How do I use a pipette?
Michael O'Henly
I'm a photographer, not a chemist, so please bear with me.
I need to accurately measure a 5 ml. volume of a developer concentrate.
I've tried a syringe (too awkward) and a small graduate (not precise
enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
You wouldn't think a simple glass tube with no moving parts would be too
hard to figure out, right? Wrong.
I want to dip the pipette in the concentrate bottle, release the bulb to
draw 5 ml. into the tube, move it to the working solution, and squeeze
the bulb to release the concentrate.
The problem is that I can't figure out how to withdraw 5 ml. exactly.
Suction is provided by the bulb and the amount I squeeze determines how
much gets drawn into the pipette. I seem to get either too little or too
much. I've tried "holding" the bulb at the point when it's drawn 5 ml.
but as soon as I remove it from the concentrate I get air bubbles in the
pipette and some of the concentrate drips out.
So please help me out here. Am I just overlooking something pathetically
obvious? Is there a nugget of lab lore that will make this pipette stand
up and sing?
Thanks in advance.
Michael O'Henly
Steven Arnold
Believe me, you're not alone! I'm a chemistry professor at a small
university, and I see students with the same problem all the time.
Here's how to do it. It takes a little practice. Press the rubber bulb
to the top of the pipet, but don't stick the pipet into the bulb so tight
that it won't come off easily. Squeeze the bulb and immerse just the tip
of the pipet into the liquid. Release the bulb until you have drawn
liquid *past* the mark, but be careful not to draw liquid into the bulb.
Quickly pull the bulb off the pipet and place your index finger (or
thumb) over the top of the pipet to keep the liquid from running out.
Touch the tip of the pipet to the side of the container or another clean
container (not the one you're really going to deliver to finally,
though). Holding the pipet vertical, roll your finger off the top a tiny
bit and allow liquid to leak out until the bottom of the curved liquid
surface (the meniscus) is lined up with the mark. (This is where the
practice comes in!) Now, touch the tip of the pipet to the side of the
container you're going to deliver to, remove your finger, and allow the
pipet to drain.
Now, there's a bit of a question: look at the top of your pipet. If it
is marked with the letters TD, then you have just delivered the proper
volume. The TD means that the pipet is calibrated "to deliver" that
volume, and you *do not* blow out the last drop that remains in the pipet
tip.
If the pipet is marked TC, which stands for "to contain" then the pipet
is calibrated to contain that volume, and you *should* blow out the last
drop, using the bulb.
I hope this helps, and let me know if there's anything that wasn't clear.
Steven Arnold
Assistant Professor of Chemistry
Oakland City University
Oakland City, IN
Diane T. Winter
mic...@tenzo.com (Michael O'Henly) wrote:
>I'm a photographer, not a chemist, so please bear with me.
>
>I need to accurately measure a 5 ml. volume of a developer concentrate.
>
>I've tried a syringe (too awkward) and a small graduate (not precise
>enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
>
>You wouldn't think a simple glass tube with no moving parts would be too
>hard to figure out, right? Wrong.
>
>I want to dip the pipette in the concentrate bottle, release the bulb to
>draw 5 ml. into the tube, move it to the working solution, and squeeze
>the bulb to release the concentrate.
>
>The problem is that I can't figure out how to withdraw 5 ml. exactly.
>Suction is provided by the bulb and the amount I squeeze determines how
>much gets drawn into the pipette. I seem to get either too little or too
>much. I've tried "holding" the bulb at the point when it's drawn 5 ml.
>but as soon as I remove it from the concentrate I get air bubbles in the
>pipette and some of the concentrate drips out.
>
>So please help me out here. Am I just overlooking something pathetically
>obvious? Is there a nugget of lab lore that will make this pipette stand
>up and sing?
>
>Thanks in advance.
>
>
> Michael O'Henly
Remove the bulb and quickly put your forefinger over the top of the
pipet. If you do it quickly enough, you won't lose too much of the
solution. Now using your forefinger to control the flow of liquid,
let out just enough solution into the concentrate till the bottom of
the liquid (the meniscus) is right on the 5 ml line. Transfer the
pipet to your working solution and remove your finger to let out
exactly 5 ml. It takes some practice to get used to it. Don't pipet
by mouth!
Diane
Ken Robertson
mic...@tenzo.com says...
>
>I'm a photographer, not a chemist, so please bear with me.
>
>I need to accurately measure a 5 ml. volume
Michael - The idea is to draw the liquid up past the 5 mL mark, quickly
remove the bulb and replace it with the old fingertip (first finger NOT
the thumb). With practice you will find that gentle lifting off and on of
the said digit allows the level to drop to the mark and Bob's your uncle.
Alternatively there are a number of pipetting devices available from lab
supply companies e.g. Pi-Pumps, or bigger rubber bulbs with a variety of
valves with which you can slowly lower the level.These last are just a
bit old-fashioned but then ain't we all!
Good luck, Ken.
Michael O'Henly
Steven Arnold <sear...@evansville.net> wrote:
> Here's how to do it.
[...]
> I hope this helps, and let me know if there's anything that wasn't clear.
Thanks, Steven. That really did help! I have a TD pipet and the only
wrinkle seems to be that the bulb doesn't slip on/off very easily. But
this may only be a question of practice.
MIchael O'Henly
knoo...@aol.com
Michael, you wrote:
>I'm a photographer, not a chemist, so please bear with me. ...
>I need to accurately measure a 5 ml. volume of a developer
concentrate....
>The problem is that I can't figure out how to withdraw 5 ml. exactly....
>So please help me out here. Am I just overlooking something pathetically
obvious? Is there a nugget of lab lore that will make this pipette stand
up and sing?
Sometimes I am amazed at the knowledge that we, as lab technologists, take
for granted. It is not pathetically obvious how you use a pipet and bulb,
until somebody tells you how.
Here's how those tricky things work. I would suggest you practice with a
glass of water until you get the hang of it. Hold the pipet, near the
top, with the thumb and three fingers from your dominant hand. Have your
index finger in a position that you can quickly cover the top of the pipet
with it. Insert the pipet in the glass. With your other hand, use the
bulb to draw up liquid higher than the 5 ml mark. Now, here comes the
tricky part. Very quickly pull the bulb away and place the index finger
from the hand holding the pipet over the top opening of the pipet. This
will stop the liquid from running out of the pipet. You will lose a
little bit of liquid, but with practice, you will still have more than 5
ml. Now, gently roll your finger so that a little air can get into the
opening and move the liquid out. Continue doing this until the bottom
curve of the liquid level is sitting right at the 5 ml line. Then hold
your finger firmly over the opening to stop the liqud from dropping. Lift
the pipet out of the glass and transfer to the destination container.
Lift your finger off the top of the pipet and the 5 ml of liquid will fall
out the bottom.
Richard Knoppow
mic...@tenzo.com (Michael O'Henly) wrote:
It occurs to me that a simple way to do this is to cut a small hole
in the top of the bulb. Cover the hole with a finger when drawing up
the solution and remove it to adjust the amount or deliver the
solution.
---
Richard Knoppow
Los Angeles, Ca.
dick...@ix.netcom.com
Jerry Houston
A far better option is to go to your local pharmacy and ask for one of the
"spoons" that you can use to measure liquid medicine doses. Mine is
graduated clearly, and has marks at 5.0 ml. and 10.0 ml., which I use to
measure Rodinal.
They're distributed for free. (At least, mine was.) I'm sure that if it
were sold in a photo equpiment store, and as a precision liquid photo
chemical graduate, it would be at least $5. Maybe $15 if it was from
Paterson.
Michael O'Henly <mic...@tenzo.com> wrote in article
<1997013018...@i1-182.islandnet.com>...
> I'm a photographer, not a chemist, so please bear with me.
>
Ron Marsh
Michael O'Henly wrote:
>
> I'm a photographer, not a chemist, so please bear with me.
>
> I need to accurately measure a 5 ml. volume of a developer concentrate.
>
> enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
>
> You wouldn't think a simple glass tube with no moving parts would be too
> hard to figure out, right? Wrong.
>
> I want to dip the pipette in the concentrate bottle, release the bulb to
> draw 5 ml. into the tube, move it to the working solution, and squeeze
> the bulb to release the concentrate.
>
> The problem is that I can't figure out how to withdraw 5 ml. exactly.
> Suction is provided by the bulb and the amount I squeeze determines how
> much gets drawn into the pipette. I seem to get either too little or too
> much. I've tried "holding" the bulb at the point when it's drawn 5 ml.
> but as soon as I remove it from the concentrate I get air bubbles in the
> pipette and some of the concentrate drips out.
>
> obvious? Is there a nugget of lab lore that will make this pipette stand
> up and sing?
>
>
> Michael O'Henly
Dear Michael
You gave me flashbacks to my 1st days in lab school,and a grin too.
to accurately measure with a pipette, you have to do this:
1st- draw the fluid you want measure to a point beyond the quantity you
desire
2nd- quickly remove the bulb and replace it with the pad of your index
finger
3rd-use a paper towel( we usually use kimwipes ) to carefully wipe the
exterior of the pipette of all the excess fluid you're measuring
4th- now the tricky part. with the tip of the pipette in the container
which you took the fluid from, ever so gently lift your finger just
until the fluid starts to move down the tube.(keeping the tube at a
slight angle)
5th- when the lowest part of the surface of your fluid ( the miniscus )
reaches your desired amount,re-apply firm pressure to the end of the
pipette ( the part where your finger is <G>)
6th- gently move the pipette to the place you desire it to go and
release your finger. the type of pipette you are using determines the
last step
7th-(A) if the pipette has TD written on it, just hold it upright until
all of the fluid runs out. there will be a small amount left in the
pipette, this is normal. remove the pipette from the container and then
expel the rest of the fluid.
(b) if the pipette has TC written on it, just let it run into the
container and then use the bulb to blow the rest in the container
ps. the TC or the TD will be at the top with the information about what
type of glass it is.
once again, thanks for the chuckle
Ron Marsh MLT(ASCP)
gerha...@aol.com
Hello,
I suppose your rubber bulb is defective or you are not unsing th right
kind.
Mine has two valves and it is no problem to work with it.
Contact a chemicals or laboratory supplier for further advice.
By the way: A syringe is by far the best instrument to mesure even small
quantities of liquids. Why not try it? It is easy to use and easy to
clean.
6 Months ago i have bought a rubber ball and two pipettes. I have since
used them once or twice but not more often and I am very fuzzy about the
correct quantity.
Use a syringe or buy a good rubber ball.
Best regards
Gerhard May
Alan J. Rubin
The post (below] by Steve is excellent (I'm also an academic chemist that
taught this technique] and quite precise. I would like to add an additional
tip. That is to slightly dampen the the finger that goes over the top of the
pipette and do not use your thumb.
Alan
In article <32F0C9...@evansville.net> Steven Arnold
<sear...@evansville.net> writes:>From: Steven Arnold <sear...@evansville.net>
>Subject: Re: How do I use a pipette?
>Date: Thu, 30 Jan 1997 08:18:58 -0800
>Michael O'Henly wrote:
>>
>> I'm a photographer, not a chemist, so please bear with me.
>>
>> I need to accurately measure a 5 ml. volume of a developer concentrate.
>>
>> I've tried a syringe (too awkward) and a small graduate (not precise
>> enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
>>
>> You wouldn't think a simple glass tube with no moving parts would be too
>> hard to figure out, right? Wrong.
>>
>> I want to dip the pipette in the concentrate bottle, release the bulb to
>> draw 5 ml. into the tube, move it to the working solution, and squeeze
>> the bulb to release the concentrate.
>>
>> The problem is that I can't figure out how to withdraw 5 ml. exactly.
>> Suction is provided by the bulb and the amount I squeeze determines how
>> much gets drawn into the pipette. I seem to get either too little or too
>> much. I've tried "holding" the bulb at the point when it's drawn 5 ml.
>> but as soon as I remove it from the concentrate I get air bubbles in the
>> pipette and some of the concentrate drips out.
>>
>> So please help me out here. Am I just overlooking something pathetically
>> obvious? Is there a nugget of lab lore that will make this pipette stand
>> up and sing?
>>
>> Thanks in advance.
>>
>> Michael O'Henly
>Believe me, you're not alone! I'm a chemistry professor at a small
>I hope this helps, and let me know if there's anything that wasn't clear.
>Steven Arnold
Jeff Klingler
Ron Marsh wrote:
>
> Michael O'Henly wrote:
> >
> > I'm a photographer, not a chemist, so please bear with me.
> >
> > I need to accurately measure a 5 ml. volume of a developer concentrate.
> >
> > I've tried a syringe (too awkward) and a small graduate (not precise
> > enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
> >
> > You wouldn't think a simple glass tube with no moving parts would be too
> > hard to figure out, right? Wrong.
> >
> > I want to dip the pipette in the concentrate bottle, release the bulb to
> > draw 5 ml. into the tube, move it to the working solution, and squeeze
> > the bulb to release the concentrate.
> >
> > The problem is that I can't figure out how to withdraw 5 ml. exactly.
> > Suction is provided by the bulb and the amount I squeeze determines how
> > much gets drawn into the pipette. I seem to get either too little or too
> > much. I've tried "holding" the bulb at the point when it's drawn 5 ml.
> > but as soon as I remove it from the concentrate I get air bubbles in the
> > pipette and some of the concentrate drips out.
> >
> > So please help me out here. Am I just overlooking something pathetically
> > obvious? Is there a nugget of lab lore that will make this pipette stand
> > up and sing?
> >
> > Thanks in advance.
> >
> > Michael O'Henly
>
Micheal:
Looks like Mr. Marsh got all the right steps forwarded to you (good job
R.M.!).
Three small points, if you are really interested in nailing EXACTLY 5ml:
1) The drop on the tip of the pipette - touch it to the inside of the
container you are delivering into. There should be a tiny amount left
in the tip if it is a TD pipette. Also, if the tip is damaged, it will
not deliver the exact amount properly. (By the way, TD means "To
Deliver" and TC means "To Contain" in case anyone was curious.)
2) Be sure to check the pipette after you have finished the transfer. If
there are any drops clinging to the inside of the pipette, then the
glassware is dirty. Clean it with hot soapy water then carefully rinse
with water and you should be back in business. If you rinse the pipette
after every use, this should not be a problem.
3)As suggested, let the liquid run out of the pipette, do not
apply pressure with the bulb to make it flow faster. These things are
calibrated to flow at certain rates. I've also seen people file off
the tip to make it flow faster - do that, and the pipet is ruined!
I am a chemist and I teach this stuff to lab technicians all the time.
It really is easy, once you get the hang of it.
Happy pipetting!
---Jeff
Stephen A. R. Carino
On Thu, 30 Jan 1997, Michael O'Henly wrote:
> I've tried a syringe (too awkward) and a small graduate (not precise
> enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
>
> You wouldn't think a simple glass tube with no moving parts would be too
> hard to figure out, right? Wrong.
>
> I want to dip the pipette in the concentrate bottle, release the bulb to
> draw 5 ml. into the tube, move it to the working solution, and squeeze
> the bulb to release the concentrate.
>
> The problem is that I can't figure out how to withdraw 5 ml. exactly.
> Suction is provided by the bulb and the amount I squeeze determines how
> much gets drawn into the pipette. I seem to get either too little or too
> much. I've tried "holding" the bulb at the point when it's drawn 5 ml.
> but as soon as I remove it from the concentrate I get air bubbles in the
> pipette and some of the concentrate drips out.
Michael,
I'm a chemist and a not so good photographer.
Just how accurate you want it to be? If you need it to be accurate to
less than 0.1 ml then you really need a pipette otherwise I'm suggesting
that you buy a 10 mL graduated cylinder. This can make it a lot easier.
This graduated cylinder can be purchased from VWR, Cole-Palmer
<http://www.colepalmer.com>, Thomas Scientific, Edmunds Scientific(??) and
a lot more places. You can use a net search engine to look for the
above-mentioned companies.
If you really need to use a pipette then you may want to buy one of those
multi-valved rubber aspirators that you can use for suction and delivery
($10-20). I really don't know what it's called but I'm sure you can find
it from the same companies I mentioned. There's even an automatic
dispensers that you can buy but I think it would cost you a little more
(~$100). For the automatic dispensers, you just put it on a container
(serves as cover, too), turn a dial to a desired volume (yes, it has
variable delivery volume) and push to dispense. If you're interested, I
can look for the catalog numbers of any of these items.
I'm teaching undergraduate general chemistry course and I can say that
it always look awkward the first time they do pippetting. Don't get
frustrated...
Stephen
Michael O'Henly
Jeff Klingler <JKLI...@concentric.net> wrote:
> Three small points, if you are really interested in nailing EXACTLY 5ml:
> 1) The drop on the tip of the pipette - touch it to the inside of the
> container you are delivering into. There should be a tiny amount left
> in the tip if it is a TD pipette.
Hmmm... I thought I had this figured out, but now you've raised another
question.
It is a TD pipette with markings like so...
-------------------------------------------------\
| | | | | | -------\
0.0 1.0 2.0 3.0 4.0 5.0 (tip)
-------/
-------------------------------------------------/
What I've been doing is placing the bottom of the miniscus at the 0.0
mark, releasing liquid until the level drops to 5.0, then stopping the
flow and returning the remainder to the concentrate bottle.
I'm assuming that the distance between the 0.0 and 5.0 markings is 5 ml.
Isn't this correct? Why should I only have a tiny amount left in the
tip?
Michael O'Henly
e...@acsu.buffalo.edu
Michael,
Most graduated pipets have a series of numbers going from 0 at the top of
the pipet to 5 or 10 or whatever at the bottom. The key here is to use the
bulb to suck up liquid past the zero mark. Then, in a quick motion, put
your finger over the top of the tube to trap the liquid in. now, slowly
lift your finger to dispense enough liquid to hit the zero mark back into
the concentrate. Now, still holding the pipet closed at zero mL, dispense
enough liquid into the destination container so that 5 mL is showing on
the pipet.
Hope this helps!
-Eric
Steven Arnold
Michael:
Have no fear, you're doing it right. The "TD" graduated pipet (the Mohr
type) will deliver the 5.0 mL when you let it run from zero to 5,
leaving the entire tip full. If you're *sure* that you haven't
contaminated the remainder, then go ahead and put that back into your
concentrate bottle. (The chemist in me would advise against putting
anything back in the bottle, but I'm cheap, and we're not doing DNA
testing, after all. ;-) )
If someone else out there should have a graduated pipet marked TC, then
it's probably graduated all the way down the tip, and is the serological
type. It is intended to be emptied all the way and then blown out with
the bulb.
Regarding other choices for delivery, for a 5 mL volume, I believe that
a pipet is the most accurate way to go. Slightly more accurate than the
graduated pipets are the transfer type, which are designed to deliver
one fixed volume, and are commonly available in 5, 10, 25, and 50 mL
sizes. The use of that pipet is exactly as described in my previous
post.
Hope this clears things up.
jl...@acsu.buffalo.edu
**************************************************************************
Boy Michael, you sure are asking a lot. Even though the glass pipette
a simple one piece tool with no moving parts, it can be a real bear to
master when your just a novice. Depends on the type of pipette, bulb, etc
that you are using.
Since on-line instructions would be very difficult, my suggestion is to
pay a visit to your friendly local hospital or private lab and ask for a
quick intro to PIPETTING 101. We Clinical Scientists are a friendly folk
and teaching comes natural to us. Good Luck and drop a note on how you
made out.
If you really get into a bind, drop a note and I'll see if I can dig up
some written instructions w/diagrams.
**************************************************************************
R. Katz
mic...@tenzo.com (Michael O'Henly) wrote:
>I'm a photographer, not a chemist, so please bear with me.
>
>I need to accurately measure a 5 ml. volume of a developer concentrate.
>
>enough). So now I'm trying a 5 ml. graduated pipette and rubber bulb.
>
>You wouldn't think a simple glass tube with no moving parts would be too
>hard to figure out, right? Wrong.
>
>
> Michael O'Henly
A scientific supply catalog will carry mechanical pipetting devices. I know of two kinds: a bulb type with its own valve system and =
a syringe-type, where you turn a wheel to create suction or apply pressure. If you want to get fancy there are plenty of neat automa=
tic types also, but these are expensive.
Richard
san...@suzy.torolab.ibm.com
Steven Arnold (sear...@evansville.net) wrote:
: Believe me, you're not alone! I'm a chemistry professor at a small
:
: Here's how to do it. It takes a little practice. Press the rubber bulb
: to the top of the pipet, but don't stick the pipet into the bulb so tight
: that it won't come off easily. Squeeze the bulb and immerse just the tip
: of the pipet into the liquid. Release the bulb until you have drawn
: liquid *past* the mark, but be careful not to draw liquid into the bulb.
I agree with the above steps but differ from here on. I've found that by
*gently* squeezing the bulb you can get the excess liquid out and get
the exact amount you are aiming for. If you then immediately lift the
tip out of the source liquid and let a small bit of air in, you can
safely move the pipette around without dripping and without having to
maintain the exact pressure on the bulb.
: <snip> Now, touch the tip of the pipet to the side of the
: container you're going to deliver to, remove your finger, and allow the
: pipet to drain.
:
: Now, there's a bit of a question: look at the top of your pipet. If it
: is marked with the letters TD, then you have just delivered the proper
: volume. The TD means that the pipet is calibrated "to deliver" that
: volume, and you *do not* blow out the last drop that remains in the pipet
: tip.
:
: If the pipet is marked TC, which stands for "to contain" then the pipet
: is calibrated to contain that volume, and you *should* blow out the last
: drop, using the bulb.
Sandor Mathe (not a chemist though)
Patricia A. Swan
ro...@iinet.net.au (Ken Robertson) wrote:
>mic...@tenzo.com says...
>>
>>I'm a photographer, not a chemist, so please bear with me.
>>
>>I need to accurately measure a 5 ml. volume
>>Thanks in advance. Michael O'Henly
>
>Michael - The idea is to draw the liquid up past the 5 mL mark, quickly
>remove the bulb and replace it with the old fingertip (first finger NOT
>the thumb). With practice you will find that gentle lifting off and on of
>the said digit allows the level to drop to the mark and Bob's your uncle.
>Alternatively there are a number of pipetting devices available from lab
>supply companies e.g. Pi-Pumps, or bigger rubber bulbs with a variety of
>valves with which you can slowly lower the level.These last are just a
>bit old-fashioned but then ain't we all!
>
>Good luck, Ken.
>
A couple of simple alternatives to the pipette if you're in the
states. A 1 teaspoon measure from your kitchen is 5 ml. Also,
some of the things they have at the pharmacy for measureing
medicines for children measure 5 ml and would work fine if you're
not trying to pour out of oversized bottles.
You also said you tried a syringe, so I assume you mean a
standard hypodermic syringe. There is also what's called a
"catheter-tip" syringe that I get at the medical supply house
that has a tapered cone about an inch (2.5 cm) long so it will
fit into tubing instead of the luer-loc and luer-slip fittings on
a regular syringe that hold the needle. The usual size I see is
60m/2 oz, but used with a length of rubber tubing it would give
you extremely good control if you're trying to get solution out
of oversized bottles.
Patricia A. Swan
--
*Patricia A. Swan, moderator, rec.arts.sf.tv.babylon5.moderated*
* newsgroup submission address: ras...@solon.com *
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DKenn473
>
>Michael - The idea is to draw the liquid up past the 5 mL mark, quickly
>remove the bulb and replace it with the old fingertip (first finger NOT
>the thumb). With practice you will find that gentle lifting off and on of
>the said digit allows the level to drop to the mark and Bob's your uncle.
>Alternatively there are a number of pipetting devices available from lab
>supply companies e.g. Pi-Pumps, or bigger rubber bulbs with a variety of
>valves with which you can slowly lower the level.These last are just a
>bit old-fashioned but then ain't we all!
>
>Good luck, Ken.
>
Michael, you can but a pipette hand pump. try Tri-ess science in Burbank
Ca. The pumps are about $10-$15.00 and well worth it. No way can you be
persice with a bulb and finger method.
David Brown
DKenn473 <dken...@aol.com> wrote in article
<19970213214...@ladder01.news.aol.com>...
I teach 30 'A' level (16-18 years) chemistry students each year who have to
manage with a bulb/pump and their thumbs to release!
Dr Robin M Allen
If you know the density of your solution and you have some accurate scales
you could weigh the liquid instead.
In article <3302283e...@snews.zippo.com>, zaf...@super.zippo.com wrote:
> ro...@iinet.net.au (Ken Robertson) wrote:
>
> >mic...@tenzo.com says...
> >>
> >>I'm a photographer, not a chemist, so please bear with me.
> >>
> >>I need to accurately measure a 5 ml. volume
> >>Thanks in advance. Michael O'Henly
> >
> >Michael - The idea is to draw the liquid up past the 5 mL mark, quickly
> >remove the bulb and replace it with the old fingertip (first finger NOT
> >the thumb). With practice you will find that gentle lifting off and on of
> >the said digit allows the level to drop to the mark and Bob's your uncle.
> >Alternatively there are a number of pipetting devices available from lab
> >supply companies e.g. Pi-Pumps, or bigger rubber bulbs with a variety of
> >valves with which you can slowly lower the level.These last are just a
> >bit old-fashioned but then ain't we all!
> >
> >Good luck, Ken.
> >
>
Miller H. Peterson
In article <19970213214...@ladder01.news.aol.com>,
dken...@aol.com (DKenn473) wrote:
> >
> >Michael - The idea is to draw the liquid up past the 5 mL mark, quickly
> >remove the bulb and replace it with the old fingertip (first finger NOT
> >the thumb). With practice you will find that gentle lifting off and on of
I started out in life as an analytical chemist so I have some experience
in pipetting. Pipetes work fine for dilute solutions. Pipettes tend to
be unsatisfactory for photographic work because some of the liquid
developer concentrates are quite syrupy. Just try pipetting HC-110. A
good alternative is to go to the local Walmart pharmacy department and buy
a 10 milliliter dosing syringe for less than two bucks. As someone has
previously posted, a syringe will work even better if you can find a short
length of latex tubing to fit over the end so you can reach down into
bottles.
Pete
--
Pete
Georges Giralt
your idea of using a syringe is a good one,but....
As time be, syringes are in some kind of plastic. And in France they DO
NOT support some chemicals used in photograpy (AGFA Rodinal for example)
In fact the piston recess holding the gasket hold a few left chemical and
dissolves silently... when you want to use it the piston goes away.
So try using a glass one.
\\\|/
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(O) (o)
+----OOO--(_)--OOOo-----------------------=| Georges |=----+
| Email ggi...@mygale.org |
| "La perfection est atteinte non pas quand il n'y a rien |
| à rajouter mais lorsque qu'il n'y a rien à enlever" |
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NapperWm
As an analytical chemist of 18 years I can pipette 5ml by hand as accurate
as any suggestion so far.
Don't get complicated!
Just practice a little with a pipette and bulb.
Hell, how accurate could you have to be for what you are doing!
You can get to within 0.1 ml (2 drops) like this.
If you need more accuracy then do a serial dilution.
Measure 50ml /and dilute 10 times more.
Works if you need absolute accuracy.