The Threshold Odor Number (TON) is a measure used to quantify the odor intensity in water. It represents the dilution factor required for an odor sample to become just detectable by a group of panelists.

Odor Number Formula

The formula for calculating the Threshold Odor Number (TON) is:

TON = $\frac{\text{Volume of diluted sample}}{\text{Volume of original odor sample}}$

Alternatively, the formula can also be expressed as:

TON = $\frac{A + B}{A}$

Where:

• $A$ = Volume of the original odor sample (in mL)
• $B$ = Volume of odor-free distilled water added (in mL)

Threshold Odor Calculation

From the question, we are given the following values:

• Volume of the original odor sample ($A$) = 20 mL
• Volume of odor-free distilled water added ($B$) = 180 mL
• Total volume of the mixture = 200 mL (This is $A+B$)

Using the formula $TON = \frac{A + B}{A}$, we can calculate the Threshold Odor Number:

Step 1: Identify the given volumes.

• $A = 20$ mL
• $B = 180$ mL

Step 2: Substitute the values into the TON formula.

TON = $\frac{20 \text{ mL} + 180 \text{ mL}}{20 \text{ mL}}$

Step 3: Perform the calculation.

TON = $\frac{200 \text{ mL}}{20 \text{ mL}}$

TON = $10$

Result Threshold Odor Number

The calculated Threshold Odor Number (TON) is 10. This means the original odor sample needed to be diluted 10 times with odor-free water before the odor became just detectable.