Improving Headspace analysis with capillaries

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

6 posts Page 1 of 1
Hey people,

I'm trying to improve the repetitiveness and cleanliness of my VOC Headspace analysis through usage of glass Glass micro capillaries

I got the idea when the local technician used those to test repetitiveness of our GC/MS and GC/FID in the yearly operational qualification test.

If they're good enough for this, they must be constant enough to carry standards, right?

I want to try using them to carry internal standards and calibration standards into headspace vials both for solvent assay tests and for EPA 8260.

There's a bit of added cost involved, but I'm thinking that the advantages overweigh the costs by far, those include:

1) More consistent standard volumes
2) Less, or even, no cross contamination at all from using syringes.
3) Less solvent and standard usage, no need to pre-rinse syringes with standards, no need to post-rinse syringes with clean solvent.
4) Less syringe wear-and-tear by simply using them less.

And I'm sure that there are even more advantages.

What do you think, is this a good solution or am I missing something important?
Hi Mark

There have been some discussions before on the use of glass micro capillaries - it may be worth looking at them.

Personally I have had great success in their use either

a) to use a pre-tared capillary tube to take up a volume of a low volatility liquid (2-10uL) - reweigh then drop the tube into a volumetric flask partially filled with solvent - then make up to the mark

b) Alternatively, use a prepared w/v solution. Dip the tube in to fill to the mark by capillary action ( if overfilled touch the tip onto some tissue to bring it down to the mark) - then drop into the solvent as above for dilution

Your query may be more complicated than it first appears

If using b) and dropping into a 25ml headspace ( you may have had to cut a portion off the top of the tube before use for it to fit in) you only need to ensure that all of the contents get out of the tube and into the headspace.

Without further information then yes to your queries 1 - 4 :-)

Kind regards

Ralph
1)The glass capillaries I've linked to in the first post are 32mm in length, short enough to fit below the 10mL MMS solution in a 8260 headspace vial, so I don't think there should be a problem with the solvent dispensing, although that's precisely one of the reasons I've asked here in the first place.

2) I don't even have to worry if 100% of the standard exits from the capillary into the headspace IF the recoveries are consistent since I'm prepared to calibrate using the capillaries so for example, if, consistently, 90% of the standard is recovered I still calibrate and thus compensate for it.
Hi Mark


I don't even have to worry if 100% of the standard exits from the capillary into the headspace IF the recoveries are consistent since I'm prepared to calibrate using the capillaries so for example, if, consistently, 90% of the standard is recovered I still calibrate and thus compensate for it.


If added to an empty vial I would still prefer to see that capillary empty. It really wouldn't take long for that to happen under normal conditions in your sealed headspace vial and for you to get everything into the headspace and equilibrate and your recovery would be consistent



The glass capillaries I've linked to in the first post are 32mm in length, short enough to fit below the 10mL MMS solution in a 8260 headspace vial,


do you mean that you already have 10ml solvent in the headspace vial and you are adding your capillary tube to it?

If added to a headspace vial containing solvent just give it a good shake

I may well be misinterpreting your post and method details. I am not familiar with this method and for that I apologise

Regards

Ralph

By standard I am assuming a standard analyte in solvent. If so what is your solvent and analyte and the size of your headspace vial?
In EPA8260/5021, we put solids in 10mL MMS solution (DDW saturated with NaCl) or 5mL liquid sample + 5mL MMS solution, and add 10uL Internal Standard to it.

I'm planning on using capillaries to add these 10uL internal standard, and for CCV tests, which use 50uL calibration standard, so I'm hoping the capillaries will help.
Microcapillaries work as accurately as syringes as long as you use them properly. They are not good for volatile solvents (but do work for solutions of non-volatiles in volatile solvents) and they are calibrated to contain not to deliver, which means that they have to be rinsed to transfer their contents. When filling, dip only the tip of the capillary in the liquid, otherwise you will get liquid stuck to the outside, you can wipe it off with a clean tissue but that risks drawing liquid out of the tube.

As an exercise to show whether capillary contents transfer into liquid; fill one with a coloured liquid (iodine dissolves in most organic solvents to give an intense colour), and see what it takes to get all the colour out of the capillary and into the solution.

Peter
Peter Apps
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