Uploaded by mrphysh on 02.02.2011

Transcript:

A common mathematical calculation in laboratories is for dilutions

the formula is normality times volume equals normality times volume

this terminology relates to acid concentration but it could be anything

concentration times volume equals concentration times volume

the example I want use is ten microliters of 2000 parts per million

and we could call it ......

it doesn't matter ...let's call it benzene

we have 10 µL of 2000 parts per million benzene

and we add it to 500 µL and this will be in..a ,.....

methylene chloride or methanol or something like that

normality times volume equals normality times volume so

our original normality is 2000.... our volume is ten and

our ending normality is a variable so this is our variable

and our ending volume is the 500 plus the 10 or 510

so the normality.... you can quickly calculate this

and find that the normality is 39.2 ppm

if the analyst wanted 40 ppm

you have to run this as plus 490 instead of 500 and then that would make this a 500

and that would make this forty

my image of this is for an internal standard

and as an internal standard, you don't really care

what the concentration is and 500 µL

is a little easier to deal with than 490

Let's push this forward with just a little bit more detail

a microliter is a millionth of a liter and since there's 1000 mL it in a liter

and a thousand microliters in a milliliter so

thousand microliters in a milliliter and thousand milliliters in a liter

so there's 1 million microliters in a liter

a part per million is a milligram per liter is a part per million

a milligram per liter is a part per million

there's a million microliters in a liter

there is a million milligrams in a liter

you could look at this and say

"but a milligram is a measure of weight and a liter is a measure of volume"

but one of the definitions that we use... this been around a very long time

is that a cubic centimeter is equal to a milliliter and it weighs..... one gram

so, when we say that one part per million is a milligram per liter

there is an aspect of that as a definition

but there is also an aspect of that, that it is true and literally correct

the implication is that our liter is of water and in applications the liter usually is water

we're taking 10 µL of 2000 ppm, then and we're adding it to 500 µL

10 µL at 2000 ppm is how many milligrams?

okay, remember that parts per million is milligrams per liter

so that the concentration is 2000 milligrams per liter

we have 10 x 10-6 Liters

recall that a microliter is 10-6 liters... so, we have ten of them.

So it's 10 x10-6 ....and if we multiply this out ....the liters fall out

and we end up with 0.020 milligrams

and that is in 510 microliters

remember that parts per million is milligrams per liter

and the way I start this out is... I say

"how many 510s are there in one liter"

to find out how many 510 microliters there are in a liter we simply divide that into liters

the complication, of course, is that we got to make sure our units match

so we changed the 510 microliters to 5.1 x 10-4......

as you all know, the units all have to match

and we end up with 1960.

our 1960 times the milligrams in one of these (0.020) gives us 39.2 milligrams

I think the take-home lesson here might be "what is a part per million"

a part per million is 1 mg per liter

and the normality times volume

it's nailed into my mind as normality times volume

but it's just concentration times volume equals concentration times volume

and quickly note that it is all directly related

and that's it

the formula is normality times volume equals normality times volume

this terminology relates to acid concentration but it could be anything

concentration times volume equals concentration times volume

the example I want use is ten microliters of 2000 parts per million

and we could call it ......

it doesn't matter ...let's call it benzene

we have 10 µL of 2000 parts per million benzene

and we add it to 500 µL and this will be in..a ,.....

methylene chloride or methanol or something like that

normality times volume equals normality times volume so

our original normality is 2000.... our volume is ten and

our ending normality is a variable so this is our variable

and our ending volume is the 500 plus the 10 or 510

so the normality.... you can quickly calculate this

and find that the normality is 39.2 ppm

if the analyst wanted 40 ppm

you have to run this as plus 490 instead of 500 and then that would make this a 500

and that would make this forty

my image of this is for an internal standard

and as an internal standard, you don't really care

what the concentration is and 500 µL

is a little easier to deal with than 490

Let's push this forward with just a little bit more detail

a microliter is a millionth of a liter and since there's 1000 mL it in a liter

and a thousand microliters in a milliliter so

thousand microliters in a milliliter and thousand milliliters in a liter

so there's 1 million microliters in a liter

a part per million is a milligram per liter is a part per million

a milligram per liter is a part per million

there's a million microliters in a liter

there is a million milligrams in a liter

you could look at this and say

"but a milligram is a measure of weight and a liter is a measure of volume"

but one of the definitions that we use... this been around a very long time

is that a cubic centimeter is equal to a milliliter and it weighs..... one gram

so, when we say that one part per million is a milligram per liter

there is an aspect of that as a definition

but there is also an aspect of that, that it is true and literally correct

the implication is that our liter is of water and in applications the liter usually is water

we're taking 10 µL of 2000 ppm, then and we're adding it to 500 µL

10 µL at 2000 ppm is how many milligrams?

okay, remember that parts per million is milligrams per liter

so that the concentration is 2000 milligrams per liter

we have 10 x 10-6 Liters

recall that a microliter is 10-6 liters... so, we have ten of them.

So it's 10 x10-6 ....and if we multiply this out ....the liters fall out

and we end up with 0.020 milligrams

and that is in 510 microliters

remember that parts per million is milligrams per liter

and the way I start this out is... I say

"how many 510s are there in one liter"

to find out how many 510 microliters there are in a liter we simply divide that into liters

the complication, of course, is that we got to make sure our units match

so we changed the 510 microliters to 5.1 x 10-4......

as you all know, the units all have to match

and we end up with 1960.

our 1960 times the milligrams in one of these (0.020) gives us 39.2 milligrams

I think the take-home lesson here might be "what is a part per million"

a part per million is 1 mg per liter

and the normality times volume

it's nailed into my mind as normality times volume

but it's just concentration times volume equals concentration times volume

and quickly note that it is all directly related

and that's it