Quantification of Total N

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Quantification of total N-nitrosamine concentrations in aqueous samples via UV-photolysis and chemiluminescence detection of nitric oxide Florian Breider, and Urs von Gunten Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03595 • Publication Date (Web): 19 Dec 2016 Downloaded from http://pubs.acs.org on December 19, 2016

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Analytical Chemistry

1

[Analytical Chemistry]

2

Quantification of total N-nitrosamine concentrations in aqueous samples

3

via UV-photolysis and chemiluminescence detection of nitric oxide

4 5 Florian Breider1 and Urs von Gunten1,2

6 1

7 8 9

School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

2

Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland

10 11

*

12

Urs von Gunten, School of Architecture, Civil and Environmental Engineering (ENAC), Ecole

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Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

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phone: +41 58 765 5270; e-mail: [email protected]

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keywords: N-nitrosamines, photolysis, chemiluminescence, nitric oxide, ultraviolet, microphotoreactor,

16

wastewater, personal care products, polyquaternium

Corresponding author:

17 ACS Paragon Plus Environment

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ABSTRACT

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N-nitrosamines are potent mutagens and carcinogens that can be formed during oxidative water

3

treatment. This study describes a novel method for the determination of total N-nitrosamines by UV-

4

photolysis and subsequent chemiluminescence detection of nitric oxide. Denitrosation of N-nitrosamines

5

was accomplished with a microphotochemical reactor consisting of a knitted reaction coil and a low-

6

pressure mercury lamp. The detection limits for differing N-nitrosamines ranged between 0.07 µM (14

7

pmol injected) and 0.13 µM (26 pmol injected). The nitric oxide formation from selected N-

8

nitrosamines was linear (R2=0.98-0.99) from 0.1 and 10 µM. The small cross-section and volume of the

9

microphotochemical reactor used in this study was optimal to reach a sensitivity level comparable to

10

chemical denitrosation-based methods. In addition, this method had several advantages over other

11

similar methods: (i) compared to chemical denitrosation with copper monochloride or triiodide, the UV-

12

photolysis doesn’t require chemicals and is not affected by interferences of by-products (e.g. formation

13

of NOI), (ii) the reproducibility of replicates was enhanced compared to the triiodide-based method and

14

(iii) a commercially available photoreactor and NO analyzer were used. The application of this method

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for the determination of the N-nitrosamine formation potential of personal care products demonstrates

16

its utility for assessing whether N-nitrosodimethylamine (NDMA) or other specific nitrosamines of

17

current interest are dominant or minor components, respectively, of the total N-nitrosamine pool in

18

technical aquatic systems or biological samples.

19 20

1. INTRODUCTION

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N-nitrosamines are disinfection by-product that can be formed during oxidative water treatment

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Reaction pathway studies have indicated that a formation of N-nitrosamines can arise from the reactions

23

of natural and synthetic amine precursors present in natural and technical aquatic systems with chemical

24

oxidants such as chloramines, chlorine or ozone 1,5. The interest in N-nitrosamines has been growing in

25

the last decade, because this class of compounds includes potent mutagens and carcinogens 6.

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Furthermore, drinking water utilities are increasingly exploiting algal- or wastewater-impacted waters to ACS Paragon Plus Environment

1–4

.

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meet the growing demand and it is suspected that these impacted source waters contain higher levels of

2

nitrogenous precursors potentially leading to N-nitrosamines 7–10.

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To assess whether N-nitrosodimethylamine (NDMA) or other specific N-nitrosamines of current interest

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are dominant or minor components of the total N-nitrosamine pool, a triiodide chemiluninescence-based

5

method to measure the total N-nitrosamine concentration in water was optimized

6

(HI3) is the most commonly used denitrosating agent. Triiodide is in equilibrium with iodine and iodide

7

(HI or I- and I2) (Eq. 1). Triiodide readily reduces nitroso-containing compounds, releasing iodide and a

8

nitrosonium cation (NO+) (Eq. 2). Then by reaction with iodide, the nitrosonium cation is readily

9

converted to NO• (Eq. 3) 12,13:

11

. Acidic triiodide

10 11

HI3 ⇄ I2 + HI

(1)

12

HI3 + R2X-NO ⟶ 3I- + R2XH + NO+ + 2Η+ (X=S or N atom; R= alkyl chain)

(2)

13

2NO+ + 2I- ⟶ 2NO• + I2

(3)

14 15

To date the triiodide-based method is the most common method for nitric oxide analysis. However, it

16

has been shown that the triiodide assay is strongly influenced by the sample composition and the

17

stability of the denitrosating agent

18

absorption spectrometry that nitrosyliodide (NOI) can be formed by reaction between triiodide and

19

nitrogen oxides. NOI is a highly potent nitrosating agent for which the fate critically depends on the

20

sample composition

21

organic compounds present in the sample, thereby forming C-, N- and S-nitroso-containing compounds.

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It has also been shown that subsequent injections of S-nitrosoglutathion, an endogenous S-nitrosothiol

23

playing a critical role in nitric oxide signalling, leads to signal attenuation and peak broadening 14. These

24

results militate against the use of triiodide-based methods to measure total N-nitrosamine concentrations

25

in complex water samples and suggest that previous results should be reassessed. Other studies have

26

shown that HBr, HI and CuCl are potent denitrosating agents 18. However, CuCl is highly unstable and

14–17

14

. Hausladen et al. have shown by gas-phase UV/visible light

. Hence, it cannot be excluded that NOI formed in the reactor can react with

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can be rapidly oxidized to CuO in presence of oxygen and may form a precipitate in the analytical

2

system (personal communication, Prof. Yunho Lee, GIST, Korea). Moreover, HBr and HI are volatile

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and therefore the concentration of these denitrosating agents decline with time due to the gas flow used

4

to purge the samples.

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Overall, quantifying the total concentration of N-nitrosamines is a difficult task due to the potential for

6

bias related to the vast number of compounds present in environmental and biological samples.

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Moreover, denitrosation agents used in chemiluminescence based-methods (see above) are very unstable

8

and may form potent nitrosating agents that might form N-nitrosamines during the analytical process.

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Alternatively, N-nitrosamines can be photolysed by UV light yielding NO• and NO2- 19,20. Photochemical

10

reactions are usually easier to control since no chemical reagents are involved and the reaction is

11

controlled by the UV dose. Based on the problems related to determinations of total N-nitrosamine

12

concentrations and the promising features of UV photolysis, we developed and evaluated a photolysis

13

chemiluminescence-based system for the analysis of the total concentration of N-nitrosamines in

14

aqueous samples. The signal stability of the UV photolysis-based method was compared with the

15

triiodide method. Furthermore, the selectivity and the sensitivity of the photolytic chemiluminescence-

16

based method were tested with various organic and inorganic nitrogenous compounds. Finally, we

17

applied this method to evaluate the total concentration of N-nitrosamines in wastewater and greywater

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samples and N-nitrosamines formed during chloramination and ozonation of aqueous samples of soaps,

19

shampoos and detergent.

20 21

2. MATERIALS AND METHODS

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Materials and analyses. Chemical compounds and information on sample pre-concentration methods

23

are provided in the Supporting Information (SI). Monochloramine (NH2Cl) was freshly prepared prior to

24

each experiment by mixing equal volumes of NH4Cl (52.5 mM, pH 9.5) and NaOCl (50 mM). The

25

concentration of monochloramine was determined spectrophotometrically (ε243nm= 461 M-1 cm-1) 21. An

26

ozone stock solution was freshly prepared in ultrapure water using an ozone generator (Innovatech, ACS Paragon Plus Environment

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CMG 3-5). Ozone gas produced from ultrapure oxygen gas (>99.9995%) was injected using a tube

2

equipped with a fritted glass into a 1 L glass bottle filled with ultrapure water maintained at low

3

temperature with an ice bath. The concentration of the ozone stock solution was measured by direct UV

4

spectrophotometry by mixing 1 mL of the ozone solution with 2 mL of a 50 mM H3PO4 solution in a 1

5

cm quartz cuvette (ε260=3200 M-1 cm-1) 20.

6

Specific N-nitrosamines were analysed by HPLC equipped with a diode array detector (Dionex Ultimate

7

3000) using a C18 column (AcclaimTM PolarAdvantage II, 5µm, 120Å, 4.6×150mm, Thermo Scientific)

8

with 10 mM phosphate buffer pH 2.3 and HPLC-grade acetonitrile as mobile phase. The method used to

9

analyse N-nitrosamines of the US-EPA 8270 standard mix, starts with an equilibration phase with 2%

10

acetonitrile during 3 min with a flow rate of 0.8 mL/min followed by a gradient from 2 to 80% of

11

acetonitrile during 15 min and a stabilisation phase with 80% acetonitrile during 5 min. Absorbance

12

chromatograms were obtained at 230 nm. The limits of detection and quantification of the method

13

calculated based on the standard error (SE) and the slope (m) of the calibration curve are 0.06 µM

14

(LOD=3.3×SE/m) and 0.19 µM (LOQ=10×SE/m), respectively (calibration range 0.025–2 µM).

15 16

Instrumentation. Figure 1 shows a schematic diagram of the photolysis-chemiluminescence system

17

used in the present study. To analyse the total concentration of N-nitrosamines, 200 µL samples were

18

injected into a N2 stream using a manual injector (Rheodyn®, model 7125, USA) equipped with a 200

19

µL or a 5000 µL loop (Supelco, USA) and connected to a microphotochemical reactor (LCTech Ltd.,

20

Germany) consisting of a low-pressure mercury lamp (λmax 254 nm) and a 1 mL knitted reaction coil

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surrounding the UV lamp (He=10.4×103 J/cm2 measured at 0.7 mL/min) (Figure 2)

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passed through the photoreactor, the liquid and NO• produced during the UV-photolysis (Eq. 4) are

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transferred by the carrier gas (ultrapure N2) to a purging system kept at 70°C to promote the degassing of

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photolyzed samples. The purging vessel is equipped with a fritted glass, a condenser cooled at -5°C

25

using a water/ethylene glycol mixture (1:1) and a gas filter to prevent contamination of the analyser. The ACS Paragon Plus Environment

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. After having

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cooling system is specifically used to reduce the amount of water vapour and eventually organic

2

compounds (e.g. methanol used for the pre-concentration) that might be transferred in the detector. NO•

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released from the purging vessel is measured using a nitric oxide analyser (Sievers, NOA model 280i,

4

USA). Because the chemiluminescence reaction is rapid and takes place in the gas phase, the nitric

5

oxide analyser can be connected directly in-line with the purging vessel from which dissolved NO• gas is

6

extracted. The principle of detection of NO• by chemiluminescence is based on the rapid reaction of NO•

7

with ozone (O3), which yields NO2⋆ in an excited state. As the excited electron returns to its ground

8

state, a photon is emitted and detected as chemiluminescence. Equations 4 to 10 summarize the

9

chemical processes from the photolysis to the chemiluminescence:

10 11

R-N-NO + hν ⟶ R-N + NO•

(4)

12

R-N-NO + hν ⟶ R-N + NO2-

(5)

13

NO2- + H2O + hν ⟶ NO• + •OH + OH-

(6)

14

NO• + NO2- ⟶ N2O3

(7)

15

N2O3 ⟶ 2HNO2 ⇄ 2NO2- + 2H+

(8)

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NO• + O3 ⟶ NO2⋆ + O2

(9)

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NO2⋆ ⟶ NO2 + hν (UV-vis light)

(10)

18 19

The emitted light is then amplified and detected by a photomultiplier tube (PMT). The analyser was

20

calibrated using solutions of differing concentrations of the US-EPA 8270 N-nitrosamines standard mix.

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To reduce the carry over, the injection loop and the photoreactor were rinsed with ultrapure water

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between each sample injection. High purity N2 (99.999%) was chosen as carrier and purging gas because

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NO• can be oxidized by oxygen producing NO2- and NO3-

17

(Eq. 11).

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2 NO• + O2 + H2O ⟶ NO2- + NO3- + 2H+


(11) 6

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For the triiodide-based method, the purging system was used as a reaction vessel and samples were

3

injected directly through a septum. The preparation of the triiodide solution and analytical conditions

4

were similar to the method described previously 11. The data files were saved as text files and processed

5

using the OriginLab® software.

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N-nitrosamine formation potentials from personal care products. Consumer products such as soaps,

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detergents and disinfection agents containing quaternary ammonium compounds are suspected to form

9

N-nitrosamines when treated with inorganic chloramines or ozone

22

. The maximum N-nitrosamine

10

concentrations that can be produced in excess of reagent also called N-nitrosamine formation potentials

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were determined by treatment of personal care products (soaps, shampoos and a washing detergent) with

12

ozone or monochloramine. 0.5 g/mL stock solutions of two shampoos, two soaps and a sample of a

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laundry detergent were prepared in ultrapure water. 20 µL of each personal care product stock solution

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was added to a 20 mL brown vial. Each sample was then treated with 9 mL of a 0.84 mM aqueous ozone

15

solution or with 2 mL of a 2.5 mM NH2Cl solution. Chloraminated samples were stored during 10 days

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at ambient temperature in the dark, then the samples were treated with 1 mL of a 100 mM sulfamic acid

17

solution to reduce nitrite potentially formed during the reaction to molecular nitrogen. To quench the

18

residual monochloramine in the chloraminated samples, 1 mL of a 1.8 M ascorbic acid solution was

19

added. Inorganic chloramines are volatiles and can be photolysed to NO• by UV light in the photoreactor

20

23

21

chloraminated samples is not due to the presence of residual monochloramine, samples of diluted

22

monochloramine (250 µM) with and without ascorbic acid treatment were analysed (Supporting

23

information Figure S3).

. This can give a false positive signal. To verify that the chemiluminescence signal measured for

24 25

3. RESULTS AND DISCUSSION


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N-nitrosamines photodecomposition. N-nitrosamines are photosensitive and UV radiation leads to the

2

photolytic cleavage of the N-N bond and the formation of NO•, which is a highly reactive gas. To

3

determine whether the fluence H of the microphotoreactor used in this study is sufficient to achieve a

4

complete cleavage of the N-N bond of N-nitrosamines, the UV doses required for 90% and 99%

5

degradation were calculated for several N-nitrosamines using the following equations 24:

6 7

ln

[C ]0 Φ cε λ ln(10) = H [C ] f 1000U λ

(12)

8 9

where C0 and Cf are the initial and final molar concentrations of N-nitrosamine, ΦC is the quantum yield,

10

ελ is the molar absorption coefficient [M-1 m-1] at the irradiation wavelength λ, Uλ is the molar photon

11

energy [J einstein-1] at the irradiation wavelength λ and H is the fluence [J m-2]. Thus the final

12

expression for the UV dose required for 90% (H90%) and 99% (H99%) degradation are:

13 14

H 90% =

1000 ×U λ × ln(10) ΦCεC ln(10)

(13)

15

H 99% =

1000 × U λ × ln (100 ) Φ C ε C ln(10)

(14)

16 17

The UV dose for 90% and 99% degradation were calculated using the quantum yields and the molar

18

absorption coefficients previously determined by Plumlee and Reinhard 2007 for a selection of N-

19

nitrosamines (SI Table S1) 27. The results of these calculations show that the UV dose required for 90%

20

photlolysis range from 0.85 - 1.36 kJ/m2 and from 1.71 - 2.72 kJ/m2 for 99% photolysis (SI Table S1).

21

Considering that the flow rate of the sample through the microphotoreactor is 8.5 mL/min, the UV dose

22

available for the photolysis of N-nitrosamines is 8.56 kJ/m2. These calculations show that the UV dose

23

provided by the microphotoreactor is approximately four times higher than the average UV dose (2.17 ACS Paragon Plus Environment

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kJ/m2) required for 99% photolysis. Hence the microphotoreactor used in this study is able to achieve a

2

complete photolysis of the N-N bond of most of the previously selected N-nitrosamines.

3 4

Signal stability and reproducibility. It has been shown previously for the triiodide method that

5

consecutive injections of S-nitrosoglutathion led to a strong signal attenuation and widening of the

6

chemiluminescence peaks

7

chemiluminescence methods, a 1 µM NDMA standard in ultrapure water was injected several

8

consecutive times with both methods. The results show that for the triiodide method consecutive

9

injections lead to a reduction of the peak area (1σ=19.7%, n=6) and to peak tailings as previously

14

. To compare the reproducibility of triiodide and photolysis-

14

10

observed for S-nitroso-containing compounds

(Figure 3a). In contrast, a comparison of three

11

injections of the standard for three fresh triiodide solutions showed a good reproducibility (1σ=6.3%,

12

n=3), suggesting that consecutive injections of NDMA into the reaction vessel lead to a decline of the

13

conversion efficiency of NDMA (Figure 3b) for the triiodide method. This likely results from the

14

competition between the reaction of triiodide with the nitroso groups (Eqs. 1-3) and the reaction of

15

nitrosyliodide (NOI) with dimethylamine thereby forming NDMA (Eqs. 15-16) 14.

16 17

NO+ + I- ⇄ NOI

(15)

18

NOI + (CH3)2NH ⟶ (CH3)2NN=O + HI

(16)

19 20

da Silva et al. have shown that the second order rate constants for the nitrosation of five secondary

21

amines by NOI ranged between 8.8×104 and 2.6×107 M-1 s-1 17. Thus the reformation of N-nitrosamines

22

(Eq. 16) in the purging vessel might lead to a loss in the apparent NO• formation for the triiodide

23

method.

24

The results obtained with the photolysis-based method (Figure 3c) demonstrate that the standard

25

deviation of the peak areas is lower (1σ=9.1%, n=9) than the value obtained for consecutive injections


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with the triiodide method (1σ=19.7%, n=6) (Figure 3a). This can be explained by the absence of

2

chemical reagent and the stable exposure of the samples to UV light. Due to its unpaired valence

3

electron, NO• is a highly reactive chemical species and its half-life time in aqueous solution is in the

4

order of seconds to minutes 26. As only a small volume of liquid (200 µL per injection) is present in the

5

purging vessel during the analysis, NO• formed by UV photolysis of N-nitrosamines is rapidly

6

transferred to the gas phase. Because the purging system and the transfer line are under partial vacuum,

7

the half-life time of NO• is probably much longer in the gas phase than in the liquid phase. Injections of

8

1 and 10 µM NDMA standards over a period of two months showed that the chemiluminescence signal

9

remains constant during the entire period (1σ(1µM)=9.8% n=25; 1σ(10µM)=9.5% n=10). Similar

10

standard deviation values were also measured for multiple injections of 1 and 10 µM US-EPA 8270 N-

11

nitrosamine standards (1σ(1µM)=12.1% n=5; 1σ(10µM)=9.8% n=5).

12

Additionally, compared to the triiodide method, the required analysis time (preparation, transformation

13

and detection) was shorter for the UV photolysis-based method (~2 min versus ~10 min) and the

14

background signal remained constant indicating that neither N-nitroso compounds, NO2- nor NO• were

15

formed in the purging vessel. Hence, these results emphasize the advantages of UV photolysis compared

16

to of the triiodide reagent for the analysis of the total N-nitrosamine concentrations in water.

17 18

Evaluation of conversion efficiency, linearity and sensitivity. The contribution of specific N-nitroso

19

compounds to the total N-nitrosamine pool can vary depending on the structural characteristics of the

20

precursors 7. Thus, to quantify the total N-nitrosamine concentration it is important that a method

21

converts all N-nitrosamines with comparable efficiencies. In this study we compared the conversion

22

efficiency of eleven N-nitrosamines using the slopes of their calibration curves measured between 0.1

23

and 5 µM using a 200 µL injection loop with the US-EPA 8270 N-nitrosamine standard mix. The results

24

indicate that all N-nitrosamines tested can be detected and quantified with comparable efficiencies. The

25

conversion efficiencies of N-nitrosamines were between 78% (N-nitrosomorpholine, NMOR) and 117%


10

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(N-nitrosomethyletylamine, NMEA) relative to the average conversion efficiency of the US-EPA 8270

2

N-nitrosamine standard mix (Table 1). Although some variation of the conversion efficiencies was

3

observed among the different N-nitrosamines, these differences can be considered as negligible as the

4

average of the individual recoveries of all N-nitrosamines is similar to the recovery of US-EPA 8270

5

standard mix.

6

Nitric oxide formation from selected N-nitrosamines was linear in the concentration range 0.1 - 10 µM

7

(R2=0.98-0.99) (Figure 4). For a 200 µL injection loop, the limits of detection (LOD) and limits of

8

quantification (LOQ) defined as 3.3 and 10 times the ratio of the standard deviation of the linear

9

regression to the slope of the regression line ranged between 0.07 and 0.13 µM and 0.20 and 0.40 µM, 11

10

respectively for the selected N-nitrosamines (Table 1)

11

decreased the LOD (0.15 µM) and LOQ (0.5 µM) for the US-EPA 8270 standard mix by a factor of 2

12

compared to a 200 µL injection loop. However, if these values are reported based the injection volume,

13

the mass-based LOD or LOQ for the 200 µL injection loop are 20 pmol or 60 pmol, respectively,

14

whereas these values are about ten times higher for the 5000 µL injection loop (LOD=170 pmol,

15

LOQ=550 pmol). This indicates that the injection volume has likely an influence on the lifetime and the

16

transfer of NO• from the liquid to the gas phase. For large sample volumes more time is required to

17

purge the NO• and therefore, NO• can be more likely consumed by reactive compounds present in the

18

purging vessel. The LOD and LOQ for a 200 µL injection loop are comparable to those for the triiodide

19

chemiluminescence method (LOD=0.11 µM, LOQ=0.30 µM) 4. Considering that nitrosamine samples

20

can be pre-concentrated by solid-phase or liquid-liquid extraction methods with a 1000-fold

21

concentration factor and a minimum extraction efficiency of 50%, the theoretical method detection limit

22

with a 200 µL injection loop would be around 200 pM or 14.8 ng/L as NDMA. The LOD defined as the

23

statistically calculated minimum concentration that can be measured with 99% confidence that the

24

reported value is greater than zero was also determined from thirteen injections of 200 µL of a solution

25

of 5 µg/L US-EPA 8270 N-nitrosamine mix (Supporting information Figure S1). Considering a 1000-

. The use of an injection loop of 5000 µL


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Page 12 of 33

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fold concentration factor and a minimum extraction efficiency of 50%, the LOD value calculated with

2

this statistical method is 130 pM or 9.6 ng/L as NDMA.

3 4

Interferences from compounds without N-nitroso groups. Complex samples such as wastewater or

5

drinking water can contain numerous compounds that might interfere with N-nitrosamines analyses. To

6

assess the selectivity of the photolysis-chemiluminescence method, a range of inorganic (nitrite, nitrate)

7

and organic nitrogen-containing compounds with differing functional groups (C-nitroso, C- and O-nitro

8

containing compounds, oximes, nitramine, N-oxide) were measured and compared to the signal

9

measured for the US-EPA 8270 standard mix. The compounds selected for this study were chosen on

10

the basis of previous literature related to total N-nitrosamines analysis and commercial availability of the

11

compounds

12

almost quantitative conversion of 96% relative to the US-EPA 8270 standard N-nitrosamines mix (Table

13

1). For instance biological nitrification-denitrification is the most commonly used process for nitrogen

14

removal from wastewater. During partial nitrification nitrite is formed and might therefore interfere with

15

the signal of N-nitrosamines.

16

Sulfamic acid is a moderately strong acid that reacts with nitrous acid to yield N2 gas

17

nucleophilic primary amine group of sulfamic acid can attack the nitrosonium cation (NO+), which

18

arises from the protonation of nitrous acid and the resulting diazonium cation dissociates to N2, sulfuric

19

acid and water (Eqs. 17-19).

11,14,16

. Among all compounds tested in this study only nitrite exhibited a measurable and

27,28

. The

20 21

NO2- + 2H+ ⇄ HNO2 + H+ ⇄ NO+ + H2O

(17)

22

NO+ + H2NSHO3 ⟶ N≡N+SHO3 + H2O

(18)

23

N≡N+SHO3 + H2O ⟶ H2SO4 + N2 + H+

(19)

24 25

To assess the potential of nitrite removal by treatment with sulfamic acid, samples prepared with

26

ultrapure water were spiked with 1 µM of NDMA and 1.5 µM of nitrite and then treated with an excess 12 ACS Paragon Plus Environment

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1

of sulfamic acid at pH 1.9. Moreover, wastewater treatment plant effluent samples containing 0.54 µM

2

of nitrite were spiked with 1 µM of NDMA and then treated with an excess of sulfamic acid (Figure 5a).

3

Treatment of the samples prepared in ultrapure water with sulfamic acid shows that the

4

chemiluminescence signal of NDMA is not significantly affected. Furthermore, after treatment the

5

nitrite signal was non-detectable (Figure 5a). These results indicate that a treatment with an excess of

6

sulfamic acid warrants an elimination of the bias related to the presence of nitrite in the samples without

7

affecting the signal of N-nitrosamines (up to 5000 µM or 230 mg/L NO2-; Supporting information

8

Figure S2). The analysis of the samples prepared with wastewater effluent without pre-concentration

9

shows that the difference between the signal of wastewater and ultrapure water spiked with NDMA is

10

equivalent to the signal in the wastewater sample (Figure 5b). After treatment with sulfamic acid, the

11

chemiluminescence signal of wastewater effluent spiked with 1 µM NDMA was similar to the signal

12

measured for 1 µM NDMA in ultrapure water indicating that nitrite was mainly responsible for the

13

matrix effect observed in the wastewater effluent sample (Figure 5b). Therefore, all water samples

14

should be pre-treated with an excess of sulfamic acid before analysis to prevent a bias due to the

15

presence of nitrite.

16

S-nitroso compounds such as S-nitrosoglutathion are also known to form NO• upon photolysis

17

However, the potential interference of S-nitrosothiol was not tested in the present study since the

18

concentration of such compounds is expected to be very low in natural and human impacted water.

19

Indeed, S-nitrosothiol are more likely to be present in biological samples since for instance red blood

20

cells are known to release S-nitrosothiols into the bloodstream to induce the vasodilation of blood

21

vessels. However, in presence of S-nitroso compounds a pre-treatment with mercuric chloride (HgCl2)

22

will lead to a conversion of these compounds to nitrite, which can subsequently be removed by a

23

sulfamic acid treatment 11,14.

14

.

24


13


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Page 14 of 33

1

Analysis of pre-concentrated wastewater effluent and greywater samples. Wastewater effluent and

2

greywater samples were pre-concentrated by solid phase extraction (~250 fold, see SI section 2). Nitrite

3

was quenched by addition of a concentrated solution of sulfamic acid (2.5mL 2 M, final conc. 2 mM)

4

and then the samples were analysed in triplicate via UV-photolysis chemiluminescence to test if this

5

method can be used to analyse the total concentration of N-nitrosamines in complex environmental

6

samples. To test the reliability of the method, a pre-concentrated sample of wastewater spiked with 15

7

nM of the US-EPA 8270 standard mix was compared with a non-spiked sample. N-nitrosamine recovery

8

during the extraction with Oasis HLB solid phase extraction cartridges ranged from 46 to 61%. A

9

comparison of the total N-nitrosamine with a spiked concentration of 15 nM of the US-EPA 8270

10

standard mix in wastewater and ultrapure water shows similar results, if the blank total N-nitrosamine

11

concentration in the wastewater is taken into consideration (Supporting information Figure S4a).

12

Although the organic matrix of the wastewater can absorb in the UV range of the reactor, thereby

13

reducing the UV dose for the photolysis of N-nitrosamines, these results demonstrate that low

14

concentrations of N-nitrosamines are quantifiable in a complex sample matrix without significant

15

reduction of the signal. Furthermore, several wastewater effluent and greywater samples have been pre-

16

concentrated and analysed via UV-photolysis and chemiluminescence detection of nitric oxide. Analyses

17

of various pre-concentrated water samples have shown that the total concentration of N-nitrosamines in

18

wastewater effluents was between 49.8±5.1nM (n=6; WWE sample A) and 50.2±4.9nM (n=6; WWE

19

sample B) whereas the concentration in greywater samples was 11.1±1.8nM (n=6; handwashing sink)

20

and 16.2±2.1nM (n=6; washing machine) (Supporting information Figure S4b). These total N-

21

nitrosamines concentrations are in the same range as previously reported

22

demonstrate that samples with initial total N-nitrosamine concentrations lower than the LOQ can be

23

analysed after a solid phase pre-concentration step.

4,7,31

. Hence, these results

24 25

Analysis of chloraminated and ozonated personal care products. Various personal care products

26

were treated with ozone and monochloramine and then analysed in triplicate via UV-photolysis and ACS Paragon Plus Environment

14

Page 15 of 33

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1

chemiluminescence detection of nitric oxide to assess their N-nitrosamine formation potential. The

2

results of these experiments indicate that the chemiluminescence signal measured for chloraminated

3

samples is due to N-nitroso compounds formed from the reaction of monochloramine with unknown

4

precursors in personal care products (Supporting information, Figure S5). When quantified with the US-

5

EPA 8270 standard mix curve, the chemiluminescence signal of the chloraminated samples was above

6

the LOQ (0.30 µM) whereas the ozonated and untreated samples were all below the LOQ. Total N-

7

nitrosamines concentrations measured for two chloraminated soaps were 0.31 µM and 0.57 µM (Table

8

2), respectively. Similar results were also obtained for two chloraminated shampoos (0.49 and 0.39 µM)

9

and a laundry detergent (0.59 µM) (Table 2). Because no signal was detected for the untreated samples

10

and all samples were treated with sulfamic acid and ascorbic acid to eliminate potential interferences of

11

nitrite and monochloramine, respectively, it can be concluded that the chemiluminescence signal

12

measured for chloraminated samples is due to the formation of N-nitroso compounds. All samples were

13

also analysed by HPLC-DAD to detect the potential formation of specific N-nitrosamines contained in

14

the US-EPA 8270 standard mix. However, no specific N-nitrosamines were detected by HPLC-DAD in

15

treated and untreated samples. This result suggests that either no N-nitrosamines present in the US-EPA

16

8270 standard mix were formed during chloramination or their concentrations were too low to be

17

detected by HPLC-DAD without pre-concentration (LOD=0.06 µM; LOQ=0.19 µM). Overall, this

18

suggests that unidentified N-nitrosamines are likely mainly responsible for the chemiluminescence

19

signal observed in the chloraminated samples. All soaps and shampoos selected for this study contain

20

either polyacrylamide-co-diallyldimethylammonium chloride (polyquaternium-7) or quaternized

21

hydroxyethylcellulose ethoxylate (polyquaternium-10). These compounds are polycationic polymers that

22

are used in personal care and cosmetic products to promote antistatic properties and for their ability to

23

form films. It has been shown that a technical grade polyquaternium-10 solution treated with

24

monochloramine leads to the formation of a small quantity of NDMA (mass yieldpolyquaternium-10= 0.01%

25

NDMA)

26

polyquaternium-10 as an additive. Nevertheless, it cannot be excluded that unidentified N-nitroso 15 ACS Paragon Plus Environment

22

. However, NDMA was not detected in monochloraminated shampoo samples containing


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Page 16 of 33

1

compounds, such as N-nitroso containing polymers (Supporting information, Figure S5c and d), were

2

formed because in the previous study only NDMA was measured and not the total N-nitrosamine

3

concentration

4

chloride (polyDADMAC) a quaternary amine-based polycationic polymer widely used for wastewater

5

treatment, water purification and in the pulp and paper industry

6

shown that polyDADMAC can form NDMA and other unidentified N-nitroso compounds during

7

chloramination and ozonation

8

chloramination of polyDADMAC can explain nearly the entire increase in total N-nitrosamine

9

concentrations 7. NDMA formation from polyDADMAC requires cleavage of the two C−N bonds

10

linking the dimethylammonium group to the polymer backbone (Supporting information Figure S5a).

11

The high molar fraction of NDMA relative to the total N-nitrosamines measured in the previous study,

12

suggests that the formation of polymer-bound N-nitrosamines is less important (Supporting information

13

Figure S5b) 7. In the previous study, samples were extracted with ethyl acetate 7. However the low ethyl

14

acetate/water partition coefficient that we measured for polyDADMAC (logKorg/wat=-4.8) suggests that

15

ethyl acetate might hinder the extraction of cationic polymer-bound N-nitrosamines (see SI, section 2).

16

In the present study, all samples were directly injected without pre-concentration. Thus the relatively

17

intense chemiluminescence signals measured for chloraminated soaps and shampoos and the absence of

18

NDMA suggest that the contribution of polymer-bound N-nitroso groups to the total N-nitrosamine pool

19

might be higher than previously proposed. Nevertheless, further research is needed to identify the new

20

N-nitrosamines and determine the contribution of polymer-bound N-nitroso groups to the total N-

21

nitrosamine pool.

24

. The structure of polyquaternium-7 is very similar to polydiallyldimethylammonium

7,24

32

. Recently several studies have also

. It has been shown that the formation of NDMA during

22 23

Conclusions. The novel method developed in this study is a significant improvement for measurements

24

of total N-nitrosamine concentrations in aqueous samples. It couples photolytic cleavage of the N-N

25

bond with chemiluminescence detection of NO• in the gas phase. By utilizing a capillary

26

microphotochemical reactor (Figure 2) to reduce the sample cross-section and volume, irradiation and ACS Paragon Plus Environment

16

Page 17 of 33

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1

the resulting N-nitrosamines photo-decomposition to NO• were optimal to reach a sensitivity level

2

comparable to other chemical denitrosation methods. Additionally, compared to chemical denitrosation

3

the reproducibility was improved and the background signal was reduced

4

developed in this study doesn’t require chemicals and is not affected by interferences of by-products

5

(e.g., formation of NOI). N-nitrosamine quantification limits without pre-concentration obtained with a

6

200 µL or 5000 µL injection loop are 0.30 µM (60 pmol) or 0.11 µM (550 pmol), respectively. Although

7

this method can be potentially used for numerous applications in the fields of water quality and

8

treatment and in biomedical research, the quantification limit might be too high for some water and

9

biological fluid samples containing extremely low N-nitrosamine concentration (e.g., tap water). In such

10

cases, considering 100% of recovery, the quantification limit can be lowered by a factor 500 (LOQ=0.66

11

nM) to 1000 (LOQ=0.33 nM) by solid phase pre-concentration of the samples. The analysis of pre-

12

concentrated wastewater and greywater samples has demonstrated the applicability of this method to the

13

analysis of environmental samples with low total N-nitrosamine concentrations. Because UV-photolysis

14

is more convenient and more reliable than the application of chemicals, this method simplifies the

15

determination of N-nitrosamine formation during water and wastewater treatment, in gastric fluids or in

16

environmental samples.

11,14

. Finally, the method

17 18

SUPPORTING INFORMATION

19

The list of chemicals and samples, sample preparation and analyses, the calibration curves, the analytical

20

protocol for the determination of ethyl acetate/water partition coefficient of polyDADMAC and

21

additional data are available in the Supporting Information (SI).

22 23

ACKNOWLEDGEMENTS

24

We thank Caroline Gachet Aquillon and Antoine Wiedmer for assistance in the laboratory.

25


17


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Page 18 of 33

1

REFERENCES

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(1) Krasner, S. W.; Mitch, W. A.; McCurry, D. L.; Hanigan, D.; Westerhoff, P. Formation, precursors, control, and occurrence of nitrosamines in drinking water: A review. Water Res. 2013, 47 (13), 4433–4450.

5 6

(2) Yoon, S.; Tanaka, H. Formation of N-nitrosamines by chloramination or ozonation of amines listed in Pollutant Release and Transfer Registers (PRTRs). Chemosphere 2014, 95, 88–95.

7 8 9

(3) Kristiana, I.; Tan, J.; Joll, C. A.; Heitz, A.; von Gunten, U.; Charrois, J. W. A. Formation of Nnitrosamines from chlorination and chloramination of molecular weight fractions of natural organic matter. Water Res. 2013, 47 (2), 535–546.

10 11

(4) Zeng, T.; Mitch, W. A. Contribution of N-Nitrosamines and Their Precursors to Domestic Sewage by Greywaters and Blackwaters. Environ. Sci. Technol. 2015.

12 13

(5) Krasner, S. W. The formation and control of emerging disinfection by-products of health concern. Philos. Trans. R. Soc. Lond. Math. Phys. Eng. Sci. 2009, 367 (1904), 4077–4095.

14 15

(6) Hrudey, S. E.; Bull, R. J.; Cotruvo, J. A.; Paoli, G.; Wilson, M. Drinking Water as a Proportion of Total Human Exposure to Volatile N-Nitrosamines. Risk Anal. 2013, 33 (12), 2179–2208.

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(7) Dai, N.; Mitch, W. A. Relative Importance of N-Nitrosodimethylamine Compared to Total NNitrosamines in Drinking Waters. Environ. Sci. Technol. 2013, 47 (8), 3648–3656.

18 19

(8) Bond, T.; Templeton, M. R.; Graham, N. Precursors of nitrogenous disinfection by-products in drinking water––A critical review and analysis. J. Hazard. Mater. 2012, 235–236, 1–16.

20 21

(9) Bond, T.; Huang, J.; Templeton, M. R.; Graham, N. Occurrence and control of nitrogenous disinfection by-products in drinking water – A review. Water Res. 2011, 45 (15), 4341–4354.

22 23 24

(10) Chuang, Y.-H.; Lin, A. Y.-C.; Wang, X.; Tung, H. The contribution of dissolved organic nitrogen and chloramines to nitrogenous disinfection byproduct formation from natural organic matter. Water Res. 2013, 47 (3), 1308–1316.

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(11) Kulshrestha, P.; McKinstry, K. C.; Fernandez, B. O.; Feelisch, M.; Mitch, W. A. Application of an Optimized Total N-Nitrosamine (TONO) Assay to Pools: Placing N-Nitrosodimethylamine (NDMA) Determinations into Perspective. Environ. Sci. Technol. 2010, 44 (9), 3369–3375.

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(12) Samouilov, A.; Zweier, J. L. Development of Chemiluminescence-Based Methods for Specific Quantitation of Nitrosylated Thiols. Anal. Biochem. 1998, 258 (2), 322–330.

30 31

(13) MacArthur, P. H.; Shiva, S.; Gladwin, M. T. Measurement of circulating nitrite and Snitrosothiols by reductive chemiluminescence. J. Chromatogr. B 2007, 851 (1–2), 93–105.

32 33

(14) Hausladen, A.; Rafikov, R.; Angelo, M.; Singel, D. J.; Nudler, E.; Stamler, J. S. Assessment of nitric oxide signals by triiodide chemiluminescence. Proc. Natl. Acad. Sci. 2007, 104 (7), 2157–2162.

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(15) Williams, D. L. H. Nitrosation, First Edition, Cambridge University Press: Cambridge ; New York, 1988.

36 37

(16) 441.

Ridd, J. H. Nitrosation, diazotisation, and deamination. Q. Rev. Chem. Soc. 1961, 15 (4), 418–


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1 2 3

(17) da Silva, G.; Kennedy, E. M.; Dlugogorski, B. Z. Nucleophilic catalysis of nitrosation: relationship between nitrosating agent equilibrium constant and catalyst nucleophilicity. J. Chem. Res. 2002, 2002 (12), 589–590.

4 5 6

(18) Wang, J.; Chan, W. G.; Haut, S. A.; Krauss, M. R.; Izac, R. R.; Hempfling, W. P. Determination of Total N-Nitroso Compounds by Chemical Denitrosation Using CuCl. J. Agric. Food Chem. 2005, 53 (12), 4686–4691.

7 8 9

(19) Lee, C.; Choi, W.; Kim, Y. G.; Yoon, J. UV Photolytic Mechanism of N-Nitrosodimethylamine in Water: Dual Pathways to Methylamine versus Dimethylamine. Environ. Sci. Technol. 2005, 39 (7), 2101–2106.

10 11

(20) Lee, C.; Choi, W.; Yoon, J. UV Photolytic Mechanism of N-Nitrosodimethylamine in Water: Roles of Dissolved Oxygen and Solution pH. Environ. Sci. Technol. 2005, 39 (24), 9702–9709.

12 13

(21) Hand, V. C.; Margerum, D. W. Kinetics and mechanisms of the decomposition of dichloramine in aqueous solution. Inorg. Chem. 1983, 22 (10), 1449–1456.

14 15

(22) von Sonntag, C.; von Gunten, U. Chemistry of ozone in water and wastewater treatment: from basic principles to applications; IWA Publishing: London, 2012.

16 17 18

(23) Lee, M.; Lee, Y.; Soltermann, F.; von Gunten, U. Analysis of N-nitrosamines and other nitro(so) compounds in water by high-performance liquid chromatography with post-column UV photolysis/Griess reaction. Water Res. 2013, 47 (14), 4893–4903.

19 20

(24) Kemper, J. M.; Walse, S. S.; Mitch, W. A. Quaternary Amines As Nitrosamine Precursors: A Role for Consumer Products? Environ. Sci. Technol. 2010, 44 (4), 1224–1231.

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(25) Soltermann, F.; Lee, M.; Canonica, S.; von Gunten, U. Enhanced N-nitrosamine formation in pool water by UV irradiation of chlorinated secondary amines in the presence of monochloramine. Water Res. 2013, 47 (1), 79–90.

24 25 26

(26) Bolton, J. R.; Stefan, M. I. Fundamental photochemical approach to the concepts of fluence (UV dose) and electrical energy efficiency in photochemical degradation reactions. Res. Chem. Intermed. 28 (7–9), 857–870.

27 28

(27) Plumlee, M. H.; Reinhard, M. Photochemical Attenuation of N-Nitrosodimethylamine (NDMA) and other Nitrosamines in Surface Water. Environ. Sci. Technol. 2007, 41 (17), 6170–6176.

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(28) Hakim, T. S.; Sugimori, K.; Camporesi, E. M.; Anderson, G. Half-life of nitric oxide in aqueous solutions with and without haemoglobin. Physiol. Meas. 1996, 17 (4), 267.

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(29) Brasted, R. C. Reaction of Sodium Nitrite and Sulfamic Acid. Anal. Chem. 1952, 24 (7), 1111– 1114.

33 34

(30) Granger, J.; Sigman, D. M. Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method. Rapid Commun. Mass Spectrom. RCM 2009, 23 (23), 3753–3762.

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(31) Dai, N.; Zeng, T.; Mitch, W. A. Predicting N-Nitrosamines: N-Nitrosodiethanolamine as a Significant Component of Total N-Nitrosamines in Recycled Wastewater. Environ. Sci. Technol. Lett. 2015.

38 39

(32) Zeng, T.; Li, R. J.; Mitch, W. A. Structural Modifications to Quaternary Ammonium Polymer Coagulants to Inhibit N-Nitrosamine Formation. Environ. Sci. Technol. 2016.


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Page 20 of 33

1

TABLES

2

Table 1. Model compounds recovery, limits of detection (LOD) and limits of quantifications (LOQ).

3

The corresponding calibration curves are available in Figure 4. Compound

Recovery a

R2 b

% N-nitrosamines US-EPA 8270 N-nitrosamines mix N-nitrosodimethylamine (NDMA) N-nitrosomethylethylamine (NMEA) N-nitrosodiethylamine (NDEA) N-nitrosodipropylamine (NDPA) N-nitrosodibutylamine (NDBA) N-nitrosodiethanolamine (NDELA) N-nitrosodiphenylamine (NDPhA) N-nitrosopiperidine (NPIP) N-nitrosopyrolidine (NPYR) N-nitrosomorpholine (NMOR)

LOD c

LOQ c

µM

µM

100±3 115±5 117±5 95±3 91±4 95±5 80±5 106±4 101±5 99±5 78±5

0.99 0.99 0.97 0.99 0.99 0.99 0.99 0.98 0.99 0.98 0.98

0.10 (0.05) d 0.07 0.07 0.08 0.07 0.07 0.13 0.10 0.09 0.10 0.12

0.30 (0.15) d 0.21 0.22 0.24 0.21 0.20 0.40 0.31 0.27 0.30 0.36

C-nitroso compounds 2-nitrosotoluene

ND e

-

-

-

C-nitro compounds 4-nitroaniline 4-nitrophenol 1,3-dinitroglycerin

ND ND ND

-

-

-

N-oxide di-terbutylnitroxide

ND

-

-

-

Oximes acetone oxime acetophenone oxime

ND ND

-

-

-

ND 96±5

0.96

-0.13

0.39

Inorganics Nitrate Nitrite a

Model compounds recovery calculated as the ratio of the slopes of the compound’s 0.1-10 µM standard curve to that of US-EPA 8270 N-nitrosamines mix. b Coefficient of determination (R2) of the calibration lines. c

Limits of detection (LOD=3.3×SE/m) and quantification (LOQ=10×SE/m) using a 200 µL injection loop.

d

The values in brackets correspond to LOD and LOQ measured with a 5000 µL injection loop. e Not detected.

4 5


20

Page 21 of 33

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1

Table 2. Total N-nitrosamines (TONO) formation potential of soaps, shampoos and washing detergent

2

treated with monochloramine and ozone. Product soap A soap B shampoo A shampoo B laundry detergent a

suspected precursors

TONO (µM) (n=3) NH2Clc O 3d

polyquaternium 10 (5) b polyquaternium 10 (6) polyquaternium 10 (6) polyquaternium 7 (5) unspecified composition

0.31 ± 0.03 0.57 ± 0.03 0.49 ± 0.02 0.39 ± 0.02 0.59 ± 0.04

Quantification of Total N

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