Where to purchase a solid sampler?

[Ento_Joe]

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[Ento_Joe]

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[James_Ball]

"1. I am using an Agilent 7890 B Gas Chromatograph coupled to an Agilent 5977 A Mass Spectrometer, which was purchased brand new and is almost 1 year old. I am currently running a dual inlet/column column system as the rear inlet and column are connected to a Markes UNITY2 thermodesorption unit for analysis of VOCs trapped on sorbent tubes, while the front inlet and column are reserved for liquid injections. It is this front inlet I would be looking to modify for use as a solid sampler. Both columns are HP5-MS. "

I am wondering, have you tried using the UNITY2 to heat the mites for analysis?

I am thinking you could load the mites into a desorption tube with a plug of glass wool at each end then do analysis at different desorption temperatures. Low temperatures would give more of the chemicals on the surface with higher temperatures bringing out compounds deeper inside the tissue. If the unit has the cold trap it would work great I believe, desorb and concentrate with the cold trap.

If you can do a slow temperature ramp directly onto a column or possibly just a guard column directly into the MS then you can get an idea of what chemicals are released at different temperatures. It somewhat reminds me of the pyrolysis work I did in college on coal samples to determine what volatiles are evolved at different temperatures to better understand the combustion cycle.

[Ento_Joe]

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[Peter Apps]

Thanks for the update, Joe.

These chromatograms look plenty good enough to me - natural extracts are always going to be a bit messy. With the dramatic differences in peaks between the extracts you could compare bioassay responses between the three - if I recall you have had good response to a hexane extract, which suggests either that the extra peaks in the polar solvents are not the cue, or that the predators are very sensitive to a compound that is only a small peak in hexane, but larger in a polar extract. If that is so, they will go crazy for a polar extract.

On the gut contents problem - can you starve them to death rather than freezing them ? Or give them a shot of laxative before you freeze them !!

Have you done a bioassay with the linoleic and stearic acids ?, my suspicion is that they are so ubiquitous that they would not be a useful cue for the predators, depending on the extent to which the predators specialise on the one prey species.

Getting just surface material off those tiny things is going to be a challenge for sure - you could try tumbling them gently with a particulate adsorbent - something like the C18 or polymer packing from an SPE tube might be worth a shot. Separating the mites from the adsorbent is then the next problem - you might be able to just sieve them out, or float them out with water.

Keep us posted.

Peter

[Ento_Joe]

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[rb6banjo]

This is a very interesting area of research. For those of us who are "helping from afar" and if you're like me, this is a completely new area to contemplate, I found this:

http://www.mdpi.com/2075-4450/5/3/639/pdf

It's a fairly quick read. Standard sorts of sampling techniques.

[GOM]

Hi Joe

The images and chromatogram details that you posted are great and really helpful

I agree with your supervisor that hexane may not be a particularly good developing solvent. It was a starting suggestion and as I said it may well need modifying.

try
Running solvent
• 5 parts of cyclohexane
• 3 parts of propanone (acetone)
• 2 parts of petroleum ether (40 - 60°C)

I like the tumbling idea

Regards

Ralph

[rb6banjo]

Since you have a thermal desorption unit, you could buy some "twister" stir bars and use those as the extraction medium. The "twister" bars are small magnetic stir bars coated with sorbents (like a SPME fiber). They fit nicely into thermal desorption tubes. Gerstel makes them.

[GOM]

Hi Joe

@rb6banjo

very interesting paper - I hadn't considered that there are male and female mites

With regard to the twister bars ( a nice idea) very expensive but a cheap alternative is PDMS tubing of which I have a metre left at home and have used successfully in this sort of investigation using 1cm lengths. I can post it to Joe for playing with and instructions for use. Essentially it is SPME where the M stands for macro

Regards

Ralph

[Ento_Joe]

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[Ento_Joe]

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[itspip]

You're correct in that PDMS is often used in SPME fibers. I'm not sure if there is anything else used in them. It, PDMS, is used a lot for sorbant analysis.

On your TLC plates, were those spotted by hand?

[GOM]

Hi Joe

Your plates are looking really good (you look like an expert ) - I think that you have a good developing solvent.

You are making faster progress than I can keep up with

Yes PDMS is the basis of one of the SPME fibres. The tubing is just a macro version and I have no problem sending you some - a good idea from rb6banjo

The images you are posting are really helpful

Regards

Ralph

[Ento_Joe]

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