Supporting Information. Facile design of phase separation for microfluidic. droplet-based liquid phase microextraction as a front end to

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1 Supporting Information Facile design of phase separation for microfluidic droplet-based liquid phase microextraction as a front end to electrothermal vaporization-icpms for the analysis of trace metals in cells Xiaoxiao Yu, Beibei Chen, Man He, Han Wang, Songbai Tian, Bin Hu * Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University, Wuhan , China Content Figure S1-S6 Table S1-S3 * Corresponding author: Fax: ; Tel: ; binhu@whu.edu.cn S1

2 Figure S1 The profile of 2 µl water droplets on (a) native PDMS and PDMS substrates modified with (b) PDA and (c) PDA/BSA. Figure S2 Microscope images of stable droplets in (a) the corner and (b) the serpentine extraction zone. S2

3 Figure S3 The SEM of the stainless steel bar s rough contour s (a) width and (b) depth, and a simplified graphic of stainless steel bar s surface (c). S3

4 2.0E6 Cd Hg Pb Bi Signal intensity(counts) 1.5E6 1.0E6 5.0E Concentration of DDTC(% (m/v)) Figure S4 Effect of DDTC (%(m/v)) concentration on the signal intensity of Cd, Hg, Pb and Bi. (c Cd, Hg, Pb, Bi = 2 µg L -1 ; extraction channel length: 470 mm; main channel width: 200 µm; aqueous phase flow rate: 20 µl min -1 ; organic phase flow rate: 1 µl min -1 ; ph=9) 1.5E6 Cd Hg Pb Bi Signal intensity(counts) 1.0E6 5.0E Flow rate of organic phase(µl min -1 ) Figure S5 Effect of flow rate of organic phase on the signal intensity of Cd, Hg, Pb and Bi. (c Cd, Hg, Pb, Bi = 2 µg L -1 ; extraction channel length: 1850 mm; main channel width: 400 µm; the flow rate ratio of aqueous phase to oil phase was 35; ph=9; 0.5% (m/v) DDTC) S4

5 Figure S6 Line flow rate of the section of inlets. (aqueous phase flow rate: 35 µl min -1 ; organic phase flow rate: 1 µl min -1 ) S5

6 Table S1 Operation conditions of ICP-MS and temperature programs of graphite furnace for ETV-ICPMS. Electrothermal vaporizer ICPMS Time-resolved data acquisition Sample volume 5 µl Drying step 200 o C, ramp 5 s, hold 12 s Vaporization step Cooling step Clean step 1500 o C, hold 5 s 200 o C, hold 4 s 2300 o C, hold 4 s Rf power 1200 W Outer gas flow rate 14 L min -1 Carrier gas flow rate 0.75 L min -1 Sampling depth 6.8 mm Sampler/skimmer diameter orifice Nickel 1.0 mm/0.4 mm Scanning mode Peak-hopping Dwell time 20 ms Isotopes for detection 111 Cd, 202 Hg, 208 Pb, 209 Bi Integration mode Peak area Points per spectral peak 1 Table S2 Relevant parameters in our theoretical model Density (kg/m 3 ) Line velocity of inlets a (m/s) Dynamic viscosity (Pa s) Surface tension force (N/m) Water n-octanol a : Input value of the line velocity of inlets for water and n-octanol was based on the optimal flow rate conditions (see Effect of the size of oil droplets and extraction conditions in main manuscript), and the line velocity data of water and n-octanol was shown in Figure S6. S6

7 Table S3 Tolerance limits of coexisting ions to target elements Coexisting ions Tolerance concentration (µg ml -1 ) Cd Hg Pb Bi K Na Ca Mg Cu Zn Fe Al NO Cl SO 4 3- PO Table S4 Comparison of analytical performance of this method with other Methods Microfluidic droplet-based LPME-ETV-ICPMS analytical approaches for the determination of Cd, Hg, Pb and Bi LOD (ng L -1 ) Sample Enrichment factor volume Cd Hg Pb Bi Cd Hg Pb Bi (µl) Chip-based LPME-ETV-ICPMS [1] Chip-based MSPME-ETV-ICPMS [2] On-line chip-based array MSPME-ICPMS [3] Microfluidic desorption-free MSPE-ICPMS [4] AuNPs modified chip-icpms [5] Online dipole-assisted SPE microchip-icpms ca.5 - [6] High-throughput SPE-ICPMS ca.2 - [7] Chip-based monolithic microextraction-icpms a [8] Chip-based array monolithic microextraction-icpms a 12.5 a 12.5 a [9] a : theoretical enrichment factor. S7 Ref. This work

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