Analysis of Chlortetracycline in animal feed

[carol]

Dear all,

I will really appreciate any comment, suggestion or advise on the analysis of chlortetracycline in animal feed. I have tried several method most of them use McIlvaine buffer or acidified methanol. I manage to get good recoveries and reproducibility when I used matrix matched samples. However, my problem raise when I used medicated feed. Recoveries in medicated feed samples are only of 14 % . I have also prepare medicated feed my self and I do not get satisfactory results, I don't understand what it is happening!!!
Does any one have experience the same problem? I will really appreciate comments,

Waiting for replays,

Carol

[oscarBAL]

Hola Carol.
I did tetracyclines in fish tissue a couple of years ago using LC-PDA, do not remember so much about the procedure I used SPE HBL Oasis cartirdges and work quite good (actually the people in that lab told me the the procedure is still working good) I remember we used McIlvaine buffe for extraccion and cartridge conditioning, and in some point we used oxalic acid for elution but one important step it was to defatt the extract with Metanol. I know some feed are very fatty and I wonder if that could be affecting your recovery?

fat remotion is very easy, put your extract in a centrifuge tube and add 2 or 5 ml of hexane, shake it and the remov organic phase. I do not remember the details; I based on a FSIS-USDA method for this.

I hope this hint help you.

BR.

Oscar

[rb6banjo]

I don't know much about this topic Carol. I'm a flavor/aroma guy. What is the pH of your buffer? What is the nature of the feed (solid pellets, viscous gel, etc.)? Do you extract the analyte from the buffer used to treat the sample or do you shoot the extract directly?

Can you give me a thumbnail sketch of how the procedure should work?