Abstract:

Brominated flame retardants （BFRs） are widely used as organic flame retardants in plastic products， with most exhibiting strong biological toxicity as well as physical and chemical stability. BFRs inevitably remain in foods consumed on a daily basis through indirect or direct contact， thereby threatening human health. Therefore， establishing a fast and effective method for detecting and analyzing BFRs is imperative. Magnetic solid-phase extraction （MSPE） has been widely used in trace-analysis applications owing to advantages that include operational simplicity and rapid magnetic separability. The key to MSPE lies in the design and preparation of efficient magnetic adsorbents. In this study， a magnetic carbon aerogel （MCA） was prepared using a sol-gel method in combination with calcination. MCA was used as a magnetic solid-phase extractant to establish a new method for the analysis of four BFRs in mineral water and instant-noodle-bowl samples in combination with high performance liquid chromatography. Fourier-transform infrared （FT-IR） spectroscopy revealed peaks at 3 454， 1 590， 757， 1 349， 1 654， and 1 076 cm^-1 that are ascribable to -NH₂， -CH， triazine-ring， C-N， C=N， and C-O-C vibrations， respectively. Brunauer-Emmett-Teller （BET） analysis revealed values of 192.16 m²/g， 0.34 cm³/g， and 7.12 nm for the surface area， pore volume and pore size of the MCA， respectively. X-ray diffractometry （XRD） revealed a characteristic peak at 2θ=34.90° that corresponds to the （110） crystal plane of Fe₂O₃， and peaks at 2θ values of 44.72°， 65.01° and 82.42° that are ascribable to the （110）， （200）， and （211） crystal planes of CoFe/Co₃Fe₇. Vibrating sample magnetometry showed that the MCA is highly magnetic （35 emu/g）， which contributes to fast magnetic solid-liquid separation. The MCA was characterized by transmission electron microscopy （TEM）， which revealed a transparent gauze-like structure with nanometer-sized squares and circular particles evenly distributed between them. High-resolution TEM （HRTEM） showed that the square particles exhibit a 0.191 nm stripe spacing that belongs to the （311） crystal plane of Fe₂O₃， while the 0.245 nm stripe spacing observed for the circular particles corresponds to the （110） crystal plane of the CoFe alloy， in good agreement with the XRD results. X-ray photoelectron spectroscopy （XPS） revealed the presence of Co 2p， Fe 2p， O 1s， N 1s， and C 1s peaks. Taken together， these results show that the MCA， which contains various functional groups， had been successfully prepared. Factors that affect MSPE， such as solution pH， amount of material， adsorption time， the concentration and volume of the elution solvent， and sample volume， were investigated using the static adsorption method. BFR adsorption by the MCA was observed to increase with time， with equilibrium eventually reached. Tetrabromobisphenol A （TBBPA） reached adsorption equilibrium at 1 h with an adsorption rate close to 100%， whereas 3-bromobiphenyl （PBB-2）， 4，4′-dibromobiphenyl （PBB-15）， and 2，2′，4，4′-tetrabromodiphenyl ether （BDE-47） reached adsorption equilibria at 2 h. BDE-47 exhibited an adsorption rate close to 80% when 20 mg/L MCA was used， whereas the remaining three BFRs exhibited values close to 100%. Absorption by the MCA initially exhibited a constant trend with increasing sample volume but began to decline as the sample volume exceeded 100 mL. BFR adsorption by the MCA was found to be almost pH-independent， which indicates that the MCA is stable over a wide pH range. In addition， the analytes were effectively eluted in 30 min using 5 mL of acetonitrile. Based on the results presented above， the optimal adsorption and desorption conditions are： 20 mg/L of adsorbent， a sample volume of 100 mL， an adsorption time of 2 h without pH adjustment， 5 mL of acetonitrile as the eluent， and desorption time of 30 min. TBBPA， PBB-2， and PBB-15 exhibited limits of detection （LODs， S/N≥3） of 0.005 mg/L each under the optimal conditions， while BDE-47 exhibited a value of 0.010 mg/L， with corresponding RSDs of 7.35%， 5.12%， 3.66%， and 5.58% （n=5， C=0.02 mg/L）， respectively， and actual enrichment times of 50， 40， 51， and 61 min， respectively. The developed method was used to determine four BFRs in mineral water and instant-noodle-bowl samples， with satisfactory recoveries obtained， thereby providing a new fast and sensitive method for the analysis of brominated flame retardants.

Key words: magnetic carbon aerogel, magnetic solid-phase extraction （MSPE）, high performance liquid chromatography （HPLC）, brominated flame retardants （BFRs）, mineral water, instant-noodle-bowl