Chromatography Forum

Hi, my company has receltly been asked by a major client to aquire accredidation in South Carolina to perform enviromental analysis. their requirements are rediculous. I am having major issues. One is the requirement to maintain 70-130% recovery of Dinoseb and PCP on Laboratory Control Samples. It is not happening. I average around 60% recovery for these two compounds, which I feel is good. I employ methylation by diazomethane. I purchase standards in acidic form and methalayte them to compensate for incomplete methylation. Is it possible to meet these requirements under this method. If so, how is it accomplished???

Has NC looked at the QC table in 8151? Page 23...

http://www.caslab.com/EPA-Methods/PDF/8151a.pdf

A note from the interferences section of the method

3.5 Alkaline hydrolysis and subsequent extraction of the basic solution removes many chlorinated hydrocarbons and phthalate esters that might otherwise interfere with the electron capture analysis. However, hydrolysis may result in the loss of dinoseb and the formation of aldol
condensation products if any residual acetone remains from the extraction of solids.

3.6 The herbicides, being strong organic acids, react readily with alkaline substances and may be lost during analysis. Therefore, glassware must be acid-rinsed and then rinsed to constant pH with organic-free reagent water. Sodium sulfate must be acidified.

3.7 Sample extracts should be dry prior to methylation or else poor recoveries will be obtained.


70-130 sounds like a generic control limit to me. Can you apply for a variance to the certification requirements?

I am well aware of this QC table as is South Carolina. Our first attempt was to apply for a variance to the limits. This was immideately shot down. South Carolina states that dinoseb and PCP have proven recovery of 70-130. We asked South Carolina where they have proof that these 2 compounds have proven recovery of 70-130. They did not reply. I investigated by calling their state laboratories. Turns out that their laboratories do not use method 8151, and have no scientific data to back them selves. The problem grows deeper in that my company is currently subcontracting these samples to laboratories certified in SC, but these laboratories are not required to SPIKE AT ALL for dinoseb and PCP. I feel that 8151 is a catch 22 between us.

That reminds me of the requirements of the DoD/NELAC in terms of spiking, that you need to spike some percentage (80%? Not sure on the exact requirement) of all analytes in your list each time your spike. However, the requirement also states that you must rotate the analytes that you spike so that you spike all analytes over a 2-year period.

Have you asked why your subcontract labs aren't required to spike for Dinoseb and PCP? They must have a reason that allows for them to be certified in SC, else you're subcontracting to a lab that isn't following the spirit of its certification protocol.

Here's another idea... - can you use method standards instead of external calibration? That way, you would have a methylated cal standard that has suffered the degradative effects of your extraction, and hopefully your dinoseb standard will have degraded enough that it will be more indicative of your regular extraction recovery (and will give you better results in your LCS recoveries).

I'm currently putting a method together for a fairly large phenols suite in environmental waters and getting recoveries for PCP and Dinoseb >70% using SPE to extract and derivitising with acetic anhydride:pyridene.

It doesn't follow 8151 but it works (so far).

Rich