Tracking the Transformation of Nanoparticulate and Ionic Silver at

Oct 11, 2017 - Copyright © 2017 American Chemical Society. *E-mail: [email protected]. Phone: +86-10-62849192. ACS AuthorChoice - This is an open acc...
0 downloads 9 Views 1022KB Size
Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article

Tracking the Transformation of Nanoparticulate and Ionic Silver at Environmentally Relevant Concentration Levels by Hollow Fiber Flow Field-Flow Fractionation Coupled to ICPMS Zhiqiang Tan, Yongguang Yin, Xiaoru Guo, Meseret Amde, Myeong Hee Moon, Jing-fu Liu, and Guibin Jiang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03439 • Publication Date (Web): 11 Oct 2017 Downloaded from http://pubs.acs.org on October 12, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29

Environmental Science & Technology

1

Tracking the Transformation of Nanoparticulate and Ionic Silver at

2

Environmentally Relevant Concentration Levels by Hollow Fiber Flow

3

Field-Flow Fractionation Coupled to ICPMS

4 5

Zhi-Qiang Tan,† Yong-Guang Yin,† Xiao-Ru Guo,† Meseret Amde,†

6

Myeong Hee Moon, ‡ Jing-Fu Liu,*,† and Gui-Bin Jiang†

7 8



9

Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research

10

100085, China

11



12

* Corresponding Author

13

*E-mail: [email protected]. Phone: +86-10-62849192.

Department of Chemistry, Yonsei University, Seoul 03722, Korea

1

ACS Paragon Plus Environment

Environmental Science & Technology

14

ABSTRACT

15

It is a great challenge to monitor the physical and chemical transformation of

16

nanoparticles at environmentally relevant concentration levels, mainly because the

17

commonly used techniques like dynamic light scattering and transmission electron

18

microscope are unable to characterize and quantify trace level nanoparticles in

19

complex matrices. Herein, we demonstrate the on-line coupled system of hollow fiber

20

flow field-flow fractionation (HF5), mini-column concentration and inductively

21

coupled plasma mass spectrometry (ICPMS) detection as an efficient approach to

22

study the aggregation, and chemical transformation of silver nanoparticles (AgNPs)

23

and ionic Ag species in the aqueous environment at ng/mL levels. Taking advantage

24

of the in-line dialysis of HF5, the selective capture of Ag(I) species by the resin in

25

mini-column, and the high selectivity and sensitivity of ICPMS detection, we

26

recorded the aggregation of 10 ng/mL AgNPs in complex matrices (e.g., NOM,

27

Na+/Ca2+); revealed an interesting tiny AgNPs formation process of photo-reduction

28

of trace level Ag(I) that is different from larger AgNPs generated at high

29

concentration of Ag(I) by accurate characterization; and respectively identified and

30

quantified newly born thiol-complexed Ag(I) and residual Ag(I) in the

31

inter-transformation of Ag(I) and AgNPs in domestic wastewater by simultaneously

32

detecting the S and Ag signals via ICPMS.

2

ACS Paragon Plus Environment

Page 2 of 29

Page 3 of 29

Environmental Science & Technology

33

■INTRODUCTION

34

Silver nanoparticles (AgNPs) have drawn remarkable attention from the scientific

35

community in recent years, mainly due to their wide applications, high environmental

36

reactivity, and potential risks.1-3 Once released into aquatic environments, AgNPs are

37

likely to undergo a variety of transformations like aggregation,4-6 dissolution and

38

re-reduction,7,8 which can affect the transport, bioavailability, and toxicity of AgNPs.

39

To understand the transformations and potential risk of AgNPs, it is crucial to

40

characterize and determine the pristine AgNPs and formed Ag species at

41

environmentally relevant conditions. Studying the aggregation processes of AgNPs is

42

of importance as it significantly affects its transport, transformation and toxicity in the

43

environment.7 However, evaluating the aggregation of AgNPs at environmentally

44

relevant concentrations in complex matrices remains challenging. While dynamic

45

light scattering (DLS) serves as a classic technique to monitor the size change in

46

studying the aggregation of AgNPs,9 it is unable to distinguish AgNPs from the

47

coexisting suspended particulates such as natural organic matter (NOM) aggregates

48

sized from nm to µm. More importantly, the low sensitivity of DLS makes it only

49

applicable for measuring particulate materials at relatively high concentration (e.g.,

50

µg/mL).10-12 Transmission electron microscopy (TEM) is also usually used to probe

51

the size distribution and variation of AgNPs, but TEM observation has to be

52

performed at relatively high nanoparticle concentrations (> µg/mL), otherwise a lot of

53

TEM images are needed to obtain their particle size information.13

54

Besides aggregation, it is also important to understand the chemical

55

transformation of AgNPs and ionic Ag species (IAg) that is relevant to the size- and

56

species-correlated toxicological effects in the environment. Because of the medium

57

redox potential of silver,14 both oxidative dissolution of AgNPs into Ag(I) and 3

ACS Paragon Plus Environment

Environmental Science & Technology

58

reduction of Ag(I) into AgNPs were observed simultaneously in the environment, 15-18

59

thus IAg and AgNPs are deemed to be coexisting in AgNPs colloids and the

60

environment. Moreover, it was generally recognized that IAg and small sized AgNPs

61

express pronounced toxic effect in comparison to the large sized AgNPs.19-21

62

Therefore, it is essential to distinguish the various environmentally relevant chemical

63

species of AgNPs. Ultrafiltration22 or cloud point extraction23 could effectively

64

achieve separation of IAg from AgNPs, but commonly were used as off-line

65

pretreatments before characterization or quantification. Although X-ray absorption

66

fine structure or X-ray fluorescence spectroscopies showed excellent separation

67

resolution for Ag species in complex matrices,24,25 these techniques failed to directly

68

analyze Ag species at environmentally relevant concentration levels due to their

69

limited sensitivity. Inductively coupled plasma-mass spectrometry (ICPMS) featured

70

with accurate determination of elements and multi-elemental analysis with high

71

sensitivity and wide dynamic range.26 Single particle ICPMS (SP-ICPMS) has gained

72

great attention in analysis of AgNPs and dissolved Ag(I) with the advantage of

73

simplicity and speed, but its applicability in complex samples is limited due to matrix

74

effects.27,28 Moreover, the size characterization sensitivity is low (~20 nm) for

75

AgNPs.29 Therefore, coupling efficient and robust separation techniques with

76

sensitive detectors (e.g., ICPMS) would pave an effective way for accurate

77

quantification and tracking transformation of Ag species at environmentally relevant

78

concentration levels in the environment.

79

Among hyphenated techniques with ICPMS as the detector, field-flow

80

fractionation (FFF) served as competitive choice to characterize AgNPs due to the

81

mild separation, high selectivity and broad application in continuous size separation

82

range (e.g., 1 nm to 100 µm).30-32 Among the FFF techniques, flow FFF was 4

ACS Paragon Plus Environment

Page 4 of 29

Page 5 of 29

Environmental Science & Technology

83

considered as the most universal mainly due to its simplicity in instrument and

84

operation and versatility in various targets analysis, thus flow FFF coupled with

85

ICPMS was regard as one of the most promising tools to characterize AgNPs.33-35

86

Poda et al. employed flow FFF coupled with ICPMS to investigate particle size

87

distribution of AgNPs in aqueous matrices including biological matrices after

88

exposure, and obtained comparable size results with that of DLS and TEM.36 Recently,

89

Lee et al. described the potential applicability of flow FFF offline hyphenated with

90

SP-ICPMS in characterizing AgNPs in real aqueous samples.37 Collectively, the

91

hyphenation of AF4 and ICP-MS was proved to be a suitable technique for AgNPs

92

separation and characterization in various matrices. However, in the focusing step in

93

flow FFF, Ag(I) and tiny AgNPs with diameter less than the membrane pore were

94

dialyzed and discarded as the waste35,36, thus there is no published study focused on

95

speciation analysis of IAg and AgNPs using conventional flow FFF based methods.

96

Hollow fiber flow field-flow fractionation (HF5), as an emerging variant of flow FFF,

97

featured with low cost in disposable channels and simple assembly, which effectively

98

reduced the run-to-run sample carryover problem from the sample matrix.38 In HF5,

99

separation was conducted in a cylindrical HF membrane instead of the thin

100

ribbon-like open channel in conventional flow FFF, and the flow field was applied

101

perpendicularly to the HF axial direction. Compared with the AF4 channel, the low

102

channel volume of HF5 channel resulted in less sample dilution. The reduced radial

103

flow rate used in HF5 made it more compatible with various detectors (especially

104

ICPMS), and sample fractions dialyzed during focusing process and eluted during

105

fractionation process could be easily collected for further analysis.39 A recent study

106

described the coupling of HF5 with multi angle light scattering detector to

107

characterize the dispersed AgNPs in aqueous media, and to off-line quantify the 5

ACS Paragon Plus Environment

Environmental Science & Technology

108

separately collected Ag(I) and AgNPs.40 To improve applicability of HF5-based

109

method in Ag speciation analysis, we recently on-line coupled HF5 and mini-column

110

concentration (MCC) with multiple detectors including UV−vis spectrometer (UV),

111

DLS and ICPMS for identification, characterization, and quantification of two IAg(I)

112

species and five different sized AgNPs at ng/mL level,41 demonstrating its potential

113

for studying the transformation of Ag species at environmentally relevant

114

concentrations.

115

In this work, by using our recently developed hyphenated method,41 we

116

investigated the aggregation and chemical transformation of AgNPs and IAg species

117

in aqueous environments at environmentally relevant concentrations. The aggregation

118

of trace level AgNPs in the presence of NOM and Na+/Ca2+ was monitored for the

119

first time via the size distribution and variation of AgNPs depicted in the ICPMS

120

elution profiles. The chemical transformation products of Ag(I), different sized

121

AgNPs and thiol-complexed Ag(I) were also identified and quantified in sunlit

122

NOM-solutions and domestic wastewaters, respectively.

123

■MATERIALS AND METHODS

124

Chemicals and Materials. Citrate coated AgNPs with nominal size of 10 nm (10

125

nm-AgNP) and 20 nm (20 nm-AgNP) (each 20 µg/mL) were bought from

126

Sigma-Aldrich (St. Louis, MO). Ag(I) standard solution (GSB04-1712-2004) at

127

concentration of 1000 µg/mL was purchased from the National Institute of Metrology

128

(Beijing, China). Analytical grade AgNO3 was obtained from Beijing Chemical Co.,

129

Ltd. Suwannee River natural organic matter (SRNOM) (1R101N) was bought from

130

the International Humic Substance Society (St. Paul, MN). L-Cysteine (Cys) (99%)

131

was obtained from J & K Scientific Ltd. (Beijing, China). Surfactant FL-70 and NaN3,

132

two carrier solution additives, were from Thermo (Fair Lawn, NJ) and Ameresco 6

ACS Paragon Plus Environment

Page 6 of 29

Page 7 of 29

Environmental Science & Technology

133

(Framingham, MA) respectively. Gold nanoparticles (Au NPs) with certified

134

diameters of 10 nm (8011), 30 nm (8012) and 60 nm (8013) purchased from the

135

National Institute of Standards and Technology (NIST, Gaithersburg, MD) were used

136

to calculate AgNPs diameters based on retention time (tR). Amberlite IR120 resin in

137

sodium, NaClO4, Ca(ClO4)2, Na2S2O3 and H2O2 were purchased from Sinopharm

138

Chemical Reagent Co. Ltd. (Beijing, China). The resin needed to be cleaned and

139

activated prior to use.41 The poly(ethersulfone) (PES) HF with a nominal molecular

140

mass cut-off (MWCO) of 10 kDa was bought from Kaihong Membrane Technology

141

Co., Inc. (Hangzhou, China).

142

Characterization and Quantification of Various Ag Species. HF5 was on-line

143

coupled

144

(HF5/MCC-UV/ICPMS)

145

quantification of various Ag species. Detailed configuration and operation of the

146

hyphenated system are described elsewhere41 and also provided in the Supporting

147

Information (SI). Briefly, the whole analytical run cycle consist of three on-line steps:

148

(I) focusing/relaxation of AgNPs and isolation of Ag(I) species, (II) fractionation,

149

characterization, and quantification of AgNPs, (III) quantification of Ag(I) species.

150

Given that particle retention in HF5 is dependent on the size, the particle size or size

151

distribution of the target particles can be calculated with standard particles (e.g.,

152

AuNPs).40,42 Considering the material-dependent retention behavior possibly due to

153

the particle-particle and particle- accumulation wall interactions,43 in step II the

154

AgNPs size was obtained with a calibration curve obtained by plotting tR measured

155

under the same fractionation conditions against the known size of standard AuNPs

156

(Figure S2A), the acceptable standard metallic NPs,44 from ICPMS fractograms of the

157

Au (197Au) and Ag (107Ag) signals (Figure S2B), and concentrations of fractioned

with

MCC

and

dual

detectors

to

achieve

the

including

separation,

7

ACS Paragon Plus Environment

UV

and

ICPMS

characterization,

and

Environmental Science & Technology

158

AgNPs were acquired by ICPMS (7700 series, Agilent Technologies, Palo Alto, CA).

159

Free Ag(I), newly born Ag(I) complex and AgNPs with diameter less than the HF pore

160

size, named tiny AgNPs, could be quantified respectively as follows: free Ag(I) ions

161

or weak Ag(I) complexes adsorbed onto the Amberlite IR120 resin through

162

ion-exchange with Na+ in mini-column concentration (MCC) during step I were

163

desorbed by Na2S2O3 and quantified by ICPMS detector in step III; For tiny AgNPs

164

againt absorption by the resin in MCC due to the electrostatic repulsion, they were

165

transferred directly to the detectors and quantified by ICPMS in step I. Strong Ag(I)

166

complexes co-eluted with tiny AgNPs in step I could be calculated based on the

167

difference of the detected Ag amount in the step III of the two runs with or without

168

introducing of diluted H2O2, respectively. The introducing of diluted H2O2 could

169

dissolve tiny AgNPs into Ag+ and adsorbed onto the Amberlite IR120 resin.

170

Additionally, the HF channel was replaced once the recovery of total Ag (including

171

AgNPs and IAg(I)) in the whole run was less than 65%.

172

Aggregation of AgNPs in the Presence of NOM and Mono- and Divalent Cations.

173

In view of that chloride (e.g., from NaCl, CaCl2) could induce the bridging between

174

individual citrate coated AgNPs due to AgCl deposit from dissolved Ag(I) ions,45 a

175

series of aqueous solutions of NaClO4 and Ca(ClO4)2 were chosen to evaluate the

176

influences of mono- and divalent cations on the aggregation of AgNPs (10 ng/mL) in

177

NOM solutions. Firstly, influences of focusing time and NOM concentration on the

178

size of AgNP aggregates were investigated to confirm the capability of HF5 to

179

maintain AgNPs intact in complex matrices through the whole separation.

180

Furthermore, the scanning transmission electron microscopy (STEM, JEOL,

181

JEM-2010F, Japan) with energy-dispersive X-ray spectroscopy (EDS) is used to

182

determine the shape and the distribution of different elements on the surface of AgNPs 8

ACS Paragon Plus Environment

Page 8 of 29

Page 9 of 29

Environmental Science & Technology

183

incubated with NOM with resolution 0.02 nm at 200 kV. Given that critical

184

coagulation concentrations for 2 µg/mL citrate coated AgNPs in NaClO4 and

185

Ca(ClO4)2 were 81.55 mM and 2.11 mM in the presence of pristine NOM,9 various

186

amount of NaClO4 (0.01-100 mM) and Ca(ClO4)2 (0.001-5 mM) were selected to

187

incubate with 10 ng/mL 10 nm-AgNP in NOM (20 µg/mL dissolved organic matter,

188

DOC) aqueous solution at pH 7.4 adjusted by 5 mM borate buffer at room

189

temperature for 1 hour. The HF5/MCC-UV/ICPMS system directly provided size

190

information about the AgNPs reacted.

191

Transformation of Ag(I) into AgNPs under Simulated Natural Conditions. Two

192

significantly different concentrations of AgNO3 (33.97 µg/mL and 33.97 ng/mL

193

respectively) and SRNOM (20 µg/mL DOC) were separately added into borate buffer

194

(5 mM, pH 8.0) under sunlight. A UV-vis spectrometer (UV-3600, Shimadzu, Japan)

195

was employed to monitor AgNPs generated during the first 6 hours. The size of

196

AgNPs formed in 0.2 mM AgNO3 solution was characterized ex situ by high

197

resolution TEM (2100F, JEOL, Japan; details for TEM sample preparation are

198

described elsewhere41). Both a fraction (10 times dilution) of AgNPs formed in 33.97

199

µg/mL AgNO3 solution and AgNPs generated in 33.97 ng/mL AgNO3 solution were

200

characterized and quantified by our proposed system directly.

201

Inter-Transformation

202

Inter-transformation of Ag(I) and AgNPs was conducted in domestic wastewater

203

obtained from a municipal wastewater treatment plant (WWTP) located in Qinghe

204

(Beijing, China). In the preliminary experiment, the concentrations of Ag(I) and

205

AgNPs in the influent of WWTP were found to be below the limit of detection (LOD)

206

of the proposed system. Therefore, the influent was spiked with Ag(I) and 10

207

nm-AgNPs (each 10 ng/mL) for this study. After 1 h, the mixture was directly

of

Ag(I)

and

AgNPs

in

9

ACS Paragon Plus Environment

Domestic

Wastewater.

Environmental Science & Technology

208

analyzed by HF5/MCC-DLS/UV/ICPMS system to examine the inter-transformation

209

products.

210

■RESULTS AND DISCUSSION

211

Aggregation of AgNPs in the Presence of NOM and Mono- or Divalent Cations.

212

To verify the applicability of the developed HF5/MCC-UV/ICPMS system to

213

characterize the aggregation of AgNPs, the possible impact of the relaxation/focusing

214

step on the size of aggregated AgNPs was assessed by measuring the average size of

215

aggregated AgNPs in NOM (20 µg/mL DOC, average concentration in natural surface

216

water46) solutions containing 10 mM NaClO4 and 0.5 mM Ca(ClO4)2, respectively,

217

with focusing times in the range of 4-8 min. Results presented a slight impact of the

218

focusing time on AgNP aggregation (data not shown). To evaluate in-line cleanup of

219

complex matrices, we compared the tR values of AgNPs in samples containing just

220

different concentrations of NOM (0, 10, 20, 50, 100 µg/mL DOC). Interestingly, the

221

elution profile of the ICPMS detector shows a slightly gradual increase of tR from

222

11.9 ± 0.14 min to 17.3 ± 0.26 min (mean ± SD, n = 3) as NOM concentration

223

increased from 0 to 100 µg/mL DOC. As shown in Figure 1A, the diameter of the

224

dominant AgNPs, calibrated from the linear regression equation of diameter of the

225

standard AuNPs against tR, increased from 8.8 ± 0.39 nm to 23.2 ± 0.70 nm (mean ±

226

SD, n = 3), demonstrating the probable formation of “NOM corona” structures around

227

AgNPs.47 To testify whether the increment of retention time in the presence of NOM

228

was resulted from the carry-over of HF used in complex matrices, we evaluated the

229

AgNPs size variation at a relatively high NOM concentration (50 µg/mL DOC) with a

230

new HF membrane. No significant change in retention times was observed for AgNP

231

colloids injected before and after NOM injection, verifying the fact that the adsorption

232

of NOM onto the membrane was largely minimized due to the electrostatic repulsion 10

ACS Paragon Plus Environment

Page 10 of 29

Page 11 of 29

Environmental Science & Technology

233

in view of the alkaline mobile phase (pH 9.6) used and the negatively charged PES

234

membrane.48 The identical extended retention time of AgNPs to that by HF used for

235

several times indicates that the changes in tR (especially in high NOM concentration)

236

could be ascribed to “NOM corona” structures forming rather than the carry-over

237

effect. To further verify the corona structure, STEM-EDS was adopted to investigate

238

nanostruactures and element distribution of AgNPs in the NOM solution (50 µg/mL

239

DOC) after incubation at room temperature for 1 hour. The red rectangular frame in

240

Figure 1B defines the region for mapping Ag, C and O distribution. Both C and O

241

enrichment areas significantly overlap Ag-enriched area, demonstrating the NOM

242

wrapping around AgNPs to form corona structure, which could lead to the increment

243

of hydrodynamic size of AgNPs in aqueous solution.

244 245

Figure 1. Effect of the NOM concentration on the average size of AgNPs (10

246

nm-AgNP, 10 ng/mL) in the presence of different amount of NOM (0, 10, 20, 50, 100

247

µg/mL DOC) (A) and STEM images and EDS mapping results of Ag, C and O (5

248

µg/mL 10 nm-AgNPs in 50 µg/mL NOM).

249

Then, aggregation of 10 ng/mL AgNPs in 20 µg/mL NOM solutions containing

250

various amount of NaClO4 (0.01-100 mM) was studied. Only NOM peaks were found

251

in the initial 8 min of the UV-vis elution profile (Figure S3A), due to the low

11

ACS Paragon Plus Environment

Environmental Science & Technology

252

sensitivity of UV detector. In the HF5-ICPMS elution profile (Figure 2A), both the tR

253

and peak shape of AgNPs changed with the increase of NaClO4 concentration,

254

demonstrating the aggregation of AgNPs even in the presence of NOM. The diameter

255

of the dominant AgNPs, calculated from the tR, progressively increased from 12.5 nm

256

to 24.7 nm with NaClO4 concentration (0.01–100 mM) (Figure 2B). The aggregation

257

of AgNPs was further investigated in the presence of 0.001–5 mM Ca(ClO4)2. Similar

258

to that of NaClO4, no significant peak of AgNPs was found here in the UV-vis elution

259

profile (Figure S3B). As shown in the ICPMS elution profiles (Figures 2C and 2D),

260

the dominant AgNP diameter increased from 11.5 nm to 18.2 nm. Variation in both the

261

retention time and peak shape of the dominant AgNPs eluted in Ca(ClO4)2 solutions

262

was more significant than that in the presence of the same concentration of NaClO4,

263

agreeing with the previous results that Ca2+ ions had a greater electrostatic screening

264

effect on AgNPs compared with Na+ ions.49 Given that the AgNPs colloids used

265

inevitably contain smaller particles with diameters less than the nominate 10 nm, the

266

peak appeared before 10 min in step (II) (Figures 2A and 2C) may stem from small

267

single dispersed AgNPs.50 In view of that high ionic strength promotes NOM

268

aggregation,51 one possible explanation for the slight change of tR for NOM peaks

269

with increasing salt concentration (Figure S3) is that the compact structure of

270

aggregated NOM at high salt concentrations promotes their dialyzing during focusing.

271

Moreover, the increased ionic strength could effectively shield the electrostatic

272

repulsion between NOM and membrane.52 Therefore, the retention time of NOM peak

273

decreased with increasing salt concentration. To some extent, NOM could provide

274

charge or steric stabilization of nanomaterial to enhance their dispersion, but this

275

dispersing effect was significantly minimized at higher ionic strength solution.47 Flow

276

field-flow fractionation, as a mild separation method, has proven to be a successful 12

ACS Paragon Plus Environment

Page 12 of 29

Page 13 of 29

Environmental Science & Technology

277

alternative for DLS in investigating aggregation behavior of nanoparticles,53,54 but the

278

hyphenation with relatively insensitive detectors (UV or multi-angle light scattering)

279

has been an obstacle for its application in low concentration of nanoparticles. In spite

280

of the similar aggregation of AgNPs at µg/mL level to that at ng/mL as reported,9 the

281

hyphenated system here for the first time provided a promising approach to track

282

aggregation of AgNPs at environmentally relevant concentration due to the high

283

efficient separation capability of HF5 and sensitive detection of Ag by ICPMS.

284 285

Figure 2. Elution profiles of ICPMS (A and C) and size (B and D) of AgNPs (10

286

ng/mL 10 nm-AgNP) in NOM solution (20 µg/mL DOC) (Error bars in B and D

287

represent one standard deviation of three replicates). Operation procedures:

288

focusing/relaxation of AgNPs and isolation of Ag(I) (I), fractionation and

289

characterization of AgNPs (II), and quantification of Ag(I) (III). Experimental

290

conditions: PES HF channel, 10 kDa pore cut-off; injected volume, 100 µL; carrier

291

solution, 0.1% (v/v) FL-70 with 0.02% (w/v) NaN3; inlet flow rate, 1.50 mL/min;

292

radial flow rate, 0.60 mL/min; axial flow, 0.90 mL/min; focusing time, 8 min; eluting

293

flow rate, 0.90 mL/min. 13

ACS Paragon Plus Environment

Environmental Science & Technology

294

Transformation of Ag(I) to AgNPs in Photoreduction of NOM. To compare

295

characterization capability of the proposed method with the TEM method, a high

296

amount of AgNPs was generated in the NOM solution (20 µg/mL DOC) containing

297

33.97 µg/mL AgNO3 incubated under natural sunlight. The picture (Figure S4A) and

298

the UV-vis spectra (Figure S4B) indicate that the photo-transformation of Ag(I) into

299

AgNPs reached equilibrium in less than 6 h. Figure 3A presents the

300

HF5/MCC-UV/ICPMS elution profile of AgNPs and Ag(I) in the irradiated solution

301

after 10-fold dilution, as recorded by UV and ICPMS detectors. The mean particle

302

diameters corresponding to these two peaks (tR= 5.6 and 7.9 min), calculated from tR,

303

were around 2.4 and 8.4 nm, agreeing well with the bimodal size distribution (2.3 nm

304

and 7.3 nm diameter) observed by TEM measurements (Figures 3C and D). It is

305

understandable that the particle diameter measured by TEM is smaller than the

306

hydrodynamic diameter measured by the HF5/MCC-UV/ICPMS (e.g. 7.3 nm by TEM

307

vs 8.4 nm by HF5-ICPMS). For the smaller AgNPs, the similar diameter from TEM

308

(2.3 nm) compared with that from HF5-ICPMS (2.4 nm) again verified the

309

comparable characterization capability of the proposed method with TEM. Therefore,

310

considering the difficulties of TEM in recognizing and counting smaller or tiny

311

AgNPs, the present method could provide more accurate information on a wider range

312

of particle size distributions. The final sharp peak (tR= 16.5 min) in the ICPMS profile

313

suggests that there was still a large amount of unreacted free Ag(I) in the sample. The

314

relative amount of Ag(I) calculated from the ratio of Ag(I) (tR = 16.5 min) and AgNPs

315

(tR = 5.6 and 7.9 min) is 17.6%, which is slightly lower than the one obtained by

316

ultrafiltration-ICPMS (21%) (details in the SI). It should be noted that in the

317

ultrafiltration procedure, the photo-produced tiny AgNPs could possibly penetrate the

318

membrane into the filtrate,18 and thus overestimate the unreacted Ag(I). 14

ACS Paragon Plus Environment

Page 14 of 29

Page 15 of 29

Environmental Science & Technology

319

A trace amount of AgNO3 as low as 33.97 ng/mL was then reacted with NOM

320

(20 µg/mL DOC) to track the transformation of Ag(I) at environmentally relevant

321

concentrations. As show in Figure 3B, in the focusing/relaxation step (step I, tR < 8

322

min), the detected wide peak was ascribed to tiny AgNPs. Two peaks (tR = 8.4 and 8.9

323

min) in the fractionation step (step II, 8 min < tR < 20 min) were assigned to the void

324

peak and larger AgNPs (mean diameter 2.3 nm), respectively. The peak from the

325

residual free or weak complex of Ag(I) trapped by the resin and desorbed by Na2S2O3

326

was recorded in the elution step (step III, tR > 20 min). To further verify the

327

assignation of the wide peak (tR < 8 min), we conducted a second run by introducing

328

diluted H2O2 (2%, v/v) in the radial outlet, in which procedure only tiny AgNPs,

329

rather than thoil-binding Ag(I), could be oxidized into Ag(I) as previously observed.41

330

This peak disappeared in the second run, and the Ag(I) peak increased

331

correspondingly. The ratio of peak area of tiny AgNPs (tR < 8 min) in the first run to

332

the incremental peak area of Ag(I) in the second run is 95%, further verifying the

333

wide peak in the focusing/relaxation step almost solely belongs to the tiny AgNPs.

334

The formation of tiny AgNPs and absence of larger AgNPs (e.g., 8.4 nm in Figure 3A)

335

at 21.6 ng/mL Ag(I) precursor suggested that low concentrated Ag cluster could

336

constrain their fusion and subsequent formation of larger AgNPs.55 This result also

337

highlights the necessity of studying the transformation of Ag(I) at environmentally

338

relevant concentrations.

339

It is noteworthy that during the 6 h irradiation, there is no significant color

340

change for the two NOM solutions with and without AgNO3 (Figure S4C), which was

341

consistent with the UV-vis results in Figure S4D. Unfortunately, the amount of AgNPs

342

formed were also too low to be identified by TEM, even with more than 50 µL of the

343

AgNPs solution successively loaded on the carbon coated copper grid (TEM images 15

ACS Paragon Plus Environment

Environmental Science & Technology

344

not shown). These results demonstrated that the proposed method is superior to

345

UV-vis and TEM in tracking tiny AgNPs formation process of photo-reduction of

346

trace level Ag(I), which is significantly meaningful considering the low concentration

347

of Ag(I) in real aqueous environments. Of note, this study does not aim to simulate

348

real-world formation of AgNPs, instead it is a fundamental study on understanding the

349

role of NOM in transformation of different amount of Ag(I) to AgNPs, so nucleation

350

and formation of AgNPs with increased incubation time are beyond the scope of the

351

study.

352 353

Figure 3. HF5/MCC-UV/ICPMS elution profile of mixtures of NOM and AgNO3 at a

354

concentration of 33.97 µg/mL (A) and 33.97 ng/mL (B), TEM image (C) and

355

size-distribution (D) of the photo-reduced AgNPs in NOM solution containing 33.97

356

µg/mL AgNO3. Operation procedures: focusing/relaxation of AgNPs and isolation of

357

Ag(I) (I), fractionation and characterization of AgNPs (II), and quantification of Ag(I)

358

(III). Experimental conditions: PES HF channel, 10 kDa pore cut-off; injected volume,

359

100 µL; carrier solution, 0.1% (v/v) FL-70 with 0.02% (w/v) NaN3; inlet flow rate,

360

1.50 mL/min; radial flow rate, 0.60 mL/min; axial flow, 0.90 mL/min; focusing time, 16

ACS Paragon Plus Environment

Page 16 of 29

Page 17 of 29

Environmental Science & Technology

361

4 min (A) or 8 min (B); eluting flow rate, 0.90 mL/min.

362

Inter-Transformation of Ag(I) and AgNPs in Domestic Wastewater. The notable

363

performance of the proposed method encouraged us to further apply it to track the

364

inter-transformation of Ag(I) and AgNPs in the influent of WWTP, which is one of

365

the major sinks of the released Ag(I) and AgNPs from industrial and

366

consumer products.56 As shown in Figure 4, a new peak (tR = 2.3 min) appeared in the

367

focusing/relaxation step (step I), indicating the spiked Ag(I) and AgNPs ( each 10

368

ng/mL) partially transformed into the thoil-binding Ag(I) (Ag-SR) or tiny AgNPs,

369

though the free Ag(I) can still be detected in the final elution step (step III). In

370

preliminary experiments, the concentration of S2- in the influent sample was found to

371

be less than 2.0 ng/mL, the LOD of ion chromatographic system (ICS-5000, Thermo

372

Fisher Scientific Inc.) equipped for amperometry with a silver working electrode, thus

373

the transformation of Ag(I) into Ag2S NPs was negligible. To ascertain Ag-SR and

374

tiny AgNPs, the signals of S (48S) and Ag (107Ag) were simultaneously recorded by

375

another ICPMS (8800 series, Agilent Technologies, Palo Alto, CA). For both the

376

blank and spiked samples, a peak (tR = 2.3 min) was detected in the ICPMS profile of

377

48

378

suggested that the new 107Ag peak at tR = 2.3 in the spiked sample should be ascribed

379

to Ag-SR. Unfortunately, the component of Ag-SR could not be further identified

380

based on our available detectors, but could be off-line identified by other techniques

381

(e.g., electrospray ionization mass spectrometry) in the future study. To test if tiny

382

AgNPs were present in the transformation process, peak areas of the new 107Ag peak

383

with or without the introduction of H2O2 in the focusing step were compared. No

384

significant difference in peak areas was observed, indicating the absence of tiny

385

AgNPs. Furthermore, we tried to indirectly identify the new

S, with tR and peak shape agreed well with the new

107

Ag peak (tR = 2.3 min). This

17

ACS Paragon Plus Environment

107

Ag peak by injecting

Environmental Science & Technology

386

Ag(I) and the mixture of Ag(I) and cysteine (Cys) into the system, respectively. As

387

shown in Figure S5, the Ag-Cys peak (tR = 2.5 min) detected in the mixture of Ag(I)

388

and Cys agreed well with the Ag-SR peak (tR = 2.3 min) in the spiked wastewater

389

sample. These results suggest that the new

390

wastewater samples could be solely assigned to Ag-SR, indicating the great potential

391

of the proposed method in separation and identification of various species of Ag(I). In

392

the fractionation step (step II), the spiked AgNPs were eluted at 8.1 min. To test the

393

proposed method in quantifying different species of Ag in complex matrices, the

394

recovery of total Ag (including free Ag(I), Ag-SR and AgNPs) in spiked solutions

395

was calculated to be within a range from 69.3% to 112%, demonstrating the reliability

396

of the proposed method. Despite the fact that ICPMS equipped with triple quadrupole

397

ICP-MS (ICP-QQQ) is recognized to be able to sensitively and selectively determine

398

S element, no obvious peak was observed in the range of 4-15 min (i.e., the

399

fractionation and characterization of NP step) aside from thiol-complexed Ag(I)

400

together with NOM identified before 4 min in Figure 4, indicating the absence of

401

Ag2S as the sulfidation product of Ag(I) or AgNPs. The relative short reaction period

402

(i.e., 1 h) in this study likely accounts for the subtle displacement of citrate by S.

403

Thus, long-term incubation (e.g., 120 h57) usually needed for the displacement and

404

sulfidation is worthy to study in future.

107

Ag peak detected in the spiked

18

ACS Paragon Plus Environment

Page 18 of 29

Page 19 of 29

Environmental Science & Technology

405 406

Figure 4. Transformation of AgNPs and Ag(I) (both were spiked at 10 ng/mL) in an

407

influent of WWTP. Operation procedures: focusing/relaxation of AgNPs and isolation

408

of Ag(I) (I), fractionation and characterization of AgNPs (II), and quantification of

409

Ag(I) (III). Experimental conditions: PES HF channel, 10 kDa pore cut-off; injected

410

volume, 100 µL; carrier solution, 0.1% (v/v) FL-70 with 0.02% (w/v) NaN3; inlet

411

flow rate, 1.50 mL/min; radial flow rate, 0.60 mL/min; axial flow, 0.90 mL/min;

412

focusing time, 4 min; eluting flow rate, 0.90 mL/min.

413

Environmental Implication. The HF5/MCC-UV/ICPMS system provides an

414

efficient technique to investigate both physical and chemical transformations of

415

AgNPs and Ag(I) at environmentally relevant concentrations. Findings in this study

416

firmly reveal different effects of Ca2+ and Na+ on the aggregation of AgNPs at ng/mL

417

in the presence of NOM, facilitating more environmentally meaningful evaluation of

418

the physical transformation of AgNPs under more realistic conditions. The

419

remarkable difference in size of AgNPs generated from photo-reduction of Ag(I) at

420

two different concentrations discovered here again highlights the necessity of further

19

ACS Paragon Plus Environment

Environmental Science & Technology

Page 20 of 29

421

studying transformations of AgNPs and Ag(I) at environmentally relevant

422

concentrations in predicting the source and fate of AgNPs in the environment. In

423

addition, the high separation efficiency and anti-interference capability of HF5 based

424

method make it applicable to more complex biological media, such as cellular

425

cultures and body fluids, which is beneficial to estimate potential risks on human and

426

environmental health. Moreover, the high selectivity and multi-element detection

427

capability of ICPMS detection make it a prospective method in widely studying the

428

heteroaggregation (e.g., with natural suspended mineral particle) and chemical

429

transformation

430

metal-containing nanoparticles (e.g., the dissolution of CdSe quantum dot) at

431

environmentally relevant concentrations under realistic scenarios.

432

■ASSOCIATED CONTENT

433

Supporting Information Available

434

The Supporting Information is available free of charge on the ACS Publications

435

website at DOI: XXXXXX.

436

Additional experimental details and results as noted in the text.

437

Notes

438

The authors declare no competing financial interest.

439

■ ACKNOWLEDGMENTS

440

Financial support from National Key Research and Development Program of China

441

(2016YFA0203102),

442

(2015CB932003), and the National Natural Science Foundation of China (21577150,

of

AgNPs

the

(e.g.,

National

selenylation

Basic

and

Research

20

ACS Paragon Plus Environment

sulfidation)

Program

and

of

other

China

Page 21 of 29

Environmental Science & Technology

443

and 21522705) is gratefully acknowledged. Z. Q. Tan also acknowledges the support

444

from the Youth Innovation Promotion Association CAS.

445

■ REFERENCES

446

(1) Maynard, A. D.; Aitken, R. J.; Butz, T.; Colvin, V.; Donaldson, K.; Oberdorster,

447

G.; Philbert, M. A.; Ryan, J.; Seaton, A.; Stone, V.; Tinkle, S. S.; Tran, L.; Walker, N.

448

J.; Warheit, D. B. Safe Handling of Nanotechnology. Nature 2006, 444 (7117),

449

267−269.

450

(2)

451

Environ. Sci.: Process Impacts 2013, 15 (1), 78−92.

452

(3)

453

Environments: Physiochemical Behavior and Antimicrobial Mechanisms. Water Res.

454

2016, 88, 403–427.

455

(4)

456

Impact on Bacterial Growth: Effect of pH, Concentration, and Organic matter.

457

Environ. Sci. Technol. 2009, 43 (19), 7285−7290.

458

(5)

459

Preliminary Assessment of the Interactions between the Capping Agents of Silver

460

Nanoparticles and Environmental Organics. Colloid Surf., A 2013, 435 (SI), 22−27.

461

(6)

462

M.; Hinton, D. E.; Meyer, J. N. Silver Nanoparticle Behavior, Uptake, and Toxicity in

463

Caenorhabditis Elegans: Effects of Natural Organic Matter. Environ. Sci. Technol.

464

2014, 48 (6), 3486–3495.

465

(7)

466

Transformations of Silver Nanoparticles: Impact on Stability and Toxicity. Environ.

467

Sci. Technol. 2012, 46 (13), 6900−6914.

Yu, S. J.; Yin, Y. G.; Liu, J. F. Silver Nanoparticles in the Environment.

Zhang, C. Q.; Hu, Z. Q.; Deng, B. L. Silver Nanoparticles in Aquatic

Fabrega, J.; Fawcett, S. R.; Renshaw, J. C.; Lead, J. R. Silver Nanoparticle

Lau, B. L. T.; Hockaday, W. C.; Ikuma, K.; Furman, O.; Decho, A. W. A

Yang, X. Y.; Jiang, C. J.; Hsu-Kim, H.; Badireddy, A. R.; Dykstra, M.; Wiesner,

Levard, C.; Hotze, E. M.; Lowry, G. V.; Brown, G. E. Environmental

21

ACS Paragon Plus Environment

Environmental Science & Technology

468

(8)

Dale, A. L.; Lowry, G. V.; Casman, E. A. Stream Dynamics and Chemical

469

Transformations Control the Environmental Fate of Silver and Zinc Oxide

470

Nanoparticles in a Watershed-Scale Model. Environ. Sci. Technol. 2015, 49 (12),

471

7285−7293.

472

(9)

473

Coating-Dependent Interaction of Molecular Weight Fractionated Natural Organic

474

Matter: Impacts on the Aggregation of Silver Nanoparticles. Environ. Sci. Technol.

475

2015, 49 (11), 6581−6589.

476

(10) Lohrke, J.; Briel, A.; Mäder, K. Characterization of Superparamagnetic Iron

477

Oxide Nanoparticles by Asymmetrical Flow-Field-Flow-Fractionation. Nanomedicine

478

2008, 3 (4), 437– 452.

479

(11) Chowdhury, I.; Mansukhani, N. D.; Guiney, L. M.; Hersam, M. C.; Bouchard, D.

480

Aggregation and Stability of Reduced Graphene Oxide: Complex Roles of Divalent

481

Cations, pH, and Natural Organic Matter. Environ. Sci. Technol. 2015, 49 (18),

482

10886−10893.

483

(12) Loosli, F.; Le Coustumer, P.; Stoll, S. TiO2 Nanoparticles Aggregation and

484

Disaggregation in Presence of Alginate and Suwannee River Humic Acids. pH and

485

Concentration Effects on Nanoparticle Stability. Water Res. 2013, 47 (16),

486

6052−6063.

487

(13) Huynh, K. A.; Chen, K. L. Aggregation Kinetics of Citrate and

488

Polyvinylpyrrolidone Coated Silver Nanoparticles in Monovalent and Divalent

489

Electrolyte Solutions. Environ. Sci. Technol. 2011, 45 (13), 5564−5571.

490

(14) Potera, C. Transformation of Silver Nanoparticles in Sewage Sludge. Environ.

491

Health. Persp. 2010, 118 (12), A526−A527.

492

(15) Liu, J. Y.; Hurt, R. H. Ion Release Kinetics and Particle Persistence in Aqueous

Yin, Y. G.; Shen, M. H.; Tan, Z. Q.; Yu, S. J.; Liu, J. F.; Jiang, G. B. Particle

22

ACS Paragon Plus Environment

Page 22 of 29

Page 23 of 29

Environmental Science & Technology

493

Nano-Silver Colloids. Environ. Sci. Technol. 2010, 44 (6), 2169−2175.

494

(16) Yin, Y. G.; Liu, J. F.; Jiang, G. B. Sunlight-Induced Reduction of Ionic Ag and

495

Au to Metallic Nanoparticles by Dissolved Organic Matter. ACS Nano 2012, 6 (9),

496

7910−7919.

497

(17) Hou, W. C.; Stuart, B.; Howes, R.; Zepp, R. G. Sunlight-Driven Reduction of

498

Silver Ions by Natural Organic Matter: Formation and Transformation of Silver

499

Nanoparticles. Environ. Sci. Technol. 2013, 47 (14), 7713−7721.

500

(18) Yu, S. J.; Yin, Y. G.; Chao, J. B.; Shen, M. H.; Liu, J. F. Highly Dynamic

501

PVP-Coated Silver Nanoparticles in Aquatic Environments: Chemical and

502

Morphology Change Induced by Oxidation of Ag0 and Reduction of Ag+. Environ. Sci.

503

Technol. 2014, 48 (1), 403−411.

504

(19) Braakhuis, H. M.; Cassee, F. R.; Fokkens, P. H. B.; de la Fonteyne, L. J. J.;

505

Oomen, A. G.; Krystek, P.; de Jong, W. H.; van Loveren, H.; Park, M. V. D. Z.

506

Identification of the Appropriate Dose Metric for Pulmonary Inflammation of Silver

507

Nanoparticles in an Inhalation Toxicity Study. Nanotoxicology 2016, 10 (1), 63–73.

508

(20) Shen, M. H.; Zhou, X. X.; Yang, X. Y.; Chao, J. B.; Liu, R.; Liu, J. F. Exposure

509

Medium: Key in Identifying Free Ag+ as the Exclusive Species of Silver

510

Nanoparticles with Acute Toxicity to Daphnia magna. Sci. Rep. 2015, 5, 9674.

511

(21) Griffitt, R. J.; Brown-Peterson, N. J.; Savin, D. A.; Manning, C. S.; Boube, I.;

512

Ryan, R.; Brouwer, M. Effects of Chronic Nanoparticulate Silver Exposure to Adult

513

and Juvenile Sheepshead Minnows (Cyprinodon Variegatus). Environ. Toxicol. Chem.

514

2012, 31 (1), 160–167.

515

(22) Ma, R.; Levard, C. M.; Marinakos, S. M.; Cheng, Y. W.; Liu, J.; Michel, F. M.;

516

Brown, G. E.; Lowry, G. V. Size-Controlled Dissolution of Organic-Coated Silver

517

Nanoparticles. Environ. Sci. Technol. 2011, 46 (2), 752−759. 23

ACS Paragon Plus Environment

Environmental Science & Technology

518

(23) Chao, J. B.; Liu, J. F.; Yu, S. J.; Feng, Y. D.; Tan, Z. Q.; Liu, R.; Yin, Y. G.

519

Speciation Analysis of Silver Nanoparticles and Silver Ions in Antibacterial Products

520

and Environmental Waters via Cloud Point Extraction-Based Separation. Anal. Chem.

521

2011, 83 (17), 6875−6882.

522

(24) Menzel, M.; Fittschen, U. E. A. Total Reflection X-ray Fluorescence Analysis of

523

Airborne Silver Nanoparticles from Fabrics. Anal. Chem. 2014, 86 (6), 3053−3059.

524

(25) Nakazawa, E.; Ikemoto, T.; Hokura, A.; Terada, Y.; Kunito, T.; Yamamoto, T.;

525

Yamada, T. K.; Rosas, F. C. W.; Fillmann, G.; Tanabe, S.; Nakai, I. Silver Speciation

526

in Liver of Marine Mammals by Synchrotron X-ray Absorption Fine Structure and

527

X-ray Fluorescence Spectroscopies. J. Environ. Monit. 2011, 13 (6), 1678−1686.

528

(26) Beauchemin, D. Inductively Coupled Plasma Mass Spectrometry. Anal. Chem.

529

2010, 82 (12), 4786−4810.

530

(27) Mitrano, D. M.; Ranville, J. F.; Bednar, A.; Kazor, K.; Hering, A. S.; Higgins, C.

531

P. Tracking Dissolution of Silver Nanoparticles at Environmentally Relevant

532

Concentrations in Laboratory, Natural, and Processed Waters Using Single Particle

533

ICP-MS (spICP-MS). Environ. Sci.: Nano 2014, 1 (3), 248−259.

534

(28) Peters, R.; Herrera-Rivera, Z.; Undas, A.; van der Lee, M.; Marvin, H.;

535

Bouwmeester, H.; Weigel, S. Single Particle ICP-MS Combined with a Data

536

Evaluation Tool as a Routine Technique for the Analysis of Nanoparticles in Complex

537

Matrices. J. Anal. At. Spectrom. 2015, 30 (6), 1274−1285.

538

(29) Tuoriniemi, J.; Cornelis, G.; Hassellöv, M. Size Discrimination and Detection

539

Capabilities of Single-Particle ICPMS for Environmental Analysis of Silver

540

Nanoparticles. Anal. Chem. 2012, 84 (9), 3965−3972.

541

(30) Somchue, W.; Siripinyanond, A.; Gale, B. K. Electrical Field-Flow

542

Fractionation for Metal Nanoparticle Characterization. Anal. Chem. 2012, 84 (11), 24

ACS Paragon Plus Environment

Page 24 of 29

Page 25 of 29

Environmental Science & Technology

543

4993−4998.

544

(31) Mitrano, D. M.; Barber, A.; Bednar, A.; Westerhoff, P.; Higgins, C. P.; Ranville,

545

J. F. Silver Nanoparticle Characterization Using Single Particle ICP-MS (SP-ICP-MS)

546

and Asymmetrical Flow Field Flow Fractionation ICP-MS (AF4-ICP-MS). J. Anal. At.

547

Spectrom. 2012, 27 (7), 1131−1142.

548

(32) Huynh, K. A.; Siska, E.; Heithmar, E.; Tadjiki, S.; Pergantisi, S. A. Detection

549

and

550

Concentrations Using Asymmetric Flow Field-Flow Fractionation Online with Single

551

Particle Inductively Coupled Plasma Mass Spectrometry. Anal. Chem. 2016, 88 (9),

552

4909−4916.

553

(33) Bolea, E.; Jimenez-Lamana, J.; Laborda, F.; Castillo, J. R. Size Characterization

554

and Quantification of Silver Nanoparticles by Asymmetric Flow Field-Flow

555

Fractionation Coupled With Inductively Coupled Plasma Mass Spectrometry. Anal.

556

Bioanal. Chem. 2011, 401 (9), 2723–2732.

557

(34) Loeschner, K.; Navratilova, J.; Legros, S.; Wagner, S.; Grombe, R.; Snell, J.;

558

von der Kammer, F.; Larsen, E. H. Optimization and Evaluation of Asymmetric Flow

559

Field-Flow Fractionation of Silver Nanoparticles. J. Chromatogr. A 2013, 1272,

560

116–125.

561

(35) Loeschner, K.; Navratilova, J.; Kobler, C.; Molhave, K.; Wagner, S.; von der

562

Kammer, F.; Larsen, E. H. Detection and Characterization of Silver Nanoparticles in

563

Chicken Meat by Asymmetric Flow Field Flow Fractionation with Detection by

564

Conventional or Single Particle ICP-MS. Anal. Bioanal. Chem. 2011, 405 (25),

565

8185–8195.

566

(36) Poda, A. R.; Bednar, A. J.; Kennedy, A. J.; Harmon, A.; Hull, M.; Mitrano, D.

567

M.; Ranville, J. F.; Steevens, J. Characterization of Silver Nanoparticles Using

Quantification

of

Silver

Nanoparticles

at

Environmentally

25

ACS Paragon Plus Environment

Relevant

Environmental Science & Technology

568

Flow-Field Flow Fractionation Interfaced to Inductively Coupled Plasma Mass

569

Spectrometry. J. Chromatogr. A 2011, 1218 (27), 4219–4225.

570

(37) Lee, W. C.; Lee, B. T.; Lee, S.; Hwang, Y. S.; Jo, E.; Eom, I. C.; Lee, S. W.;

571

Kim, S. O. Optimisation, Evaluation and Application of Asymmetrical Flow

572

Field-Flow Fractionation with Single Particle Inductively Coupled Plasma Mass

573

Spectrometry (SP-ICP-MS) to Characterise Silver Nanoparticles in Environmental

574

Media. Microchem. J. 2016, 129, 219–230.

575

(38) Zattoni, A.; Casolari, S.; Rambaldi, D. C.; Reschiglian, P. Hollow-Fiber Flow

576

Field-Flow Fractionation. Curr. Anal. Chem. 2007, 3 (4), 310−323.

577

(39) Reschiglian, P.; Zattoni, A.; Roda, B.; Cinque, L.; Parisi, D.; Roda, A.; Dal Piaz,

578

F.; Moon, M. H.; Min, B. R. On-Line Hollow-Fiber Flow Field-Flow

579

Fractionation-Electrospray Ionization/Time-of-Flight Mass Spectrometry of Intact

580

Proteins. Anal. Chem. 2005, 77 (1), 47−56.

581

(40) Marassi, V.; Casolari, S.; Roda, B.; Zattoni, A.; Reschiglian, P.; Panzavolta, S.;

582

Tofail, S. A. M.; Ortelli, S.; Delpivo, C.; Blosi, M.; Costa, A. L. Hollow-Fiber Flow

583

Field-Flow Fractionation and Multi-Angle Light Scattering Investigation of the Size,

584

Shape and Metal-Release of Silver Nanoparticles in Aqueous Medium for Nano-Risk

585

Assessment. J. Pharm. Biomed. Anal. 2015, 106 (SI), 92−99.

586

(41) Tan, Z. Q.; Liu, J. F.; Guo, X. R.; Yin, Y. G.; Byeon, S. K.; Moon, M. H.; Jiang,

587

G. B. Toward Full Spectrum Speciation of Silver Nanoparticles and Ionic Silver by

588

On-Line Coupling of Hollow Fiber Flow Field-Flow Fractionation and Minicolumn

589

Concentration with Multiple Detectors. Anal. Chem. 2015, 87 (16), 8441–8447.

590

(42) Kim, H. J.; Oh, S.; Moon, M. H. Hollow-Fiber Flow/Hyperlayer Field-Flow

591

Fractionation for the Size Characterization of Airborne Particle Fractions Obtained by

592

SPLITT Fractionation. J. Sep. Sci. 2006, 29 (3), 423−428. 26

ACS Paragon Plus Environment

Page 26 of 29

Page 27 of 29

Environmental Science & Technology

593

(43) Gigault, J.; Hackley, V. A. Observation of Size-Independent Effects in

594

Nanoparticle Retention Behavior during Asymmetric-Flow Field-Flow Fractionation.

595

Anal. Bioanal. Chem. 2013, 405 (19), 6251–6258.

596

(44) Heroult, J.; Nischwitz, V.; Bartczak, D.; Goenaga-Infante, H. The Potential of

597

Asymmetric Flow Field-Flow Fractionation Hyphenated to Multiple Detectors for the

598

Quantification and Size Estimation of Silica Nanoparticles in a Food Matrix. Anal.

599

Bioanal. Chem. 2014, 406 (16), 3919–3927.

600

(45) Li, X.; Lenhart, J. J.; Walker, H. W. Aggregation Kinetics and Dissolution of

601

Coated Silver Nanoparticles. Langmuir 2012, 28 (2), 1095–1104.

602

(46) Maurice,

603

Namjesnik-Dejanovic, K.; Aiken, G. R. A Comparison of Surface Water Natural

604

Organic Matter in Raw Filtered Water Samples, XAD, and Reverse Osmosis Isolates.

605

Water Res. 2002, 36 (9), 2357–2371.

606

(47) Lowry, G. V.; Gregory, K. B.; Apte, S. C.; Lead, J. R. Transformations of

607

Nanomaterials in the Environment. Environ. Sci. Technol. 2012, 46 (13), 6893–6899.

608

(48) Yuan,W.; Zydney, A. L. Effects of Solution Environment on Humic Acid Fouling

609

during Microfiltration. Desalination 1999, 122 (1), 63–76.

610

(49) Akaighe, N.; Depner, S. W.; Banerjee, S.; Sharma, V. K.; Sohn, M. The effects

611

of Monovalent and Divalent Cations on the Stability of Silver Nanoparticles Formed

612

from Direct Reduction of Silver Ions by Suwannee River Humic Acid/Natural

613

Organic Matter. Sci. Total Environ. 2012, 441, 277–289.

614

(50) Zou, X. Y; Li, P. H; Lou, J.; Fu, X. Y.; Zhang, H. W. Stability of Single

615

Dispersed Silver Nanoparticles in Natural and Synthetic Freshwaters: Effects of

616

Dissolved Oxygen. Environ. Pollut. 2017, 230, 674−682.

617

(51) Parker, K. M.; Pignatello, J. J.; Mitch, W. A. Influence of Ionic Strength on

P.

A.;

Pullin,

M.

J.;

Cabaniss,

S.

27

ACS Paragon Plus Environment

E.;

Zhou,

Q.

H.;

Environmental Science & Technology

Page 28 of 29

618

Triplet-State Natural Organic Matter Loss by Energy Transfer and Electron Transfer

619

Pathways. Environ. Sci. Technol. 2013, 47 (19), 10987–10994.

620

(52) Jones, K. L.; O'Melia, C. R. Protein and Humic Acid Adsorption onto

621

Hydrophilic Membrane Surfaces: Effects of pH and Ionic Strength. J. Membr. Sci.

622

2000, 165 (1), 31–46.

623

(53) Assemi, S.; Tadjiki, S.; Donose, B. C.; Nguyen, A. V.; Miller, J. D. Aggregation

624

of Fullerol C60(OH)24 Nanoparticles as Revealed Using Flow Field-Flow

625

Fractionation and Atomic Force Microscopy. Langmuir 2010, 26 (20), 16063–16070.

626

(54) Kim, S. T.; Lee, Y. J.; Hwang, Y. S.; Lee, S. Study on Aggregation Behavior of

627

Cytochrome

628

Field-Flow Fractionation. Talanta 2015, 132, 939–944.

629

(55) Yin, Y. G.; Shen, M. H.; Zhou, X. X.; Yu, S. J.; Chao, J. B.; Liu, J. F.; Jiang, G.

630

B. Photoreduction and Stabilization Capability of Molecular Weight Fractionated

631

Natural Organic Matter in Transformation of Silver Ion to Metallic Nanoparticle.

632

Environ. Sci. Technol. 2015, 48 (16), 9366–9373.

633

(56) Mueller, N. C.; Nowack, B. Exposure Modeling of Engineered Nanoparticles in

634

the Environment. Environ. Sci. Technol. 2008, 42 (12), 4447–4453.

635

(57) Azodi, M.; Sultan, Y.; Ghoshal, S. Dissolution Behavior of Silver Nanoparticles

636

and Formation of Secondary Silver Nanoparticles in Municipal Wastewater by Single

637

Particle ICP-MS. Environ. Sci. Technol. 2016, 50 (24), 13318–13327.

C-Conjugated

Silver

Nanoparticles

Using Asymmetrical

28

ACS Paragon Plus Environment

Flow

Page 29 of 29

Environmental Science & Technology

638

Table of Content Art

639

29

ACS Paragon Plus Environment