Molecularly Imprinted Polymers for Compound-Specific Isotope

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Article

Molecularly-imprinted polymers for compound-specific isotope analysis of polar organic micropollutants in aquatic environments Rani Bakkour, Jakov Bolotin, Börje Sellergren, and Thomas B. Hofstetter Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b00493 • Publication Date (Web): 20 May 2018 Downloaded from http://pubs.acs.org on May 20, 2018

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Analytical Chemistry

Molecularly-imprinted polymers for compound-specific isotope analysis of polar organic micropollutants in aquatic environments Rani Bakkour,†,‡, ¶ Jakov Bolotin,† Börje Sellergren,§ and Thomas B. Hofstetter∗,†,‡ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland, , and Department of Biomedical Sciences, Malmö University, Malmö, Sweden E-mail: [email protected]

∗ To

whom correspondence should be addressed

† Eawag ‡ ETH

Zürich address: Technical University of Munich, Chair for Analytical Chemistry and Water Chemistry, München,

¶ present

Germany § Malmö University

1

ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract

1

2

Compound-specific isotope analysis (CSIA) of polar organic micropollutants in environ-

3

mental waters requires a processing of large sample volumes to obtain the required analyte

4

masses for analysis by gas chromatography / isotope-ratio mass spectrometry (GC/IRMS).

5

However, the accumulation of organic matter of unknown isotopic composition in standard en-

6

richment procedures currently compromises the accurate determination of isotope ratios. We

7

explored the use of molecularly-imprinted polymers (MIPs) for selective analyte enrichment

8

for 13 C/12 C and 15 N/14 N ratio measurements by GC/IRMS using 1H-benzotriazole, a typical

9

corrosion inhibitor in dishwashing detergents, as example of a widely detected polar organic

10

micropollutant. We developed procedures for the treatment of > 10 L of water samples, in

11

which custom-made MIPs enabled the selective cleanup of enriched analytes in organic sol-

12

vents obtained through conventional solid phase extractions. Hydrogen bonding interactions

13

between the traziole moiety of 1H-benzotriazole and the MIP were responsible for selective

14

interactions through an assessment of interaction enthalpies and 15 N isotope effects. The pro-

15

cedure was applied successfully without causing isotope fractionation to river water samples

16

as well as in- and effluents of wastewater treatment plants containing µg/L concentrations of

17

1H-benzotriazole and dissolved organic carbon (DOC) loads of up to 28 mg C/L. MIP-based

18

treatments offer new perspectives for CSIA of organic micropollutants through the reduction

19

of the DOC-to-micropollutant ratios.

2


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20

Introduction

21

The analysis of stable isotope ratios in organic soil and water contaminants has become a widely used

22

approach to identify the sources of pollution and to identify (bio)degradation pathways. 1–7 Whereas

23

constant ratios of 13 C/12 C, 2 H/1 H, 15 N/14 N, and of other elements in a compound enable one to infer

24

precursor materials, synthesis routes, and formation pathways of pollutants, 8–14 changes of isotope

25

ratios lead to stable isotope fractionation patterns that reveal the (bio)chemical reaction by which a

26

pollutant is degraded. 15–21 However, due to the poor sensitivity of gas and liquid chromatography

27

used in combination with isotope-ratio mass spectrometry, 22–25 the applications of compound-

28

specific isotope analysis (CSIA) have largely focused on so-called legacy contaminants such as

29

halogenated solvents, nitroaromatic explosives, and fuel constituents 26–33 Those compounds are

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often found in the high µg L−1 to mg L−1 concentration range and can be extracted from the

31

environmental matrices in straightforward procedures, for example, through transfer of the analytes

32

into the gas phase and enrichment onto solid sorbents. 32–37 Unfortunately, such procedures are

33

not necessarily applicable for CSIA of polar organic micropollutants of current interest 38 such as

34

pesticides, pharmaceuticals, consumer chemicals, and personal care products. Their sub-µg L−1

35

concentrations in natural and treated waters require the processing of large sample volumes greater

36

than 5 L by solid-phase extractions (SPE, e.g., 39 ) to obtain the necessary analyte mass for isotope-

37

ratio mass spectrometry. Moreover, the inherently poor selectivity of SPE-based procedures will

38

very likely lead to a co-enrichment of organic matter of unknown isotopic composition and thus

39

compromise accurate isotope ratio measurements.

40

One promising option to increase the selectivity of analyte enrichment procedures is the use of

41

molecularly-imprinted polymers (MIPs). MIPs are synthetic, typically custom-made materials ca-

42

pable of molecular recognition of a target analyte through specific intermolecular interactions. 40–44

43

Synthesis is carried out in the presence of the target analyte and involves the polymerization of

44

functional monomers that are selected based on their ability to interact with functional groups

45

of the target molecule. Therefore, the final materials exhibit a three-dimensional structure with

46

high specificity. 45 Even though the concept of solid-phase extraction with molecularly-imprinted 3



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47

polymers (MISPE) has been used successfully for years, 40,46–48 it has never been applied in com-

48

bination with isotopic analyses. In fact, MISPE based on non-covalent interaction between analyte

49

and sorbent seems ideally suited for the treatment of SPE-extracts, in which polar organic micropol-

50

lutants are normally enriched from large volumes of water samples. 49 Only µL volumes of organic

51

solvents can be injected onto gas chromatographs coupled to isotope-ratio mass spectrometers.

52

The substantial analyte enrichment to the mg L−1 level causes concomitant enrichment of organic

53

matrix and, therefore, requires further sample treatment. Because those extracts typically consist

54

of organic solvents, polar organic micropollutants can be extracted based on H-bonding and ionic

55

interactions with the MIP without interferences of water.

56

The goal of this work was to explore new sample clean-up strategies based on molecularly-

57

imprinted polymers for the stable isotope analysis of polar organic micropollutants in aquatic

58

environments. Here, we focused our work on the analysis of

59

benzotriazole (1H-BT), a corrosion inhibitor, which is widely used in dishwashing detergents.

60

Like many polar organic micropollutants, 1H-BT is too persistent to be degraded in waste water

61

treatment plants (WWTP) and therefore found in µg L−1 concentrations in rivers as well as influents

62

and effluents of WWTPs containing very different organic matrices. 50–52 The specific objectives of

63

our work were to (i) propose sample treatment procedures for MISPE-based stable isotope analysis

64

through the synthesis and application of a custom-made MIP for 1H-BT. (ii) We characterized

65

the selectivity of our materials in a comparison with other polar organic micropollutants such as

66

triazines and substituted benzotriazoles and (iii) evaluated the potential of method-induced isotope

67

fractionation from incomplete analyte recovery. (iv) Finally, we illustrate how MISPE-based

68

procedures for CSIA can be applied in different matrices by analysing δ13 C and δ15 N of 1H-BT in

69

riverwater, influent and effluent of a WWTPs, as well as in dishwashing detergent taps.

4


13 C/12 C

and

15 N/14 N

ratios of 1H-

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70

Experimental section

71

A list of all chemicals including suppliers and purities is provided in the Supporting Information

72

(SI).

73

Safety considerations

74

Milling and sieving the synthesized polymers can generate dust. The processing of materials should

75

be carried out under the fumehood. Additionally, gloves, goggles and respiration mask are advised

76

to be worn. The radical generator, azobisisobutyronitrile, decompose at temperature ≥ 45 °C and

77

may explode if large amounts are exposed to high temperatures. Do not exceed temperature of 40

78

°C during its purification.

79

Synthesis of molecularly-imprinted polymers

80

Molecularly-imprinted polymers were synthesized following an adapted procedure of Chapuis

81

et al. 53 for terbutylazine. The polymerization mixture consisted of 119.1 mg (1 mmol) 1H-

82

benzotriazole (1H-BT) as template, 344.4 mg (4 mmol) methacrylic acid as a functional monomer,

83

3964 mg (20 mmol) ethylene glycol dimethacrylate as crosslinker, 39.4 mg (0.24 mmol) azobi-

84

sisobutyronitrile as radical generator, and 5.6 mL dichloromethane as porogene. We dissolved

85

the template in the functional monomer, cooled the solution to 0℃ for 15 minutes and added the

86

remaining reagents. The polymerization mixture was purged with N2 in a borosilicate glass tube

87

(OD = 18 mm, ID = 15 mm), sealed with a screw-cap, and placed in an ice bath for 30 minutes. The

88

same procedure was used for preparation of non-imprinted polymer (NIP) except for the absence

89

of the template 1H-BT.

90

Polymerization took place over 24 hours at 2 ± 0.2℃ by immersing the glass tubes in a merry-

91

go-round photoreactor (DEMA 125, Hans Mangels GmbH, Bornheim-Roisdorf, Germany; Figure

92

S1) filled with a sodium nitrate filter solution (0.15 M, cut-off of wavelength > 320 nm) and

93

centred with a medium pressure mercury lamp (150 W) surrounded by a borosilicate glass jacket. 54

5



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94

After polymerization, the tubes were removed and crushed to recover the polymer monoliths.

95

The polymers were sequentially ground (Mixer Mill MM 301, Retsch GmbH, Germany) and

96

sieved through 100 µm sieve (Retsch GmbH, Germany). The particle fraction < 100µm was

97

sedimented in methanol to obtain particle size distribution between 20 and 100 µm. We removed

98

the template by ten repetitive cycles of Soxhlet extraction using mixtures of methanol and formic

99

acid (90/10 vol-%) until ≥ 98% of the 1H-benzotriazole was recovered. Nonimprinted polymers

100

were extrated in the identical manner. The identical procedure was applied to synthesize a MIP

101

with 5-,6-(CH3 )2 -benzotriazole as template for the quantitative analysis of imprinting efficiency.

102

Possible interferences of residual analytes on the accuracy of stable isotope analysis were evaluated

103

exemplarily for 1H-BT through (a) quantification of its concentration before and after the use of

104

MIPs with 1H-BT in organic solvent and (b) the comparison of

105

1H-BT before and after the use of MIPs with 1H-BT spiked river water samples.

106

Sample preparation procedures using molecularly-imprinted polymers

107

The multi-step procedure for the enrichment and purification of 1H-BT in (a) in- an effluent of

108

waste water treatment plants (WWTP), (b) spiked river water, and (c) dishwashing tabs is shown

109

schematically in Figure 1. Generally, sample preparation consisted of two solid phase extraction

110

steps (Fig. 1, B and D) with different pre- and post treatments.

111

Enrichment of 1H-BT from waste water plant influent and effluent

112

Samples from WWTP influent (5 L, sample no. 1 in Figure 1, step A) and effluent (10 L) were

113

filtered through 0.7 µm glass fiber filters (Whatman, GF/F 47mm) and acidified with HCl (32 %) to

114

pH 2.0. Filtered samples 2 containing 1H-BT were enriched by conventional solid phase extraction

115

using OASIS HLB cartridges (Waters, 6 g, 35 mL) in step B using a 12-port vacuum extraction

116

manifold (Supelco, Switzerland). Prior to sample loading, cartridges were conditioned with 100

117

mL hexane, 100 mL ethyl acetate, 100 mL methanol and 100 mL MiliQ water. Water samples

118

2 were percolated through the cartridges using a vacuum pump at a flow rate of ≤ 7.2 mL/min 6


13 C/12 C

and

15 N/14 N

ratios of

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WWTP influent/effluent

aqueous sample (1) filtration acidification

B

flow rate 1-CH3 -BT. The observed sequence

307

agrees with the notion that IF are highest for the template used for synthesis. 48 We verified this

308

outcome by assessing IF of the same analytes on another custom-made MIP, where 5-,6-(CH3 )2 -

309

BT was employed as a template instead of 1H-BT. The IF (CH3 )2 −BT -values are shown in Table 1

310

for the 5-,6-(CH3 )2 -BT-imprinted MIP and they are of similar magnitude as IF-values for 1H-

311

BT imprinted polymers. IF (CH3 )2 −BT decrease in the sequence 5-,6-(CH3 )2 -BT > 5-CH3 -BT >

312

1H-BT > 1-CH3 -BT confirming that the selectivity was highest for the template molecule. With

313

both MIPs, we did not observe selective interactions of 1-CH3 -BT. Absence of selectivity for N-

314

substituted benzotriazole suggests that the interactions of analytes with the polymer was based on

315

hydrogen bonding of the triazole moiety with the carboxylic acid functional group of the monomer

316

(methacrylic acid, Figure 3). Substitution at the 1H position on the triazole ring caused complete

317

loss of selectivity towards 1-(CH3 )-BT on both polymers.

318

Further evidence for the selectivity of the MIPs was obtained from the comparisons of the

319

apparent interaction enthalpies, ∆HMIP , 63 with various analytes, and interaction enthalpies of non-

320

imprinted polymers, ∆HNIP (Table 1). ∆HMIP were most negative, that is most favourable, for the

321

template molecule 1H-BT and became less negative for the substituted benzotriazoles. ∆HMIP -

322

values ranged between 7.0 and 16 kJ/mol which is in the lower range of interaction enthalpies for

323

hydrogen bonding (8-84 kJ/mol, 64,65 ). Note that interactions of benzotriazoles with non-imprinted

324

materials were also exothermic but the difference between MIP and NIP, ∆HMIP − ∆HNIP , revealed

325

the larger selectivity of the MIPs. ∆HMIP − ∆HNIP for benzotriazoles followed the same sequence

326

reported for IF-values. However, values approached zero for the remaining compounds showing

327

the lack of selective interactions of the MIP with benzothiazole, naphthalene, and atrazine.

328

Isotope fractionation from incomplete analyte extraction

329

We quantified the extent of C and N isotope fractionation from analyte-MIP interactions in a

330

separate experiment on MISPE cleanup step E (Figure 1). Table 2 shows mass fractions, mi , 18


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(a)

(b) HO

HO

H N N

CH3

N

N

N

H O

O

O

N

H

O

O

O

Figure 3. (a) Hydrogen bonding between the template, 1H -BT, and the functional monomer, methacrylic acid, used for imprinting enables selective interactions. (b) Absence of selective binding due to N-methyl substitution in 1-CH3 -BT. 331

and the corresponding δ13 C and δ15 N-values of 1H-BT recovered in three sample fractions (Fi ).

332

The total 1H-BT recovery was 99%. F1 corresponds to the fraction of analyte collected after

333

breakthrough during the loading of the cartridge with 1H-BT in dichloromethane. This fraction

334

amounted to 41% of the total analyte mass. F2 is the fraction of analyte obtained through washing

335

of the cartridge with the identical solvent (42%). F3 reflects the remaining 16% of 1H-BT that

336

were recovered from the MIP through elution with methanol. The same type of experiment was

337

carried out with dichloromethane extracts of river water using five-fold higher MIP (500 mg). As a

338

consequence of higher retention capacity, no 1H-BT was detected in F1 , whereas all 1H-BT mass

339

was recovered in the two remaining fractions, F2 (74%, Table 2) and F3 (26%).

340

The C isotope signatures of 1H-BT in the presence and absence of organic matrix from river

341

water samples varied only slightly (±1h) in the three fractions. The extent of C isotope fractionation

342

pertinent to the MISPE cleanup step calculated with eq. 4, ∆13 C, was negligible regardless of the

343

sample matrix (−0.6 ± 1.4h and 0.1 ± 1.1h, Table 2). By contrast, δ15 N values of 1H-BT varied

344

substantially (up to 13h) between the three sample fractions F1 to F3 . Due to the almost complete

345

recovery of the analyte after the elution with methanol, MISPE induced N isotope fractionation, 19



εN = -5.0 ± 2.2 ‰

-18 -20

15

δ Ni,MIP (‰)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 31

-22 -24 -26 -28 1.0

0.8

0.6

0.4

0.2

0.0

c/c0

Figure 4. N isotope fractionation of 1H -BT through stepwise elution from the MIP. δ15 Ni MIP (±1σ ) stand for the calculated N isotope signatures of 1H -BT remaining on the MIP after elution of different 1H -BT fractions. c/c0 is the fraction of 1H -BT remaining associated with the MIP. The data was generated by using information from Table 2 and eqs. 6 and 7. The solid line was obtained through non-linear regression of eq. 5 with an N of −5.0 ± 2.2h.

346

∆15 N is, nevertheless, negligible within uncertainty in both sample matrices (−1.4 ± 1.3h and

347

−0.2 ± 1.1h).

348

These observations suggests that a non-stoichiometric recovery of the analyte after the MISPE

349

cleanup step would not cause systematic C isotope fractionation whereas N isotope signatures could

350

be biassed towards more positive δ15 N values. We tentatively quantified an operational N isotope

351

enrichment factor, N , from the small data set for the MISPE cleanup step E in absence of organic

352

matrix using eq. 5. Figure 4 shows the average N isotope signatures of 1H-BT that remained

353

associated with the MIP (δ15 Ni,MIP , eq. 7) after sequential loading step F1 and F2 , respectively

354

(blue and green areas). The most enriched fraction of 1H-BT, F3 , with a δ15 N of −18.1 ± 0.9h,

355

was eluted from the MIP through the change of solvent (red area in Figure 3). The N isotope

356

fractionation trend was quantified with an N of −5.0 ± 2.2h (eq. 5) and illustrates that the 15 N-

357

containing 1H-BT is retained preferentially by the MIP. This isotopic preference corresponds to

358

an apparent 15 N kinetic isotope effect of 1.0054 ± 0.0022 (eq. 8) under the chosen experimental

20


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21

(h) c (h) c

∆13 C ∆15 N

F1

0.0 ± 1.3 0.0 ± 1.2

1.00 ± 0.03 0.41 ± 0.02 −26.1 ± 0.5 −25.4 ± 0.3 −26.9 ± 0.2 −28.3 ± 0.1

reference F3

−0.6 ± 1.4 −1.4 ± 1.3

0.42 ± 0.02 0.16 ± 0.03 −25.8 ± 0.4 −24.9 ± 0.1 −25.6 ± 0.2 −18.1 ± 0.9

no matrix F2 n.d n.d. n.d.

F1

0.1 ± 1.1 −0.2 ± 1.1

0.74 ± 0.02 −26.4 ± 0.2 −30.5 ± 0.3

0.26 ± 0.02 −25.6 ± 0.6 −17.5 ± 0.6

river water extract F2 F3

for F1 and F2 determined from 1H-BT in dichloromethane, F3 in methanol, n.d. = not detected due to larger MIP b uncertainties are ±1σ of triplicate measurements of concentrations or isotope mass used in MISPE cleanup step; c propagated uncertainties (95% confidence intervals). ratios;

a Data

(-) b (h) b (h) b

mi δ13 C δ15 N

Fi

Table 2. Sample fractions of 1H -BT, Fi collected during the MISPE cleanup step E (Figure 1): mass fractions of 1H -BT, mi , C and N isotope signatures, δ13 C and δ15 N, and extent of C and N isotope fractionation, ∆13 C and ∆15 N derived with eq. 4. a

Page 21 of 31 Analytical Chemistry


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359

conditions. The observation of N isotope fractionation in the absence of any isotope fractionation

360

for C implies that the N atoms of 1H-BT were involved in the interactions with the MIP and

361

confirms the above conclusion that the selectivity of the MIP is indeed based on H-bonding with

362

the triazole moiety of the analyte (Figure 3). Finally, this

363

recoveries during the MISPE cleanup step of ≥ 81% are sufficient to limit such shifts of δ15 N to

364

≤ 1.1h (eq. 9), that is to the typical precision of N isotope ratio measurements by GC/C/IRMS. 5

365

Application in wastewater treatment plants

366

We applied the sample preparation procedures shown in Figure 1 to determine the C and N isotope

367

signatures of 1H-BT in the influent and effluent of a WWTP, one of the frequently encountered

368

matrices of the pollutant with DOC contents of several mg C/L. 51,52 The outcome was verified

369

through a comparison the δ13 C and δ15 N values with those from 1H-BT in dishwashing detergents

370

sold in villages that discharge their sewer into the studied WWTP.

15 N

isotope effect implies that 1H-BT

371

Figure 5 shows the δ13 C and δ15 N values of 1H-BT in the influent and effluent of the WWTP

372

as well as in dishwashing detergents sold by retailers in the study area. δ13 C and δ15 N values of

373

1H-BT in dishwashing detergents span from −27h to −23h and −11h to 1h, respecitvely. δ13 C

374

cover a similar range observed previously by Spahr et al. 55 with a simplified approach whereas our

375

analysis reveals an even wider distribution of δ15 N in 1H-BT. The wastewater samples (2 in Figure 1)

376

contained substantial amounts of DOC that amounted to 7.3 and 28 mg C/L for effluent and influent,

377

respectively. The substantial interferences on C isotope ratio measurements were reduced through

378

an additional liquid-liquid extraction during step F (Figure 1). δ15 N values of 1H-BT in influent

379

and effluent samples were identical within uncertainty (−4.5 ± 0.9h vs. −5.6 ± 1.3h) whereas

380

the difference of their δ13 C was only minimal (−26.8 ± 0.2h vs. −26.1 ± 0.4h). Even though a

381

quantitative analysis of the C and N isotope signatures in the WWTP and in dishwashing detergents

382

is beyond the scope of this work, data in Figure 5 reveals some consistent trends which confirm the

383

applicability of MISPE-based procedures for CSIA. Similar C and N isotope signatures of 1H-BT

384

in influent and effluent agree with the frequently made observation that this micropollutant is not 22


Page 23 of 31

Migros Denner Spar average

Coop Dorfladen Volg

2 0 -2

15

δ N (‰)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-4 -6 -8 -10 Influent Effluent

-12 -28

-26

-24

13

δ C (‰)

Figure 5. C and N isotope signatures of 1H -BT in the influent and effluent of a WWTP (coloured triangles) as well as in various solid, liquid, and gel-like dishwashing detergents sold by retailers in the study area (grey symbols). The dashed lines correspond to the arithmetic mean of δ13 C and δ15 N of 1H -BT in detergent samples. Error bars represent ±1σ . 1H -BT influent and effluent concentrations were 4.3 and 3.8 µg/L, respectively.

385

degraded during the waste water treatment process. 51,52 Moreover, those values are also within the

386

range of δ13 C and δ15 N values found in dishwashing detergents that are sold in the study area and

387

they are within less than 1h of their average values.

23



388

Conclusion

389

Our work illustrates that sample treatment procedures which rely on the selective cleanup of

390

enriched organic micropollutants by molecularly-imprinted polymer offer new perspectives for

391

CSIA. Extractions of organic micropollutants in large volume samples by conventional SPE are

392

an essential step to enrich adequate amounts of analytes for isotope-ratio mass spectrometry but

393

they will inevitably lead to concomitant enrichment of organic matter. This matrix can be removed

394

selectively in organic extracts with MIPs. The application of molecularly-imprinted polymers

395

for CSIA of 1H-BT especially in influent and effluent samples from WWTPs revealed, however,

396

that despite good selectivity, organic matrix interferences may become too large thus making the

397

application of MISPE impracticable. Our analysis suggest that the C-normalized concentration

398

ratio of dissolved organic carbon (DOC) to micropollutant can be a useful parameter to assess the

399

feasibility of MISPE-based sample cleanup for CSIA, particularly for measurements of C isotope

400

ratios. In fact, the C-normalized DOC:1H-BT ratio decreased systematically as a consequence of

401

the series of treatment of WWTP samples. Whereas the DOC:1H-BT ratio in the aqueous WWTP

402

influent was 11000 (1 in Figure 1), it decreased to 860 in sample 3 after SPE and 340 in sample

403

5 after MISPE. In WWTP effluent, the DOC:1H-BT ratio decreased from 3200 in the aqueous

404

effluent (1) to 190 after SPE (3) and 76 (5) after MISPE. Whereas we implemented liquid-liquid

405

extraction in order to further reduce DOC:1H-BT ratios in WWTP samples, alternative approaches

406

such as preparative HPLC on sample 5 could also be applied. 39 A systematic and quantitative

407

assessment of the acceptable ratio of matrix:micropollutant is warranted to assess the feasibility

408

of MISPE sample preparation for CSIA more generally. Such efforts will enable the application

409

of stable isotope analyses for tracking sources and transformation processes of many contaminants

410

of emerging concerns including, for example, pharmaceuticals, pesticides, and water disinfection

411

byproducts. 11,12,16,17,39

24


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412

Acknowledgement

413

This work was supported by the Swiss National Science Foundation (grant no. CRSII2-141805).

414

We thank Stefanie Jucker, Hans-Jürgen Schindler, Samuel Derrer, Marius Wiesmann, Alessandra

415

Sodero, Tony Merle, and Aileen Melsbach for experimental support.

416

Supporting Information Available

417

Description of field site and sampling campaign, additional preparation steps for dishwashing

418

detergents, derivation of interaction enthalpies, molecular structure of analytes. This material is

419

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

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m/z 44 (mV)

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pre-MISPE post-MISPE N

standard

N N H

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time (sec)

Molecularly Imprinted Polymers for Compound-Specific Isotope

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