Electronic SupportingMaterials (ESM)
Magnetic porous carbon derived from a zinc-cobalt metal-organic framework: A adsorbent for magnetic solid phase extraction of flunitrazepam
Qiuhua Wu†,a,b*· Si Cheng†,a· Chenhuan Wanga,c· Xiyang Lia·Zhi Lia,b·Chen Haoa*
a Center for Intelligent Chemical Instrumentation, Department of Chemistry and Biochemistry, Edison Biotechnology Institute, Ohio University, Athens, OH 45701, USA
b College of Science, Agricultural University of Hebei, Baoding 071001, China
c College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China
*Correspondence authors: E-mail: (HaoChen), E-mail: (Qiuhua Wu)
Optimization of experimental conditions
In order to optimize the extraction efficiency, the amount of the Co-NPC, stirring time, sample solution pH, and desorption conditions were investigated. All the experiments were performed in triplicate using 10 mL deionized water spiked with 10.0 ng mL-1 flunitrazepam and the means of the results were used for optimization.
Enrichment efficiency of the material
The enrichment efficiency of the Co-NPC was tested by comparing the MS peak signal of 10.0 ng mL-1flunitrazepam in acetonitrile (Fig. S3A) with that of the desorption solution obtained after the extraction of 10 mL deionized water spiked with 10.0 ng mL-1 flunitrazepam (Fig. S3B). It can be seen clearly that the MS peak of protonated flunitrazepam (m/z 314.094) increased greatly after the extraction, indicating that the Co-NPC has excellent extraction efficiency for flunitrazepam. The enrichment factor was about 55. The mass error of m/z 314.0937(experimental value) and m/z 314.0935 (theoretical value) are calculated to be 0.636 ppm, which demonstrates the enriched compound is the flunitrazepam.
The effect of the dosage of adsorbents
In order to select the optimum dosage of the Co-NPC for extracting flunitrazepam, different amounts of the Co-NPC were investigated in the range from 2 to 9 mg. The results shown in Fig. S4 indicated that the extraction recoveries were increased with the dosage of the adsorbent increased from 2 to 5 mg, and then reached the maximum plateau and remained almost unchanged from 5 to 9 mg. To ensure that the adsorbent was sufficient for the extraction, 6 mg of Co-NPC was used in the following experiment.
The effect of the sample solution pH
The pH of the sample solution plays an important role in MSPE because it can influence both the existing form and the stability of the analytes [S1]. Therefore, the effect of pH value of the sample solution was studied. As it is difficult to protonate the analyte in base condition to gain good MS signal, high pH was not investigated in this experiment. The pH values of the sample solution were changed from 2.0 to 8.0 using 1 mol L-1 HCl or NaOH solution to adjust the solution pH value. As shown in Figure S5, there is a maximum extraction efficiency occurring at about pH 6. The reason for this may be explained as follows: the analytes in the molecular form will be favorable for them to be adsorbed on the adsorbent. In acid condition, the flunitrazepam will be positively charged and has increased polarity thus the absorption will decrease [S2-S3]. When the pH values of the sample solution are above 6, the hydrolysis might be a problem since it has the amide and enamine structure, and therefore its adsorption on the adsorbent would decrease.
The effect of the stirring time
The stirring time will influence the partition of the analytes between the sample solution and the adsorbent. A certain stirring time is required to reach the partition equilibrium. To investigate the effect of stirring time on extraction efficiency, the stirring time was changed from 5 to 40 min. The experimental results (Fig. S6) showed that the extraction efficiency for the analytes was increased from 5 to 25 min and then remained almost unchanged. On the basis of the above result, 25 min of stirring time was chosen in subsequent experiments.
Optimization of the desorption conditions
To ensure a complete desorption of the analytes from the adsorbent, it is very important to desorb effectively the analytes from the Co-NPC. The most commonly used organic solvent, acetonitrile and methanol, as desorption solvents were investigated, and the result showed that no obvious difference was observed in the desorption efficiency, and we chose acetonitrile as the desorption solvent in the following experiments. The effect of the volume of acetonitrile on desorption efficiency was also investigated. It was found that the analyte is effectively desorbed with two portions of acetonitrile (80 μL each).
FigureS1. The XRD patterns of the Co-NPC.
Element / Wt% / At%CK / 83.66 / 92.21
OK / 06.82 / 05.65
CoK / 09.52 / 02.14
Matrix / Correction / ZAF
Figure S2. The EDS of Co-NPC (a), TEM image of ZIF-8 derived NPC (b).
FigureS3.ESI-MS spectrum of 10 ng mL-1flunitrazepam before and after extraction
FigureS4. Effect of the amount of the Co-NPCon the extraction efficiency
FigureS5. Effect of sample solution pH on the extraction efficiency
FigureS6. Effect ofstirring timeon the extraction efficiency
References
S1. Liu XL, Wang C, Wu QW, Wang Z (2016) Magnetic porous carbon-based solid-phase extraction of carbamates prior to HPLC analysis, Microchim Acta 183:415–421
S2. Staeheli SN, Poetzsch M, Kraemer T, Steuer AE (2015) Development and validation of a dynamic range-extended LC-MS/MS multi-analyte method for 11 different postmortem matrices for redistribution studies applying solvent calibration and additional 13C isotope monitoring. Anal Bioanal Chem 407:8681-8712
S3. Versace F, Sporkert F, Mangin P, Staub C (2012) Rapid sample pre-treatment prior to GC–MS and GC–MS/MS urinary toxicological screening.Talanta 101:299-306
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