On-line microdialysis coupled solid-phase extraction to decrease matrix interference in the HPLC analysis of urinary ketamine and its metabolites

A microdialysis sampling (MDS) on-line SPE (MDS/SPE) has been applied to redeem the detection after dilution to decrease matrix interference in the analysis of ketamine (K) and its two main metabolites, norketamine (NK) and dehydronorketamine (DHNK) in urine by HPLC. After being filtrated, diluted and adjusting the pH, K and its metabolites in the diluted sample solution were collected through MDS and then trapped on an on-line SPE for HPLC analysis. The optimal conditions for MDS/SPE were investigated and then applied to real sample analysis. Experimental results indicated that the MDS/SPE by using regenerated cellulose hollow fiber (8-cm length) and 1 mM sulfuric acid as the perfusate at 20 microL/min flow-rate to collect analytes from 100-fold diluted urine sample (20 mL at pH 6.0), and then having been trapped in octadecyl-modified silica phase SPE for 30 min, offered the optimum efficiency. The concentration levels of 41, 42 and 28% (m/m) for K, NK and DHNK, respectively, in urine were redeemed for determination. The detection limits were 0.38, 0.33 and 0.34 ng/mL (in 100-fold diluted sample) for K, NK and DHNK, respectively. The method provides a very simple, inexpensive and eco-friendly procedure to determine K, NK and DHNK in urine.