Solid phase microextraction of benzenes in river water by pomelo peel biochar

doi:10.3724/SP.J.1123.2022.02006

Abstract

Abstract:

Pomelo peel, as a by-product of pomelo consumption, is rich in various fiber and functional compounds. The utilization of the valuable components found in pomelo peel may mitigate environmental concerns. In this study, pomelo peel rich in lignin and oxygen-containing functional groups was used to prepare pomelo peel biochar (PPB) via temperature-programmed pyrolysis at different temperatures (800 ℃ and 1000 ℃). Their structures were investigated by N₂ adsorption-desorption isotherms and BJH pore size distribution. The results showed that PPB1000 (pomelo peel biochar prepared at 1000 ℃) had a higher specific surface area (749.9 m²/g), larger pore volume (0.42 cm³/g), more concentrated pore size distribution (2-3 nm), and better adsorption performance than commercial activated carbon. PPB1000 exhibited excellent capability to capture benzenes (BTEX, including benzene (B), toluene (T), ethylbenzene (E), and xylene (X)) through hydrogen bonds, π-π, and electrostatic interactions. Additionally, their honeycomb porous structure could provide additional adsorption sites and material transport paths. PPB1000 was coated on iron wire using the sol-gel method to prepare chemically and mechanically stable solid phase microextraction (SPME) fibers. By combining PPB1000-based SPME analysis with gas chromatography-flame ionization detection (GC-FID), an effective method was developed for the extraction and determination of BTEX. The optimized method had low LODs (0.004-0.032 μg/L), wide linear range (1-100 μg/L), and good linear relationship (determination coefficients, r²≥0.9919). The RSDs of the intra-batch (n=6) and inter-batch (n=5) precisions were 1.04%-6.56% and 1.03%-12.42%, respectively. The method validation results showed that PPB1000 had good stability. Compared with the commercial reagent polydimethylsiloxane (7 μm), PPB1000 had a higher extraction efficiency. When applied to the analysis of BTEX in natural water samples, trace levels of ethylbenzene (4.80 μg/L), o-xylene (3. 00 μg/L), and m-xylene and p-xylene (2.46 μg/L) were detected. Recovery tests were performed to validate the reliability of the method, and recoveries were between 75.7% and 117.6%. This effective pretreatment process combined with GC-FID could realize the rapid detection of BTEX and is promising for the analysis of BTEX in complex matrixes in the future.

Key words: gas chromatography-flame ionization detection (GC-FID), solid phase microextraction (SPME), pyrolysis temperature, pomelo peel biochar (PPB), benzenes (BTEX), river water

CLC Number:

O658

CHEN Jingjing, ZHANG Zhuoran, YU Jianfeng, TANG Shiming, CUI Bingwen, ZENG Jingbin. Solid phase microextraction of benzenes in river water by pomelo peel biochar[J]. Chinese Journal of Chromatography, 2022, 40(11): 1031-1038.

Figures/Tables 7

Fig. 1 (a) N2 adsorption-desorption isotherms and (b) pore size distribution curves of PPB800 and PPB1000 PPB800: pomelo peel biochar (PPB) prepared at 800 pyrolysis temperature; PPB1000: PPB prepared at 1000 pyrolysis temperature.

Fig. 2 (a) Fourier transform-infrared spectrum and (b, c) scanning electron microscope images of PPB1000

Fig. 3 Effects of (a) desorption time, (b) ionic strength, (c) extraction time and (d) stirring rate on the peak areas of benzenes (BTEX) B: benzene; T: toluene; E: ethylbenzene; m-X: m-xylene; p-X: p-xylene; o-X: o-xylene.

Table 1 Linear ranges, limits of detection (LODs), determination coefficients (r2), and precisions of the proposed method

Analyte	Linear range/ (μg/L)	LOD/ (μg/L)	r²	RSDs/%
Analyte	Linear range/ (μg/L)	LOD/ (μg/L)	r²	Intra-batch (n=6)	Inter-batch (n=5)
B	1-100	0.032	0.9952	5.20	4.75
T	1-100	0.023	0.9948	1.04	1.03
E	1-100	0.020	0.9919	6.56	6.95
m-X+p-X	1-100	0.005	0.9975	5.76	12.42
o-X	1-100	0.004	0.9952	6.01	9.29

Fig. 4 Comparison of extraction efficiencies of benzenes between PPB1000 coating and polydimethylsiloxane (PDMS) coating

Fig. 5 Chromatograms of (a) PPB1000 coating, (b) blank river water sample and (c) spiked (50 μg/L) river water sample 1. B; 2. T; 3. T; 4. m-X+p-X; 5. o-X.

Table 2 Recoveries of the six benzenes spiked in river water samples

Analyte	Content/(μg/L)	Recoveries/%
Analyte	Content/(μg/L)	5 μg/L	50 μg/L	100 μg/L
B	-	98.8	111.9	87.4
T	-	76.5	107.1	117.6
E	4.80	90.9	99.5	108.0
m-X+p-X	2.46	100.1	109.6	111.6
o-X	3.00	75.7	105.4	94.2

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