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we are tryng to dose ropivacaine in children after central block.
Unfortunately our technicins are not able to do that, they have write.....
=2E......................" Blood samples were collected in heparinised
Venoject tubes with green stoppers. The blood was centrifuged and the plasma
was stored at -20=B0C until analysis.
Two standard solutions (about 3mg/ml) of ropivacaine and penticaine were
prepared. After addition of 300ng of ropivacaine and penticaine, the
drug-free plasma (0.5ml) was adjusted to pH 9.2 by the addition of 0.5 ml 2%
sodium tetraborate, and the analytes were extracted into 10 ml diethylether
by shaking vigorously for 5 min. After centrifugation (3000rpm for 5 min)
the organic phase was back-extracted into 0.2 ml 0.1 M H2SO4 by shaking well
for 1 min. After discarding the organic phase, aliquots of the acid were
injected into the HPLC. The HPCL system consisted of Merck Li ChroCART
250-4 LiChromopher 100 RP-18 (5?m) and a solvent of 25% acetonitrile in 45
mM phosphate buffer pH 3. Eluiting compounds were detected by absorbance at
220 nm, flow 1.5 ml/min.
But it don't work
Could someone help us
thank in advance,
Dott Marco Calamandrei
Pediatric hospital "A. Meyer" Firenze Italia
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Dear Dr Calamandrei
You didn't say what didn't work. There should be no problem
as ropivacaine is an easy analyte that does not decompose.
Presumably, direct injection verified that the
chromatography was OK. That leaves the extraction. If it was
the extraction, it may be because the pH of 9.2 was too low
for a good recovery of ropivacaine which has a pKa of 8.
There is no need to use borate buffer - use sodium hydroxide
with a pH of 12+ to force the base concentration.
We have published extensively on such drugs. We use a higher
pH for extraction. Our first attempt was a very general
method used for these drugs.
Mather LE. Tucker GT. Meperidine and other basic drugs:
general method for their determination in plasma. Journal of
Pharmaceutical Sciences. 63(2):306-7, 1974 Feb
Our most recent attempt was using enantiomeric verification
and is also a reasonably general method. Gu XQ. Fryirs B.
Mather LE. High-performance liquid chromatographic
separation and nanogram quantitation of bupivacaine
enantiomers in blood. Journal of Chromatography. B,
Biomedical Sciences & Applications. 719(1-2):135-40, 1998
Professor of Anaesthesia and Analgesia (Research)
University of Sydney at Royal North Shore Hospital
Centre for Anaesthesia and Pain Management Research
St Leonards, NSW 2065, Australia
Phone +61 2 9926 8420; Fax +61 2 9906 4079
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