How do I quantify my FAs using a ITSD and a extraction STD

Discussions about GC and other "gas phase" separation techniques.

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Hello,
I am working on a graduate research project where I am conducting a qualitative and quantitative PLFA analysis using a GC-MS fitted with a Agilent HP5 column. I have adapted the methods from:

https://www.jove.com/video/54360/extrac ... s-in-soils

So this method utilizes two standards: the internal standard which is added right before injection to the GC to assess loss of analyte during injection, and a surrogate standard added to samples before a modified Bligh and Dyer extraction to assess the efficiency of the lipid extraction. Both standards are phospholipids not expected to be present in the sample. I also have a standard mix of 37 phospholipids that I was going to use to help identify the lipid species in my samples via comparing retention times.

The issue I am having is my adviser told me that the formula in the Quideau et al. 2016 method paper for quantifying PLFAs is for a protocol that uses a FID, not a MS, so I cannot use it. I have been searching for methods to help me write a formula that allows me to use these standards to quantify PLFAs and have yet to be able to figure this out.

I am new to this method and would really appreciate any help! I am primarily interested in the FA 16:1w5, but being able to quantify total PLFAs would be nice to include in my analysis. Thanks for any insight!
You have a standard that contains your 37 target analytes and you have an internal standard solution. Make a series of calibration standards with concentrations spanning your expected concentration range, keeping the internal standards constant at the concentration you intend to add to the sample extracts.
Build a set of calibration curves for your target analytes and evaluate your samples against those.

For background try: https://www.epa.gov/sites/production/fi ... /8000d.pdf
For a GC/MS semivolatile method try:
https://www.epa.gov/sites/production/fi ... 2017_0.pdf

There are plenty of other examples but these are ones I worked on.
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