Column-switching HPLC-MS/MS analysis of ropivacaine in serum, ultrafiltrate and drainage blood for validating the safety of blood reinfusion.

A high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) method, using back-flush column-switching was developed for total drug concentrations of ropivacaine in serum and drainage blood in the measuring range 0.1-10microg/mL. Samples were diluted with internal standard ((2)H(7)-ropivacaine) and extraction buffer, centrifuged and injected directly onto a BioTrap 500 MS extraction column. Using a time programmed six-port valve switch, ropivacaine was back-flushed onto a Zorbax SB-Aq analytical column, gradient eluted and finally detected after electro spray ionisation and multiple reaction monitoring (MRM) of the transitions m/z 275-->m/z 126 and m/z 282-->m/z 133 for ropivacaine and (2)H(7)-ropivacaine, respectively. Accuracy (bias-%) was -1.5 to 5.8% and intermediate precision (C.V.) was 1.4-3.1%. The low sample amount required (10microL), high specificity and short run time (6 min) makes it very suitable for determination of ropivacaine. Using the same methodology as described above and 200microL ultrafiltrate, the free drug concentrations of ropivacaine in serum could be precisely determined with a C.V. below 3%. The method was used to investigate the safety of reinfusion of drainage blood after knee and hip arthroplasty when ropivacaine (Naropin) was used for local analgesia. Data for 30 patients are summarised.