LOD / LOQ Calculator
Two estimation methods (Signal-to-Noise and Calibration Residuals), experimental LOQ confirmation, and back-calculation to sample units — matching the Battery Method Validation walkthrough.
Analyte & Instrument
Method 1 — Signal-to-Noise
S/N = peak height / (2 × RMS noise)
| Conc (µg/L) | Peak (cps) | S/N | Flag |
|---|---|---|---|
| 0.0100 | 25.2 | 1.50 | below |
| 0.0200 | 50.4 | 3.00 | ≥ LOD |
| 0.0500 | 168 | 10.00 | ≥ LOQ |
| 0.100 | 336 | 20.00 | ≥ LOQ |
Interpolated Limits
LOD = 0.0200 µg/L (S/N = 3:1)
LOQ = 0.0500 µg/L (S/N = 10:1)
Method 2 — Calibration Residuals
LOD = 3.3σ/S · LOQ = 10σ/S
Results
LOD = 3.3 × 18.5 / 3360
LOD = 0.0182 µg/L
LOQ = 10 × 18.5 / 3360
LOQ = 0.0551 µg/L
M1 LOQ = 0.0500 µg/L · M2 LOQ = 0.0551 µg/L · Methods consistent ✓
S/N vs Concentration — Cu (m/z 63, He-KED)
LOQ Confirmation
n ≥ 6 reps at LOQ concentration · RSD ≤ 10% · recovery 80–120%
Replicate Values (µg/L)
n = 6| # | Found (µg/L) | Recovery % |
|---|---|---|
| 1 | 0.0480 | 96.00% |
| 2 | 0.0510 | 102.00% |
| 3 | 0.0490 | 98.00% |
| 4 | 0.0520 | 104.00% |
| 5 | 0.0470 | 94.00% |
| 6 | 0.0500 | 100.00% |
n = 6 x̄ = 0.0495 µg/L
SD = 0.00187 µg/L
RSD = 3.78% (≤ 10%) ✓
Recovery = 99.00% (80–120%) ✓
LOQ in Sample Units
LOQsample (ppm) = LOQsol (µg/L) × V (mL) / (m (g) × 1000)
LOQ to use (µg/L)
Calculation Trace
LOQsol = 0.0500 µg/L
Dilution factor = 500.00 mL/g
= 0.0500 × 500.00 / 1000
LOQsample = 0.0250 ppm
= 0.50% of spec limit (5 ppm) ✓ ≤ 10%