how can i brought the concentration from 3000 to 100 ppm plz

[Ronaldo]

Hi,

I would like to prepare 100 mg/L from my stock 3000 mg/L , i need it very precise without fraction something like ( 3.3333 ml ) is difficult to tranfere it exactly to 100 ml flask >>> i am really in trouble as my analyte is very expensive and i need to transfer mls exactly withlout fraction

also i don't have 30 ml volumetric flask or 300 ml flask ( i start hate any things come with number three even my three children )

plz help i am very frustrated

[tom jupille]

Do your dilution by weight. If you want to be *very* precise, you can look up the density of water as a function of temperature here:
http://www.simetric.co.uk/si_water.htm

A couple of things to keep in mind:
- First of all, how precise do you need to be?
- Second, how accurate and precise is the "3000 mg/L of your stock solution?

Those will affect how much you need to worry about things like the density of your stock solution taking into account the presence of your analyte.

[haiedc]

Suppose you have 10 mL flask and micropipetes 0-200 and 200 - 1000 ul.

You take 334 ul of stock and level it to 10mL, then add 20 ul of solvent. The concentration C is calculated as:

C = 3000*334/(10020) = 100 mg/L

[chromatographer1]

Assuming you have 10mL and 100mL volumetric flasks.

Determine how much 100mg/mL standard you wish to make. (100mL for example)

Take 10mL flask and fill it to the mark.

Add to a 100mL flask.

Fill the 10mL flask twice to the mark with solvent and add both 10mL volumes to the 10mL in the 100mL flask.

Mix thoroughly the 30 mL of 1000mg/mL solution in the flask by swirling.

Take 10mL of this solution and add it to another 100mL flask.

Add solvent to mark.

You now have a std at 100mg/mL.

Take the 20mL of remaining 1000mg/mL solution and make two more 100mL std solutions.

Adjust according to the flasks/pipettes you have available.

ROdney George

[lcguy1]

chromatographer1, the problem with the method you propose, is that volumetric flasks are designed to contain, not to deliver, their specified volume. The easiest way would be to obtain some micropipettes, as already mentioned, calibrate them, and then use them to do the dilution.

[chromatographer1]

Yes. But if care is exercised this first dilution can be as accurate as the error of the flask. Anytime you make a dilution you have to account for the error of the measurement device. Pipettes have a 1% error as do A-class flasks, other flasks have even larger errors.

The best method of all is to weigh out a standard for dissolution and to make 1 single dissolution. But that wasn't the question posed.

Given a shortage of hardware and the desire to be as accurate as possible given the conditions of the problem, I think my proposal is about as good as one could hope, but not ideal, I agree.

Any better ideas out there? I am willing to learn, but I am from Missouri, please show me !

Rodney George

[HW Mueller]

Rodney, I didn´t see from where your 1000mg/mL is coming.

I would think that all the proposed methods are legitimate if it is stated what was done. As far as I understood what has been proposed, none of the methods allow to formally express the outcome as 100mg/L.

Without knowing what Ronaldo has regarding measuring devices I can´t see how I could help him.

[tom jupille]

I think we've offered all we can until we hear back from Ronaldo!

[Ronaldo]

Thanks all

i follow what Rodney said because i don't have micropipete but it seems to me that the subject is controversial !!