Sample recovery

[Mburuc]

Hi!
How do i optimize sample recovery. Am only able to achieve 70 - 80% of the desired. My excipients are rice bran powder and coconut shell powder for a pesticide. Could these be interfering with the recovery of my intended. Anyone out there with a solution. I will be glad.

Cathy

[skunked_once]

Cathy,

I was a pesticide analytical chemist in a past life so I understand your problem. In order to answer your question we need more information. Are you following a published method for that pesticide in the sample matrices you are working with? If so, what are the recovery values reported in the method? It is possible that 70-80% recovery is the best you can do for your pesticide sample combination. The reproducibility of your recoveries is also important. If your recovery is consistantly in the 70-80% range, that may be adequate for this analysis. What recovery and reproducibality values are specified in your SOP (assuming you have one)? Can you give some details of the method or tell us the pesticide you are measuring?

[Consumer Products Guy]

Cathy - are you basing the recovery on a lab-prepared sample or are you spiking placebo product with pesticide (for example, pipeting an aliquot of pesticide into a volumetric flask containing some placebo product)?

Cathy, I was a pesticide analytical chemist in a past life

Skunked_Once: looks like you've had more past lives than Shirley MacLaine, and each of them posted the same response....






sorry, couldn't resist....

[Mburuc]

Hi
Sorry it has taken so long to respond. Am still not able to recover. My instructor did advice me to add a little of acetone(2ml) and then top up with methanol (50ml). I sonicated the sample and for sometime thought i had a breakthrough because the values went up but am afraid the results am getting are not satisfactory. I am analyzing permethrin and pirimiphos methyl with a concentration of 0.3%w/w and 1.6%W/w in a dust pesticide.

Note: No method of analysis has been provided. am working from trial and error though my peaks look okay. Am supposed to develop methods of analysis for many more other products but am a little hesistant because of the cost involved.
thanks

[Bruce Hamilton]

Often, an hour in the library can save a week in the laboratory. Even a search of the WWW should help you find some relevant information.

Seach on each compound and HPLC, and choose a couple of articles that focus on the developemnt of an analytical method from a matrix most closely matches yours. Evaluate solvents forrecovery of each compound separately, so you understand what conditions are needed for each.

I would be looking at the sample preparation and solvent loading and the composition of the extraction solvent, and ensuring that the extraction solvent is also the most approprite laoding solvent for the HPLC.

I should note that some sources on the WWW may not provide useful, relevant information, so always review abstracts carefully before ordering articles.

A Google search for Permethrin and HPLC hit a summary report from the European Agency for the Evaluation of Medicinal Products that consistently, but incorrectly, used HPLC when they apparently meant GLC ( unless they somehow managed to use " the GLC column and quantified using ECD" on an HPLC ).

Bruce Hamilton

[Russ]

We have done pesticides in a dust formulation without too much trouble, including (I think) Permethrin. How long did you sonicate? We did one hour, though that may be overkill. Some formulations we have tested have also required a post-sonication stirring time (generally one hour) to get better recovery.

[LCbob]

hi

I also worked with pesticides in a previous life basically analysing at residue levels. Permethrin can be a problem, I vaguely remember we used toluene to extract from aqueous matrices, this gave the best recoveries. The company I worked for also sold a product consisting of pirimiphos methyl dried onto coconut shell, this we analysed by the addition of chloroform and sonication, this gave 100% recoveries. Analysis was cap. GC with FID. Note permethrin can appear as two isomer peaks.

Hope this helps