Chemosphere xxx (2015) xxx–xxx
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Effectiveness of activated carbon disk for the analysis of iodine in water
samples using wavelength dispersive X-ray fluorescence spectrometry
Junseok Lee a, Jinsung An b, Joo-Ae Kim a, Hye-On Yoon a,⇑
a
b
Seoul Center, Korea Basic Science Institute, 6-7, Inchon-ro 22-gil, Seongbuk-gu, Seoul 136-075, Republic of Korea
Department of Civil & Environmental Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea
h i g h l i g h t s
A novel approach for the analysis of iodine in water samples was developed.
Iodine preconcentrated on the AC disk was directly analyzed using WDXRF spectrometry.
The AC disks were sufficiently durable for repeatable measurements until 8 days.
The accuracy of the proposed AC-WDXRF method was confirmed by spike tests.
a r t i c l e
i n f o
Article history:
Received 28 November 2014
Received in revised form 5 June 2015
Accepted 8 June 2015
Available online xxxx
Keywords:
Iodine
Disinfection by product
Wavelength dispersive X-ray fluorescence
spectrometry
Activated carbon disk
a b s t r a c t
A novel approach using wavelength dispersive X-ray fluorescence (WDXRF) spectrometry combined with
an activated carbon (AC) disk was developed for the determination of total iodine concentrations in water
samples. Dissolved iodine species (i.e., I and IO
3 ) in water samples were preconcentrated on the AC disk
and directly analyzed by WDXRF spectrometry. The adsorption behavior of I and IO
3 on the AC disk was
assessed at varying pH levels (4, 6, and 8). The AC disks completely retained the I and IO
3 for all the pH
levels tested. The calibration curve obtained from the iodine concentrations (i.e., 0, 20, 200, and 400 lg)
of AC disks and the measured X-ray intensity from the WDXRF analysis showed a good linearity
(R2 = 0.9960), with a relatively low limit of detection (0.575 lg). The durability of the AC disk for repeatable
measurements was also assessed to validate the sustainability of the proposed method and consequently
the measured X-ray intensity for the AC disks was constant until 8 d of analysis time. The accuracy of the
proposed AC-WDXRF method was confirmed by measuring iodine concentration spiked in drinking water
using inductively coupled plasma-mass spectrometry (ICP-MS). The proposed method is simple, rapid, efficient, and environmental friendly for iodine analysis in water samples. As a precursor of disinfection by
products (DBPs), it is important to determine the total iodine concentrations in raw water.
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Although iodine is an essential micronutrient for all mammals,
including human (Gilfedder et al., 2009), it has received considerable attention in the field of water/wastewater treatment. Iodine
concentrations of 45–90, 2–20, and 0.5–20 lg L1 in seawater,
river water, and fresh water were commonly reported in the UK
(Whitehead, 1979, 1984). During disinfection process in water
treatment facilities, iodide (I) can be oxidized by the disinfectants
(e.g., ozone (O3), chlorine, and chloramine) to hypoiodous acid
(HOI) and/or hypoiodite (OI), which can further react with natural
⇑ Corresponding author.
E-mail address: dunee@kbsi.re.kr (H.-O. Yoon).
organic matter (NOM) to form iodinated disinfection by products
(I-DBPs) in source water with a high I concentration (Bichsel
and von Gunten, 1999; Richardson et al., 2008). I-DBPs are currently regulated in the US owing to their higher toxicities than
those of chlorinated and brominated DBPs (Plewa et al., 2004;
Krasner et al., 2006). Therefore, determination of total iodine contents in source water is imperative in order to assess the iodine
levels that can participate in the formation of I-DBPs.
Recently, X-ray fluorescence (XRF) analysis combined with a
preconcentration method using solid phase extraction (SPE) disks
has been widely applied to determine various elements in aqueous
samples. Because XRF spectrometry is a suitable method for the
direct analysis of elements in solid samples, preconcentration procedures with thin SPE disks may be ideal method to make sample
http://dx.doi.org/10.1016/j.chemosphere.2015.06.017
0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Lee, J., et al. Effectiveness of activated carbon disk for the analysis of iodine in water samples using wavelength dispersive
X-ray fluorescence spectrometry. Chemosphere (2015), http://dx.doi.org/10.1016/j.chemosphere.2015.06.017
2
J. Lee et al. / Chemosphere xxx (2015) xxx–xxx
specimen prior to XRF analysis (An et al., 2013, 2014; Margui et al.,
2008, 2012). In previous studies (An et al., 2013, 2014), anion and
cation exchange disks have been employed as solid sorbents to
retain elements such as bromine and methylated arsenic (i.e.,
dimethylarsinic
acid)
in
water
samples,
respectively.
Furthermore, active thin layer and chelating disks have also been
used to collect metal cations present in different aqueous matrices
(Margui et al., 2008, 2012). With the use of these combined techniques, the direct quantitative determination of various elements
retained in solid sorbents is possible, and therefore the elution step
can be avoided.
In this study, we proposed a new method for rapid determination of total iodine contents in water samples by wavelength dispersive X-ray fluorescence (WDXRF) analysis after employing a
preconcentration procedure using activated carbon (AC) disks as
a follow-up and extension research of An et al. (2014). The retention behavior of I and iodate (IO
3 ), dominant species existing in
natural waters, on AC disks was assessed at different pH levels to
validate the suitability of the preconcentration method for iodine
analysis. The calibration curve for different iodine concentrations
retained on the AC disk was established, and the limit of detection
(LOD) and method detection limit (MDL) were determined. The
iodine concentrations spiked in drinking water samples were
assessed to verify the accuracy of the proposed method. The
AC-WDXRF method aims to decrease the analysis time and eliminate complicated pretreatment procedures for the rapid analysis
of iodine in water samples. The effectiveness of this study is
demonstrated by the fact that iodine, as a precursor of I-DBPs in
raw water, can be rapidly determined using the proposed method.
It enables us to establish an appropriate management plan.
2. Materials and methods
2.1. SPE disk
AC (model 2272) and anion exchange (AX, model 2252) disks
obtained from 3M Empore (St. Paul, MN, USA), with a diameter
of 47 mm and a thickness of 0.5 mm, were used to preconcentrate
the I and IO
3 in water samples. The properties of the AC disk were
as follows: surface area >1100 mm2 g1, particle size 10 lm, and
nominal carbon mass 50 mg. The AC surface is consists of a complex combination of positive and negative charges, providing
adsorption and retention capacities of soluble and volatile analytes. The AX disk was based on polystyrene divinylbenzene with
quaternary ammonium of functional groups. Both disks were conditioned prior to use in accordance with manufacturer’s instructions. The AC disk was sequentially conditioned using 5 mL of
methanol and deionized (DI) water. The AX disk was prepared with
10 mL of acetone, methanol, DI water, and 1 M sodium hydroxide.
The extraction of I and IO
3 in water samples using the AC and AX
disks was performed by simple vacuum filtration.
2.2. Instruments
The concentration of iodine retained on AC disks was determined using WDXRF spectrometry (PW 2404, Phillips,
Netherlands). The camber of X-ray pathway was set in a vacuum
state to prevent signal loss due to air absorption. The inductively
coupled plasma-mass spectrometry (ICP-MS) (Agilent 7700S,
Agilent Technologies, Japan) was employed to confirm the iodine
concentrations in water samples as reference values. A tuning solution was preliminarily used to optimize the analytical sensitivity
prior to the analysis. Detailed instrumental conditions of WDXRF
and ICP-MS systems used in this study are presented in Table 1.
Table 1
Instrumental conditions for the iodine analysis.
Parameter
Measurement condition
Wavelength dispersive X-ray fluorescence (WDXRF) spectrometry
X-ray tube
Rhodium (Rh) target (30 kV, 100 mA)
Diffraction crystal
LiF 220 (thickness = 0.2848 nm)
Window
Be window
Collimator
300 lm
Detector
Flow type
Peak angle
102.85 (°2h) for I-La line
Offset background
1.8916 (°2h)
Analysis time
100 s
Inductively coupled plasma-mass spectrometry (ICP-MS)
RF power
1550 W
Plasma gas flow rate
Ar 1.1 L min1
Extract 1 and 2 lens voltage
8.3 V for extract 1 and 195 V for extract 2
Omega lens voltage
11.9 V
Torch
Standard Quartz 2.5 mm
Nebulizer
Micromist
Sampling and skimmer cone Nickel
Integration time
0.33 s
Monitored mass
167 m/z
2.3. Effect of pH on the retention behavior of I and IO
3 on the AC disk
The retention behavior was evaluated at different pH levels in
order to test the suitability of the AC disks for the preconcentration
of I and IO
3 in water samples. Ammonium iodide (NH4I, Junsei,
Japan) and potassium iodate (KIO3) solution (Fluka, Switzerland)
were used to prepare stock solutions by dilution with DI water.
Solutions containing 1 mg L1 of iodine with different pH levels
(i.e. 4, 6, and 8) were prepared and 20 mL of each solution was
passed through the AC disks. The pH was adjusted by adding
appropriate amounts of 1 N NaOH and HNO3. The total amount
of iodine retained on the disk was calculated from the difference
of the iodine concentrations between in the initial solution and
effluent determined using ICP-MS analysis.
2.4. Calibration standards
The AC disks were prepared with different iodine concentrations (0, 20, 200, and 400 lg) by passing 20 mL of 0, 1, 10, and
20 mg L1 iodine solutions to make the calibration standards.
After drying at 60 °C for 5 min, the preconcentrated AC disks were
directly analyzed using WDXRF spectrometry in order to establish
the calibration curve. Before exposing to X-ray, the AC disks were
coated with X-ray film (ChemplexÒ, SE Waaler St. Stuart, FL, USA)
in order to prevent damage to the AC disk surface from the X-ray
irradiation (Abe et al., 2006). It was confirmed that the intensity
of the X-ray emitted from iodine is not absorbed by X-ray film
because of its high energy. The LOD and MDL values were calculated and compared to those of other conventional methods to
assess analytical sensitivity. The LOD and MDL values were defined
as three times the standard deviation of blank measurements (rb)
divided by the slope of the calibration line (p) and the standard
deviation of seven replicates of sample measurements (rS) multiplied by Student’s t-value at the 99% confidence level (t = 3.143
at 6 degrees of freedom), respectively (Zorn et al., 1999; ICH, 1999).
2.5. Application to drinking water sample
Drinking water samples were used for the spike tests in order to
confirm the applicability of the proposed AC-WDXRF method. The
water sample contained 144 lg L1 of total organic carbon (TOC).
The water samples were spiked with NH4I stock solution to make
1 and 5 mg L1 iodine concentrations. Afterwards, 20 mL of the
spiked samples was filtered through the AC disk and total iodine
Please cite this article in press as: Lee, J., et al. Effectiveness of activated carbon disk for the analysis of iodine in water samples using wavelength dispersive
X-ray fluorescence spectrometry. Chemosphere (2015), http://dx.doi.org/10.1016/j.chemosphere.2015.06.017
3
J. Lee et al. / Chemosphere xxx (2015) xxx–xxx
Table 2
Adsorption behavior of I and IO
3 on AC disks at different pH levels.
a
I concentration (lg L1)
Initial solution
Effluent
4
6
8
1013.0
1006.4
999.2
NDb
ND
ND
Recoverya (%)
1
IO
)
3 concentration (lg L
Initial solution
Effluent
100
100
100
1010.9
1009.8
1006.5
ND
ND
ND
Recovery (%)
100
100
100
Recovery was defined as (difference in iodine concentrations between initial solution and effluent 100)/iodine concentration of initial solution.
ND = Not Detected.
X-ray intensity (kcps)
measured at Bragg angle of 102.85o
b
Solution pH
I and IO
3 in water samples although it can be retain anionic species from water samples. Additional study relating to the low
retention capacity of the AX disk for iodine which is negatively
charged is needed. The adsorption capacity of the AC disk is superior to that of the AX disk, and therefore the AC disk was used as
the preconcentration sorbent for the iodine analysis before
WDXRF analysis in this study.
12
y = 0.0274x + 0.2388
(R2 = 0.9960)
10
8
6
4
2
3.2. Analysis of AC disk preconcentrated with iodine using WDXRF
spectrometry
0
-2
100
0
200
300
400
500
Amount of iodine retained in AC disk (µg)
Fig. 1. Calibration curve for iodine established using the standards (i.e., 0, 20, 200,
400 lg of iodine retained on the AC disk). Error bars indicate the relative standard
deviations (n = 3).
concentrations retained on the AC disk were measured using
WDXRF analysis. The nominal (spiked) values and concentrations
measured using AC-WDXRF and ICP-MS methods were compared
to validate the analytical accuracy.
3. Results and discussion
3.1. Retention behavior of I and IO
3 on the AC disk
The retention behavior of I and IO
3 on the AC and AX disks was
studied at different pH levels (4, 6, and 8) because I and IO
3 are
dominant dissolve iodine species in aquatic systems. As shown in
Table 2, I and IO
3 were completely retained on the AC disks for
all the pH levels tested. This result implied that the AC disk is suitable for the preconcentration of I and IO
3 , regardless of pH of the
water sample. It is the expected result because of its high adsorption capacity, along with the fact that iodine number is used as a
relative indicator of the porosity and surface area of AC (ASTM,
2011). On the other hand, the AX disk was incapable of retaining
The calibration curve established using the La line emitted from
the iodine on the AC disk showed good linearity in the range of
0–400 lg (determination coefficient, R2 = 0.9960) (Fig. 1). This
result indicated that the AC disks retaining various iodine concentrations are applicable as calibration standards for WDXRF analysis. The LOD and MDL values were calculated in order to assess
the analytical sensitivity of the proposed AC-WDWRF method.
The p and rb values were 0.0274 and 0.00525, respectively.
Therefore, the calculated LOD and limit of quantification (LOQ) values for iodine analysis using the AC-WDXRF method were 0.575
and 1.92 lg of iodine, respectively. In addition, the MDL yielded
29.3 lg that is approximately two orders of magnitude higher than
LOD value as referred in Kim et al. (2013). These results implied
that a quantitative analysis could be employed for samples containing more than 1.92 lg L1 of iodine for 1 L of water sample pretreated using the AC disk. The LOD value obtained from the
proposed method is comparable to those of conventional methods
employed for iodine analysis, such as high performance liquid
chromatography (HPLC) and ICP-MS (Table 3) (Takayanagi and
Wong, 1986; Ito, 1997; Leiterer et al., 2001; Schwehr and
Santschi, 2003; Pan and Zhang, 2013). The LOD values for the
HPLC and ICP-MS systems for iodine analysis are 0.2 and
1.1 lg L1, respectively (Schwehr and Santschi, 2003; Leiterer
et al., 2001). Since the iodine concentration in environmental water
samples previously reported ranged from 0.5 to 20 lg L1
(Whitehead, 1979, 1984), the proposed AC-WDXRF method is reasonable for the detection and monitoring of iodine.
Table 3
Comparison of existing methods for iodine analysis in different water samples.
Analytical technique
Pretreatment method
Sample
LOD
(lg L1)
Run timea
(h)
Reference
UPLC/ESI-MSb
Derivatization of I and IO
3 to
organic iodine
Oxidation using hypochlorite
Tap water/seawater/
wastewater
Seawater
3.7
2
1.3–2.5
24
Gong and Zhang (2013) and Pan and
Zhang (2013)
Takayanagi and Wong (1986)
Anion-exchange resin
Dehydrohalogenation and reduction
IC
AC disk
Seawater
Freshwater/seawater
Milk
DI water
0.2
0.2
1.1
29
1–2
7
0.5–1
0.3
Ito (1997)
Schwehr and Santschi (2003)
Leiterer et al. (2001)
This study
Differential pulse
polarography
Ion chromatography
HPLCc
ICP–MS
WDXRF spectrometry
a
b
c
Run time is calculated by adding of sample preparation, pretreatment process, and analyzing time.
Ultra performance liquid chromatography/electrospray ionization-mass spectrometry.
High performance liquid chromatography.
Please cite this article in press as: Lee, J., et al. Effectiveness of activated carbon disk for the analysis of iodine in water samples using wavelength dispersive
X-ray fluorescence spectrometry. Chemosphere (2015), http://dx.doi.org/10.1016/j.chemosphere.2015.06.017
4
J. Lee et al. / Chemosphere xxx (2015) xxx–xxx
X-ray Intensity (kcps)
12
10
8
6
4
2
0
-2
0
2
4
6
8
10
Analysis time (days)
Fig. 2. Variation in the X-ray intensities of AC disks containing different iodine
concentrations (blank (d), 1 lg (s), 10 lg (.), and 20 lg (4)) with analysis time at
1 d interval. Error bars indicate the relative standard deviations (n = 3).
The WDXRF analysis combined with AC disks proved to be a
simpler and faster method for iodine analysis (Table 3). The
proposed method requires about 20 min calculated as follows:
1–15 min of preconcentration, 5 min of drying, and 100 s of
WDXRF analysis. In addition, there is no need to adjust the pH levels
of water samples and it can be thus avoided to use the acid/base
solutions. In the case of ICP-MS and IC analyses, a dilution and/or
pretreatment step are needed for certain water samples containing
high TDS. On the other hand, the proposed AC-WDXRF method is
applicable for a wide range of iodine concentrations by adjusting
the filtering volume of water samples and consequently pretreatment process can be eliminated. It is therefore reasonable to infer
that the AC-WDXRF method is appropriate for the determination
of iodine concentrations in environmental water samples.
3.3. Interference effects on iodine intensity by peak overlap
Iodine intensity can be affected by peak overlap with elements
that have similar energy levels of the emitted X-ray compared to
the I-La line, consequently resulting in analytical bias. In such
cases, an additional calibration and/or a correction factor is needed
to compensate for the interference effects (An et al., 2015). In order
to confirm the presence of elements that can affect to iodine intensity on the AC disk, an element scan program (IQ+ method) for
qualitative analysis (Panalytical, 2004) was performed. The IQ+
method covers elements from beryllium (Be) to uranium (U) using
various diffraction crystals. The result showed that there is no
interfering elements in the AC disks having the Bragg angle close
to the I-La line, and therefore no correction for the interference
by the peak overlap was necessary for iodine analysis using the
AC-WDXRF method proposed in this study.
3.4. Durability test
In order to assess the durability of AC disks for WDXRF analysis,
the intensity of the AC disk was measured repeatedly at regular
Table 4
Comparison of the iodine concentrations in drinking water samples measured by the
AC-WDXRF and ICP-MS analysis.
Nominal concentration
(lg)
AC-WDXRF
(lg)
ICP-MS
(lg)
Relative error
(%)a
20
100
15.4b
97.9
21.4
103
28.1
4.60
a
Relative error is determined by the ratio of the difference between iodine
concentrations measured using AC-WDXRF and ICP-MS analyses to iodine concentration measured by ICP-MS analysis.
b
Average value for measurements in triplicate.
intervals. The AC disks were coated with an X-ray film prior to
the WDXRF analysis in order to protect the AC disks composed of
cross-linked carbon particles on a polymer backbone that can be
damaged by high energy X-ray. The durability of the AC disk was
affected by the energy of the X-ray beam and the irradiation time.
Because the X-ray power for iodine analysis is fixed at 3 kW (30 kV,
100 mA), we evaluated the variation in the emitted X-ray intensities as a function of time. The variation in the emitted X-ray intensities of the AC disks containing various concentrations of iodine in
relation to analyzing time are presented in Fig. 2. All measurements were performed in triplicate. The measured intensities for
the AC disks showed constant values until 8 d of analysis time
(i.e., 1 analysis per day, 8 d in a row). These results indicated that
the AC disks provided a durable preconcentration method for
WDXRF analysis to determine iodine concentrations in water samples. Therefore, the calibration curve and the preconcentrated AC
disks could be used continuously without the need to repeat the
preconcentration process until 8 d. In addition, the relative standard deviations (RSDs) of the measured intensities ranged from
0.001 to 0.243, which indicates a substantially high consistency
of the AC-WDXRF method.
3.5. Validation of the proposed method
The suitability of the proposed AC-WDXRF method for iodine
measurements in drinking water sample was investigated. The
iodine concentrations in real water and spiked water samples measured by the AC-WDXRF method were compared with those
obtained using ICP-MS analysis. The results showed good agreement with relative errors of 4.60–28.1% between the two analytical
methods and it was consequently implied that the proposed
AC-WDXRF method is suitable for iodine analysis in water
(Table 4). In addition, the RSDs of AC-WDXRF method were relatively small, indicating the enhanced reproducibility of the proposed method. In the water treatment process, AC can be used to
capture the substances from natural water and subsequently their
concentrations can be measured by WDXRF spectrometry. In addition, the proposed method has advantage to be applicable for various field conditions. Contrary to the aforementioned analysis in
laboratory, iodine concentration can be promptly screened and
detected in field measurement using portable XRF combined with
AC disk when sampling and sending to laboratory are difficult.
Thus, the proposed method is very useful for the analysis of a variety of precursor in raw water.
4. Conclusions
In this study, we aimed to demonstrate a novel method for the
determination of iodine concentrations in water samples using
WDXRF spectrometry with a preconcentration step using AC disks.
The AC disk is suitable for the adsorption of I and IO
3 in water
sample, regardless of the pH levels. The proposed AC-WDXRF
method achieved an LOD of 0.575 lg and MDL of 29.3 lg for iodine
analysis comparable to those of other conventional methods. The
X-ray intensities of the AC disks remained constant during repeatable measurements, indicating a high durability of the AC disks for
WDXRF analysis. The results of the spike tests using drinking water
samples were in good agreement with relative errors of 4.60–
28.1%, validating the applicability of the proposed method. The
proposed AC-WDXRF method is simpler and faster than other
methods that require complicated and time-consuming pretreatment procedures. In addition, there is no need to adjust the pH
and to perform elution step, thereby eliminating the use of
acid/base solutions. Therefore, the proposed method is appropriate
for rapid monitoring of iodine in environmental water samples
Please cite this article in press as: Lee, J., et al. Effectiveness of activated carbon disk for the analysis of iodine in water samples using wavelength dispersive
X-ray fluorescence spectrometry. Chemosphere (2015), http://dx.doi.org/10.1016/j.chemosphere.2015.06.017
J. Lee et al. / Chemosphere xxx (2015) xxx–xxx
with such advantages as simplicity, efficiency, and environmental
friendliness.
Acknowledgement
This research was supported by a Grant from the Korea Basic
Science Institute (Project No. E34300).
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Please cite this article in press as: Lee, J., et al. Effectiveness of activated carbon disk for the analysis of iodine in water samples using wavelength dispersive
X-ray fluorescence spectrometry. Chemosphere (2015), http://dx.doi.org/10.1016/j.chemosphere.2015.06.017