Help!!! Low recovery with QuEChERS [urgent]

[catlover]

Hi everyone,

I am recently playing with QuECHERS for OP pesticides. The recovery is quite bad.
I am wondering if I did anything wrong or having poor technique of QuEChERS method.
I scale down the material because of limitation of instruments (e.g. I can only use 15mL Centrifuge tube)

Here are the producers of my QuEChERS method:
1. 5 mL DI water as blank into 15 mL CT. Spike 1 ppm mixed standard.
2. 5 mL 1% acetic acid in ACN is added, then shake it with 30 seconds.
3. Salt mixture of 2g MgSO4 and 0.5g sodium acetate is added, I.S. of dichlorvos-d8 is added,
4. Then shake it with 30 seconds.
5. Centrifuge with 3800 rpm for 3 mins. (centrifuge speed is maximized)
6. 2 mL organic layer is transferred to dSPE tube. (without GCB, wondering if I should replace it with activated carbon or not in order to remove pigment)
7. Shake it then centrifuge with 3800 rpm for 3 mins.
8. Dilute the solution for LC-MSMS analysis.

I guess I have no problem in the LC-MSMS (Waters instrument) part because the internal calibration give r^2 more and less 0.99.
Are there anything I need to pay attention with?
By the way, the d-SPE CT contain 900mg MgSO4, 150 mg PSA and 150mg C18.

Please kindly reply if you have any idea. Thank you so much ><

[Don Shelly]

Try reducing water to 2.5 ml.

[catlover]

Try reducing water to 2.5 ml.

Thank you sooooo much for your respond , I tried to reduce the water volume and most of the recovery are finally within acceptable range (80 ~ 110 %).
I would like to ask more if there is a must to create aqueous condition for QuEChERS and what should be the reason behind. Thank you again if you know.

[Don Shelly]

Try reducing water to 2.5 ml.

Thank you sooooo much for your respond , I tried to reduce the water volume and most of the recovery are finally within acceptable range (80 ~ 110 %).
I would like to ask more if there is a must to create aqueous condition for QuEChERS and what should be the reason behind. Thank you again if you know.

The only "must" is to do what works for you.

Don