Question

how to prepare 10.0ml solutions 2ppm adding 50% v/v of the TISAB?

Answer 1

For a liquid-liquid mixture, we defined 1 ppm concentration as 1 µL/L; therefore, 2 ppm = 2 µL/L.

The stock solution of TISAB has a concentration of 50% (v/v), i.e, 50 mL TISAB/100 mL water. Express the concentration in ppm as [(50 mL)*(1000 µL/1 mL)/(100 mL)*(1 L/1000 mL)] = (50000 µL/0.1 L) = 500,000 µL/L = 500,000 ppm.

The dilution needed is (500000 µL/L)/(2 µL/L) = 250,000.

It is difficult to prepare a 2 ppm solution directly from 50% (v/v) solution. We will need to use step-wise dilution.

Prepare the following table.

Initial concentration of TISAB (ppm)	Final concentration of TISAB (ppm)	Volume of stock (initial concentration) of TISAB required (mL)	Final volume of solution (final concentration) (mL)
500,000	100,000	10.00	50.00
100,000	10,000	5.00	50.00
10,000	1,000	5.00	50.00
1,000	100	5.00	50.00
100	10	5.00	50.00
10	2	2.00	10.00

We have used the dilution equation, M₁*V₁ = M₂*V₂ to get the volumes of the stock solutions required. We equate M₁ = initial concentration of TISAB (ppm), M₂ = final concentration of TISAB (ppm) and V₂ = final volume of the dilute solution.