Supporting Information (SI) Headspace Solid-Phase Microextraction Coupled to. Miniaturized Microplasma Optical Emission Spectrometry

Transcription

1 Supporting Information (SI) Headspace Solid-Phase Microextraction Coupled to Miniaturized Microplasma Optical Emission Spectrometry for Detection of Mercury and Lead Chengbin Zheng,, Ligang Hu, Xiandeng Hou, Bin He,* and Guibin Jiang State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing , China Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan , China S1

2 Table of Contents 1. Background Correction Method. 2. Atomic Emission Lines Generated with PVG-PD-OES Using N 2 or He as Discharge Gas 3. Effect of Discharge Voltage on the Atomic Emission Intensities of Hg and Pb. 4. Intensities of Molecular Emission of OH and Atomic Emissions of Hg and Pb Obtained at Different Extraction Temperature 5. Effect of Desorption Temperature on the Peak Shape of Atomic Emission of Hg and Pb. 6. Effects of Ionic Strength and Stir Rate on Responses of Atomic Emission for Hg and Pb 7. Interferences of coexisting Ions on the Determination of 2 μg L -1 of Hg (II) and Pb (II) 8. Precision S2

3 1. Background Correction Method According to previous works, a similar background correction method was used to improve the stability for the sensitive determination of Hg and Pb by simultaneously recording the responses of Hg nm, Pb nm and the background emission intensities at nm and nm. The net emission intensities of Hg nm and Pb nm were obtained by subtracting the background signals at and nm from the signals obtained at analytical emission lines. S3

4 2. Atomic Emission Lines Generated with PVG-PD-OES Using N 2 or He as Discharge Gas Figure S1. Atomic emission lines generated with PVG-PD-OES using N 2 or He as discharge gas. S4

5 3. Effect of Discharge Voltage on the Atomic Emission Intensities of Hg and Pb. It is should be noted that stable PD microplasma could not be obtained when the discharge voltage between the tungsten electrodes was lower than 1.8 kv. Thus, effect of the discharge voltage on the emission intensities was investigated in the range of 1.8 to 3.2 kv. As shown in Figure S2b, the net-emission intensities of Hg and Pb increased with the discharge voltage increased to 2.5 kv, and then kept stable at higher voltage. Therefore, a discharge voltage of 2.5 kv was adopted for subsequent experiments. As such, power consumption is less than 10 W. Figure S2. Effects of instrumental parameters on the PD microplasma. (a) Argon flow rate; (b) discharge voltage. S5

6 4. Intensities of Molecular Emission of OH and Atomic Emissions of Hg and Pb Obtained at Different Extraction Temperature Figure S3. Intensities of molecular emission of OH at 283 nm, atomic emissions of Hg at nm and Pb at nm obtained at different extraction temperature (35-50 C). S6

7 5. Effect of Desorption Temperature on the Peak Shapes of Atomic Emission of Hg and Pb Figure S4. Effect of desorption temperature on the peak shapes of atomic emission for Hg (a) and Pb (b). S7

8 6. Effects of Ionic Strength and Stir Rate on Responses of Atomic Emission for Hg and Pb Addition of salt (usually NaCl) can increase the ionic strength of solution, which always decreases the solubility of non-polar compounds in liquid phase. Therefore, the effect of ionic strength on the HS-SPME of Hg and Pb was investigated by adding various concentration of NaCl. As can be seen from Figure S5, the response of Pb increased with NaCl concentration from 0% to 30% (w/v), whereas the response from Hg is significantly decreased with increasing concentration of NaCl. This is because that the concentration of Hg 2+ in the solution is reduced via formation of complex between Hg 2+ and Cl - at high concentration of NaCl, thus decreasing the signal of Hg. Meanwhile, the effect of stir rate on responses from Hg and Pb were also studied. The results summarized in Figure S5b show that responses of Hg and Pb increased significantly with increasing concentration of formic acid throughout the range rpm, followed by a plateau at higher stir rate. A stir rate of 1000 rpm was thus used for subsequent experiments. Figure S5. Effect of ionic strength (a) and stir rate (b) on responses of atomic emission for Hg and Pb. S8

9 7. Interferences of Coexisting Ions on the Determination of 2 μg L -1 of Hg(II) and Pb(II) Table S1. Influence of Concomitant Ions on Recovery of Response from Hg (II) and Pb (II) a Concomitant Ions [M n+ ], μg L -1 Recovery-Hg, % Recovery-Hg, % K Ca Na Mg Cu Cd (2000) 92 (68) 94 (55) Ni Fe Sn (2000) 88 (43) 87 (50) AsO (2000) 86 (45) 88 (62) Cl NO 3 - SO a 2 μg L -1 of Hg 2+ and 2 μg L -1 of Pb 2+ ; typical precision of recovery is ±3% RSD. S9

10 8. Precision Figure S6. Temporal emission profiles of seven consecutive measurements of 1 µg L 1 Hg or 1 µg L 1 Pb standard solution. S10