I am a grad student at the Medical College of Georgia. I am developing a GC/MS procedure for fentanyl, sufentayl, and alfentanyl. I have been having some problems finding sources on the diffence between relative and absolute recovery. My professor refusses help me on this one. There are some GC/MS books in our library (Sunshine, Tietz, but no Watson), but I have not found anything yet. I would like to know the difference between the two and a procedure acceptible for GC/MC procedure development. I am not really lazy I have been looking for a while, and I have found nothing on absolute recovery (Medline, library books, etc.). Please donate a good source for this info. It is going to a good cause. firstname.lastname@example.org
By Anonymous on Wednesday, September 8, 1999 - 11:21 am:
Recovery relative to what? Are you talking about recoveries relative to fortified samples? Those would typically be near 100%. Recoveries relative to theoretical values? Could be anything. The chemist usually needs to know both values when finished with a method, and has to judge whether they are good enough for the purpose of the data.
I don't know the drug field--maybe there are legal requirements for the type of study you are doing.
I've never seen a formal procedure for developing methods, but in general:
Research the chemical(s) of interest-- solubility data, metabolites, spectral and chromatographic characteristics, etc. Manufacturers are usually excellent sources of info. Talk to anyone who might be able to help--what this forum is about.
Look for existing methods for similar compounds that might be easily altered, or simply extended to include the new chemicals. Preferably, in the same matrix you will be dealing with. If you don't find anything, see the paragraph above, and add copious amounts of time, talent and money.
By Anonymous on Wednesday, September 8, 1999 - 04:29 pm:
Too bad that the manufacturers of fentanyl (China White) are street-smart chemists who *rarely* publish information in the PDR :)
By Scott Fredrickson on Friday, September 10, 1999 - 02:10 pm:
I admitted I didn't know much about drugs--but I hadn't intended to prove it! I did a handful of analyses years ago, and decided not to pursue that career line.
I assumed you were interested in blood/urine analyses, since 'recoveries' aren't usually considered when assaying relatively pure samples, as far as I know. Or maybe that's what they call them in that part of the field, while the rest of us mean something else.
If you haven't already checked, your state forensic lab might be helpful. The Feds used to publish (in the '70's) an analytical manual that might have some clues; maybe they still do.
You always have my last paragraph to fall back on! Best of luck.
By Dan Vassilaros on Thursday, September 16, 1999 - 11:26 am:
The best GC-MS recovery studies are done by spiking the matrix with the deuterated analog of the target/analyte molecule. The deuterated molecule behaves approximately the same as the target molecule through the various sample preparation steps, and can be easily distinguished from it in the analysis--even if it coelutes with it--because its mass fragments are several daltons higher. By calibrating the response of a significant ion in the spectrum of the deuterated analog, and assuming that the two analogous molecules have equal responses, you can calculate a recovery of the target compound from the recovery of the spike.
Of course, this approach only permits recovery studies of free molecules rather than those bound to the matrix.
Another technique to calculate recoveries is to spike the matrix with a C-14 labeled analog, and then do scintillation counting of volumetric/gravimetric portions at each step of the sample prep.
With drugs in biological systems you have to find the free residues as well as all of the metabolites in the fluid/tissue you are analyzing to do pharmacokinetic studies. Do you intend to account for the total dose? Consider radioisotope labeled analogs.
By Wilhelm on Wednesday, September 22, 1999 - 07:20 pm:
Absolute recovery is the % amount of drug recovered from the matrix (e.g. biological fluid) versus the standard (unextracted). The relative recovery is the % amount of drug recovered from the matrix with reference to the extracted standard (standard spiked into the same matrix). You can find information from the FDA guideline on validation of bioanalytical methods.check the FDA website. Good Luck!
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