Synthesis of novel MOF-on-MOF composite as a magnetic sorbent to dispersive micro solid phase extraction of benzodiazepine drugs prior to determination with HPLC-UV

Diazepam and lorazepam are two benzodiazepine drugs widely prescribed as antidepressants and antiepileptics. A straightforward and time-save dispersive micro solid phase extraction method as a sample preparation strategy was developed to extract these drugs in human urine and real water samples prior to their determination by HPLC-UV. A novel sorbent based on growing Co-MOF on Fe-MOF was synthesized and then magnetized using magnetic Fe3O4 nanoparticles and a sol–gel strategy. The sorbent (Fe3O4@SiO2@Co-MOF@Fe-MOF composite) showed the highest extraction efficiency toward diazepam and lorazepam compared to Fe-MOF and Co-MOF@Fe-MOF as sorbents. The effects of various factors on diazepam and lorazepam determination were studied by experimental design, in which a Plackett-Burman design and Box-Behnken design were used for screening the factors and optimizing the significant factors, respectively. Under optimum conditions, the method linearity for the diazepam and lorazepam determination was 0.3–450 and 0.2–400 ng mL−1 with an R2 of 0.9926 and 0.9943, respectively. Proper detection limits of 0.09 and 0.06 ng mL−1 were obtained for the diazepam and lorazepam determination. Also, intra-day and inter-day RSDs (n = 3) were in the range of 3.42–3.75 % and 4.76–5.39 % for the diazepam and lorazepam determination, respectively. The method exhibits a high preconcentration factor of 654.3 and 719.1 for the diazepam and lorazepam determination. Besides, the recoveries and RSDs were evaluated by analysis of tap, river, and well water, and two human urine samples using the method. RSDs were in the range of 3.09–6.80 %, with recoveries between 88.2 and 97.5 % for analysis of spiked real water and urine samples.