8270 GC/MS Initial Calibration


Uploaded by mrphysh on 11.07.2011

Transcript:
The consultants at the Wal-Mart site send in a sample for 8270
they get a result back that tells them that they have 70 parts per billion 2-methylnaphthalene
where does that number come from?
one way to approach it is this: we take a liter .... this is like a big graduated cylinder
the liter mark is right here.
we fill it up... we put in 200 mg of 2-methylnaphthalene
200 mg in a liter is two hundred parts per million
this implies that there's 1,000,000 mg in a liter, which in fact, there is
200 mg is 2/10 of gram which is spatula full... it's not difficult to weigh.
our sample comes in, in a small vial .... we subject a microliter of the sample
from the site to our chromatographic analysis
and we get a response factor of 237
we subject a microliter of our standard to our chromatographic analysis
and get response factor of 1239
the way I think of it this is:
I say
"okay, start with the 200 multiply by little number and divide by the big number"
and we find out that our sample is 70.5 ppm 2-methylnaphthalene.
The 8270 list has 70 compounds
it's more than just 2-methylnaphthalene so the way to.... using the same approach
would be to simply put 200 mg of phenol, 200 mg of indene, 200 mg of dinitrophenol,
200 mg of the 2-hexylethylphthalate, 200mg of di-n-octylphthalate
200 mg of benezidine 200 mg of straight naphthalene etc. etc. etc.
and then we would end up with in the same approach.. will now quantity for all 70 compounds
a kind of important little..observation is that, as we add 200 mg of this
200 mg this 200 mg this our volume is going to go up over a liter
we don't want the volume over the over a liter
we want the volume to stay at one liter
which means that in actual practice we add
200 mg 200 mg 200 mg and then bring it up to volume
at one liter so it stays in one liter
we have our standard at 200
we want to make a calibration curve with this 200
the calibration curve is at 20, 50, 80,120 and 160
so we simply dilute 200 down to these five levels
it's pretty straightforward
we need to pick a volume
let's take a volume that will fit in these jars.
it's arbitrary... let's say 25 mls
so we want to dilute our 200 standard down to 160
and we want 25 mls total
so we go to our concentration times volume equals concentration times volume
and 25 mls total
so we do the calculations and we find that
we want to put five mls of this plus 20 mils of the solvent (methylene chloride)
for the 160
for the 120 we want 10 plus 15 ....for the 80 we want 15 plus 10
for the 50 6.5+18.75 mils
for the 20 we want... this is pretty diluted now
2.5 mils this and 22.5 mils of the solvent
and this will give us our standard
so ..now to run the initial calibration
we simply run an injection of this , an injection of this , an
injection of this and a injection of this
I know when I....I wasn't a very smart kid and I would be confused by this big jar these little jars
I would go
"but wait a minute.. it this is a big jar and this is a small jar""
it's one microliter of each no matter what you do............ so the size of the container doesn't matter
what you do
Like I say, I wasn't a very smart kid
this is an approach which will work.
I see no scientific, particular reason why this approach wouldn't work
there are problems with it. It is never actually done this way.
the problems are related to the chemicals themselves
the 8270 is a list of hazardous waste.
The compounds on the 8270 list are carcinogenic and toxic
these are like bad guys
you don't go out and buy a container of 2-methylnaphthalene.
you don't go buying benezidine
let's buy some 2-nitrophenol
no.... you don't buy this stuff
anything that comes in to the lab is eventually
going to be toxic waste
any... any hazardous compound that's produced
ends up as hazardous waste
so you don't want this stuff hanging around your lab
and then another factor is that a container of this at 200ppb
would last a laboratory about 100 years
you use a microliter at a time
and another point, and this is on a technical , scientific side
is that the standards are unstable when they're mixed.
most of the 8270 compounds are very stable chemically but some of them are not
and when they're mixed together
some of the compounds will combine with other compounds
and the result of this is that the standards
are not stable when they are mixed
you mix them and they're good
the next day they're good, the third day ...they're probably still good
but a standard that is a this week old ....they start to break down and you really can't use them when they get old
you have to be constantly making them up fresh
the way this works in a real laboratory is the standards are purchased at 2000 ppm
they come in the mix so that they come purchased and diluted 2000 ppm
but there separated such that they will be stable
in the mix
they are not stable when they're mixed together but they're separated and put in groups that will be stable together like for example the
benezidine is separated all by itself
the phenols will all be together
the PAHs will all be together
the mix consists of five very small break off vials. The five vials together form the 8270 calibration curve
the way this starts out is that the analyst gets the five break off vials and carefully labels five autosampler vials
the autosampler vials ....the most important label
is the 'primary control number' to go into the log for the EPA ..
this EPA mandated and everything has to be documented
So the first thing you do is document the standards of the EPA
they are given an ascension number on the jar and
then an ascension number in a book
and so it would have ascension number and then maybe a label for what it is or not
and in the description goes into the book
so the vials are broken off, transferred into the appropriate vial.... the first one's broken
off transferred
the second one is broken off.... transferred
third one's broken off.... transferred
fourth one's broken off..... transferred
fifth one's broken offf... transferred
it has to be done such that they don't get contaminated
we have these five standards
we want to dilute them down to make a calibration curve
and we want them to have half a milliliter total
remember we picked the 25 mils
we said "well let's make 25 mils"
this is like.... has to be a half a ml.
so we want to have a half a ml of these guys mixed together for 20
we want to have half a ml of these guys mixed together for a 50
a half a ml of these guys mixed together for an 80
a half a ml these guys mixed together for 120
and you have to have half a ml mixed together for 160
so how are we going to do this?
let's start with our 20
we want to make a 20 standard and
we want a half a ml total and want to put it in one of these
okay we want 20 standard
we want 20 standard and we want it made.....
these guys diluted all appropriately such that it comes out as 20 part per million these are at 2000 ppm
we want to dilute these five guys down equally
so that when we are done we will have 20 ppm and a half a mill total
okay this is how works
concentration times volume equals concentration times volume
we want 0.5 mls as the final volume
we want 20 ppm as the final concentration
we are starting out with 2000 ppm and the volume is our variable
so we do the calculations and we find the volume to be .005 milliliters.
"0.005 milliliters!"
.005 milliliters is 5 microns... that's not a problem
we have this syringe that will do 5 µL
so we put 5 µL of this one in it
5 µL of this one in it
5 µL of this one in it
5 µL of this one in it and we're done with that one.
set that one aside
okay we need one that's 50 ppm
so we want a vial that's 50 ppm of each of these 50 ppm and
we want .5 mL when we are done
so let's take a look at this
concentration times volume equals concentration times volume our final volume is .5 mils
our final concentration is 50 ppm
our initial concentration is 2000 ppm
how much do we need to add
well... we end up with 0.0125 mL that's 12.5 µL ....not a problem
we take this guy,,, put 12.5 µL from this one ,
12.5 µL from this one
12.5 µL of this
12.5 µL from this one in here and we're done
moving forward... we want to make an 80
take a vial,...label it..... this also needs to go in your EPA standards control log
incidentally this needs to be logged in also
label it as an 80 opportunity how much do we need...well same thing
concentration times volume equals concentration times volume
80 x .5 ml concentration times volume 2000 ppm what's our volume going to be? Our volume is going to be 0.020 which is 20ul
so we put in 20 µL of this
20 µL of this
20 µL of this
20 µL of this
20 µL of this and we're done .....so go on to the next one
120 which is 30 µL so 30 ul of each one
and our 160 is 40 µL each one
okay labeled and everything
and we end up with their five points
we've added each of the five to each of our five standards so we're done with these ...cap these off real good
put them away somewhere where they're safe... they're expensive
and we have our 20, our 50, our 80, our 120, and our 160
these are all nicely labeled
they go in the our control log for the EPA
but we are not quite done with them are we.
we need to have a half a ml for each one so
so 160 ....we have added 200 we need to add 300 to dilute it up to 500 ul
in theory you could bring it up to volume at a half a ml
but in actual fact you really can't do that
it you need to calculate and add it
so we add 300ml to the "160"
so we add 350 mils to the "120"
we add 400 mils to the "80"
we add 437 mils to the "50" and we add 475 mls to the "20"
and then we are done
let me give you a quick walk-through on how to actually do this
The way this is actually done is..... I think this is kind of important
it's a trick but it's not anything that's completely insurmountable
so.... starting from scratch let me give it to you
as a lab tech... as a veteran lab tech
let me give you the technique you use
you get a solid displacement pipette
start with the ... 20...
solid displacement pipette
turn it so that it will give you 5 µL (microliters)
we take the first one
draw 5 µL ....put it in the first vial, labeled of course,
go through a series of rinses
the rinses are dirty, not so dirty clean clean super clean
so you go through it (noise, noise etc) and you're done with the first one
take out the second one...take out 5 µL ...add it ...
go through the series of rinses..... take the next one
add it...go to the series of rinses
take the next one
add it ...go through the series of rinses
take the last one .....add it ....go through the series of rinses
take the last one, add it
go through the series of rinses
okay so this one's done
take your 50
you want to dial the 50 to 12.5
dial your solid displacement pipette to 12.5
go 50 ( noise) go through a series of rinses
go 50 (noise) go to your series of rinses
50 go through your series of rinses
50 go through your series of rinses
50 go through your series of rinses
I like solid displacement pipettes because they're easy to clean
you can just reuse the same sleeve
just clean it which you really can't do very well
the alternative would be to use a disposable tip
And then the way to add the methylene chloride
to bring it up to volume at .5ml
is to get a pipette,, automated,, adjustable, pipette with 1 mL,
dial in the first volume you want
air out the pipette
the methylene chloride is very volatile
and it will tend to want a blow out
of the pipette and mess up your volumes
so let it come to equilibrium
the whole.... let the pipette come to equilibrium
and then do the first one
punch in a new number....do the second one
punch in a new number....do the third one
punch in a new number....do the fourth one
punch in a new number....do the last one
and throw the pipette tip away
it's all methylene chloride
so you don't need to use bunch of different tips
so we have our five points
we have our 20 50 80 120 160
we get some samples in to run.
so we line them up
we have a prep blank it has to have half of a ml
we have three samples.... they each have a half a mill in them
and we have a couple of spiked samples.... a couple of quality control samples
they each have a half a ml in them
in the half a milliliter later is extremely important
the half a milliliter is not an approximate half a milliliter
It is exactly at half a milliliter
and you should be able to look across them and see that they all have the exact same volume
exact.... exact same volume
it's not any great trick
but it's important to understand
that it is very important that the volumes be right
now the last step is.... we take a ...an internal standard
the internal standard comes at 4000 ppm
and we put 5 µL in
each one so we put 5 µL of internal standard
in each one of them
remember that the internal standard quantitation
is based upon the ratio of the internal standard to the total volume
so the volume has to be exactly .5
and the internal standard has to be exactly 5 µL
so be careful..... this is a good time to be as careful as you can
And now ... like next week.... you need make a continuing calibration standard at 50
just follow the same directions
take a vial, put in 12.5 uL of each one
add 437.5 µL to bring it up to 500
add 5 µL of internal standard ...exactly of the same internal standard
and you can hit the iCal every time
if the other variables are correct
if the GC is working properly you can hit the iCal every time
it's.....its fairly ....it's actually pretty satisfying
the initial calibration is complicated
but when it comes out... which it will... if you're careful
it's cool
it's cool