Concentrations Part 5 - serial dilution 

The Hh yes its a mistake

_getfree, This depends on the application of the serial dilutions, If you were trying to obtain a solution that is 1/32 of the concentration of the stock then you would use the two fold, but you wouldn't use the two fold if you needed to obtain extremely diluted solutions from a stock such as 1/1000000 dilution, as performing 20 dilutions is grossly impractical.

I had this same question as I was watching.

-I think your issue is in calculating concentration. Which volume do you use? 270 or 300. If i'm right keep reading :) -Yes. the new volume for that container is 270ul. However, when you made the mixture the total volume was 300. Removing volume after the fact doesn't change the concentration. If you make a new mixture - freeze. calculate concentration with that. -analogy: When you pour a glass of orange juice, the orange juice in the jug has the same concentration there is just less volume. you didn't dilute the orange juice. -hopefully that helps :)

thanks it does,

This is a satisfactory explanation. When any tube was first diluted after addition of 30 uL from the previous tube and was for a moment at 300 ul. After the then diluted product was removed from the 300 uL the final volume was 270 ul. At both 300 ul level after the initial 30 was added AND at 270 AFTER the 30 was removed for the next tube the concentration remain the same. The exact volumes after dilutions are complete might be useful for downstream analyses, but does not affect concentrations. You could take 30 from the very last dilution and discard it, and then all tubes would have appropriate concentrations and all would have 270 ul of sample remaining.

you're right

+Samiksha Ghimire Once we make require concentration , then we can take any volume from the vial, it does not matter...

but during measurment of turbidity it will

absolutely right

That does not really matter because the concentration does not change. If you reduce the last volume to 270microL it is still the same concentration. So why waste 30microL?

but in case of elisa .....concentration matters a lot

You probably don't need the explanation now, but.... 1micoL/100L is equal to (1x10^-6)/100L= 0.00000001microG/microL or 100,000,000x dilution.

In this example, the dilution factor is 10. All you have to do is multiply your final concentration by the dilution factor (10) to calculate the concentration of the preceding solution. You would repeat this step, calculating backwards until you finally get to your stock solution.

There's no need to change tips. You are literally transferring the same solution from one beaker to the next.

The total volume of solution is 300 um once the 30 um of stock solution is added to the 270 um of water. 30:300 = 1:10

yh, you can keep the same tip in this case

just take out the 1ml of the final tube

Then it's not a serial dilution.

300 um was the final volume of the new solution produced. You calculate the concentration of that solution, then dilute it to make the next solution.

If you watch for 10 more seconds he fixes it to Micro liter

I can see why you find it confusing (maybe the fact that he's adding the 270microL first?) but the dilutions are correct.

Also, maybe instead of just saying that there are mistakes, how about just pointing them out?