मुफ्त शिखर विषमता कैलकुलेटर
क्रोमैटोग्राफी शिखर की विषमता (पीक एसिमेट्री) निकालें।
Limit of Detection (LOD, 3sigma)
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Limit of Detection (LOD, 3sigma) vs Standard Deviation of Blank (sigma)
सूत्र
## Limit of Detection and Quantitation LOD is the lowest analyte concentration that can be reliably detected (S/N ≈ 3). LOQ is the lowest concentration that can be quantified with acceptable precision (S/N ≈ 10). ### Formulas (ICH Method) **LOD = 3.3 × sigma / S** (often simplified to 3 × sigma / S) **LOQ = 10 × sigma / S** where sigma is the standard deviation of the blank response and S is the slope of the calibration curve. This is the most common approach in pharmaceutical and environmental analysis.
हल किया गया उदाहरण
Blank standard deviation = 0.005, calibration slope = 2500 signal/M.
- 01LOD = 3 × 0.005 / 2500 = 0.015 / 2500 = 6.0 × 10⁻⁶ M = 6.0 uM
- 02LOQ = 10 × 0.005 / 2500 = 0.05 / 2500 = 2.0 × 10⁻⁵ M = 20 uM
अक्सर पूछे जाने वाले प्रश्न
What is the difference between LOD and LOQ?
LOD answers "is the analyte present?" (qualitative). LOQ answers "how much is present?" (quantitative). LOQ is about 3× higher than LOD because greater S/N is needed for reliable quantitation.
How is the blank standard deviation determined?
Measure the response of 10-20 blank samples (same matrix as unknowns but without analyte). The standard deviation of these measurements is sigma. Use the same instrumental conditions as actual samples.
Are there other methods to determine LOD?
Yes. Visual evaluation (lowest visible S/N ≈ 3), signal-to-noise method (directly measuring S/N at low concentrations), and EPA method detection limit (MDL) using t-distribution statistics on replicate measurements.
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