Syringe for sticky samples ?

[koenvanderdrift]

We're developing a GC method for a component that is very sticky, we suspect it binds to the glass barrel, and we cannot predict if the next injection will be ok. We've seen bent plungers and/or injections were no material gets injected.

We've tried many different wash solvents, and it keeps happening.

The boiling point of the analyte is 105C, and if it works, we get a very useful and reproducible chromatogram.

We are using an Agilent 6890 GC with the 7683 autosampler.

Are there any syringes that are for instance made of different materials, that we could try ?

[rb6banjo]

105 °C is not terribly high. Toluene boils at 111 °C. Perhaps headspace analysis is the way to go with this?

[koenvanderdrift]

We don't have a headspace sampler for our GC, but I will look into it. - Thanks.

[Peter Apps]

Headspace is a good idea.

Presumably the sticky substance is in solution in the samples, and so must be soluble in the solvent that samples are dissolved in. Assuming that you have tried the same solvent as a syringe wash - and if you have not you should - then something must be happening to it in the syringe to make it insoluble.

A possibility is exposure to residue of another wash solvent in which it is not soluble. Could the metal plunger tip catalyse some reaction (not knowing what the mystery substance is I am just guessing here).

There are some macromolecules that "unwind" under liquid shear and then crosslink to one another but that sounds unlikely with a boiling point of 105C. Are you sure that it is the low boiler that is gumming up the syringe - where do you samples come from, do they have anything else in there that might be sticky ? I have gummed up very narrow bore HPLC tubing with plant extracts, presumably due to shear-induced cross linking.

Peter

[koenvanderdrift]

Yes, the sample is in solution (hexane), but even then we occasionally see gumming up of the syringe. You could be very correct that it reacts with some part of the syringe (we now use a Hamilton 80080)

Are there syringes on the market that are made of different materials? It would beat a headspace sampler in price

[rb6banjo]

No headspace sampler? You might consider solid-phase microextraction. If the sampling must be automated, that will present a problem as the sampler is quite specialized (LEAP Technologies, Gerstel, etc.). However, you can get very low detection limits on many analytes using SPME - even in the manual mode.

[dlbenach]

Does your syringe plunger have a teflon tip? Maybe a teflon tip would make a better seal between the plunger and syringe barrel. The other way to go is to try a syringe without the teflon tip if that's what your using now. Does your autosampler allow you to draw up an air plug before the sample? Maybe an air plug would help get all of the sample out. One final thought is that some autosamplers also allow a post-injection delay that would help get any remaining sample out of the syringe needle. Maybe that would help?????

[CE Instruments]

We are using an Agilent 6890 GC with the 7683 autosampler.

The Agilent systems "like" very fast injections, so if you have a sample that gets sticky you will bend syringes. Can you on the 7683 slow the plunger speed down for the sample take up and rinses etc. Can you try a slower injection speed to see if the sample is still as reproducable with a lower risk of plunger destruction ?

[koenvanderdrift]

Yeah, we tried that too, but we still get gunk leftovers after an injection and syringe wash.

[rb6banjo]

What is the matrix? Before you dilute it in hexane.

[koenvanderdrift]

It's an alkoxysilane that we purchased, with a high purity, so there is no other matrix.

[skunked_once]

Check out http://www.chromatographyonline.com/node/227744.
I have had significantly fewer plungers sticking since I started incorporating N-methyl-2-pyrrolidone for syringe washes.
Be sure to read the Safety Data Sheet for this chemical if you decide to try it.

[koenvanderdrift]

Unfortunately, the N-methyl-2-pyrrolidone didn't work for us. The problem with all solvents is that once a clog forms, no liquid will be sucked up, and the syringe cannot be cleaned. The only way to clean it is to take it out, remove the plunger and squirt solvent from the top into the barrel. Which is not practical in an overnight run. And water is the best solvent to dissolve the clogs and clean the syringe.

We know that the material is sensitive to moisture and can easily polymerize -> clogs.

We have tested our hexane for water content by KF and there is none. Are there any potential places in the Agilent 6890/7683 injection system that can introduce moisture to the sample?

[Peter Apps]

Unfortunately, the N-methyl-2-pyrrolidone didn't work for us. The problem with all solvents is that once a clog forms, no liquid will be sucked up, and the syringe cannot be cleaned. The only way to clean it is to take it out, remove the plunger and squirt solvent from the top into the barrel. Which is not practical in an overnight run. And water is the best solvent to dissolve the clogs and clean the syringe. This sounds like the needle is blocking rather than the plunger sticking

We know that the material is sensitive to moisture and can easily polymerize -> clogs.

We have tested our hexane for water content by KF and there is none. Are there any potential places in the Agilent 6890/7683 injection system that can introduce moisture to the sample? The is moisture in the atmosphere - an ordinary autosampler and syringe has no way to prevent it entering. If you want to use these moisture sensitive compounds then you need to contrive a way of putting a flushed dry box over the autosampler