standards preparation, calibration range, number of calibration points), and your uncertainty budget identifying the main sources of measurement error.

What gets checked

• Technique justification is specific to the analyte and matrix — not 'spectrophotometry can measure concentrations' but 'UV-Vis spectrophotometry at 540nm is appropriate because the iron(II)–phenanthroline complex has a molar absorptivity of >11000 L/mol/cm in this wavelength region'
• Calibration protocol specifies at minimum 5 calibration standards spanning the expected analyte concentration range — not a single standard
• Uncertainty budget identifies instrument, calibration, sampling, and method contributions separately — at minimum three distinct sources

Common mistakes

• Not specifying the calibration range — quantitative analysis outside the calibration range is extrapolation, not measurement; the protocol must define the linear range of the method
• Selecting a technique without considering the matrix interferences — many quantitative techniques are affected by other species in the sample; the protocol must address how interferences are handled

Resources

What a verifier looks for

• Ask the submitter to justify the number of calibration standards and the concentration range they selected — too few standards or too narrow a range are common quantitative analysis errors.
• Ask what the detection limit of their method is and how they estimate it — distinguishing limit of detection from limit of quantitation is fundamental analytical chemistry.
• Ask what matrix effect they are most concerned about and how they addressed it in the protocol.

Proof required

Submit your calibration data table, the calibration curve plot with the regression equation and R² value, your sample measurement data, the quantitative result with full uncertainty propagation showing how each measurement's uncertainty contributes to the final concentration uncertainty, and a statement comparing the result against the expected or reference value.

What gets checked

• Calibration plot shows R² ≥ 0.99 — a lower correlation coefficient indicates a calibration problem that must be investigated before reporting results
• Uncertainty propagation is shown explicitly — the equation for propagated uncertainty with each measurement's contribution quantified; not 'the uncertainty is approximately ±X'
• Result is compared against a reference value — either a certified reference material value, a spiked sample recovery, or the published value from the accessible alternative dataset

Common mistakes

• Forcing a linear regression through the origin without justification — the calibration intercept has physical meaning (blank absorbance, reagent background); it should only be forced to zero if justified by the blank measurement
• Not assessing the calibration linearity — reporting results from a calibration that shows visual curvature without addressing it

Resources

What a verifier looks for

• Ask the submitter to walk through the uncertainty propagation from a single measurement uncertainty to the final concentration uncertainty step by step.
• Ask what their recovery (or agreement with reference value) was and what a good recovery for this type of analysis is — analytical chemists typically target 95–105% recovery.
• Ask whether the calibration covers the analyte concentration in the sample — a sample that falls outside the calibration range must be diluted and re-measured.

Proof required

Submit your complete analytical chemistry report (1500–2500 words: introduction with the analytical problem, methods with the full protocol, results including the calibration curve, quantitative result with uncertainty, and comparison with reference, discussion addressing the method's performance characteristics and sources of error) plus a Q&A record showing specific challenges to the calibration or uncertainty analysis and your responses. The reviewer must be named and their analytical chemistry or laboratory science background stated.

What gets checked

• Method performance characteristics are reported — at minimum linear range, precision (expressed as %RSD), and accuracy (expressed as % recovery)
• Discussion explains the dominant source of uncertainty quantitatively — not all uncertainty contributions are equal; the report must identify which one dominates
• Q&A record shows at least two challenges and substantive responses

Common mistakes

• Reporting precision as a single repeat measurement — reproducibility (multiple measurements on the same day) and repeatability (measurements on different days) are different; the report should specify which is being reported
• A reviewer without quantitative analysis experience — the Q&A must probe calibration statistics and error treatment, which requires analytical chemistry knowledge

Resources

What a verifier looks for

• Ask what the method detection limit is and whether the sample concentration was well above it — a result close to the detection limit has proportionally higher uncertainty.
• Ask whether the result would change if a different calibration range was used — tests understanding of the relationship between calibration design and measurement reliability.
• Verify the reviewer has analytical chemistry or quantitative laboratory science experience.