Please look at the following below links which may help you in your analysis:

http://www.eurl-pesticides.eu/userfiles/file/StabilityStockSolutions_HubertZipper.pdf

https://selamat.net/upload_mm/b/5/0/db064559-efc8-4be4-98d0-0f769999b4f2_a11.pdf

Thanks

There should not be any confusion. It is a matter of serial dilution. Prepare a 1000 ppm soultion (1mg/ml is 1000 ppm) of standards. From this stock solution, do serial dilutions to get 4 ppm.

Each stock pesticide standard having ppm values:

201 std (1000ppm), 1 (100ppm) & 3 (2000ppm)

Aim is obtaining 4 ppm in final dilution

Step-I now calculation is 100ppm/25mL is 4 ppm

So, take each stock standard to get 100-ppm solution

Step-II 201 *1000ppm*100uL (0.1mL) we get 100ppm of each

Similarly, 1 * 100ppm * 1000uL (1mL), 100 ppm

3 * 2000ppm * 50uL (0.05mL), each 100 ppm

Now overall volume is 21,250uL (21.25mL) ( 250000uL- 21250uL = 3.75mL)

According to the step-I, we need total final volume should be 25mL, that’s why 3.75mL of acetone for the remaining volume.

That’s it. I hope you understand.

Dilution factors :

1000ppm:4ppm = 250

100ppm:4ppm = 25

2000ppm:4ppm = 500

Volume of standard solutions :

25mL/vol std = 250, so vol std = 0.1 mL of each 1000 ppm solution

25mL/vol std = 25, so vol std = 1 mL of each 100 ppm solution

25mL/vol std = 500, so vol std = 0.05 mL of each 2000 ppm solution

Total volume of standard solutions :

201*0.1 + 1*1 + 3*0.05 = 21.25 mL

25 - 21.25 = 3.75 mL acetone