Chromatography Forum

I am reviewing the topic on Sig. Fig. right now.

Use stock solution of 4 fatty acids, I prepared a standard solution using hexane that has about 1mM of each of these fatty acids. Let's call the fatty acids F1 (13.9mM), F2 (12.3mM), F3 (10.9mM ) and F4 (9.9mM). I use 1ml of each and diluted volumetrically into 10 ml vol flask.

Using M1V1= M2V2, would the concentrations in the standard (with significant figures) be as follow?
F1 = (13.9 * 1)/10 = 13.9/10 = 1.39mM
F2 = (12.3 * 1)/10 = 1.23mM
F3 = (10.9 * 1)/10 = 1.09mM
F4 = (9.9 * 1)/10 = 1.0mM

Then I prepared a standard solution using F1 (13.9mM), F3 (10.9mM ), and F4 (9.9mM) aiming to get exactly 1mM concentration of each, using 719 ul , 917ul , 1010ul.
Since 719 ul is 0.079 ml, 917ul is 0.917 ml, and 1010 ul is 1.010 , plugging in the formula, I get

F1 = (13.9 * 0.079)/10 = 9.9941/10 = 0.99941 but with application of significant numbers, it would be 1.00mM, right?

F3 = (10.9 * 0.917)/10 =9.9953/10 = 0.9953 but with application of significant numbers, it would be 1.00mM, right??

F4 = (9.9 * 1.010)/10 = 9.999/10 = 0.9999 but with application of significant numbers, would it be 1.0mM?

Check "error of computed results" and "propagation of error" in analytical chemistry texts (I have not checked the internet on this, but that might have plenty of info., "significant figures" might be a good phrase to look up also).
One thing I remember and would like to point out right away: You do not increase your significant figures by a dilution, also the value with the lowest precision, and thus lowest number of significant figures, dominates.

I have spotted the deliberate mistake.

Do I get a prize ?

How do you measure those odd volumes to the nearest microliter ?

Peter

Hi Sandra

1) What is the accuracy, precision and the convergence needed for the final result?
Go there do not know where, fetch not know what (c,fairy tale story)
/ scan unknown / , from zero to one, plus / minus kilometer (50-150%) or exactly - 99,9-100,1% wich prescribed norms .
Proceeding from this point and you hit the target - it will be clear to how many characters may be rounded.

2) Usually, all the calculations are no more than two additional significant digits. Again, the accuracy - if the volume of volumetric flask to 10 + / - 0.04 ml it will limit your reliable result 3 significant digits.

Now it's your fault. You have selected volume "Pipetmanom (automatic pipette with a tip) - you should not believe her passport, the mechanism of a pipette worn with time and precision it falls.

Okay, the anecdote about the Rabinovich passport think I will not. That there was no flooding.

Now it's your fault. You have selected volume "Pipetmanom (automatic pipette with a tip) - you should not believe her passport, the mechanism of a pipette worn with time and precision it falls.

Okay, the anecdote about the Rabinovich passport think I will not. That there was no flooding.

The anecdote about the micropipette made me smile because I once informed the Chem Stockroom about the inaccuracy in the micropipette and they're not happy. They said I questions everything, etc. and complained to the prof.

The anecdote about the micropipette made me smile because I once informed the Chem Stockroom about the inaccuracy in the micropipette and they're not happy. They said I questions everything, etc. and complained to the prof.

Hi Sandra
About the micropipette is not a joke. If you take a new micropipette and the micropipette old and weighing the water to make 10 units of 0,5 ml - you'll see that the new micropipette good accuracy (0,494-0,504 g) and precision (0.01 g), fundamental error makes the true amount of the tip.
If you take the old micropipette and make 10 weighings of water you'll see that the old bad precision micropipettes - 0.5 -0.1 g and no amount of accuracy - in the sample will meet the mass and 0,3 and 0,5. The reason - air leak at the plunger due to wear of seals and the weakening of the return spring.

Therefore, use an automatic pipette for the selection of the exact amount should not be, and if you use it - the result must be controlled by mass.
I have long argued this my co-worker, who previously worked in biochemistry.

__________________________________________________________________________

* Anecdote is not about a micropipette, but about what is written in the paper can not be true. Sadness and subtext, finish : - Ruby, but now will not beat up your passport , but beat in the you face!

My question about measuring odd volumes was a non sequitur.

The deliberate mistake is ..........

Peter