GIFSQ Tools · Module 15 — Metrology, Validation & Laboratory Accreditation · Tool 286 of 500
Estimate the limit of quantification (LOQ) of a quantitative method from the blank standard deviation and the calibration slope — the metrology estimator of ISO 11843 and IUPAC. Distinct from Tool 74, which covers the microbial LOQ worksheet.
Try sample values — fills the form with the worked example below.
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LOQ (mg/L)
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LOD for reference (mg/L)
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LOQ ÷ LOD
Equation: LOQ = 10 × s₀ ÷ slope. For reference, LOD = 3.3 × s₀ ÷ slope, so LOQ ÷ LOD = 10 ÷ 3.3 = 3.03.
Method: Quantification-limit estimation per ISO 11843-2 and the IUPAC definition: the lowest amount that can be quantified with acceptable precision and trueness. This is the METROLOGY/statistical estimator for chemical methods — distinct from Tool 74 (Limit of Quantification Worksheet), which covers the microbial plate-count LOQ, and from Tool 285 (the LOD estimator).
Assumptions: the blank standard deviation comes from at least 10 independent blank measurements; the response is linear near the quantification limit; the slope is the calibration slope in the same response units as s₀.
Limitations: the 10σ rule is a convention, not a proof of fitness — confirm the LOQ by spiking at that level and checking recovery and precision against your method criteria; matrix effects are not captured.
Rounding: LOQ and LOD to 3 decimal places; ratio to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Quantification-limit estimation per ISO 11843-2 and the IUPAC definition: the lowest amount that can be quantified with acceptable precision and trueness. This is the METROLOGY/statistical estimator for chemical methods — distinct from Tool 74 (Limit of Quantification Worksheet), which covers the microbial plate-count LOQ, and from Tool 285 (the LOD estimator).
Assumptions: the blank standard deviation comes from at least 10 independent blank measurements; the response is linear near the quantification limit; the slope is the calibration slope in the same response units as s₀.
Limitations: the 10σ rule is a convention, not a proof of fitness — confirm the LOQ by spiking at that level and checking recovery and precision against your method criteria; matrix effects are not captured.
Rounding: LOQ and LOD to 3 decimal places; ratio to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Blank SD 0.02 AU with slope 0.5 AU per mg/L: LOQ = 10 × 0.02 ÷ 0.5 = 0.400 mg/L; LOD = 0.132 mg/L; LOQ ÷ LOD = 3.03.
Enter values above to see results.
Never report a value below the LOQ as a number — report it as below the LOQ. Tool 286 of 500 — GIFSQ
