[jqo2]

I want to prepare a standard solutions (4 times)

I have:

• 2500 mg/L Stock solutions Paracetamol
  
• 463,50 mg/L Stock solutions Caffeine
  

four standards:
                 

             Paracetamol (µg/ml)                    caffeine (µg/ml)

1 -                50                                           20
2-                 75                                           30
3-                100                                           40
4-                125                                           50

In (four) 100 ml flask, can anyone help?

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy.

This is a simple dilution. Have you checked if it can be done in one step? What is the lowest volume you can measure accurately?

[jqo2]

I have a pipet p200 (20 µl).

Oke just paracetamol:

1ml Paracetamol stock (2500mg/L) in 99ml H2O gives us solution 25 mg/1000ml.

And then 0,002 from this solution in 9,998 ml H2O --> 50 µg / 1000 ml but a need 50 µg/ml

[Borek]

If you have no other pipettes or volumetric flasks, you may be not able to prepare the concentration you need.

But in general you are on the right track. It would be probably easier if you were to use μg/mL all the time. For example, what is

25 mg/1000ml

in μg/mL?

[jqo2]

25 μg/mL

Yes i have other pipettes and volumetric flasks.

[Borek]

25 μg/mL

So you have already overshot your first target.