Quantification of Short-Chain Chlorinated Paraffins by

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Quantification of Short-Chain Chlorinated Paraffins (SCCPs) by Deuterodechlorination Combined with Gas Chromatography–Mass Spectrometry Yuan Gao, Haijun Zhang, Lili Zou, Ping Wu, Zhengkun Yu, Xianbo Lu, and Jiping Chen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b05115 • Publication Date (Web): 03 Mar 2016 Downloaded from http://pubs.acs.org on March 3, 2016

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Environmental Science & Technology

ABSTRACT

20

Analysis of short-chain chlorinated paraffins (SCCPs) is extremely difficult because of their

21

complex compositions with thousands of isomers and homologues. A novel analytical method,

22

deuterodechlorination combined with high resolution gas chromatography–high resolution mass

23

spectrometry

24

deuterodechlorination of SCCPs with LiAlD4, and the formed deuterated n-alkanes of different

25

alkane chains can be distinguished readily from each other on the basis of their retention time

26

and fragment mass ([M]+) by HRGC–HRMS. An internal standard quantification of individual

27

SCCP congeners was achieved, in which branched C10-CPs and branched C12-CPs were used as

28

the extraction and reaction internal standards, respectively. A maximum factor of 1.26 of the

29

target SCCP concentrations were determined by this method, and the relative standard deviations

30

for quantification of total SCCPs were within 10%. This method was applied to determine the

31

congener compositions of SCCPs in commercial chlorinated paraffins, environmental and biota

32

samples after method validation. Low-chlorinated SCCP congeners (Cl1–4) were found to account

33

for 32.4%–62.4% of the total SCCPs. The present method provides an attractive perspective for

34

further studies on the toxicological and environmental characteristics of SCCPs.

35

INTRODUCTION

(HRGC–HRMS),

was

developed.

A

protocol

is

applied

in

the

36

Short-chain chlorinated paraffins (SCCPs) are synthetic mixtures of chlorinated n-alkanes

37

ranging from C10 to C13 with a chlorine content of 30%–70% (mass weight). As a constituent

38

part of chlorinated paraffins (CPs), SCCPs are extensively used in metal-working fluids, paints,

39

sealants, adhesives, and leather finishing agents as well as flame retardants and plasticizers in

40

rubbers and polymers.1 SCCPs are high production volume chemicals with total world

41

production of approximately 150 kt per year.1, 2 Most of the SCCPs are used by blending with

ACS Paragon Plus Environment

2


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medium (C14−C17) and long (> C17) chain CP components.2 Because of their potential for long-

43

range transport, persistence in the environment and high toxicity to aquatic organisms, SCCPs

44

have been listed as “candidate” persistent organic pollutants (POPs) by the Convention’s POP

45

Review Committee (POPRC).3, 4

46

SCCPs have thousands of isomers via free radical chlorination with respect to C10−13 chains

47

bonding with various numbers of chlorine atoms and different chlorine positions, and thus it is

48

very difficult to completely separate SCCP congeners from each other on a GC capillary column.

49

Comprehensive two-dimensional gas chromatography (GC×GC) coupled with time-of-flight

50

mass spectrometry (TOF/MS) or micro electron capture detection (µECD) can remarkably

51

improve the separation of SCCP congeners in the GC section,5,

52

chromatographic separation of individual congeners with GC remains impossible.7 Therefore,

53

SCCPs have been described as “the most challenging group of substances to analyze and

54

quantify”.8

6

Nevertheless, complete

55

High resolution gas chromatography (HRGC) coupled with high/low resolution mass

56

spectrometry (HRMS or LRMS) in electron capture negative ionization (ECNI) mode has been

57

most commonly applied for the quantitative analysis of SCCPs in environmental matrices and

58

biota.5, 9−14 However, large quantification errors of 65%–940% can occur if the chlorine content

59

of the standard was changed or did not fit to the sample,15, 16 which is mainly resulted from the

60

strong dependence of the ECNI/MS response factors of SCCP congeners on their chlorine atom

61

numbers.7, 17 The highly chlorinated SCCP congeners are prone to have the higher ECNI/MS

62

response factors, while the low chlorinated congeners (Cl1−4) are not usually detected by

63

ECNI/MS. Many efforts have been made to decrease or offset the influence of chlorination

64

contents on the quantification of SCCPs. Zencak et al.10 used a mixture of methane and


3

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65

dichloromethane (DCM) (80: 20) as reagent gas for negative ion chemical ionization in

66

combination with GC–LRMS. Similar response factors were obtained for SCCP congeners with

67

different chlorine contents, opening a possibility of the detection of low chlorinated congeners

68

(Cl3–5). However, the methane/DCM reagent mixture can lead to a rapid deterioration of the ion

69

source due to the formation of black carbon residues that affect the performance of the MS

70

system.18 Reth et al.15 developed a linear relationship between the total response factors and the

71

chlorine contents, which improved the precision of the results and has the most frequently been

72

used. The linearity range is usually limited to the chlorine contents of 50%−70%, and thus it is

73

not suitable for the quantitative analysis of SCCPs with a high proportion of low chlorinated

74

congeners (Cl1−4). Harada et al.19 developed a semi-quantitative method for individual SCCP

75

congeners with Cl5–9, in which the individual SCCP congeners in samples were calculated using

76

a linear regression between the peak areas determined by HRGC–ECNI/HRMS and the

77

concentrations determined by HRGC–electron impact ionization (EI)/TOFMS. In addition, based

78

on the analysis of GC–ECNI/MS, Geiβ et al.11 developed a multiple linear regression procedure

79

for the quantification of total SCCPs with a chlorine content of 49%–67% in water.

80

HRMS or LRMS in atmospheric pressure chemical ionization (APCI) or chloride-enhanced

81

APCI mode have been also developed for the analysis of chlorinated paraffins.20, 21 The response

82

factors were less dependent on the chlorination content than in ECNI/MS methods. Nevertheless,

83

the low chlorinated SCCPs (Cl1−4) are still not detected. Another interesting analysis approach of

84

carbon skeleton reaction gas chromatography was achieved by detecting the corresponding n-

85

alkanes generated from the catalytic hydrodechlorination of CPs on a Pd catalyst.22–24 However,

86

the information on the chlorination content is lost.


4


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Accurate quantification of the individual SCCP congeners, especially the low chlorinated

88

SCCPs, remains challenging, although interlaboratory studies since 2010 showed improving data

89

agreements.7, 25 The environmental fates and toxicities of SCCPs have not yet characterized well

90

due to the limitation in analysis method. Reliable measurement data regarding SCCPs are

91

strongly desired in view of the ongoing global regulatory actions and deliberations by all

92

countries and regulatory bodies.4, 7, 17 In this study, we report a novel approach for the analysis of

93

SCCPs based on deuterodechlorination combined with HRGC−EI/HRMS, through which the

94

concentrations of individual SCCP congeners with different carbon and chlorine numbers can be

95

determined. Reduction of SCCPs with lithium aluminum deuteride (LiAlD4) was conducted in

96

ethylene glycol diethyl ether (EGDE), which generated the corresponding deuterated n-alkanes.

97

Deuterated n-alkanes were then completely separated on a GC capillary column in according

98

with their carbon chain length, rather than the coelution profile of the original SCCPs. The

99

molecular ions ([M]+) of the deuterated n-alkanes, reflecting the chlorine distribution of SCCPs,

100

were thus monitored. This method enabled us to quantify the individual SCCP congeners even

101

with less than 5 chlorine atoms.

102

EXPERIMENTAL SECTION

103

Synthesis of the Calibration Standards for Method Development. A series of SCCP

104

calibration standards with fixed carbon chain lengths, C10-CPs, C11-CPs, C12-CPs and C13-CPs,

105

were synthesized by the substitution reaction of individual n-alkanes with sulfuryl chloride

106

(SO2Cl2). The information on the carbon chain lengths and chlorine contents of the synthetic

107

calibration standards are shown in Table S1. Chlorinated 2-methyl nonane (branched C10-CPs)

108

and chlorinated 2-methyl undecane (branched C12-CPs), were also synthesized by the

109

substitution reaction of 2-methyl nonane and 2-methyl undecane with SO2Cl2, respectively.


5

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Under argon atmosphere, about 1 mL of alkane was treated with SO2Cl2 (9 mL) in DCM (30

111

mL). The reaction mixture was irradiated with UV-light (6 W mercury vapor lamp) and refluxed

112

at 70 °C. The reaction was continued for different times in order to obtain SCCP calibration

113

standards with different chlorine contents (Table S1). At the end of reaction, the reaction flask

114

was placed into an ice-bath and bubbled with a gentle stream of argon for 10 min. The solvent

115

and excess SO2Cl2 were removed by distillation at 50–100 oC under atmospheric pressure. The

116

residue was cooled to ambient temperature after ice bath, resolved with DCM (40 mL), and then

117

washed with saturated NH4Cl (40 mL), saturated NaHCO3 (40 mL) and purified water (40 mL).

118

The organic phase was dried over anhydrous Na2SO4 and filtered. All the volatiles were removed

119

under reduced pressure at 35 oC, and the products were dried in vacuum. The chlorine content of

120

the prepared SCCP calibration standards were calculated by the weight difference between the

121

substrate alkane and the generated chlorinated alkane (Details in the Supporting Inforamtion).

122

The details on all purchased chemicals and reagents are also shown in the Supporting

123

Information.

124

Procedure for the Deuterodechlorination of SCCPs. Firstly, the saturated solution of

125

LiAlD4 in EGDE was prepared. Prior to use, EGDE was distilled by rectifying column with

126

sodium reflux. Approximate 0.05 g of LiAlD4 was added into 1.0 mL of the distilled EGDE in a

127

reaction vial, and then heated at 110 oC for about 8 h until the upper solution became pellucid.

128

The reaction vial was centrifuged at 3000 rpm for 10 min. The clear supernatant, i.e., the

129

saturated solution of LiAlD4, was used for the deuterodechlorination of SCCPs.

130

Sample collection, extraction and cleanup of environmental samples were described in the

131

Supporting Information. Prior to extraction, 5 µL of branched C10-CPs (1 µg/µL nonane) was

132

spiked into the sample as the extraction internal standard. Alkanes and other organochlorine


6


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133

compounds in environmental samples have been found to interfere with the instrumental analysis

134

and the deuterodechlorination reaction, respectively. Gel permeation chromatography (GPC) and

135

a successive silica gel and basic alumina columns have been used for the removal of lipids and

136

other organochlorine compounds in samples.26 The SCCP-containing extract was concentrated to

137

about 1 mL, and then transferred to a micro-reaction vial. 5 µL of branched C12-CPs (1 µg/µL

138

nonane) was spiked into the micro-reaction vial as the reaction internal standard, and then

139

concentrated to near dryness by a gentle stream of N2. The deuterodechlorination of SCCPs was

140

conducted in a glove box with the moisture content of < 1 ppm. 100 µL of the saturated solution

141

of LiAlD4 in EGDE was added into the micro-reaction vial containing SCCPs, and then heated at

142

90 oC for 72 h under nitrogen atmosphere. After reaction, the solution was transferred to a screw

143

thread GC vial. The micro-reaction vial was further rinsed by 100 µL of DCM for three times,

144

and then the rinse solution was combined with the reaction solution. The reaction was quenched

145

by adding 100 µL of the deionized water to the solution dropwise, while the deionized water was

146

further absorbed by about 0.3 g of anhydrous Na2SO4. The supernatant liquid was transferred to

147

another GC vial after centrifugation, and concentrated to near dryness by a gentle stream of N2.

148

50 µL of n-hexane containing phenanthrene as the injection internal standard was added, and the

149

vial was mixed by vortexing prior to instrumental analysis.

150

Instrumental Analysis. The generated deuterated alkanes were analyzed using an Autospec

151

Ultima high resolution mass spectrometer (Micromass, UK) interfaced with a Hewlett– Packard

152

(Palo Alto, CA, USA) 6890 Plus gas chromatograph. A capillary DB-5 column (60 m × 0.25 mm

153

i.d. × 0.25 µm film thickness, J&W Scientific, USA) was used. A sample volume of 1 µL was

154

injected in the splitless mode with an injector temperature of 280 °C, which was made by a CTC

155

A200SE autosampler under data system control. The oven temperature program was as follows:


7

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50 °C, isothermal for 0.5 min, then 20 °C/min to 80 °C, keeping 8 min, then 5 °C/min to 280 °C,

157

and final isothermal for 20 min. The ion source was operated at 260 °C, and the mass

158

spectrometer was tuned to a mass resolution of 5000 under positive EI conditions. The molecular

159

ion clusters, [M]+, of the formed deuterated alkanes, were monitored in SIM mode, and four

160

windows during the scanning were divided to improve the efficiency. The m/z values of the

161

monitored ions for deuterated alkanes with different carbon chain lengths and deuterium atom

162

numbers are shown in Table S2.

163

In order to develop and validate the deuterodechlorination combined with HRGC–EI/HRMS

164

method for SCCP analysis, SCCPs in some samples were also analyzed by the traditional

165

HRGC–ECNI/LRMS method, carbon skeleton reaction GC with flame ionisation detection (FID)

166

method and the deuterodechlorination combined with HRGC–EI/LRMS method. The detailed

167

conditions for instrumental analysis are described in the Supporting Information.

168

RESULTS AND DISCUSSION

169

Optimization for the Deuterodechlorination Reaction of SCCPs. In our case, LiAlD4 was

170

selected as the deuterium sources. The corresponding deuterated n-alkanes were formed as the

171

major products (Figure S1). Preliminary experiments were carried out to improve the

172

deuterodechlorination rates of SCCPs, which was calculated as the percentage of SCCPs reacted

173

to the corresponding deuterated n-alkanes (Detailed equations see the Supporting Information).

174

The influences of reaction temperature and reaction time on deuterodechlorination rates of

175

SCCPs were investigated. Two kinds of SCCP mixture stock standard solutions (51% Cl and

176

63 %Cl, respectively, purchased from Dr. Ehrenstorfer GmbH, Augsburg, Germany) were tested,

177

and the generated deuterated n-alkanes were analyzed using HRGC–EI/LRMS method. The

178

deuterodechlorination rates exhibited an increasing tendency with the increase of the reaction


8


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time, whereas higher temperature depressed the generation of the corresponding deuterated n-

180

alkanes (Tables S3 and S4). The highest deuterodechlorination rates for the reduction of SCCPs

181

was obtained at 90 oC for 96 h. Under this condition, 56.4% and 47.6% of SCCPs in two tested

182

SCCP mixture standards (51% Cl and 63 % Cl,) have been deuterodechlorinated to the

183

corresponding deuterated n-alkanes, respectively. During the deuterodechlorination reaction of

184

SCCPs with LiAlD4, deuterated n-alkenes were generated (Figure S2). The relative abundance of

185

the deuterated n-alkenes decreased with the decreasing of the reaction temperature. A small

186

quantity

187

deuterodechlorination reaction (Figure S3), which was discussed in details in the Supporting

188

Information.

of

low

chlorinated

deuterated

n-alkanes

was

also

formed

during

the

189

Fractionation and MS Detection. The formed deuterated n-alkanes were eluted from a DB-5

190

column, in which the deuterated n-alkanes were completely separated according to the number

191

of carbon atoms (Figure 1a). The chromatography profiles of the formed deuterated n-alkanes

192

were similar to the n-alkane distribution patterns determined by carbon skeleton reaction with

193

GC/FID (Figure S4).

194

The EI mode was used to ionize the individual deuterated n-alkanes. Figure 2 illustrated the EI

195

mass spectra of the deuterated n-tridecane generated from the deuterodechlorination of the SCCP

196

mixture standard (C10–13, 51% Cl) and synthesized SCCP calibration standard (C13, 65.3% Cl),

197

respectively. The resultant mass spectra were dominated by the fragment ion clusters with low

198

mass-to-charge ratios (m/z), such as [C3H6D]+, [C3H5D2]+, [C4H8D]+, [C4H7D2]+, [C5H9D2]+

199

[C5H8D3]+, [C6H11D2]+and [C6H9D4]+. Meanwhile, the molecular ion clusters, [M]+, of the

200

deuterated n-alkanes with different deuterium atom numbers, reflecting the chlorine distributions

201

of SCCPs, were also detected (enlarged images in Figure 2). Because of the low abundances of


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202

the molecular ion clusters, HRMS was used to improve the selectivity and minimize matrix

203

interference as well as interferences from deuterated n-alkenes, low-chlorinated deuterated n-

204

alkanes and

205

quantification of individual SCCP congeners with different carbon and chlorine numbers, the

206

SIM mode was adopted to monitor the molecular ion clusters of the formed deuterated n-alkanes.

207

The SIM chromatograms of the deuterated n-alkanes generated from the deuterodechlorination

208

of the SCCP mixture standard (C10–13, 51% Cl) is shown in Figure 1b. The influence of the

209

deuterium atom numbers on the response factors of the deuterated n-alkanes was investigated. As

210

compared with that of n-octane, the relative response factor of the molecular ion [M]+ of n-

211

octane-d18 (Cambridge Isotope Laboratories, Inc., Andover, MA, USA) only increased by 0.16-

212

fold (Figure S5). This result reveals that the deuteration degree does not exhibit an obvious

213

impact on the signal intensities of the individual deuterated n-alkanes generated from SCCPs

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usually containing 3−10 chlorine atoms. Therefore, the chlorine distribution of SCCPs can be

215

calculated according to the deuteration degree of the formed deuterated n-alkanes with different

216

deuterium atom numbers. The calculated chlorine contents in two tested SCCP mixture standards

217

(51% Cl and 63% Cl) were 50.0% and 60.9%, respectively. The chlorine distribution on the

218

fixed carbon chain is nearly conformed to a Gaussian curve (Figure S6).

13

C isotope (Details in the Supporting Information). To achieve simultaneous

219

Quantitative Analysis of SCCPs in Samples. An internal standard calibration method for

220

SCCP quantification was developed. Branched C10-CPs and branched C12-CPs were used as the

221

extraction and the reaction internal standards, respectively. They have not been detected in

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commercial chlorinated paraffins, environmental samples or biota samples (see the Supporting

223

Information). Similar behaviors of the extraction internal standard were found in sample

224

extraction and column cleanup procedures with SCCPs. The average recoveries of branched C10-


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CPs were calculated to be 92.5% (see the Supporting Information). The deuterodechlorination

226

rates of branched C10-CPs and branched C12-CPs were also evaluated, which were calculated to

227

be 50.7% and 55.1%, respectively, under the optimized condition. Their deuterodechlorination

228

products, deuterated 2-methyl nonane and deuterated 2-methyl undecane, can be completely

229

separated from the deuterated n-alkanes on the DB-5 column. The molecular ion clusters of the

230

deuterated branched-chain alkanes exhibited relative lower signal intensities due to the isomeric

231

effects. By comparing the standard mass spectrums from NIST database, the relative signal

232

intensity of 2-methyl nonane was found to be about 20% of the value of n-decane. In this study,

233

the

234

deuterodechlorination rates, and however the relative signal intensity of the generated deuterated

235

2-methyl nonane was only about 15% of the value of the generated deuterated n-decane.

extraction

internal

standard

and

straight-chain

C10-CPs

have

the

similar

236

To quantify the indivdual SCCP congeners, the relative correction factor (RCFi) of individual

237

deuterated n-alkane with fixed carbon chain length (i) generated from the SCCP calibration

238

standard compared to the deuterated 2-methyl nonane generated from the extraction internal

239

standard, was calculated according to eq. 1.

240

RCFi =

Qd-IS TAd-CS, i × Qd-CS, i TAd-IS

(1)

241

where Qd-IS and Qd-CS, i are the theoretical masses of deuterated 2-methyl nonane and deuterated

242

n-alkanes generated from the extraction internal standard and SCCP calibration standard,

243

respectively; TAd-IS and TAd-CS, i are the actually measured total peak areas of deuterated 2-methyl

244

nonane and deuterated n-alkanes generated from the extraction internal standard and SCCP

245

calibration standard, respectively. The total peak area was the sum of the peak areas of individual

246

deuterated alkanes with different deuterium atom numbers monitored in SIM mode. Three

247

replicates were applied for each SCCP calibration standard. The relative standard deviations of


11

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248

RCFi values for each SCCP calibration standard with fixed carbon chain length and different

249

chlorine contents were within 30% (Table S5).

250 251

The theoretical masses of deuterated 2-methyl nonane and deuterated n-alkanes, i. e. Qd-IS and Qd-CS, i, can be calculated according to eq. 2 and 3, respectively.

252

Qd-IS = QIS × (1 −

253

Qd-CS, i = QCS, i × (1 −

M Cl − M D × K IS ) M Cl

(2)

M Cl − M D × K CS, i ) M Cl

(3)

254

where QIS

255

standard, respectively; MCl and MD are the molecular weights of Cl atom (average: 35.5) and D

256

atom, respectively; KIS and KCS, i are the chlorine contents (mass percentage) of the extraction

257

internal standard and SCCP calibration standard, respectively.

and

QCS, i are the masses of the extraction internal standard and SCCP calibration

258

Combining eqs. 1−3, the RCFi values of SCCP homologues with fixed carbon chain lengths

259

can be obtained. According to the calculation procedure described above, the obtained RCFi

260

generally reflect the deviation in the deuterodechlorination rates, sample preparation and

261

instrumental response between deuterated n-alkanes and deuterated branched-chain alkanes. As

262

shown in Figure 3a, there are no statistically significant differences in RCFi values among C10-

263

CPs, C11-CPs and C12-CPs; whereas C13-CPs showed higher RCFi values compared with C10-CPs

264

and C12-CPs. Meanwhile, for the different SCCP homologues with fixed carbon chain lengths,

265

the RCFi values did not present a consistent variation with the change of the chlorine content

266

(Figure 3b). As a whole, the RCFi values seemed to be independent on the chlorine contents.

267

Therefore, the RCFi values of individual SCCP homologues with fixed carbon chain lengths and

268

different chlorine contents could be considered as constants.


12


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269

In view of the similar deuterodechlorination probability of individual SCCP congeners, the

270

abundances of deuterated n-alkanes with different deuterium atom numbers can reflect the

271

quantities of the individual SCCP congeners. Therefore, the chlorine content of SCCPs with

272

fixed carbon chain length (Ki, %) can be calculated from the deuteration degree of the formed

273

deuterated n-alkanes and their relative abundances according to eq. 4. 1− n

Ki = ∑ j Ri, j ×

274

j × M Cl M formula

(4)

275

where j is the number of deuterium atoms, and n is the maximum number of deuterium atoms.

276

Mformula is the molecular weight of the individual SCCP congener, which can be calculated by the

277

molecular formula. Ri, j is the relative abundance (%) of each deuterated n-alkane with fixed

278

carbon chain length (i) and different number of deuterium atoms (j) compared to the total amount

279

of the individual deuterated n-alkane with fixed carbon chain length (i), which can be calculated

280

according to eq. 5.

281

Ri, j =

Ad −CS, i, j TAd −CS, i

×100%

(5)

282

where Ad-CS, i, j is the peak area of the deuterated n-alkane with fixed carbon chain length and

283

fixed deuterium atom number generated from the SCCP calibration standard. It was found that

284

the calculated chlorine contents in SCCP calibration standards were very close to those values

285

measured by the weight difference, with a linear slope factor of 0.97 (Figure 3c).

286

In view of the fact that individual SCCP homologues with fixed carbon chain length and

287

different chlorine contents had similar RCF values, average RCFi value ( RCFi ) was used for the

288

quantification of individual SCCP homologues in actual samples. According to eq. 1, the

289

following equation can be obtained:


13

Page 13 of 28


RCFi =

290

Qd-IS Qd-sample, i

×

TAd-sample, i TAd-IS

(6)

291

where Qd-sample, i and TAd-sample, i are the actually determined mass and total peak area of the

292

deuterated n-alkanes with fixed carbon chain length (i) generated from SCCPs in the sample,

293

respectively. The total peak area was the sum of the peak areas of individual deuterated n-

294

alkanes with fixed carbon chain length and different deuterium atom numbers monitored in SIM

295

mode.

296

According to eq. 3, Qd-sample, i can be expressed by the following equation:

Qd-sample, i = Qsample, i × (1 −

297

M Cl − M D × Ksample, i ) M Cl

(7)

298

where Qsample, i and Ksample, i are the mass and chlorine content of the individual SCCP homologue

299

with fixed carbon chain length (i) in the sample, respectively. Qsample, i can be expressed by eq. 8

300

after combining eqs. 6 and 7.

301

302 303 304

Qsample, i =

Qd-IS TAd-sample, i M Cl × × TAd-IS M Cl − ( M Cl − M D ) × K sample, i RCF

(8)

According to eq. 8, the total mass of SCCPs in the sample (Qsample) can be calculated by the following equation: 10−13

Qsample = ∑ i

 Qd-IS TAd-sample, i  M Cl × ×   TAd-IS M Cl − ( M Cl − M D ) × Ksample,i   RCF

(9)

305

Considering the chlorine atoms in SCCPs is one-to-one replaced by deuterium atoms, the mass

306

of the individual SCCP congeners with fixed carbon chain length and fixed number of chlorine

307

atoms (Qsample-i,j) can be calculated based on the relative abundance (Ri, j) of the individual

308

deuterated n-alkanes as follows:


14


309

Qsample-i. j = Qsample, i × Ri, j =

Qd-IS TAd-sample, i M Cl × × × Ri, j TAd-IS M Cl − ( M Cl − M D ) × K sample, i RCF

Page 14 of 28

(10)

310

where i and j are the carbon chain length and number of chlorine atoms, respectively. Table S6

311

and S7 listed the Ri, j values for each deuterated n-alkane in actual samples. The sum of Ri, j

312

values for individual homologue with fixed carbon chain length (i) was 1.

313

Method Performance. Method performance of the whole analytical procedure was

314

investigated according to EURACHEM and EPA guidelines.27, 28 Method selectivity and linearity,

315

instrumental detection limit (IDL) of n-alkanes and method detection limit (MDL) of SCCPs,

316

have been evaluated in the Supporting Information. There was a good linearity (R2 > 0.99) in the

317

range of 17−212 µg/L for the four kinds of n-alkanes with diferent carbon chain lengths, n-

318

decane, n-undecane, n-dodecane and n-tridecane n-alkane, respectively (Figure S7). The IDL

319

value for n-alkanes (C10−C13) was estimated to be 1.5 pg at a signal-to-noise ratio (S/N) of 3: 1,

320

respectively. The blank sediment sample was prepared using Soxhlet extraction until no

321

detectable quantities of SCCPs analyzed by HRGC−ECNI/LRMS method. The MDL value for

322

total SCCPs, calculated as 3-fold the standard deviation of SCCPs in blank sediment samples,

323

was 33 ng/g (n = 8). The value was a little higher than that by ECNI/LRMS method (14 ng/g)3,

324

which was undoubtedly sensitive for high chlorinated SCCPs. The average chlorine content of

325

SCCPs in blank sendiment samples was calculated to be 55.0%.

326

Four kinds of SCCP homologue stock standard solutions (C10-CPs, 60.09% Cl; C11-CPs,

327

55.2% Cl; C12-CPs, 65.08% Cl; C13-CPs, 65.18% Cl; 10 ng/µL in cyclohexane) and a SCCP

328

mixture stock standard solution (C10–13; 51% Cl, 100 ng/µL in cyclohexane) were used to test the

329

reliablity of deuterodechlorination combined with HRGC−EI/HRMS method for the analysis of

330

SCCPs. The determined mass and chlorine content of SCCPs were shown in Table S8. The

331

relative errors between the expected and the determined values were within 21% for the


15

Page 15 of 28


332

quantification of total SCCPs, and within 6% for the chlorine content. The relative standard

333

deviations of the determined values were within 10% for the concentration of total SCCPs, and

334

within 1% for the chlorine content.

335

The method repeatability and precision for the analysis of SCCPs in environmental samples

336

were evaluated using the blank sediment sample. Approximately 5 g of the blank sediment

337

sample was spiked with the SCCP homologue stock standard solutions (C10-CPs, 60.09% Cl;

338

C11-CPs, 55.2% Cl; C12-CPs, 65.08% Cl; C13-CPs, 65.18% Cl; 10 ng/µL in cyclohexane) and the

339

internal standards, respectively. Sample pretreatment, deuterodechlorination reaction and

340

quantification of SCCPs were conducted. The relative errors between the expected and the

341

determined values were within 26% for the quantification of total SCCPs, and within 7% for the

342

chlorine content (Table S9). The relative standard deviations of the determined values were

343

within 10% for the concentration of total SCCPs, and within 1% for the chlorine content.

344

The recoveries of the extraction (Rex) and reaction internal standard (Rre) have been used for

345

the evaluation of the sample pretreatment and deuterodechlorination reaction in samples,

346

respectively. They were calculated as described in details in the Supporting Information, taking

347

the EPA 1613 method as a reference.28 The recoveries of the extraction internal standard

348

throughout the sample pretreatment were above 75% (Table S9) while the recoveries of the

349

reaction internal standard were above 79% (Table S8, S9).

350

Analysis of SCCPs in Commercial CP Products and Environmental Samples. The

351

concentrations and chlorine contents of SCCPs and their individual homologue groups in

352

commercial CP products, sediment and biota samples, respectively, were analyzed. The contents

353

of SCCPs in the three commercial CP mixtures, CP-42 (CPs with a chlorine content of 42%),

354

CP-52 and CP-70, were determined to be 3.1%, 40.2% and 1.7%, respectively (Table S10). The


16


Page 16 of 28

355

corresponding chlorine contents of the SCCPs were determined to be 42.9%, 54.9% and 65.2%,

356

respectively. The contents of SCCPs in CP-42 and CP-70 products were relatively low (< 5%),

357

while high content of SCCPs was found in CP-52. The results were also in agreement with those

358

values determined by HRGC–ECNI/LRMS.12 Significant differences in SCCP homologue

359

profiles have been found among the three commercial CP products (Figure S8). C10-CPs

360

predominated in the congener profiles in CP-42 while the amounts of the four homologues were

361

comparable in CP-52 and CP-70 products. The chlorine profiles of the SCCP homologues with

362

fixed carbon chain length almost exhibited a Gaussian distribution. Similar chlorine contents of

363

the individual SCCP homologues have been found. The most abundant chlorine congeners were

364

Cl2–4 congeners in CP-42, Cl5–6 congeners in CP-52, Cl8–10 congeners in CP-70, respectively.

365

The concentrations of total SCCPs in two sediment samples were determined to be 2.71 µg/g

366

dry weight (dw) and 3.28 µg/g dw, with chlorine contents of 52.9% and 52.4%, respectively

367

(Table S11). The concentrations of the total SCCPs in the loach and frog sample were

368

determined to be 4.92 µg/g dw and 4.49 µg/g dw, respectively, corresponding to the chlorine

369

contents of 47.6% and 52.0%, respectively (Table S11). A near Gaussian distribution was also

370

found in the chlorine profile of the SCCP homologues with fixed carbon chain length in the

371

sediment and biota samples (Figure 4). The longest chain C13-CPs were the predominant

372

congeners of SCCPs in sediment samples, followed by C12-CPs, C11-CPs and C10-CPs. The Cl4–6

373

congeners were the most abundant congeners in the sediment samples. Smaller differences

374

among the concentrations of the four SCCP homologues were indicated in biota samples. The

375

Cl4 congeners showed the highest abundances in the loach sample while more congeners have

376

been detected in the frog sample. It was found that Cl4-8 congeners for C10-CPs and C11-CPs, and

377

Cl3-5 congeners for C12-CPs and C13-CPs predominated in the congener profile.


17

Page 17 of 28


378

In addition, we analyzed the sediment and biota samples by the HRGC–ECNI/LRMS method

379

(Table S12). As compared to the HRGC–ECNI/LRMS analysis, the results obtained by

380

deuterodechlorination combined with HRGC−EI/HRMS showed higher concentrations of total

381

SCCPs and lower chlorine content (Table S11, S12). The concentrations and chlorine contents of

382

SCCPs determined by the deuterodechlorination combined with HRGC−EI/HRMS were

383

1.7−13.6 times and 0.82−0.90 times the values determined by HRGC–ECNI/LRMS method,

384

respectively. This result should be partly attributed to the detection of a larger quantity of low

385

chlorinated SCCP congeners (Cl1−4), which are ignored by the HRGC−ECNI/LRMS analysis.29

386

In our study, SCCPs with Cl1−4 accounted for 32.4%−62.4% of the total SCCPs in the tested

387

sediment and biota samples. The large quantitive difference of total SCCPs between carbon

388

skeleton analysis and GC–ECNI/LRMS analysis was also observed by Hussy et al., who found

389

that the concentrations of SCCPs in sediments determined by carbon skleton reaction combined

390

with GC/FID were 0.4−50 times the values determined by GC‒ECNI/LRMS.30

391

In this work, we present a new analytical method for SCCPs, i.e. deuterodechlorination

392

combined with HRGC−EI/HRMS. This analytical approach can achieve accurate quantification

393

of individual SCCP congeners, and the method reliability can be ensured by internal standard

394

calibration. This method overcomes some disadvantages of the previously reported ECNI/MS

395

methods. SCCP congeners with Cl1−4 can be detected, and the calculated concentration of SCCPs

396

does not considerably depend on the distribution profile of SCCP congeners in the selected

397

analytical standards. The present method can simultaneously acquire both carbon and chlorine

398

profiles of SCCPs, which guarantees a promising application in further studies on the

399

toxicological and environmental characteristics of SCCPs.

400

ASSOCIATED CONTENT


18


Page 18 of 28

401

Supporting Information. Detail information on chemicals and reagents, sample collection

402

and pretreatment, instrumental analysis, generation of byproducts and their interferences, method

403

performance, calculation of the deuterodechlorination rates and recoveries; tables showing the

404

calibration standards for method development (Table S1), m/z values of the molecular ions [M]+

405

for the deuterated n-alkanes (Table S2), deuterodechlorination rates and calculated chlorine

406

contents of SCCPs (Table S3, S4), calculated RCF and Ri,

407

quantitative results of SCCP congeners in different stock standard solutions, commercial CPs,

408

sediment and biota samples (Tables S8−S11), and the concentrations and chlorine contents of

409

SCCPs in sediment and biota samples analyzed by HRGC−ECNI/LRMS (Table S12); figures

410

showing the reduction of SCCPs with LiAlD4 (Figure S1), mass spectra and HRGC‒EI/LRMS

411

chromatogram for the products from the deuterodechlorination (Figure S2, S3), the SCCP

412

homologue profiles determined by the deuterodechlorination combined with HRGC−EI/HRMS

413

and carbon skeleton reaction with GC/FID (Figure S4), the dependence of the relative response

414

factor on the deuteration degree of n-octane (Figure S5), congener profiles of SCCPs in standard

415

mixtures and commercial CP mixtures (Figure S6, S8), and linear correlation between the n-

416

alkane concentrations and its relative peak areas determined by HRGC−EI/HRMS (Figure S7).

417

This material is available free of charge via the Internet at http://pubs.acs.org.

418

AUTHOR INFORMATION

419

Corresponding Author

420

* Phone/fax: +86-411-8437-9562; E-mail: [email protected]

421

Notes

422

The patent (CN104181266 A) is relevant to the deuterodechlorination reaction and quantification

423

method principle of SCCPs and MCCPs.


j

values (Tables S5−S7), the

19

Page 19 of 28


424

ACKNOWLEDGMENT

425

This work was financially supported by the National Natural Science Foundation of China

426

(Grant No. 21307128 and 21337002), the Chinese National Basic Research Program (Grant No.

427

2015CB453100), and the Special Fund for Agro-scientific Research in the Public Interest (Grant

428

No. 201503108).

429

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430

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431

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515 516

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523

(30) Hussy, I.; Webster, L.; Russell, M.; Moffat, C. Determination of chlorinated paraffins in

524

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525

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526

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527


24


C12

a Relative abundance

Page 24 of 28

C11 C13

C10

D13

b

D12 D11 D10

Relative abundance

D9 D8 D7 D6 D5 D4 D3 D2 D1

14

528

16

18

20 22 Time (min)

24

26

529

Figure 1. HRGC–EI/HRMS TIC (a) and SIM (b) chromatograms of deuterated n-decane (C10), deuterated n-

530

undecane (C11), deuterated n-dodecane (C12), and deuterated n-tridecane (C13), respectively, produced from the

531

deuterodechlorination of the SCCP mixture standard (C10–13, 51% Cl). D1 to D13 represents the number of

532

deuterium atom substitutation in the corresponding deuterated n-alkanes.

533


25

Page 25 of 28


534 100 44.0

a

Relative abundance (%)

[C3H6D] 80

58.0

80

[C4H8D]+

40

40

45.0 80

188.1 190.

[C5H9D2]

+

20

187.1

40

0

87.0 [C6H11D2]

+ 180

185

190

195

200

20

80 60 40

[C5H8D3]+ 20 89.1 0 [C6H9D4]+ 180

191.2

185

190

194.2

195

200

20

101. 115.

103.

[M]+

0

[M]+

117.

0 40

535

74.0

192.2 193.2

100

[C4H7D2]+

60

191.1

b

[C3H5D2]+

60

60

73.0

59.0

100

189.1

100

+

60

80

100

120 140 m/z

160

180

200

220

40

60

80

100

120 140 m/z

160

180

200

220

536

Figure 2. LRMS spectrum of the yielding deuterated n-tridecane from the deuterodechlorination of SCCP

537

mixture standard (C10–13, 51% Cl) (a) and synthesized SCCP calibration standard (C13, 65.3% Cl) (b) in full

538

scan mode. [M]+ represents the molecular ion clusters.

539


26


Page 26 of 28

540 50

C10-CPs C11-CPs

40

C12-CPs C13-CPs

* RCF

RCF

30 20

20

10

10

0

0

10

541

30

11 12 Carbon Chain length

13

40

50 60 Cl content (%)

deuteration degree (%)

b *

40

Cl content calculated from

50

a

70

70

c

y = 0.974x R2 = 0.932

60

50

40 40 50 60 70 Cl content on mass basis (%)

542

Figure 3. Variation of RCF values with carbon chain lengths (a) and chlorine contents (b) of SCCPs as well as

543

the correlation between the chlorine contents calculated from the deuteration degree and those calculated from

544

the weight differences (c). A total of 20 synthetic SCCP calibration standards with fixed carbon chain lengths

545

(C10, C11, C12, and C13) were adopted, each of which consisted of 5 chlorine contents (41.1%−69.6%). Three

546

replicates were applied for each SCCP calibration standard. * represents the significant differences of RCF

547

values at 0.05 level.

548


27

Page 27 of 28


549 0.2

C10-CPs

C11-CPs

C12-CPs

C13-CPs

Sediment 1 0.1 0.0

Sediment 2

Concentration (µg/g)

0.2 0.1 0.0

Loach

0.4 0.2 0.0 0.3

Frog

0.2 0.1 0.0 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 91011121314

Chlorine atom number

550 551

Figure 4. Congener profiles of SCCPs in sediment and biota samples determined by the method of

552

deuterodechlorination combined with HRGC–EI/HRMS.

553


28

Quantification of Short-Chain Chlorinated Paraffins by

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