Supplementary material
Oleate functionalized magnetic nanoparticles as sorbent for the analysis of polychlorinated biphenyls in juices
Rosa Ana Pérez, Beatriz Albero, José Luis Tadeo, Consuelo Sánchez-Brunete
Departamento de Medio Ambiente, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Ctra de la Coruña, 7, 28040 Madrid, Spain.
Corresponding author. Tel.: +34 91 347 6820; fax: +34 91 357 2293
E-Mail address: (C.Sánchez-Brunete)
Figure S1. TEM image (a); DTA curve of Ol-coated MNPs (b).
Optimization of the two step procedure based on dispersive liquid-liquid microextraction and magnetic retrieval
Three different volumes of 1-octanol were injected using 50 mg of MNPs in the D-µ-SPE step. Figure 2S shows that the recoveries of the analytes were similar when 25 and 50 mL of 1-octanol were used but they decreased with 100 mL. The dependence of the extractive yield with the volume of 1-octanol has been previously described [1-3], indicating that the dilution effect became predominant over extraction capacity. In addition, with 25 µL of extractive solvent the recoveries presented higher variability than with 50 µL. The effect in the recoveries of the amount of MNPs added in the D-μ-SPE step (30 mg and 50 mg) was investigated, and the results obtained were similar for all compounds. Therefore, 50 mL of 1-octanol and 30 mg of MNPs were considered optimum and were chosen for further studies. To evaluate the pH effect in the PCBs recoveries, the method was carried out at pH 3.5 and 7 and the results showed a decrease in the recovery of all the analytes at neutral pH.
In a previous work, we observed that the addition of MeOH gave a significant increase in the recoveries of PCBs from soil leachates using mSPE [4]. Furthermore, MeOH is usually used in DLLME as disperser solvent [5]. The effect of MeOH in the PCBs extraction was evaluated and the results indicated that the peak areas of most of the PCBs decreased with the addition of a 10% of MeOH previous to the DLLME (data not shown). Nevertheless, as shown in Figure 3Sb, the simultaneous injection of a mixture of 50 mL of 1-octanol and 5 mL of methanol into the sample solution yielded an improvement in the recoveries.
In the magnetic retrieval step when the extraction time was increased from 2 to 10 min, the recoveries did not improve. This result is similar to those reported by other authors, implying that the MNPs can retrieve the 1-octanol very efficiently [2, 6]. Therefore 2 min extraction time was selected to minimize the time of the complete process.
Figure S2. Effect of the volume of 1-octanol on the recoveries of PCBs from apple juice, spiked at 0.72 ng mL-1 of PCBs, by the two step procedure using DLLME and magnetic retrieval. Emulsification time: 2 min and mSPE: 50 mg of MNPs (2 min) and EtAc as desorption solvent. Number of replicates n=3.
Figure S3. Effect of the presence or absence of MeOH as dispersion solvent in apple juice spiked at 0.72 ng mL-1 of PCBs extracted by DLLME and magnetic retrieval. Number of replicates n=3.
Figure S4. Effect of the addition of NaCl in 50 mL of diluted apple juice (50:50 v/v), at pH7 and 10 % MeOH, spiked at 0.72 ng mL-1 of PCBs after 10 min of extraction with 50 mg of Ol-coated MNPs. Number of replicates n=3.
Figure S5. Effect of the amount of Ol-coated MNPs on chromatographic response in an apple juice sample spiked at 0.72 ng mL-1 of PCBs. Number of replicates n=3.
Figure S6. Slope ratios between matrix-matched and solvent-based standards obtained for PAHs with external standard (ESTD) or internal standard (ISTD) quantification by GC-MS/MS.
It was observed that isotope labeled standards counteracted matrix effects, achieving slope ratios around 1 for the compounds and were used in the GC-MS/MS analysis.
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