How It Works
This tool works in 4 steps.
Enter the instrument reading
Type the value the instrument reported, in its unit.
Add each dilution step
Type each DF, or each pair of aliquot and final volumes, in the order performed.
Add extraction data for solids
Type the extract volume and the sample mass weighed.
Read the original concentration
The tool multiplies all factors and returns mg/L or mg/kg with the full correction chain.
The Formula
The formula multiplies the reading by every dilution factor and, for solids, by extract volume per sample mass.
C_sample = C_read × Π DFᵢC_sample (mg/kg) = C_read (mg/L) × Π DFᵢ × V_extract (mL) / m_sample (g)DFᵢ = V_final,i / V_aliquot,i- C_read:
- Instrument reading
- DFᵢ:
- Dilution factor of step i
- V_extract:
- Extract volume
- m_sample:
- Sample mass
A 0.5 g soil sample is extracted into 10 mL, the extract is diluted 1:2, and the instrument reads 12.5 mg/L. C = 12.5 × 2 × 10 / 0.5 = 500 mg/kg.
Conversion Table
The conversion table applies recorded dilution chains and extraction ratios to 6 instrument readings.
| Instrument reading | Dilution chain | Extract / mass | Original sample |
|---|---|---|---|
| 2.4 mg/L | 10 | — | 24 mg/L |
| 0.85 mg/L | 5 × 20 | — | 85 mg/L |
| 12.5 mg/L | 2 | 10 mL / 0.5 g | 500 mg/kg |
| 0.32 mg/L | 10 × 10 | 25 mL / 2 g | 400 mg/kg |
| 48 mg/L | 1 | 50 mL / 5 g | 480 mg/kg |
| 3.1 mg/L | 4 × 5 × 10 | — | 620 mg/L |
What Is the Back-Calculated Sample Concentration Tool?
The Back-Calculated Sample Concentration Tool is a tool that applies every recorded dilution and preparation correction, in order, to an instrument reading and returns the concentration in the original sample. The tool handles liquid dilutions, extraction volumes, and sample masses in one chain.
Lab results pass through several steps: a solid is extracted into solvent, the extract is diluted, and the instrument reads the dilution. Each step changes the factor. The tool lists every step with its own factor, multiplies them, and reports the result per liter (mg/L) for liquids or per kilogram (mg/kg) for solids.
Common Uses
There are 5 main uses of this tool.
Soil and sediment analysis
Environmental labs report mg/kg dry weight from extracts.
Food testing
Food labs report residues per kg of product.
Wastewater results
Utilities correct diluted effluent readings.
Tissue analysis
Toxicology labs report drug levels per gram of tissue.
LIMS checks
Data reviewers verify LIMS correction factors by hand.