Chromatography Forum

Hello everybody.

We are developing a GRO method by head space ( G1888) technique in soils.
The matrix modifier solution is NaCL ( 180g/500mL water) according to EPA 5021. The blank soil is a sample baked to 400°C we use for QC purposes, so far, so good. But when we spiked GRO standard in real samples the recovery dropped to 50% over and over again.

The G1888's parameters are:

*Vial size=20mL
* Sample=2gr
*Modifier=10mL
* Vial press= 102Kpa
* Carrier press=103Kpa
*Oven=85°C
*Loop=90°C
*Transfer line=100°C

*Vial equilb=50min.
*Press. time=0.6min.
*loop fill=0.5min
*loop equilib=0.05min
*Injection time=1min.
*Shake=high.

Any suggestions?

Best regards.

How are you calculating recovery - specifically, what do you take as your reference for 100% recovery ?

Peter

It is: the obtained value / the added value.
In the matrix spike/ matrix spike duplicate samples, the obtained value is lower, about the 60%.

It is: the obtained value / the added value.
In the matrix spike/ matrix spike duplicate samples, the obtained value is lower, about the 60%.

With purge and trap GRO spiked into a sand matrix will give nearly 100% recovery, but once you start spiking into soils that contain clay it will drop quickly. Sandy-loam soils are probably in the 60-80% recovery range, sandy-clay similar and clay-loam can be lower. If you are getting 60% recovery the you are probably about where you should be, and every soil will be different.

Thank you James.

So, I will try calibration curves in different kind of soils.

Best regards.

That's a little more severe than what I'm used to seeing out of HS. Your matrix swamping appears correct, and your temperature is high enough of GRO. Are you seeing your surrogates drop down that much as well?

James is correct in that clay does make for a nice sorbent bed in your aqueous matrix, but we typically expect 60-130% recovery for that range.

Dear Mark.

Yes, it is. The surrogate drops down and behaves in the same way as the standard.

Best regards.