PCN-222 metal-organic framework: a selective and highly efficient sorbent for the extraction of aspartame from gum, juice, and diet soft drink before its spectrophotometric determination

Abstract

In this paper, we describe synthesis and application of an iron porphyrinc metal-organic framework PCN-222(Fe) for solid phase extraction of aspartame, an artificial non-saccharine sweetener, from gum, juice and diet soft drink samples prior to its determination by spectrophotometry. The mesoporous MOF was synthesized solvo-thermally and characterized by Fourier transform-infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller techniques. To obtain the best extraction efficiency of aspartame, significant affecting parameters such as pH of sample solution, amount of the sorbent, type and volume of eluting solvent, and adsorption and desorption times were investigated and optimized. Under optimum conditions, the calibration graph for aspartame was linear in the range of 0.1 to 100.0 mg.L^-1 and relative standard deviation of aspartame was 1.7% (n = 7). Limit of detection of method calculated as 0.019 mg.L^-1 and the enrichment factor of 350 folds was obtained. Adsorption capacity of synthesized sorbent was found to be 356 mg.g^-1. Hierarchical porosity, the eight terminal-OH groups of the Zr₆ node, and hydrogen bonding possibly play vital role for selective adsorption of aspartame. The optimized method was successfully applied to the determination of aspartame in real samples with reasonable recoveries (> 98%).

Keywords: Aspartame; Diet soft drink analysis; PCN-222(Fe); Solid-phase extraction; Spectrophotometry; Zirconium-based metal–organic framework.

Fig. 1

PXRD pattern of synthesized PCN-222(Fe) MOF

Fig. 2

FT-IR spectrum of PCN-222(Fe) and PCN-222(Fe)-ASP

Fig. 3

Nitrogen adsorption–desorption isotherms for PCN-222(Fe) at 77 K

Fig. 4

DFT pore size distribution for the PCN-222(Fe)

Fig. 5

SEM of PCN-222(Fe)

Fig. 6

Effect of pH on extraction recovery of ASP (adsorption conditions: 100 µL of 10.0 mg L⁻¹ ASP solution; 10 mg of adsorbent; 15 min contact time)

Fig. 7

Effect of eluent type on extraction recovery of ASP (adsorption conditions: 100 µL of 10.0 mg L⁻¹ ASP solution; 10 mg of adsorbent; 15 min contact time; pH:6)

Fig. 8

Effect of volume of eluting solvent on extraction recovery of ASP (adsorption conditions: 100 µL of 10.0 mg L⁻¹ ASP solution; 10 mg of adsorbent; 15 min contact time; pH:6)

Fig. 9

Effect of amount of PCN-222(Fe) MOF on extraction recovery of ASP (adsorption conditions: 100 µL of 10.0 mg L⁻¹ ASP solution; 15 min contact time; pH:6)

Fig. 10

Effect of adsorption and elution contact times on extraction recovery of ASP (adsorption conditions: 100 µL of 10.0 mg L⁻¹ ASP solution; pH:6; 7 mg of adsorbent)

Fig. 11

Spectrum of cola drink sample spiked with 50 µg L⁻¹ of ASP after MOF-SPE extraction