I want to set up a GC analysis on anesthetic drugs in blood. I have read several articles about this assay using headspace analysis with FID or Mass Spec detection. My question is, is it possible to do this assay without using headspace methodology? Is it possible to just do extraction of the volatile drugs in blood and inject them into the system using standard GC autosampler for liquid extracts? The anesthetic drugs that I have in mind have a boiling point of between 45C to 60C. Do I need to use a gas sampling valve or not? Due to our tight budget, I want to set up a method which is reliable but not too expensive. Would appreciate any help that you can give me on this. Thanks!
By Anonymous on Friday, July 11, 2003 - 07:46 am:
I suppose it depends on your detector and the anesthetics you wish to analyse. Do have MS?
Enflurane has been analysed using heptane as an extraction solvent with 98% efficiency. Is this one your targets? Could it work for the others?
Previous workers have injected whole blood samples.
1. using a solvent with a higher boiling point than your analytes so it elutes after them.
2. use SPME headspace - in manual mode this is a cheap but effective method.
3. Talk to Supelco or Varian - they would have some good ideas
By Anonymous on Friday, July 11, 2003 - 07:48 am:
The higher boiling point solvent I was thinking of would be something like tetradecane
By Anonymous on Friday, July 11, 2003 - 11:59 am:
SPME can be used effectively for these analytes. You would simply put 1mL of serum or plasma into a 2 or 4mL vial and seal with a PTFE silicone septum and cap. Extract the analytes with a SPME fiber for 3-5min in the headspace of the vial. Depending upon the concentration of the anlaytes, either the 100µm PDMS fiber (For ppm (µg/mL) levels) or the Carboxen-PDMS fiber (for ppb (ng/mL)levels. After extraction the anlaytes are desorbed in the injection port of the GC.
Heating the sample at 35-40°C would help improve precesion by keeping the temperature constant. A low volume inlet liner will improve the peak shape of the analytes.
You can get started in SPME with a holder, box of fibers and a liner for under $500.00. The items can be obtained from Supelco. Good Luck
By Anonymous on Friday, July 11, 2003 - 07:11 pm:
Dear Ralph and Bob,
Thank you for responding to my enquiry. The system that we have at the lab is a GC 5890A model and the detectors are FID and NPD. We don't have a headspace sampler. We have to buy one in order to do headspace analysis. We only have the standard liquid sampler attached to our GC. This is why I want to ask if it is possible to do the assay without too much expense without compromising the reliability of the results obrained. The volatile anesthetic gases that I am interested in are Enflurane, Isoflurane and Halothane. Can I do this assay using just the standard liquid-liquid extraction and our existing liquid sampler?Can I get reliable results using this method as compared to using a headspace method?
Ralph, could you please explain the SPME (manual mode)? Ho is it done? I'm sorry but I am not familiar with this.
Thanks once again
By Anonymous on Saturday, July 12, 2003 - 12:05 pm:
As Bob said, SPME is a cheap way of doing headspace which would suit your analysis. See
http://infonew.sigma-aldrich.com/Graphics/Supelco/objects/10900/10862.pdf for an explanation.
You will find it a useful technique to have anyway and if you do, - a narrow bore liner is important to keep peaks sharp. For aqueous samples the addition of salt improves the partition into the headspace.
If you have a lot of samples I can understand the need for an autosampler method. The liquid/liquid extraction method I mentioned appears to give a high extraction efficiency so should give reliable results. I will sort out the reference for you.
By Anonymous on Monday, July 14, 2003 - 02:46 am:
anesthetic.doc (21 k)
To Anonymous of Friday, July 11, 2003 - 07:11 pm
You have to have a headspace analyzer to perform AUTOMATED headspace analysis.
But you do NOT need one to do headspace analysis as Ralph and Bob have stated.
The manual mode of SPME headspace does not require a headspace analyzer.
Please review the reference given, and GOOD LUCK.