EPA/600/R-16/073 I May 2016
www.epa.gov/homeland-security-research
United States
Environmental Protection
Agency
Degradation of Nicotine in Chlorinated
Water: Pathways and Kinetics
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Office of Research and Development
Homeland Security Research Program
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EPA/600/R-16/073
May 2016
Degradation of Nicotine in Chlorinated Water: Pathways and Kinetics
U. S. Environmental Protection Agency
Cincinnati, Ohio 45268
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Disclaimer
The U.S. Environmental Protection Agency (EPA), through its Office of Research and
Development's National Homeland Security Research Center (NHSRC), funded and managed
this project under contract EP-C-14-012 with CB&I Federal Services LLC, Cincinnati, Ohio
45212. This report has been peer and administratively reviewed and has been approved for
publication as an EPA document. It does not necessarily reflect the views of the EPA. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for use of a specific product.
Questions concerning this document or its application should be addressed to:
John Hall
National Homeland Security Research Center
Office of Research and Development
U.S. Environmental Protection Agency
26 W. Martin Luther King Drive Cincinnati,
OH 45268
hall.iohn@epa.gov
Jeff Szabo, Ph.D., P.E.
National Homeland Security Research Center
Office of Research and Development
U.S. Environmental Protection Agency
26 W. Martin Luther King Drive Cincinnati,
OH 45268
szabo.ieff@epa.gov
1
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Acknowledgements
Contributions of the following organizations to the development of this document are
acknowledged:
CB&I Federal Services LLC, under contract EP-C-14-012
We would like to acknowledge all of the EPA's Test & Evaluation Facility technical staff
that participated in this study.
2
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Table of Contents
Disclaimer 1
Acknowledgements 2
Table of Contents 3
List of Figures 4
List of Tables 4
List of Abbreviations 5
Executive Summary 6
Introduction 7
Experimental Procedure 8
Materials 8
Methods 8
Results and Discussion 10
Nicotine and Chlorine Reaction Order and Reaction Rate Constants 11
Nicotine and Chlorine Reaction Pathway Determination 18
Conclusions 21
References 21
3
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List of Figures
Figure 1: Structure of nicotine 7
Figure 2: Selected nicotine test results 11
Figure 3: Effect of pH on the distribution of hypochlorous acid and hypochlorite ion in water 12
Figure 4: Pseudo first order rate constant (k1) for nicotine reaction with chlorine during the rapid initial
reaction stage in deionized water 13
Figure 5: Pseudo first order rate constant (k1) for nicotine reaction with chlorine during the rapid initial
reaction stage in tap water 14
Figure 6: Determination of pseudo first order rate constant (k1) during the second reaction stage 15
Figure 7: Determination of pseudo second order rate constant (k) for deionized water 17
Figure 8: Determination of pseudo second order rate constant for tap water 17
Figure 9: Chromatograph of a sample to identify intermediate compounds by GC/MS 19
List of Tables
Table 1: Summary of test conditions 10
Table 2: Pseudo zero order and pseudo first order rate constants for nicotine reaction with free chlorine
during the rapid initial reaction stage 12
Table 3: Pseudo zero order and pseudo first order rate constants for nicotine reaction with free chlorine
during the second reaction stage 15
Table 4: Reaction order, rate constants and half life for nicotine in chlorinated water 18
Table 5: GC/MS identified intermediate compounds produced by the nicotine-chlorine reaction 20
4
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List of Abbreviations
DPD N, N-diethyl-p-phenylenediamine
EPA Environmental Protection Agency
GC/MS Gas chromatography/Mass Spectrometry
IC Ion Chromatography
R2 Regression coefficient
UV Ultraviolet
5
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Executive Summary
Nicotine was used as a target compound to evaluate the degradation of alkaloid pesticides in
chlorinated drinking water. Nicotine was found to degrade rapidly in the presence of free
chlorine. Data from this study was used to determine rate constants and rate coefficients for
nicotine under varying experimental conditions.
A series of bench-scale kinetic tests were conducted to determine the fate of nicotine in
chlorinated water. The tests were performed using deionized water and chlorinated tap water,
various concentrations of nicotine and free chlorine, and at various pH levels. In both types of
water, a two-stage reaction was observed—a rapid initial stage followed by a slower second
stage. The rapid initial stage followed first-order reaction kinetics, with a rate constant of
0.0067 sec 1 for deionized water and 0.013 sec 1 for tap water. The slower stage followed
second-order kinetics for deionized water, with a rate constant of 18 M 1 sec"1. Tap water did
not follow second-order kinetics, and the reaction order was qualitatively estimated as first-
order with a rate constant of 1.6 x 10~4 sec1, two orders of magnitude lower than the rapid
initial stage. The study found pH to be very stable during each test.
6
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Introduction
Interest in the toxic effects of chemical compounds that are listed in the Chemicals of
Environmental Protection Agency Interest, which might be introduced into drinking water, has
been elevated due to the threat of terrorist attacks. Because of inherent dilution factors, rivers,
lakes, and reservoirs are the least likely potential targets. The quantities of toxic chemicals
needed to sufficiently poison drinking water in a reservoir would be logistically impractical. The
area of most concern is therefore within water distribution systems.
Of particular interest are the effects of chlorinated drinking water on pesticides. Prior pesticide
studies have shown that chlorpyrifos (Duirk and Collette, 2006), diazinon (Zhang and Pehkonen,
1999), aldicarb (Miles, 1991), carbamate (Mason et al., 1990), phorate (Hong and Pehkonen,
1998), thiobencarb (Magara et al., 1994), and carbaryl (Miles et al., 1988) degrade in the
presence of chlorinated water. However, these studies were conducted using deionized water.
Further, in many cases, the deionized water was spiked with chlorine to levels that were above
the U.S. Environmental Protection Agency's (EPA's) maximum contaminant level (MCL) of 4
mg/L (USEPA, 2006). A review article (Wolfe, 1980) cites half-life determinations for pesticides
that were conducted in river and pond waters; however, there were no studies cited that
examined finished drinking water. Data on the persistence of pesticides in drinking water is
limited.
Nicotine is an alkaloid compound, and a pesticide. Alkaloids are nitrogenous bases (usually
heterocyclic) widely found in plants. Nicotine formerly found wide use as a pesticide against
sucking insects on plants and against lice and mites in chicken coops. (PMEP, 1985) Nicotine
[CASRN 54-11-5], with the chemical formula C10H14N2, consists of a pyridine ring bonded to a
pyrrolidine ring, as presented in Figure 1.
The degradation of nicotine in water has been studied, but under severe oxidizing conditions
(Zaafarany, 2010). In this study described here, nicotine is subjected to typical drinking water
chlorination conditions to evaluate how it degrades. The objective of the study is to illustrate
how drinking water would affect alkaloid pesticides, and to address the issue by (a)
investigating the fate of nicotine in chlorinated drinking water and deionized water, (b)
determining the reaction rate and pathway of the reaction between nicotine and aqueous
Figure 1: Structure of nicotine
7
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chlorine, (c) identifying nicotine's degradation products, and (d) providing data that can be used
to assess the potential threat from nicotine in drinking water.
Experimental Procedure
Materials
Nicotine stock solution with a reagent purity of 99.5% was purchased from Chem Service (West
Chester, PA). Second source nicotine standards were prepared from a solution obtained from
Sigma Aldrich (St. Louis, MO). Deionized water was buffered to pH 7 using anhydrous sodium
dihydrogen phosphate (Sigma, ACS reagent grade) and anhydrous disodium hydrogen
phosphate (Fisher, Pittsburg, PA; ACS reagent grade). The pH standards used were pH 4, pH 7,
and pH 10 (Fisher Certified). The chlorine source was derived from a 10-13% reagent grade
sodium hypochlorite solution (Ulrich Chemical Inc., Indianapolis, IN). The free chlorine
standards (25-30 mg/L Cb) were purchased from Hach (Hach Company, Loveland CO).
The deionized water used in the study was produced by passing moderate-quality deionized
water through a Barnstead™ Nanopure® water purification system (Thermo Scientific,
Waltham, MA) equipped with pretreatment carbon filtration, cation exchange filtration, mixed
cation/anion exchange filtration, and a final carbon/ion exchange filtration.
The drinking water used in the study was chlorinated Cincinnati tap water. Before sampling,
the tap water was allowed to flow from the faucet for approximately 15 minutes. After this
flush, the chlorine concentration was checked over the course of several minutes; sampling
commenced after a stable chlorine level was achieved.
Deionized water was buffered to pH 7 using a buffer made from sodium dihydrogen phosphate
and disodium hydrogen phosphate. Fresh buffer solution was prepared once a week during the
experiments. No pH adjustment was made to tap water.
Methods
Tap water was dechlorinated by aeration for 5 days prior to each experiment. Free chlorine in
the water was monitored to verify effective chlorine loss. Water with a free chlorine
concentration of less than 0.10 mg/L was deemed suitable for use as dechlorinated water, or as
a starting point for rechlorination.
All experiments were conducted in a laboratory held at a temperature of 20 ± 2°C.
Nicotine was spiked into the appropriate test water by adding a known amount of neat nicotine
to 2 liters of test water contained in a 10-L glass carboy. In a separate 4-L beaker, a known
amount of sodium hypochlorite solution was added to 2 liters of water. These solutions were
assayed for nicotine or chlorine prior to use. Free chlorine analysis was conducted immediately
8
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after sampling. Once the free chlorine level was confirmed, the newly chlorinated water was
added to the nicotine solution in the carboy. The reaction mixture was mixed by swirling for
approximately 25 seconds. The zero-time sample was collected immediately after mixing. The
carboy was then covered with foil and the mixture stirred continuously during the remainder of
the experiment using a magnetic stir bar and stir plate. Additional samples were collected at
designated time intervals. These samples were tested immediately for free chlorine and pH,
followed by ion chromatography (IC) analysis for nicotine. The aliquot used for nicotine analysis
was immediately quenched with the required amount of sodium thiosulfate (5% solution) to
destroy the chlorine.
Nicotine and free chlorine concentrations, as well as pH, were critical parameters for this study.
The concentration of nicotine was determined using an IC method developed by (Ayers et al.,
1998). Ayers et al. reported a sensitive and rapid (10 minutes per analysis) method for
determination of aqueous nicotine employing solvent gradient elution with ultraviolet (UV)
detection. The method was found to be linear in response over the concentration range
investigated (0.5-512 |aM, 0.081-83 mg/L) and has a limit of detection of (~0.01 |aM, ~2 |ag/L) for
a 50 |j.L injection. Our laboratory analyzed 10 microliters of sample.
This study also employed GC/MS to analyze some nicotine samples, followed by a library search
to identify intermediate compounds and by-products of the nicotine reaction with chlorine.
These samples were extracted by a modified EPA Method 507 (Engels and Graves, 1989).
The Hach® Pocket Colorimeter™ kit used for free chlorine analysis was set at a wavelength of
530 nm. A Hach SwifTest™ dispenser was used to introduce N, N-diethyl-p-phenylenediamine
(DPD) directly into the water samples. DPD reacts with hypochlorous acid and/or hypochlorite
ion to form a pink color; the intensity of the color is proportional to the free chlorine
concentration (Hach, 2005; Harp, 2002). This method is accurate from 0.02 to 2.00 milligrams
per liter (mg/L). When determining free chlorine concentrations that were above the analytical
range, samples were diluted with the appropriate amount of deionized water to bring the final
concentration into the analytical range. The samples were analyzed immediately after dilution.
Measurements of the pH were conducted using a Thermo Orion 720 pH Meter (Thermo
Scientific). A three-point calibration was conducted daily, prior to pH measurement, using pH
standards at pH 4, 7, and 10.
A Mettler™ Research Electronic Balance (AE200; Mettler-Toledo, LLC, Columbus, OH) was used
to determine the mass of nicotine standards. The balance calibration was checked daily before
use with three weights from a weight set that is calibrated annually. The three weights were
selected to bracket the mass of the neat nicotine compound. The balance was rechecked with
one calibration weight after use.
9
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Results and Discussion
Table 1 summarizes the test conditions for both deionized water and Cincinnati tap water.
Table 1: Summary of test conditions
Test ID
Matrix
Target Concentrations
Starting
PH
Nicotine
Chlorine
(mg/L)
(mM)
(mg/L)
(mM)
Tap Control 1
Chlorinated Tap
0
0
2
0.03
Tap Control 2
Cincinnati Tap
5
0.03
0
0
Tap 3
Chlorinated Tap
1.25
0.01
2
0.03
7.93
Tap 5
Chlorinated Tap
1.25
0.01
10
0.14
7.91
Tap 6
Chlorinated Tap
1.25
0.01
0.5
0.01
7.96
Tap 7
Chlorinated Tap
25
0.15
25
0.35
6.95
Tap 8
Chlorinated Tap
0.5
0
0.5
0.01
7.92
Nano Control 1
Nanopure Water, Buffered pH 7
5
0.03
0
0
6.92
Nano 2
Nanopure Water, Buffered pH 7
2
0.01
2
0.03
6.95
Nano 3
Nanopure Water, Buffered pH 7
1.25
0.01
4
0.06
6.92
Nano 4
Nanopure Water, Buffered pH 7
1.25
0.01
0.5
0.01
6.92
Nano 5
Nanopure Water, Buffered pH 7
0.5
0
0.5
0.01
6.93
Nano 6
Nanopure Water, Buffered pH 7
0.5
0
4
0.06
6.94
Nano 7
Nanopure Water, Buffered pH 7
25
0.15
25
0.35
7.00
Nano 8
Nanopure Water, Buffered pH 7
0.5
0
2
0.03
6.99
Nano 9
Nanopure Water, Buffered pH 7
1.25
0.01
2
0.03
7.00
Nano 10
Nanopure Water, Buffered pH 7
25
0.15
1
0.01
6.96
Figure 2 presents some of the test results.
6
1 "
C A A
8 i
§5" 3
0 at »
= & 2 I
g > a
1 1 »
f 0Xm-
8 o
Tap Water (Tap 2)
Tap Water (Tap 3)
Free Chlorine
-Nicotine
500 1000 1500
Reaction Time (Minutes)
2000
c
o
2
c
0)
o
§?
0 at
?£
TO
C
1
TO
*-»
c
o
o
2 «
- Free Chlorine
-Nicotine
500
1000
1500
2000
Reaction Time (Minutes)
10
-------
Deionized Water (Nano 6)
Deionized Water (Nano 8)
500
Free Chlorine
—*— Nicotine
1000
1500
¦£ oi i
2000 8 0
^ A
2 V
+¦»
c
c
o
2
500
Free Chlorine
—*— Nicotine
1000
1500
2000
Reaction Time (Minutes)
Reaction Time (Minutes)
Figure 2: Selected nicotine test results
As the figure indicates, both nicotine and free chlorine concentrations decreased significantly
over time until they reached equilibrium. Each test scenario showed two-stage reaction
kinetics, i.e., a rapid initial stage followed by a slower stage.
Nicotine and Chlorine Reaction Order and Reaction Rate Constants
As mentioned above, the reaction between nicotine and chlorine exhibited a rapid initial
reaction stage (Stage 1) followed by a slower reaction stage (Stage 2). Similar phenomena were
observed by (Westerhoff et al., 2004) for the reaction between natural organic matter and free
chlorine/bromine. Stage 1 lasted 1-3 minutes for nicotine. Initial nicotine or chlorine
consumption was not caused by their reactions with other inorganics/organics present in
solutions or glassware, as the control experiments (which omitted either nicotine or chlorine)
showed no significant decrease in nicotine or chlorine concentrations. Therefore, high initial
consumption of nicotine or chlorine shown in the experiments was most likely due to the
reaction between nicotine and chlorine.
In water, free chlorine combines with water to form hypochlorous acid (HOCI) and hydrochloric
acid (Sawyer et al., 1994).
Cl2 + H20-> HOCI + H++ Cl"
The hypochlorous acid formed is a weak acid and is poorly dissociated at pH levels below 6.
HOCI -> OCI + H+(pKa = 7.5)
The relative amounts of HOCI and OCI" in solution as a function of pH are shown in Figure 3
(Sawyer et al., 1994). The pKa of hypochlorous acid is 7.5; at pH levels below 7.5, more HOCI
exists in solution than OCI", and vice versa at pH levels higher than 7.5.
11
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pH
Figure 3: Effect of pH on the distribution of hypochlorous acid and hypochlorite ion in
water
Two different pH levels were investigated in this study: pH 7.1±0.1 for deionized water and pH
7.9-8.8 for tap water. Because of the significant effects that pH has on the chemistry of
chlorine in water, the nicotine and chlorine reaction orders and rate constants were
determined separately for the two different pH levels.
Due to fast reactions during Stage 1, rate constants could only be estimated from pseudo-zero-
order calculations using the observed data, i.e., calculations of change in nicotine concentration
over a period of one minute: A[nicotine]imin (Westerhoff et al., 2004). Table 2 summarizes the
calculated pseudo-zero-order and pseudo-first-order rate constants.
Table 2: Pseudo zero order and pseudo first order rate constants for nicotine reaction with
free chlorine during the rapid initial reaction stage
Matrix
ID
Initial Free Chlorine
Concentration (mM)
Pseudo-zero-order Change
(A[nicotine] in mM1)
Pseudo-first-
order Rate
Constant
Regression
Coefficent
K' (sec1)
R2
Nano 1
0.0563
0.0171
Nano 2
0.008
0.0018
Nano 3
0.0479
0.0007
Nano 4
0.006
0.0011
Deionized
Nano 5
0.0062
0.0034
Water
Nano 6
0.0451
0.0035
Nano 7
0.2871
0.1105
Nano 8
0.0271
0.0009
Nano 9
0.0277
0.0029
Nano 10
0.0133
0.0026
0.0067
0.97
12
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Tap 2
0.0563
0.0367
Tap 3
0.0282
0.0075
Tap 4
0.0563
0.0197
Tap Water3
Tap 5
-
-
Tap 6
0.0061
0.0026
Tap 7
0.3134
0.2303
Tap 8
0.0057
0.0006
0.013
0.99
aThe Tap 1 test was conducted before the experimental procedure was finalized. Therefore, the first sample
was collected 30 minutes after the test began, which had consequently already passed Stage 1. Therefore, the
Tap 1 data was not used for the rate constant calculation.
Pseudo-first-order rate constants were obtained by plotting the pseudo-zero-order constants as
a function of initial free chlorine ([HOCI]i0tai = [HOCI] + [OCI ]) for each test run. Figure 4 and
Figure 5 present pseudo-first-order rate constants for nicotine reactions with chlorine during
Stage 1 in deionized and tap water. The calculated pseudo-first-order rate constant k' is 0.0067
sec 1 and 0.013 sec 1 for deionized and tap water, respectively.
Nanopure Water - 1st Stage Rate Constant
ts
a
¦B
O
o
a
<1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Initial Chlorine Concentration (mM)
Figure 4: Pseudo first order rate constant (k') for nicotine reaction with chlorine during the
rapid initial reaction stage in deionized water
y = 0.4045x - 0.0065
R = 0.9653
k' = 0.40 nun
= 0 OOhy s
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Tap Water - 1st Stage Rate Constant
^ 0.3
T! 0.2
I 02
^7 0.1
.a
o 0.1
_ o
& 0.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Initial Chlorine Concentration (mM)
y = 0.7584x- 0.0094
Figure 5: Pseudo first order rate constant (k') for nicotine reaction with chlorine during the
rapid initial reaction stage in tap water
The observed decrease in nicotine concentration in the presence of free chlorine during Stage 2
is initially assumed to be first order with respect to nicotine concentration. If linearity is
observed when plotting ln([nicotine]/[nicotine]o) versus time, then this assumption would be
valid when free chlorine is present in excess. The slope of the regression line from such a plot
yields the pseudo-first-order rate constant (k', sec"1) as described by the following expression
(Duirk and Collette, 2005; Laidler, 1965):
\Nicotine 1
In 7— = -k't
[Nicotine JO
Figure 6 shows selected graphs of pseudo-first-order rate constants obtained from Stage 2 for
deionized and tap water. The first-order rate coefficients were determined from regression line
slopes.
14
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Tap Water (Tap 5)
0)
c
o
o
0)
c
o
o
0.2155x + 1.4351
R2 = 0.9653
k' = 0.2155 min-1
10 20
Time (minutes)
Tap Water (Tap 9)
y = -0.0621x-0.326
R2 = 0.9782
o -0.5
k' = 0.0621 min
10 20
Time (minutes)
"oT 0.0
c
Z -0.4
0
z -0.8
H" -1.2
1 -1-6
E; -2.0
c
Deionized Water (Nano 1)
Deionized Water (Nano 8)
-0 . n 7R7
R2 = 0.9344
k'
= 0.0683 min-1
10 15
Time (minutes)
20
= -0.1123x
0.0922
R2 = 0.9928
k' = 0.1123 min1
20 30
Time (minutes)
Figure 6: Determination of pseudo first order rate constant (k') during the second reaction
stage
Table 3 is a summary of pseudo-first-order rate constants during Stage 2. As can be seen in the
table, regression coefficients (R2) ranged between 0.82 and 0.99 for deionized water and
between 0.85 and 0.98 for tap water. As demonstrated by the high regression coefficients,
nicotine exhibited first-order dependency with respect to itself in the presence of free chlorine.
Table 3: Pseudo zero order and pseudo first order rate constants for nicotine reaction with
ree chlorine during the second reaction stage
Matrix
ID
Initial Free Chlorine
Concentration (mM)
K', min 1
R2
Pseudo-first-
order Rate
Constant
K (M^sec1)
Regression
Coefficient
R2
Deionized
Water
Nano 1
Nano 2
Nano 3
Nano 4
Nano 5
Nano 6
Nano 7
Nano 8
Nano 9
Nano 10
0.0563
0.008
0.0479
0.006
0.0062
0.0451
0.2871
0.0271
0.0277
'0.0133
0.0683
0.0235
0.0595
0.0101
0.0117
0.0346
0.0119
0.1123
0.0344
0.0045
0.93
0.87
0.82
0.94
0.91
0.94
0.91
0.99
0.88
0.99
18
0.97
15
-------
Tap 2
0.0563
0.0097
0.86
Tap 3
0.0282
0.0057
0.92
Tap 4
0.0563
0.0049
0.85
Tap Water3
Tap 5
Tap 6
0.1183
0.0061
0.2155
0.0051
0.97
0.87
NA
0.22
Tap 7
0.3134
0.0078
0.97
Tap 8
0.0057
0.0041
0.91
Tap 9
0.1507
0.0621
0.98
aThe Tap 1 test was conducted before the experimental procedure was finalized. Therefore, the first sample
was collected 30 minutes after the test began, which had consequently already passed Stage 1. Therefore, the
Tap 1 data was not used for the rate constant calculation.
R, regression coefficient.
The pseudo-second-order rate constant (k, M_1sec_1) was determined by plotting the pseudo-
first-order rate constant [k') versus the initial free chlorine concentration ([HOCI]i0tai) for each
test matrix. Since both species of free chlorine (HOCI and OCI ) are present, the decrease of
nicotine in the presence of free chlorine can be described by the following expression:
d [Nicotine1
- = —k'[Nicotine] = k[HOCl]Total[Nicotine]
Where k' = /f[HOCI]i0tai
Figures 7 and 8 show the pseudo-second-order rate constant for nicotine's reaction with
chlorine during Stage 2 in deionized and tap water, respectively. As can be seen in Figure 7, k1
increased linearly with an increase in free chlorine concentration for deionized water, and the
calculated pseudo-second-order rate constant (k) is 18 M_1sec_1. A linear relationship was not
established between k1 and free chlorine concentration for tap water, as shown by the very low
regression coefficient (R2) (0.2208) in Figure 8. This is most likely due to interference from
other contaminants in tap water. Therefore, second-order reaction assumptions are not valid
for tap water. It was observed, however, that the pseudo-first-order rate constants did not
change significantly with the change of free chlorine concentration, thus the reaction of
nicotine with chlorine in tap water might follow first-order kinetics in Stage 2. The first-order
rate constant ranged between 0.0041-0.0097 min 1 (6.8 x 10"5 - 1.6 x 10"4 sec"1) with the
average of 0.0062 min 1 (1.6 x 10~4 sec-1), which is two orders of magnitude lower than Stage 1.
16
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s
eS
S
o
U
•- -
a>
¦a
•-
o
o
¦a
s
a>
0.10
0.08
.9 0.06
S
^ 0.04
0.02
0.00
Deionized Water - 2nd Stage Rate of Constant
y = 1.0776x4- 0.0073
R = 0.972
k = 1.08 mM'inin'
= 18 M'sec"1
0.00
0.01
0.02
0.03
0.04
0.05
Initial Free Chlorine Concentration (mM)
0.06
Figure 7: Determination of pseudo second order rate constant (k) for deionized water
Tap Water - 2nd Stage Rate of Constant
0.012
y = 0.0084x+0.0056
0.010
R = 0.2208
0.008
S 0.006
0.004
0.002
0.000
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Initial Free Chlorine Concentration (mM)
0.35
Figure 8: Determination of pseudo second order rate constant for tap water
The half-life of nicotine was calculated using the following equations (Laidler -, 1965):
First order reaction ti/2 = -* Zn(2)
17
-------
Second order reaction ti/2 =
(fc)* [Nicotine]0
Table 4 presents a summary of the reaction order, rate constants, and half-life of nicotine at
two reaction stages.
Table 4: Reaction order, rate constants and half life for nicotine in ch
orinated water
Test Matrix
Reaction Stage
Reaction Order
Reaction Rate
Constant
Half-life of
Nicotine (sec)
Deionized
1
First Order
0.0067 sec 1
103
Water
2
Second Order
18 M1 sec1
i
18\Nicotine]0
Tap
1
First Order
0.013 sec 1
53
Water
2
Second Order
1.6 x 10 4 sec 1
4332
* [Nicotine]o is the initial nicotine concentration in moles/liter (M)
Nicotine and Chlorine Reaction Pathway Determination
Qualitative identification of intermediate compounds and byproducts from nicotine-chlorine
reaction was performed via GC/MS. The identification of byproducts and intermediate
compounds can assist with the identification of reaction mechanism and pathways between
nicotine and chlorine. In addition, the intermediate compounds may be more toxic than the
initial compound (nicotine in this case); therefore, it is important to identify the intermediate
and final compounds.
Figure 9 presents a GC/MS chromatograph of a sample used to identify intermediate
compounds produced by the nicotine-chlorine reaction.
18
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1.75-
1.5ft-
1.25-
0.75-
0.8ft-
0,Z§-
0-00-
'40:300
nicotO. 5-1-ZOOS. 11-42-08 pra.sms TfC
1A
JU
minutes
19&
Sag 2,
-------
Table 5: GC/MS identified intermediate compounds produced by the nicotine-chlorine
reaction
Retention Time
(min)
Compound
Molecular Formula
Structure
17.65
Nicotine
3-(l-methyl-2-
pyrrolidyljpyridine
C10H14N2
/ \
Ml
18.741
Myosmine,
3-(pyrrolin-2-
yl)pyridine
C9H10N2
r
V
Nc.
j
19.405
5-methyl-4-phenyl-
lH-pyrazole
C10H10N2
N —
j
—N
\
19.70
Methyl-3-pyridyl-
ketone
C7H7NO
O
0
20.40
4-chloro-l-methyl-
l,2-dihydro-l,5-
naphthyridin-2-one
C9H7CIN2O
\
W
a
22.112
Cotinine,
l-methyl-5-(3-
pyridyl)pyrrolidin-2-
one
C10H12N2O
CJ1
K
J:Hj
20
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Conclusions
Two-stage reaction kinetics were observed for the reaction of nicotine with free chlorine—a
rapid initial stage followed by a slower reaction stage. The initial stage followed first-order
reaction kinetics with a first-order rate constant k1 of 0.0067 sec 1 for deionized water, and
0.013 sec 1 for tap water. For the slower reaction stage, the reaction followed second-order
kinetics in deionized water with a second-order rate constant k of 18 M_1sec_1. In tap water, the
reaction did not follow second-order kinetics, and the reaction order was estimated as first-
order with a rate constant k1 of 1.6 x 10~4 sec1, which was two orders of magnitude lower than
the rapid initial reaction stage.
GC/MS proved to be a reliable and convenient way to identify reaction products. The following
intermediate compounds were identified: myosmine, 5-methyl-4-phenyl-lH-pyrazole, methyl-
3-pyridyl ketone, 4-chloro-l-methyl-l,2-dihydro-l,5-naphthyridin-2-one, and cotinine.
Additional efforts are needed to identify and quantify dominant intermediate compounds to
determine the mechanism of the nicotine-chlorine reaction.
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