Understanding LOD and LOQ
Limit of detection and limit of quantitation support method validation. LOD is the lowest amount that can be detected with reasonable confidence. LOQ is the lowest amount that can be measured with useful precision. A calibration curve links known concentration with instrument response. The slope shows sensitivity. A steep slope usually lowers both limits, when noise remains stable.
Why Calibration Curve Quality Matters
A reliable curve needs clear standards, repeat readings, and a suitable range. The calculator estimates slope, intercept, and R squared from entered pairs. It can also use a manual slope when your laboratory report already has one. The standard deviation may come from residual error, blank readings, or a manual value. Each option fits a different validation design. Residual error uses all curve points. Blank deviation focuses on zero level noise. Manual deviation is useful when an approved protocol gives sigma.
Practical Analytical Use
Detection and quantitation limits are not universal constants. They depend on method setup, matrix, reagent quality, instrument stability, and operator practice. Use the same units for concentration across every standard. Use response units that match the selected deviation source. Review outliers before trusting the final value. A poor curve can make limits look better or worse than reality.
Interpreting Results
The result table shows calculated slope, intercept, sigma, LOD, and LOQ. It also displays response thresholds near the blank intercept. Compare LOQ with your lowest calibration standard. The lowest standard should usually be at or below the target reporting level. If LOQ is higher than required, improve the method. You may lower noise, add replicates, adjust extraction, or increase detector sensitivity.
Good Documentation Practice
Keep raw calibration data with the exported report. Record the sigma source, factors, units, analyst, and date. Many laboratories use 3.3 times sigma over slope for LOD. They often use 10 times sigma over slope for LOQ. Always follow your own validation procedure. This tool supports transparent calculations. It does not replace regulatory judgment, laboratory controls, or formal quality assurance.
Advanced Checks
Test several sigma sources when rules allow comparison. Large differences can reveal drift, blank contamination, or curved response. Rebuild the calibration after maintenance, new reagents, major dilution changes, or scheduled detector service.