EPA 8270 with 3511 Microextraction

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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I am trying to get my wastewater/groundwater lab set up to run SVO's using the EPA 8270 on a Shimadzu QP 2010SE GCMS. I would really like to use the 3511 microextraction method if possible. It seems like there is a large discrepancy between the extraction and analysis methods regarding surrogate concentrations: The extraction suggests 10 ug of the surrogate(s), extracted into 2 mL methylene chloride, which about 5 *ug/L* final volume. However, 8270 method advises that the surrogate concentration should be near the middle of the calibration curve. Most of the calibration curves I've seen for this method range from 5-150 *ug/mL*. Why is the extraction method's surrogate concentration so much lower? Which one should I use? Thanks for your help; I'm new to environmental labs and EPA methods. :shock:
The first thing that springs to mind is that the method expects a larger injection volume. If your extract surrogate concentration is 50 ug/L and you inject 1 uL you should have (approximately) the same response if you have an extract surrogate concentration of 5 ug/L and you inject 10 uL.

I am not terribly familiar with the method though.
Notice that the method is for aromatics. These respond quite well in a MS; typically you can see 0.1 to 0.2 ug/mL MAH and PAH in full scan with a decent MS (I have an older Agilent 5973). So, when you are talking about the midpoint of a MAH/PAH curve it might easily be 5 ug/mL. This is definitely NOT true for nitroaromatics, brominated compounds, etc. but method 3511 is not for the full 8270 list. It states that it is specifically for the compounds listed, which all exhibit exceptional MS responses.

I have run a variant of this method (Texas has used a variant for total petroleum hydrocarbons for years) and I like the small extraction size. You do have some issues with sample to sample variability when you drop down to 40 mL from 1000 mL, but since all environmental samples are essentially grab samples I have never found it to be a problem.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
Welcome to the world of EPA methods! Unlike Office of Water methods, SW-846 methods, except for method defined parameters, are not written for a specific regulatory purpose so there is an inherent flexibility written into them.
It is up to the laboratory to show that the method, as used, is fit for its intended purpose. Of course, that means that the lab has to know what the data will be used for.
Micro extraction techniques can be useful for more than just PAH and ECD analyses but the sensitivity is not as good and may not meet data usability goals unless large volume injections and/or SIM is used. At the time 3511 was last updated only limited data was available, thus only PAHs (at neutral pH) were considered.
Surrogate concentrations in the determinative methods are provided as guidance, they may be adjusted as required to meet data quality objectives.
Johannah14 wrote:
I am trying to get my wastewater/groundwater lab set up to run SVO's using the EPA 8270 on a Shimadzu QP 2010SE GCMS. I would really like to use the 3511 microextraction method if possible. It seems like there is a large discrepancy between the extraction and analysis methods regarding surrogate concentrations: The extraction suggests 10 ug of the surrogate(s), extracted into 2 mL methylene chloride, which about 5 *ug/L* final volume. However, 8270 method advises that the surrogate concentration should be near the middle of the calibration curve. Most of the calibration curves I've seen for this method range from 5-150 *ug/mL*. Why is the extraction method's surrogate concentration so much lower? Which one should I use? Thanks for your help; I'm new to environmental labs and EPA methods. :shock:


The normal extraction used for 8270 is 1L of sample to 1ml final volume. This makes 5ug/L in the sample become 5ug/ml in the injected solvent. You have to calculate the extracted concentration into the injected concentration to make the units work out.

10ug surrogate into 2ml final volume would be 5ug/ml concentration in the injected solvent. If the initial volume is 40ml of sample then you have a concentration of 5ug/40ml sample or 0.125ug/ml which is equal to 125ug/L in the sample. This would be in the range of the 8270 method which would be 5ug/ml injected concentration equal to 5ug/L in the sample due to the 1000:1 concentration factor of that extraction.

If you want things to be equal between the 1L to 1ml extraction then you must lower the calibration curve on the instrument by a 40:1000 ratio to maintain the same detection limits when using the smaller sample volume of 3511.
The past is there to guide us into the future, not to dwell in.
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