1. What is Direct Isotope Dilution Analysis (DIDA)?

Definition: DIDA is an analytical technique used to determine the quantity of an unknown substance by adding a known amount of a radioisotope of the same element and measuring the change in specific activity.

Purpose: It's widely used in chemistry, biochemistry, and environmental science for precise quantification of substances in complex mixtures.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( x \) — Unknown amount of compound (kg)
• \( y \) — Amount of labelled compound added (kg)
• \( S_i \) — Specific activity of pure labelled compound (Bq/kg)
• \( S_f \) — Specific activity of mixed compound (Bq/kg)

Explanation: The formula calculates the unknown quantity by comparing the dilution of radioactivity when mixed with the unknown substance.

3. Importance of DIDA

Details: DIDA provides highly accurate measurements even in complex matrices where other analytical methods might fail, and doesn't require complete separation of the analyte.

4. Using the Calculator

Tips: Enter the mass of labelled compound added (y), initial specific activity (S_i), and final specific activity after mixing (S_f). All values must be > 0 and S_i > S_f.

5. Frequently Asked Questions (FAQ)

Q1: What units should I use for the inputs?
A: Mass should be in kilograms (kg) and specific activity in becquerels per kilogram (Bq/kg).

Q2: Why must S_i be greater than S_f?
A: This indicates dilution occurred. If they're equal, no unknown substance was present to dilute the radioactivity.

Q3: What if I get a negative result?
A: Check your inputs - this usually means S_f was greater than S_i, which isn't physically possible in this context.

Q4: How precise should my measurements be?
A: For best results, use as precise measurements as possible, especially for specific activities.

Q5: Can I use different units?
A: Yes, but all units must be consistent (e.g., all in grams and Bq/g).