METHOD VALIDATION · SPECIFICITY

Specificity Calculator

Interactive companion to the Battery Method Validation technical note. Enter your ICP-OES / ICP-MS specificity data and receive instant numerical results with interpretation.

LOD Criterion

Blank signals must be below the Limit of Detection

Inputs

σ_blank — std. dev. of blank signal (cps) Use ≥ 10 replicate blank injections Reagent blank signal (cps) Matrix acid without sample (e.g. 2% HNO₃) Matrix blank signal (cps) Major elements at expected concentration, analyte absent

Results

LOD Calculation

σ_blank = 60 cps

LOD = 3 × 60 = 180 cps

Blank Assessment

Reagent blank = 45 cps 45 < 180 ✓

Matrix blank = 62 cps 62 < 180 ✓

Both blank signals are below the LOD. No detectable signal contribution from the reagent or matrix — specificity criterion satisfied.

Polyatomic Interference Check

No-gas vs. He-KED mode comparison (ICP-MS)

Inputs

Interference check standard — No-gas mode (cps) Analyte-only standard (e.g. 1 µg/L Fe) in no-gas acquisition mode Same standard — He-KED mode (cps) Same standard in He-KED collision cell mode

Results

Ratio Calculation

No-gas = 48,200 cps

He-KED = 2,310 cps

Ratio = 48,200 / 2,310 = 20.9×

Interpretation

Polyatomic contribution = 95.2% of no-gas signal

→ He-KED / DRC mode required ✗

Significant polyatomic interference (95.2% of no-gas signal). He-KED or DRC mode is required. Standard acquisition would report a severely biased result.

Matrix Effect

Sensitivity comparison — aqueous vs. matrix-matched

Inputs

Aqueous calibration slope (cps / µg L⁻¹) Slope from a standard aqueous calibration Matrix-matched slope (cps / µg L⁻¹) Slope from calibration prepared in the sample matrix

Results

Matrix Effect Calculation

S_aq = 2,310 cps/(µg/L)

S_matrix = 2,199 cps/(µg/L)

Effect = (2,199 − 2,310) / 2,310 × 100

= -4.8%

|-4.8%| ≤ 10% ✓

Matrix effect within the ±10% acceptance limit. Aqueous calibration is valid; internal standard correction is sufficient.

Internal Standard Recovery

Verify IS signal is within the acceptance window

Inputs

Expected IS signal (cps) IS signal in aqueous standard (baseline) Measured IS signal in sample matrix (cps) IS signal co-introduced with the sample

Lower limit (%) Upper limit (%)

Results

IS Recovery Calculation

Expected = 125,000 cps

Measured = 119,375 cps

Recovery = (119,375 / 125,000) × 100

= 95.5%

85% ≤ 95.5% ≤ 115% ✓

IS recovery of 95.5% is within the 85–115% acceptance window. Internal standard correction is performing as expected.

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