With sample:solvent ratio of 1:2 (5 g with 10 mL acetonitrile), you have good overall recovery. I used 0.5 g of oil with 30 mL acetonitrile just to maintain amount of oil at 0.5 g for fear of damaging the GC column. The idea of freezing should help out a lot to get rid of the oil. The method is good for lower the LOW to 10 ppb.
Data An improved dispersive solid-phase extraction clean-up metho...
You can go for acid extraction or leaching.Solvent leaching or extraction takes time. Solubilizationnis main issue with lipophilic pesticides. Purity, pH, temperature, stability and combustion are main issues.
@ Upadhyay, I had a question for the paper above where the sample to solvent ratio is 1:2 (5 g in 10 mL). According to my experience, the lipophilic pesticide (hexachlorobenzene) will stay in oil sample and result in low recovery. Normal QuEChERS extraction with 1:1 or 1:2 sample:solvent ration in fatty food usually yield low recovery of lipophilic pesticides.
HCB is always a tricky one, it likes to stick to glass ware too. the Mills method using acetonitrile / hexane partitioning works well for HCB but you need to pay attention to the volumes, and as previously stated freezing out can help get rid of carry over fats.
If you have lots of samples for HCB in fats, you might look at the Assisted distillation method in my pubs, we analysed tens of thousands of samples for OCs and OPs in animal fats that way.
I have already develop a method using 0.5 g oil and 25-30 mL acetonitrile to increase solvent/sample ratio and got good recovery. However, with a smaller sample size, my LOQ is much higher. See my profile on publication of pesticide in olive oil.
Thanks for your answer. I understand it is a very good proposition.
Dear Narong Chamkasem
I am doing recovery in rice sample with using QuEChERS extraction method with 0.1% acetic acid with 10 ml acetonitrile in 5 g sample to add 5ml water.
After extraction and cleanup and final sample prepare in 1 ml hexane, and analysed by GC MS Ion trap (SIM method), after analyed we observed all recovery found more than 150 to 200 %. some recovery found in less than 10 % basically Fipronil and diazinon, and alphaendosulfan found as negative peak.
Kindly suggest me for where can I modify this method for found good recovery mostly for herbicides and Organophosphoras pesticides in rice.
Dear Sondhiya:
Your protocol is strange. Why not inject the acetonitrile extract directly to the GC. The issue of hexane solvent exchange is OP is very polar compound compare with other pesticide and it may not dissolve in hexane, so I would expect the low recovery. The reason you have high recovyery is may be due to matrix effect in the injector port. Do a simple test to see if it is true. Prepare the blank matrix until the end (hexane) and add standard to it and inject against standard in solvent. I bet you will get higher response on standard in matrix. This effect is well known, because the analyte will break down in hot injector liner. The matrix will protect the degradation. To fix this, you need to prepare standard in sample matrix. We check rice from India and usually found Tricyclazole fungicide. Do you have LC/MS? For OP, which is very polar analyte will run better on LC on polar column on GC.
My suggestion to your protocol is inject the acetonitrile extract to GC and use matrix matched standard. If you have multimode inlet of Agilent, I would do "cold splitless injection method" where you inject sample at colder temperature say 60 C to evaparate solvent injector port and ramp the liner temperature to 300 C quickly. This way will reduce analyte degradation in the hot injector port.
For normal analog detectors such as UV or ECD, you measure the noise level of the baseline, the analyte concentration giving 10 times the noise, is LOQ. However, GC/MS/MS has no noise. You can keep lowing the amount of the analyte, but the noise will be flat. Until you don't see the signal. What you do is inject a few lowest standard solution and calculate the standard deviation. LOQ = 10 std dev.
I don't quite understand your question. The standard curve has nothing to do with it.
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