A lot of your work in the laboratory will involve you using reagents to accomplish a task
and the reagents will often come in concentrations or in a state that you cannot use as is. so for
instance if you want to go and lyse some cells or lyse some tissues or prepare reagents that will
break up in cells or tissues so that you can extract the components in order to study it,
you may need to make what is called a lysis buffer and this will have components that will
indeed break open a cell and the breaking open of the cell can be in a gentle way so that you can
only you break open on a specific components of the cell or in a harsh way that breaks everything
up because you're going to extract everything. And so in these scenarios you often need to make the
reagent that you need to use may be communicated to you in terms of a percent solution or it may
be in terms of a molar concentration. so percent solutions are really easy to calculate but if you
don't understand what the convention is, then it may be confusing. so a percent solution whenever
you're told to go make a percent solution this is referring to gram quantities per 100 milliliters
where the reagent is not a solid but a liquid such as a detergent that you need to use to make a
certain percentage of, then it's not gram per 100 milliliters but milliliters per 100 milliliters
so for instance if we want to make an 80 percent solution
and our reagent that we're weighing out is a solid like a salt like Tris in a buffer then we when we
see 80 percent what we need to think of is 80 gram in every 100 milliliters. If it's a liquid like
we've got Tween-20 it's the detergent Tween-20 that we need to make in our reagent then the 80
when we see that should translate to 80 milliliters in every 100 milliliters
let's do it again say it's a 70 percent solution when we see that if we're thinking of a liquid
then it's 70 milliliters in every 100 milliliter volume percentage automatically means per 100
and so if it's a solid if the reagent we're about to use is a solid then it's 70 grams
per 100 milliliter volume. so say i don't want a hundred milliliters because maybe i've only got
one plate of cells i only need, say, one milliliter to make the lysis for the lysis buffer
i only need one milliliter to be able to achieve my task well you're not just always going to make
a certain gram per 100 milliliters you will go ahead and adjust accordingly. So say i
want to make a lysis buffer and what i need the reagent that i need requires me to make it at
0.5 percent say i'm using a detergent it's called sodium deoxycolate and what for my preparation i
need it at 0.5 percent. Now all i have to think about is that i want 0.5 in every 100 milliliters.
Percent means per 100 per 100 and so if you always remember this then you can scale as you need to
scale the amount that you need according to 100 milliliters so i want 0.5 percent and it means i
want 0.5 in every 100 milliliters now i only need one milliliter because i don't have a lot of cells
to prepare or i don't have whatever i'm doing i don't need 100 milliliters so let's scale that.
Some other detergents that are used routinely in the laboratory include Triton X-100 or you
may be using Tween-20 and these are different strengths of detergents and the volume that
you may typically make in microliter volume, of course milliliters rarely you would need
liter volumes but if you're making big washing buffers for instance then you may need to make
liter volumes and so of course if i'm making microlitre (ul) volumes i would have to scale it
according to the 100 milliliter standard volume that a percent solution refers to. And of course
if i'm making liter volumes and i'll also have to scale that so in this example the experiment that
i'm doing i need 15 microliters (ul) per sample that i'm processing and i actually have 23 samples
so you would times 50 microliters by 23. however it's always a good idea to give a little bit
extra volume because while you're preparing you may you know you may lose some the accuracies
of the pipette may vary and so you wouldn't have exactly the volume you need for all 23 samples so
i will scale it so that i have 25 samples worth so i'll just times 15 microliters by 25 and i know i
in total i would need 375 microliters (375 ul) of the detergent at 0.5 for my experiment. However
to make matters easy i'm actually just going to make a milliliter (ml) of the reagent so i
am making excess, a lot extra but i'm not wasting too much reagent.
So we're gonna go ahead and just make a milliliter worth so the easiest way to go about it is you
know you want zero point five percent which is the same as i want 0.5 in every 100 and so i'm
going to divide 0.5 by 100 and so we adjust by going 0.5 divide by 100 and that just sets it to
the amount that i would take per one milliliter and so i go ahead and multiply by the volume
that i want which is one milliliter and so is 0.005 milliliters (ml) which gives us 5
microliters (5ul) of the reagent to be dissolved in your solution that you're using to dissolve it.
But hey, why did i start this video with a dozen eggs in the frame well that was to communicate
the idea of molar concentration which is what the solutions the reagents that you need that you need
to make may also be communicated in, and so join me over in the other video where i will go over
how to work out molar concentrations. Alright, take care, all the best with your experiments