Electronic Supplementary Material
Rapid extraction and determination of atrazine and its degradation products from microporous mineral sorbents using microwave-assisted solvent extraction followed by Ultra-HPLC-MS/MS
Erdan Hu1,2, Hefa Cheng1*
1 State Key Laboratory of Organic Geochemistry
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
Guangzhou 510640, China
2 University of Chinese Academy of Sciences
Beijing 100049, China
* Corresponding author phone: (+86) 20 8529-0175; fax: (+86) 20 8529-0706; e-mail:
Soxlet extraction and ultrasonic extraction
Soxhlet extraction was performed with a Soxhlet apparatus using 150 mL of dichloromethane (maintained at 40 °C with a water bath). The mineral sorbents (~0.2 g) were mixed with 10.0 g of anhydrous sodium sulfate, transferred into cellulose extraction thimbles, and then introduced into the Soxhlet assemblies. After 72 h of extraction, the extracts were concentrated to 1 mL using a combination of rotary evaporator and nitrogen blowdown.
Ultrasonic extraction was conducted by adding accurately weighed mineral sorbents (~0.2 g) into 50 mL Teflon FEP centrifuge tubes containing 20 mL of dichloromethane. The centrifuge tubes were sealed and then placed in an air-bath shaker set at 25 °C and 120 rpm for 12 h. The tubes were subsequently sonicated at 30 °C for 30 min in an ultrasonic bath (frequency 40 Hz, 200 W). After the extraction, the tubes were centrifuged at 4,000 rpm for 10 min, and the solvent was decanted into evaporation flasks. The shaking and extraction cycle was repeated three times. Finally, the extracts from the three repeated extractions were combined and concentrated to 1 mL by rotary evaporation and nitrogen blowdown.
Microwave irradiation treatment
Atrazine-enriched CBV-720 was prepared by equilibrating 1.3 g of CBV-720 with 100 mL of 7.9 mg L-1 atrazine solution for 24 h, while atrazine-enriched CBV-100 was prepared by equilibrating 1.6 g of CBV-100 with 120 mL of 21.1 mg L-1 atrazine solution for 24 h. The zeolites were separated from the aqueous solutions by vacuum filtration, followed by freeze-drying at -50°C for 12 h to remove the excess water sorbed. The atrazine-enriched zeolites were then transferred into the OMNI vessels from a MARS system (Matthews, NC, USA, www.cem.com). Microwave irradiation treatment was carried out in a commercial microwave oven at the constant power output of 700 W. A series of the sorbents were irradiated for 2, 4, 6, 8, 10 min, respectively. With the formation of micro-scale “hot spots” in the micropores of the essentially microwave-transparent Y zeolites, the sorbed atrazine underwent pyrolytic degradation under continuous microwave irradiation [1,2]. The irradiated sorbents were quantitatively transferred to the Greenchem vessels after cooling and extracted by MAE under the optimal extraction conditions. The contents of atrazine and its degradation products in the extracts obtained were determined by ultra-HPLC-MS/MS to track the degradation of atrazine during the microwave irradiation treatment.
It should be noted that the microwave irradiation treatment is fundamentally different from the MAE. In closed-vessel MAE, the mineral sorbents were immersed in an extraction solvent and microwave energy was used to heat the solvent to form a high temperature and high pressure environment surrounding the mineral sorbents, which accelerated the desorption of the organic compounds from the micropores. The microwave power output varied constantly to maintain a steady extraction temperature during MAE. On the other hand, the mineral sorbents (containing little water) were irradiated with microwave energy under a high and constant level of power to cause degradation of the organic compounds in microwave irradiation treatment. No indication on degradation of atrazine was observed during MAE under the optimal extraction conditions.
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Tables
Table S1. Summary of key physical and chemical properties of the mineral sorbents used in this study.
Sorbent / Silica sand / CBV-100 / CBV-712 / CBV-720 / CBV-780Si/Al mole ratioa / — / 2.55 / 6 / 15 / 40
BET surface area (m2/g)a / 0.8 / 900 / 730 / 780 / 780
Theoretical micropore volume (cm3/g)a / — / 0.48 / 0.48 / 0.48 / 0.48
Hydrophobicity and surface cation typea / Hydrophilic (99.5% quartz, 0.2% alumina, 0.3% others) / Hydrophilic, Na+ (2.12 sites/nm2)b / Hydrophilic, NH4+ (1.11 sites/nm2)b / Hydrophobic, H+ (0.42 sites/nm2)b / Hydrophobic, H+ (0.16 sites/nm2)b
Particle size (mm)a / 8 (median diameter) / 1-2 / 1-2 / 1-2 / 1-2
Pore size (nm)a / — / 0.74-1.2 / 0.74-1.2 / 0.74-1.2 / 0.74-1.2
Structure / Tectosilicate / FAU / FAU / FAU / FAU
Supplier / U.S. Silica (Berkeley Springs, WV) / Zeolyst (Valley Forge, PA) / Zeolyst (Valley Forge, PA) / Zeolyst (Valley Forge, PA) / Zeolyst (Valley Forge, PA)
Notes:
a – From supplier’s product data sheet;
b – The surface density of monovalent cation is calculated from the Si/Al mole ratio of the Y zeolite based on the general molecular formula of faujasite [(Mg, Na2, Ca)3.5 [Al7Si17O48]. 32(H2O)].
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Table S2. Selected physical properties of the solvents used in MAE of this study.
Solvent / Dielectric constant / Dipole moment (Debye) / Boiling point (°C) / Atrazine solubility (g L-1)Dichloromethane / 8.93 / 1.14 / 40 / 28a,b
Acetone / 20.7 / 2.91 / 56 / 31a,b
Methanol / 32.6 / 2.87 / 65 / 15a,b
Water / 78.3 / 2.3 / 100 / 0.033b,c
Dichloromethane/acetone (1:1) / — / — / 58 / —
Methanol/water (1:1) / — / — / 79 / —
Notes:
a — Solubility at 25 °C;
b — from ref. [3];
c —Solubility at 20 °C.
References
[1] Hu E, Cheng H, Hu Y. (2012) Microwave-induced degradation of atrazine sorbed in mineral micropores. Environ Sci Technol 46: 5067-5076.
[2] Hu E, Cheng H (2013) Impact of surface chemistry on microwave-induced degradation of atrazine in mineral micropores. Environ Sci Technol 47: 533-541.
[3] International Agency for Research on Cancer (1999) IARC Monograph on the Evaluation of the Carcinogenic Risks to Humans, Vol. 73, Some Chemicals that Cause Tumours of the Kidney or Urinary Bladder in Rodents, and Some Other Substances. International Agency for Research on Cancer, Lyon.
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